Sample records for stiffness measurement lsm

  1. The relationship between liver stiffness measurement and outcome in patients with chronic hepatitis C and cirrhosis: a retrospective longitudinal hospital study.

    PubMed

    Sultanik, P; Kramer, L; Soudan, D; Bouam, S; Meritet, J-F; Vallet-Pichard, A; Fontaine, H; Bousquet, L; Boueyre, E; Corouge, M; Sogni, P; Pol, S; Mallet, V

    2016-09-01

    There is a relationship between liver stiffness measurement (LSM) and outcome of HCV patients. To evaluate the performance of LSM to predict outcome of HCV patients at risk of liver-related complication. We established a retrospective longitudinal cohort of 341 HCV patients with unequivocal cirrhosis. All underwent LSM and were followed from September 2006 to July 2015. Outcome measure was a composite end-point of end-stage liver disease (ESLD) and/or hepatocellular carcinoma (HCC). Cox models and areas under receiver operating characteristic (AUROC) curves were used to evaluate independent risk factors of outcome. Overall, LSM was below the 12.5 kPa threshold in 129 (37.8%) patients, including three-fourth and one-third of patients with or without a sustained virological response respectively. Liver disease progressed in 136 (39.9%) patients after a median observational period of 23.5 months. Older age, male gender, alcohol use disorders, metabolic syndrome and LSM were independent risk factors of liver disease progression. Age, alcohol use disorders and LSM were independently associated with ESLD. Age, gender and metabolic syndrome, but not LSM, were associated with HCC. The AUROC curves for disease progression, ESLD and HCC were 0.67, 0.70 and 0.58 respectively. Patients with a liver stiffness >12.5 kPa were at the highest risk of liver disease progression; below 12.5 kPa, liver stiffness was not discriminant. Liver stiffness measurement is not a surrogate of disease progression of HCV patients with cirrhosis. HCV patients with cirrhosis should undergo the recommended follow-up, regardless of liver stiffness measurement. © 2016 John Wiley & Sons Ltd.

  2. Applicability and variability of liver stiffness measurements according to probe position

    PubMed Central

    Ingiliz, Patrick; Chhay, Kim Pav; Munteanu, Mona; Lebray, Pascal; Ngo, Yen; Roulot, Dominique; Benhamou, Yves; Thabut, Dominique; Ratziu, Vlad; Poynard, Thierry

    2009-01-01

    AIM: To investigate the liver stiffness measurement (LSM) applicability and variability with reference to three probe positions according to the region of liver biopsy. METHODS: The applicability for LSM was defined as at least 10 valid measurements with a success rate greater than 60% and an interquartile range/median LSM < 30%. The LSM variability compared the inter-position concordance and the concordance with FibroTest. RESULTS: Four hundred and forty two consecutive patients were included. The applicability of the anterior position (81%) was significantly higher than that of the reference (69%) and lower positions (68%), (both P = 0.0001). There was a significant difference (0.5 kPa, 95% CI 0.13-0.89; P < 0.0001) between mean LSM estimated at the reference position (9.3 kPa) vs the anterior position (8.8 kPa). Discordance between positions was associated with thoracic fold (P = 0.008). The discordance rate between the reference position result and FibroTest was higher when the 7.1 kPa cutoff was used to define advanced fibrosis instead of 8.8 kPa (33.6% vs 23.5%, P = 0.03). CONCLUSION: The anterior position of the probe should be the first choice for LSM using Fibroscan, as it has a higher applicability without higher variability compared to the usual liver biopsy position. PMID:19610141

  3. A novel 2-step approach combining the NAFLD fibrosis score and liver stiffness measurement for predicting advanced fibrosis.

    PubMed

    Chan, Wah-Kheong; Nik Mustapha, Nik Raihan; Mahadeva, Sanjiv

    2015-10-01

    The non-alcoholic fatty liver disease (NAFLD) fibrosis score (NFS) is indeterminate in a proportion of NAFLD patients. Combining the NFS with liver stiffness measurement (LSM) may improve prediction of advanced fibrosis. We aim to evaluate the NFS and LSM in predicting advanced fibrosis in NAFLD patients. The NFS was calculated and LSM obtained for consecutive adult NAFLD patients scheduled for liver biopsy. The accuracy of predicting advanced fibrosis using either modality and in combination were assessed. An algorithm combining the NFS and LSM was developed from a training cohort and subsequently tested in a validation cohort. There were 101 and 46 patients in the training and validation cohort, respectively. In the training cohort, the percentages of misclassifications using the NFS alone, LSM alone, LSM alone (with grey zone), both tests for all patients and a 2-step approach using LSM only for patients with indeterminate and high NFS were 5.0, 28.7, 2.0, 2.0 and 4.0 %, respectively. The percentages of patients requiring liver biopsy were 30.7, 0, 36.6, 36.6 and 18.8 %, respectively. In the validation cohort, the percentages of misclassifications were 8.7, 28.3, 2.2, 2.2 and 8.7 %, respectively. The percentages of patients requiring liver biopsy were 28.3, 0, 41.3, 43.5 and 19.6 %, respectively. The novel 2-step approach further reduced the number of patients requiring a liver biopsy whilst maintaining the accuracy to predict advanced fibrosis. The combination of NFS and LSM for all patients provided no apparent advantage over using either of the tests alone.

  4. Liver stiffness measurement, better than APRI, Fibroindex, Fib-4, and NBI gastroscopy, predicts portal hypertension in patients with cirrhosis.

    PubMed

    Zhang, Wei; Wang, Liqiong; Wang, Lei; Li, Gang; Huang, Aoshuang; Yin, Ping; Yang, Zhenhua; Ling, Changquan; Wang, Lingtai

    2015-03-01

    Liver stiffness measurement (LSM) is frequently used as non-invasive alternative for liver fibrosis including cirrhosis, which can lead to portal hypertension. This study was conducted to evaluate the predictive value of LSM in cirrhosis-induced portal hypertension patients. Between July 2011 and December 2013, 153 participants were enrolled into a single-center, prospective, cross-sectional study. Each subject received both gastroscopy and LSM. Baseline biochemical, APRI, Fibroindex, and Fib-4 were also performed. LSM of cirrhosis patients with portal hypertension was significantly higher compared to those without portal hypertension (P < 0.05). A LSM ≥ 13.6 kPa had a sensitivity of 83.87 % and a specificity of 72.53 % with an accuracy of 77.1 for the prediction of portal hypertension, which are higher than those of APRI, Fib-4, and Fibroscan separately. A combination of Fibroscan combined with Fib-4 achieved a maximum AUC of 0.833 and accuracy of 77.8. Discriminant and internal validation analysis showed that Fibroscan plus APRI obtained a lower false negative rate compared to Fibroscan plus Fib-4 and Fibroscan plus Fibroindex (9.68, 17.74, and 11.29 %, respectively). A good relationship was found between LSM and NBI mean optical density both by linear and polynomial correlation analysis (r = 0.5533 and r = 0.7349, both P < 0.001). There was a trend toward a better performance of LSM for assessing portal hypertension compared with NBI gastroscopy mean optical density (P = 0.028 and P = 0.05, respectively). Better than APRI, Fibroindex, Fib-4, and NBI gastroscopy, LSM can predict portal hypertension in cirrhosis patients. A LSM of 13.6 kPa can be considered to be the predictive value for portal hypertension.

  5. [Correlation of liver stiffness measured by FibroTouch and FibroScan with Ishak fibrosis score in patients with chronic hepatitis B].

    PubMed

    Chen, G F; Ping, J; Gu, H T; Zhao, Z M; Zhou, Y; Xing, F; Tao, Y Y; Mu, Y P; Liu, P; Liu, C H

    2017-02-20

    Objective: To investigate the correlation of liver stiffness measured by FibroTouch (FT) and FibroScan (FS) with Ishak fibrosis score in patients with chronic hepatitis B. Methods: A total of 313 patients with chronic hepatitis B who visited Department of Liver Cirrhosis in Shuguang Hospital Affiliated to Shanghai University of Traditional Chinese Medicine from November 2014 to May 2016 were enrolled. All the patients underwent liver biopsy, and FT and FS were used to determine liver stiffness measurement (LSM). Serum biochemical parameters were measured, and the aspartate aminotransferase-to-platelet ratio index (APRI) in a multi-parameter model of liver fibrosis and fibrosis-4 (FIB-4) index were calculated. The consistency between the results of four noninvasive examinations and Ishak fibrosis score was compared. The t-test was used for comparison of LSM determined by FT and FS. Pearson correlation analysis was used investigate the correlation between LSM determined by FT and FS; Spearman correlation analysis was used to investigate the correlation of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels and Knodell score with LSM determined by FT and FS; the correlation between LSM determined by FT and FS and fibrosis stage was analyzed by partial correlation analysis adjusted by Knodell score for liver inflammatory activity; Spearman correlation analysis was used for APRI, FIB-4, and fibrosis stage. Based on the Ishak fibrosis score, the receiver operating characteristic (ROC) curve was used to analyze the values of four noninvasive methods in the diagnosis of liver fibrosis. Results: There was no significant difference in LSM measured by FT and FS in all patients (15.75±9.42 kPa vs 15.42±10.52 kPa, P > 0.05) and Pearson correlation analysis indicated a significant positive correlation between them ( r = 0.858, P < 0.01); serum ALT and AST levels and liver inflammatory activity were correlated with LSM determined by FT and FS. There

  6. Non-invasive evaluation of liver stiffness after splenectomy in rabbits with CCl4-induced liver fibrosis.

    PubMed

    Wang, Ming-Jun; Ling, Wen-Wu; Wang, Hong; Meng, Ling-Wei; Cai, He; Peng, Bing

    2016-12-14

    To investigate the diagnostic performance of liver stiffness measurement (LSM) by elastography point quantification (ElastPQ) in animal models and determine the longitudinal changes in liver stiffness by ElastPQ after splenectomy at different stages of fibrosis. Liver stiffness was measured in sixty-eight rabbits with CCl 4 -induced liver fibrosis at different stages and eight healthy control rabbits by ElastPQ. Liver biopsies and blood samples were obtained at scheduled time points to assess liver function and degree of fibrosis. Thirty-one rabbits with complete data that underwent splenectomy at different stages of liver fibrosis were then included for dynamic monitoring of changes in liver stiffness by ElastPQ and liver function according to blood tests. LSM by ElastPQ was significantly correlated with histologic fibrosis stage ( r = 0.85, P < 0.001). The optimal cutoff values by ElastPQ were 11.27, 14.89, and 18.21 kPa for predicting minimal fibrosis, moderate fibrosis, and cirrhosis, respectively. Longitudinal monitoring of the changes in liver stiffness by ElastPQ showed that early splenectomy (especially F1) may delay liver fibrosis progression. ElastPQ is an available, convenient, objective and non-invasive technique for assessing liver stiffness in rabbits with CCl 4 -induced liver fibrosis. In addition, liver stiffness measurements using ElastPQ can dynamically monitor the changes in liver stiffness in rabbit models, and in patients, after splenectomy.

  7. Spleen and Liver Stiffness Is Positively Correlated with the Risk of Esophageal Variceal Bleeding.

    PubMed

    Buechter, Matthias; Kahraman, Alisan; Manka, Paul; Gerken, Guido; Jochum, Christoph; Canbay, Ali; Dechêne, Alexander

    2016-01-01

    Portal hypertension (PH) is a common complication of chronic liver disease and results in esophageal and gastric variceal bleeding, which is associated with a high mortality rate. Measurement of the hepatic venous pressure gradient (HVPG) is considered the gold standard for diagnosing PH and estimating the risk of varices and bleeding. In contrast, upper gastrointestinal (GI) endoscopy (UGE) can reliably demonstrate the presence of varices and bleeding. Both measures are invasive, and HVPG is mainly restricted to tertiary centers. Therefore, the development of noninvasive methods of assessing the severity of PH and the risk of variceal bleeding is warranted. We retrospectively examined the correlation of spleen stiffness (SSM) and liver stiffness measurements (LSM) with the incidence of variceal bleeding among 143 patients who underwent combined liver and spleen elastography between 2013 and 2015. For 19 of 103 patients (16.8%), upper GI variceal bleeding was diagnosed and treated endoscopically. The median SSM of all patients was 35.3 kilopascals (kPa); the median LSM, 11.7 kPa. Patients with previous bleeding episodes had significantly higher SSM (75.0 kPa) and LSM (37.3 kPa) than those without a history of bleeding (SSM, 30.6 kPa; LSM, 8.2 kPa; p < 0.0001). Seventy-five patients (66.4%) underwent UGE in addition to SSM and LSM: 25 with no esophageal varices (EVs; SSM, 29.5 kPa; LSM, 11.4 kPa), 16 with EV grade 1 (SSM, 35.9 kPa; LSM, 33.4 kPa), 21 with EV grade 2 (SSM, 67.8 kPa; LSM, 27.0 kPa) and 13 with EV grade 3 (SSM, 75.0 kPa; LSM, 26.3 kPa). No statistically significant differences were found between respective grades of EV but were found between the presence and absence of varices. At a calculated cutoff level of 42.6 kPa (with application of 95% CI), SSM had sensitivity of 89% and specificity of 64% in determining the risk of bleeding, with a negative predictive value (NPV) of 0.97 (LSM sensitivity, 84%; LSM specificity, 80%; LSM NPV, 0.96 at LSM cutoff

  8. A combined model based on spleen stiffness measurement and Baveno VI criteria to rule out high-risk varices in advanced chronic liver disease.

    PubMed

    Colecchia, Antonio; Ravaioli, Federico; Marasco, Giovanni; Colli, Agostino; Dajti, Elton; Di Biase, Anna Rita; Bacchi Reggiani, Maria Letizia; Berzigotti, Annalisa; Pinzani, Massimo; Festi, Davide

    2018-05-03

    Recently, Baveno VI guidelines suggested that esophagogastroduodenoscopy (EGD) can be avoided in patients with compensated advanced chronic liver disease (cACLD) who have a liver stiffness measurement (LSM) <20 kPa and platelet count >150,000/mm 3 . We aimed to: assess the performance of spleen stiffness measurement (SSM) in ruling out patients with high-risk varices (HRV); validate Baveno VI criteria in a large population and assess how the sequential use of Baveno VI criteria and SSM could safely avoid the need for endoscopy. We retrospectively analyzed 498 patients with cACLD who had undergone LSM/SSM by transient elastography (TE) (FibroScan®), platelet count and EGDs from 2012 to 2016 referred to our tertiary centre. The new combined model was validated internally by a split-validation method, and externally in a prospective multicentre cohort of 115 patients. SSM, LSM, platelet count and Child-Pugh-B were independent predictors of HRV. Applying the newly identified SSM cut-off (≤46 kPa) or Baveno VI criteria, 35.8% and 21.7% of patients in the internal validation cohort could have avoided EGD, with only 2% of HRVs being missed with either model. The combination of SSM with Baveno VI criteria would have avoided an additional 22.5% of EGDs, reaching a final value of 43.8% spared EGDs, with <5% missed HRVs. Results were confirmed in the prospective external validation cohort, as the combined Baveno VI/SSM ≤46 model would have safely spared (0 HRV missed) 37.4% of EGDs, compared to 16.5% when using the Baveno VI criteria alone. A non-invasive prediction model combining SSM with Baveno VI criteria may be useful to rule out HRV and could make it possible to avoid a significantly larger number of unnecessary EGDs compared to Baveno VI criteria only. Spleen stiffness measurement assessed by transient elastography, the most widely used elastography technique, is a non-invasive technique that can help the physician to better stratify the degree of portal

  9. Non-invasive evaluation of liver stiffness after splenectomy in rabbits with CCl4-induced liver fibrosis

    PubMed Central

    Wang, Ming-Jun; Ling, Wen-Wu; Wang, Hong; Meng, Ling-Wei; Cai, He; Peng, Bing

    2016-01-01

    AIM To investigate the diagnostic performance of liver stiffness measurement (LSM) by elastography point quantification (ElastPQ) in animal models and determine the longitudinal changes in liver stiffness by ElastPQ after splenectomy at different stages of fibrosis. METHODS Liver stiffness was measured in sixty-eight rabbits with CCl4-induced liver fibrosis at different stages and eight healthy control rabbits by ElastPQ. Liver biopsies and blood samples were obtained at scheduled time points to assess liver function and degree of fibrosis. Thirty-one rabbits with complete data that underwent splenectomy at different stages of liver fibrosis were then included for dynamic monitoring of changes in liver stiffness by ElastPQ and liver function according to blood tests. RESULTS LSM by ElastPQ was significantly correlated with histologic fibrosis stage (r = 0.85, P < 0.001). The optimal cutoff values by ElastPQ were 11.27, 14.89, and 18.21 kPa for predicting minimal fibrosis, moderate fibrosis, and cirrhosis, respectively. Longitudinal monitoring of the changes in liver stiffness by ElastPQ showed that early splenectomy (especially F1) may delay liver fibrosis progression. CONCLUSION ElastPQ is an available, convenient, objective and non-invasive technique for assessing liver stiffness in rabbits with CCl4-induced liver fibrosis. In addition, liver stiffness measurements using ElastPQ can dynamically monitor the changes in liver stiffness in rabbit models, and in patients, after splenectomy. PMID:28028365

  10. The usefulness of liver stiffness measurement using FibroScan in chronic hepatitis C in South Korea: a multicenter, prospective study.

    PubMed

    Kim, Seung Up; Jang, Hui Won; Cheong, Jae Youn; Kim, Ja Kyung; Lee, Myung Hee; Kim, Dong Joon; Yang, Jin Mo; Cho, Sung Won; Lee, Kwan Sik; Choi, Eun Hee; Park, Young Nyun; Han, Kwang-Hyub

    2011-01-01

    We investigated the accuracy of liver stiffness measurement (LSM) in chronic hepatitis C (CHC) in a multicenter, prospective study in South Korea. Between June 2005 and July 2009, 91 CHC patients without a previous history of antiviral treatment, clinical evidences of cirrhosis, coinfection with other viruses, and heavy alcohol consumption and with alanine aminotransferase (ALT) ≤5x upper limit of normal, total bilirubin ≤1.5 mg/dL, sufficient liver biopsy quality (≥15 mm and more than six portal tracts), interquartile range to median liver stiffness (LS) value ratio ≤0.21, and more than 10 valid measurements, were recruited. The Batts and Ludwig scoring system was used for histologic assessment. Age-platelet index (API), aspartate aminotransferase (AST)-to-platelet ratio index (APRI), and age-spleen-platelet ratio index (ASPRI) were calculated. Area under the receiver operating characteristic curve (AUROC) was used to evaluate the performance of LSM and other noninvasive models. The mean age was 47.9 years, and the mean LS value was 7.7 kPa (44 men and 47 women). LS value was highly correlated to the fibrosis stages (r=0.835, P<0.001). The AUROCs of LSM were 0.909 for ≥F2, 0.993 for ≥F3, and 0.970 for F=4 and were superior to those of API (0.72, 0.858, and 0.948, respectively), APRI (0.780, 0.887, and 0.904, respectively), and ASPRI (0.713, 0.862, and 0.957, respectively). The optimal cutoff LS values were 6.2 kPa for ≥F2, 7.7 kPa for ≥F3, and 11.0 kPa for F=4. Our data suggest that LSM can accurately assess liver fibrosis in patients with CHC and be applied in South Korea. © 2010 Journal of Gastroenterology and Hepatology Foundation and Blackwell Publishing Asia Pty Ltd.

  11. Association between hepatitis B co-infection and elevated liver stiffness among HIV-infected adults in Lusaka, Zambia.

    PubMed

    Vinikoor, Michael J; Mulenga, Lloyd; Siyunda, Alice; Musukuma, Kalo; Chilengi, Roma; Moore, Carolyn Bolton; Chi, Benjamin H; Davies, Mary-Ann; Egger, Matthias; Wandeler, Gilles

    2016-11-01

    To describe liver disease epidemiology among HIV-infected individuals in Zambia. We recruited HIV-infected adults (≥18 years) at antiretroviral therapy initiation at two facilities in Lusaka. Using vibration controlled transient elastography, we assessed liver stiffness, a surrogate for fibrosis/cirrhosis, and analysed liver stiffness measurements (LSM) according to established thresholds (>7.0 kPa for significant fibrosis and >11.0 kPa for cirrhosis). All participants underwent standardised screening for potential causes of liver disease including chronic hepatitis B (HBV) and C virus co-infection, herbal medicine, and alcohol use. We used multivariable logistic regression to identify factors associated with elevated liver stiffness. Among 798 HIV-infected patients, 651 had a valid LSM (median age, 34 years; 53% female). HBV co-infection (12%) and alcohol use disorders (41%) were common and hepatitis C virus co-infection (<1%) was rare. According to LSM, 75 (12%) had significant fibrosis and 13 (2%) had cirrhosis. In multivariable analysis, HBV co-infection as well as male sex, increased age and WHO clinical stage 3 or 4 were independently associated with LSM >7.0 kPa (all P < 0.05). HBV co-infection was the only independent risk factor for LSM >11.0 kPa. Among HIV-HBV patients, those with elevated ALT and HBV viral load were more likely to have significant liver fibrosis than patients with normal markers of HBV activity. HBV co-infection was the most important risk factor for liver fibrosis and cirrhosis and should be diagnosed early in HIV care to optimise treatment outcomes. © 2016 John Wiley & Sons Ltd.

  12. Impact of hepatitis C virus genotype-4 eradication following direct acting antivirals on liver stiffness measurement.

    PubMed

    Tag-Adeen, Mohammed; Sabra, Ahlam Mohamed; Akazawa, Yuko; Ohnita, Ken; Nakao, Kazuhiko

    2017-01-01

    Liver fibrosis is the most important prognostic factor in chronic hepatitis C virus (HCV) patients, and Egypt shows the highest worldwide HCV prevalence with genotype-4 pre-dominance. The aim of this study was to investigate the degree of liver stiffness measurement (LSM) improvement after successful HCV eradication. The study included 84 chronic HCV Egyptian patients, and was conducted at Qena University Hospital from November 1, 2015 till October 31, 2016. LSM was obtained by FibroScan® before starting direct acting antiviral (DAA) treatment and after achieving sustained virologic response-24 (SVR-24). Based on baseline LSM, patients were stratified into F0-F1, F2, F3 and F4 groups (METAVIR). LSM and laboratory data after achieving SVR-24 was compared with that before starting therapy in each fibrosis group (F0-F4), p -value <0.05 was statistically significant. Following DAA treatment, 80 patients achieved SVR-24; of these, 50 were males (62.5%), mean age: 54.2±7.6 years, and mean body mass index: 28.6±2.2 kg/m 2 . Mean baseline LSM dropped from 15.6±10.8 to 12.1±8.7 kPa post-SVR; the maximum change of -5.8 occurred in F4 versus -2.79, -1.28 and +0.08 in F3, F2 and F0-F1 respectively ( p <0.0001). At baseline, 41 patients were in the F4 group; only 16 (39%) regressed to non-cirrhotic range (<12.5 kPa), while 25 (61%) were still cirrhotic despite achieving SVR-24 ( p <0.0001). Patients who achieved LSM improvement (n=64) have had significantly higher baseline aspartate transferase (AST) and alanine transaminase (ALT). Also, those patients showed significant improvement in AST, AST/platelets ratio index (APRI) and fibrosis-4 index (Fib-4) after achieving SVR; 91% showed AST improvement ( p =0.01) and APRI improvement ( p =0.01) and 81% showed Fib-4 improvement ( p =0.04). Females, diabetics, patients with S3 steatosis and patients older than 50 years showed less LSM improvements than their counterparts. Baseline LSM ≥9 kPa, bilirubin ≥1 mg/dl, ALT ≥36 U

  13. Improved noninvasive prediction of liver fibrosis by liver stiffness measurement in patients with nonalcoholic fatty liver disease accounting for controlled attenuation parameter values.

    PubMed

    Petta, Salvatore; Wong, Vincent Wai-Sun; Cammà, Calogero; Hiriart, Jean-Baptiste; Wong, Grace Lai-Hung; Marra, Fabio; Vergniol, Julien; Chan, Anthony Wing-Hung; Di Marco, Vito; Merrouche, Wassil; Chan, Henry Lik-Yuen; Barbara, Marco; Le-Bail, Brigitte; Arena, Umberto; Craxì, Antonio; de Ledinghen, Victor

    2017-04-01

    Liver stiffness measurement (LSM) frequently overestimates the severity of liver fibrosis in nonalcoholic fatty liver disease (NAFLD). Controlled attenuation parameter (CAP) is a new parameter provided by the same machine used for LSM and associated with both steatosis and body mass index, the two factors mostly affecting LSM performance in NAFLD. We aimed to determine whether prediction of liver fibrosis by LSM in NAFLD patients is affected by CAP values. Patients (n = 324) were assessed by clinical and histological (Kleiner score) features. LSM and CAP were performed using the M probe. CAP values were grouped by tertiles (lower 132-298, middle 299-338, higher 339-400 dB/m). Among patients with F0-F2 fibrosis, mean LSM values, expressed in kilopascals, increased according to CAP tertiles (6.8 versus 8.6 versus 9.4, P = 0.001), and along this line the area under the curve of LSM for the diagnosis of F3-F4 fibrosis was progressively reduced from lower to middle and further to higher CAP tertiles (0.915, 0.848-0.982; 0.830, 0.753-0.908; 0.806, 0.723-0.890). As a consequence, in subjects with F0-F2 fibrosis, the rates of false-positive LSM results for F3-F4 fibrosis increased according to CAP tertiles (7.2% in lower versus 16.6% in middle versus 18.1% in higher). Consistent with this, a decisional flowchart for predicting fibrosis was suggested by combining both LSM and CAP values. In patients with NAFLD, CAP values should always be taken into account in order to avoid overestimations of liver fibrosis assessed by transient elastography. (Hepatology 2017;65:1145-1155). © 2016 by the American Association for the Study of Liver Diseases.

  14. Rapid liver and spleen stiffness improvement in compensated advanced chronic liver disease patients treated with oral antivirals.

    PubMed

    Pons, Mònica; Santos, Begoña; Simón-Talero, Macarena; Ventura-Cots, Meritxell; Riveiro-Barciela, Mar; Esteban, Rafael; Augustin, Salvador; Genescà, Joan

    2017-08-01

    We aimed to investigate the early changes in liver and spleen stiffness measurement (LSM, SSM) in hepatitis C virus (HCV) patients with compensated advanced chronic liver disease (cACLD) treated with new antivirals (DAA) to elucidate factors determining the initial change in stiffness and its implications for the long-term follow up of HCV-cured patients. A total of 41 patients with cACLD who started DAA therapy underwent LSM and SSM at baseline, week 4, end of treatment (EOT), 24 and 48 weeks of follow up using transient elastography. LSM improved rapidly during the first 4 weeks of treatment (baseline: 20.8kPa; week 4: 17.5kPa, p = 0.002), with no significant changes between week 4 and EOT (18.3kPa, p = 0.444) and between EOT and 48-week follow up (14.3kPa, p = 0.148). Likewise, SSM improved rapidly (baseline: 45.7kPa; week 4: 33.8kPa, p = 0.047), with no significant changes between week 4 and EOT (30.8kPa, p = 0.153) and between EOT and 48-week follow up (31.2kPa, p = 0.317). A higher decrease in LSM was observed in patients with baseline ALT ⩾ twofold upper limit normal (2 × ULN) than in those with ALT < 2 × ULN (-5.7kPa versus -1.6kPa). Patients who presented a decrease in LSM ⩾ 10% during treatment compared with those with LSM < 10% decrease, showed lower SSM values, higher platelet counts and lower bilirubin levels at 24-week follow up. Those with decrease in SSM ⩾ 10%, presented a higher increase in platelets than those with SSM < 10% change ( p = 0.015). LSM and SSM decrease very rapidly during DAA treatment in cACLD patients suggesting that it most probably reflects a reduction in inflammation rather than in fibrosis. cACLD patients should be maintained under surveillance independently of stiffness changes, because advanced fibrosis can still be present.

  15. Hepatocellular carcinoma risk assessment by the measurement of liver stiffness variations in HCV cirrhotics treated with direct acting antivirals.

    PubMed

    Ravaioli, Federico; Conti, Fabio; Brillanti, Stefano; Andreone, Pietro; Mazzella, Giuseppe; Buonfiglioli, Federica; Serio, Ilaria; Verrucchi, Gabriella; Bacchi Reggiani, Maria Letizia; Colli, Agostino; Marasco, Giovanni; Colecchia, Antonio; Festi, Davide

    2018-06-01

    Direct-acting antivirals (DAA) are an effective treatment for hepatitis C virus infection. However, sustained virologic response (SVR) after DAA treatment does not seem to reduce the risk of hepatocellular carcinoma (HCC) development in these patients. Liver stiffness measurement (LSM) may predict the risk of developing HCC in liver cirrhosis patients. The aim of our study was to evaluate the role of LSM variation as predictor of HCC development in patients treated with DAA. In 139 HCV-related cirrhotic patients, LSM and laboratory tests were carried out at baseline (BL) and at the end of DAA treatment (EOT). Patients were followed for at least 6 months after the EOT. LSM reduction was expressed as Delta LS (∆LS). Cox regression analysis was used to identify prognostic factors for HCC development after DAA. Median LSM values were significantly reduced from BL to EOT (from 18.6 to 13.8 kPa; p < 0.001). The median ∆LS was -26.7% (IQR: -38.4% -13.6%). During a median follow-up of 15 months after DAA treatment, 20 (14.4%) patients developed HCC. Significant LSM reduction was observed both in patients who developed HCC and in those who did not, but this was significantly lower in the patients who developed HCC (-18.0% vs -28.9% p = 0.005). At multivariate analysis, ∆LS lower than -30%, Child-Turcotte-Pugh-B and history of HCC were independently associated with HCC development. Our results indicate that ∆LS is a useful non-invasive marker for predicting HCC development after DAA treatment. Copyright © 2018 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd. All rights reserved.

  16. Portal pressure and liver stiffness measurements in the prediction of fibrosis regression after sustained virological response in recurrent hepatitis C.

    PubMed

    Mauro, Ezequiel; Crespo, Gonzalo; Montironi, Carla; Londoño, Maria-Carlota; Hernández-Gea, Virginia; Ruiz, Pablo; Sastre, Lydia; Lombardo, Julissa; Mariño, Zoe; Díaz, Alba; Colmenero, Jordi; Rimola, Antoni; Garcia-Pagán, Juan Carlos; Brunet, Mercé; Forns, Xavier; Navasa, Miquel

    2018-05-01

    Sustained virological response (SVR) improves survival in post-liver transplant (LT) recurrent hepatitis C. However, the impact of SVR on fibrosis regression is not well defined. In addition, the performance of noninvasive methods to evaluate the presence of fibrosis and portal hypertension (PH) post-SVR has been scarcely evaluated. We aimed to investigate the degree of fibrosis regression (decrease ≥1 METAVIR stage) after-SVR and its associated factors in recurrent hepatitis C, as well as the diagnostic capacity of noninvasive methods in the assessment of liver fibrosis and PH after viral clearance. We evaluated 112 hepatitis C virus-infected LT recipients who achieved SVR between 2001 and 2015. A liver biopsy was performed before treatment and 12 months post-SVR. Hepatic venous pressure gradient (HVPG), liver stiffness measurement (LSM), and Enhanced Liver Fibrosis (ELF) score were also determined at the same time points. Sixty-seven percent of the cohort presented fibrosis regression: 43% in recipients with cirrhosis and 72%-85% in the remaining stages (P = 0.002). HVPG, LSM, and ELF significantly decreased post-SVR. Liver function significantly improved, and survival was significantly better in patients achieving fibrosis regression. Baseline HVPG and LSM as well as decompensations before therapy were independent predictors of fibrosis regression. One year post-SVR, LSM had a high diagnostic accuracy to discard the presence of advanced fibrosis (AF) and clinically significant PH (AUROC, 0.902 and 0.888). In conclusion, SVR post-LT induces fibrosis regression in most patients, leading to significant clinical benefits. Pretreatment HVPG and LSM are significant determinants of the likelihood of fibrosis regression. Finally, LSM accurately predicts the presence of AF and PH 1 year after SVR and thus can be used to determine monitoring strategies. (Hepatology 2018;67:1683-1694). © 2017 by the American Association for the Study of Liver Diseases.

  17. Coffee and herbal tea consumption is associated with lower liver stiffness in the general population: The Rotterdam study.

    PubMed

    Alferink, Louise J M; Fittipaldi, Juliana; Kiefte-de Jong, Jessica C; Taimr, Pavel; Hansen, Bettina E; Metselaar, Herold J; Schoufour, Josje D; Ikram, M Arfan; Janssen, Harry L A; Franco, Oscar H; Darwish Murad, Sarwa

    2017-08-01

    Coffee and tea have been proposed to limit the progression of liver fibrosis in established liver disease, but it is unknown if this is also true for subclinical fibrosis. We therefore aimed to evaluate whether coffee and tea consumption are associated with liver stiffness in the general population. The Rotterdam Study is an ongoing prospective population-based cohort. We included participants who underwent transient elastography, ultrasound and completed a food frequency questionnaire. Coffee and tea consumption were categorized into no, moderate (>0-3), or frequent (⩾3) intake (cups/day), and tea further into green, black and herbal tea (no/any). Significant fibrosis was defined as liver stiffness measurements (LSM) ⩾8.0kPa. We performed regression analyses relating coffee and tea intake with fibrosis, steatosis and log-transformed LSM and adjusted for energy, sugar and creamer intake, age, gender, BMI, steatosis/LSM, HOMA-IR, ALT, alcohol, smoking, soda, healthy diet index and physical activity. We included 2,424 participants (age 66.5±7.4; 43% male) of whom 5.2% had LSM ⩾8.0kPa and 34.6% steatosis. Proportion of LSM ⩾8.0kPa decreased with higher coffee consumption (7.8%, 6.9% and 4.1% for no, moderate and frequent respectively; P trend =0.006). This inverse association was confirmed in multivariable regression (OR mod 0.75, 95% CI 0.33-1.67; OR freq 0.39, 95% CI 0.18-0.86; p=0.005). Amongst tea consumers, only herbal tea consumers (36.3%) had lower log-transformed LSM after adjustment (Beta-0.05, 95% CI-0.08;-0.02, p=0.001). Subtypes of tea were associated with steatosis in univariate but not multivariable analysis. In the general population, frequent coffee and herbal tea consumption were inversely related with liver stiffness but not steatosis. Longitudinal analyses, as well as studies validating and unravelling underlying mechanisms are needed. The Rotterdam Study is a large ongoing population study of suburban inhabitants of Rotterdam in whom data

  18. Basal values and changes of liver stiffness predict the risk of disease progression in compensated advanced chronic liver disease.

    PubMed

    Pons, Mònica; Simón-Talero, Macarena; Millán, Laura; Ventura-Cots, Meritxell; Santos, Begoña; Augustin, Salvador; Genescà, Joan

    2016-10-01

    Transient elastography has been proposed as a tool to predict the risk of decompensation in patients with chronic liver disease. We aimed to identify risk groups of disease progression, using a combination of baseline liver stiffness measurement (LSM) and its change over time (delta-LSM) in patients with compensated advanced chronic liver disease (cACLD). Ninety-four patients with baseline LSM ≥10kPa, Child-Pugh score 5 and without previous decompensation were included. A second LSM was performed during follow-up and data on liver function and liver-related events were collected. The primary endpoint was a composite that included death, liver decompensation and impairment in at least 1 point in Child-Pugh score. After a median follow-up of 43.6 months, 15% of patients presented the primary endpoint. Multivariate analysis identified baseline LSM (OR 1.12, P=0.002) and delta-LSM (OR 1.02, P=0.048) as independent predictors of the primary endpoint. A high risk group represented by patients with baseline LSM ≥21kPa and delta-LSM ≥10% (risk of progression 47.1%, 95% CI: 23-71%) was identified, while patients with LSM <21kPa and delta-LSM <10% presented zero risk of progression (P=0.03). Simple classification rules using baseline LSM and delta-LSM identify cACLD patients at low or high risk of disease progression. Copyright © 2016 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd. All rights reserved.

  19. Measuring spleen stiffness to predict varices in chronic hepatitis B cirrhotic patients with or without receiving non-selective beta-blockers.

    PubMed

    Wong, Grace Lai-Hung; Kwok, Raymond; Chan, Henry Lik-Yuen; Tang, Stephen Pui-Kit; Lee, Eugenia; Lam, Thomas Chi-Ho; Lau, Tiffany Wing-Yan; Ma, Teresa Man-Kee; Wong, Betsy Chi-Kuen; Wong, Vincent Wai-Sun

    2016-08-01

    we aimed to investigate the accuracy of liver (LSM) spleen stiffness measurement (SSM) with transient elastography (TE) to predict varices in the presence of non-selective beta-blockers (NSBB). In this cross-sectional study of consecutive patients with chronic hepatitis B (CHB) and cirrhosis, all patients underwent TE and upper endoscopic examinations. LSM and SSM in predicting varices in patients receiving and not receiving NSBB were evaluated. Altogether 144 CHB patients (29 receiving NSBB; 35 with any varices, 31 and 11 with esophageal and gastric varices, respectively) were recruited. Their mean LSM and SSM were 13.3 ± 9.0 kPa and 32.8 ± 19.2 kPa, respectively. The correlation between LSM and SSM was better in the NSBB subgroup (r = 0.525, P = 0.003) than its counterpart (r = 0.329, P  < 0.001). The area under receiver operating characteristic curve (AUROC) of LSM and SSM for any varices was 0.675 and 0.685 (P = 0.002 and 0.001), respectively. SSM of 18.9 kPa had a negative predictive value of 92.1% and negative likelihood ratio of 0.27 for ruling out any varices; and SSM of 54.9 kPa had a positive predictive value of 56.5% and a positive likelihood ratio of 4.05 to rule in varices. The AUROC of LSM for varices was 0.742 and 0.549 in patients with or without NSBB, respectively; the corresponding AUROC of SSM was 0.572 and 0.603, respectively. SSM only has modest accuracy to predict varices independent of NSBB use. An SSM cutoff value of 18.9 kPa may be adopted to achieve a high negative predictive value to rule out varices. © 2016 Chinese Medical Association Shanghai Branch, Chinese Society of Gastroenterology, Renji Hospital Affiliated to Shanghai Jiaotong University School of Medicine and John Wiley & Sons Australia, Ltd.

  20. Relationship of liver stiffness and controlled attenuation parameter measured by transient elastography with diabetes mellitus in patients with chronic liver disease.

    PubMed

    Ahn, Jem Ma; Paik, Yong-Han; Kim, So Hyun; Lee, Jun Hee; Cho, Ju Yeon; Sohn, Won; Gwak, Geum-Youn; Choi, Moon Seok; Lee, Joon Hyeok; Koh, Kwang Cheol; Paik, Seung Woon; Yoo, Byung Chul

    2014-08-01

    High prevalence of diabetes mellitus in patients with liver cirrhosis has been reported in many studies. The aim of our study was to evaluate the relationship of hepatic fibrosis and steatosis assessed by transient elastography with diabetes in patients with chronic liver disease. The study population consisted of 979 chronic liver disease patients. Liver fibrosis and steatosis were assessed by liver stiffness measurement (LSM) and controlled attenuation parameter (CAP) on transient elastography. Diabetes was diagnosed in 165 (16.9%) of 979 patients. The prevalence of diabetes had significant difference among the etiologies of chronic liver disease. Higher degrees of liver fibrosis and steatosis, assessed by LSM and CAP score, showed higher prevalence of diabetes (F0/1 [14%], F2/3 [18%], F4 [31%], P<0.001; S0/1 [15%], S2 [17%], S3 [26%], P=0.021). Multivariate analysis showed that the independent predictive risk factors for diabetes were hypertension (OR, 1.98; P=0.001), LSM F4 (OR, 1.86; P=0.010), male gender (OR, 1.60; P=0.027), and age>50 yr (OR, 1.52; P=0.046). The degree of hepatic fibrosis but not steatosis assessed by transient elastography has significant relationship with the prevalence of diabetes in patients with chronic liver disease.

  1. Electrophoretic deposition of bi-layered LSM/LSM-YSZ cathodes for solid oxide fuel cell

    NASA Astrophysics Data System (ADS)

    Itagaki, Yoshiteru; Watanabe, Shinji; Yamaji, Tsuyoshi; Asamoto, Makiko; Yahiro, Hidenori; Sadaoka, Yoshihiko

    2012-09-01

    Bi-layered cathodes with the LSM/LSM-YSZ structure for solid oxide fuel cells were successfully formed on the carbon-sputtered surface of a YSZ sheet by electrophoretic deposition (EPD). The thicknesses of the first layer of LSM-YSZ (LY) and the second layer of La0.8Sr0.2MnO3 (LSM) could be controlled by adjusting the deposition time in the EPD process. The cathodic properties of the bi-layered structures were superior to those of the mono-layered structures, and were dependent on the thickness of each layer. Decreasing the thickness of the first layer and increasing that of the second layer tended to reduce both polarization and ohmic resistances. The optimal thickness of the first layer at the operating temperature of 600 °C was 4 μm, suggesting that an effective three-phase boundary was extended from the interface between the electrolyte and cathode film to around 4 μm thickness.

  2. The combination of liver stiffness measurement and NAFLD fibrosis score improves the noninvasive diagnostic accuracy for severe liver fibrosis in patients with nonalcoholic fatty liver disease.

    PubMed

    Petta, Salvatore; Vanni, Ester; Bugianesi, Elisabetta; Di Marco, Vito; Cammà, Calogero; Cabibi, Daniela; Mezzabotta, Lavinia; Craxì, Antonio

    2015-05-01

    The accuracy of noninvasive tools for the diagnosis of severe fibrosis in patients with nonalcoholic fatty liver disease(NAFLD) in clinical practice is still limited. We aimed at assessing the diagnostic performance of combined noninvasive tools in two independent cohorts of Italian NAFLD patients. We analysed data from 321 Italian patients(179 Sicilian-training cohort, and 142 northern Italy-validation cohort) with an histological diagnosis of NAFLD. Severe fibrosis was defined as fibrosis ≥ F3 according to Kleiner classification. The APRI, AST/ALT, BARD, FIB-4, and NFS scores were calculated according to published algorithms. Liver stiffness measurement(LSM) was performed by FibroScan. Cut-off points of LSM, NFS and FIB-4 for rule-in or rule-out F3-F4 fibrosis were calculated by the reported formulas. In the Sicilian cohort AUCs of LSM, NFS, FIB-4, LSM plus NFS, LSM plus FIB-4, and NFS plus FIB-4 were 0.857, 0.803, 0.790, 0.878, 0.888 and 0.807, respectively, while in the northern Italy cohort the corresponding AUCs were 0.848, 0.730, 0.703, 0.844, 0.850, and 0.733 respectively. In the training cohort, the combination of LSM plus NFS was the best performing strategy, providing false positive, false negative and uncertainty area rates of 0%,1.1% and 48% respectively. Similar results were obtained in the validation cohort with false positive, false negative and uncertainty area rates of 0%,7.3% and 40.8%. The combination of LSM with NFS, two complementary, easy-to-perform, and widely available tools, is able to accurately diagnose or exclude the presence of severe liver fibrosis, also reducing of about 50-60% the number of needed diagnostic liver biopsies. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  3. Evaluation of Liver and Spleen Stiffness with Acoustic Radiation Force Impulse Quantification Elastography for Diagnosing Clinically Significant Portal Hypertension.

    PubMed

    Attia, D; Schoenemeier, B; Rodt, T; Negm, A A; Lenzen, H; Lankisch, T O; Manns, M; Gebel, M; Potthoff, A

    2015-12-01

    Hepatic vein pressure gradient (HVPG) is the gold standard for diagnosing clinically significant portal hypertension (CSPH). The aim of this study was to investigate-in comparison to HVPG-the ability to diagnose CSPH by liver and spleen stiffness measurements obtained by acoustic radiation force impulse (ARFI) imaging. A total of 78 patients (mean age: 53 ± 13 years, 62 % male) with chronic liver disease were enrolled in this study. Each patient received liver (LSM) and spleen (SSM) stiffness measurements by ARFI, an HVPG measurement and a transjugular liver biopsy on the same day. Patients were classified according to their HVPG into three different groups: HVPG < 10 mmHg, HVPG ≥ 10-< 12 mmHg and HVPG ≥ 12 mmHg. LSM, SSM were significantly higher in patients with HVPG ≥ 10 - < 12 in comparison to HVPG < 10 mmHg (p < 0.001 and p < 0.001, respectively), and in patients with HVPG ≥ 12 mmHg in comparison to ≥ 10 - < 12 mmHg (p < 0.001 and p < 0.001, respectively). LSM and SSM were able to diagnose HVPG ≥ 10 mmHg and HVPG ≥ 12 mmHg with high diagnostic performance (AUC LSM: 0.93 and 0.87, respectively; AUC SSM: 0.97 and 0.95, respectively). The AUC of SSM in predicting esophageal varices (EVs) plus HVPG ≥ 10 mmHg and EVs plus HVPG ≥ 12 mmHg were higher compared to LSM in both groups of patients (SSM: 0.90 and 0.93 vs. LSM: 0.84 and 0.88, respectively). No significant difference between both AUCs was detected in the different HVPG groups. In the multivariate -analysis SSM remained a factor predicting HVPG (HVPG > 10 mmHg p = 0.007; HVPG ≥ 12 mmHg p = 0.003). LSM and SSM by ARFI are noninvasive diagnostic tools that may help in diagnosing CSPH. LSM and SSM could be used as a guiding noninvasive screening tool in patients with esophageal varices requiring endoscopic evaluation. © Georg Thieme Verlag KG Stuttgart · New York.

  4. Diagnostic value of FIB-4, aspartate aminotransferase-to-platelet ratio index and liver stiffness measurement in hepatitis B virus-infected patients with persistently normal alanine aminotransferase.

    PubMed

    Tan, You-Wen; Zhou, Xing-Bei; Ye, Yun; He, Cong; Ge, Guo-Hong

    2017-08-21

    To assess the diagnostic value of FIB-4, aspartate aminotransferase-to-platelet ratio index (APRI), and liver stiffness measurement (LSM) in patients with hepatitis B virus infection who have persistently normal alanine transaminase (PNALT). We enrolled 245 patients with chronic hepatitis B: 95 in PNALT group, 86 in intermittently elevated alanine transaminase (PIALT1) group [alanine transaminase (ALT) within 1-2 × upper limit of normal value (ULN)], and 64 in PIALT2 group (ALT > 2 × ULN). All the patients received a percutaneous liver biopsy guided by ultrasonography. LSM, biochemical tests, and complete blood cell counts were performed. The pathological examination revealed moderate inflammatory necrosis ratios of 16.81% (16/95), 32.56% (28/86), and 45.31% (28/64), and moderate liver fibrosis of 24.2% (23/95), 33.72% (29/86), and 43.75% (28/64) in the PNALT, PIALT1, and PIALT2 groups, respectively. The degrees of inflammation and liver fibrosis were significantly higher in the PIALT groups than in the PNALT group ( P < 0.05). No significant difference was found in the areas under the curve (AUCs) between APRI and FIB-4 in the PNALT group; however, significant differences were found between APRI and LSM, and between FIB-4 and LSM in the PNALT group ( P < 0.05 for both). In the PIALT1 and PIALT2 groups, no significant difference ( P > 0.05) was found in AUCs for all comparisons ( P > 0.05 for all). In the overall patients, a significant difference in the AUCs was found only between LSM and APRI ( P < 0.05). APRI and FIB-4 are not the ideal noninvasive hepatic fibrosis markers for PNALT patients. LSM is superior to APRI and FIB-4 in PNALT patients because of the influence of liver inflammation and necrosis.

  5. Diagnostic value of FIB-4, aspartate aminotransferase-to-platelet ratio index and liver stiffness measurement in hepatitis B virus-infected patients with persistently normal alanine aminotransferase

    PubMed Central

    Tan, You-Wen; Zhou, Xing-Bei; Ye, Yun; He, Cong; Ge, Guo-Hong

    2017-01-01

    AIM To assess the diagnostic value of FIB-4, aspartate aminotransferase-to-platelet ratio index (APRI), and liver stiffness measurement (LSM) in patients with hepatitis B virus infection who have persistently normal alanine transaminase (PNALT). METHODS We enrolled 245 patients with chronic hepatitis B: 95 in PNALT group, 86 in intermittently elevated alanine transaminase (PIALT1) group [alanine transaminase (ALT) within 1-2 × upper limit of normal value (ULN)], and 64 in PIALT2 group (ALT > 2 × ULN). All the patients received a percutaneous liver biopsy guided by ultrasonography. LSM, biochemical tests, and complete blood cell counts were performed. RESULTS The pathological examination revealed moderate inflammatory necrosis ratios of 16.81% (16/95), 32.56% (28/86), and 45.31% (28/64), and moderate liver fibrosis of 24.2% (23/95), 33.72% (29/86), and 43.75% (28/64) in the PNALT, PIALT1, and PIALT2 groups, respectively. The degrees of inflammation and liver fibrosis were significantly higher in the PIALT groups than in the PNALT group (P < 0.05). No significant difference was found in the areas under the curve (AUCs) between APRI and FIB-4 in the PNALT group; however, significant differences were found between APRI and LSM, and between FIB-4 and LSM in the PNALT group (P < 0.05 for both). In the PIALT1 and PIALT2 groups, no significant difference (P > 0.05) was found in AUCs for all comparisons (P > 0.05 for all). In the overall patients, a significant difference in the AUCs was found only between LSM and APRI (P < 0.05). CONCLUSION APRI and FIB-4 are not the ideal noninvasive hepatic fibrosis markers for PNALT patients. LSM is superior to APRI and FIB-4 in PNALT patients because of the influence of liver inflammation and necrosis. PMID:28883700

  6. Predictive value of liver and spleen stiffness in advanced alcoholic cirrhosis with refractory ascites.

    PubMed

    Lindner, Franziska; Mühlberg, Reinhard; Wiegand, Johannes; Tröltzsch, Michael; Hoffmeister, Albrecht; Keim, Volker; Karlas, Thomas

    2018-06-01

     Recurrent ascitic decompensation is a frequent complication of advanced alcoholic liver disease. Ascites can be controlled by transjugular intrahepatic portosystemic shunt (TIPS) implantation, but specific pre-procedural outcome predictors are not well established. Liver and spleen stiffness measurement (LSM, SSM) correlate with outcome of compensated liver disease, but data for decompensated cirrhosis disease are scarce. Therefore, the predictive value of LSM and SSM was evaluated in patients with refractory ascites treated with TIPS insertion or receiving conservative therapy.  Patients with alcoholic liver cirrhosis and recurrent or refractory ascites were stratified according to TIPS eligibility. LSM was prospectively assessed by transient elastography (TE, XL probe) and point shear wave elastography (pSWE). pSWE was also used for SSM. The primary study endpoint was transplant-free survival after 12 months. In addition, correlation of LSM and SSM with TIPS complications was analyzed.  43 patients (16 % female, age 55.5 [28.6 - 79.6] years) were recruited, n = 20 underwent TIPS and n = 23 were treated with repeated paracenteses only. 15 patients died and five underwent liver transplantation during follow-up. LSM and SSM at baseline did not predict the patients' outcome in the TIPS cohort and in patients with conservative therapy. SSM was increased in two cases with spontaneous TIPS occlusion and declined after revision.  LSM and SSM cannot be recommended for risk stratification in cirrhotic patients with refractory ascites. SSM may be useful in monitoring TIPS function during follow-up. © Georg Thieme Verlag KG Stuttgart · New York.

  7. Liver stiffness identifies two different patterns of fibrosis progression in patients with hepatitis C virus recurrence after liver transplantation.

    PubMed

    Carrión, José A; Torres, Ferran; Crespo, Gonzalo; Miquel, Rosa; García-Valdecasas, Juan-Carlos; Navasa, Miquel; Forns, Xavier

    2010-01-01

    Significant liver fibrosis (F >or= 2) and portal hypertension (hepatic venous pressure gradient [HVPG] >or= 6 mmHg) at 1 year after liver transplantation (LT) identify patients with severe hepatitis C recurrence. We evaluated whether repeated liver stiffness measurements (LSM) following LT can discriminate between slow and rapid "fibrosers" (fibrosis stage F2-F4 at 1 year after LT). Eighty-four patients who had undergone LT and who were infected with hepatitis C virus (HCV) and 19 LT controls who were not infected with HCV underwent LSM at 3, 6, 9, and 12 months after LT. All HCV-infected patients underwent liver biopsy 12 months after LT (paired HVPG measurements in 74); 31 (37%) were rapid fibrosers. Median LSM (in kilopascal) at months 6, 9, and 12 were significantly higher in rapid fibrosers (9.9, 9.5, 12.1) than in slow fibrosers (6.9, 7.5, 6.6) (P < 0.01 all time points). The slope of liver stiffness progression (kPa x month) in rapid fibrosers (0.42) was significantly greater than in slow fibrosers (0.05) (P < 0.001), suggesting two different speeds of liver fibrosis progression. Figures were almost identical for patients with HVPG >or= 6 mmHg or HVPG < 6 mmHg at 1 year after LT. Multivariate analysis identified donor age, bilirubin level, and LSM as independent predictors of fibrosis progression and portal hypertension in the estimation group (n = 50) and were validated in a second group of 34 patients. The areas under the receiver operating characteristic curve that could identify rapid fibrosers and patients with portal hypertension as early as 6 months after LT were 0.83 and 0.87, respectively, in the estimation group and 0.75 and 0.80, respectively, in the validation group. Early and repeated LSM following hepatitis C recurrence in combination with clinical variables discriminates between rapid and slow fibrosers after LT.

  8. Development of a stiffness-angle law for simplifying the measurement of human hair stiffness.

    PubMed

    Jung, I K; Park, S C; Lee, Y R; Bin, S A; Hong, Y D; Eun, D; Lee, J H; Roh, Y S; Kim, B M

    2018-04-01

    This research examines the benefits of caffeine absorption on hair stiffness. To test hair stiffness, we have developed an evaluation method that is not only accurate, but also inexpensive. Our evaluation method for measuring hair stiffness culminated in a model, called the Stiffness-Angle Law, which describes the elastic properties of hair and can be widely applied to the development of hair care products. Small molecules (≤500 g mol -1 ) such as caffeine can be absorbed into hair. A common shampoo containing 4% caffeine was formulated and applied to hair 10 times, after which the hair stiffness was measured. The caffeine absorption of the treated hair was observed using Fourier-transform infrared spectroscopy (FTIR) with a focal plane array (FPA) detector. Our evaluation method for measuring hair stiffness consists of a regular camera and a support for single strands of hair. After attaching the hair to the support, the bending angle of the hair was observed with a camera and measured. Then, the hair strand was weighed. The stiffness of the hair was calculated based on our proposed Stiffness-Angle Law using three variables: angle, weight of hair and the distance the hair was pulled across the support. The caffeine absorption was confirmed by FTIR analysis. The concentration of amide bond in the hair certainly increased due to caffeine absorption. After caffeine was absorbed into the hair, the bending angle and weight of the hair changed. Applying these measured changes to the Stiffness-Angle Law, it was confirmed that the hair stiffness increased by 13.2% due to caffeine absorption. The theoretical results using the Stiffness-Angle Law agree with the visual examinations of hair exposed to caffeine and also the known results of hair stiffness from a previous report. Our evaluation method combined with our proposed Stiffness-Angle Law effectively provides an accurate and inexpensive evaluation technique for measuring bending stiffness of human hair. © 2018

  9. OroSTIFF: Face-referenced measurement of perioral stiffness in health and disease.

    PubMed

    Chu, Shin-Ying; Barlow, Steven M; Kieweg, Douglas; Lee, Jaehoon

    2010-05-28

    A new device and automated measurement technology known as OroSTIFF is described to characterize non-participatory perioral stiffness in healthy adults for eventual application to patients with orofacial movement disorders associated with neuromotor disease, traumatic injury, or congenital clefts of the upper lip. Previous studies of perioral biomechanics required head stabilization for extended periods of time during measurement, which precluded sampling patients with involuntary body/head movements (dyskinesias), or pediatric subjects. The OroSTIFF device is face-referenced and avoids the complications associated with head-restraint. Supporting data of non-participatory perioral tissue stiffness using OroSTIFF are included from 10 male and 10 female healthy subjects. The OroSTIFF device incorporates a pneumatic glass air cylinder actuator instrumented for pressure, and an integrated subminiature displacement sensor to encode lip aperture. Perioral electromyograms were simultaneously sampled to confirm passive muscle state for the superior and inferior divisions of the orbicularis oris muscles. Perioral stiffness, derived as a quotient from resultant force (DeltaF) and interangle span (DeltaX), was modeled with multilevel regression techniques. Real-time calculation of the perioral stiffness function demonstrated a significant quadratic relation between imposed interangle stretch and resultant force. This stiffness growth function also differed significantly between males and females. This study demonstrates the OroSTIFF 'proof-of-concept' for cost-effective non-invasive stimulus generation and derivation of perioral stiffness in a group of healthy unrestrained adults, and a case study to illustrate the dose-dependent effects of Levodopa on perioral stiffness in an individual with advanced Parkinson's disease who exhibited marked dyskinesia and rigidity. Copyright 2010 Elsevier Ltd. All rights reserved.

  10. Feasibility study of superconducting LSM rocket launcher system

    NASA Technical Reports Server (NTRS)

    Yoshida, Kinjiro; Ohashi, Takaaki; Shiraishi, Katsuto; Takami, Hiroshi

    1994-01-01

    A feasibility study is presented concerning an application of a superconducting linear synchronous motor (LSM) to a large-scale rocket launcher, whose acceleration guide tube of LSM armature windings is constructed 1,500 meters under the ground. The rocket is released from the linear launcher just after it gets to a peak speed of about 900 kilometers per hour, and it flies out of the guide tube to obtain the speed of 700 kilometers per hour at the height of 100 meters above ground. The linear launcher is brought to a stop at the ground surface for a very short time of 5 seconds by a quick control of deceleration. Very large current variations in the single-layer windings of the LSM armature, which are produced at the higher speed region of 600 to 900 kilometers per hour, are controlled successfully by adopting the double-layer windings. The proposed control method makes the rocket launcher ascend stably in the superconducting LSM system, controlling the Coriolis force.

  11. Diagnostic accuracy and prognostic significance of blood fibrosis tests and liver stiffness measurement by FibroScan in non-alcoholic fatty liver disease.

    PubMed

    Boursier, Jérôme; Vergniol, Julien; Guillet, Anne; Hiriart, Jean-Baptiste; Lannes, Adrien; Le Bail, Brigitte; Michalak, Sophie; Chermak, Faiza; Bertrais, Sandrine; Foucher, Juliette; Oberti, Frédéric; Charbonnier, Maude; Fouchard-Hubert, Isabelle; Rousselet, Marie-Christine; Calès, Paul; de Lédinghen, Victor

    2016-09-01

    NAFLD is highly prevalent but only a small subset of patients develop advanced liver fibrosis with impaired liver-related prognosis. We aimed to compare blood fibrosis tests and liver stiffness measurement (LSM) by FibroScan for the diagnosis of liver fibrosis and the evaluation of prognosis in NAFLD. Diagnostic accuracy was evaluated in a cross-sectional study including 452 NAFLD patients with liver biopsy (NASH-CRN fibrosis stage), LSM, and eight blood fibrosis tests (BARD, NAFLD fibrosis score, FibroMeter(NAFLD), aspartate aminotransferase to platelet ratio index (APRI), FIB4, FibroTest, Hepascore, FibroMeter(V2G)). Prognostic accuracy was evaluated in a longitudinal study including 360 NAFLD patients. LSM and FibroMeter(V2G) were the two best-performing tests in the cross-sectional study: AUROCs for advanced fibrosis (F3/4) were, respectively, 0.831±0.019 and 0.817±0.020 (p⩽0.041 vs. other tests); rates of patients with ⩾90% negative/positive predictive values for F3/4 were 56.4% and 46.7% (p<0.001 vs. other tests); Obuchowski indexes were 0.834±0.014 and 0.798±0.016 (p⩽0.036 vs. other tests). Two fibrosis classifications were developed to precisely estimate the histological fibrosis stage from LSM or FibroMeter(V2G) results without liver biopsy (diagnostic accuracy, respectively: 80.8% vs. 77.4%, p=0.190). Kaplan-Meier curves in the longitudinal study showed that both classifications categorised NAFLD patients into subgroups with significantly different prognoses (p<0.001): the higher was the class of the fibrosis classification, the worse was the prognosis. LSM and FibroMeter(V2G) were the most accurate of nine evaluated tests for the non-invasive diagnosis of liver fibrosis in NAFLD. LSM and FibroMeter(V2G) fibrosis classifications help physicians estimate both fibrosis stage and patient prognosis in clinical practice. The amount of liver fibrosis is the main determinant of the liver-related prognosis in patients with non-alcoholic fatty liver

  12. Direct-Acting Antiviral Therapy for Chronic HCV Infection Results in Liver Stiffness Regression Over 12 Months Post-treatment.

    PubMed

    Chan, Justin; Gogela, Neliswa; Zheng, Hui; Lammert, Sara; Ajayi, Tokunbo; Fricker, Zachary; Kim, Arthur Y; Robbins, Gregory K; Chung, Raymond T

    2018-02-01

    Liver fibrosis stage determines risk of morbidity and mortality from chronic hepatitis C virus (HCV) infection. Prior data have shown long-term reversal of liver fibrosis, measured by vibration-controlled transient elastography (VCTE), in patients successfully treated with interferon-based therapies. Our study sought to determine the effect of treatment with modern HCV direct-acting antiviral (DAA) therapy on noninvasive liver fibrosis measurements. A total of 70 patients had VCTE-based liver stiffness measurement (LSM) taken before treatment, directly after treatment completion, and at least 12 months after completion of DAA therapy. Our primary outcome was a >30% improvement in VCTE score at the end of follow-up, relative to baseline. The sustained virologic response rate in our cohort was 95.7%. In our cohort, 34 (48.6%) met the primary outcome. Those who had baseline elevated alanine aminotransferase (OR 3.27; 95% CI 1.13-9.47) and genotype 1 (OR 14.63; 95% CI 1.70-125.83) had higher odds of meeting that outcome, and this remained significant after adjusting for age, baseline body mass index, gender, baseline elevated alkaline phosphatase levels, treatment experience, liver transplant status, smoking, and baseline liver stiffness. Treatment of chronic HCV with modern DAA therapy was associated with a significant improvement in LSM by VCTE measurement, suggesting possible early improvement in liver fibrosis along with resolution of inflammation over the first year after treatment completion.

  13. Defining essential elements and genetic interactions of the yeast Lsm2-8 ring and demonstration that essentiality of Lsm2-8 is bypassed via overexpression of U6 snRNA or the U6 snRNP subunit Prp24.

    PubMed

    Roth, Allen J; Shuman, Stewart; Schwer, Beate

    2018-06-01

    A seven-subunit Lsm2-8 protein ring assembles on the U-rich 3' end of the U6 snRNA. A structure-guided mutational analysis of the Saccharomyces cerevisiae Lsm2-8 ring affords new insights to structure-function relations and genetic interactions of the Lsm subunits. Alanine scanning of 39 amino acids comprising the RNA-binding sites or intersubunit interfaces of Lsm2, Lsm3, Lsm4, Lsm5, and Lsm8 identified only one instance of lethality (Lsm3-R69A) and one severe growth defect (Lsm2-R63A), both involving amino acids that bind the 3'-terminal UUU trinucleotide. All other Ala mutations were benign with respect to vegetative growth. Tests of 235 pairwise combinations of benign Lsm mutants identified six instances of inter-Lsm synthetic lethality and 45 cases of nonlethal synthetic growth defects. Thus, Lsm2-8 ring function is buffered by a network of internal genetic redundancies. A salient finding was that otherwise lethal single-gene deletions lsm2 Δ, lsm3 Δ, lsm4 Δ, lsm5 , and lsm8 Δ were rescued by overexpression of U6 snRNA from a high-copy plasmid. Moreover, U6 overexpression rescued myriad lsm Δ lsm Δ double-deletions and lsm Δ lsm Δ lsm Δ triple-deletions. We find that U6 overexpression also rescues a lethal deletion of the U6 snRNP protein subunit Prp24 and that Prp24 overexpression bypasses the essentiality of the U6-associated Lsm subunits. Our results indicate that abetting U6 snRNA is the only essential function of the yeast Lsm2-8 proteins. © 2018 Roth et al.; Published by Cold Spring Harbor Laboratory Press for the RNA Society.

  14. Improvement of liver stiffness measurement, acoustic radiation force impulse measurements, and noninvasive fibrosis markers after direct-acting antivirals for hepatitis C virus G4 recurrence post living donor liver transplantation: Egyptian cohort.

    PubMed

    Alem, Shereen Abdel; Said, Mohamed; Anwar, Ismail; Abdellatif, Zeinab; Elbaz, Tamer; Eletreby, Rasha; AbouElKhair, Mahmoud; El-Serafy, Magdy; Mogawer, Sherif; El-Amir, Mona; El-Shazly, Mostafa; Hosny, Adel; Yosry, Ayman

    2018-05-02

    Progression of recurrent hepatitis C is accelerated in liver transplant (LT) recipients. Direct-acting antivirals (DAAs) have recently emerged as a promising therapeutic regimen for the treatment of hepatitis C virus infection. Rates of sustained virological response (SVR) have drastically improved since the introduction of DAAs. The aim is to elucidate the changes in liver stiffness measurement (LSM) by transient elastography (TE) as well as acoustic radiation force impulse (ARFI) elastography and fibrosis scores after DAA treatment in LT recipients with hepatitis C virus recurrence. A single-center, prospective study including 58 LT recipients with hepatitis C recurrence who received different sofosbuvir-based treatment regimens. Transient elastography and ARFI elastography values were recorded as well as fibrosis 4 score (FIB-4) and aspartate aminotransferase-to-platelet ratio index were calculated at baseline and SVR at week 24 (SVR24). The outcome was improvement in LSM and at least a 20% decrease in LSM at SVR24 compared with baseline. The sustained virological response was 98.1%. There was improvement of platelet counts, alanine aminotransferase, and aspartate aminotransferase, which in turn caused improvement in fibrosis scores at SVR24. LSM by TE and ARFI elastography decreased from the baseline median value of 6.3 kPa (interquartile range [IQR]; 4.6 to 8.8 kPa) and 1.28 m/s (IQR; 1.07 to 1.53 m/s) to an SVR24 median value of 6.2 kPa (IQR; 4.85 to 8.9 kPa) and 1.12 (IQR; 0.97 to 1.30 m/s), respectively. Logistic regression analysis showed that baseline viral load was the only significant predictor of improvement in LS after DAA therapy at SVR24. Sofosbuvir-based treatment resulted in an early improvement in parameters of liver fibrosis in post-LT patients with hepatitis C recurrence. © 2018 Wiley Periodicals, Inc.

  15. On-treatment changes of liver stiffness at week 26 could predict 2-year clinical outcomes in HBV-related compensated cirrhosis.

    PubMed

    Wu, Shanshan; Kong, Yuanyuan; Piao, Hongxin; Jiang, Wei; Xie, Wen; Chen, Yongpeng; Lu, Lungen; Ma, Anlin; Xie, Shibin; Ding, Huiguo; Shang, Jia; Zhang, Xuqing; Feng, Bo; Han, Tao; Xu, Xiaoyuan; Huo, Lijuan; Cheng, Jilin; Li, Hai; Wu, Xiaoning; Zhou, Jialing; Sun, Yameng; Ou, Xiaojuan; Zhang, Hui; You, Hong; Jia, Jidong

    2018-06-01

    It is unclear whether liver stiffness measurement (LSM) dynamic changes after anti-HBV treatment could predict the risk of liver-related events (LREs), particularly in patients with HBV-related compensated cirrhosis. Treatment-naïve patients with HBV-related compensated cirrhosis were enrolled. All patients were under entecavir-based antiviral therapy, and followed up every 26 weeks for 2 years. The association between LSM and LREs was analysed by Cox proportional hazard model and Harrell C-index analysis. A total of 438 patients were included in the study. At the follow-up of 104 weeks, LREs developed in 33/438 (7.8%) patients, including 16 episodes of decompensation, 18 HCC and 3 deaths. The median LSM remained high from 20.9, 18.6, 20.4 to 20.3 Kpa at week 0, 26, 52 and 78 among patients with LREs, whereas the LSM decreased from 17.8, 12.3, 10.6 to 10.2 Kpa in patients without LREs respectively. Percentage changes of LSM at 26 weeks from baseline were significantly associated with LREs (excluding 11 cases occurred within the first 26 weeks), with a crude hazard ratio of 2.94 (95% CI: 1.73-5.00) and an albumin-adjusted hazard ratio of 2.47 (95% CI: 1.49-4.11). The Harrell C-index of these 2 models for predicting 2-year LREs were 0.68 (95% CI: 0.56-0.80) and 0.75 (95% CI: 0.65-0.85) respectively. Nomograms were developed to identify individuals at high risk for point-of-care application. Dynamic changes of LSM alone, or combined with baseline albumin, could predict LREs in patients with HBV-related compensated cirrhosis during antiviral therapy. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  16. Arterial Stiffness in Children: Pediatric Measurement and Considerations

    PubMed Central

    Savant, Jonathan D.; Furth, Susan L.; Meyers, Kevin E.C.

    2014-01-01

    Background Arterial stiffness is a natural consequence of aging, accelerated in certain chronic conditions, and predictive of cardiovascular events in adults. Emerging research suggests the importance of arterial stiffness in pediatric populations. Methods There are different indices of arterial stiffness. The present manuscript focuses on carotid-femoral pulse wave velocity and pulse wave analysis, although other methodologies are discussed. Also reviewed are specific measurement considerations for pediatric populations and the literature describing arterial stiffness in children with certain chronic conditions (primary hypertension, obesity, diabetes, chronic kidney disease, hypercholesterolemia, genetic syndromes involving vasculopathy, and solid organ transplant recipients). Conclusions The measurement of arterial stiffness in children is feasible and, under controlled conditions, can give accurate information about the underlying state of the arteries. This potentially adds valuable information about the functionality of the cardiovascular system in children with a variety of chronic diseases well beyond that of the brachial artery blood pressure. PMID:26587447

  17. Direct measurement of the intrinsic ankle stiffness during standing.

    PubMed

    Vlutters, M; Boonstra, T A; Schouten, A C; van der Kooij, H

    2015-05-01

    Ankle stiffness contributes to standing balance, counteracting the destabilizing effect of gravity. The ankle stiffness together with the compliance between the foot and the support surface make up the ankle-foot stiffness, which is relevant to quiet standing. The contribution of the intrinsic ankle-foot stiffness to balance, and the ankle-foot stiffness amplitude dependency remain a topic of debate in the literature. We therefore developed an experimental protocol to directly measure the bilateral intrinsic ankle-foot stiffness during standing balance, and determine its amplitude dependency. By applying fast (40 ms) ramp-and-hold support surface rotations (0.005-0.08 rad) during standing, reflexive contributions could be excluded, and the amplitude dependency of the intrinsic ankle-foot stiffness was investigated. Results showed that reflexive activity could not have biased the torque used for estimating the intrinsic stiffness. Furthermore, subjects required less recovery action to restore balance after bilateral rotations in opposite directions compared to rotations in the same direction. The intrinsic ankle-foot stiffness appears insufficient to ensure balance, ranging from 0.93±0.09 to 0.44±0.06 (normalized to critical stiffness 'mgh'). This implies that changes in muscle activation are required to maintain balance. The non-linear stiffness decrease with increasing rotation amplitude supports the previous published research. With the proposed method reflexive effects can be ruled out from the measured torque without any model assumptions, allowing direct estimation of intrinsic stiffness during standing. Copyright © 2015 Elsevier Ltd. All rights reserved.

  18. Estimating chronic hepatitis C prognosis using transient elastography-based liver stiffness: A systematic review and meta-analysis.

    PubMed

    Erman, A; Sathya, A; Nam, A; Bielecki, J M; Feld, J J; Thein, H-H; Wong, W W L; Grootendorst, P; Krahn, M D

    2018-05-01

    Chronic hepatitis C (CHC) is a leading cause of hepatic fibrosis and cirrhosis. The level of fibrosis is traditionally established by histology, and prognosis is estimated using fibrosis progression rates (FPRs; annual probability of progressing across histological stages). However, newer noninvasive alternatives are quickly replacing biopsy. One alternative, transient elastography (TE), quantifies fibrosis by measuring liver stiffness (LSM). Given these developments, the purpose of this study was (i) to estimate prognosis in treatment-naïve CHC patients using TE-based liver stiffness progression rates (LSPR) as an alternative to FPRs and (ii) to compare consistency between LSPRs and FPRs. A systematic literature search was performed using multiple databases (January 1990 to February 2016). LSPRs were calculated using either a direct method (given the difference in serial LSMs and time elapsed) or an indirect method given a single LSM and the estimated duration of infection and pooled using random-effects meta-analyses. For validation purposes, FPRs were also estimated. Heterogeneity was explored by random-effects meta-regression. Twenty-seven studies reporting on 39 groups of patients (N = 5874) were identified with 35 groups allowing for indirect and 8 for direct estimation of LSPR. The majority (~58%) of patients were HIV/HCV-coinfected. The estimated time-to-cirrhosis based on TE vs biopsy was 39 and 38 years, respectively. In univariate meta-regressions, male sex and HIV were positively and age at assessment, negatively associated with LSPRs. Noninvasive prognosis of HCV is consistent with FPRs in predicting time-to-cirrhosis, but more longitudinal studies of liver stiffness are needed to obtain refined estimates. © 2017 John Wiley & Sons Ltd.

  19. Laser speckle micro-rheology for biomechanical evaluation of breast tumors (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Hajjarian Kashany, Zeinab; Nadkarni, Seemantini K.

    2016-03-01

    The stiffness of the extra cellular matrix (ECM) is recognized as a key regulator of cancer cell proliferation, migration and invasion. Therefore technologies that quantify ECM stiffness with micro-scale scale resolution will likely provide important insights into neoplastic progression. Laser Speckle Micro-Rheology (LSM) is a novel optical tool for measuring tissue viscoelastic properties with micro-scale resolution. In LSM, speckle images are collected through an objective lens by a high-speed camera. Spatio-temporal correlation analysis of speckle frames yields the intensity autocorrelation function, g2(t), for each pixel, and subsequently a 2D map of viscoelastic modulus, G*(ω) is reconstructed. Here, we investigate the utility of LSM for micro-mechanical evaluation of the ECM in human breast lesions. Specimens collected 18 women undergoing lumpectomy or mastectomy were evaluated with LSM. Because collagen is the key protein associated with ECM stiffness, G*(ω) maps obtained from LSM were compared with collagen content measured by second harmonic generation (SHG) microscopy. Regions of low G*(ω), identified by LSM, corresponded to low-intensity SHG signal and adipose tissue. Likewise, regions with high G*(ω) in LSM images matched high intensity SHG signal caused by desmoplastic collagen accumulation. Quantitative regression analysis demonstrated a strong, statistically significant correlation between G*(ω) and SHG signal intensity (R=0.66 p< 0.01). These findings highlight the capability of LSM for quantifying the ECM micro-mechanics, potentially providing important insights into the biomechanical regulators of breast cancer progression.

  20. Measuring the Characteristic Topography of Brain Stiffness with Magnetic Resonance Elastography

    PubMed Central

    Murphy, Matthew C.; Huston, John; Jack, Clifford R.; Glaser, Kevin J.; Senjem, Matthew L.; Chen, Jun; Manduca, Armando; Felmlee, Joel P.; Ehman, Richard L.

    2013-01-01

    Purpose To develop a reliable magnetic resonance elastography (MRE)-based method for measuring regional brain stiffness. Methods First, simulation studies were used to demonstrate how stiffness measurements can be biased by changes in brain morphometry, such as those due to atrophy. Adaptive postprocessing methods were created that significantly reduce the spatial extent of edge artifacts and eliminate atrophy-related bias. Second, a pipeline for regional brain stiffness measurement was developed and evaluated for test-retest reliability in 10 healthy control subjects. Results This technique indicates high test-retest repeatability with a typical coefficient of variation of less than 1% for global brain stiffness and less than 2% for the lobes of the brain and the cerebellum. Furthermore, this study reveals that the brain possesses a characteristic topography of mechanical properties, and also that lobar stiffness measurements tend to correlate with one another within an individual. Conclusion The methods presented in this work are resistant to noise- and edge-related biases that are common in the field of brain MRE, demonstrate high test-retest reliability, and provide independent regional stiffness measurements. This pipeline will allow future investigations to measure changes to the brain’s mechanical properties and how they relate to the characteristic topographies that are typical of many neurologic diseases. PMID:24312570

  1. Spicule matrix protein LSM34 is essential for biomineralization of the sea urchin spicule.

    PubMed

    Peled-Kamar, Mira; Hamilton, Patricia; Wilt, Fred H

    2002-01-01

    Biomineralized skeletal structures are composite materials containing mineral and matrix protein(s). The cell biological mechanisms that underlie the formation, secretion, and organization of the biomineralized materials are not well understood. Although the matrix proteins influence physical properties of the structures, little is known of the role of these matrix proteins in the actual formation of the biomineralized structure. We present here results using an antisense oligonucleotide directed against a spicule matrix protein, LSM34, present in spicules of embryos of Lytechinus pictus. After injection of anti-LSM34 into the blastocoel of a sea urchin embryo, LSM34 protein in the primary mesenchyme cells decreases and biomineralization ceases, demonstrating that LSM34 function is essential for the formation of the calcareous endoskeletal spicule of the embryo. Since LSM34 is found primarily in a specialized extracellular matrix surrounding the spicule, it is probable that this matrix is important for the biomineralization process.

  2. Non-Contact Stiffness Measurement of a Suspended Single Walled Carbon Nanotube Device

    NASA Technical Reports Server (NTRS)

    Zheng, Yun; Su, Chanmin; Getty, Stephanie

    2010-01-01

    A new nanoscale electric field sensor was developed for studying triboelectric charging in terrestrial and Martian dust devils. This sensor is capable to measure the large electric fields for large dust devils without saturation. However, to quantify the electric charges and the field strength it is critical to calibrate the mechanical stiffness of the sensor devices. We performed a technical feasibility study of the Nano E-field Sensor stiffness by a non-contact stiffness measurement method. The measurement is based on laser Doppler vibrometer measurement of the thermal noise due to energy flunctuations in the devices. The experiment method provides a novel approach to acquire data that is essential in analyzing the quantitative performance of the E-field Nano Sensor. To carry out the non-contact stiffness measurement, we fabricated a new Single-Walled Carbon Nanotube (SWCNT) E-field sensor with different SWCNTs suspension conditions. The power spectra of the thermal induced displacement in the nano E-field sensor were measured at the accuracy of picometer. The power spectra were then used to derive the mechanical stiffness of the sensors. Effect of suspension conditions on stiffness and sensor sensitivty was discussed. After combined deformation and resistivity measurement, we can compare with our laboratory testing and field testing results. This new non-contact measurement technology can also help to explore to other nano and MEMS devices in the future.

  3. Elevated liver stiffness is linked to increased biomarkers of inflammation and immune activation in HIV/hepatitis C virus-coinfected patients.

    PubMed

    Medrano, Luz M; Garcia-Broncano, Pilar; Berenguer, Juan; González-García, Juan; Jiménez-Sousa, Ma Ángeles; Guardiola, Josep M; Crespo, Manuel; Quereda, Carmen; Sanz, José; Canorea, Isabel; Carrero, Ana; Hontañón, Victor; Muñoz-Fernández, Ma Ángeles; Resino, Salvador

    2018-06-01

    Immune dysregulation is a hallmark of HIV and hepatitis C virus (HCV) infections. We aimed to evaluate the relationship between liver stiffness measurement (LSM) and biomarkers of T-cell activation, bacterial translocation, inflammation, endothelial dysfunction, and coagulopathy in HIV/HCV-coinfected patients. Cross-sectional study. We studied 238 HIV/HCV-coinfected patients, 32 healthy controls, and 39 HIV-monoinfected patients. Patients were stratified according to LSM into four groups: less than 12.5, 12.5-25, 25-40, and more than 40 kPa. T-cell subsets were measured using flow cytometry and plasma biomarkers using immunoassays. HIV/HCV-coinfected patients had higher biomarker levels of immune activation in peripheral blood [T-cell activation (CD4CD38 and CD8CD38), bacterial translocation (soluble CD14), inflammation [IL-1b, IL-6, IL-8, IL-18, IFN-γ-inducible protein 10 (IP-10)] endothelial dysfunction [soluble vascular cell adhesion molecule 1 (sVCAM1), soluble intercellular cell adhesion molecule 1 (sICAM1), and soluble tumor necrosis factor receptor 1 (sTNFR1)], and coagulopathy (plasminogen activator inhibitor-1)] than healthy controls and HIV-monoinfected patients. Moreover, in HIV/HCV-coinfected patients, a direct relationship between LSM and immune activation [T-cell activation (CD8CD38 bacterial translocation (lipopolysaccharide), inflammation (IL-8, IP-10), endothelial dysfunction (sVCAM1, sICAM1, and sTNFR1), and coagulopathy (D-dimer)] was found. Subsequently, patients were stratified into different fibrosis stages, finding that patients with cirrhosis who had LSM at least 40 kPa showed higher biomarker values of immune activation [T-cell activation (CD4CD38 and CD8CD38), bacterial translocation (lipopolysaccharide), inflammation (IL-8, IL-6, IP-10), endothelial dysfunction (sVCAM1, sICAM1, and sTNFR1), and coagulopathy (D-dimer)] than patients from the other three groups (<12.5, 12.5-25, and 25-40 kPa). T-cell activation, bacterial

  4. Measurement of stiffness of standing trees and felled logs using acoustics: A review.

    PubMed

    Legg, Mathew; Bradley, Stuart

    2016-02-01

    This paper provides a review on the use of acoustics to measure stiffness of standing trees, stems, and logs. An outline is given of the properties of wood and how these are related to stiffness and acoustic velocity throughout the tree. Factors are described that influence the speed of sound in wood, including the different types of acoustic waves which propagate in tree stems and lumber. Acoustic tools and techniques that have been used to measure the stiffness of wood are reviewed. The reasons for a systematic difference between direct and acoustic measurements of stiffness for standing trees, and methods for correction, are discussed. Other techniques, which have been used in addition to acoustics to try to improve stiffness measurements, are also briefly described. Also reviewed are studies which have used acoustic tools to investigate factors that influence the stiffness of trees. These factors include different silvicultural practices, geographic and environmental conditions, and genetics.

  5. Stiffness measurement of a biomaterial by optical manipulation of microparticle

    NASA Astrophysics Data System (ADS)

    Kim, Jung-Dae; Waleed, Muhammad; Lee, Yong-Gu

    2013-02-01

    Since the discovery of the trapping nature of laser beam, optical tweezers have been extensively employed to measure various parameters at micro/nano level. Optical tweezers show exceptional sensitivity to weak forces making it one of the most sensitive force measurement devices. In this work, we present a technique to measure the stiffness of a biomaterial at different points. For this purpose, a microparticle stuck at the bottom of the dish is illuminated by the trapping laser and respective QPD signal as a function of the distance between the focus of the laser and the center of the microparticle is monitored. After this, microparticle is trapped and manipulated towards the target biomaterial and when it touches the cell membrane, QPD signal shows variation. By comparing two different QPD signals and measuring the trap stiffness, a technique is described to measure the stiffness of the biomaterial at a particular point. We believe that this parameter can be used as a tool to identify and classify different biomaterials.

  6. PolyMUMPs MEMS device to measure mechanical stiffness of single cells in aqueous media

    NASA Astrophysics Data System (ADS)

    Warnat, S.; King, H.; Forbrigger, C.; Hubbard, T.

    2015-02-01

    A method of experimentally determining the mechanical stiffness of single cells by using differential displacement measurements in a two stage spring system is presented. The spring system consists of a known MEMS reference spring and an unknown cellular stiffness: the ratio of displacements is related to the ratio of stiffness. A polyMUMPs implementation for aqueous media is presented and displacement measurements made from optical microphotographs using a FFT based displacement method with a repeatability of ~20 nm. The approach was first validated on a MEMS two stage spring system of known stiffness. The measured stiffness ratios of control structures (i) MEMS spring systems and (ii) polystyrene microspheres were found to agree with theoretical values. Mechanical tests were then performed on Saccharomyces cerevisiae (Baker’s yeast) in aqueous media. Cells were placed (using a micropipette) inside MEMS measuring structures and compressed between two jaws using an electrostatic actuator and displacements measured. Tested cells showed stiffness values between 5.4 and 8.4 N m-1 with an uncertainty of 11%. In addition, non-viable cells were tested by exposing viable cells to methanol. The resultant mean cell stiffness dropped by factor of 3 × and an explicit discrimination between viable and non-viable cells based on mechanical stiffness was seen.

  7. Optoelectronic tweezers for the measurement of the relative stiffness of erythrocytes

    NASA Astrophysics Data System (ADS)

    Neale, Steven L.; Mody, Nimesh; Selman, Colin; Cooper, Jonathan M.

    2012-10-01

    In this paper we describe the first use of Optoelectronic Tweezers (OET), an optically controlled micromanipulation method, to measure the relative stiffness of erythrocytes in mice. Cell stiffness is an important measure of cell health and in the case of erythrocytes, the most elastic cells in the body, an increase in cell stiffness can indicate pathologies such as type II diabetes mellitus or hypertension (high blood pressure). OET uses a photoconductive device to convert an optical pattern into and electrical pattern. The electrical fields will create a dipole within any polarisable particles in the device, such as cells, and non-uniformities of the field can be used to place unequal forces onto each side of the dipole thus moving the particle. In areas of the device where there are no field gradients, areas of constant illumination, the force on each side of the dipole will be equal, keeping the cell stationary, but as there are opposing forces on each side of the cell it will be stretched. The force each cell will experience will differ slightly so the stretching will depend on the cells polarisability as well as its stiffness. Because of this a relative stiffness rather than absolute stiffness is measured. We show that with standard conditions (20Vpp, 1.5MHz, 10mSm-1 medium conductivity) the cell's diameter changes by around 10% for healthy mouse erythrocytes and we show that due to the low light intensities required for OET, relative to conventional optical tweezers, multiple cells can be measured simultaneously.

  8. Flexural Stiffness of Myosin Va Subdomains as Measured from Tethered Particle Motion

    PubMed Central

    Michalek, Arthur J.; Kennedy, Guy G.; Warshaw, David M.; Ali, M. Yusuf

    2015-01-01

    Myosin Va (MyoVa) is a processive molecular motor involved in intracellular cargo transport on the actin cytoskeleton. The motor's processivity and ability to navigate actin intersections are believed to be governed by the stiffness of various parts of the motor's structure. Specifically, changes in calcium may regulate motor processivity by altering the motor's lever arm stiffness and thus its interhead communication. In order to measure the flexural stiffness of MyoVa subdomains, we use tethered particle microscopy, which relates the Brownian motion of fluorescent quantum dots, which are attached to various single- and double-headed MyoVa constructs bound to actin in rigor, to the motor's flexural stiffness. Based on these measurements, the MyoVa lever arm and coiled-coil rod domain have comparable flexural stiffness (0.034 pN/nm). Upon addition of calcium, the lever arm stiffness is reduced 40% as a result of calmodulins potentially dissociating from the lever arm. In addition, the flexural stiffness of the full-length MyoVa construct is an order of magnitude less stiff than both a single lever arm and the coiled-coil rod. This suggests that the MyoVa lever arm-rod junction provides a flexible hinge that would allow the motor to maneuver cargo through the complex intracellular actin network. PMID:26770194

  9. Mapping microscopic order in plant and mammalian cells and tissues: novel differential polarization attachment for new generation confocal microscopes (DP-LSM)

    NASA Astrophysics Data System (ADS)

    Steinbach, G.; Pawlak, K.; Pomozi, I.; Tóth, E. A.; Molnár, A.; Matkó, J.; Garab, G.

    2014-03-01

    Elucidation of the molecular architecture of complex, highly organized molecular macro-assemblies is an important, basic task for biology. Differential polarization (DP) measurements, such as linear (LD) and circular dichroism (CD) or the anisotropy of the fluorescence emission (r), which can be carried out in a dichrograph or spectrofluorimeter, respectively, carry unique, spatially averaged information about the molecular organization of the sample. For inhomogeneous samples—e.g. cells and tissues—measurements on macroscopic scale are not satisfactory, and in some cases not feasible, thus microscopic techniques must be applied. The microscopic DP-imaging technique, when based on confocal laser scanning microscope (LSM), allows the pixel by pixel mapping of anisotropy of a sample in 2D and 3D. The first DP-LSM configuration, which, in fluorescence mode, allowed confocal imaging of different DP quantities in real-time, without interfering with the ‘conventional’ imaging, was built on a Zeiss LSM410. It was demonstrated to be capable of determining non-confocally the linear birefringence (LB) or LD of a sample and, confocally, its FDLD (fluorescence detected LD), the degree of polarization (P) and the anisotropy of the fluorescence emission (r), following polarized and non-polarized excitation, respectively (Steinbach et al 2009 Acta Histochem.111 316-25). This DP-LSM configuration, however, cannot simply be adopted to new generation microscopes with considerably more compact structures. As shown here, for an Olympus FV500, we designed an easy-to-install DP attachment to determine LB, LD, FDLD and r, in new-generation confocal microscopes, which, in principle, can be complemented with a P-imaging unit, but specifically to the brand and type of LSM.

  10. Dynamics of liver stiffness values by means of transient elastography in patients with HCV liver cirrhosis undergoing interferon free treatment.

    PubMed

    Sporea, Ioan; Lupușoru, Raluca; Mare, Ruxandra; Popescu, Alina; Gheorghe, Liana; Iacob, Speranța; Șirli, Roxana

    2017-06-01

    Liver stiffness (LS) measurement by Transient Elastography (TE) has been widely accepted as a tool for fibrosis assessment. The aim of this study was to assess LS dynamics in a group of patients with HCV liver cirrhosis after interferon free treatment (IFT). This two-center clinical trial included 225 patients with compensated HCV cirrhosis (all genotype 1b), who received IFT for 12 weeks. All patients were evaluated by means of TE at the beginning and at the end of treatment (EOT), and a subgroup (170 patients) also 12 weeks after EOT; all of them had sustained viral response (SVR). Reliable LS measurements (LSM) were defined as a median value of 10 valid LSM, with IQR <30% and SR >/=60%. Both M and XL probes were used. For diagnosing cirrhosis we used a cut-off value of 12kPa as proposed by the Tsochatzis meta-analysis. We considered a decrease or increase of more than 10% in LSM as being significant. Out of 225 subjects, reliable measurements were obtained in 93.7%, so that the final analysis included 211 patients. The mean LS values decreased significantly after IFT: 26.4+/-11.7 vs. 23.5+/-13.3 kPa (p=0.01). Most patients, 59.2% (125/211) presented more than 10% decrease in LS values, 24.1% (51/211) had stable LS values, while in 16.4% (35/211) cases, the LS values increased. In the subgroup of 170 patients with LSM also performed 12 weeks after EOT (SVR), the mean LS values were significantly lower as compared to baseline: 21.3+/-11 kPa vs. 27.4+/-11.9 kPa (p<0.0001) and also as compared to EOT: 21.3+/-11 kPa vs. 23.7+/-13.3 kPa (p<0.0001). In our patients with HCV liver cirrhosis, the mean LS values evaluated by TE significantly decreased after antiviral treatment at EOT and also 12 weeks after EOT as compared to baseline. Overall, about 60% of patients had LS values at EOT lower than at baseline, while 12 weeks after EOT about 75% of patients had LS values lower than at baseline.

  11. Electromechanical Dynamics Simulations of Superconducting LSM Rocket Launcher System in Attractive-Mode

    NASA Technical Reports Server (NTRS)

    Yoshida, Kinjiro; Hayashi, Kengo; Takami, Hiroshi

    1996-01-01

    Further feasibility study on a superconducting linear synchronous motor (LSM) rocket launcher system is presented on the basis of dynamic simulations of electric power, efficiency and power factor as well as the ascending motions of the launcher and rocket. The advantages of attractive-mode operation are found from comparison with repulsive-mode operation. It is made clear that the LSM rocket launcher system, of which the long-stator is divided optimally into 60 sections according to launcher speeds, can obtain high efficiency and power factor.

  12. High temperature oxidation behavior of interconnect coated with LSCF and LSM for solid oxide fuel cell by screen printing

    NASA Astrophysics Data System (ADS)

    Lee, Shyong; Chu, Chun-Lin; Tsai, Ming-Jui; Lee, Jye

    2010-01-01

    The current study examined the effect of La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) and La 0.7Sr 0.3MnO 3 (LSM) coatings on the electrical properties and oxidation resistance of Crofer22 APU at 800 °C hot air. LSCF and LSM were coated on Crofer22 APU by screen printing and sintered over temperatures ranging from 1000 to 1100 °C in N 2. The coated alloy was first checked for compositions, morphology and interface conditions and then treated in a simulated oxidizing environment at 800 °C for 200 h. After measuring the long-term electrical resistance, the area specific resistance (ASR) at 800 °C for the alloy coated with LSCF was less than its counterpart coated with LSM. This work used LSCF coating as a metallic interconnect to reduce working temperature for the solid oxide fuel cell.

  13. “An Impediment to Living Life”: Why and How Should We Measure Stiffness in Polymyalgia Rheumatica?

    PubMed Central

    Mackie, Sarah Louise; Hughes, Rodney; Walsh, Margaret; Day, John; Newton, Marion; Pease, Colin; Kirwan, John; Morris, Marianne

    2015-01-01

    Objectives To explore patients’ concepts of stiffness in polymyalgia rheumatica (PMR), and how they think stiffness should be measured. Methods Eight focus groups were held at three centres involving 50 patients with current/previous PMR. Each group had at least one facilitator and one rapporteur making field notes. An interview schedule was used to stimulate discussion. Interviews were recorded, transcribed and analysed using an inductive thematic approach. Results Major themes identified were: symptoms: pain, stiffness and fatigue; functional impact; impact on daily schedule; and approaches to measurement. The common subtheme for the experience of stiffness was “difficulty in moving”, and usually considered as distinct from the experience of pain, albeit with a variable overlap. Some participants felt stiffness was the “overwhelming” symptom, in that it prevented them carrying out “fundamental activities” and “generally living life”. Diurnal variation in stiffness was generally described in relation to the daily schedule but was not the same as stiffness severity. Some participants suggested measuring stiffness using a numeric rating scale or a Likert scale, while others felt that it was more relevant and straightforward to measure difficulty in performing everyday activities rather than about stiffness itself. Conclusions A conceptual model of stiffness in PMR is presented where stiffness is an important part of the patient experience and impacts on their ability to live their lives. Stiffness is closely related to function and often regarded as interchangeable with pain. From the patients’ perspective, visual analogue scales measuring pain and stiffness were not the most useful method for reporting stiffness; participants preferred numerical rating scales, or assessments of function to reflect how stiffness impacts on their daily lives. Assessing function may be a pragmatic solution to difficulties in quantifying stiffness. PMID:25955770

  14. Development of Self-made LSM Software using in Neuroscience

    NASA Astrophysics Data System (ADS)

    Doronin, Maxim; Makovkin, Sergey; Popov, Alexander

    2017-07-01

    One of the main and modern visualization method in neuroscience is two-photon microscopy. However, scientists need to upgrade their microscopy system so regular because they are interested to get more specific data. Self-developed microscopy system allows to modify the construction of microscope in not-complicated manner depending on specialized experimental models and scientific tasks. Earlier we reported about building of self-made laser scanning microscope (LSM) using in neuroscience both for in vivo and in vitro experiments. Here we will report how to create software AMAScan for LSM controlling in MATLAB. The work was performed with financial support of the government represented by the Ministry of Education and Science of the Russian Federation, the unique identifier of the project is RFMEFI58115X0016, the agreement on granting a subsidy №14.581.21.0016 dated 14.10.2015.

  15. Measuring Age-Dependent Myocardial Stiffness across the Cardiac Cycle using MR Elastography: A Reproducibility Study

    PubMed Central

    Wassenaar, Peter A; Eleswarpu, Chethanya N; Schroeder, Samuel A; Mo, Xiaokui; Raterman, Brian D; White, Richard D; Kolipaka, Arunark

    2015-01-01

    Purpose To assess reproducibility in measuring left ventricular (LV) myocardial stiffness in volunteers throughout the cardiac cycle using magnetic resonance elastography (MRE) and to determine its correlation with age. Methods Cardiac MRE (CMRE) was performed on 29 normal volunteers, with ages ranging from 21 to 73 years. For assessing reproducibility of CMRE-derived stiffness measurements, scans were repeated per volunteer. Wave images were acquired throughout the LV myocardium, and were analyzed to obtain mean stiffness during the cardiac cycle. CMRE-derived stiffness values were correlated to age. Results Concordance correlation coefficient revealed good inter-scan agreement with rc of 0.77, with p-value<0.0001. Significantly higher myocardial stiffness was observed during end-systole (ES) compared to end-diastole (ED) across all subjects. Additionally, increased deviation between ES and ED stiffness was observed with increased age. Conclusion CMRE-derived stiffness is reproducible, with myocardial stiffness changing cyclically across the cardiac cycle. Stiffness is significantly higher during ES compared to ED. With age, ES myocardial stiffness increases more than ED, giving rise to an increased deviation between the two. PMID:26010456

  16. Optical Phase Measurements of Disorder Strength Link Microstructure to Cell Stiffness.

    PubMed

    Eldridge, Will J; Steelman, Zachary A; Loomis, Brianna; Wax, Adam

    2017-02-28

    There have been sustained efforts on the part of cell biologists to understand the mechanisms by which cells respond to mechanical stimuli. To this end, many rheological tools have been developed to characterize cellular stiffness. However, measurement of cellular viscoelastic properties has been limited in scope by the nature of most microrheological methods, which require direct mechanical contact, applied at the single-cell level. In this article, we describe, to our knowledge, a new analysis approach for quantitative phase imaging that relates refractive index variance to disorder strength, a parameter that is linked to cell stiffness. Significantly, both disorder strength and cell stiffness are measured with the same phase imaging system, presenting a unique alternative for label-free, noncontact, single-shot imaging of cellular rheologic properties. To demonstrate the potential applicability of the technique, we measure phase disorder strength and shear stiffness across five cellular populations with varying mechanical properties and demonstrate an inverse relationship between these two parameters. The existence of this relationship suggests that predictions of cell mechanical properties can be obtained from examining the disorder strength of cell structure using this, to our knowledge, novel, noncontact technique. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  17. Serial Liver Stiffness Measurements and Monitoring of Liver-Transplanted Patients in a Real-Life Clinical Practice

    PubMed Central

    Rinaldi, Luca; Valente, Giovanna; Piai, Guido

    2016-01-01

    Background Liver transplanted patients need close surveillance for early signs of graft disease. Objectives Transient elastography can safely be repeated over time, offering serial liver stiffness measurement values. Serial stiffness measurements were compared to single baseline stiffness measurements in predicting the appearance of liver-related clinical events and guiding subsequent clinical decisions. Methods One hundred and sixty liver transplanted patients were observed for three years in our real-life practice. Results Liver stiffness measurements were stable in 75% of patients, decreased in 4% of patients, and increased in 21% of patients. The pattern of increased stiffness measurements was associated with both HCV-RNA positive status and the presence of an active biliary complication of liver transplantation and was more predictive of a clinically significant event resulting from any disease of the transplanted liver when compared to a stable pattern or to a single liver stiffness measurement. The procedures that were consequently performed were often diagnostic for unexpected situations, both in HCV-RNA positive and HCV-RNA negative patients. Conclusions The pattern of longitudinally increased liver stiffness measurements efficiently supported clinical decisions for individualized management strategies. Repeated transient elastography in real-life clinical practice appears to have a practical role in monitoring liver transplanted patients. PMID:28123442

  18. Correlations among measures of knee stiffness, gait performance and complaints in individuals with knee osteoarthritis.

    PubMed

    Oatis, Carol A; Wolff, Edward F; Lockard, Margery A; Michener, Lori A; Robbins, Steven J

    2013-03-01

    Stiffness is a common complaint in individuals with knee osteoarthritis and is a component of the osteoarthritis diagnosis. Yet the relationship between stiffness and function is poorly understood and methods to quantify stiffness are limited. Using a cross-sectional observational design with 66 subjects with knee osteoarthritis, stiffness and damping coefficients were calculated from a relaxed knee oscillation procedure. Gait parameters were measured using an electronic walkway. Self-reported pain, stiffness, and function were measured with the Western Ontario and McMaster Osteoarthritis Index. Correlation and Alexander's normalized-t approximation analyses were used to assess associations among the variables. Subset analysis was performed on subjects with and without tibiofemoral joint crepitus. Slight to moderate correlations existed between stiffness and damping coefficients and most gait parameters ((| r |=0.30-0.56; P<.05) and between Western Ontario and McMaster Osteoarthritis Index scores and all gait parameters (| r |=0.35-0.62; P<.05). The damping coefficient was only slightly associated with patient-rated Western Ontario and McMaster Osteoarthritis Index stiffness subscale scores. Subset analysis revealed significant correlations that differed between those with and without crepitus. These findings suggest that laboratory measured stiffness and damping coefficients, Western Ontario and McMaster Osteoarthritis Index scores and gait-related measurements assess different aspects related to movement in individuals with knee osteoarthritis. Stiffness and damping coefficients may offer the ability to explain gait changes in the knee that are independent of a person's perceptions particularly in the early stages of the disease. Copyright © 2013 Elsevier Ltd. All rights reserved.

  19. Relationships between acoustic variables and different measures of stiffness in standing Pinus taeda trees

    Treesearch

    Christian R. Mora; Laurence R. Schimleck; Fikret Isik; Jerry M. Mahon Jr.; Alexander Clark III; Richard F. Daniels

    2009-01-01

    Acoustic tools are increasingly used to estimate standing-tree (dynamic) stiffness; however, such techniques overestimate static stiffness, the standard measurement for determining modulus of elasticity (MOE) of wood. This study aimed to identify correction methods for standing-tree estimates making dynamic and static stiffness comparable. Sixty Pinus taeda L...

  20. The yeast cytoplasmic LsmI/Pat1p complex protects mRNA 3' termini from partial degradation.

    PubMed Central

    He, W; Parker, R

    2001-01-01

    A key aspect of understanding eukaryotic gene regulation will be the identification and analysis of proteins that bind mRNAs and control their function. Recently, a complex of seven Lsm proteins and the Pat1p have been shown to interact with yeast mRNAs and promote mRNA decapping. In this study we present several observations to indicate that the LsmI/Pat1 complex has a second distinct function in protecting the 3'-UTR of mRNAs from trimming. First, mutations in the LSM1 to LSM7, as well as PAT1, genes led to the accumulation of MFA2pG and PGK1pG transcripts that had been shortened by 10-20 nucleotides at their 3' ends (referred to as trimming). Second, the trimming of these mRNAs was more severe at the high temperature, correlating with the inability of these mutant strains to grow at high temperature. In contrast, trimming did not occur in a dcp1 Delta strain, wherein the decapping enzyme is lacking. This indicates that trimming is not simply a consequence of the inhibition of mRNA decapping. Third, the temperature-sensitive growth of lsm and pat1 mutants was suppressed by mutations in the exosome or the functionally related Ski proteins, which are required for efficient 3' to 5' mRNA degradation of mRNA. Moreover, in lsm ski double mutants, higher levels of the trimmed mRNAs accumulated, indicating that exosome function is not required for mRNA trimming but that the exosome does degrade the trimmed mRNAs. These results raise the possibility that the temperature-sensitive growth of the lsm1-7 and pat1 mutants is at least partially due to mRNA trimming, which either inactivates the function of the mRNAs or makes them available for premature 3' to 5' degradation by the exosome. PMID:11514438

  1. Dynamic CT imaging of volumetric changes in pulmonary nodules correlates with physical measurements of stiffness.

    PubMed

    Lartey, Frederick M; Rafat, Marjan; Negahdar, Mohammadreza; Malkovskiy, Andrey V; Dong, Xinzhe; Sun, Xiaoli; Li, Mei; Doyle, Timothy; Rajadas, Jayakumar; Graves, Edward E; Loo, Billy W; Maxim, Peter G

    2017-02-01

    A major challenge in CT screening for lung cancer is limited specificity when distinguishing between malignant and non-malignant pulmonary nodules (PN). Malignant nodules have different mechanical properties and tissue characteristics ('stiffness') from non-malignant nodules. This study seeks to improve CT specificity by demonstrating in rats that measurements of volumetric ratios in PNs with varying composition can be determined by respiratory-gated dynamic CT imaging and that these ratios correlate with direct physical measurements of PN stiffness. Respiratory-gated MicroCT images acquired at extreme tidal volumes of 9 rats with PNs from talc, matrigel and A549 human lung carcinoma were analyzed and their volumetric ratios (δ) derived. PN stiffness was determined by measuring the Young's modulus using atomic force microscopy (AFM) for each nodule excised immediately after MicroCT imaging. There was significant correlation (p=0.0002) between PN volumetric ratios determined by respiratory-gated CT imaging and the physical stiffness of the PNs determined from AFM measurements. We demonstrated proof of concept that PN volume changes measured non-invasively correlate with direct physical measurements of stiffness. These results may translate clinically into a means of improving the specificity of CT screening for lung cancer and/or improving individual prognostic assessments based on lung tumor stiffness. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  2. Modeling of the oxygen reduction reaction for dense LSM thin films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yang, Tao; Liu, Jian; Yu, Yang

    In this study, the oxygen reduction reaction mechanism is investigated using numerical methods on a dense thin (La 1-xSr x) yMnO 3±δ film deposited on a YSZ substrate. This 1-D continuum model consists of defect chemistry and elementary oxygen reduction reaction steps coupled via reaction rates. The defect chemistry model contains eight species including cation vacancies on the A- and B-sites. The oxygen vacancy is calculated by solving species transportation equations in multiphysics simulations. Due to the simple geometry of a dense thin film, the oxygen reduction reaction was reduced to three elementary steps: surface adsorption and dissociation, incorporation onmore » the surface, and charge transfer across the LSM/YSZ interface. The numerical simulations allow for calculation of the temperature- and oxygen partial pressure-dependent properties of LSM. The parameters of the model are calibrated with experimental impedance data for various oxygen partial pressures at different temperatures. The results indicate that surface adsorption and dissociation is the rate-determining step in the ORR of LSM thin films. With the fine-tuned parameters, further quantitative analysis is performed. The activation energy of the oxygen exchange reaction and the dependence of oxygen non-stoichiometry on oxygen partial pressure are also calculated and verified using the literature results.« less

  3. Modeling of the oxygen reduction reaction for dense LSM thin films

    DOE PAGES

    Yang, Tao; Liu, Jian; Yu, Yang; ...

    2017-10-17

    In this study, the oxygen reduction reaction mechanism is investigated using numerical methods on a dense thin (La 1-xSr x) yMnO 3±δ film deposited on a YSZ substrate. This 1-D continuum model consists of defect chemistry and elementary oxygen reduction reaction steps coupled via reaction rates. The defect chemistry model contains eight species including cation vacancies on the A- and B-sites. The oxygen vacancy is calculated by solving species transportation equations in multiphysics simulations. Due to the simple geometry of a dense thin film, the oxygen reduction reaction was reduced to three elementary steps: surface adsorption and dissociation, incorporation onmore » the surface, and charge transfer across the LSM/YSZ interface. The numerical simulations allow for calculation of the temperature- and oxygen partial pressure-dependent properties of LSM. The parameters of the model are calibrated with experimental impedance data for various oxygen partial pressures at different temperatures. The results indicate that surface adsorption and dissociation is the rate-determining step in the ORR of LSM thin films. With the fine-tuned parameters, further quantitative analysis is performed. The activation energy of the oxygen exchange reaction and the dependence of oxygen non-stoichiometry on oxygen partial pressure are also calculated and verified using the literature results.« less

  4. Regardless-of-Speed Superconducting LSM Controlled-Repulsive MAGLEV Vehicle

    NASA Technical Reports Server (NTRS)

    Yoshida, Kinjiro; Egashira, Tatsuya; Hirai, Ryuichi

    1996-01-01

    This paper proposes a new repulsive Maglev vehicle which a superconducting linear synchronous motor (LSM) can levitate and propel simultaneously, independently of the vehicle speeds. The combined levitation and propulsion control is carried out by controlling mechanical-load angle and armature-current. Dynamic simulations show successful operations with good ride-quality by using a compact control method proposed here.

  5. System identification of velocity mechanomyogram measured with a capacitor microphone for muscle stiffness estimation.

    PubMed

    Uchiyama, Takanori; Tomoshige, Taiki

    2017-04-01

    A mechanomyogram (MMG) measured with a displacement sensor (displacement MMG) can provide a better estimation of longitudinal muscle stiffness than that measured with an acceleration sensor (acceleration MMG), but the displacement MMG cannot provide transverse muscle stiffness. We propose a method to estimate both longitudinal and transverse muscle stiffness from a velocity MMG using a system identification technique. The aims of this study are to show the advantages of the proposed method. The velocity MMG was measured using a capacitor microphone and a differential circuit, and the MMG, evoked by electrical stimulation, of the tibialis anterior muscle was measured five times in seven healthy young male volunteers. The evoked MMG system was identified using the singular value decomposition method and was approximated with a fourth-order model, which provides two undamped natural frequencies corresponding to the longitudinal and transverse muscle stiffness. The fluctuation of the undamped natural frequencies estimated from the velocity MMG was significantly smaller than that from the acceleration MMG. There was no significant difference between the fluctuations of the undamped natural frequencies estimated from the velocity MMG and that from the displacement MMG. The proposed method using the velocity MMG is thus more advantageous for muscle stiffness estimation. Copyright © 2017 Elsevier Ltd. All rights reserved.

  6. A Review on Atherosclerotic Biology, Wall Stiffness, Physics of Elasticity, and Its Ultrasound-Based Measurement.

    PubMed

    Patel, Anoop K; Suri, Harman S; Singh, Jaskaran; Kumar, Dinesh; Shafique, Shoaib; Nicolaides, Andrew; Jain, Sanjay K; Saba, Luca; Gupta, Ajay; Laird, John R; Giannopoulos, Argiris; Suri, Jasjit S

    2016-12-01

    Functional and structural changes in the common carotid artery are biomarkers for cardiovascular risk. Current methods for measuring functional changes include pulse wave velocity, compliance, distensibility, strain, stress, stiffness, and elasticity derived from arterial waveforms. The review is focused on the ultrasound-based carotid artery elasticity and stiffness measurements covering the physics of elasticity and linking it to biological evolution of arterial stiffness. The paper also presents evolution of plaque with a focus on the pathophysiologic cascade leading to arterial hardening. Using the concept of strain, and image-based elasticity, the paper then reviews the lumen diameter and carotid intima-media thickness measurements in combined temporal and spatial domains. Finally, the review presents the factors which influence the understanding of atherosclerotic disease formation and cardiovascular risk including arterial stiffness, tissue morphological characteristics, and image-based elasticity measurement.

  7. Optimization of the arthroscopic indentation instrument for the measurement of thin cartilage stiffness

    NASA Astrophysics Data System (ADS)

    Lyyra-Laitinen, Tiina; Niinimäki, Mia; Töyräs, Juha; Lindgren, Reijo; Kiviranta, Ilkka; Jurvelin, Jukka S.

    1999-10-01

    Structural alterations associated with early, mostly reversible, degeneration of articular cartilage induce tissue softening, generally preceding fibrillation and, thus, visible changes of the cartilage surface. We have already developed an indentation instrument for measuring arthroscopic stiffness of cartilage with typical thickness >2 mm. The aim of this study was to extend the applicability of the instrument for the measurement of thin (<2 mm) cartilage stiffness. Variations in cartilage thickness, which will not be known during arthroscopy, can nonetheless affect the indentation measurement, and therefore optimization of the indenter dimensions is necessary. First, we used theoretical and finite element models to compare plane-ended and spherical-ended indenters and, then, altered the dimensions to determine the optimal indenter for thin cartilage measurements. Finally, we experimentally validated the optimized indenter using bovine humeral head cartilage. Reference unconfined compression measurements were carried out with a material testing device. The spherical-ended indenter was more insensitive to the alterations in cartilage thickness (20% versus 39% in the thickness range 1.5-5 mm) than the plane-ended indenter. For thin cartilage, the optimal dimensions for the spherical-ended indenter were 0.5 mm for diameter and 0.1 mm for height. The experimental stiffness measurements with this indenter correlated well with the reference measurements (r = 0.811, n = 31, p<0.0001) in the cartilage thickness range 0.7-1.8 mm. We conclude that the optimized indenter is reliable and well suited for the measurement of thin cartilage stiffness.

  8. Measurement of Liver Stiffness Using Shear Wave Elastography in a Rat Model: Factors Impacting Stiffness Measurement with Multiple- and Single-Tracking-Location Techniques.

    PubMed

    Langdon, Jonathan H; Elegbe, Etana; Gonzalez, Raul S; Osapoetra, Laurentius; Ford, Tristan; McAleavey, Stephen A

    2017-11-01

    The clinical use of elastography for monitoring fibrosis progression is challenged by the subtle changes in liver stiffness associated with early-stage fibrosis and the comparatively large variance in stiffness estimates provided by elastography. Single-tracking-location (STL) shear wave elasticity imaging (SWEI) is an ultrasound elastography technique previously found to provide improved estimate precision compared with multiple-tracking-location (MTL) SWEI. Because of the improved precision, it is reasonable to expect that STL-SWEI would provide improved ability to differentiate liver fibrosis stage compared with MTL-SWEI. However, this expectation has not been previously challenged rigorously. In this work, the performance of STL- and MTL-SWEI in the setting of a rat model of liver fibrosis is characterized, and the advantages of STL-SWEI in staging fibrosis are explored. The purpose of this study was to determine what advantages, if any, arise from using STL-SWEI instead of MTL-SWEI in the characterization of fibrotic liver. Thus, the ability of STL-SWEI to differentiate livers at various METAVIR fibrosis scores, for ex vivo postmortem measurements, is explored. In addition, we examined the effect of the common confounding factor of fluid versus solid boundary conditions in SWEI experiments. Sprague-Dawley rats were treated with carbon tetrachloride over several weeks to produce liver disease of varying severity. STL and MTL stiffness measurements were performed ex vivo and compared with the METAVIR scores from histological analysis and the duration of treatment. A strong association was observed between liver stiffness and weeks of treatment with the liver toxin carbon tetrachloride. Direct comparison of STL- and MTL-SWEI measurements revealed no significant difference in ability to differentiate fibrosis stages based on SWEI mean values. However, image interquartile range was greatly improved in the case of STL-SWEI, compared with MTL-SWEI, at small beam

  9. Contact stiffness and damping identification for hardware-in-the-loop contact simulator with measurement delay compensation

    NASA Astrophysics Data System (ADS)

    Qi, Chenkun; Zhao, Xianchao; Gao, Feng; Ren, Anye; Sun, Qiao

    2016-06-01

    The hardware-in-the-loop (HIL) contact simulator is to simulate the contact process of two flying objects in space. The contact stiffness and damping are important parameters used for the process monitoring, compliant contact control and force compensation control. In this study, a contact stiffness and damping identification approach is proposed for the HIL contact simulation with the force measurement delay. The actual relative position of two flying objects can be accurately measured. However, the force measurement delay needs to be compensated because it will lead to incorrect stiffness and damping identification. Here, the phase lead compensation is used to reconstruct the actual contact force from the delayed force measurement. From the force and position data, the contact stiffness and damping are identified in real time using the recursive least squares (RLS) method. The simulations and experiments are used to verify that the proposed stiffness and damping identification approach is effective.

  10. A novel mechatronic system for measuring end-point stiffness: mechanical design and preliminary tests.

    PubMed

    Masia, L; Sandini, G; Morasso, P G

    2011-01-01

    Measuring arm stiffness is of great interest for many disciplines from biomechanics to medicine especially because modulation of impedance represents one of the main mechanism underlying control of movement and interaction with external environment. Previous works have proposed different methods to identify multijoint hand stiffness by using planar or even tridimensional haptic devices, but the associated computational burden makes them not easy to implement. We present a novel mechanism conceived for measuring multijoint planar stiffness by a single measurement and in a reduced execution time. A novel mechanical rotary device applies cyclic radial perturbation to human arm of a known displacement and the force is acquired by means of a 6-axes commercial load cell. The outcomes suggest that the system is not only reliable but allows obtaining a bi-dimensional estimation of arm stiffness in reduced amount of time and the results are comparable with those reported in previous researches. © 2011 IEEE

  11. Ultrasound elastography: the new frontier in direct measurement of muscle stiffness.

    PubMed

    Brandenburg, Joline E; Eby, Sarah F; Song, Pengfei; Zhao, Heng; Brault, Jeffrey S; Chen, Shigao; An, Kai-Nan

    2014-11-01

    The use of brightness-mode ultrasound and Doppler ultrasound in physical medicine and rehabilitation has increased dramatically. The continuing evolution of ultrasound technology has also produced ultrasound elastography, a cutting-edge technology that can directly measure the mechanical properties of tissue, including muscle stiffness. Its real-time and direct measurements of muscle stiffness can aid the diagnosis and rehabilitation of acute musculoskeletal injuries and chronic myofascial pain. It can also help monitor outcomes of interventions affecting muscle in neuromuscular and musculoskeletal diseases, and it can better inform the functional prognosis. This technology has implications for even broader use of ultrasound in physical medicine and rehabilitation practice, but more knowledge about its uses and limitations is essential to its appropriate clinical implementation. In this review, we describe different ultrasound elastography techniques for studying muscle stiffness, including strain elastography, acoustic radiation force impulse imaging, and shear-wave elastography. We discuss the basic principles of these techniques, including the strengths and limitations of their measurement capabilities. We review the current muscle research, discuss physiatric clinical applications of these techniques, and note directions for future research. Copyright © 2014 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.

  12. Ultrasound Elastography: The New Frontier in Direct Measurement of Muscle Stiffness

    PubMed Central

    Brandenburg, Joline E.; Eby, Sarah F.; Song, Pengfei; Zhao, Heng; Brault, Jeffrey S.; Chen, Shigao; An, Kai-Nan

    2014-01-01

    The use of brightness-mode ultrasound and Doppler ultrasound in physical medicine and rehabilitation has increased dramatically. The continuing evolution of ultrasound technology has also produced ultrasound elastography, a cutting-edge technology that can directly measure the mechanical properties of tissue, including muscle stiffness. Its real-time and direct measurements of muscle stiffness can aid the diagnosis and rehabilitation of acute musculoskeletal injuries and chronic myofascial pain. It can also help monitor outcomes of interventions affecting muscle in neuromuscular and musculoskeletal diseases, and it can better inform the functional prognosis. This technology has implications for even broader use of ultrasound in physical medicine and rehabilitation practice, but more knowledge about its uses and limitations is essential to its appropriate clinical implementation. In this review, we describe different ultrasound elastography techniques for studying muscle stiffness, including strain elastography, acoustic radiation force impulse imaging, and shear-wave elastography. We discuss the basic principles of these techniques, including the strengths and limitations of their measurement capabilities. We review the current muscle research, discuss physiatric clinical applications of these techniques, and note directions for future research. PMID:25064780

  13. Experimental measure of arm stiffness during single reaching movements with a time-frequency analysis

    PubMed Central

    Pierobon, Alberto; DiZio, Paul; Lackner, James R.

    2013-01-01

    We tested an innovative method to estimate joint stiffness and damping during multijoint unfettered arm movements. The technique employs impulsive perturbations and a time-frequency analysis to estimate the arm's mechanical properties along a reaching trajectory. Each single impulsive perturbation provides a continuous estimation on a single-reach basis, making our method ideal to investigate motor adaptation in the presence of force fields and to study the control of movement in impaired individuals with limited kinematic repeatability. In contrast with previous dynamic stiffness studies, we found that stiffness varies during movement, achieving levels higher than during static postural control. High stiffness was associated with elevated reflexive activity. We observed a decrease in stiffness and a marked reduction in long-latency reflexes around the reaching movement velocity peak. This pattern could partly explain the difference between the high stiffness reported in postural studies and the low stiffness measured in dynamic estimation studies, where perturbations are typically applied near the peak velocity point. PMID:23945781

  14. UPDATES AND EVALUATION OF THE PX-LSM IN MM5

    EPA Science Inventory

    Starting with Version 3.4, there is a new land surface model known as the Pleim-Xiu LSM available in the MM5 system. Pleim and Xiu (1995) described the initial development and testing of this land surface and workshop proceedings provided a basic description of the model and s...

  15. Prospective comparison among transient elastography, supersonic shear imaging, and ARFI imaging for predicting fibrosis in nonalcoholic fatty liver disease

    PubMed Central

    Joo, Sae Kyung; Woo, Hyunsik; Lee, Dong Hyeon; Jung, Yong Jin; Kim, Byeong Gwan; Lee, Kook Lae

    2017-01-01

    The diagnostic performance of supersonic shear imaging (SSI) in comparison with those of transient elastography (TE) and acoustic radiation force impulse imaging (ARFI) for staging fibrosis in nonalcoholic fatty liver disease (NAFLD) patients has not been fully assessed, especially in Asian populations with relatively lean NAFLD compared to white populations. Thus, we focused on comparing the diagnostic performances of TE, ARFI, and SSI for staging fibrosis in a head-to-head manner, and identifying the clinical, anthropometric, biochemical, and histological features which might affect liver stiffness measurement (LSM) in our prospective biopsy-proven NAFLD cohort. In this study, ninety-four patients with biopsy-proven NAFLD were included prospectively. Liver stiffness was measured using TE, SSI, and ARFI within 1 month of liver biopsy. The diagnostic performance for staging fibrosis was assessed using receiver operating characteristic (ROC) analysis. Anthropometric data were evaluated as covariates influencing LSM by regression analyses. Liver stiffness correlated with fibrosis stage (p < 0.05); the area under the ROC curve of TE (kPa), SSI (kPa), and ARFI (m/s) were as follows: 0.757, 0.759, and 0.657 for significant fibrosis and 0.870, 0.809, and 0.873 for advanced fibrosis. Anthropometric traits were significant confounders affecting SSI, while serum liver injury markers significantly confounded TE and ARFI. In conclusion, the LSM methods had similar diagnostic performance for staging fibrosis in patients with NAFLD. Pre-LSM anthropometric evaluation may help predict the reliability of SSI. PMID:29176844

  16. Insight into conformational changes of a single α-helix peptide molecule through stiffness measurements

    NASA Astrophysics Data System (ADS)

    Kageshima, Masami; Lantz, Mark A.; Jarvis, Suzanne P.; Tokumoto, Hiroshi; Takeda, Seiji; Ptak, Arkadiusz; Nakamura, Chikashi; Miyake, Jun

    2001-07-01

    Stiffness variations during the conformational change of a single α-helix polylysine peptide molecule were measured in a liquid environment using atomic force microscopy (AFM) with magnetic cantilever modulation. At the initial stage of the stretching process the stiffness decreased due to the breaking of hydrogen bonds and then increased due to the stretching of the helix backbone. These changes were reversible on reversal of the stretching motion. Below p K, the stiffness did not show increase on reversal, indicating that the reforming of hydrogen bonds did not take place. Conformational changes in the molecule were examined via these changes in stiffness.

  17. Finite Element Analysis of Single Cell Stiffness Measurements Using PZT-Integrated Buckling Nanoneedles

    PubMed Central

    Rad, Maryam Alsadat; Tijjani, Auwal Shehu; Ahmad, Mohd Ridzuan; Auwal, Shehu Muhammad

    2016-01-01

    This paper proposes a new technique for real-time single cell stiffness measurement using lead zirconate titanate (PZT)-integrated buckling nanoneedles. The PZT and the buckling part of the nanoneedle have been modelled and validated using the ABAQUS software. The two parts are integrated together to function as a single unit. After calibration, the stiffness, Young’s modulus, Poisson’s ratio and sensitivity of the PZT-integrated buckling nanoneedle have been determined to be 0.7100 N·m−1, 123.4700 GPa, 0.3000 and 0.0693 V·m·N−1, respectively. Three Saccharomyces cerevisiae cells have been modelled and validated based on compression tests. The average global stiffness and Young’s modulus of the cells are determined to be 10.8867 ± 0.0094 N·m−1 and 110.7033 ± 0.0081 MPa, respectively. The nanoneedle and the cell have been assembled to measure the local stiffness of the single Saccharomyces cerevisiae cells The local stiffness, Young’s modulus and PZT output voltage of the three different size Saccharomyces cerevisiae have been determined at different environmental conditions. We investigated that, at low temperature the stiffness value is low to adapt to the change in the environmental condition. As a result, Saccharomyces cerevisiae becomes vulnerable to viral and bacterial attacks. Therefore, the proposed technique will serve as a quick and accurate process to diagnose diseases at early stage in a cell for effective treatment. PMID:28025571

  18. Finite Element Analysis of Single Cell Stiffness Measurements Using PZT-Integrated Buckling Nanoneedles.

    PubMed

    Rad, Maryam Alsadat; Tijjani, Auwal Shehu; Ahmad, Mohd Ridzuan; Auwal, Shehu Muhammad

    2016-12-23

    This paper proposes a new technique for real-time single cell stiffness measurement using lead zirconate titanate (PZT)-integrated buckling nanoneedles. The PZT and the buckling part of the nanoneedle have been modelled and validated using the ABAQUS software. The two parts are integrated together to function as a single unit. After calibration, the stiffness, Young's modulus, Poisson's ratio and sensitivity of the PZT-integrated buckling nanoneedle have been determined to be 0.7100 N·m -1 , 123.4700 GPa, 0.3000 and 0.0693 V·m·N -1 , respectively. Three Saccharomyces cerevisiae cells have been modelled and validated based on compression tests. The average global stiffness and Young's modulus of the cells are determined to be 10.8867 ± 0.0094 N·m -1 and 110.7033 ± 0.0081 MPa, respectively. The nanoneedle and the cell have been assembled to measure the local stiffness of the single Saccharomyces cerevisiae cells The local stiffness, Young's modulus and PZT output voltage of the three different size Saccharomyces cerevisiae have been determined at different environmental conditions. We investigated that, at low temperature the stiffness value is low to adapt to the change in the environmental condition. As a result, Saccharomyces cerevisiae becomes vulnerable to viral and bacterial attacks. Therefore, the proposed technique will serve as a quick and accurate process to diagnose diseases at early stage in a cell for effective treatment.

  19. Measurement of the passive stiffness of ankle joint in 3 DOF using stewart platform type ankle foot device.

    PubMed

    Nomura, Kenta; Yonezawa, Teru; Mizoguchi, Hiroshi; Takemura, Hiroshi

    2016-08-01

    This paper presents a method to measure the passive stiffness of an ankle joint in three degrees of freedom (DOF) under two motion speeds (1 Hz and 5 degree/s) using a developed Stewart platform-type device. The developed device can reproduce input motions of the foot in 6 DOF by controlling six pneumatic linear motion actuators. We used the device to measure the passive stiffness of an ankle joint undergoing three kinds of motion, namely dorsi-plantar flexion, inversion-eversion, and adduction-abduction. The measured values of the passive stiffness of the ankle joint in dorsiflexion that we obtained agreed well with that obtained in a previous study, indicating that the developed device is useful for measuring the passive stiffness of ankle joint. In addition, the developed device can be used to measure the stiffness in inversion-eversion and adduction-abduction motions as well, parameters that have never been measured. The results we obtained demonstrated certain interesting features as we varied both the direction and pace of motion (e.g., there were significant differences in the stiffness not only between adduction and abduction during the faster pace, but also between these and the other motions).

  20. Trabecular meshwork stiffness in glaucoma.

    PubMed

    Wang, Ke; Read, A Thomas; Sulchek, Todd; Ethier, C Ross

    2017-05-01

    Alterations in stiffness of the trabecular meshwork (TM) may play an important role in primary open-angle glaucoma (POAG), the second leading cause of blindness. Specifically, certain data suggest an association between elevated intraocular pressure (IOP) and increased TM stiffness; however, the underlying link between TM stiffness and IOP remains unclear and requires further study. We here first review the literature on TM stiffness measurements, encompassing various species and based on a number of measurement techniques, including direct approaches such as atomic force microscopy (AFM) and uniaxial tension tests, and indirect methods based on a beam deflection model. We also briefly review the effects of several factors that affect TM stiffness, including lysophospholipids, rho-kinase inhibitors, cytoskeletal disrupting agents, dexamethasone (DEX), transforming growth factor-β 2 (TGF-β 2 ), nitric oxide (NO) and cellular senescence. We then describe a method we have developed for determining TM stiffness measurement in mice using a cryosection/AFM-based approach, and present preliminary data on TM stiffness in C57BL/6J and CBA/J mouse strains. Finally, we investigate the relationship between TM stiffness and outflow facility between these two strains. The method we have developed shows promise for further direct measurements of mouse TM stiffness, which may be of value in understanding mechanistic relations between outflow facility and TM biomechanical properties. Copyright © 2016 Elsevier Ltd. All rights reserved.

  1. Experimental validation of arthroscopic cartilage stiffness measurement using enzymatically degraded cartilage samples

    NASA Astrophysics Data System (ADS)

    Lyyra, T.; Arokoski, J. P. A.; Oksala, N.; Vihko, A.; Hyttinen, M.; Jurvelin, J. S.; Kiviranta, I.

    1999-02-01

    In order to evaluate the ability of the arthroscopic indentation instrument, originally developed for the measurement of cartilage stiffness during arthroscopy, to detect cartilage degeneration, we compared changes in the stiffness with the structural and constitutional alterations induced by enzymes on the tissue in vitro. The culturing of osteochondral plugs on Petri dishes was initiated in Minimum Essential Medium with Earle's salts and the baseline stiffness was measured. Then, the experimental specimens were digested using trypsin for 24 h, chondroitinase ABC or purified collagenase (type VII) for 24 h or 48 h ( n = 8-15 per group). The control specimens were incubated in the medium. After the enzyme digestion, the end-point stiffness was measured and the specimens for the microscopic analyses were processed. The proteoglycan (PG) distribution was analysed using quantitative microspectrophotometry and the quantitative evaluation of the collagen network was made using a computer-based polarized light microscopy analysis. Decrease of cartilage stiffness was found after 24 h trypsin (36%) and 48 h chondroitinase ABC (24%) digestion corresponding to a decrease of up to 80% and up to 30% in the PG content respectively. Decrease of the superficial zone collagen content or arrangement (78%, ) after 48 h collagenase digestion also induced a decrease (30%, ) in cartilage stiffness. We conclude that our instrument is capable of

  2. Effect of pistachio nut consumption on endothelial function and arterial stiffness.

    PubMed

    Kasliwal, Ravi R; Bansal, Manish; Mehrotra, Rahul; Yeptho, Kajal Pandya; Trehan, Naresh

    2015-05-01

    Previous studies have demonstrated beneficial effects of regular consumption of pistachio nuts on glycemic, lipid, and oxidative stress parameters. The aim of this study was to determine its effect on vascular health, which has not been adequately studied so far. In this open label, randomized parallel-group study, 60 adults with mild dyslipidemia were randomized to lifestyle modification (LSM) alone or LSM with consumption of 80 g (in-shell) pistachios (equivalent to 40 g or 1.5 oz shelled pistachios) daily for 3 mo. Biochemical parameters, brachial artery flow-mediated vasodilation (BAFMD), and carotid-femoral and brachial-ankle pulse wave velocity (cfPWV and baPWV, respectively) were measured before and after the intervention. At 3 mo, there was no change in any of the clinical or biochemical parameters in the LSM group. However, the patients in the pistachio group had a significant increase in high-density lipoprotein cholesterol (HDL-C; 35.7 ± 8.8 mg/dL versus 37.8 ± 10.1 mg/dL; P = 0.04) and a reduction in low-density lipoprotein cholesterol (137.2 ± 32.6 mg/dL versus 127.6 ± 34.0 mg/dL; P = 0.02), total cholesterol (TC)-to-HDL-C ratio (5.8 ± 1.3 mg/dL versus 5.3 ± 1.1 mg/dL; P = 0.001), and fasting blood sugar (88.8 ± 7.1 mg/dL versus 86.6 ± 6.3 mg/dL; P = 0.05). Additionally, whereas LSM alone was associated with no improvement in BAFMD or PWV, individuals in the pistachio group had significant reduction in left baPWV (1261.7 ± 187.5 cm/sec versus 1192.4 ± 152.5 cm/sec; P = 0.02) and statistically nonsignificant improvement in most other parameters, including BAFMD. As a result, at 3 mo the patients in the pistachio group had lower cfPWV (770.9 ± 96.5 cm/sec versus 846.4 ± 162.0 cm/sec; P = 0.08), lower left baPWV (1192.4 ± 152.5 cm/sec versus 1326.3 ± 253.7 cm/sec; P = 0.05), and lower average baPWV (1208.2 ± 118.4 cm/sec versus 1295.8 ± 194.1 cm/sec; P = 0.08) compared

  3. Accuracy and reproducibility of bending stiffness measurements by mechanical response tissue analysis in artificial human ulnas.

    PubMed

    Arnold, Patricia A; Ellerbrock, Emily R; Bowman, Lyn; Loucks, Anne B

    2014-11-07

    Osteoporosis is characterized by reduced bone strength, but no FDA-approved medical device measures bone strength. Bone strength is strongly associated with bone stiffness, but no FDA-approved medical device measures bone stiffness either. Mechanical Response Tissue Analysis (MRTA) is a non-significant risk, non-invasive, radiation-free, vibration analysis technique for making immediate, direct functional measurements of the bending stiffness of long bones in humans in vivo. MRTA has been used for research purposes for more than 20 years, but little has been published about its accuracy. To begin to investigate its accuracy, we compared MRTA measurements of bending stiffness in 39 artificial human ulna bones to measurements made by Quasistatic Mechanical Testing (QMT). In the process, we also quantified the reproducibility (i.e., precision and repeatability) of both methods. MRTA precision (1.0±1.0%) and repeatability (3.1 ± 3.1%) were not as high as those of QMT (0.2 ± 0.2% and 1.3+1.7%, respectively; both p<10(-4)). The relationship between MRTA and QMT measurements of ulna bending stiffness was indistinguishable from the identity line (p=0.44) and paired measurements by the two methods agreed within a 95% confidence interval of ± 5%. If such accuracy can be achieved on real human ulnas in situ, and if the ulna is representative of the appendicular skeleton, MRTA may prove clinically useful. Copyright © 2014 Elsevier Ltd. All rights reserved.

  4. Application of the combined FibroMeter vibration-controlled transient elastography algorithm in Chinese patients with non-alcoholic fatty liver disease.

    PubMed

    Loong, Thomson Chi-Wang; Wei, Jeremy Lok; Leung, Jonathan Chung-Fai; Wong, Grace Lai-Hung; Shu, Sally She-Ting; Chim, Angel Mei-Ling; Chan, Anthony Wing-Hung; Choi, Paul Cheung-Lung; Tse, Yee-Kit; Chan, Henry Lik-Yuen; Wong, Vincent Wai-Sun

    2017-07-01

    The FibroMeter vibration-controlled transient elastography (FM VCTE) is a new formula combining the serum test FM and liver stiffness measurement (LSM) by VCTE. We tested the accuracy and utility of FM VCTE for fibrosis staging in patients with non-alcoholic fatty liver disease (NAFLD). Two hundred fifteen NAFLD patients with LSM, FM NAFLD, FM VCTE, and other serum tests (aspartate aminotransferase-to-platelet ratio index, fibrosis-4 index, BARD score, NAFLD fibrosis score, and aspartate aminotransferase-to-alanine aminotransferase ratio) performed 1 day before liver biopsy were evaluated. Sixty-nine (32.1%) and 43 (20.0%) patients had F2-4 and F3-4, respectively. LSM had higher diagnostic accuracy (area under receiver-operating characteristics curves [AUROC] 0.851 for F2-4, 0.940 for F3-4; Obuchowski index 0.937 ± 0.007) than all evaluated serum tests, while FM NAFLD was the most accurate serum test (AUROC 0.775 and 0.774; Obuchowski index 0.891 ± 0.013). FM VCTE had similar accuracy to LSM (AUROC 0.855 and 0.901; Obuchowski index 0.927 ± 0.009). LSM had excellent negative predictive values of 92.4% and 99.2% to exclude F2-4 and F3-4, but the positive predictive values (PPV) were only 71.4% and 61.0%, respectively. In patients with high LSM, the use of FM VCTE improved the PPV from 71.4% to 84.4% for F2-4 and from 61.0% to 88.9% for F3-4. Liver biopsy could be spared in around 50-65% of patients. Liver stiffness measurement alone can confidently exclude significant and advanced fibrosis in NAFLD patients. Using FM VCTE in patients with high liver stiffness can increase the positive predictive value to rule in F2-4 and F3-4. © 2016 Journal of Gastroenterology and Hepatology Foundation and John Wiley & Sons Australia, Ltd.

  5. Aortic-Brachial Pulse Wave Velocity Ratio: A Measure of Arterial Stiffness Gradient Not Affected by Mean Arterial Pressure.

    PubMed

    Fortier, Catherine; Desjardins, Marie-Pier; Agharazii, Mohsen

    2018-03-01

    Aortic stiffness, measured by carotid-femoral pulse wave velocity (cf-PWV), is used for the prediction of cardiovascular risk. This mini-review describes the nonlinear relationship between cf-PWV and operational blood pressure, presents the proposed methods to adjust for this relationship, and discusses a potential place for aortic-brachial PWV ratio (a measure of arterial stiffness gradient) as a blood pressure-independent measure of vascular aging. PWV is inherently dependent on the operational blood pressure. In cross-sectional studies, PWV adjustment for mean arterial pressure (MAP) is preferred, but still remains a nonoptimal approach, as the relationship between PWV and blood pressure is nonlinear and varies considerably among individuals due to heterogeneity in genetic background, vascular tone, and vascular remodeling. Extrapolations from the blood pressure-independent stiffness parameter β (β 0 ) have led to the creation of stiffness index β, which can be used for local stiffness. A similar approach has been used for cardio-ankle PWV to generate a blood pressure-independent cardio-ankle vascular index (CAVI). It was recently demonstrated that stiffness index β and CAVI remain slightly blood pressure-dependent, and a more appropriate formula has been proposed to make the proper adjustments. On the other hand, the negative impact of aortic stiffness on clinical outcomes is thought to be mediated through attenuation or reversal of the arterial stiffness gradient, which can also be influenced by a reduction in peripheral medium-sized muscular arteries in conditions that predispose to accelerate vascular aging. Arterial stiffness gradient, assessed by aortic-brachial PWV ratio, is emerging to be at least as good as cf-PWV for risk prediction, but has the advantage of not being affected by operating MAP. The negative impacts of aortic stiffness on clinical outcomes are proposed to be mediated through attenuation or reversal of arterial stiffness gradient

  6. Integration of Acoustic Radiation Force and Optical Imaging for Blood Plasma Clot Stiffness Measurement

    PubMed Central

    Wang, Caroline W.; Perez, Matthew J.; Helmke, Brian P.; Viola, Francesco; Lawrence, Michael B.

    2015-01-01

    Despite the life-preserving function blood clotting serves in the body, inadequate or excessive blood clot stiffness has been associated with life-threatening diseases such as stroke, hemorrhage, and heart attack. The relationship between blood clot stiffness and vascular diseases underscores the importance of quantifying the magnitude and kinetics of blood’s transformation from a fluid to a viscoelastic solid. To measure blood plasma clot stiffness, we have developed a method that uses ultrasound acoustic radiation force (ARF) to induce micron-scaled displacements (1-500 μm) on microbeads suspended in blood plasma. The displacements were detected by optical microscopy and took place within a micro-liter sized clot region formed within a larger volume (2 mL sample) to minimize container surface effects. Modulation of the ultrasound generated acoustic radiation force allowed stiffness measurements to be made in blood plasma from before its gel point to the stage where it was a fully developed viscoelastic solid. A 0.5 wt % agarose hydrogel was 9.8-fold stiffer than the plasma (platelet-rich) clot at 1 h post-kaolin stimulus. The acoustic radiation force microbead method was sensitive to the presence of platelets and strength of coagulation stimulus. Platelet depletion reduced clot stiffness 6.9 fold relative to platelet rich plasma. The sensitivity of acoustic radiation force based stiffness assessment may allow for studying platelet regulation of both incipient and mature clot mechanical properties. PMID:26042775

  7. Integration of acoustic radiation force and optical imaging for blood plasma clot stiffness measurement.

    PubMed

    Wang, Caroline W; Perez, Matthew J; Helmke, Brian P; Viola, Francesco; Lawrence, Michael B

    2015-01-01

    Despite the life-preserving function blood clotting serves in the body, inadequate or excessive blood clot stiffness has been associated with life-threatening diseases such as stroke, hemorrhage, and heart attack. The relationship between blood clot stiffness and vascular diseases underscores the importance of quantifying the magnitude and kinetics of blood's transformation from a fluid to a viscoelastic solid. To measure blood plasma clot stiffness, we have developed a method that uses ultrasound acoustic radiation force (ARF) to induce micron-scaled displacements (1-500 μm) on microbeads suspended in blood plasma. The displacements were detected by optical microscopy and took place within a micro-liter sized clot region formed within a larger volume (2 mL sample) to minimize container surface effects. Modulation of the ultrasound generated acoustic radiation force allowed stiffness measurements to be made in blood plasma from before its gel point to the stage where it was a fully developed viscoelastic solid. A 0.5 wt % agarose hydrogel was 9.8-fold stiffer than the plasma (platelet-rich) clot at 1 h post-kaolin stimulus. The acoustic radiation force microbead method was sensitive to the presence of platelets and strength of coagulation stimulus. Platelet depletion reduced clot stiffness 6.9 fold relative to platelet rich plasma. The sensitivity of acoustic radiation force based stiffness assessment may allow for studying platelet regulation of both incipient and mature clot mechanical properties.

  8. Deletion of the Sm1 encoding motif in the lsm gene results in distinct changes in the transcriptome and enhanced swarming activity of Haloferax cells.

    PubMed

    Maier, Lisa-Katharina; Benz, Juliane; Fischer, Susan; Alstetter, Martina; Jaschinski, Katharina; Hilker, Rolf; Becker, Anke; Allers, Thorsten; Soppa, Jörg; Marchfelder, Anita

    2015-10-01

    Members of the Sm protein family are important for the cellular RNA metabolism in all three domains of life. The family includes archaeal and eukaryotic Lsm proteins, eukaryotic Sm proteins and archaeal and bacterial Hfq proteins. While several studies concerning the bacterial and eukaryotic family members have been published, little is known about the archaeal Lsm proteins. Although structures for several archaeal Lsm proteins have been solved already more than ten years ago, we still do not know much about their biological function, however one can confidently propose that the archaeal Lsm proteins will also be involved in RNA metabolism. Therefore, we investigated this protein in the halophilic archaeon Haloferax volcanii. The Haloferax genome encodes a single Lsm protein, the lsm gene overlaps and is co-transcribed with the gene for the ribosomal L37.eR protein. Here, we show that the reading frame of the lsm gene contains a promoter which regulates expression of the overlapping rpl37R gene. This rpl37R specific promoter ensures high expression of the rpl37R gene in exponential growth phase. To investigate the biological function of the Lsm protein we generated a lsm deletion mutant that had the coding sequence for the Sm1 motif removed but still contained the internal promoter for the downstream rpl37R gene. The transcriptome of this deletion mutant was compared to the wild type transcriptome, revealing that several genes are down-regulated and many genes are up-regulated in the deletion strain. Northern blot analyses confirmed down-regulation of two genes. In addition, the deletion strain showed a gain of function in swarming, in congruence with the up-regulation of transcripts encoding proteins required for motility. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

  9. Comparison of local stiffness of composite honeycomb sandwich structures measured by tap test and mechanical test

    NASA Astrophysics Data System (ADS)

    Peters, John J.; Nielsen, Zachary A.; Hsu, David K.

    2001-04-01

    This paper shows that the local spring stiffness of composite honeycomb sandwiches, such as those used in aircraft flight control structures, can be obtained with a tap test. A simple spring model is invoked for converting the time of contact measured in a tap test to the local stiffness. The validity of the model is verified using test results obtained on aircraft components. The stiffness obtained from the tap test is compared with that measured in a static loading test. Good agreements are obtained for a variety of composite sandwiches with and without defects.

  10. A photosynthesis-based two-leaf canopy stomatal conductance model for meteorology and air quality modeling with WRF/CMAQ PX LSM

    NASA Astrophysics Data System (ADS)

    Ran, Limei; Pleim, Jonathan; Song, Conghe; Band, Larry; Walker, John T.; Binkowski, Francis S.

    2017-02-01

    A coupled photosynthesis-stomatal conductance model with single-layer sunlit and shaded leaf canopy scaling is implemented and evaluated in a diagnostic box model with the Pleim-Xiu land surface model (PX LSM) and ozone deposition model components taken directly from the meteorology and air quality modeling system - WRF/CMAQ (Weather Research and Forecast model and Community Multiscale Air Quality model). The photosynthesis-based model for PX LSM (PX PSN) is evaluated at a FLUXNET site for implementation against different parameterizations and the current PX LSM approach with a simple Jarvis function (PX Jarvis). Latent heat flux (LH) from PX PSN is further evaluated at five FLUXNET sites with different vegetation types and landscape characteristics. Simulated ozone deposition and flux from PX PSN are evaluated at one of the sites with ozone flux measurements. Overall, the PX PSN simulates LH as well as the PX Jarvis approach. The PX PSN, however, shows distinct advantages over the PX Jarvis approach for grassland that likely result from its treatment of C3 and C4 plants for CO2 assimilation. Simulations using Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) rather than LAI measured at each site assess how the model would perform with grid averaged data used in WRF/CMAQ. MODIS LAI estimates degrade model performance at all sites but one site having exceptionally old and tall trees. Ozone deposition velocity and ozone flux along with LH are simulated especially well by the PX PSN compared to significant overestimation by the PX Jarvis for a grassland site.

  11. Clinical Application of Vibration Controlled Transient Elastography in Patients with Chronic Hepatitis B

    PubMed Central

    Liang, Xie-Er; Chen, Yong-Peng

    2017-01-01

    Abstract Evaluation of the extent and progression of liver fibrosis and cirrhosis is of critical importance in the management and prognosis of patients with chronic hepatitis B. Due to the limitation of liver biopsy, non-invasive methods, especially liver stiffness measurement (LSM) by vibration controlled transient elastography, have been developed and widely applied for liver fibrosis assessment. LSM aims to reduce, but not to substitute, the need for liver biopsy for fibrosis/cirrhosis diagnosis. While LSM may have potential utility in monitoring treatment response, its applications in prediction of liver complications in terms of portal hypertension and esophageal varices, as well as disease prognosis, have been gradually validated. Here, we review the latest clinical applications of LSM in patients with chronic hepatitis B. PMID:29226103

  12. Benchmarking LSM root-zone soil mositure predictions using satellite-based vegetation indices

    USDA-ARS?s Scientific Manuscript database

    The application of modern land surface models (LSMs) to agricultural drought monitoring is based on the premise that anomalies in LSM root-zone soil moisture estimates can accurately anticipate the subsequent impact of drought on vegetation productivity and health. In addition, the water and energy ...

  13. Measuring the Carotid to Femoral Pulse Wave Velocity (Cf-PWV) to Evaluate Arterial Stiffness.

    PubMed

    Ji, Hongwei; Xiong, Jing; Yu, Shikai; Chi, Chen; Bai, Bin; Teliewubai, Jiadela; Lu, Yuyan; Zhang, Yi; Xu, Yawei

    2018-05-03

    For the elderly, arterial stiffening is a good marker for aging evaluation and it is recommended that the arterial stiffness be determined noninvasively by the measurement of carotid to femoral pulse wave velocity (cf-PWV) (Class I; Level of Evidence A). In literature, numerous community-based or disease-specific studies have reported that higher cf-PWV is associated with increased cardiovascular risk. Here, we discuss strategies to evaluate arterial stiffness with cf-PWV. Following the well-defined steps detailed here, e.g., proper position operator, distance measurement, and tonometer position, we will obtain a standard cf-PWV value to evaluate arterial stiffness. In this paper, a detailed stepwise method to record a good quality PWV and pulse wave analysis (PWA) using a non-invasive tonometry-based device will be discussed.

  14. The importance of accurate measurement of aortic stiffness in patients with chronic kidney disease and end-stage renal disease.

    PubMed

    Adenwalla, Sherna F; Graham-Brown, Matthew P M; Leone, Francesca M T; Burton, James O; McCann, Gerry P

    2017-08-01

    Cardiovascular (CV) disease is the leading cause of death in chronic kidney disease (CKD) and end-stage renal disease (ESRD). A key driver in this pathology is increased aortic stiffness, which is a strong, independent predictor of CV mortality in this population. Aortic stiffening is a potentially modifiable biomarker of CV dysfunction and in risk stratification for patients with CKD and ESRD. Previous work has suggested that therapeutic modification of aortic stiffness may ameliorate CV mortality. Nevertheless, future clinical implementation relies on the ability to accurately and reliably quantify stiffness in renal disease. Pulse wave velocity (PWV) is an indirect measure of stiffness and is the accepted standard for non-invasive assessment of aortic stiffness. It has typically been measured using techniques such as applanation tonometry, which is easy to use but hindered by issues such as the inability to visualize the aorta. Advances in cardiac magnetic resonance imaging now allow direct measurement of stiffness, using aortic distensibility, in addition to PWV. These techniques allow measurement of aortic stiffness locally and are obtainable as part of a comprehensive, multiparametric CV assessment. The evidence cannot yet provide a definitive answer regarding which technique or parameter can be considered superior. This review discusses the advantages and limitations of non-invasive methods that have been used to assess aortic stiffness, the key studies that have assessed aortic stiffness in patients with renal disease and why these tools should be standardized for use in clinical trial work.

  15. The importance of accurate measurement of aortic stiffness in patients with chronic kidney disease and end-stage renal disease

    PubMed Central

    Adenwalla, Sherna F.; Leone, Francesca M.T.; Burton, James O.; McCann, Gerry P.

    2017-01-01

    Abstract Cardiovascular (CV) disease is the leading cause of death in chronic kidney disease (CKD) and end-stage renal disease (ESRD). A key driver in this pathology is increased aortic stiffness, which is a strong, independent predictor of CV mortality in this population. Aortic stiffening is a potentially modifiable biomarker of CV dysfunction and in risk stratification for patients with CKD and ESRD. Previous work has suggested that therapeutic modification of aortic stiffness may ameliorate CV mortality. Nevertheless, future clinical implementation relies on the ability to accurately and reliably quantify stiffness in renal disease. Pulse wave velocity (PWV) is an indirect measure of stiffness and is the accepted standard for non-invasive assessment of aortic stiffness. It has typically been measured using techniques such as applanation tonometry, which is easy to use but hindered by issues such as the inability to visualize the aorta. Advances in cardiac magnetic resonance imaging now allow direct measurement of stiffness, using aortic distensibility, in addition to PWV. These techniques allow measurement of aortic stiffness locally and are obtainable as part of a comprehensive, multiparametric CV assessment. The evidence cannot yet provide a definitive answer regarding which technique or parameter can be considered superior. This review discusses the advantages and limitations of non-invasive methods that have been used to assess aortic stiffness, the key studies that have assessed aortic stiffness in patients with renal disease and why these tools should be standardized for use in clinical trial work. PMID:28852490

  16. Measurements of stiff-material compliance on the nanoscale using ultrasonic force microscopy

    NASA Astrophysics Data System (ADS)

    Dinelli, F.; Biswas, S. K.; Briggs, G. A. D.; Kolosov, O. V.

    2000-05-01

    Ultrasonic force microscopy (UFM) was introduced to probe nanoscale mechanical properties of stiff materials. This was achieved by vibrating the sample far above the first resonance of the probing atomic force microscope cantilever where the cantilever becomes dynamically rigid. By operating UFM at different set force values, it is possible to directly measure the absolute values of the tip-surface contact stiffness. From this an evaluation of surface elastic properties can be carried out assuming a suitable solid-solid contact model. In this paper we present curves of stiffness as a function of the normal load in the range of 0-300 nN. The dependence of stiffness on the relative humidity has also been investigated. Materials with different elastic constants (such as sapphire lithium fluoride, and silicon) have been successfully differentiated. Continuum mechanics models cannot however explain the dependence of stiffness on the normal force and on the relative humidity. In this high-frequency regime, it is likely that viscous forces might play an important role modifying the tip-surface interaction. Plastic deformation might also occur due to the high strain rates applied when ultrasonically vibrating the sample. Another possible cause of these discrepancies might be the presence of water in between the two bodies in contact organizing in a solidlike way and partially sustaining the load.

  17. Measurement techniques for determining the static stiffness of foundations for machine tools

    NASA Astrophysics Data System (ADS)

    Myers, A.; Barrans, S. M.; Ford, D. G.

    2005-01-01

    The paper presents a novel technique for accurately measuring the static stiffness of a machine tool concrete foundation using various items of metrology equipment. The foundation was loaded in a number of different ways which simulated the erection of the machine, traversing of the axes and loading of the heaviest component. The results were compared with the stiffness tolerances specified for the foundation which were deemed necessary in order that the machine alignments could be achieved. This paper is a continuation of research previously published for a FEA of the foundation.

  18. A STUDY OF DISPLACEMENT-LEVEL DEPENDENCY OF VERTICAL STIFFNESS OF PILE - COMPARISONS BETWEEN STATIC LOADING TEST AND MEASUREMENTS DURING TRAIN PASSING -

    NASA Astrophysics Data System (ADS)

    Nihei, Tatsuya; Nishioka, Hidetoshi; Kawamura, Chikara; Nishimura, Masahiro; Edamatsu, Masayuki; Koda, Masayuki

    In order to introduce the performance based design of pile foundation, vertical stiffness of pile is one of the important design factors. Although it had been es timated the vertical stiffness of pile had the displacement-level dependency, it had been not clarified. We compared the vertical stiffness of pile measured by two loading conditions at pile foundation of the railway viaduct. Firstly, we measured the vertical stiffness at static loading test under construction of the viaduct. Secondly, we measured the vertical stiffness at the time of train passing. So, we recognized that the extrapolation of the displacement level dependency in static loading test could evaluate the vertical stiffness of pile during train passing.

  19. Measurement of the UH-60A Hub Large Rotor Test Apparatus Control System Stiffness

    NASA Technical Reports Server (NTRS)

    Kufeld, Robert M.

    2014-01-01

    This purpose of this report is to provides details of the measurement of the control system stiffness of the UH-60A rotor hub mounted on the Large Rotor Test Apparatus (UH-60A/LRTA). The UH-60A/LRTA was used in the 40- by 80-Foot Wind Tunnel to complete the full-scale wind tunnel test portion of the NASA / ARMY UH-60A Airloads Program. This report describes the LRTA control system and highlights the differences between the LRTA and UH-60A aircraft. The test hardware, test setup, and test procedures are also described. Sample results are shown, including the azimuthal variation of the measured control system stiffness for three different loadings and two different dynamic actuator settings. Finally, the azimuthal stiffness is converted to fixed system values using multi-blade transformations for input to comprehensive rotorcraft prediction codes.

  20. Intermittent, moderate-intensity aerobic exercise for only eight weeks reduces arterial stiffness: evaluation by measurement of stiffness parameter and pressure-strain elastic modulus by use of ultrasonic echo tracking.

    PubMed

    Tanaka, Midori; Sugawara, Motoaki; Ogasawara, Yasuo; Izumi, Tadafumi; Niki, Kiyomi; Kajiya, Fumihiko

    2013-04-01

    Aerobic exercise has been reported to be associated with reduced arterial stiffness. However, the intensity, duration, and frequency of aerobic exercise required to improve arterial stiffness have not been established. In addition, most reports base their conclusions on changes in pulse wave velocity, which is an indirect index of arterial stiffness. We studied the effects of short-term, intermittent, moderate-intensity exercise training on arterial stiffness based on measurements of the stiffness parameter (β) and pressure-strain elastic modulus (E p), which are direct indices of regional arterial stiffness. A total of 25 young healthy volunteers (18 men) were recruited. By use of ultrasonic diagnostic equipment we measured β and E p of the carotid artery before and after 8 weeks of exercise training. After exercise training, systolic pressure (P s), diastolic pressure (P d), pulse pressure, systolic arterial diameter (D s), and diastolic arterial diameter (D d) did not change significantly. However, the pulsatile change in diameter ((D s - D d)/D d) increased significantly, and β and E p decreased significantly. For healthy young subjects, β and E p were reduced by intermittent, moderate-intensity exercise training for only 8 weeks.

  1. Evaluation of Stiffness Changes in a High-Rise Building by Measurements of Lateral Displacements Using GPS Technology

    PubMed Central

    Choi, Se Woon; Kim, Ill Soo; Park, Jae Hwan; Kim, Yousok; Sohn, Hong Gyoo; Park, Hyo Seon

    2013-01-01

    The outrigger truss system is one of the most frequently used lateral load resisting structural systems. However, little research has been reported on the effect of installation of outrigger trusses on improvement of lateral stiffness of a high-rise building through full-scale measurements. In this paper, stiffness changes of a high-rise building due to installation of outrigger trusses have been evaluated by measuring lateral displacements using a global positioning system (GPS). To confirm the error range of the GPS measurement system used in the full-scale measurement tests, the GPS displacement monitoring system is investigated through a free vibration test of the experimental model. Then, for the evaluation of lateral stiffness of a high-rise building under construction, the GPS displacement monitoring system is applied to measurements of lateral displacements of a 66-story high-rise building before and after installation of outrigger truss. The stiffness improvement of the building before and after the installation is confirmed through the changes of the natural frequencies and the ratios of the base shear forces to the roof displacements. PMID:24233025

  2. Measurement of gastrocnemius muscle elasticity by shear wave elastography: association with passive ankle joint stiffness and sex differences.

    PubMed

    Chino, Kentaro; Takahashi, Hideyuki

    2016-04-01

    Passive joint stiffness is an important quantitative measure of flexibility, but is affected by muscle volume and all of the anatomical structures located within and over the joint. Shear wave elastography can assess muscle elasticity independent of the influences of muscle volume and the other nearby anatomical structures. We determined how muscle elasticity, as measured using shear wave elastography, is associated with passive joint stiffness and patient sex. Twenty-six healthy men (24.4 ± 5.9 years) and 26 healthy women (25.2 ± 4.8 years) participated in this study. The passive ankle joint stiffness and tissue elasticity of the medial gastrocnemius (MG) were quantified with the ankle in 30° plantar flexion (PF), a neutral anatomical position (NE), and 20° dorsiflexion (DF). No significant difference in passive joint stiffness by sex was observed with the ankle in PF, but significantly greater passive ankle joint stiffness in men than in women was observed in NE and DF. The MG elasticity was not significantly associated with joint stiffness in PF or NE, but it was significantly associated with joint stiffness in DF. There were no significant differences in MG elasticity by sex at any ankle position. Muscle elasticity, measured independent of the confounding effects of muscle volume and the other nearby anatomical structures, is associated with passive joint stiffness in the joint position where the muscle is sufficiently lengthened, but does not vary by sex in any joint position tested.

  3. Arterial Stiffness and Pharmacological Interventions – The TRanscend Arterial stiffNess Substudy (TRANS study)

    PubMed Central

    Topouchian, Jirar; El Feghali, Ramzi; Pannier, Bruno; Wang, Shuyu; Zhao, Feng; Smetana, Karel; Teo, Koon; Asmar, Roland

    2007-01-01

    The degree of arterial stiffness is correlated with the risk of cardiovascular diseases and it is a powerful predictor for morbidity and mortality. Studies have shown that arterial stiffness reduction is associated with an improvement in survival. Reduction of arterial stiffness by pharmacological drugs varies according to the drugs and doses used and duration of treatment. This effect on the arteries differs among the various classes of drugs and among individual drugs in the same class. Quantification of the stiffness and other properties of the arterial wall can be used to monitor the responses to therapy in individuals with hypertension and other cardiovascular diseases. These measures can then be used as surrogate markers for the risk of clinical events. Inhibition of the renin-angiotensin system (RAS) is associated with an important decrease in cardiovascular risk. Findings from clinical trials support the hypothesis that the protective effects of RAS inhibition are partly independent from blood pressure reduction and related to several mechanisms including vascular protective effects. The aim of the TRanscend Arterial stiffNess Substudy (TRANS) is to assess the effect of an angiotensin II receptor blocker (ARB), telmisartan, on the arterial stiffness in a subgroup of patients from the Telmisartan Randomized Assessment Study in aCE iNtolerant subjects with cardiovascular Disease (TRANSCEND) trial. The TRANSCEND trial is an international, multicenter, randomized double blind placebo controlled trial of telmisartan that enrolled patients at high risk for cardiovascular events. Some clinical baseline data of the TRANS substudy are reported. When completed, the results of the TRANS substudy will show whether the beneficial effects of treatment with telmisartan on cardiovascular outcome may be related to an improvement in arterial stiffness. PMID:17969367

  4. The Interday Measurement Consistency of and Relationships Between Hamstring and Leg Musculo-articular Stiffness.

    PubMed

    Waxman, Justin P; Schmitz, Randy J; Shultz, Sandra J

    2015-10-01

    Hamstring stiffness (K(HAM)) and leg stiffness (K(LEG)) are commonly examined relative to athletic performance and injury risk. Given these may be modifiable, it is important to understand day-to-day variations inherent in these measures before use in training studies. In addition, the extent to which K(HAM) and K(LEG) measure similar active stiffness characteristics has not been established. We investigated the interday measurement consistency of K(HAM) and K(LEG), and examined the extent to which K(LEG) predicted K(HAM) in 6 males and 9 females. K(HAM) was moderately consistent day-to-day (ICC(2,5) = .71; SEM = 76.3 N·m(-1)), and 95% limits of agreement (95% LOA) revealed a systematic bias with considerable absolute measurement error (95% LOA = 89.6 ± 224.8 N·m(-1)). Day-to-day differences in procedural factors explained 59.4% of the variance in day-to-day differences in K(HAM). Bilateral and unilateral K(LEG) was more consistent (ICC(2,3) range = .87-.94; SEM range = 1.0-2.91 kN·m(-1)) with lower absolute error (95% LOA bilateral= -2.0 ± 10.3; left leg = -0.36 ± 3.82; right leg = -1.05 ± 3.61 kN·m(-1)). K(LEG) explained 44% of the variance in K(HAM) (P < .01). Findings suggest that procedural factors must be carefully controlled to yield consistent and precise K(HAM) measures. The ease and consistency of K(LEG), and moderate correlation with K(HAM), may steer clinicians toward K(LEG) when measuring lower-extremity stiffness for screening studies and monitoring the effectiveness of training interventions over time.

  5. Environment-dependent regulation of spliceosome activity by the LSM2-8 complex in Arabidopsis.

    PubMed

    Carrasco-López, Cristian; Hernández-Verdeja, Tamara; Perea-Resa, Carlos; Abia, David; Catalá, Rafael; Salinas, Julio

    2017-07-07

    Spliceosome activity is tightly regulated to ensure adequate splicing in response to internal and external cues. It has been suggested that core components of the spliceosome, such as the snRNPs, would participate in the control of its activity. The experimental indications supporting this proposition, however, remain scarce, and the operating mechanisms poorly understood. Here, we present genetic and molecular evidence demonstrating that the LSM2-8 complex, the protein moiety of the U6 snRNP, regulates the spliceosome activity in Arabidopsis, and that this regulation is controlled by the environmental conditions. Our results show that the complex ensures the efficiency and accuracy of constitutive and alternative splicing of selected pre-mRNAs, depending on the conditions. Moreover, miss-splicing of most targeted pre-mRNAs leads to the generation of nonsense mediated decay signatures, indicating that the LSM2-8 complex also guarantees adequate levels of the corresponding functional transcripts. Interestingly, the selective role of the complex has relevant physiological implications since it is required for adequate plant adaptation to abiotic stresses. These findings unveil an unanticipated function for the LSM2-8 complex that represents a new layer of posttranscriptional regulation in response to external stimuli in eukaryotes. © The Author(s) 2017. Published by Oxford University Press on behalf of Nucleic Acids Research.

  6. Equilibrium-point control hypothesis examined by measured arm stiffness during multijoint movement.

    PubMed

    Gomi, H; Kawato

    1996-04-05

    For the last 20 years, it has been hypothesized that well-coordinated, multijoint movements are executed without complex computation by the brain, with the use of springlike muscle properties and peripheral neural feedback loops. However, it has been technically and conceptually difficult to examine this "equilibrium-point control" hypothesis directly in physiological or behavioral experiments. A high-performance manipulandum was developed and used here to measure human arm stiffness, the magnitude of which during multijoint movement is important for this hypothesis. Here, the equilibrium-point trajectory was estimated from the measured stiffness, the actual trajectory, and the generated torque. Its velocity profile differed from that of the actual trajectory. These results argue against the hypothesis that the brain sends as a motor command only an equilibrium-point trajectory similar to the actual trajectory.

  7. Contribution of cation-π interactions to the stability of Sm/LSm oligomeric assemblies.

    PubMed

    Mucić, Ivana D; Nikolić, Milan R; Stojanović, Srđan Đ

    2015-07-01

    In this work, we have analyzed the influence of cation-π interactions to the stability of Sm/LSm assemblies and their environmental preferences. The number of interactions formed by arginine is higher than lysine in the cationic group, while histidine is comparatively higher than phenylalanine and tyrosine in the π group. Arg-Tyr interactions are predominant among the various pairs analyzed. The furcation level of multiple cation-π interactions is much higher than that of single cation-π interactions in Sm/LSm interfaces. We have found hot spot residues forming cation-π interactions, and hot spot composition is similar for all aromatic residues. The Arg-Phe pair has the strongest interaction energy of -8.81 kcal mol(-1) among all the possible pairs of amino acids. The extent of burial of the residue side-chain correlates with the ΔΔG of binding for residues in the core and also for hot spot residues cation-π bonded across the interface. Secondary structure of the cation-π residues shows that Arg and Lys preferred to be in strand. Among the π residues, His prefers to be in helix, Phe prefers to be in turn, and Tyr prefers to be in strand. Stabilization centers for these proteins showed that all the five residues found in cation-π interactions are important in locating one or more of such centers. More than 50 % of the cation-π interacting residues are highly conserved. It is likely that the cation-π interactions contribute significantly to the overall stability of Sm/LSm proteins.

  8. Measurement of Intramolecular Energy Dissipation and Stiffness of a Single Peptide Molecule by Magnetically Modulated Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Kageshima, Masami; Takeda, Seiji; Ptak, Arkadiusz; Nakamura, Chikashi; Jarvis, Suzanne P.; Tokumoto, Hiroshi; Miyake, Jun

    2004-12-01

    A method for measuring intramolecular energy dissipation as well as stiffness variation in a single biomolecule in situ by atomic force microscopy (AFM) is presented. An AFM cantilever is magnetically modulated at an off-resonance frequency while it elongates a single peptide molecule in buffer solution. The molecular stiffness and the energy dissipation are measured via the amplitude and phase lag in the response signal. Data showing a peculiar feature in both profiles of stiffness and dissipation is presented. This suggests that the present method is more sensitive to the state of the molecule than the conventional force-elongation measurement is.

  9. Differential rigor development in red and white muscle revealed by simultaneous measurement of tension and stiffness.

    PubMed

    Kobayashi, Masahiko; Takemori, Shigeru; Yamaguchi, Maki

    2004-02-10

    Based on the molecular mechanism of rigor mortis, we have proposed that stiffness (elastic modulus evaluated with tension response against minute length perturbations) can be a suitable index of post-mortem rigidity in skeletal muscle. To trace the developmental process of rigor mortis, we measured stiffness and tension in both red and white rat skeletal muscle kept in liquid paraffin at 37 and 25 degrees C. White muscle (in which type IIB fibres predominate) developed stiffness and tension significantly more slowly than red muscle, except for soleus red muscle at 25 degrees C, which showed disproportionately slow rigor development. In each of the examined muscles, stiffness and tension developed more slowly at 25 degrees C than at 37 degrees C. In each specimen, tension always reached its maximum level earlier than stiffness, and then decreased more rapidly and markedly than stiffness. These phenomena may account for the sequential progress of rigor mortis in human cadavers.

  10. MEMS squeezer for the measurement of single cell rupture force, stiffness change, and hysteresis

    NASA Astrophysics Data System (ADS)

    Barazani, B.; Warnat, S.; Fine, A.; Hubbard, T.

    2017-02-01

    A MEMS squeezer able to compress single living cells underwater until rupture was designed and tested. The relatively large motion range of the device in aqueous media (~2.5 µm) allows provoking cell disruption while measuring cell mechanical properties before and after membrane rupture. An AC driven electrothermal micro actuator with mechanical amplification pressed single cells against a reference back spring. Deformations of the cell and the reference spring were measured with nanoscale resolution using optical Fourier transform techniques. The motion of the reference spring divided by the cell deformation provides the cell stiffness relative to the reference spring constant. An abrupt change in the cell stiffness and the appearance of cracks indicated the cell wall rupture force was reached. A total of 22 baker’s yeast cells (Saccharomyces cerevisiae) were squeezed with the micro device. The average force necessary to rupture the cell membrane was 0.47  ±  0.1 µN. Before rupture the cells had an average stiffness of 9.3  ±  3.1 N m-1 the post-rupture stiffness dropped to 0.94  ±  0.57 N m-1. Cell hysteresis was also measured: cells squeezed and released before reaching the rupture force showed residual deformations below 100 nm, while cells squeezed past the rupture force and then released showed residual deformations between 490 and 990 nm.

  11. Measurement of passive ankle stiffness in subjects with chronic hemiparesis using a novel ankle robot

    PubMed Central

    Roy, Anindo; Bever, Christopher T.; Forrester, Larry W.; Macko, Richard F.; Hogan, Neville

    2011-01-01

    Our objective in this study was to assess passive mechanical stiffness in the ankle of chronic hemiparetic stroke survivors and to compare it with those of healthy young and older (age-matched) individuals. Given the importance of the ankle during locomotion, an accurate estimate of passive ankle stiffness would be valuable for locomotor rehabilitation, potentially providing a measure of recovery and a quantitative basis to design treatment protocols. Using a novel ankle robot, we characterized passive ankle stiffness both in sagittal and in frontal planes by applying perturbations to the ankle joint over the entire range of motion with subjects in a relaxed state. We found that passive stiffness of the affected ankle joint was significantly higher in chronic stroke survivors than in healthy adults of a similar cohort, both in the sagittal as well as frontal plane of movement, in three out of four directions tested with indistinguishable stiffness values in plantarflexion direction. Our findings are comparable to the literature, thus indicating its plausibility, and, to our knowledge, report for the first time passive stiffness in the frontal plane for persons with chronic stroke and older healthy adults. PMID:21346215

  12. Muscle short-range stiffness can be used to estimate the endpoint stiffness of the human arm

    PubMed Central

    Hu, Xiao; Murray, Wendy M.

    2011-01-01

    The mechanical properties of the human arm are regulated to maintain stability across many tasks. The static mechanics of the arm can be characterized by estimates of endpoint stiffness, considered especially relevant for the maintenance of posture. At a fixed posture, endpoint stiffness can be regulated by changes in muscle activation, but which activation-dependent muscle properties contribute to this global measure of limb mechanics remains unclear. We evaluated the role of muscle properties in the regulation of endpoint stiffness by incorporating scalable models of muscle stiffness into a three-dimensional musculoskeletal model of the human arm. Two classes of muscle models were tested: one characterizing short-range stiffness and two estimating stiffness from the slope of the force-length curve. All models were compared with previously collected experimental data describing how endpoint stiffness varies with changes in voluntary force. Importantly, muscle properties were not fit to the experimental data but scaled only by the geometry of individual muscles in the model. We found that force-dependent variations in endpoint stiffness were accurately described by the short-range stiffness of active arm muscles. Over the wide range of evaluated arm postures and voluntary forces, the musculoskeletal model incorporating short-range stiffness accounted for 98 ± 2, 91 ± 4, and 82 ± 12% of the variance in stiffness orientation, shape, and area, respectively, across all simulated subjects. In contrast, estimates based on muscle force-length curves were less accurate in all measures, especially stiffness area. These results suggest that muscle short-range stiffness is a major contributor to endpoint stiffness of the human arm. Furthermore, the developed model provides an important tool for assessing how the nervous system may regulate endpoint stiffness via changes in muscle activation. PMID:21289133

  13. Effect of SDC-impregnated LSM cathodes on the performance of anode-supported YSZ films for SOFCs

    NASA Astrophysics Data System (ADS)

    Chen, Kongfa; Lü, Zhe; Ai, Na; Chen, Xiangjun; Hu, Jinyan; Huang, Xiqiang; Su, Wenhui

    Sm 0.2Ce 0.8O 1.9 (SDC)-impregnated La 0.7Sr 0.3MnO 3 (LSM) composite cathodes were fabricated on anode-supported yttria-stabilized zirconia (YSZ) thin films. Electrochemical performances of the solid oxide fuel cells (SOFCs) were investigated in the present study. Four single cells, i.e., Cell-1, Cell-2, Cell-3 and Cell-4 were obtained after the fabrication of four different cathodes, i.e., pure LSM and SDC/LSM composites in the weight ratios of 25/75, 36/64 and 42/58, respectively. Impedance spectra under open-circuit conditions showed that the cathode performance was gradually improved with the increasing SDC loading. Similarly, the maximum power densities (MPD) of the four cells were increased with the SDC amount below 700 °C. Whereas, the cell performance of Cell-4 was lower than that of Cell-3 at 800 °C, arising from the increased concentration polarization at high current densities. This was caused by the lowered porosity with the impregnation cycle. This disadvantage could be suppressed by lowering the operating temperature or by increasing the oxygen concentration at the cathode side. The ratio of electrode polarization loss in the total voltage drop versus current density showed that the cell performance was primarily determined by the electrode polarization. The contribution of the ohmic resistance was increased when the operating temperature was lowered. When a 100 ml min -1 oxygen flow was introduced to the cathode side, Cell-3 produced MPDs of 1905, 1587 and 1179 mW cm -2 at 800, 750 and 700 °C, respectively. The high cell outputs demonstrated the merits of the novel and effective SDC-impregnated LSM cathodes.

  14. Measuring multi-joint stiffness during single movements: numerical validation of a novel time-frequency approach.

    PubMed

    Piovesan, Davide; Pierobon, Alberto; DiZio, Paul; Lackner, James R

    2012-01-01

    This study presents and validates a Time-Frequency technique for measuring 2-dimensional multijoint arm stiffness throughout a single planar movement as well as during static posture. It is proposed as an alternative to current regressive methods which require numerous repetitions to obtain average stiffness on a small segment of the hand trajectory. The method is based on the analysis of the reassigned spectrogram of the arm's response to impulsive perturbations and can estimate arm stiffness on a trial-by-trial basis. Analytic and empirical methods are first derived and tested through modal analysis on synthetic data. The technique's accuracy and robustness are assessed by modeling the estimation of stiffness time profiles changing at different rates and affected by different noise levels. Our method obtains results comparable with two well-known regressive techniques. We also test how the technique can identify the viscoelastic component of non-linear and higher than second order systems with a non-parametrical approach. The technique proposed here is very impervious to noise and can be used easily for both postural and movement tasks. Estimations of stiffness profiles are possible with only one perturbation, making our method a useful tool for estimating limb stiffness during motor learning and adaptation tasks, and for understanding the modulation of stiffness in individuals with neurodegenerative diseases.

  15. Measuring Multi-Joint Stiffness during Single Movements: Numerical Validation of a Novel Time-Frequency Approach

    PubMed Central

    Piovesan, Davide; Pierobon, Alberto; DiZio, Paul; Lackner, James R.

    2012-01-01

    This study presents and validates a Time-Frequency technique for measuring 2-dimensional multijoint arm stiffness throughout a single planar movement as well as during static posture. It is proposed as an alternative to current regressive methods which require numerous repetitions to obtain average stiffness on a small segment of the hand trajectory. The method is based on the analysis of the reassigned spectrogram of the arm's response to impulsive perturbations and can estimate arm stiffness on a trial-by-trial basis. Analytic and empirical methods are first derived and tested through modal analysis on synthetic data. The technique's accuracy and robustness are assessed by modeling the estimation of stiffness time profiles changing at different rates and affected by different noise levels. Our method obtains results comparable with two well-known regressive techniques. We also test how the technique can identify the viscoelastic component of non-linear and higher than second order systems with a non-parametrical approach. The technique proposed here is very impervious to noise and can be used easily for both postural and movement tasks. Estimations of stiffness profiles are possible with only one perturbation, making our method a useful tool for estimating limb stiffness during motor learning and adaptation tasks, and for understanding the modulation of stiffness in individuals with neurodegenerative diseases. PMID:22448233

  16. Brachial artery stiffness estimation using ARTSENS.

    PubMed

    Kiran, V Raj; Nabeel, P M; Joseph, Jayaraj; Sivaprakasam, Mohanasankar

    2017-07-01

    Central and peripheral arteries stiffening prominently affect hemodynamics thus increasing the risk of coronary heart disease, chronic kidney disease and end stage renal disease. There are several commercially available non-invasive measurement technologies for the evaluation of stiffness that are expensive, demand dedicated expertise and fall short for mass screening. Considering this, we have developed ARTSENS ® , a highly compact and portable image-free ultrasound device for evaluation of arterial stiffness. The capability of the device to perform accurate measurements of carotid artery stiffness has been validated through extensive in-vivo studies. In this paper we demonstrate the feasibility of using ARTSENS ® for measuring brachial artery stiffness. An inter-operator repeatability study was done based on in-vivo experiments on 9 young healthy subjects. The study included measurement of distension, end diastolic lumen diameter, arterial compliance and stiffness index performed both on carotid artery and brachial artery by two operators successively. The degree of agreement between the measurements made by operators has been investigated based on Bland-Altman plots and paired t-test. The measurements were populated within the limits of agreement. No statistically significant difference (p-values from paired t-test for end-diastolic diameter, distension, stiffness index, arterial compliance were 0.36, 0.24, 0.47 and 0.11 respectively) was seen for the brachial artery measurements performed by the two operators. The correlation between the measurement made by the operators was highly significant (r=0.86, p-value=0.003).

  17. A new method of measuring the stiffness of corpus cavernosum penis with ShearWave™ Elastography.

    PubMed

    Zhang, J-J; Qiao, X-H; Gao, F; Li, F; Bai, M; Zhang, H-P; Liu, Y; Du, L-F; Xing, J-F

    2015-04-01

    To evaluate the feasibility of measuring the stiffness of corpus cavernosum penis (CCP) with ShearWave™ Elastography (SWE; SuperSonic Imagine, Aix-en-Provence, France). 40 healthy volunteers with ages ranging from 19 to 81 years (mean, 36 years; standard deviation, 17 years) were selected in this study. The ultrafast ultrasound device Aixplorer(®) (SuperSonic Imagine) was used for the research and the probe selected was SuperLinear™ SL15-4 (SuperSonic Imagine). The shear wave stiffness (SWS) of CCP was measured using SWE images. The measurement indexes of SWS included (1) SWS of CCP measured in the transverse section (SWS-T), (2) SWS of CCP measured in the longitudinal section (SWS-L) and (3) mean of SWS-T and SWS-L (SWS-M). The interval between hormone test and SWE examination of each subject was less than 7 days. The paired t-test was used to analyse the differences between SWS-T and SWS-L. The Pearson correlation was used to analyse the correlation of SWS of CCP with age as well as with sex hormone levels. There was no significant difference between SWS-T and SWS-L (p > 0.05). SWS (SWS-T, SWS-L, SWS-M) was negatively correlated with age and oestradiol value, and SWS (SWS-T, SWS-L, SWS-M) was positively correlated with testosterone value. SWE could serve as a new non-invasive method of evaluating the stiffness of CCP. It is the first time that we have discussed the feasibility of measuring the stiffness of CCP with SWE and analysed the correlation of SWS of CCP with age as well as with sex hormone levels.

  18. A structured review of spinal stiffness as a kinesiological outcome of manipulation: its measurement and utility in diagnosis, prognosis and treatment decision-making.

    PubMed

    Snodgrass, Suzanne J; Haskins, Robin; Rivett, Darren A

    2012-10-01

    To review and discuss the methods used for measuring spinal stiffness and factors associated with stiffness, how stiffness is used in diagnosis, prognosis, and treatment decision-making and the effects of manipulative techniques on stiffness. A systematic search of MEDLINE, EMBASE, CINAHL, AMED and ICL databases was conducted. Included studies addressed one of four constructs related to stiffness: measurement, diagnosis, prognosis and/or treatment decision-making, and the effects of manipulation on stiffness. Spinal stiffness was defined as the relationship between force and displacement. One hundred and four studies are discussed in this review, with the majority of studies focused on the measurement of stiffness, most often in asymptomatic persons. Eight studies investigated spinal stiffness in diagnosis, providing limited evidence that practitioner-judged stiffness is associated with radiographic findings of sagittal rotational mobility. Fifteen studies investigated spinal stiffness in prognosis or treatment decision-making, providing limited evidence that spinal stiffness is unlikely to independently predict patient outcomes, though stiffness may influence a practitioner's application of non-thrust manipulative techniques. Nine studies investigating the effects of manipulative techniques on spinal stiffness provide very limited evidence that there is no change in spinal stiffness following thrust or non-thrust manipulation in asymptomatic individuals and non-thrust techniques in symptomatic persons, with only one study supporting an immediate, but not sustained, stiffness decrease following thrust manipulation in symptomatic individuals. The existing limited evidence does not support an association between spinal stiffness and manipulative treatment outcomes. There is a need for additional research investigating the effects of manipulation on spinal stiffness in persons with spinal pain. Copyright © 2012 Elsevier Ltd. All rights reserved.

  19. Measurement of lower leg compression in vivo: recommendations for the performance of measurements of interface pressure and stiffness: consensus statement.

    PubMed

    Partsch, Hugo; Clark, Michael; Bassez, Sophie; Benigni, Jean-Patrick; Becker, Francis; Blazek, Vladimir; Caprini, Joseph; Cornu-Thénard, André; Hafner, Jürg; Flour, Mieke; Jünger, Michael; Moffatt, Christine; Neumann, Martino

    2006-02-01

    Interface pressure and stiffness characterizing the elastic properties of the material are the parameters determining the dosage of compression treatment and should therefore be measured in future clinical trials. To provide some recommendations regarding the use of suitable methods for this indication. This article was formulated based on the results of an international consensus meeting between a group of medical experts and representatives from the industry held in January 2005 in Vienna, Austria. Proposals are made concerning methods for measuring the interface pressure and for assessing the stiffness of a compression device in an individual patient. In vivo measurement of interface pressure is encouraged when clinical and experimental outcomes of compression treatment are to be evaluated.

  20. Liver stiffness measurement by transient elastography predicts late posthepatectomy outcomes in patients undergoing resection for hepatocellular carcinoma.

    PubMed

    Rajakannu, Muthukumarassamy; Cherqui, Daniel; Ciacio, Oriana; Golse, Nicolas; Pittau, Gabriella; Allard, Marc Antoine; Antonini, Teresa Maria; Coilly, Audrey; Sa Cunha, Antonio; Castaing, Denis; Samuel, Didier; Guettier, Catherine; Adam, René; Vibert, Eric

    2017-10-01

    Postoperative hepatic decompensation is a serious complication of liver resection in patients undergoing hepatectomy for hepatocellular carcinoma. Liver fibrosis and clinical significant portal hypertension are well-known risk factors for hepatic decompensation. Liver stiffness measurement is a noninvasive method of evaluating hepatic venous pressure gradient and functional hepatic reserve by estimating hepatic fibrosis. Effectiveness of liver stiffness measurement in predicting persistent postoperative hepatic decompensation has not been investigated. Consecutive patients with resectable hepatocellular carcinoma were recruited prospectively and liver stiffness measurement of nontumoral liver was measured using FibroScan. Hepatic venous pressure gradient was measured intraoperatively by direct puncture of portal vein and inferior vena cava. Hepatic venous pressure gradient ≥10 mm Hg was defined as clinically significant portal hypertension. Primary outcome was persistent hepatic decompensation defined as the presence of at least one of the following: unresolved ascites, jaundice, and/or encephalopathy >3 months after hepatectomy. One hundred and six hepatectomies, including 22 right hepatectomy (20.8%), 3 central hepatectomy (2.8%), 12 left hepatectomy (11.3%), 11 bisegmentectomy (10.4%), 30 unisegmentectomy (28.3%), and 28 partial hepatectomy (26.4%) were performed in patients for hepatocellular carcinoma (84 men and 22 women with median age of 67.5 years; median model for end-stage liver disease score of 8). Ninety-day mortality was 4.7%. Nine patients (8.5%) developed postoperative hepatic decompensation. Multivariate logistic regression bootstrapped at 1,000 identified liver stiffness measurement (P = .001) as the only preoperative predictor of postoperative hepatic decompensation. Area under receiver operating characteristic curve for liver stiffness measurement and hepatic venous pressure gradient was 0.81 (95% confidence interval, 0.506-0.907) and 0

  1. Enhanced Soil Moisture Initialization Using Blended Soil Moisture Product and Regional Optimization of LSM-RTM Coupled Land Data Assimilation System.

    NASA Astrophysics Data System (ADS)

    Nair, A. S.; Indu, J.

    2017-12-01

    Prediction of soil moisture dynamics is high priority research challenge because of the complex land-atmosphere interaction processes. Soil moisture (SM) plays a decisive role in governing water and energy balance of the terrestrial system. An accurate SM estimate is imperative for hydrological and weather prediction models. Though SM estimates are available from microwave remote sensing and land surface model (LSM) simulations, it is affected by uncertainties from several sources during estimation. Past studies have generally focused on land data assimilation (DA) for improving LSM predictions by assimilating soil moisture from single satellite sensor. This approach is limited by the large time gap between two consequent soil moisture observations due to satellite repeat cycle of more than three days at the equator. To overcome this, in the present study, we have performed DA using ensemble products from the soil moisture operational product system (SMOPS) blended soil moisture retrievals from different satellite sensors into Noah LSM. Before the assimilation period, the Noah LSM is initialized by cycling through seven multiple loops from 2008 to 2010 forcing with Global data assimilation system (GDAS) data over the Indian subcontinent. We assimilated SMOPS into Noah LSM for a period of two years from 2010 to 2011 using Ensemble Kalman Filter within NASA's land information system (LIS) framework. Results show that DA has improved Noah LSM prediction with a high correlation of 0.96 and low root mean square difference of 0.0303 m3/m3 (figure 1a). Further, this study has also investigated the notion of assimilating microwave brightness temperature (Tb) as a proxy for SM estimates owing to the close proximity of Tb and SM. Preliminary sensitivity analysis show a strong need for regional parameterization of radiative transfer models (RTMs) to improve Tb simulation. Towards this goal, we have optimized the forward RTM using swarm optimization technique for direct Tb

  2. A new method of measuring the stiffness of corpus cavernosum penis with ShearWave™ Elastography

    PubMed Central

    Zhang, J-J; Qiao, X-H; Gao, F; Li, F; Bai, M; Zhang, H-P; Liu, Y; Du, L-F

    2015-01-01

    Objective: To evaluate the feasibility of measuring the stiffness of corpus cavernosum penis (CCP) with ShearWave™ Elastography (SWE; SuperSonic Imagine, Aix-en-Provence, France). Methods: 40 healthy volunteers with ages ranging from 19 to 81 years (mean, 36 years; standard deviation, 17 years) were selected in this study. The ultrafast ultrasound device Aixplorer® (SuperSonic Imagine) was used for the research and the probe selected was SuperLinear™ SL15-4 (SuperSonic Imagine). The shear wave stiffness (SWS) of CCP was measured using SWE images. The measurement indexes of SWS included (1) SWS of CCP measured in the transverse section (SWS-T), (2) SWS of CCP measured in the longitudinal section (SWS-L) and (3) mean of SWS-T and SWS-L (SWS-M). The interval between hormone test and SWE examination of each subject was less than 7 days. The paired t-test was used to analyse the differences between SWS-T and SWS-L. The Pearson correlation was used to analyse the correlation of SWS of CCP with age as well as with sex hormone levels. Results: There was no significant difference between SWS-T and SWS-L (p > 0.05). SWS (SWS-T, SWS-L, SWS-M) was negatively correlated with age and oestradiol value, and SWS (SWS-T, SWS-L, SWS-M) was positively correlated with testosterone value. Conclusion: SWE could serve as a new non-invasive method of evaluating the stiffness of CCP. Advances in knowledge: It is the first time that we have discussed the feasibility of measuring the stiffness of CCP with SWE and analysed the correlation of SWS of CCP with age as well as with sex hormone levels. PMID:25694260

  3. Bending stiffness of catheters and guide wires.

    PubMed

    Wünsche, P; Werner, C; Bloss, P

    2002-01-01

    An important property of catheters and guide wires to assess their pushability behavior is their bending stiffness. To measure bending stiffness, a new bending module with a new clamping device was developed. This module can easily be mounted in commercially available tensile testing equipment, where bending force and deflection due to the bending force can be measured. To achieve high accuracy for the bending stiffness, the bending distance has to be measured with even higher accuracy by using a laser-scan micrometer. Measurement results of angiographic catheters and guide wires were presented and discussed. The bending stiffness shows a significant dependence on the angle of the test specimen's rotation around its length axis.

  4. An Examination of the True Reliability of Lower Limb Stiffness Measures During Overground Hopping.

    PubMed

    Diggin, David; Anderson, Ross; Harrison, Andrew J

    2016-06-01

    Evidence suggests reports describing the reliability of leg-spring (kleg) and joint stiffness (kjoint) measures are contaminated by artifacts originating from digital filtering procedures. In addition, the intraday reliability of kleg and kjoint requires investigation. This study examined the effects of experimental procedures on the inter- and intraday reliability of kleg and kjoint. Thirty-two participants completed 2 trials of single-legged hopping at 1.5, 2.2, and 3.0 Hz at the same time of day across 3 days. On the final test day a fourth experimental bout took place 6 hours before or after participants' typical testing time. Kinematic and kinetic data were collected throughout. Stiffness was calculated using models of kleg and kjoint. Classifications of measurement agreement were established using thresholds for absolute and relative reliability statistics. Results illustrated that kleg and kankle exhibited strong agreement. In contrast, kknee and khip demonstrated weak-to-moderate consistency. Results suggest limits in kjoint reliability persist despite employment of appropriate filtering procedures. Furthermore, diurnal fluctuations in lower-limb muscle-tendon stiffness exhibit little effect on intraday reliability. The present findings support the existence of kleg as an attractor state during hopping, achieved through fluctuations in kjoint variables. Limits to kjoint reliability appear to represent biological function rather than measurement artifact.

  5. Model-Based Estimation of Knee Stiffness

    PubMed Central

    Pfeifer, Serge; Vallery, Heike; Hardegger, Michael; Riener, Robert; Perreault, Eric J.

    2013-01-01

    During natural locomotion, the stiffness of the human knee is modulated continuously and subconsciously according to the demands of activity and terrain. Given modern actuator technology, powered transfemoral prostheses could theoretically provide a similar degree of sophistication and function. However, experimentally quantifying knee stiffness modulation during natural gait is challenging. Alternatively, joint stiffness could be estimated in a less disruptive manner using electromyography (EMG) combined with kinetic and kinematic measurements to estimate muscle force, together with models that relate muscle force to stiffness. Here we present the first step in that process, where we develop such an approach and evaluate it in isometric conditions, where experimental measurements are more feasible. Our EMG-guided modeling approach allows us to consider conditions with antagonistic muscle activation, a phenomenon commonly observed in physiological gait. Our validation shows that model-based estimates of knee joint stiffness coincide well with experimental data obtained using conventional perturbation techniques. We conclude that knee stiffness can be accurately estimated in isometric conditions without applying perturbations, which presents an important step towards our ultimate goal of quantifying knee stiffness during gait. PMID:22801482

  6. Exchange Stiffness in Thin-Film Cobalt Alloys

    NASA Astrophysics Data System (ADS)

    Eyrich, Charles

    The exchange stiffness, Aex, is one of the key parameters controlling magnetization reversal in magnetic materials but is very difficult to measure, especially in thin films. We developed a new technique for measuring the exchange stiffness of a magnetic material based on the formation of a spin spiral within two antiferromagnetically coupled ferromagnetic films [1]. Using this method, I was able to measure the exchange stiffness of thin film Co alloyed with Cr, Fe, Ni, Pd, Pt and Ru. The results of this work showed that the rate at which a substituent element reduces the exchange stiffness is not directly related to its effect on the magnetization of the alloy. These measured trends have been understood by combining measurements of element specific magnetic moments obtained using X-ray magnetic circular dichroism (XMCD) and material specific modeling based on density functional theory (DFT) within the local density approximation (LDA). The experimental results also hint at significant reduction of the exchange stiffness at the interface that can account for the difference between our results and those obtained on bulk materials.

  7. In-situ AFM measurement of single fibrin fiber stiffness before and after addition of Factor XIII

    NASA Astrophysics Data System (ADS)

    Houser, John; O'Brien, E. Timothy; Lord, Susan T.; Superfine, Richard; Falvo, Michael R.

    2008-10-01

    Fibrin fibers are the main structural component of blood clots. Ligation of fibrin by native Factor XIII (FXIII) serves to fine tune the mechanical properties of the clot. Mechanical alteration is important because a clot must be stiff enough to resist forces from blood flow but compliant enough to prevent embolism (fracture). Cone and Plate measurements of fibrin gels, which represent the vast majority of mechanical measurements on fibrin, show that FXIII increases clot stiffness. More recently, measurements on individual fibrin fibers show that they exhibit remarkable extensibility, breaking at strains up to 300%. As of yet, the origin of this extensibility is not fully understood. The different responses of ligated and unligated fibrin fibers can give us clues as to it's mechanism of extension. We use a combined fluorescence/atomic force microscope to stretch individual, isolated, fibrin fibers and then compare force extension curves of the same fiber before and after addition of FXIII. We found up to a 3.5-fold increase in fiber stiffness after addition of FXIII. We also show stiffening of individual fibrin fibers after crosslinking by gluteraldehyde.

  8. Intracortical stiffness of mid-diaphysis femur bovine bone: lacunar-canalicular based homogenization numerical solutions and microhardness measurements.

    PubMed

    Hage, Ilige S; Hamade, Ramsey F

    2017-09-01

    Microscale lacunar-canalicular (L-C) porosity is a major contributor to intracortical bone stiffness variability. In this work, such variability is investigated experimentally using micro hardness indentation tests and numerically using a homogenization scheme. Cross sectional rings of cortical bones are cut from the middle tubular part of bovine femur long bone at mid-diaphysis. A series of light microscopy images are taken along a line emanating from the cross-section center starting from the ring's interior (endosteum) ring surface toward the ring's exterior (periosteum) ring surface. For each image in the line, computer vision analysis of porosity is conducted employing an image segmentation methodology based on pulse coupled neural networks (PCNN) recently developed by the authors. Determined are size and shape of each of the lacunar-canalicular (L-C) cortical micro constituents: lacunae, canaliculi, and Haversian canals. Consequently, it was possible to segment and quantify the geometrical attributes of all individual segmented pores leading to accurate determination of derived geometrical measures such as L-C cortical pores' total porosity (pore volume fraction), (elliptical) aspect ratio, orientation, location, and number of pores in secondary and primary osteons. Porosity was found to be unevenly (but linearly) distributed along the interior and exterior regions of the intracortical bone. The segmented L-C porosity data is passed to a numerical microscale-based homogenization scheme, also recently developed by the authors, that analyses a composite made up of lamella matrix punctuated by multi-inclusions and returns corresponding values for longitudinal and transverse Young's modulus (matrix stiffness) for these micro-sized spatial locations. Hence, intracortical stiffness variability is numerically quantified using a combination of computer vision program and numerical homogenization code. These numerically found stiffness values of the homogenization

  9. The IL7RA rs6897932 polymorphism is associated with progression of liver fibrosis in patients with chronic hepatitis C: Repeated measurements design.

    PubMed

    Jiménez-Sousa, María Ángeles; Gómez-Moreno, Ana Zaida; Pineda-Tenor, Daniel; Medrano, Luz Maria; Sánchez-Ruano, Juan José; Fernández-Rodríguez, Amanda; Artaza-Varasa, Tomas; Saura-Montalbán, José; Vázquez-Morón, Sonia; Ryan, Pablo; Resino, Salvador

    2018-01-01

    The polymorphisms at the α-chain of the IL-7 receptor (IL7RA) have been related to T-cell homeostasis and development and may contribute to immune system deregulation. In the present study, we analyzed the association between IL7RA polymorphisms and the progression of liver fibrosis in patients infected with HCV. We carried out a retrospective study with a design consisting of repeated measurements in 187 HCV-infected patients, to study the risk prediction of liver fibrosis progression using genetic factors. We genotyped the rs6897932, rs987106 and rs3194051 IL7RA polymorphisms using the Agena Bioscience's MassARRAY. Transient elastography was used to measure liver stiffness. The used cut-offs were: <7.1 kPa (F0-F1), 7.1-9.4 kPa (F2; significant fibrosis), 9.5-12.4 kPa (F3; advanced fibrosis), and ≥12.5 kPa (F4; cirrhosis). All HCV genotypes were analyzed. The median of follow-up time was 47.9 months. Baseline liver stiffness measurement (LSM) values did not show significant statistical differences for IL7RA genotypes (p>0.05). In univariate analysis, the rs6897932 T allele had a positive relationship with an increase in LSM (arithmetic mean ratio (AMR) = 1.21 (95%CI = 1.08; 1.36); p = 0.001), progression to advanced fibrosis (F≥3) (odds ratio (OR) = 2.51 (95%CI = 1.29; 4.88); p = 0.006) and progression to cirrhosis (F4) (OR = 2.71 (95%CI = 0.94; 5.03); p = 0.069). In multivariable analysis, the rs6897932 T allele was related to a higher increase of LSM values during follow-up (adjusted AMR = 1.27 (95%CI = 1.13; 1.42); p<0.001) and higher odds of progression to advanced fibrosis [adjusted OR = 4.46 (95%CI = 1.87; 10.62); p = 0.001], and progression to cirrhosis [adjusted OR = 3.92 (95%CI = 1.30; 11.77); p = 0.015]. Regarding IL7RA rs987106 and rs3194051 polymorphisms, we did not find significant results except for the relationship between IL7RA rs987106 and the increase in LSM values [adjusted OR = 1.12 (95%CI = 1.02; 1.23); p = 0.015]. The IL7RA rs6897932

  10. Right Ventricular Myocardial Stiffness in Experimental Pulmonary Arterial Hypertension: Relative Contribution of Fibrosis and Myofibril Stiffness.

    PubMed

    Rain, Silvia; Andersen, Stine; Najafi, Aref; Gammelgaard Schultz, Jacob; da Silva Gonçalves Bós, Denielli; Handoko, M Louis; Bogaard, Harm-Jan; Vonk-Noordegraaf, Anton; Andersen, Asger; van der Velden, Jolanda; Ottenheijm, Coen A C; de Man, Frances S

    2016-07-01

    The purpose of this study was to determine the relative contribution of fibrosis-mediated and myofibril-mediated stiffness in rats with mild and severe right ventricular (RV) dysfunction. By performing pulmonary artery banding of different diameters for 7 weeks, mild RV dysfunction (Ø=0.6 mm) and severe RV dysfunction (Ø=0.5 mm) were induced in rats. The relative contribution of fibrosis- and myofibril-mediated RV stiffness was determined in RV trabecular strips. Total myocardial stiffness was increased in trabeculae from both mild and severe RV dysfunction in comparison to controls. In severe RV dysfunction, increased RV myocardial stiffness was explained by both increased fibrosis-mediated stiffness and increased myofibril-mediated stiffness, whereas in mild RV dysfunction, only myofibril-mediated stiffness was increased in comparison to control. Histological analyses revealed that RV fibrosis gradually increased with severity of RV dysfunction, whereas the ratio of collagen I/III expression was only elevated in severe RV dysfunction. Stiffness measurements in single membrane-permeabilized RV cardiomyocytes demonstrated a gradual increase in RV myofibril stiffness, which was partially restored by protein kinase A in both mild and severe RV dysfunction. Increased expression of compliant titin isoforms was observed only in mild RV dysfunction, whereas titin phosphorylation was reduced in both mild and severe RV dysfunction. RV myocardial stiffness is increased in rats with mild and severe RV dysfunction. In mild RV dysfunction, stiffness is mainly determined by increased myofibril stiffness. In severe RV dysfunction, both myofibril- and fibrosis-mediated stiffness contribute to increased RV myocardial stiffness. © 2016 The Authors.

  11. Shearwave Dispersion Ultrasonic Vibrometry (SDUV) for measuring prostate shear stiffness and viscosity – An in vitro pilot study

    PubMed Central

    Urban, M.W.; Fatemi, M.; Greenleaf, J.F.

    2011-01-01

    This paper reports shear stiffness and viscosity “virtual biopsy” measurements of three excised non-cancerous human prostates using shearwave dispersion ultrasound vibrometry (SDUV) in vitro. Improved methods for prostate guided-biopsy are required to effectively guide needle biopsy to the suspected site. In addition, tissue stiffness measurement helps identifying a suspected site to perform biopsy because stiffness has been shown to correlate with pathology. More importantly, early detection of prostate cancer may guide minimally-invasive therapy and eliminate insidious procedures. In this work, “virtual” biopsies were taken in multiple locations in three excised prostates. Then, SDUV shear elasticity and viscosity measurements have been performed at the selected “suspicious” locations within the prostates. SDUV measurements of prostate elasticity and viscosity are generally in agreement with preliminary values reported previously in the literature. It is however important to emphasize that the obtained viscoelastic parameters values are local, and not a mean value for the whole prostate. PMID:20595086

  12. Prediction of posthepatectomy liver failure using transient elastography in patients with hepatitis B related hepatocellular carcinoma.

    PubMed

    Lei, Jie-Wen; Ji, Xiao-Yu; Hong, Jun-Feng; Li, Wan-Bin; Chen, Yan; Pan, Yan; Guo, Jia

    2017-12-29

    It is essential to accurately predict Postoperative liver failure (PHLF) which is a life-threatening complication. Liver hardness measurement (LSM) is widely used in non-invasive assessment of liver fibrosis. The aims of this study were to explore the application of preoperative liver stiffness measurements (LSM) by transient elastography in predicting postoperative liver failure (PHLF) in patients with hepatitis B related hepatocellular carcinoma. The study included 247 consecutive patients with hepatitis B related hepatocellular carcinoma who underwent hepatectomy between May 2015 and September 2015. Detailed preoperative examinations including LSM were performed before hepatectomy. The endpoint was the development of PHLF. All of the patients had chronic hepatitis B defined as the presence of hepatitis B surface antigen (HBsAg) for more than 6 months and 76 (30.8%) had cirrhosis. PHLF occurred in 37 (14.98%) patients. Preoperative LSM (odds ratio, OR, 1.21; 95% confidence interval, 95% CI: 1.13-1.29; P < 0.001) and international normalized ratio (INR) (OR, 1.07; 95% CI: 1.01-1.12; P < 0.05) were revealed to be independent risk factors for PHLF, and a new model was defined as LSM-INR index (LSM-INR index = 0.191*LSM + 6.317*INR-11.154). The optimal cutoff values of LSM and LSM-INR index for predicting PHLF were 14 kPa (AUC 0.86, 95% CI: 0.811-0.901, P < 0.001) and -1.92 (AUC 0.87, 95% CI: 0.822-0.909, P < 0.001), respectively. LSM can be helpful for surgeons to make therapeutic decisions in patients with hepatitis B related hepatocellular carcinoma.

  13. Hypertension and arterial stiffness in heart transplantation patients

    PubMed Central

    de Souza-Neto, João David; de Oliveira, Ítalo Martins; Lima-Rocha, Hermano Alexandre; Oliveira-Lima, José Wellington; Bacal, Fernando

    2016-01-01

    OBJECTIVES: Post-transplantation hypertension is prevalent and is associated with increased cardiovascular morbidity and subsequent graft dysfunction. The present study aimed to identify the factors associated with arterial stiffness as measured by the ambulatory arterial stiffness index. METHODS: The current study used a prospective, observational, analytical design to evaluate a group of adult heart transplantation patients. Arterial stiffness was obtained by monitoring ambulatory blood pressure and using the ambulatory arterial stiffness index as the surrogate outcome. Multivariate logistic regression analyses were performed to control confounding. RESULTS: In a group of 85 adult heart transplantation patients, hypertension was independently associated with arterial stiffness (OR 4.98, CI 95% 1.06-23.4) as well as systolic and diastolic blood pressure averages and nighttime descent. CONCLUSIONS: Measurement of ambulatory arterial stiffness index is a new, non-invasive method that is easy to perform, may contribute to better defining arterial stiffness prognosis and is associated with hypertension. PMID:27652829

  14. Distributed Application of the Unified Noah LSM with Hydrologic Flow Routing on an Appalachian Headwater Basin

    NASA Astrophysics Data System (ADS)

    Garcia, M.; Kumar, S.; Gochis, D.; Yates, D.; McHenry, J.; Burnet, T.; Coats, C.; Condrey, J.

    2006-05-01

    Collaboration between scientists at UMBC-GEST and NASA-GSFC, the NCAR Research Applications Laboratory (RAL), and Baron Advanced Meteorological Services (BAMS), has produced a modeling framework for the application of traditional land surface models (LSMs) in a distributed hydrologic system which can be used for diagnosis and prediction of routed stream discharge hydrographs. This collaboration is oriented on near-term system implementation across Romania for flood and flash-flood analyses and forecasting as part of the World Bank-funded Destructive Waters Abatement (DESWAT) program. Meteorological forcing from surface observations, model analyses and numerical forecasts are employed in the NASA-GSFC Land Information System (LIS) to drive the Unified Noah LSM with Noah-Distributed components, stream network delineation and routing schemes original to this work. The Unified Noah LSM is the outgrowth of a joint modeling effort between several research partners including NCAR, the NOAA National Center for Environmental Prediction (NCEP), and the Air Force Weather Agency (AFWA). At NCAR, hydrologically-oriented extensions to the Noah LSM have been developed for LSM applications in a distributed domain in order to address the lateral redistribution of soil moisture by surface and subsurface flow processes. These advancements have been integrated into the NASA-GSFC Land Information System (LIS) and coupled with an original framework for hydraulic channel network definition and specification, linkages with the Noah-Distributed overland and subsurface flow framework, and distributed cell- to-cell (or link-node) hydraulic routing. This poster presents an overview of the system components and their organization, as well as results of the first U.S. case study performed with this system under various configurations. The case study simulated precipitation events over a headwater basin in the southern Appalachian Mountains in October 2005 following the landfall of Tropical

  15. The link between exercise and titin passive stiffness.

    PubMed

    Lalande, Sophie; Mueller, Patrick J; Chung, Charles S

    2017-09-01

    What is the topic of this review? This review focuses on how in vivo and molecular measurements of cardiac passive stiffness can predict exercise tolerance and how exercise training can reduce cardiac passive stiffness. What advances does it highlight? This review highlights advances in understanding the relationship between molecular (titin-based) and in vivo (left ventricular) passive stiffness, how passive stiffness modifies exercise tolerance, and how exercise training may be therapeutic for cardiac diseases with increased passive stiffness. Exercise can help alleviate the negative effects of cardiovascular disease and cardiovascular co-morbidities associated with sedentary behaviour; this may be especially true in diseases that are associated with increased left ventricular passive stiffness. In this review, we discuss the inverse relationship between exercise tolerance and cardiac passive stiffness. Passive stiffness is the physical property of cardiac muscle to produce a resistive force when stretched, which, in vivo, is measured using the left ventricular end diastolic pressure-volume relationship or is estimated using echocardiography. The giant elastic protein titin is the major contributor to passive stiffness at physiological muscle (sarcomere) lengths. Passive stiffness can be modified by altering titin isoform size or by post-translational modifications. In both human and animal models, increased left ventricular passive stiffness is associated with reduced exercise tolerance due to impaired diastolic filling, suggesting that increased passive stiffness predicts reduced exercise tolerance. At the same time, exercise training itself may induce both short- and long-term changes in titin-based passive stiffness, suggesting that exercise may be a treatment for diseases associated with increased passive stiffness. Direct modification of passive stiffness to improve exercise tolerance is a potential therapeutic approach. Titin passive stiffness itself may

  16. The decapping activator Edc3 and the Q/N-rich domain of Lsm4 function together to enhance mRNA stability and alter mRNA decay pathway dependence in Saccharomyces cerevisiae.

    PubMed

    Huch, Susanne; Müller, Maren; Muppavarapu, Mridula; Gommlich, Jessie; Balagopal, Vidya; Nissan, Tracy

    2016-10-15

    The rate and regulation of mRNA decay are major elements in the proper control of gene expression. Edc3 and Lsm4 are two decapping activator proteins that have previously been shown to function in the assembly of RNA granules termed P bodies. Here, we show that deletion of edc3, when combined with a removal of the glutamine/asparagine rich region of Lsm4 (edc3Δ lsm4ΔC) reduces mRNA stability and alters pathways of mRNA degradation. Multiple tested mRNAs exhibited reduced stability in the edc3Δ lsm4ΔC mutant. The destabilization was linked to an increased dependence on Ccr4-mediated deadenylation and mRNA decapping. Unlike characterized mutations in decapping factors that either are neutral or are able to stabilize mRNA, the combined edc3Δ lsm4ΔC mutant reduced mRNA stability. We characterized the growth and activity of the major mRNA decay systems and translation in double mutant and wild-type yeast. In the edc3Δ lsm4ΔC mutant, we observed alterations in the levels of specific mRNA decay factors as well as nuclear accumulation of the catalytic subunit of the decapping enzyme Dcp2. Hence, we suggest that the effects on mRNA stability in the edc3Δ lsm4ΔC mutant may originate from mRNA decay protein abundance or changes in mRNPs, or alternatively may imply a role for P bodies in mRNA stabilization. © 2016. Published by The Company of Biologists Ltd.

  17. The decapping activator Edc3 and the Q/N-rich domain of Lsm4 function together to enhance mRNA stability and alter mRNA decay pathway dependence in Saccharomyces cerevisiae

    PubMed Central

    Huch, Susanne; Müller, Maren; Muppavarapu, Mridula; Gommlich, Jessie; Balagopal, Vidya; Nissan, Tracy

    2016-01-01

    ABSTRACT The rate and regulation of mRNA decay are major elements in the proper control of gene expression. Edc3 and Lsm4 are two decapping activator proteins that have previously been shown to function in the assembly of RNA granules termed P bodies. Here, we show that deletion of edc3, when combined with a removal of the glutamine/asparagine rich region of Lsm4 (edc3Δ lsm4ΔC) reduces mRNA stability and alters pathways of mRNA degradation. Multiple tested mRNAs exhibited reduced stability in the edc3Δ lsm4ΔC mutant. The destabilization was linked to an increased dependence on Ccr4-mediated deadenylation and mRNA decapping. Unlike characterized mutations in decapping factors that either are neutral or are able to stabilize mRNA, the combined edc3Δ lsm4ΔC mutant reduced mRNA stability. We characterized the growth and activity of the major mRNA decay systems and translation in double mutant and wild-type yeast. In the edc3Δ lsm4ΔC mutant, we observed alterations in the levels of specific mRNA decay factors as well as nuclear accumulation of the catalytic subunit of the decapping enzyme Dcp2. Hence, we suggest that the effects on mRNA stability in the edc3Δ lsm4ΔC mutant may originate from mRNA decay protein abundance or changes in mRNPs, or alternatively may imply a role for P bodies in mRNA stabilization. PMID:27543059

  18. Non-invasive measurement using cardiovascular magnetic resonance of changes in pulmonary artery stiffness with exercise.

    PubMed

    Forouzan, Omid; Warczytowa, Jared; Wieben, Oliver; François, Christopher J; Chesler, Naomi C

    2015-12-13

    Exercise stress tests are commonly used in clinical settings to monitor the functional state of the heart and vasculature. Large artery stiffness is one measure of arterial function that can be quantified noninvasively during exercise stress. Changes in proximal pulmonary artery stiffness are especially relevant to the progression of pulmonary hypertension (PH), since pulmonary artery (PA) stiffness is the best current predictor of mortality from right ventricular failure. Cardiovascular magnetic resonance (CMR) was used to investigate the effect of exercise stress on PA pulse wave velocity (PWV) and relative area change (RAC), which are both non-invasive measures of PA stiffness, in healthy subjects. All 21 subjects (average age 26 ± 4 years; 13 female and 8 male) used a custom-made MR-compatible stepping device to exercise (two stages of mild-to-moderate exercise of 3-4 min duration each) in a supine position within the confines of the scanner. To measure the cross-sectional area and blood flow velocity in the main PA (MPA), two-dimensional phase-contrast (2D-PC) CMR images were acquired. To measure the reproducibility of metrics, CMR images were analyzed by two independent observers. Inter-observer agreements were calculated using the intraclass correlation and Bland-Altman analysis. From rest to the highest level of exercise, cardiac output increased from 5.9 ± 1.4 L/min to 8.2 ± 1.9 L/min (p < 0.05), MPA PWV increased from 1.6 ± 0.5 m/s to 3.6 ± 1.4 m/s (p < 0.05), and MPA RAC decreased from 0.34 ± 0.11 to 0.24 ± 0.1 (p < 0.05). While PWV also increased from the first to second exercise stage (from 2.7 ± 1.0 m/s to 3.6 ± 1.4 m/s, p < 0.05), there was no significant change in RAC between the two exercise stages. We found good inter-observer agreement for quantification of MPA flow, RAC and PWV. These results demonstrate that metrics of MPA stiffness increase in response to acute moderate exercise in

  19. Relationship between bone turnover markers and the heel stiffness index measured by quantitative ultrasound in middle-aged and elderly Japanese men

    PubMed Central

    Nishimura, Takayuki; Arima, Kazuhiko; Abe, Yasuyo; Kanagae, Mitsuo; Mizukami, Satoshi; Okabe, Takuhiro; Tomita, Yoshihito; Goto, Hisashi; Horiguchi, Itsuko; Aoyagi, Kiyoshi

    2018-01-01

    Abstract The aim of the present study was to investigate the age-related patterns and the relationships between serum levels of tartrate-resistant acid phosphatase-5b (TRACP-5b) or bone-specific alkaline phosphatase (BAP), and the heel stiffness index measured by quantitative ultrasound (QUS) in 429 Japanese men, with special emphasis on 2 age groups (40–59 years and 60 years or over). The heel stiffness index (bone mass) was measured by QUS. Serum samples were collected, and TRACP-5b and BAP levels were measured. The stiffness index was significantly decreased with age. Log (TRACP-5b) was significantly increased with age, but Log (BAP) was stable. Generalized linear models showed that higher levels of Log (TRACP-5b) and Log (BAP) were correlated with a lower stiffness index after adjusting for covariates in men aged 60 years or over, but not in men aged 40 to 59 years. In conclusion, higher rates of bone turnover markers were associated with a lower stiffness index only in elderly men. These results may indicate a different mechanism of low bone mass among different age groups of men. PMID:29465590

  20. Passive stiffness of coupled wrist and forearm rotations.

    PubMed

    Drake, Will B; Charles, Steven K

    2014-09-01

    Coordinated movement requires that the neuromuscular system account and compensate for movement dynamics. One particularly complex aspect of movement dynamics is the interaction that occurs between degrees of freedom (DOF), which may be caused by inertia, damping, and/or stiffness. During wrist rotations, the two DOF of the wrist (flexion-extension and radial-ulnar deviation, FE and RUD) are coupled through interaction torques arising from passive joint stiffness. One important unanswered question is whether the DOF of the forearm (pronation-supination, PS) is coupled to the two DOF of the wrist. Answering this question, and understanding the dynamics of wrist and forearm rotations in general, requires knowledge of the stiffness encountered during rotations involving all three DOF (PS, FE, and RUD). Here we present the first-ever measurement of the passive stiffness encountered during simultaneous wrist and forearm rotations. Using a wrist and forearm robot, we measured coupled wrist and forearm stiffness in 10 subjects and present it as a 3-by-3 stiffness matrix. This measurement of passive wrist and forearm stiffness will enable future studies investigating the dynamics of wrist and forearm rotations, exposing the dynamics for which the neuromuscular system must plan and compensate during movements involving the wrist and forearm.

  1. Stiff muscle fibers in calf muscles of patients with cerebral palsy lead to high passive muscle stiffness.

    PubMed

    Mathewson, Margie A; Chambers, Henry G; Girard, Paul J; Tenenhaus, Mayer; Schwartz, Alexandra K; Lieber, Richard L

    2014-12-01

    Cerebral palsy (CP), caused by an injury to the developing brain, can lead to alterations in muscle function. Subsequently, increased muscle stiffness and decreased joint range of motion are often seen in patients with CP. We examined mechanical and biochemical properties of the gastrocnemius and soleus muscles, which are involved in equinus muscle contracture. Passive mechanical testing of single muscle fibers from gastrocnemius and soleus muscle of patients with CP undergoing surgery for equinus deformity showed a significant increase in fiber stiffness (p<0.01). Bundles of fibers that included their surrounding connective tissues showed no stiffness difference (p=0.28).). When in vivo sarcomere lengths were measured and fiber and bundle stiffness compared at these lengths, both fibers and bundles of patients with CP were predicted to be much stiffer in vivo compared to typically developing (TD) individuals. Interestingly, differences in fiber and bundle stiffness were not explained by typical biochemical measures such as titin molecular weight (a giant protein thought to impact fiber stiffness) or collagen content (a proxy for extracellular matrix amount). We suggest that the passive mechanical properties of fibers and bundles are thus poorly understood. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

  2. Telemetric ambulatory arterial stiffness index, a predictor of cardio-cerebro-vascular mortality, is associated with aortic stiffness-determining factors.

    PubMed

    Li, Zhi-Yong; Xu, Tian-Ying; Zhang, Sai-Long; Zhou, Xiao-Ming; Xu, Xue-Wen; Guan, Yun-Feng; Lo, Ming; Miao, Chao-Yu

    2013-09-01

    Ambulatory arterial stiffness index (AASI) has been proposed as a new measure of arterial stiffness for predicting cardio-cerebro-vascular morbidity and mortality. However, there has been no research on the direct relationships between AASI and arterial stiffness-determining factors. We utilized beat-to-beat intra-aortic blood pressure (BP) telemetry to characterize AASI in Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). By determination of aortic structural components and analysis of their correlations with AASI, we provided the first direct evidence for the associations between AASI and arterial stiffness-determining factors including the collagen content and collagen/elastin. Ambulatory arterial stiffness index was positively correlated with pulse pressure in both WKY and SHR, less dependent on BP and BP variability than pulse pressure, and relatively stable, especially the number of BP readings not less than ~36. The correlations between AASI and aortic components were comparable for various AASI values derived from BP readings not less than ~36. Not only AASI but also BP variability and pulse pressure demonstrated a direct relationship with arterial stiffness. These findings indicate AASI may become a routine measure in human arterial stiffness assessment. It is recommended to use a cluster of parameters such as AASI, BP variability, and pulse pressure for evaluating arterial stiffness. © 2013 John Wiley & Sons Ltd.

  3. Spatial and temporal modulation of joint stiffness during multijoint movement.

    PubMed

    Mah, C D

    2001-02-01

    Joint stiffness measurements during small transient perturbations have suggested that stiffness during movement is different from that observed during posture. These observations are problematic for theories like the classical equilibrium point hypothesis, which suggest that desired trajectories during movement are enforced by joint stiffness. We measured arm impedances during large, slow perturbations to obtain detailed information about the spatial and temporal modulation of stiffness and viscosity during movement. While our measurements of stiffness magnitudes during movement generally agreed with the results of measurements using fast perturbations, they revealed that joint stiffness undergoes stereotyped changes in magnitude and aspect ratio which depend on the direction of movement and show a strong dependence on joint angles. Movement simulations using measured parameters show that the measured modulation of impedance acts as an energy conserving force field to constrain movement. This mechanism allows for a computationally simplified account of the execution of multijoint movement. While our measurements do not rule out a role for afferent feedback in force generation, the observed stereotyped restoring forces can allow a dramatic relaxation of the accuracy requirements for forces generated by other control mechanisms, such as inverse dynamical models.

  4. Stiffness Control of Surgical Continuum Manipulators

    PubMed Central

    Mahvash, Mohsen; Dupont, Pierre E.

    2013-01-01

    This paper introduces the first stiffness controller for continuum robots. The control law is based on an accurate approximation of a continuum robot’s coupled kinematic and static force model. To implement a desired tip stiffness, the controller drives the actuators to positions corresponding to a deflected robot configuration that produces the required tip force for the measured tip position. This approach provides several important advantages. First, it enables the use of robot deflection sensing as a means to both sense and control tip forces. Second, it enables stiffness control to be implemented by modification of existing continuum robot position controllers. The proposed controller is demonstrated experimentally in the context of a concentric tube robot. Results show that the stiffness controller achieves the desired stiffness in steady state, provides good dynamic performance, and exhibits stability during contact transitions. PMID:24273466

  5. Dynamic vehicle-track interaction in switches and crossings and the influence of rail pad stiffness - field measurements and validation of a simulation model

    NASA Astrophysics Data System (ADS)

    Pålsson, Björn A.; Nielsen, Jens C. O.

    2015-06-01

    A model for simulation of dynamic interaction between a railway vehicle and a turnout (switch and crossing, S&C) is validated versus field measurements. In particular, the implementation and accuracy of viscously damped track models with different complexities are assessed. The validation data come from full-scale field measurements of dynamic track stiffness and wheel-rail contact forces in a demonstrator turnout that was installed as part of the INNOTRACK project with funding from the European Union Sixth Framework Programme. Vertical track stiffness at nominal wheel loads, in the frequency range up to 20 Hz, was measured using a rolling stiffness measurement vehicle (RSMV). Vertical and lateral wheel-rail contact forces were measured by an instrumented wheel set mounted in a freight car featuring Y25 bogies. The measurements were performed for traffic in both the through and diverging routes, and in the facing and trailing moves. The full set of test runs was repeated with different types of rail pad to investigate the influence of rail pad stiffness on track stiffness and contact forces. It is concluded that impact loads on the crossing can be reduced by using more resilient rail pads. To allow for vehicle dynamics simulations at low computational cost, the track models are discretised space-variant mass-spring-damper models that are moving with each wheel set of the vehicle model. Acceptable agreement between simulated and measured vertical contact forces at the crossing can be obtained when the standard GENSYS track model is extended with one ballast/subgrade mass under each rail. This model can be tuned to capture the large phase delay in dynamic track stiffness at low frequencies, as measured by the RSMV, while remaining sufficiently resilient at higher frequencies.

  6. Stiffness optimization of non-linear elastic structures

    DOE PAGES

    Wallin, Mathias; Ivarsson, Niklas; Tortorelli, Daniel

    2017-11-13

    Our paper revisits stiffness optimization of non-linear elastic structures. Due to the non-linearity, several possible stiffness measures can be identified and in this work conventional compliance, i.e. secant stiffness designs are compared to tangent stiffness designs. The optimization problem is solved by the method of moving asymptotes and the sensitivities are calculated using the adjoint method. And for the tangent cost function it is shown that although the objective involves the third derivative of the strain energy an efficient formulation for calculating the sensitivity can be obtained. Loss of convergence due to large deformations in void regions is addressed bymore » using a fictitious strain energy such that small strain linear elasticity is approached in the void regions. We formulate a well-posed topology optimization problem by using restriction which is achieved via a Helmholtz type filter. The numerical examples provided show that for low load levels, the designs obtained from the different stiffness measures coincide whereas for large deformations significant differences are observed.« less

  7. Stiffness optimization of non-linear elastic structures

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wallin, Mathias; Ivarsson, Niklas; Tortorelli, Daniel

    Our paper revisits stiffness optimization of non-linear elastic structures. Due to the non-linearity, several possible stiffness measures can be identified and in this work conventional compliance, i.e. secant stiffness designs are compared to tangent stiffness designs. The optimization problem is solved by the method of moving asymptotes and the sensitivities are calculated using the adjoint method. And for the tangent cost function it is shown that although the objective involves the third derivative of the strain energy an efficient formulation for calculating the sensitivity can be obtained. Loss of convergence due to large deformations in void regions is addressed bymore » using a fictitious strain energy such that small strain linear elasticity is approached in the void regions. We formulate a well-posed topology optimization problem by using restriction which is achieved via a Helmholtz type filter. The numerical examples provided show that for low load levels, the designs obtained from the different stiffness measures coincide whereas for large deformations significant differences are observed.« less

  8. Arterial stiffness and fetal growth in normotensive pregnancy.

    PubMed

    Elvan-Taspinar, Ayten; Franx, Arie; Bots, Michiel L; Koomans, Hein A; Bruinse, Hein W

    2005-03-01

    Normal pregnancy is characterized by a decrease in peripheral resistance and generalized vasodilation resulting in plasma volume expansion, which is associated with intrauterine growth. Stiffness of the arterial system may be a measure of the degree of plasma volume expansion. Pulse wave velocity (PWV), measured by applanation tonometry, is a validated approach to determine arterial stiffness. Pulse pressure (PP) is considered a surrogate measure for arterial stiffness. The aim of this study was to evaluate the association between arterial stiffness and fetal growth. In 50 normotensive pregnancies, carotid-femoral PWV was measured in the third trimester in 30 degrees lateral position. Blood pressure measurements were performed with conventional auscultatory sphygmomanometry. Birth weight centiles and weight centiles at the age of 6 months were recorded. Linear regression models were used for statistical analyses. There was a significant relationship in PWV with both birth weight centiles and catch-up growth after birth, independent of mean arterial pressure (MAP). An increase of 1 m/sec in PWV was associated with a decrease in birth weight centiles by 17.6% and a catch-up of 22.3% in weight centiles after birth. A stronger association was found for pulse pressure and birth weight centiles. An increase of 1 mm Hg was associated with a decrease in birth weight centiles by 1.8%. There was no association between MAP and birth weight centiles. In normotensive pregnancy arterial stiffness is associated with birth weight centile and catch-up growth after birth, independently from MAP. This suggests that arterial stiffness reflects maternal vascular adaptation to pregnancy better than blood pressure.

  9. Lower Body Stiffness Modulation Strategies in Well Trained Female Athletes.

    PubMed

    Millett, Emma L; Moresi, Mark P; Watsford, Mark L; Taylor, Paul G; Greene, David A

    2016-10-01

    Millett, EL, Moresi, MP, Watsford, ML, Taylor, PG, and Greene, DA. Lower body stiffness modulation strategies in well trained female athletes. J Strength Cond Res 30(10): 2845-2856, 2016-Lower extremity stiffness quantifies the relationship between the amount of leg compression and the external load to which the limb are subjected. This study aimed to assess differences in leg and joint stiffness and the subsequent kinematic and kinetic control mechanisms between athletes from various training backgrounds. Forty-seven female participants (20 nationally identified netballers, 13 high level endurance athletes and 14 age and gender matched controls) completed a maximal unilateral countermovement jump, drop jump and horizontal jump to assess stiffness. Leg stiffness, joint stiffness and associated mechanical parameters were assessed with a 10 camera motion analysis system and force plate. No significant differences were evident for leg stiffness measures between athletic groups for any of the tasks (p = 0.321-0.849). However, differences in joint stiffness and its contribution to leg stiffness, jump performance outcome measures and stiffness control mechanisms were evident between all groups. Practitioners should consider the appropriateness of the task utilised in leg stiffness screening. Inclusion of mechanistic and/or more sports specific tasks may be more appropriate for athletic groups.

  10. Arterial Stiffness Measured with the Cuff Oscillometric Method Is Predictive of Exercise Capacity in Patients with Cardiac Diseases.

    PubMed

    Tazawa, Yasushi; Mori, Nobuyoshi; Ogawa, Yoshiko; Ito, Osamu; Kohzuki, Masahiro

    2016-06-01

    Arterial stiffness is widely used in assessing arteriosclerosis in the background of increased cardiovascular events. Arteriosclerosis also causes reduction in exercise capacity, which is a most important prognostic factor in patients with cardiovascular disease; however, data on the association between arterial stiffness and exercise capacity are limited. Therefore, a simple and noninvasive measurement of arterial stiffness that reflects the central circulation and exercise capacity is needed. The arterial velocity pulse index (AVI) is a parameter of arterial stiffness measurable with the cuff oscillometric method; however, the clinical utility of this method is unclear. We aimed to evaluate the trend of AVI in patients with coronary artery disease (CAD), and the association between AVI and exercise capacity. A cross-sectional study of 116 patients with cardiac disease (34 CAD and 82 non-CAD patients) was performed. Non-CAD patients were those with any cardiac diseases who did not have proven CAD. The results showed that the AVI was significantly higher in CAD patients than non-CAD patients (P < 0.05, analysis of covariance). The AVI was inversely correlated with peakVO2 (r = -0.239, P < 0.05) and was a significant explanatory variable for peakVO2 in stepwise regression analysis (β = -14.62, t = -2.5, P < 0.05). These results indicate that the AVI is strongly associated with CAD and predictive of the exercise capacity in patients with cardiac diseases. We, therefore, propose that the cuff oscillometric method is clinically useful in evaluating arterial stiffness in patients with cardiac diseases, especially CAD.

  11. Arterial stiffness estimation based photoplethysmographic pulse wave analysis

    NASA Astrophysics Data System (ADS)

    Huotari, Matti; Maatta, Kari; Kostamovaara, Juha

    2010-11-01

    Arterial stiffness is one of the indices of vascular healthiness. It is based on pulse wave analysis. In the case we decompose the pulse waveform for the estimation and determination of arterial elasticity. Firstly, optically measured with photoplethysmograph and then investigating means by four lognormal pulse waveforms for which we can find very good fit between the original and summed decomposed pulse wave. Several studies have demonstrated that these kinds of measures predict cardiovascular events. While dynamic factors, e.g., arterial stiffness, depend on fixed structural features of the vascular wall. Arterial stiffness is estimated based on pulse wave decomposition analysis in the radial and tibial arteries. Elucidation of the precise relationship between endothelial function and vascular stiffness awaits still further study.

  12. Investigation on Prototype Superconducting Linear Synchronous Motor (LSM) for 600-km/h Wheel-Type Railway

    NASA Astrophysics Data System (ADS)

    Eom, Beomyong; Lee, Changhyeong; Kim, Seokho; Lee, Changyoung; Yun, Sangwon

    The existing wheel-type high-speed railway with a rotatable motor has a limit of 600 km/h speed. The normal conducting electromagnet has several disadvantages to realize 600 km/h speed. Several disadvantages are the increased space and weight, and the decreased electric efficiency to generate the required high magnetic field. In order to reduce the volume and weight, superconducting electromagnets can be considered for LSM (Linear Synchronous Motor). Prior to the fabrication of the real system, a prototype demo-coil is designed and fabricated using 2G high temperature superconducting wire. The prototype HTS coil is cooled by the conduction using a GM cryocooler. To reduce the heat penetration, thermal design was performed for the current leads, supporting structure and radiation shield considering the thermal stress. The operating temperature and current are 30∼40 K and 100 A. The coil consists of two double pancake coils (N, S pole, respectively) and it is driven on a test rail, which is installed for the test car. This paper describes the design and test results of the prototype HTS LSM system. Thermal characteristics are investigated with additional dummy thermal mass on the coil after turning off the cryocooler.

  13. Real-Time Vision-Based Stiffness Mapping †.

    PubMed

    Faragasso, Angela; Bimbo, João; Stilli, Agostino; Wurdemann, Helge Arne; Althoefer, Kaspar; Asama, Hajime

    2018-04-26

    This paper presents new findings concerning a hand-held stiffness probe for the medical diagnosis of abnormalities during palpation of soft-tissue. Palpation is recognized by the medical community as an essential and low-cost method to detect and diagnose disease in soft-tissue. However, differences are often subtle and clinicians need to train for many years before they can conduct a reliable diagnosis. The probe presented here fills this gap providing a means to easily obtain stiffness values of soft tissue during a palpation procedure. Our stiffness sensor is equipped with a multi degree of freedom (DoF) Aurora magnetic tracker, allowing us to track and record the 3D position of the probe whilst examining a tissue area, and generate a 3D stiffness map in real-time. The stiffness probe was integrated in a robotic arm and tested in an artificial environment representing a good model of soft tissue organs; the results show that the sensor can accurately measure and map the stiffness of a silicon phantom embedded with areas of varying stiffness.

  14. Real-Time Vision-Based Stiffness Mapping †

    PubMed Central

    Althoefer, Kaspar; Asama, Hajime

    2018-01-01

    This paper presents new findings concerning a hand-held stiffness probe for the medical diagnosis of abnormalities during palpation of soft-tissue. Palpation is recognized by the medical community as an essential and low-cost method to detect and diagnose disease in soft-tissue. However, differences are often subtle and clinicians need to train for many years before they can conduct a reliable diagnosis. The probe presented here fills this gap providing a means to easily obtain stiffness values of soft tissue during a palpation procedure. Our stiffness sensor is equipped with a multi degree of freedom (DoF) Aurora magnetic tracker, allowing us to track and record the 3D position of the probe whilst examining a tissue area, and generate a 3D stiffness map in real-time. The stiffness probe was integrated in a robotic arm and tested in an artificial environment representing a good model of soft tissue organs; the results show that the sensor can accurately measure and map the stiffness of a silicon phantom embedded with areas of varying stiffness. PMID:29701704

  15. A Novel Technique to Measure In Vivo Uterine Suspensory Ligament Stiffness

    PubMed Central

    Smith, Tovia M.; Luo, Jiajia; Hsu, Yvonne; Ashton-Miller, James A.; Delancey, John O.L.

    2013-01-01

    Objective To describe a new computer-controlled research apparatus for measuring in vivo uterine ligament force-displacement behavior and stiffness and to present pilot data in women with and without prolapse. Study Design Seventeen women with varying uterine support underwent testing in the operating room (OR) after anesthetic induction. A tripod-mounted computer-controlled linear servoactuator was used to quantify force-displacement behavior of the cervix and supporting ligaments. The servoactuator applied a caudally-directed force to a tenaculum at 4 mm/s velocity until the traction force reached 17.8N (4 lbs.). Cervix location on POP-Q in clinic, in the OR at rest, and with minimal force (<1.1N), and maximum force (17.8N) was recorded. Ligament “stiffness” between minimum and maximum force was calculated. Results The mean (SD) subject age was 54.5 (12.7) years, parity 2.9 (1.1), BMI 29.0 (4.3) kg/m2, and POP-Q point C −3.1 (3.9) cm. POP-Q point C was most strongly correlated with cervix location at maximum force (r=+0.68, p=.003) and at rest (r=+0.62, p=.009). Associations between cervix location at minimum force (r=+0.46, p=.059) and ligament stiffness (r= −0.44,p=.079) were not statistically significant. Cervix location in the OR with minimal traction lay below the lowest point found on POP-Q for 13 women. Conclusions POP-Q point C was strongly correlated with cervix location at rest and at maximum traction force; however only 19% of the variation in POP-Q point C location was explained by ligament stiffness. The cervix location in the OR at minimal traction lay below POP-Q point C value in ¾ of women. PMID:23747493

  16. Nonparticipatory Stiffness in the Male Perioral Complex

    ERIC Educational Resources Information Center

    Chu, Shin-Ying; Barlow, Steven M.; Lee, Jaehoon

    2009-01-01

    Purpose: The objective of this study was to extend previous published findings in the authors' laboratory using a new automated technology to quantitatively characterize nonparticipatory perioral stiffness in healthy male adults. Method: Quantitative measures of perioral stiffness were sampled during a nonparticipatory task using a…

  17. Measuring the effects of aging and sex on regional brain stiffness with MR elastography in healthy older adults

    PubMed Central

    Arani, Arvin; Murphy, Matthew C; Glaser, Kevin J; Manduca, Armando; Lake, David S; Kruse, Scott; Jack, Clifford R; Ehman, Richard; Huston, John

    2015-01-01

    Changes in tissue composition and cellular architecture have been associated with neurological disease, and these in turn can affect biomechanical properties. Natural biological factors such as aging and an individual’s sex also affect underlying tissue biomechanics in different brain regions. Understanding the normal changes is necessary before determining the efficacy of stiffness imaging for neurological disease diagnosis and therapy monitoring. The objective of this study was to evaluate global and regional changes in brain stiffness as a function of age and sex, using improved MRE acquisition and processing that has been shown to provide median stiffness values that are typically reproducible to within 1% in global measurements and within 2% for regional measurements. Furthermore, this is the first study to report the effects of age and sex over the entire cerebrum volume and over the full frontal, occipital, parietal, temporal, deep gray matter/white matter (insula, deep gray nuclei and white matter tracts), and cerebellum volumes. In 45 volunteers, we observed a significant linear correlation between age and brain stiffness in the cerebrum (P<.0001), frontal lobes (P<.0001), occipital lobes (P=.0005), parietal lobes (P=.0002), and the temporal lobes (P<.0001) of the brain. No significant linear correlation between brain stiffness and age was observed in the cerebellum (P=.74), and the sensory-motor regions (P=.32) of the brain, and a weak linear trend was observed in the deep gray matter/white matter (P=.075). A multiple linear regression model predicted an annual decline of 0.011±0.002 kPa in cerebrum stiffness with a theoretical median age value (76 years old) of 2.56±0.08 kPa. Sexual dimorphism was observed in the temporal (P=.03) and occipital (P=.001) lobes of the brain, but no significant difference was observed in any of the other brain regions (P>.20 for all other regions). The model predicted female occipital and temporal lobes to be 0.23 k

  18. Face-Referenced Measurement of Perioral Stiffness and Speech Kinematics in Parkinson's Disease

    ERIC Educational Resources Information Center

    Chu, Shin Ying; Barlow, Steven M.; Lee, Jaehoon

    2015-01-01

    Purpose: Perioral biomechanics, labial kinematics, and associated electromyographic signals were sampled and characterized in individuals with Parkinson's disease (PD) as a function of medication state. Method: Passive perioral stiffness was sampled using the OroSTIFF system in 10 individuals with PD in a medication ON and a medication OFF state…

  19. Measurements of Tibiofemoral Kinematics During Soft and Stiff Drop Landings Using Biplane Fluoroscopy

    PubMed Central

    Myers, Casey A.; Torry, Michael R.; Peterson, Daniel S.; Shelburne, Kevin B.; Giphart, J. Erik; Krong, Jacob P.; Woo, Savio L-Y.; Steadman, J. Richard

    2014-01-01

    Background Previous laboratory studies of landing have defined landing techniques in terms of soft or stiff landings according to the degree of maximal knee flexion angle attained during the landing phase and the relative magnitude of the ground-reaction force. Current anterior cruciate ligament injury prevention programs are instructing athletes to land softly to avoid excessive strain on the anterior cruciate ligament. Purpose This study was undertaken to measure, describe, and compare tibiofemoral rotations and translations of soft and stiff landings in healthy individuals using biplane fluoroscopy. Study Design Controlled laboratory study. Methods The in vivo, lower extremity, 3-dimensional knee kinematics of 16 healthy adults (6 male and 10 female) instructed to land softly and stiffly in different trials were collected in biplane fluoroscopy as they performed the landing from a height of 40 cm. Results Average and maximum relative anterior tibial translation (average, 2.8 ± 1.2 mm vs 3.0 ± 1.4 mm; maximum, 4.7 ± 1.6 mm vs 4.4 ± 0.8 mm), internal/external rotation (average, 3.7° ± 5.1° vs 2.7° ± 4.3°; maximum, 5.6° ± 5.5° vs 4.9° ± 4.7°), and varus/valgus (average, 0.2° ± 1.2° vs 0.2° ± 1.0°; maximum, 1.7° ± 1.2° vs 1.6° ± 0.9°) were all similar between soft and stiff landings, respectively. The peak vertical ground-reaction force was significantly larger for stiff landings than for soft landings (2.60 ± 1.32 body weight vs 1.63 ± 0.73; P < .001). The knee flexion angle total range of motion from the minimum angle at contact to the maximum angle at peak knee flexion was significantly greater for soft landings than for stiff (55.4° ± 8.8° vs 36.8° ± 11.1°; P < .01). Conclusion Stiff landings, as defined by significantly lower knee flexion angles and significantly greater peak ground-reaction forces, do not result in larger amounts of anterior tibial translation or knee rotation in either varus/valgus or internal

  20. Measurement of knee stiffness and laxity in patients with documented absence of the anterior cruciate ligament.

    PubMed

    Markolf, K L; Kochan, A; Amstutz, H C

    1984-02-01

    Thirty-five patients with documented absence of the anterior cruciate ligament were tested on the University of California, Los Angeles, instrumented clinical knee-testing apparatus and we measured the response curves for the following testing modes: anterior-posterior force versus displacement at full extension and at 20 and 90 degrees of flexion; varus-valgus moment versus angulation at full extension and 20 degrees of flexion; and tibial torque versus rotation at 20 degrees of flexion. Absolute values of stiffness and laxity and right-left differences for these injured knees were compared with identical quantities measured previously for a control population of forty-nine normal subjects with no history of treatment for injury to the knee. For both the uninjured knees and the knees without an anterior cruciate ligament, at 20 and 90 degrees of flexion the anterior-posterior laxity was greatest at approximately 15 degrees of external rotation of the foot. The injured knees demonstrated significantly increased total anterior-posterior laxity and decreased anterior stiffness when compared with the uninjured knees in all tested positions of the foot and knee. The mean increase in paired anterior-posterior laxity for the injured knees in this group of patients at +/- 200 newtons of applied anterior-posterior force was 3.1 millimeters (+39 per cent) at full extension, 5.5 millimeters (+57 per cent) at 20 degrees of flexion, and 2.5 millimeters (+34 per cent) at 90 degrees of flexion. The mean reduction in anterior stiffness for injured knees was also greatest (-54 per cent) at 20 degrees of knee flexion. Only slight reduction in posterior stiffness (-16 per cent) was measured at 20 degrees of flexion, and this probably reflected the presence of associated capsular and meniscal injuries. In the group of anterior cruciate-deficient knees, the patients with an absent medial meniscus showed greater total anterior-posterior laxity in all three positions of knee flexion

  1. Face-Referenced Measurement of Perioral Stiffness and Speech Kinematics in Parkinson's Disease

    PubMed Central

    Barlow, Steven M.; Lee, Jaehoon

    2015-01-01

    Purpose Perioral biomechanics, labial kinematics, and associated electromyographic signals were sampled and characterized in individuals with Parkinson's disease (PD) as a function of medication state. Method Passive perioral stiffness was sampled using the OroSTIFF system in 10 individuals with PD in a medication ON and a medication OFF state and compared to 10 matched controls. Perioral stiffness, derived as the quotient of resultant force and interoral angle span, was modeled with regression techniques. Labial movement amplitudes and integrated electromyograms from select lip muscles were evaluated during syllable production using a 4-D computerized motion capture system. Results Multilevel regression modeling showed greater perioral stiffness in patients with PD, consistent with the clinical correlate of rigidity. In the medication-OFF state, individuals with PD manifested greater integrated electromyogram levels for the orbicularis oris inferior compared to controls, which increased further after consumption of levodopa. Conclusions This study illustrates the application of biomechanical, electrophysiological, and kinematic methods to better understand the pathophysiology of speech motor control in PD. PMID:25629806

  2. Tension-referenced measures of gastrocnemius slack length and stiffness in Parkinson's disease.

    PubMed

    Tan, Benedict; Double, Kay L; Burne, John; Diong, Joanna

    2016-12-01

    It is not known how passive muscle length and stiffness contribute to rigidity in Parkinson's disease. The objective of this study was to compare passive gastrocnemius muscle-tendon slack length and stiffness at known tension in Parkinson's disease subjects with ankle rigidity and in able-bodied people. Passive ankle torque-angle curves were obtained from 15 Parkinson's disease subjects with rigidity and 15 control subjects. Torque-angle data were used to derive passive gastrocnemius length-tension data and calculate slack length and stiffness of the gastrocnemius muscle. Between-group comparisons were made with linear models. Gastrocnemius muscle-tendon slack lengths (adjusted between-group difference, 0.01 m; 95% CI, -0.02 to 0.04 m; P = 0.37) and stiffness (adjusted between-group difference, 15.7 m -1 ; 95% CI, -8.5 to 39.9 m -1 ; P = 0.19) were not significantly different between groups. Parkinson's disease subjects with ankle rigidity did not have significantly shorter or stiffer gastrocnemius muscles compared with control subjects. © 2016 International Parkinson and Movement Disorder Society. © 2016 International Parkinson and Movement Disorder Society.

  3. Evolution of noninvasive tests of liver fibrosis is associated with prognosis in patients with chronic hepatitis C.

    PubMed

    Vergniol, Julien; Boursier, Jérôme; Coutzac, Clélia; Bertrais, Sandrine; Foucher, Juliette; Angel, Camille; Chermak, Faiza; Hubert, Isabelle Fouchard; Merrouche, Wassil; Oberti, Frédéric; de Lédinghen, Victor; Calès, Paul

    2014-07-01

    No data are available about the prediction of long-term survival using repeated noninvasive tests of liver fibrosis in chronic hepatitis C (CHC). We aimed to assess the prognostic value of 3-year liver stiffness measurement (LSM), aspartate aminotransferase to platelet ratio index (APRI), and fibrosis 4 (FIB-4) evolution in CHC. CHC patients with two LSM (1,000-1,500 days interval) were prospectively included. Blood fibrosis tests APRI and FIB-4 were calculated the day of baseline (bLSM) and follow-up (fLSM) LSM. Evolution of fibrosis tests was expressed as delta: (follow-up-baseline results)/duration. Date and cause of death were recorded during follow-up that started the day of fLSM. In all, 1,025 patients were included. Median follow-up after fLSM was 38.0 months (interquartile range [IQR]: 27.7-46.1) during which 35 patients died (14 liver-related death) and seven had liver transplantation. Prognostic accuracy (Harrell C-index) of multivariate models including baseline and delta results was not significantly different between LSM and FIB-4 (P ≥ 0.24), whereas FIB-4 provided more accurate prognostic models than APRI (P = 0.03). By multivariate analysis including LSM variables, overall survival was independently predicted by bLSM, delta (dLSM), and sustained virological response (SVR). Prognosis was excellent in patients having bLSM <7 kPa, SVR, or no increase (<1 kPa/year) in 7-14 kPa bLSM. Prognosis was significantly impaired in patients with an increase (≥ 1 kPa/year) in 7-14 kPa bLSM, or decrease (≤ 0 kPa/year) in ≥ 14 kPa bLSM (P = 0.949 between these two groups). Patients with an increase (>0 kPa/year) in ≥ 14 kPa bLSM had the worst prognosis. Baseline and delta FIB-4 also identified patient subgroups with significantly different prognosis. Three-year evolution of noninvasive tests of liver fibrosis has a strong prognostic value in CHC patients. These tests should be repeated to monitor patients and predict their outcome. © 2014 by the American

  4. Acute changes in arterial stiffness following exercise in people with metabolic syndrome.

    PubMed

    Radhakrishnan, Jeyasundar; Swaminathan, Narasimman; Pereira, Natasha M; Henderson, Keiran; Brodie, David A

    This study aims to examine the changes in arterial stiffness immediately following sub-maximal exercise in people with metabolic syndrome. Ninety-four adult participants (19-80 years) with metabolic syndrome gave written consent and were measured for arterial stiffness using a SphygmoCor (SCOR-PVx, Version 8.0, Atcor Medical Private Ltd, USA) immediately before and within 5-10min after an incremental shuttle walk test. The arterial stiffness measures used were pulse wave velocity (PWV), aortic pulse pressure (PP), augmentation pressure, augmentation index (AI), subendocardial viability ratio (SEVR) and ejection duration (ED). There was a significant increase (p<0.05) in most of the arterial stiffness variables following exercise. Exercise capacity had a strong inverse correlation with arterial stiffness and age (p<0.01). Age influences arterial stiffness. Exercise capacity is inversely related to arterial stiffness and age in people with metabolic syndrome. Exercise induced changes in arterial stiffness measured using pulse wave analysis is an important tool that provides further evidence in studying cardiovascular risk in metabolic syndrome. Copyright © 2016 Diabetes India. Published by Elsevier Ltd. All rights reserved.

  5. Is stiffness related to athletic groin pain?

    PubMed

    Gore, S J; Franklyn-Miller, A; Richter, C; Falvey, E C; King, E; Moran, K

    2018-06-01

    Athletic groin pain (AGP) is a common injury prevalent in field sports. One biomechanical measure that may be of importance for injury risk is stiffness. To date however, stiffness has not been examined in AGP. The primary aim was to determine whether AGP affects vertical and joint stiffness and if so, whether successful rehabilitation is associated with a change in stiffness. Sixty-five male patients with AGP and fifty male controls were recruited to this study. Assessment included a biomechanical examination of stiffness during a lateral hurdle hop test. Subjects with AGP were tested pre- and post-rehabilitation, while controls were tested once. AGP subjects were cleared for return to play in a median time of 9.14 weeks (5.14-29.0). Stiffness was significantly different at pre-rehabilitation in comparison with controls for four of the ten stiffness values examined: ankle plantar flexor, knee extensor, hip abductor, and vertical stiffness (P < .05, D = 0.36-0.79). Despite clearance for return to play, of these four variables, only hip abductor stiffness changed significantly from pre- to post-rehabilitation (P = .05, D = 0.35) to become non-significantly different to the uninjured group (P = .18, D = 0.26). These findings suggest that hip abductor stiffness may represent a target for AGP rehabilitation. Conversely, given the clearance for return to play, the lower sagittal plane and vertical stiffness in the AGP group in comparison with the uninjured controls likely represents either a compensatory mechanism to reduce the risk of further injury or a consequence of neuromuscular detraining. © 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  6. Association of objectively measured physical activity and sedentary time with arterial stiffness in women with systemic lupus erythematosus with mild disease activity.

    PubMed

    Morillas-de-Laguno, Pablo; Vargas-Hitos, José A; Rosales-Castillo, Antonio; Sáez-Urán, Luis Manuel; Montalbán-Méndez, Cristina; Gavilán-Carrera, Blanca; Navarro-Mateos, Carmen; Acosta-Manzano, Pedro; Delgado-Fernández, Manuel; Sabio, José M; Ortego-Centeno, Norberto; Callejas-Rubio, José L; Soriano-Maldonado, Alberto

    2018-01-01

    To examine the association of objectively measured physical activity (PA) intensity levels and sedentary time with arterial stiffness in women with systemic lupus erythematosus (SLE) with mild disease activity and to analyze whether participants meeting the international PA guidelines have lower arterial stiffness than those not meeting the PA guidelines. The study comprised 47 women with SLE (average age 41.2 [standard deviation 13.9]) years, with clinical and treatment stability during the 6 months prior to the study. PA intensity levels and sedentary time were objectively measured with triaxial accelerometry. Arterial stiffness was assessed through pulse wave velocity, evaluated by Mobil-O-Graph® 24h pulse wave analysis monitor. The average time in moderate to vigorous PA in bouts of ≥10 consecutive minutes was 135.1±151.8 minutes per week. There was no association of PA intensity levels and sedentary time with arterial stiffness, either in crude analyses or after adjusting for potential confounders. Participants who met the international PA guidelines did not show lower pulse wave velocity than those not meeting them (b = -0.169; 95% CI: -0.480 to 0.143; P = 0.280). Our results suggest that PA intensity levels and sedentary time are not associated with arterial stiffness in patients with SLE. Further analyses revealed that patients with SLE meeting international PA guidelines did not present lower arterial stiffness than those not meeting the PA guidelines. Future prospective research is needed to better understand the association of PA and sedentary time with arterial stiffness in patients with SLE.

  7. Association of objectively measured physical activity and sedentary time with arterial stiffness in women with systemic lupus erythematosus with mild disease activity

    PubMed Central

    Vargas-Hitos, José A.; Gavilán-Carrera, Blanca; Navarro-Mateos, Carmen; Acosta-Manzano, Pedro; Delgado-Fernández, Manuel; Sabio, José M.; Ortego-Centeno, Norberto; Callejas-Rubio, José L.; Soriano-Maldonado, Alberto

    2018-01-01

    Objectives To examine the association of objectively measured physical activity (PA) intensity levels and sedentary time with arterial stiffness in women with systemic lupus erythematosus (SLE) with mild disease activity and to analyze whether participants meeting the international PA guidelines have lower arterial stiffness than those not meeting the PA guidelines. Methods The study comprised 47 women with SLE (average age 41.2 [standard deviation 13.9]) years, with clinical and treatment stability during the 6 months prior to the study. PA intensity levels and sedentary time were objectively measured with triaxial accelerometry. Arterial stiffness was assessed through pulse wave velocity, evaluated by Mobil-O-Graph® 24h pulse wave analysis monitor. Results The average time in moderate to vigorous PA in bouts of ≥10 consecutive minutes was 135.1±151.8 minutes per week. There was no association of PA intensity levels and sedentary time with arterial stiffness, either in crude analyses or after adjusting for potential confounders. Participants who met the international PA guidelines did not show lower pulse wave velocity than those not meeting them (b = -0.169; 95% CI: -0.480 to 0.143; P = 0.280). Conclusions Our results suggest that PA intensity levels and sedentary time are not associated with arterial stiffness in patients with SLE. Further analyses revealed that patients with SLE meeting international PA guidelines did not present lower arterial stiffness than those not meeting the PA guidelines. Future prospective research is needed to better understand the association of PA and sedentary time with arterial stiffness in patients with SLE. PMID:29694382

  8. A randomized controlled trial for the effect of passive stretching on measures of hamstring extensibility, passive stiffness, strength, and stretch tolerance.

    PubMed

    Marshall, Paul W M; Cashman, Anthony; Cheema, Birinder S

    2011-11-01

    To measure hamstring extensibility, stiffness, stretch tolerance, and strength following a 4-week passive stretching program. Randomized controlled trial. Twenty-two healthy participants were randomly assigned to either a 4-week stretching program consisting of 4 hamstring and hip stretches performed 5 times per week, or a non-stretching control group. Hamstring extensibility and stiffness were measured before and after training using the instrumented straight leg raise test (iSLR). Stretch tolerance was measured as the pain intensity (visual analog scale; VAS) elicited during the maximal stretch. Hamstring strength was measured using isokinetic dynamometry at 30 and 120° s(-1). Hamstring extensibility increased by 20.9% in the intervention group following 4 weeks of training (p<0.001; d=0.86). Passive stiffness was reduced by 31% in the intervention group (p<0.05; d=-0.89). Stretch tolerance VAS scores were not different between groups at either time point, and no changes were observed following training. There were no changes in hamstring concentric strength measured at 30 and 120° s(-1). Passive stretching increases hamstring extensibility and decreases passive stiffness, with no change in stretch tolerance defined by pain intensity during the stretch. Compared to previous research, the volume of stretching was higher in this study. The volume of prescribed stretching is important for eliciting the strong clinical effect observed in this study. Copyright © 2011 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

  9. Intraventricular filling under increasing left ventricular wall stiffness and heart rates

    NASA Astrophysics Data System (ADS)

    Samaee, Milad; Lai, Hong Kuan; Schovanec, Joseph; Santhanakrishnan, Arvind; Nagueh, Sherif

    2015-11-01

    Heart failure with normal ejection fraction (HFNEF) is a clinical syndrome that is prevalent in over 50% of heart failure patients. HFNEF patients show increased left ventricle (LV) wall stiffness and clinical diagnosis is difficult using ejection fraction (EF) measurements. We hypothesized that filling vortex circulation strength would decrease with increasing LV stiffness irrespective of heart rate (HR). 2D PIV and hemodynamic measurements were acquired on LV physical models of varying wall stiffness under resting and exercise HRs. The LV models were comparatively tested in an in vitro flow circuit consisting of a two-element Windkessel model driven by a piston pump. The stiffer LV models were tested in comparison with the least stiff baseline model without changing pump amplitude, circuit compliance and resistance. Increasing stiffness at resting HR resulted in diminishing cardiac output without lowering EF below 50% as in HFNEF. Increasing HR to 110 bpm in addition to stiffness resulted in lowering EF to less than 50%. The circulation strength of the intraventricular filling vortex diminished with increasing stiffness and HR. The results suggest that filling vortex circulation strength could be potentially used as a surrogate measure of LV stiffness. This research was supported by the Oklahoma Center for Advancement of Science and Technology (HR14-022).

  10. Importance of software version for measurement of arterial stiffness: Arteriograph as an example.

    PubMed

    Ring, Margareta; Eriksson, Maria J; Nyberg, Gunnar; Caidahl, Kenneth

    2018-01-01

    Current guidelines recommend the measurement of arterial stiffness in terms of aortic pulse wave velocity (PWV) as an important cardio-vascular risk marker. Both aortic PWV and the aortic augmentation index (AIxao) can be measured using different techniques, e.g., the Arteriograph and SphygmoCor. A new version of the software for the Arteriograph (v. 3.0.0.1, TensioMed, Budapest, Hungary; Arteriograph II) is now available. We wanted to determine whether this improved software differs from the previous version (Arteriograph v. 1.9.9.12; Arteriograph I). We compared the estimated aortic PWV (ePWVao) and AIxao measured with both versions of Arteriograph software and analysed the agreement of these values with those measured by SphygmoCor (v. 7.01, AtCor Medical, Sydney, Australia). Eighty-seven subjects without known cardio-vascular disease (23 men and 64 women) aged 54.2 ± 8.7 years (mean ± standard deviation; range 33-68 years) were included in the study. Estimated PWVao and AIxao were measured by both Arteriograph and SphygmoCor. We compared Arteriograph I and Arteriograph II with each other and with SphygmoCor. Estimated PWVao measured by Arteriograph II was lower than that measured by Arteriograph I, while the AIxao was higher. Divergence in ePWVao values was especially noted above 9 m/s. Estimated PWVao measured by Arteriograph II (7.2 m/s, 6.6-8.0 [median, 25th-75th percentile]) did not differ from that measured by SphygmoCor (7.1 m/s, 6.7-7.9 [median, 25th-75th percentile]). However, the AIao measured by Arteriograph II was significantly higher (P < 0.001). Regularly upgraded software versions resulting from continuous technical development are needed for quality improvement of methods. However, the changes in software, even if the basic patented operational algorithm has not changed, may influence the measured values as shown in the present study. Therefore, attention should be paid to the software version of the method used when comparing arterial

  11. Increased muscle belly and tendon stiffness in patients with Parkinson's disease, as measured by myotonometry.

    PubMed

    Marusiak, Jarosław; Jaskólska, Anna; Budrewicz, Sławomir; Koszewicz, Magdalena; Jaskólski, Artur

    2011-09-01

    Based on Davis's law, greater tonus of the muscle belly in individuals with Parkinson's disease can create greater tension in the tendon, leading to structural adjustment and an increase in tendon stiffness. Our study aimed to separately assess passive stiffness in the muscle belly and tendon in medicated patients with Parkinson's disease, using myotonometry. We tested 12 patients with Parkinson's disease and 12 healthy matched controls. Passive stiffness of muscle belly and tendon was estimated by myotonometry, electromyography, and mechanomyography in relaxed biceps and triceps brachii muscles. Compared with controls, patients with Parkinson's disease had higher stiffness in the muscle belly and tendon of the biceps brachii and in the tendon of the triceps brachii. In patients with Parkinson's disease, there was a positive correlation between muscle belly stiffness and parkinsonian rigidity in the biceps brachii. Patients with Parkinson's disease have higher passive stiffness of the muscle belly and tendon than healthy matched controls. Copyright © 2011 Movement Disorder Society.

  12. Knee stiffness and viscosity: New implementation and perspectives in prosthesis development

    PubMed Central

    Bohinc, Klemen; Vantur, Nejc; Torkar, Drago; Lampe, Tomaž; Hribernik, Marija; Jakovljević, Miroljub

    2017-01-01

    The pendulum test is a method applied to measure passive resistance of the knee. A new and simple pendulum test with instrumentation based on infrared camera was used to evaluate knee stiffness and viscosity on a female human cadaver. The stiffness and viscosity were calculated based on the kinetic data. During the measurements, the periarticular and intraarticular soft tissue of the knee was gradually removed to determine the stiffness and viscosity as a function of the tissue removal rate. The measurements showed that the removal of tissue around the joint reduces the damping of leg oscillation, and therefore decreases the stiffness and viscosity. The contribution to knee joint damping was 10% for the skin, 20% for ligaments, and 40% for muscles and tendons. Tissue removal has a very large impact on the knee stiffness and viscosity. PMID:28422623

  13. Knee stiffness and viscosity: New implementation and perspectives in prosthesis development.

    PubMed

    Bohinc, Klemen; Vantur, Nejc; Torkar, Drago; Lampe, Tomaž; Hribernik, Marija; Jakovljević, Miroljub

    2017-05-20

    The pendulum test is a method applied to measure passive resistance of the knee. A new and simple pendulum test with instrumentation based on infrared camera was used to evaluate knee stiffness and viscosity on a female human cadaver. The stiffness and viscosity were calculated based on the kinetic data. During the measurements, the periarticular and intraarticular soft tissue of the knee was gradually removed to determine the stiffness and viscosity as a function of the tissue removal rate. The measurements showed that the removal of tissue around the joint reduces the damping of leg oscillation, and therefore decreases the stiffness and viscosity. The contribution to knee joint damping was 10% for the skin, 20% for ligaments, and 40% for muscles and tendons. Tissue removal has a very large impact on the knee stiffness and viscosity.

  14. Elastin in large artery stiffness and hypertension

    PubMed Central

    Wagenseil, Jessica E.; Mecham, Robert P.

    2012-01-01

    Large artery stiffness, as measured by pulse wave velocity (PWV), is correlated with high blood pressure and may be a causative factor in essential hypertension. The extracellular matrix components, specifically the mix of elastin and collagen in the vessel wall, determine the passive mechanical properties of the large arteries. Elastin is organized into elastic fibers in the wall during arterial development in a complex process that requires spatial and temporal coordination of numerous proteins. The elastic fibers last the lifetime of the organism, but are subject to proteolytic degradation and chemical alterations that change their mechanical properties. This review discusses how alterations in the amount, assembly, organization or chemical properties of the elastic fibers affect arterial stiffness and blood pressure. Strategies for encouraging or reversing alterations to the elastic fibers are addressed. Methods for determining the efficacy of these strategies, by measuring elastin amounts and arterial stiffness, are summarized. Therapies that have a direct effect on arterial stiffness through alterations to the elastic fibers in the wall may be an effective treatment for essential hypertension. PMID:22290157

  15. Biomechanics of hair cell kinocilia: experimental measurement of kinocilium shaft stiffness and base rotational stiffness with Euler–Bernoulli and Timoshenko beam analysis

    PubMed Central

    Spoon, Corrie; Grant, Wally

    2011-01-01

    Vestibular hair cell bundles in the inner ear contain a single kinocilium composed of a 9+2 microtubule structure. Kinocilia play a crucial role in transmitting movement of the overlying mass, otoconial membrane or cupula to the mechanotransducing portion of the hair cell bundle. Little is known regarding the mechanical deformation properties of the kinocilium. Using a force-deflection technique, we measured two important mechanical properties of kinocilia in the utricle of a turtle, Trachemys (Pseudemys) scripta elegans. First, we measured the stiffness of kinocilia with different heights. These kinocilia were assumed to be homogenous cylindrical rods and were modeled as both isotropic Euler–Bernoulli beams and transversely isotropic Timoshenko beams. Two mechanical properties of the kinocilia were derived from the beam analysis: flexural rigidity (EI) and shear rigidity (kGA). The Timoshenko model produced a better fit to the experimental data, predicting EI=10,400 pN μm2 and kGA=247 pN. Assuming a homogenous rod, the shear modulus (G=1.9 kPa) was four orders of magnitude less than Young's modulus (E=14.1 MPa), indicating that significant shear deformation occurs within deflected kinocilia. When analyzed as an Euler–Bernoulli beam, which neglects translational shear, EI increased linearly with kinocilium height, giving underestimates of EI for shorter kinocilia. Second, we measured the rotational stiffness of the kinocilium insertion (κ) into the hair cell's apical surface. Following BAPTA treatment to break the kinocilial links, the kinocilia remained upright, and κ was measured as 177±47 pN μm rad–1. The mechanical parameters we quantified are important for understanding how forces arising from head movement are transduced and encoded by hair cells. PMID:21307074

  16. Ultra-high speed OCT allows measurement of intraocular pressure, corneal geometry, and corneal stiffness using a single instrument

    NASA Astrophysics Data System (ADS)

    Singh, Manmohan; Han, Zhaolong; Nair, Achuth; Schill, Alexander; Twa, Michael D.; Larin, Kirill V.

    2018-02-01

    Screening for ocular diseases, such as glaucoma and keratoconus, includes measuring the eye-globe intraocular pressure (IOP) and corneal biomechanical properties. However, currently available clinical tools cannot quantify corneal tissue material parameters, which can provide critical information for detecting diseases and evaluating therapeutic outcomes. Here, we demonstrate measurement of eye-globe IOP, corneal elasticity, and corneal geometry of in situ porcine corneas with a technique termed applanation optical coherence elastography (Appl-OCE) with single instrument. We utilize an ultrafast phase-sensitive optical coherence tomography system comprised of a 4X buffered Fourier domain mode-locked swept source laser with an Ascan rate of 1.5 MHz and a 7.3 kHz resonant scanner. The IOP was measured by imaging the response of in situ porcine corneas to a large force air-puff. As with other noncontact tonometers, the time when the cornea was applanated during the inwards and outwards motion was correlated to a measure air-pressure temporal profile. The IOP was also measured with a commercially available rebound tonometer for comparison. The stiffness of the corneas was assessed by directly imaging and analyzing the propagation of a focused micro air-pulse induced elastic wave, and the corneal geometry was obtained from the OCT structural image. Our results show that corneal thickness decreased as IOP increased, and that corneal stiffness increased with IOP. Moreover, the IOP measurements made by Appl-OCE were more closely correlated with the artificially set IOP than the rebound tonometer, demonstrating the capabilities of Appl-OCE to measure corneal stiffness, eye-globe IOP, and corneal geometry with a single instrument.

  17. Review of MRI-based measurements of pulse wave velocity: a biomarker of arterial stiffness

    PubMed Central

    Wentland, Andrew L.; Grist, Thomas M.

    2014-01-01

    Atherosclerosis is the leading cause of cardiovascular disease (CVD) in the Western world. In the early development of atherosclerosis, vessel walls remodel outwardly such that the vessel luminal diameter is minimally affected by early plaque development. Only in the late stages of the disease does the vessel lumen begin to narrow—leading to stenoses. As a result, angiographic techniques are not useful for diagnosing early atherosclerosis. Given the absence of stenoses in the early stages of atherosclerosis, CVD remains subclinical for decades. Thus, methods of diagnosing atherosclerosis early in the disease process are needed so that affected patients can receive the necessary interventions to prevent further disease progression. Pulse wave velocity (PWV) is a biomarker directly related to vessel stiffness that has the potential to provide information on early atherosclerotic disease burden. A number of clinical methods are available for evaluating global PWV, including applanation tonometry and ultrasound. However, these methods only provide a gross global measurement of PWV—from the carotid to femoral arteries—and may mitigate regional stiffness within the vasculature. Additionally, the distance measurements used in the PWV calculation with these methods can be highly inaccurate. Faster and more robust magnetic resonance imaging (MRI) sequences have facilitated increased interest in MRI-based PWV measurements. This review provides an overview of the state-of-the-art in MRI-based PWV measurements. In addition, both gold standard and clinical standard methods of computing PWV are discussed. PMID:24834415

  18. Life prediction for white OLED based on LSM under lognormal distribution

    NASA Astrophysics Data System (ADS)

    Zhang, Jianping; Liu, Fang; Liu, Yu; Wu, Helen; Zhu, Wenqing; Wu, Wenli; Wu, Liang

    2012-09-01

    In order to acquire the reliability information of White Organic Light Emitting Display (OLED), three groups of OLED constant stress accelerated life tests (CSALTs) were carried out to obtain failure data of samples. Lognormal distribution function was applied to describe OLED life distribution, and the accelerated life equation was determined by Least square method (LSM). The Kolmogorov-Smirnov test was performed to verify whether the white OLED life meets lognormal distribution or not. Author-developed software was employed to predict the average life and the median life. The numerical results indicate that the white OLED life submits to lognormal distribution, and that the accelerated life equation meets inverse power law completely. The estimated life information of the white OLED provides manufacturers and customers with important guidelines.

  19. Evidence that breast tissue stiffness is associated with risk of breast cancer.

    PubMed

    Boyd, Norman F; Li, Qing; Melnichouk, Olga; Huszti, Ella; Martin, Lisa J; Gunasekara, Anoma; Mawdsley, Gord; Yaffe, Martin J; Minkin, Salomon

    2014-01-01

    Evidence from animal models shows that tissue stiffness increases the invasion and progression of cancers, including mammary cancer. We here use measurements of the volume and the projected area of the compressed breast during mammography to derive estimates of breast tissue stiffness and examine the relationship of stiffness to risk of breast cancer. Mammograms were used to measure the volume and projected areas of total and radiologically dense breast tissue in the unaffected breasts of 362 women with newly diagnosed breast cancer (cases) and 656 women of the same age who did not have breast cancer (controls). Measures of breast tissue volume and the projected area of the compressed breast during mammography were used to calculate the deformation of the breast during compression and, with the recorded compression force, to estimate the stiffness of breast tissue. Stiffness was compared in cases and controls, and associations with breast cancer risk examined after adjustment for other risk factors. After adjustment for percent mammographic density by area measurements, and other risk factors, our estimate of breast tissue stiffness was significantly associated with breast cancer (odds ratio = 1.21, 95% confidence interval = 1.03, 1.43, p = 0.02) and improved breast cancer risk prediction in models with percent mammographic density, by both area and volume measurements. An estimate of breast tissue stiffness was associated with breast cancer risk and improved risk prediction based on mammographic measures and other risk factors. Stiffness may provide an additional mechanism by which breast tissue composition is associated with risk of breast cancer and merits examination using more direct methods of measurement.

  20. Evidence That Breast Tissue Stiffness Is Associated with Risk of Breast Cancer

    PubMed Central

    Boyd, Norman F.; Li, Qing; Melnichouk, Olga; Huszti, Ella; Martin, Lisa J.; Gunasekara, Anoma; Mawdsley, Gord; Yaffe, Martin J.; Minkin, Salomon

    2014-01-01

    Background Evidence from animal models shows that tissue stiffness increases the invasion and progression of cancers, including mammary cancer. We here use measurements of the volume and the projected area of the compressed breast during mammography to derive estimates of breast tissue stiffness and examine the relationship of stiffness to risk of breast cancer. Methods Mammograms were used to measure the volume and projected areas of total and radiologically dense breast tissue in the unaffected breasts of 362 women with newly diagnosed breast cancer (cases) and 656 women of the same age who did not have breast cancer (controls). Measures of breast tissue volume and the projected area of the compressed breast during mammography were used to calculate the deformation of the breast during compression and, with the recorded compression force, to estimate the stiffness of breast tissue. Stiffness was compared in cases and controls, and associations with breast cancer risk examined after adjustment for other risk factors. Results After adjustment for percent mammographic density by area measurements, and other risk factors, our estimate of breast tissue stiffness was significantly associated with breast cancer (odds ratio = 1.21, 95% confidence interval = 1.03, 1.43, p = 0.02) and improved breast cancer risk prediction in models with percent mammographic density, by both area and volume measurements. Conclusion An estimate of breast tissue stiffness was associated with breast cancer risk and improved risk prediction based on mammographic measures and other risk factors. Stiffness may provide an additional mechanism by which breast tissue composition is associated with risk of breast cancer and merits examination using more direct methods of measurement. PMID:25010427

  1. Numerical assessment of the stiffness index.

    PubMed

    Epstein, Sally; Vergnaud, Anne-Claire; Elliott, Paul; Chowienczyk, Phil; Alastruey, Jordi

    2014-01-01

    Elevated systemic vascular stiffness is associated with increased risk of cardiovascular disease. It has been suggested that the time difference between the two characteristic peaks of the digital volume pulse (DVP) measured at the finger using photoplethysmography is related to the stiffness of the arterial tree, and inversely proportional to the stiffness index (SI). However, the precise physical meaning of the SI and its relation to aortic pulse wave velocity (aPWV) is yet to be ascertained. In this study we investigated numerically the effect of changes in arterial wall stiffness, peripheral resistances, peripheral compliances or peripheral wave reflections on the SI and aPWV. The SI was calculated from the digital area waveform simulated using a nonlinear one-dimensional model of pulse wave propagation in a 75-artery network, which includes the larger arteries of the hand. Our results show that aPWV is affected by changes in aortic stiffness, but the SI is primarily affected by changes in the stiffness of all conduit vessels. Thus, the SI is not a direct substitute for aPWV. Moreover, our results suggest that peripheral reflections in the upper body delay the time of arrival of the first peak in the DVP. The second peak is predominantly caused by the impedance mismatch within the 75 arterial segments, rather than by peripheral reflections.

  2. Right Ventricular Myocardial Stiffness in Experimental Pulmonary Arterial Hypertension

    PubMed Central

    Rain, Silvia; Andersen, Stine; Najafi, Aref; Gammelgaard Schultz, Jacob; da Silva Gonçalves Bós, Denielli; Handoko, M. Louis; Bogaard, Harm-Jan; Vonk-Noordegraaf, Anton; Andersen, Asger; van der Velden, Jolanda; Ottenheijm, Coen A.C.

    2016-01-01

    Background— The purpose of this study was to determine the relative contribution of fibrosis-mediated and myofibril-mediated stiffness in rats with mild and severe right ventricular (RV) dysfunction. Methods and Results— By performing pulmonary artery banding of different diameters for 7 weeks, mild RV dysfunction (Ø=0.6 mm) and severe RV dysfunction (Ø=0.5 mm) were induced in rats. The relative contribution of fibrosis- and myofibril-mediated RV stiffness was determined in RV trabecular strips. Total myocardial stiffness was increased in trabeculae from both mild and severe RV dysfunction in comparison to controls. In severe RV dysfunction, increased RV myocardial stiffness was explained by both increased fibrosis-mediated stiffness and increased myofibril-mediated stiffness, whereas in mild RV dysfunction, only myofibril-mediated stiffness was increased in comparison to control. Histological analyses revealed that RV fibrosis gradually increased with severity of RV dysfunction, whereas the ratio of collagen I/III expression was only elevated in severe RV dysfunction. Stiffness measurements in single membrane-permeabilized RV cardiomyocytes demonstrated a gradual increase in RV myofibril stiffness, which was partially restored by protein kinase A in both mild and severe RV dysfunction. Increased expression of compliant titin isoforms was observed only in mild RV dysfunction, whereas titin phosphorylation was reduced in both mild and severe RV dysfunction. Conclusions— RV myocardial stiffness is increased in rats with mild and severe RV dysfunction. In mild RV dysfunction, stiffness is mainly determined by increased myofibril stiffness. In severe RV dysfunction, both myofibril- and fibrosis-mediated stiffness contribute to increased RV myocardial stiffness. PMID:27370069

  3. Subspace methods for identification of human ankle joint stiffness.

    PubMed

    Zhao, Y; Westwick, D T; Kearney, R E

    2011-11-01

    Joint stiffness, the dynamic relationship between the angular position of a joint and the torque acting about it, describes the dynamic, mechanical behavior of a joint during posture and movement. Joint stiffness arises from both intrinsic and reflex mechanisms, but the torques due to these mechanisms cannot be measured separately experimentally, since they appear and change together. Therefore, the direct estimation of the intrinsic and reflex stiffnesses is difficult. In this paper, we present a new, two-step procedure to estimate the intrinsic and reflex components of ankle stiffness. In the first step, a discrete-time, subspace-based method is used to estimate a state-space model for overall stiffness from the measured overall torque and then predict the intrinsic and reflex torques. In the second step, continuous-time models for the intrinsic and reflex stiffnesses are estimated from the predicted intrinsic and reflex torques. Simulations and experimental results demonstrate that the algorithm estimates the intrinsic and reflex stiffnesses accurately. The new subspace-based algorithm has three advantages over previous algorithms: 1) It does not require iteration, and therefore, will always converge to an optimal solution; 2) it provides better estimates for data with high noise or short sample lengths; and 3) it provides much more accurate results for data acquired under the closed-loop conditions, that prevail when subjects interact with compliant loads.

  4. Experimental measurements of hydrodynamic stiffness matrices for a centrifugal pump impeller

    NASA Technical Reports Server (NTRS)

    Chamieh, D. S.; Acosta, A. J.; Brennen, C. E.; Caughey, T. K.; Franz, R.

    1982-01-01

    The objective of the Rotor Force Test Facility at the California Institute of Technology is to artificially orbit the center of rotation of an impeller enclosed within a volute over a range of frequencies from zero to synchronous and to measure the resulting forces on the impeller. Preliminary data from the first stage experiments in which the shaft is orbited at low frequency is reported. Steady volute forces along with stiffness matrices due to the change in position of the rotor center are measured. Static pressure taps around the volute are used to obtain volute pressure distributions for various fixed positions of the impeller center and for various flow rates. Static pressure forces are calculated from these pressure distributions allowing a more complete analysis of the components of the impeller forces. Comparison is made with various existing theoretical and experimental results.

  5. Multi-fingered haptic palpation utilizing granular jamming stiffness feedback actuators

    NASA Astrophysics Data System (ADS)

    Li, Min; Ranzani, Tommaso; Sareh, Sina; Seneviratne, Lakmal D.; Dasgupta, Prokar; Wurdemann, Helge A.; Althoefer, Kaspar

    2014-09-01

    This paper describes a multi-fingered haptic palpation method using stiffness feedback actuators for simulating tissue palpation procedures in traditional and in robot-assisted minimally invasive surgery. Soft tissue stiffness is simulated by changing the stiffness property of the actuator during palpation. For the first time, granular jamming and pneumatic air actuation are combined to realize stiffness modulation. The stiffness feedback actuator is validated by stiffness measurements in indentation tests and through stiffness discrimination based on a user study. According to the indentation test results, the introduction of a pneumatic chamber to granular jamming can amplify the stiffness variation range and reduce hysteresis of the actuator. The advantage of multi-fingered palpation using the proposed actuators is proven by the comparison of the results of the stiffness discrimination performance using two-fingered (sensitivity: 82.2%, specificity: 88.9%, positive predicative value: 80.0%, accuracy: 85.4%, time: 4.84 s) and single-fingered (sensitivity: 76.4%, specificity: 85.7%, positive predicative value: 75.3%, accuracy: 81.8%, time: 7.48 s) stiffness feedback.

  6. Cell Sheet Stiffness Sensing without taking out from culture liquid.

    PubMed

    Uchida, Ryohei; Tanaka, Nobuyuki; Higashimori, Mitsuru; Tadakuma, Kenjiro; Kaneko, Makoto; Kondo, Makoto; Yamato, Masayuki

    2010-01-01

    Stiffness could be an important index for evaluating the vitality of cell sheet. This paper challenges the measurement of stiffness of transparent cell sheet in culture liquid without taking it out from petri dish. The system is composed of a micro air nozzle for supplying an air jet and a regular reflective type laser sensor for measuring the the deformation of transparent cell sheet. This system is called as Cell Sheet Stiffness Sensing system (CS(3) system). When an air jet is given to a cell sheet in culture liquid, it pushes away the liquid toward the outer direction at initial phase and reaches the surface of cell sheet. Without any switching motion, the air jet continuously imparts a force to the surface of cell sheet so that the sensor can measure the stiffness of the cell sheet.

  7. Experimental and theoretical rotordynamic stiffness coefficients for a three-stage brush seal

    NASA Astrophysics Data System (ADS)

    Pugachev, A. O.; Deckner, M.

    2012-08-01

    Experimental and theoretical results are presented for a multistage brush seal. Experimental stiffness is obtained from integrating circumferential pressure distribution measured in seal cavities. A CFD analysis is used to predict seal performance. Bristle packs are modeled by the porous medium approach. Leakage is predicted well by the CFD method. Theoretical stiffness coefficients are in reasonable agreement with the measurements. Experimental results are also compared with a three-teeth-on-stator labyrinth seal. The multistage brush seal gives about 60% leakage reduction over the labyrinth seal. Rotordynamic stiffness coefficients are also improved: the brush seal has positive direct stiffness and smaller cross-coupled stiffness.

  8. Evaluation of transient elastography in assessing liver fibrosis in patients with autoimmune hepatitis.

    PubMed

    Xu, Qinyu; Sheng, Li; Bao, Han; Chen, Xiaoyu; Guo, Canjie; Li, Hai; Ma, Xiong; Qiu, Dekai; Hua, Jing

    2017-03-01

    Transient elastography (TE) can reliably stage liver fibrosis via liver stiffness measurement (LSM) in chronic liver disease. However, the accuracy of TE for assessment of liver fibrosis in patients with autoimmune hepatitis (AIH) is still limited. We evaluate TE in staging liver fibrosis in AIH patients and compare with other noninvasive diagnostic tools. A total of 100 patients with biopsy-proven AIH were included. The correlation between LSM and fibrosis stage was analyzed using Spearman correlation test. The optimal cut-off values of LSM were calculated for predicting individual fibrosis stages using receiver-operating characteristic curve. The diagnostic accuracy of LSM for severe fibrosis was compared with those of serum biochemical scores. Median LSM in AIH patients was higher than that of healthy controls (11.2 ± 8.2 kPa vs 4.3 ± 1.4 kPa, P < 0.01). LSM had significant correlation with fibrosis (r = 0.752, P < 0.01) and increased progressively with increasing fibrosis stages in AIH patients. AUROC values of LSM for stages F ≥ 2, F ≥ 3, and F4 were 0.878 (95%CI: 0.789-0.967), 0.883 (0.820-0.946), and 0.914 (0.852-0.976), respectively. The optimal cut-off values of LSM for fibrosis stages F ≥ 2, F ≥ 3, and F4 were 6.45, 8.75, and 12.50 kPa, respectively. LSM was superior to APRI score and FIB-4 score in detecting severe fibrosis (F ≥ 3). Serum ALT levels had minor effect on LSM values. Transient elastography is an accurate and reliable noninvasive tool in assessing liver fibrosis in AIH. Hepatic inflammatory activity had no significant effect on LSM determination. © 2016 Journal of Gastroenterology and Hepatology Foundation and John Wiley & Sons Australia, Ltd.

  9. A photosynthesis-based two-leaf canopy stomatal conductance model for meteorology and air quality modeling with WRF/CMAQ PX LSM

    EPA Science Inventory

    A coupled photosynthesis-stomatal conductance model with single-layer sunlit and shaded leaf canopy scaling is implemented and evaluated in a diagnostic box model with the Pleim-Xiu land surface model (PX LSM) and ozone deposition model components taken directly from the meteorol...

  10. Sway‐dependent changes in standing ankle stiffness caused by muscle thixotropy

    PubMed Central

    Sakanaka, Tania E.; Lakie, Martin

    2016-01-01

    Key points The passive stiffness of the calf muscles contributes to standing balance, although the properties of muscle tissue are highly labile.We investigated the effect of sway history upon intrinsic ankle stiffness and demonstrated reductions in stiffness of up to 43% during conditions of increased baseline sway.This sway dependence was most apparent when using low amplitude stiffness‐measuring perturbations, and the short‐range stiffness component was smaller during periods of high sway.These characteristics are consistent with the thixotropic properties of the calf muscles causing the observed changes in ankle stiffness.Periods of increased sway impair the passive stabilization of standing, demanding more active neural control of balance. Abstract Quiet standing is achieved through a combination of active and passive mechanisms, consisting of neural control and intrinsic mechanical stiffness of the ankle joint, respectively. The mechanical stiffness is partly determined by the calf muscles. However, the viscoelastic properties of muscle are highly labile, exhibiting a strong dependence on movement history. By measuring the effect of sway history upon ankle stiffness, the present study determines whether this lability has consequences for the passive stabilization of human standing. Ten subjects stood quietly on a rotating platform whose axis was collinear with the ankle joint. Ankle sway was increased by slowly tilting this platform in a random fashion, or decreased by fixing the body to a board. Ankle stiffness was measured by using the same platform to simultaneously apply small, brief perturbations (<0.6 deg; 140 ms) at the same time as the resulting torque response was recorded. The results show that increasing sway reduces ankle stiffness by up to 43% compared to the body‐fixed condition. Normal quiet stance was associated with intermediate values. The effect was most apparent when using smaller perturbation amplitudes to measure stiffness (0

  11. Inflammation and Arterial Stiffness in Chronic Kidney Disease: Findings From the CRIC Study.

    PubMed

    Peyster, Eliot; Chen, Jing; Feldman, Harold I; Go, Alan S; Gupta, Jayanta; Mitra, Nandita; Pan, Qiang; Porter, Anna; Rahman, Mahboob; Raj, Dominic; Reilly, Muredach; Wing, Maria R; Yang, Wei; Townsend, Raymond R

    2017-04-01

    Chronic kidney disease (CKD) and arterial stiffness are associated with increased cardiovascular morbidity and mortality. Inflammation is proposed to have a role in the development of arterial stiffness, and CKD is recognized as a proinflammatory state. Arterial stiffness is increased in CKD, and cross-sectional data has suggested a link between increased inflammatory markers in CKD and higher measures of arterial stiffness. However, no large scale investigations have examined the impact of inflammation on the progression of arterial stiffness in CKD. We performed baseline assessments of 5 inflammatory markers in 3,939 participants from the chronic renal insufficiency cohort (CRIC), along with serial measurements of arterial stiffness at 0, 2, and 4 years of follow-up. A total of 2,933 participants completed each of the follow-up stiffness measures. In cross-sectional analysis at enrollment, significant associations with at least 2 measures of stiffness were observed for fibrinogen, interleukin-6, high-sensitivity C-reactive protein, proteinuria, and composite inflammation score after adjustment for confounders. In longitudinal analyses, there were few meaningful correlations between baseline levels of inflammation and changes in metrics of arterial stiffness over time. In a large cohort of CKD participants, we observed multiple significant correlations between initial markers of inflammation and metrics of arterial stiffness, but baseline inflammation did not predict changes in arterial stiffness over time. While well-described biologic mechanisms provide the basis for our understanding of the cross-sectional results, continued efforts to design longitudinal studies are necessary to fully elucidate the relationship between chronic inflammation and arterial stiffening. © American Journal of Hypertension, Ltd 2017. All rights reserved. For Permissions, please email: journals.permissions@oup.com

  12. Quantification of Regional Aortic Stiffness Using MR Elastography: A Phantom and Ex-vivo Porcine Aorta Study

    PubMed Central

    Zhang, Nan; Chen, Jun; Yin, Meng; Glaser, Kevin J.; Xu, Lei; Ehman, Richard L.

    2015-01-01

    MR Elastography (MRE) is a noninvasive technique for measuring tissue stiffness that has been used to assess the average stiffness of the abdominal aorta. The utility of aortic MRE would be improved if it could provide information about local variations in aortic stiffness. We hypothesize that regional variations in aortic stiffness can also be measured with MRE and the purpose of this work was to demonstrate that MRE can measure regional stiffness variations in a vascular phantom and in ex vivo porcine aortas. A vascular phantom was fabricated, containing two silicone tubes embedded in gel. A segment of one of the tubes was modified to increase its stiffness. MRE was performed on the phantom with a continuous flow of water through the tubes. The stiffness distribution along the modified tube was measured and compared to the reference tube. MRE was also performed in porcine aortas embedded in gel with segments treated with saline or formalin for 4 days. The stiffness difference between saline- and formalin-treated aortic segments was measured by MRE and mechanical tests. A positive correlation was found between the regional stiffnesses measured by MRE and mechanical tests. The results indicate that MRE can be used to evaluate the local stiffness distribution in silicone tubes and ex vivo porcine aortas. It may therefore be possible to apply MRE to measure regional stiffness variations of the aorta in vivo. PMID:26597836

  13. Free vibration analysis of a cracked shear deformable beam on a two-parameter elastic foundation using a lattice spring model

    NASA Astrophysics Data System (ADS)

    Attar, M.; Karrech, A.; Regenauer-Lieb, K.

    2014-05-01

    The free vibration of a shear deformable beam with multiple open edge cracks is studied using a lattice spring model (LSM). The beam is supported by a so-called two-parameter elastic foundation, where normal and shear foundation stiffnesses are considered. Through application of Timoshenko beam theory, the effects of transverse shear deformation and rotary inertia are taken into account. In the LSM, the beam is discretised into a one-dimensional assembly of segments interacting via rotational and shear springs. These springs represent the flexural and shear stiffnesses of the beam. The supporting action of the elastic foundation is described also by means of normal and shear springs acting on the centres of the segments. The relationship between stiffnesses of the springs and the elastic properties of the one-dimensional structure are identified by comparing the homogenised equations of motion of the discrete system and Timoshenko beam theory.

  14. Force measurements in stiff, 3D, opaque granular materials

    NASA Astrophysics Data System (ADS)

    Hurley, Ryan C.; Hall, Stephen A.; Andrade, José E.; Wright, Jonathan

    2017-06-01

    We present results from two experiments that provide the first quantification of inter-particle force networks in stiff, 3D, opaque granular materials. Force vectors between all grains were determined using a mathematical optimization technique that seeks to satisfy grain equilibrium and strain measurements. Quantities needed in the optimization - the spatial location of the inter-particle contact network and tensor grain strains - were found using 3D X-ray diffraction and X-ray computed tomography. The statistics of the force networks are consistent with those found in past simulations and 2D experiments. In particular, we observe an exponential decay of normal forces above the mean and a partition of forces into strong and weak networks. In the first experiment, involving 77 single-crystal quartz grains, we also report on the temporal correlation of the force network across two sequential load cycles. In the second experiment, involving 1099 single-crystal ruby grains, we characterize force network statistics at low levels of compression.

  15. Dynamically variable negative stiffness structures.

    PubMed

    Churchill, Christopher B; Shahan, David W; Smith, Sloan P; Keefe, Andrew C; McKnight, Geoffrey P

    2016-02-01

    Variable stiffness structures that enable a wide range of efficient load-bearing and dexterous activity are ubiquitous in mammalian musculoskeletal systems but are rare in engineered systems because of their complexity, power, and cost. We present a new negative stiffness-based load-bearing structure with dynamically tunable stiffness. Negative stiffness, traditionally used to achieve novel response from passive structures, is a powerful tool to achieve dynamic stiffness changes when configured with an active component. Using relatively simple hardware and low-power, low-frequency actuation, we show an assembly capable of fast (<10 ms) and useful (>100×) dynamic stiffness control. This approach mitigates limitations of conventional tunable stiffness structures that exhibit either small (<30%) stiffness change, high friction, poor load/torque transmission at low stiffness, or high power active control at the frequencies of interest. We experimentally demonstrate actively tunable vibration isolation and stiffness tuning independent of supported loads, enhancing applications such as humanoid robotic limbs and lightweight adaptive vibration isolators.

  16. A novel stiffness control method for series elastic actuator

    NASA Astrophysics Data System (ADS)

    Lin, Guangmo; Zhao, Xingang; Han, Jianda

    2017-01-01

    Compliance plays an important role in human-robot cooperation. However, fixed compliance, or fixed stiffness, is difficult to meet the growing needs of human machine collaboration. As a result, the robot actuator is demanded to be able to adjust its stiffness. This paper presents a stiffness control scheme for a single DOF series elastic actuator (SEA) with a linear spring mounted in series in the mechanism. In this proposed method, the output angle of the spring is measured and used to calculate the input angle of the spring, thus the equivalent stiffness of the robot actuator revealed to the human operator can be rendered in accordance to the desired stiffness. Since the techniques used in this method only involve the position information of the system, there is no need to install an expensive force/torque sensor on the actuator. Further, the force/torque produced by the actuator can be estimated by simply multiplying the deformation angle of the spring and its constant stiffness coefficient. The analysis of the stiffness controller is provided. Then a simulation that emulates a human operates the SEA while the stiffness controller is running is carried out and the results also validate the proposed method.

  17. Influence of Passive Stiffness of Hamstrings on Postural Stability

    PubMed Central

    Kuszewski, Michał; Gnat, Rafał; Sobota, Grzegorz; Myśliwiec, Andrzej

    2015-01-01

    The aim of the study was to explore whether passive stiffness of the hamstrings influences the strategy of maintaining postural stability. A sample of 50 subjects was selected; the final analyses were based on data of 41 individuals (33 men, 8 women) aged 21 to 29 (mean = 23.3, SD = 1.1) years. A quasi- experimental ex post facto design with repeated measures was used. Categories of independent variables were obtained directly prior to the measurement of the dependent variables. In stage one of the study, passive knee extension was measured in the supine position to assess hamstring stiffness. In stage two, the magnitude of postural sway in antero-posterior direction was measured, while varying the body position on a stabilometric platform, both with and without visual control. The margin of safety was used as a measure of postural control. The magnitude of the margin of safety increased significantly between the open-eye and closed-eye trials. However, although we registered a visible tendency for a larger increase of the margin of safety associated with lower levels of passive hamstrings stiffness, no significant differences were found. Therefore, this study demonstrated that hamstring stiffness did not influence the strategy used to maintain postural stability. PMID:25964809

  18. Influence of passive stiffness of hamstrings on postural stability.

    PubMed

    Kuszewski, Michał; Gnat, Rafał; Sobota, Grzegorz; Myśliwiec, Andrzej

    2015-03-29

    The aim of the study was to explore whether passive stiffness of the hamstrings influences the strategy of maintaining postural stability. A sample of 50 subjects was selected; the final analyses were based on data of 41 individuals (33 men, 8 women) aged 21 to 29 (mean = 23.3, SD = 1.1) years. A quasi- experimental ex post facto design with repeated measures was used. Categories of independent variables were obtained directly prior to the measurement of the dependent variables. In stage one of the study, passive knee extension was measured in the supine position to assess hamstring stiffness. In stage two, the magnitude of postural sway in antero-posterior direction was measured, while varying the body position on a stabilometric platform, both with and without visual control. The margin of safety was used as a measure of postural control. The magnitude of the margin of safety increased significantly between the open-eye and closed-eye trials. However, although we registered a visible tendency for a larger increase of the margin of safety associated with lower levels of passive hamstrings stiffness, no significant differences were found. Therefore, this study demonstrated that hamstring stiffness did not influence the strategy used to maintain postural stability.

  19. A review of models of vertical, leg, and knee stiffness in adults for running, jumping or hopping tasks.

    PubMed

    Serpell, Benjamin G; Ball, Nick B; Scarvell, Jennie M; Smith, Paul N

    2012-01-01

    The 'stiffness' concept originates from Hooke's law which states that the force required to deform an object is related to a spring constant and the distance that object is deformed. Research into stiffness in the human body is undergoing unprecedented popularity; possibly because stiffness has been associated with sporting performance and some lower limb injuries. However, some inconsistencies surrounding stiffness measurement exists bringing into question the integrity of some research related to stiffness. The aim of this study was to review literature which describes how vertical, leg and knee stiffness has been measured in adult populations while running, jumping or hopping. A search of the entire MEDLINE, PubMed and SPORTDiscus databases and an iterative reference check was performed. Sixty-seven articles were retrieved; 21 measured vertical stiffness, 51 measured leg stiffness, and 22 measured knee stiffness. Thus, some studies measured several 'types' of stiffness. Vertical stiffness was typically the quotient of ground reaction force and centre of mass displacement. For leg stiffness it was and change in leg length, and for the knee it was the quotient of knee joint moments and change in joint angle. Sample size issues and measurement techniques were identified as limitations to current research.

  20. Investigation of the torsional stiffness of flexible disc coupling

    NASA Astrophysics Data System (ADS)

    Buryy, A.; Simonovsky, V.; Obolonik, V.

    2017-08-01

    Calculation of flexible coupling torsional stiffness is required when analyzing the torsional vibrations of the reciprocating machinery train. While having the lowest torsional stiffness of all the elements of the train, flexible coupling has a significant influence on the natural frequencies of torsional vibration. However, considering structural complexity of coupling, precise definition of its torsional stiffness is quite a difficult task. The paper presents a method for calculating the torsional stiffness of flexible disc coupling based on the study of its finite element model response under the action of torque. The analysis of the basic parameters that quantitatively and qualitatively affect the coupling torsional stiffness has been also provided. The results of the calculation as well as model adequacy, sufficient for practical application, have been confirmed at the experimental measurement of flexible disc coupling torsional stiffness. The obtained elastic characteristics (dependences of applied torque and torsional stiffness versus twist angle) are nonlinear in the initial stage of loading. This feature should be taken into account when creating reliable mathematical models of torsional vibrations of reciprocating machinery trains containing flexible disc couplings.

  1. Relationship between increased carotid artery stiffness and idiopathic subjective tinnitus.

    PubMed

    Bayraktar, C; Taşolar, S

    2017-05-01

    Tinnitus is defined as perception of sound with no external stimulus, and can separate into pulsatile and non-pulsatile types. Arterial stiffness is a parameter that can predict the cardiovascular event and associated with incidence of stroke. It has been shown that increased arterial stiffness may lead to microvascular damage in brain. Our aim was to assess the arterial stiffness of the carotid system in the development and severity of idiopathic subjective tinnitus. Forty subjective tinnitus patients and 40 age- and sex-matched controls were enrolled in the study. The parameters obtained from the participants included pure tone hearing (dB), serum lipid profile (mg/dl), fasting glucose (mg/dl), blood pressure (mmHg), and body mass index (BMI, kg/m 2 ). The common carotid artery (CCA) stiffness index, Young's elastic modulus (YEM), common carotid intima-media thickness (CIMT), peak systolic velocity (PSV), end-diastolic velocity (EDV), resistive index (RI), pulsatility index (PI), vessel diameter, mean velocity (MV), and volume flow (VF) were measured in both the right and left common carotid arteries in both groups. The CCA stiffness index, YEM measurements, right CIMT, and left PI were found to be significantly higher in the patients than those in the control group (p < 0.05). With regard to the severity of the tinnitus and the patient characteristics, there was a significant positive correlation with the CCA stiffness index, YEM measurements, left CIMT, and neutrophil-to-lymphocyte ratio (NLR). However, only the right and left CCA stiffness parameters were found to be statistically significant in the multivariate analysis as independent predictors of a moderate to high degree of tinnitus. The increased stiffness index of the common carotid arteries was significantly associated with the formation and severity of tinnitus. Therefore, an assessment of the carotideal system may be helpful in these patients.

  2. Subclinical hypothyroidism and diabetes as risk factors for postoperative stiff shoulder.

    PubMed

    Blonna, Davide; Fissore, Francesca; Bellato, Enrico; La Malfa, Marco; Calò, Michel; Bonasia, Davide Edoardo; Rossi, Roberto; Castoldi, Filippo

    2017-07-01

    Postoperative stiffness can be a disabling condition after arthroscopic shoulder surgery. The purpose of this study was to analyse the potential contribution of subclinical forms of hypothyroidism and diabetes in the development of postoperative shoulder stiffness. A prospective study was conducted on 65 consecutive patients scheduled for arthroscopic subacromial decompression or rotator cuff tear repair. Patients with preoperative stiffness were excluded. Preoperative measurements of free thyroxine, free triiodothyronine, thyroid-stimulating hormone and fasting glycaemia were taken in all patients to detect subclinical forms of diabetes and hypothyroidism. A follow-up was planned at 30, 60, 90 and 180 days after surgery. According to range of motion measurements, postoperative stiffness was classified as severe or moderate at follow-up. Univariate and logistic regression analyses were performed for the assessment of risk factors for stiffness. The overall incidence of postoperative stiffness was 29 % (19/65) in our cohort. Considering only the arthroscopic rotator cuff repairs, this incidence was 23 % (7/31). A new diagnosis of subclinical forms of diabetes or hypothyroidism was made in five cases. All five of these cases developed postoperative stiffness. The logistic regression analysis demonstrated that hypothyroidism was a risk factor for severe stiffness (RR = 25; p = 0.001) and that diabetes was a risk factor for moderate stiffness (RR = 5.7; p = 0.03). The postoperative stiffness in the majority of patients can be predicted by a careful analysis of past medical history and by detecting subclinical forms of hypothyroidism and diabetes. Prognostic study, Level II.

  3. Martial arts training attenuates arterial stiffness in middle aged adults.

    PubMed

    Douris, Peter C; Ingenito, Teresa; Piccirillo, Barbara; Herbst, Meredith; Petrizzo, John; Cherian, Vincen; McCutchan, Christopher; Burke, Caitlin; Stamatinos, George; Jung, Min-Kyung

    2013-09-01

    Arterial stiffness increases with age and is related to an increased risk of coronary artery disease. Poor trunk flexibility has been shown to be associated with arterial stiffness in middle-aged subjects. The purpose of our research study was to measure arterial stiffness and flexibility in healthy middle-aged martial artists compared to age and gender matched healthy sedentary controls. Ten martial artists (54.0 ± 2.0 years), who practice Soo Bahk Do (SBD), a Korean martial art, and ten sedentary subjects (54.7 ± 1.8 years) for a total of twenty subjects took part in this cross-sectional study. Arterial stiffness was assessed in all subjects using pulse wave velocity (PWV), a recognized index of arterial stiffness. Flexibility of the trunk and hamstring were also measured. The independent variables were the martial artists and matched sedentary controls. The dependent variables were PWV and flexibility. There were significant differences, between the SBD practitioners and sedentary controls, in PWV (P = 0.004), in trunk flexibility (P= 0.002), and in hamstring length (P= 0.003). The middle-aged martial artists were more flexible in their trunk and hamstrings and had less arterial stiffness compared to the healthy sedentary controls. The flexibility component of martial art training or flexibility exercises in general may be considered as a possible intervention to reduce the effects of aging on arterial stiffness.

  4. Dynamically variable negative stiffness structures

    PubMed Central

    Churchill, Christopher B.; Shahan, David W.; Smith, Sloan P.; Keefe, Andrew C.; McKnight, Geoffrey P.

    2016-01-01

    Variable stiffness structures that enable a wide range of efficient load-bearing and dexterous activity are ubiquitous in mammalian musculoskeletal systems but are rare in engineered systems because of their complexity, power, and cost. We present a new negative stiffness–based load-bearing structure with dynamically tunable stiffness. Negative stiffness, traditionally used to achieve novel response from passive structures, is a powerful tool to achieve dynamic stiffness changes when configured with an active component. Using relatively simple hardware and low-power, low-frequency actuation, we show an assembly capable of fast (<10 ms) and useful (>100×) dynamic stiffness control. This approach mitigates limitations of conventional tunable stiffness structures that exhibit either small (<30%) stiffness change, high friction, poor load/torque transmission at low stiffness, or high power active control at the frequencies of interest. We experimentally demonstrate actively tunable vibration isolation and stiffness tuning independent of supported loads, enhancing applications such as humanoid robotic limbs and lightweight adaptive vibration isolators. PMID:26989771

  5. The comfort and safety of a novel rolling mechanical indentation device for the measurement of lumbar trunk stiffness in young adults.

    PubMed

    Brown, Benjamin T; Blacke, Alexandra; Carroll, Vanessa; Graham, Petra L; Kawchuk, Greg; Downie, Aron; Swain, Michael

    2017-01-01

    The measurement of Posterior-Anterior (P-A) spinal stiffness is a common component of the physical examination of patients presenting with spinal disorders. The aim of this assessment is to provoke pain and/or to determine the degree of resistance or compliance of these structures and the associated soft-tissues to loading. This information, combined with other patient-specific history and examination findings, is integrated into the clinical reasoning process and is used to guide treatment decisions. Unfortunately, there are inter-rater reliability and standardisation issues associated with the manual performance of this type of assessment. In an attempt to remedy these issues researchers have developed mechanical devices for the measurement of spinal stiffness. The aim of this research is to investigate the comfort and safety of a novel device for measuring P-A trunk stiffness in a sample of young adults. A sample of young adults from a general population was recruited in May 2016 from Sydney, Australia. Demographic, anthropometric and clinical variables were collected prior to participants undergoing a lumbar P-A trunk stiffness assessment involving a mechanical indentation device called the VerteTrack. The primary outcomes for the study were key feasibility items; overall assessment time, perceived comfort measured both during and after the procedure, and adverse events. Univariate ordinal logistic regression was used to identify key variables associated with a participant's subjective report of comfort both during and after the VerteTrack assessment. Eighty four participants (35% female) with a median age of 23 years (IQR = 3) took part in the research. The mean assessment time for the Vertetrack assessment was 11.6 min (SD = 2.1). Increasing load ( p  < 0.001) and increasing number of days with lower back pain ( p  = 0.009) were associated with decreased comfort ratings during the procedure. The vast majority 63/84 (75%) of participants rated the

  6. Effect of long-term isometric training on core/torso stiffness.

    PubMed

    Lee, Benjamin C Y; McGill, Stuart M

    2015-06-01

    Although core stiffness enhances athletic performance traits, controversy exists regarding the effectiveness of isometric vs. dynamic core training methods. This study aimed to determine whether long-term changes in stiffness can be trained, and if so, what is the most effective method. Twenty-four healthy male subjects (23 ± 3 years; 1.8 ± 0.06 m; 77.5 ± 10.8 kg) were recruited for passive and active stiffness measurements before and after a 6-week core training intervention. Twelve subjects (22 ± 2 years; 1.8 ± 0.08 m; 78.3 ± 12.3 kg) were considered naive to physical and core exercise. The other 12 subjects (24 ± 3 years; 1.8 ± 0.05 m; 76.8 ± 9.7 kg) were Muay Thai athletes (savvy). A repeated-measures design compared core training methods (isometric vs. dynamic, with a control group) and subject training experience (naive vs. savvy) before and after a 6-week training period. Passive stiffness was assessed on a "frictionless" bending apparatus and active stiffness assessed through a quick release mechanism. Passive stiffness increased after the isometric training protocol. Dynamic training produced a smaller effect, and as expected, there was no change in the control group. Active stiffness did not change in any group. Comparisons between subject and training groups did not reveal any interactions. Thus, an isometric training approach was superior in terms of enhancing core stiffness. This is important since increased core stiffness enhances load bearing ability, arrests painful vertebral micromovements, and enhances ballistic distal limb movement. This may explain the efficacy reported for back and knee injury reduction.

  7. Optimizing phase to enhance optical trap stiffness.

    PubMed

    Taylor, Michael A

    2017-04-03

    Phase optimization offers promising capabilities in optical tweezers, allowing huge increases in the applied forces, trap stiff-ness, or measurement sensitivity. One key obstacle to potential applications is the lack of an efficient algorithm to compute an optimized phase profile, with enhanced trapping experiments relying on slow programs that would take up to a week to converge. Here we introduce an algorithm that reduces the wait from days to minutes. We characterize the achievable in-crease in trap stiffness and its dependence on particle size, refractive index, and optical polarization. We further show that phase-only control can achieve almost all of the enhancement possible with full wavefront shaping; for instance phase control allows 62 times higher trap stiffness for 10 μm silica spheres in water, while amplitude control and non-trivial polarization further increase this by 1.26 and 1.01 respectively. This algorithm will facilitate future applications in optical trapping, and more generally in wavefront optimization.

  8. Hydration status influences the measurement of arterial stiffness.

    PubMed

    Caldwell, Aaron R; Tucker, Matthew A; Burchfield, Jenna; Moyen, Nicole E; Satterfield, Alf Z; Six, Ashley; McDermott, Brendon P; Mulvenon, Sean W; Ganio, Matthew S

    2018-05-01

    Consensus guidelines have attempted to standardize the measurement and interpretation of pulse wave velocity (PWV); however, guidelines have not addressed whether hydration status affects PWV. Moreover, multiple studies have utilized heat stress to reduce arterial stiffness which may lead to dehydration. This study utilized two experiments to investigate the effects of dehydration on PWV at rest and during passive heat stress. In experiment 1, subjects (n = 19) completed two trials, one in which they arrived euhydrated and one dehydrated (1·2[1·0]% body mass loss). In experiment 2, subjects (n = 11) began two trials euhydrated and in one trial did not receive water during heat stress, thus becoming dehydrated (1·6[0·6]% body mass loss); the other trial subjects remained euhydrated. Using Doppler ultrasound, carotid-to-femoral (central) and carotid-to-radial (peripheral) PWVs were measured. PWV was obtained at a normothermic baseline, and at a 0·5°C and 1°C elevation in rectal temperature (via passive heating). In experiment 1, baseline central PWV was significantly higher when euhydrated compared to dehydrated (628[95] versus 572[91] cm s -1 , respectively; P<0·05), but peripheral PWV was unaffected (861[117] versus 825[149] cm s -1 ; P>0·05). However, starting euhydrated and becoming dehydrated during heating in experiment 2 did not affect PWV measures (P>0·05), and independent of hydration status peripheral PWV was reduced when rectal temperature was elevated 0·5°C (-74[45] cm s -1 ; P<0·05) and 1·0°C (-70[48] cm s -1 ; P<0·05). Overall, these data suggest that hydration status affects measurements of central PWV in normothermic, resting conditions. Therefore, future guidelines should suggest that investigators ensure adequate hydration status prior to measures of PWV. © 2017 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.

  9. Martial Arts Training Attenuates Arterial Stiffness in Middle Aged Adults

    PubMed Central

    Douris, Peter C.; Ingenito, Teresa; Piccirillo, Barbara; Herbst, Meredith; Petrizzo, John; Cherian, Vincen; McCutchan, Christopher; Burke, Caitlin; Stamatinos, George; Jung, Min-Kyung

    2013-01-01

    Purpose Arterial stiffness increases with age and is related to an increased risk of coronary artery disease. Poor trunk flexibility has been shown to be associated with arterial stiffness in middle-aged subjects. The purpose of our research study was to measure arterial stiffness and flexibility in healthy middle-aged martial artists compared to age and gender matched healthy sedentary controls. Methods Ten martial artists (54.0 ± 2.0 years), who practice Soo Bahk Do (SBD), a Korean martial art, and ten sedentary subjects (54.7 ± 1.8 years) for a total of twenty subjects took part in this cross-sectional study. Arterial stiffness was assessed in all subjects using pulse wave velocity (PWV), a recognized index of arterial stiffness. Flexibility of the trunk and hamstring were also measured. The independent variables were the martial artists and matched sedentary controls. The dependent variables were PWV and flexibility. Results There were significant differences, between the SBD practitioners and sedentary controls, in PWV (P = 0.004), in trunk flexibility (P= 0.002), and in hamstring length (P= 0.003). Conclusion The middle-aged martial artists were more flexible in their trunk and hamstrings and had less arterial stiffness compared to the healthy sedentary controls. The flexibility component of martial art training or flexibility exercises in general may be considered as a possible intervention to reduce the effects of aging on arterial stiffness. PMID:24427479

  10. Investigation of In Vivo skin stiffness anisotropy in breast cancer related lymphoedema.

    PubMed

    Coutts, L V; Miller, N R; Mortimer, P S; Bamber, J C

    2016-01-04

    There is a limited range of suitable measurement techniques for detecting and assessing breast cancer related lymphoedema (BCRL). This study investigated the suitability of using skin stiffness measurements, with a particular focus on the variation in stiffness with measurement direction (known as anisotropy). In addition to comparing affected tissue with the unaffected tissue on the corresponding site on the opposite limb, volunteers without BCRL were tested to establish the normal variability in stiffness anisotropy between these two corresponding regions of skin on each opposite limb. Multi-directional stiffness was measured with an Extensometer, within the higher stiffness region that skin typically displays at high applied strains, using a previously established protocol developed by the authors. Healthy volunteers showed no significant difference in anisotropy between regions of skin on opposite limbs (mean decrease of 4.7 +/-2.5% between non-dominant and dominant arms), whereas BCRL sufferers showed a significant difference between limbs (mean decrease of 51.0+/-16.3% between unaffected and affected arms). A large difference in anisotropy was apparent even for those with recent onset of the condition, indicating that the technique may have potential to be useful for early detection. This difference also appeared to increase with duration since onset. Therefore, measurement of stiffness anisotropy has potential value for the clinical assessment and diagnosis of skin conditions such as BCRL. The promising results justify a larger study with a larger number of participants. Copyright © 2015 Elsevier Ltd. All rights reserved.

  11. Ambulatory (24 h) blood pressure and arterial stiffness measurement in Marfan syndrome patients: a case control feasibility and pilot study.

    PubMed

    Hillebrand, Matthias; Nouri, Ghazaleh; Hametner, Bernhard; Parragh, Stephanie; Köster, Jelena; Mortensen, Kai; Schwarz, Achim; von Kodolitsch, Yskert; Wassertheurer, Siegfried

    2016-05-06

    The aim of this work is the investigation of measures of ambulatory brachial and aortic blood pressure and indices of arterial stiffness and aortic wave reflection in Marfan patients. A case-control study was conducted including patients with diagnosed Marfan syndrome following Ghent2 nosology and healthy controls matched for sex, age and daytime brachial systolic blood pressure. For each subject a 24 h ambulatory blood pressure and 24 h pulse wave analysis measurement was performed. All parameters showed a circadian pattern whereby pressure dipping was more pronounced in Marfan patients. During daytime only Marfan patients with aortic root surgery showed increased pulse wave velocity. In contrast, various nighttime measurements, wave reflection determinants and circadian patterns showed a significant difference. The findings of our study provide evidence that ambulatory measurement of arterial stiffness parameters is feasible and that these determinants are significantly different in Marfan syndrome patients compared to controls in particular at nighttime. Further investigation is therefore indicated.

  12. Shear wave elastography results correlate with liver fibrosis histology and liver function reserve.

    PubMed

    Feng, Yan-Hong; Hu, Xiang-Dong; Zhai, Lin; Liu, Ji-Bin; Qiu, Lan-Yan; Zu, Yuan; Liang, Si; Gui, Yu; Qian, Lin-Xue

    2016-05-07

    To evaluate the correlation of shear wave elastography (SWE) results with liver fibrosis histology and quantitative function reserve. Weekly subcutaneous injection of 60% carbon tetrachloride (1.5 mL/kg) was given to 12 canines for 24 wk to induce experimental liver fibrosis, with olive oil given to 2 control canines. At 24 wk, liver condition was evaluated using clinical biochemistry assays, SWE imaging, lidocaine metabolite monoethylglycine-xylidide (MEGX) test, and histologic fibrosis grading. Clinical biochemistry assays were performed at the institutional central laboratory for routine liver function evaluation. Liver stiffness was measured in triplicate from three different intercostal spaces and expressed as mean liver stiffness modulus (LSM). Plasma concentrations of lidocaine and its metabolite MEGX were determined using high-performance liquid chromatography repeated in duplicate. Liver biopsy samples were fixed in 10% formaldehyde, and liver fibrosis was graded using the modified histological activity index Knodell score (F0-F4). Correlations among histologic grading, LSM, and MEGX measures were analyzed with the Pearson linear correlation coefficient. At 24 wk liver fibrosis histologic grading was as follows: F0, n = 2 (control); F1, n = 0; F2, n = 3; F3, n = 7; and F4, n = 2. SWE LSM was positively correlated with histologic grading (r = 0.835, P < 0.001). Specifically, the F4 group had a significantly higher elastic modulus than the F3, F2, and F0 groups (P = 0.002, P = 0.003, and P = 0.006, respectively), and the F3 group also had a significantly higher modulus than the control F0 group (P = 0.039). LSM was negatively associated with plasma MEGX concentrations at 30 min (r = -0.642; P = 0.013) and 60 min (r = -0.651; P = 0.012), time to ½ of the maximum concentration (r = -0.538; P = 0.047), and the area under the curve (r = -0.636; P = 0.014). Multiple comparisons showed identical differences in these three measures: significantly lower with F4 (P

  13. Hamstrings Stiffness and Landing Biomechanics Linked to Anterior Cruciate Ligament Loading

    PubMed Central

    Blackburn, J. Troy; Norcross, Marc F.; Cannon, Lindsey N.; Zinder, Steven M.

    2013-01-01

    Context: Greater hamstrings stiffness is associated with less anterior tibial translation during controlled perturbations. However, it is unclear how hamstrings stiffness influences anterior cruciate ligament (ACL) loading mechanisms during dynamic tasks. Objective: To evaluate the influence of hamstrings stiffness on landing biomechanics related to ACL injury. Design: Cross-sectional study. Setting: Research laboratory. Patients or Other Participants: A total of 36 healthy, physically active volunteers (18 men, 18 women; age = 23 ± 3 years, height = 1.8 ± 0.1 m, mass = 73.1 ± 16.6 kg). Intervention(s): Hamstrings stiffness was quantified via the damped oscillatory technique. Three-dimensional lower extremity kinematics and kinetics were captured during a double-legged jump-landing task via a 3-dimensional motion-capture system interfaced with a force plate. Landing biomechanics were compared between groups displaying high and low hamstrings stiffness via independent-samples t tests. Main Outcome Measure(s): Hamstrings stiffness was normalized to body mass (N/m·kg−1). Peak knee-flexion and -valgus angles, vertical and posterior ground reaction forces, anterior tibial shear force, internal knee-extension and -varus moments, and knee-flexion angles at the instants of each peak kinetic variable were identified during the landing task. Forces were normalized to body weight, whereas moments were normalized to the product of weight and height. Results: Internal knee-varus moment was 3.6 times smaller in the high-stiffness group (t22 = 2.221, P = .02). A trend in the data also indicated that peak anterior tibial shear force was 1.1 times smaller in the high-stiffness group (t22 = 1.537, P = .07). The high-stiffness group also demonstrated greater knee flexion at the instants of peak anterior tibial shear force and internal knee-extension and -varus moments (t22 range = 1.729–2.224, P < .05). Conclusions: Greater hamstrings stiffness was associated with landing

  14. Lamb Wave Stiffness Characterization of Composites Undergoing Thermal-Mechanical Aging

    NASA Technical Reports Server (NTRS)

    Seale, Michael D.; Madaras, Eric I.

    2004-01-01

    The introduction of new, advanced composite materials into aviation systems requires a thorough understanding of the long term effects of combined thermal and mechanical loading upon those materials. Analytical methods investigating the effects of intense thermal heating combined with mechanical loading have been investigated. The damage mechanisms and fatigue lives were dependent on test parameters as well as stress levels. Castelli, et al. identified matrix dominated failure modes for out-of-phase cycling and fiber dominated damage modes for in-phase cycling. In recent years, ultrasonic methods have been developed that can measure the mechanical stiffness of composites. To help evaluate the effect of aging, a suitably designed Lamb wave measurement system is being used to obtain bending and out-of-plane stiffness coefficients of composite laminates undergoing thermal-mechanical loading. The system works by exciting an antisymmetric Lamb wave and calculating the velocity at each frequency from the known transducer separation and the measured time-of-flight. The same peak in the waveforms received at various distances is used to measure the time difference between the signals. The velocity measurements are accurate and repeatable to within 1% resulting in reconstructed stiffness values repeatable to within 4%. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the dispersion curve. A mechanical scanner is used to move the sensors over the surface to map the time-of-flight, velocity, or stiffnesses of the entire specimen. Access to only one side of the material is required and no immersion or couplants are required because the sensors are dry coupled to the surface of the plate. In this study, the elastic stiffnesses D(sub 11), D(sub 22), A(sub 44), and A(sub 55) as well as time-of-flight measurements for composite samples that have undergone combined thermal and mechanical aging for

  15. Arterial stiffness and cognitive impairment.

    PubMed

    Li, Xiaoxuan; Lyu, Peiyuan; Ren, Yanyan; An, Jin; Dong, Yanhong

    2017-09-15

    Arterial stiffness is one of the earliest indicators of changes in vascular wall structure and function and may be assessed using various indicators, such as pulse-wave velocity (PWV), the cardio-ankle vascular index (CAVI), the ankle-brachial index (ABI), pulse pressure (PP), the augmentation index (AI), flow-mediated dilation (FMD), carotid intima media thickness (IMT) and arterial stiffness index-β. Arterial stiffness is generally considered an independent predictor of cardiovascular and cerebrovascular diseases. To date, a significant number of studies have focused on the relationship between arterial stiffness and cognitive impairment. To investigate the relationships between specific arterial stiffness parameters and cognitive impairment, elucidate the pathophysiological mechanisms underlying the relationship between arterial stiffness and cognitive impairment and determine how to interfere with arterial stiffness to prevent cognitive impairment, we searched PUBMED for studies regarding the relationship between arterial stiffness and cognitive impairment that were published from 2000 to 2017. We used the following key words in our search: "arterial stiffness and cognitive impairment" and "arterial stiffness and cognitive impairment mechanism". Studies involving human subjects older than 30years were included in the review, while irrelevant studies (i.e., studies involving subjects with comorbid kidney disease, diabetes and cardiac disease) were excluded from the review. We determined that arterial stiffness severity was positively correlated with cognitive impairment. Of the markers used to assess arterial stiffness, a higher PWV, CAVI, AI, IMT and index-β and a lower ABI and FMD were related to cognitive impairment. However, the relationship between PP and cognitive impairment remained controversial. The potential mechanisms linking arterial stiffness and cognitive impairment may be associated with arterial pulsatility, as greater arterial pulsatility

  16. Influence of Hepatic Inflammation on FibroScan Findings in Diagnosing Fibrosis in Patients with Chronic Hepatitis B.

    PubMed

    Zeng, Xianghua; Xu, Cheng; He, Dengming; Zhang, Huiyan; Xia, Jie; Shi, Dairong; Kong, Lingjun; He, Xiaoqin; Wang, Yuming

    2015-06-01

    Hepatic inflammation may affect the performance of FibroScan. This prospective study investigated the influence of hepatic inflammation on liver stiffness measurement (LSM) values by assessing FibroScan and liver biopsy findings in 325 patients with chronic hepatitis B. Liver fibrosis and inflammation were classified into five stages (S0-S4) and grades (G0-G4) according to the Scheuer scoring system. LSM values were correlated with fibrosis stage and inflammation grade (r = 0.479, p < 0.001, and r = 0.522, p < 0.001, respectively). Although LSM values increased in parallel with inflammation grade, no significant differences were found between patients with significant fibrosis (S2-S4) (p > 0.05). For inflammation grades G0, G1, G2 and G3, areas under receiver operating characteristic curves of FibroScan for significant fibrosis were 0.8267 (p < 0.001), 0.6956 (p < 0.001), 0.709 (p = 0.0012) and 0.6947 (p = 0.137), respectively. Inflammation has a significant influence on LSM values in patients with chronic hepatitis B with mild fibrosis, but not in those with significant fibrosis. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

  17. A Meta-analysis for the Diagnostic Performance of Transient Elastography for Clinically Significant Portal Hypertension.

    PubMed

    You, Myung-Won; Kim, Kyung Won; Pyo, Junhee; Huh, Jimi; Kim, Hyoung Jung; Lee, So Jung; Park, Seong Ho

    2017-01-01

    We aimed to evaluate the correlation between liver stiffness measurement using transient elastography (TE-LSM) and hepatic venous pressure gradient and the diagnostic performance of TE-LSM in assessing clinically significant portal hypertension through meta-analysis. Eleven studies were included from thorough literature research and selection processes. The summary correlation coefficient was 0.783 (95% confidence interval [CI], 0.737-0.823). Summary sensitivity, specificity and area under the hierarchical summary receiver operating characteristic curve (AUC) were 87.5% (95% CI, 75.8-93.9%), 85.3 % (95% CI, 76.9-90.9%) and 0.9, respectively. The subgroup with low cut-off values of 13.6-18 kPa had better summary estimates (sensitivity 91.2%, specificity 81.3% and partial AUC 0.921) than the subgroup with high cut-off values of 21-25 kPa (sensitivity 71.2%, specificity 90.9% and partial AUC 0.769). In summary, TE-LSM correlated well with hepatic venous pressure gradient and represented good diagnostic performance in diagnosing clinically significant portal hypertension. For use as a sensitive screening tool, we propose using low cut-off values of 13.6-18 kPa in TE-LSM. Copyright © 2016 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

  18. Micromechanical contact stiffness devices and application for calibrating contact resonance atomic force microscopy.

    PubMed

    Rosenberger, Matthew R; Chen, Sihan; Prater, Craig B; King, William P

    2017-01-27

    This paper reports the design, fabrication, and characterization of micromechanical devices that can present an engineered contact stiffness to an atomic force microscope (AFM) cantilever tip. These devices allow the contact stiffness between the AFM tip and a substrate to be easily and accurately measured, and can be used to calibrate the cantilever for subsequent mechanical property measurements. The contact stiffness devices are rigid copper disks of diameters 2-18 μm integrated onto a soft silicone substrate. Analytical modeling and finite element simulations predict the elastic response of the devices. Measurements of tip-sample interactions during quasi-static force measurements compare well with modeling simulation, confirming the expected elastic response of the devices, which are shown to have contact stiffness 32-156 N m -1 . To demonstrate one application, we use the disk sample to calibrate three resonant modes of a U-shaped AFM cantilever actuated via Lorentz force, at approximately 220, 450, and 1200 kHz. We then use the calibrated cantilever to determine the contact stiffness and elastic modulus of three polymer samples at these modes. The overall approach allows cantilever calibration without prior knowledge of the cantilever geometry or its resonance modes, and could be broadly applied to both static and dynamic measurements that require AFM calibration against a known contact stiffness.

  19. Micromechanical contact stiffness devices and application for calibrating contact resonance atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Rosenberger, Matthew R.; Chen, Sihan; Prater, Craig B.; King, William P.

    2017-01-01

    This paper reports the design, fabrication, and characterization of micromechanical devices that can present an engineered contact stiffness to an atomic force microscope (AFM) cantilever tip. These devices allow the contact stiffness between the AFM tip and a substrate to be easily and accurately measured, and can be used to calibrate the cantilever for subsequent mechanical property measurements. The contact stiffness devices are rigid copper disks of diameters 2-18 μm integrated onto a soft silicone substrate. Analytical modeling and finite element simulations predict the elastic response of the devices. Measurements of tip-sample interactions during quasi-static force measurements compare well with modeling simulation, confirming the expected elastic response of the devices, which are shown to have contact stiffness 32-156 N m-1. To demonstrate one application, we use the disk sample to calibrate three resonant modes of a U-shaped AFM cantilever actuated via Lorentz force, at approximately 220, 450, and 1200 kHz. We then use the calibrated cantilever to determine the contact stiffness and elastic modulus of three polymer samples at these modes. The overall approach allows cantilever calibration without prior knowledge of the cantilever geometry or its resonance modes, and could be broadly applied to both static and dynamic measurements that require AFM calibration against a known contact stiffness.

  20. End-on soft x ray imaging of Field-Reversed Configurations (FRCs) on the Field-Reversal-C (FRX-C)/Large Scale Modification (LSM) experiment

    NASA Astrophysics Data System (ADS)

    Taggart, D. P.; Gribble, R. J.; Bailey, A. D., III; Sugimoto, S.

    Recently, a prototype soft x ray pinhole camera was fielded on FRX-C/LSM at Los Alamos and TRX at Spectra Technology. The soft x ray FRC images obtained using this camera stand out in high contrast to their surroundings. It was particularly useful for studying the FRC during and shortly after formation when, at certain operating conditions, flute-like structures at the edge and internal structures of the FRC were observed which other diagnostics could not resolve. Building on this early experience, a new soft x ray pinhole camera was installed on FRX-C/LSM, which permits more rapid data acquisition and briefer exposures. It will be used to continue studying FRC formation and to look for internal structure later in time which could be a signature of instability. The initial operation of this camera is summarized.

  1. Biomechanical measurements of stiffness and strength for five types of whole human and artificial humeri.

    PubMed

    Aziz, Mina S R; Nicayenzi, Bruce; Crookshank, Meghan C; Bougherara, Habiba; Schemitsch, Emil H; Zdero, Radovan

    2014-05-01

    The human humerus is the third largest longbone and experiences 2-3% of all fractures. Yet, almost no data exist on its intact biomechanical properties, thus preventing researchers from obtaining a full understanding of humerus behavior during injury and after being repaired with fracture plates and nails. The aim of this experimental study was to compare the biomechanical stiffness and strength of "gold standard" fresh-frozen humeri to a variety of humerus models. A series of five types of intact whole humeri were obtained: human fresh-frozen (n = 19); human embalmed (n = 18); human dried (n = 15); artificial "normal" (n = 12); and artificial "osteoporotic" (n = 12). Humeri were tested under "real world" clinical loading modes for shear stiffness, torsional stiffness, cantilever bending stiffness, and cantilever bending strength. After removing geometric effects, fresh-frozen results were 585.8 ± 181.5 N/mm2 (normalized shear stiffness); 3.1 ± 1.1 N/(mm2 deg) (normalized torsional stiffness); 850.8 ± 347.9 N/mm2 (normalized cantilever stiffness); and 8.3 ± 2.7 N/mm2 (normalized cantilever strength). Compared to fresh-frozen values, statistical equivalence (p ≥ 0.05) was obtained for all four test modes (embalmed humeri), 1 of 4 test modes (dried humeri), 1 of 4 test modes (artificial "normal" humeri), and 1 of 4 test modes (artificial "osteoporotic" humeri). Age and bone mineral density versus experimental results had Pearson linear correlations ranging from R = -0.57 to 0.80. About 77% of human humeri failed via a transverse or oblique distal shaft fracture, whilst 88% of artificial humeri failed with a mixed transverse + oblique fracture. To date, this is the most comprehensive study on the biomechanics of intact human and artificial humeri and can assist researchers to choose an alternate humerus model that can substitute for fresh-frozen humeri.

  2. Estimating Human Trabecular Meshwork Stiffness by Numerical Modeling and Advanced OCT Imaging.

    PubMed

    Wang, Ke; Johnstone, Murray A; Xin, Chen; Song, Shaozhen; Padilla, Steven; Vranka, Janice A; Acott, Ted S; Zhou, Kai; Schwaner, Stephen A; Wang, Ruikang K; Sulchek, Todd; Ethier, C Ross

    2017-09-01

    The purpose of this study was to estimate human trabecular meshwork (hTM) stiffness, thought to be elevated in glaucoma, using a novel indirect approach, and to compare results with direct en face atomic force microscopy (AFM) measurements. Postmortem human eyes were perfused to measure outflow facility and identify high- and low-flow regions (HF, LF) by tracer. Optical coherence tomography (OCT) images were obtained as Schlemm's canal luminal pressure was directly manipulated. TM stiffness was deduced by an inverse finite element modeling (FEM) approach. A series of AFM forcemaps was acquired along a line traversing the anterior angle on a radially cut flat-mount corneoscleral wedge with TM facing upward. The elastic modulus of normal hTM estimated by inverse FEM was 70 ± 20 kPa (mean ± SD), whereas glaucomatous hTM was slightly stiffer (98 ± 19 kPa). This trend was consistent with TM stiffnesses measured by AFM: normal hTM stiffness = 1.37 ± 0.56 kPa, which was lower than glaucomatous hTM stiffness (2.75 ± 1.19 kPa). None of these differences were statistically significant. TM in HF wedges was softer than that in LF wedges for both normal and glaucomatous eyes based on the inverse FEM approach but not by AFM. Outflow facility was significantly correlated with TM stiffness estimated by FEM in six human eyes (P = 0.018). TM stiffness is higher, but only modestly so, in glaucomatous patients. Outflow facility in both normal and glaucomatous human eyes appears to associate with TM stiffness. This evidence motivates further studies to investigate factors underlying TM biomechanical property regulation.

  3. Artificial muscles with adjustable stiffness

    NASA Astrophysics Data System (ADS)

    Mutlu, Rahim; Alici, Gursel

    2010-04-01

    This paper reports on a stiffness enhancement methodology based on using a suitably designed contact surface with which cantilevered-type conducting polymer bending actuators are in contact during operation. The contact surface constrains the bending behaviour of the actuators. Depending on the topology of the contact surface, the resistance of the polymer actuators to deformation, i.e. stiffness, is varied. As opposed to their predecessors, these polymer actuators operate in air. Finite element analysis and modelling are used to quantify the effect of the contact surface on the effective stiffness of a trilayer cantilevered beam, which represents a one-end-free, the-other-end-fixed polypyrrole (PPy) conducting polymer actuator under a uniformly distributed load. After demonstrating the feasibility of the adjustable stiffness concept, experiments were conducted to determine the stiffness of bending-type conducting polymer actuators in contact with a range (20-40 mm in radius) of circular contact surfaces. The numerical and experimental results presented demonstrate that the stiffness of the actuators can be varied using a suitably profiled contact surface. The larger the radius of the contact surface is, the higher is the stiffness of the polymer actuators. The outcomes of this study suggest that, although the stiffness of the artificial muscles considered in this study is constant for a given geometric size, and electrical and chemical operation conditions, it can be changed in a nonlinear fashion to suit the stiffness requirement of a considered application. The stiffness enhancement methodology can be extended to other ionic-type conducting polymer actuators.

  4. A Single Test Combining Blood Markers and Elastography is More Accurate Than Other Fibrosis Tests in the Main Causes of Chronic Liver Diseases.

    PubMed

    Ducancelle, Alexandra; Leroy, Vincent; Vergniol, Julien; Sturm, Nathalie; Le Bail, Brigitte; Zarski, Jean Pierre; Nguyen Khac, Eric; Salmon, Dominique; de Ledinghen, Victor; Calès, Paul

    2017-08-01

    International guidelines suggest combining a blood test and liver stiffness measurement (LSM) to stage liver fibrosis in chronic hepatitis C (CHC) and non-alcoholic fatty liver disease (NAFLD). Therefore, we compared the accuracies of these tests between the main etiologies of chronic liver diseases. Overall, 1968 patients were included in 5 etiologies: CHC: 698, chronic hepatitis B: 152, human immunodeficiency virus/CHC: 628, NAFLD: 225, and alcoholic liver disease (ALD): 265. Sixteen tests [13 blood tests, LSM (Fibroscan), 2 combined: FibroMeters] were evaluated. References were Metavir staging and CHC etiology. Accuracy was evaluated mainly with the Obuchowski index (OI) and accessorily with area under the receiver operating characteristics (F≥2, F≥3, cirrhosis). OIs in CHC were: FibroMeters: 0.812, FibroMeters: 0.785 to 0.797, Fibrotest: 0.762, CirrhoMeters: 0.756 to 0.771, LSM: 0.754, Hepascore: 0.752, FibroMeter: 0.750, aspartate aminotransferase platelet ratio index: 0.742, Fib-4: 0.741. In other etiologies, most tests had nonsignificant changes in OIs. In NAFLD, CHC-specific tests were more accurate than NAFLD-specific tests. The combined FibroMeters had significantly higher accuracy than their 2 constitutive tests (FibroMeters and LSM) in at least 1 diagnostic target in all etiologies, except in ALD where LSM had the highest OI, and in 3 diagnostic targets (OIs and 2 area under the receiver operating characteristics) in CHC and NAFLD. Some tests developed in CHC outperformed other tests in their specific etiologies. Tests combining blood markers and LSM outperformed single tests, validating recent guidelines and extending them to main etiologies. Noninvasive fibrosis evaluation can thus be simplified in the main etiologies by using a unique test: either LSM alone, especially in ALD, or preferably combined to blood markers.

  5. Sexual Function Is an Indicator of Central Arterial Stiffness and Arterial Stiffness Gradient in Japanese Adult Men.

    PubMed

    Kumagai, Hiroshi; Yoshikawa, Toru; Myoenzono, Kanae; Kosaki, Keisei; Akazawa, Nobuhiko; Asako, Zempo-Miyaki; Tsujimoto, Takehiko; Kidokoro, Tetsuhiro; Tanaka, Kiyoji; Maeda, Seiji

    2018-05-05

    As arterial stiffness increases in the absence of subjective symptoms, a personal indicator that reflects increased risk of cardiovascular disease is necessary. Penile erection is regulated by vascular function, and atherosclerosis affects the penile artery earlier than it affects the coronary and carotid arteries. Therefore, we hypothesized that deterioration of erectile function could be a marker of increased risk for cardiovascular disease. To test our hypothesis, we assessed erectile function and arterial stiffness in a cross-sectional study. Carotid-femoral pulse wave velocity (PWV), brachial-ankle PWV, femoral-ankle PWV, and arterial stiffness gradient (PWV ratio: carotid-femoral PWV/femoral-ankle PWV) were measured as indexes of central, systemic, and peripheral arterial stiffness and peripheral organ damage, respectively, in 317 adult men. In addition, erectile function was assessed by using the questionnaire International Index of Erectile Function 5 (a descending score indicates worsening of erectile function). The scores of male sexual function were inversely correlated with carotid-femoral PWV ( r s =-0.41), brachial-ankle PWV ( r s =-0.35), femoral-ankle PWV ( r s =-0.19), and PWV ratio ( r s =-0.33). Furthermore, multivariate linear regression analyses revealed that International Index of Erectile Function 5 scores were significantly associated with carotid-femoral PWV (β=-0.22) and PWV ratio (β=-0.25), but not with brachial-ankle PWV and femoral-ankle PWV. Our results indicated that erectile function is independently associated with central arterial stiffness and peripheral organ damage. These findings suggest that male sexual function could be an easily identifiable and independent marker of increased central arterial stiffness and peripheral organ damage. © 2018 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley.

  6. Human arm stiffness and equilibrium-point trajectory during multi-joint movement.

    PubMed

    Gomi, H; Kawato, M

    1997-03-01

    By using a newly designed high-performance manipulandum and a new estimation algorithm, we measured human multi-joint arm stiffness parameters during multi-joint point-to-point movements on a horizontal plane. This manipulandum allows us to apply a sufficient perturbation to subject's arm within a brief period during movement. Arm stiffness parameters were reliably estimated using a new algorithm, in which all unknown structural parameters could be estimated independent of arm posture (i.e., constant values under any arm posture). Arm stiffness during transverse movement was considerably greater than that during corresponding posture, but not during a longitudinal movement. Although the ratios of elbow, shoulder, and double-joint stiffness were varied in time, the orientation of stiffness ellipses during the movement did not change much. Equilibrium-point trajectories that were predicted from measured stiffness parameters and actual trajectories were slightly sinusoidally curved in Cartesian space and their velocity profiles were quite different from the velocity profiles of actual hand trajectories. This result contradicts the hypothesis that the brain does not take the dynamics into account in movement control depending on the neuromuscular servo mechanism; rather, it implies that the brain needs to acquire some internal models of controlled objects.

  7. Comparison of cervical spine stiffness in individuals with chronic nonspecific neck pain and asymptomatic individuals.

    PubMed

    Ingram, Lewis A; Snodgrass, Suzanne J; Rivett, Darren A

    2015-03-01

    Clinical measurement, cross-sectional. To determine if spinal joint stiffness is different in individuals with nonspecific neck pain, and whether stiffness magnitude is associated with pain intensity and disability. Manual therapists commonly evaluate spinal joint stiffness in patients presenting with nonspecific neck pain. However, a relationship between stiffness and neck pain has not yet been demonstrated. Spinal stiffness at C7 was objectively measured in participants with chronic nonspecific neck pain whose symptomatic spinal level was identified as C7 (n = 12) and in age- and sex-matched asymptomatic controls (n = 12). Stiffness (slope of the linear region of the force-displacement curve) was quantified using a device that applied 5 standardized mechanical force cycles to the C7 spinous process, while concurrently measuring displacement and resistance to movement. Stiffness was compared between groups using an independent t test. Spearman rho and Pearson r were used to determine the extent to which stiffness magnitude was associated with pain intensity (visual analog scale) and level of disability (Neck Disability Index), respectively, in the group with neck pain. Participants with nonspecific neck pain had greater spinal joint stiffness at C7 compared with asymptomatic individuals (mean difference, 1.78 N/mm; 95% confidence interval: 0.28, 3.27; P = .022). However, stiffness magnitude in the group with neck pain was not associated (P>.05) with pain intensity or level of disability. These preliminary results suggest that cervical spine stiffness may be greater in the presence of nonspecific neck pain. However, judgments regarding pain intensity and level of disability should not be inferred from examinations of spinal joint stiffness.

  8. The study of stiffness modulus values for AC-WC pavement

    NASA Astrophysics Data System (ADS)

    Lubis, AS; Muis, Z. A.; Iskandar, T. D.

    2018-02-01

    One of the parameters of the asphalt mixture in order for the strength and durability to be achieved as required is the stress-and-strain showing the stiffness of a material. Stiffness modulus is a very necessary factor that will affect the performance of asphalt pavements. If the stiffness modulus value decreases there will be a cause of aging asphalt pavement crack easily when receiving a heavy load. The high stiffness modulus asphalt concrete causes more stiff and resistant to bending. The stiffness modulus value of an asphalt mixture material can be obtained from the theoretical (indirect methods) and laboratory test results (direct methods). For the indirect methods used Brown & Brunton method, and Shell Bitumen method; while for the direct methods used the UMATTA tool. This study aims to determine stiffness modulus values for AC-WC pavement. The tests were conducted in laboratory that used 3 methods, i.e. Brown & Brunton Method, Shell Bitumen Method and Marshall Test as a substitute tool for the UMATTA tool. Hotmix asphalt made from type AC-WC with pen 60/70 using a mixture of optimum bitumen content was 5.84% with a standard temperature variation was 60°C and several variations of temperature that were 30, 40, 50, 70 and 80°C. The stiffness modulus value results obtained from Brown & Brunton Method, Shell Bitumen Method and Marshall Test which were 1374,93 Mpa, 235,45 Mpa dan 254,96 Mpa. The stiffness modulus value decreases with increasing temperature of the concrete asphalt. The stiffness modulus value from the Bitumen Shell method and the Marshall Test has a relatively similar value.The stiffness modulus value from the Brown & Brunton method is greater than the Bitumen Shell method and the Marshall Test, but can not measure the stiffness modulus value at temperature above 80°C.

  9. Stiffness map of the grasping contact areas of the human hand.

    PubMed

    Pérez-González, Antonio; Vergara, Margarita; Sancho-Bru, Joaquin L

    2013-10-18

    The elasticity and damping of the soft tissues of the hand contribute to dexterity while grasping and also help to stabilise the objects in manipulation tasks. Although some previous works have studied the force-displacement response of the fingertips, the responses in all other regions of the hand that usually participate in grasping have not been analysed to date. In this work we performed experimental measurements in 20 subjects to obtain a stiffness map of the different grasping contact areas of the human hand. A force-displacement apparatus was used to simultaneously measure force and displacement at 39 different points on the hand at six levels of force ranging from 1N to 6N. A non-linear force-displacement response was found for all points, with stiffness increasing with the amount of force applied. Mean stiffness for the different points and force levels was within the range from 0.2N/mm to 7.7N/mm. However, the stiffness range and variation with level of force were found to be different from point to point. A total of 13 regions with similar stiffness behaviours were identified. The stiffness in the fingertips increased linearly with the amount of force applied, while in the palm it remained more constant for the range of forces considered. It is hypothesised that the differences in the stiffness behaviour from one region to another allow these regions to play different roles during grasping. © 2013 Elsevier Ltd. All rights reserved.

  10. Variable stiffness mechanisms with SMA actuators

    NASA Astrophysics Data System (ADS)

    Siler, Damin J.; Demoret, Kimberly B. J.

    1996-05-01

    Variable stiffness is a new branch of smart structures development with several applications related to aircraft. Previous research indicates that temporarily reducing the stiffness of an airplane wing can decrease control actuator sizing and improve aeroelastic roll performance. Some smart materials like shape memory alloys (SMA) can change their material stiffness properties, but they tend to gain stiffness in their `power on' state. An alternative is to integrate mechanisms into a structure and change stiffness by altering boundary conditions and structural load paths. An innovative concept for an axial strut mechanism was discovered as part of research into variable stiffness. It employs SMA springs (specifically Ni-Ti) in a way that reduces overall stiffness when the SMA springs gain stiffness. A simplified mathematical model for static analysis was developed, and a 70% reduction in stiffness was obtained for a particular selection of springs. The small force capacity of commercially available SMA springs limits the practicality of this concept for large load applications. However, smart material technology is still immature, and future advances may permit development of a heavy-duty, variable stiffness strut that is small and light enough for use in aircraft structures.

  11. A method for accounting for test fixture compliance when estimating proximal femur stiffness.

    PubMed

    Rossman, Timothy; Dragomir-Daescu, Dan

    2016-09-06

    Fracture testing of cadaveric femora to obtain strength and stiffness information is an active area of research in developing tools for diagnostic prediction of bone strength. These measurements are often used in the estimation and validation of companion finite element models constructed from the femora CT scan data, therefore, the accuracy of the data is of paramount importance. However, experimental stiffness calculated from force-displacement data has largely been ignored by most researchers due to inherent error in the differential displacement measurement obtained when not accounting for testing apparatus compliance. However, having such information is necessary for validation of computational models. Even in the few cases when fixture compliance was considered the measurements showed large lab-to-lab variation due to lack of standardization in fixture design. We examined the compliance of our in-house designed cadaveric femur test fixture to determine the errors we could expect when calculating stiffness from the collected experimental force-displacement data and determined the stiffness of the test fixture to be more than 10 times the stiffness of the stiffest femur in a sample of 44 femora. When correcting the apparent femur stiffness derived from the original data, we found that the largest stiffness was underestimated by about 10%. The study confirmed that considering test fixture compliance is a necessary step in improving the accuracy of fracture test data for characterizing femur stiffness, and highlighted the need for test fixture design standardization for proximal femur fracture testing. Copyright © 2016 Elsevier Ltd. All rights reserved.

  12. Stiffness and Damping in Postural Control Increase with Age

    PubMed Central

    Cenciarini, Massimo; Loughlin, Patrick J.; Sparto, Patrick J.; Redfern, Mark S.

    2011-01-01

    Upright balance is believed to be maintained through active and passive mechanisms, both of which have been shown to be impacted by aging. A compensatory balance response often observed in older adults is increased co-contraction, which is generally assumed to enhance stability by increasing joint stiffness. We investigated the effect of aging on standing balance by fitting body sway data to a previously-developed postural control model that includes active and passive stiffness and damping parameters. Ten young (24 ± 3 y) and seven older (75 ± 5 y) adults were exposed during eyes-closed stance to perturbations consisting of lateral pseudorandom floor tilts. A least-squares fit of the measured body sway data to the postural control model found significantly larger active stiffness and damping model parameters in the older adults. These differences remained significant even after normalizing to account for different body sizes between the young and older adult groups. An age effect was also found for the normalized passive stiffness, but not for the normalized passive damping parameter. This concurrent increase in active stiffness and damping was shown to be more stabilizing than an increase in stiffness alone, as assessed by oscillations in the postural control model impulse response. PMID:19770083

  13. Fluorescence spectroscopy for non-invasive measurement of mechanical stiffness after photo-crosslinking of rabbit cornea

    NASA Astrophysics Data System (ADS)

    Williams, Maura; Lewis, William; Ortega-Martinez, Antonio; Franco, Walfre

    2017-02-01

    Background and Objectives: Keratoconus is a disease characterized by progressive steepening and thinning of the cornea, altering visual acuity and sometimes potentiating the need for corneal transplant if the disease progresses.1-3 Corneal crosslinking, a procedure that uses topical riboflavin and UV light to increase the stiffness of the cornea through the creation of collagen crosslinks was recently approved by the FDA for use in the U.S. The objective of the present study was to investigate whether endogenous collagen fluorescence changes following treatment can be correlated to alterations in the stiffness of the cornea, thereby guiding treatment parameters. Study Design and Results: 78 ex-vivo rabbit eyes divided into three groups: riboflavin solution plus UV irradiation, dextran solution plus UV irradiation, and riboflavin solution only. An additional group of eyes received no treatment. The epithelium was removed from each sample and topical riboflavin was applied. Eyes were irradiated with a 365 nm black ray UV lamp for various treatment times, ranging from half the clinical treatment time to three times the length. Mechanical testing was performed to determine the force/displacement relationship for the various treatment times. Fluorescence spectral changes following treatment corresponded with changes in stiffness. In particular, a decrease in the value of fluorescence intensity at 290/340 nm excitation/emission wavelengths corresponded to an increase in corneal stiffness following treatment. It may be possible to use fluorescence spectral changes of endogenous corneal crosslinks to evaluate mechanical stiffness changes non-invasively.

  14. Identification of a parametric, discrete-time model of ankle stiffness.

    PubMed

    Guarin, Diego L; Jalaleddini, Kian; Kearney, Robert E

    2013-01-01

    Dynamic ankle joint stiffness defines the relationship between the position of the ankle and the torque acting about it and can be separated into intrinsic and reflex components. Under stationary conditions, intrinsic stiffness can described by a linear second order system while reflex stiffness is described by Hammerstein system whose input is delayed velocity. Given that reflex and intrinsic torque cannot be measured separately, there has been much interest in the development of system identification techniques to separate them analytically. To date, most methods have been nonparametric and as a result there is no direct link between the estimated parameters and those of the stiffness model. This paper presents a novel algorithm for identification of a discrete-time model of ankle stiffness. Through simulations we show that the algorithm gives unbiased results even in the presence of large, non-white noise. Application of the method to experimental data demonstrates that it produces results consistent with previous findings.

  15. Theoretical and experimental investigation of architected core materials incorporating negative stiffness elements

    NASA Astrophysics Data System (ADS)

    Chang, Chia-Ming; Keefe, Andrew; Carter, William B.; Henry, Christopher P.; McKnight, Geoff P.

    2014-04-01

    Structural assemblies incorporating negative stiffness elements have been shown to provide both tunable damping properties and simultaneous high stiffness and damping over prescribed displacement regions. In this paper we explore the design space for negative stiffness based assemblies using analytical modeling combined with finite element analysis. A simplified spring model demonstrates the effects of element stiffness, geometry, and preloads on the damping and stiffness performance. Simplified analytical models were validated for realistic structural implementations through finite element analysis. A series of complementary experiments was conducted to compare with modeling and determine the effects of each element on the system response. The measured damping performance follows the theoretical predictions obtained by analytical modeling. We applied these concepts to a novel sandwich core structure that exhibited combined stiffness and damping properties 8 times greater than existing foam core technologies.

  16. Assessment of Liver Fibrosis by Transient Elastography Should Be Done After Hemodialysis in End Stage Renal Disease Patients with Liver Disease.

    PubMed

    Taneja, Sunil; Borkakoty, Amritangsu; Rathi, Sahaj; Kumar, Vivek; Duseja, Ajay; Dhiman, Radha K; Gupta, Krishan L; Chawla, Yogesh

    2017-11-01

    The patients with end stage renal disease (ESRD) are at greater risk of acquiring chronic hepatitis B or C and subsequently development of liver disease. The aim of the study was to assess liver fibrosis by transient elastography (TE) and look for factors associated with change in liver stiffness measurement (LSM) with one session of hemodialysis (HD). Consecutive ESRD patients on maintenance hemodialysis (MHD) with suspected liver disease were enrolled. They underwent LSM by TE before and after one session of HD. Bioelectric impedance analysis was done to evaluate the volume status at the time of TE. Sixty-eight patients with mean age of 40 ± 14 years were included. There was a significant reduction in LSM after HD (18.5 [95% CI 14.8-23.1] vs. 11.2 [95% CI 8.8-13.7] kPa, p < 0.001), with a mean LSM reduction of 7.2 [95% CI 5.25-9.19] kPa. On stratification in two groups by net ultrafiltration during HD (> or < 2.5 liters [L]), change in LSM was substantially higher in patients when total fluid removed was > 2.5 L (8.6 [95% CI 5.7-11.5] vs. 5.1 [95% CI 2.9-7.5], p = 0.05). In 18 patients who underwent liver biopsy, LSM after HD performed better at detecting significant fibrosis, with area under receiver operating characteristics curve 0.71 [95% CI 0.46-0.97], versus 0.64 [95% CI 0.38-0.90], respectively. An LSM value of 12.2 kPa after HD was 71% sensitive and 74% specific for detection of significant fibrosis (≥ F2), while values less than 9 kPa ruled out significant fibrosis with a sensitivity and specificity of 37 and 100%, respectively. LSM by TE decreases significantly after HD in patients with ESRD on long-term MHD. Hence, TE should be done after HD for accurate assessment of liver fibrosis.

  17. Modification of Perioral Stiffness in Patients With Repaired Cleft Lip and Palate

    PubMed Central

    Barlow, Steven M.; Trotman, Carroll-Ann; Chu, Shin-Ying; Lee, Jaehoon

    2013-01-01

    Objective To measure and compare the perioral stiffness among three groups of pediatric subjects: a group of patients with a repaired cleft lip (and palate) who had a secondary lip revision surgery (revision), another group of patients with repaired cleft lip (and palate) who did not have secondary surgery (nonrevision), and a group of noncleft “normal” patients (noncleft). Design A parallel, three-group, nonrandomized clinical trial. Participants A total of 16 patients with repaired cleft lip/palate who did not have lip revision, 13 patients with repaired cleft lip/palate who had lip revision surgery and were tested at 18 to 24 months postsurgery, and 27 noncleft patients. Analysis Nonparticipatory perioral stiffness was sampled using a recently developed face-referenced measurement technology known as OroSTIFF. Perioral stiffness, derived as a quotient from resultant force and interangle lip span, was modeled with multilevel regression techniques. Real-time calculation of the perioral stiffness function demonstrated a significant quadratic relation between imposed interangle stretch and resultant force for each of the three groups. Results This nonlinear stiffness growth function was significantly elevated in the nonrevision patients compared with the noncleft controls and is likely due to the presence of scar tissue in the upper lip; it was significantly lower among patients with cleft lip/palate who completed lip revision surgery. Conclusion This study demonstrates the efficacy of applying an objective measurement to map differences in perioral tissue biomechanics among patients born with orofacial clefts. PMID:21247345

  18. Lower Extremity Stiffness Changes after Concussion in Collegiate Football Players.

    PubMed

    Dubose, Dominique F; Herman, Daniel C; Jones, Deborah L; Tillman, Susan M; Clugston, James R; Pass, Anthony; Hernandez, Jorge A; Vasilopoulos, Terrie; Horodyski, Marybeth; Chmielewski, Terese L

    2017-01-01

    Recent research indicates that a concussion increases the risk of musculoskeletal injury. Neuromuscular changes after concussion might contribute to the increased risk of injury. Many studies have examined gait postconcussion, but few studies have examined more demanding tasks. This study compared changes in stiffness across the lower extremity, a measure of neuromuscular function, during a jump-landing task in athletes with a concussion (CONC) to uninjured athletes (UNINJ). Division I football players (13 CONC and 26 UNINJ) were tested pre- and postseason. A motion capture system recorded subjects jumping on one limb from a 25.4-cm step onto a force plate. Hip, knee, and ankle joint stiffness were calculated from initial contact to peak joint flexion using the regression line slopes of the joint moment versus the joint angle plots. Leg stiffness was (peak vertical ground reaction force [PVGRF]/lower extremity vertical displacement) from initial contact to peak vertical ground reaction force. All stiffness values were normalized to body weight. Values from both limbs were averaged. General linear models compared group (CONC, UNINJ) differences in the changes of pre- and postseason stiffness values. Average time from concussion to postseason testing was 49.9 d. The CONC group showed an increase in hip stiffness (P = 0.03), a decrease in knee (P = 0.03) and leg stiffness (P = 0.03), but no change in ankle stiffness (P = 0.65) from pre- to postseason. Lower extremity stiffness is altered after concussion, which could contribute to an increased risk of lower extremity injury. These data provide further evidence of altered neuromuscular function after concussion.

  19. Quantifying Parameter Sensitivity, Interaction and Transferability in Hydrologically Enhanced Versions of Noah-LSM over Transition Zones

    NASA Technical Reports Server (NTRS)

    Rosero, Enrique; Yang, Zong-Liang; Wagener, Thorsten; Gulden, Lindsey E.; Yatheendradas, Soni; Niu, Guo-Yue

    2009-01-01

    We use sensitivity analysis to identify the parameters that are most responsible for shaping land surface model (LSM) simulations and to understand the complex interactions in three versions of the Noah LSM: the standard version (STD), a version enhanced with a simple groundwater module (GW), and version augmented by a dynamic phenology module (DV). We use warm season, high-frequency, near-surface states and turbulent fluxes collected over nine sites in the US Southern Great Plains. We quantify changes in the pattern of sensitive parameters, the amount and nature of the interaction between parameters, and the covariance structure of the distribution of behavioral parameter sets. Using Sobol s total and first-order sensitivity indexes, we show that very few parameters directly control the variance of the model output. Significant parameter interaction occurs so that not only the optimal parameter values differ between models, but the relationships between parameters change. GW decreases parameter interaction and appears to improve model realism, especially at wetter sites. DV increases parameter interaction and decreases identifiability, implying it is overparameterized and/or underconstrained. A case study at a wet site shows GW has two functional modes: one that mimics STD and a second in which GW improves model function by decoupling direct evaporation and baseflow. Unsupervised classification of the posterior distributions of behavioral parameter sets cannot group similar sites based solely on soil or vegetation type, helping to explain why transferability between sites and models is not straightforward. This evidence suggests a priori assignment of parameters should also consider climatic differences.

  20. Systematic profiling of spatiotemporal tissue and cellular stiffness in the developing brain.

    PubMed

    Iwashita, Misato; Kataoka, Noriyuki; Toida, Kazunori; Kosodo, Yoichi

    2014-10-01

    Accumulating evidence implicates the significance of the physical properties of the niche in influencing the behavior, growth and differentiation of stem cells. Among the physical properties, extracellular stiffness has been shown to have direct effects on fate determination in several cell types in vitro. However, little evidence exists concerning whether shifts in stiffness occur in vivo during tissue development. To address this question, we present a systematic strategy to evaluate the shift in stiffness in a developing tissue using the mouse embryonic cerebral cortex as an experimental model. We combined atomic force microscopy measurements of tissue and cellular stiffness with immunostaining of specific markers of neural differentiation to correlate the value of stiffness with the characteristic features of tissues and cells in the developing brain. We found that the stiffness of the ventricular and subventricular zones increases gradually during development. Furthermore, a peak in tissue stiffness appeared in the intermediate zone at E16.5. The stiffness of the cortical plate showed an initial increase but decreased at E18.5, although the cellular stiffness of neurons monotonically increased in association with the maturation of the microtubule cytoskeleton. These results indicate that tissue stiffness cannot be solely determined by the stiffness of the cells that constitute the tissue. Taken together, our method profiles the stiffness of living tissue and cells with defined characteristics and can therefore be utilized to further understand the role of stiffness as a physical factor that determines cell fate during the formation of the cerebral cortex and other tissues. © 2014. Published by The Company of Biologists Ltd.

  1. Reliability of Leg and Vertical Stiffness During High Speed Treadmill Running.

    PubMed

    Pappas, Panagiotis; Dallas, Giorgos; Paradisis, Giorgos

    2017-04-01

    In research, the accurate and reliable measurement of leg and vertical stiffness could contribute to valid interpretations. The current study aimed at determining the intraparticipant variability (ie, intraday and interday reliabilities) of leg and vertical stiffness, as well as related parameters, during high speed treadmill running, using the "sine-wave" method. Thirty-one males ran on a treadmill at 6.67 m∙s -1 , and the contact and flight times were measured. To determine the intraday reliability, three 10-s running bouts with 10-min recovery were performed. In addition, to examine the interday reliability, three 10-s running bouts on 3 separate days with 48-h interbout intervals were performed. The reliability statistics included repeated-measure analysis of variance, average intertrial correlations, intraclass correlation coefficients (ICCs), Cronbach's α reliability coefficient, and the coefficient of variation (CV%). Both intraday and interday reliabilities were high for leg and vertical stiffness (ICC > 0.939 and CV < 4.3%), as well as related variables (ICC > 0.934 and CV < 3.9%). It was thus inferred that the measurements of leg and vertical stiffness, as well as the related parameters obtained using the "sine-wave" method during treadmill running at 6.67 m∙s -1 , were highly reliable, both within and across days.

  2. Arterial stiffness, central hemodynamics, and cardiovascular risk in hypertension

    PubMed Central

    Palatini, Paolo; Casiglia, Edoardo; Gąsowski, Jerzy; Głuszek, Jerzy; Jankowski, Piotr; Narkiewicz, Krzysztof; Saladini, Francesca; Stolarz-Skrzypek, Katarzyna; Tikhonoff, Valérie; Van Bortel, Luc; Wojciechowska, Wiktoria; Kawecka-Jaszcz, Kalina

    2011-01-01

    This review summarizes several scientific contributions at the recent Satellite Symposium of the European Society of Hypertension, held in Milan, Italy. Arterial stiffening and its hemodynamic consequences can be easily and reliably measured using a range of noninvasive techniques. However, like blood pressure (BP) measurements, arterial stiffness should be measured carefully under standardized patient conditions. Carotid-femoral pulse wave velocity has been proposed as the gold standard for arterial stiffness measurement and is a well recognized predictor of adverse cardiovascular outcome. Systolic BP and pulse pressure in the ascending aorta may be lower than pressures measured in the upper limb, especially in young individuals. A number of studies suggest closer correlation of end-organ damage with central BP than with peripheral BP, and central BP may provide additional prognostic information regarding cardiovascular risk. Moreover, BP-lowering drugs can have differential effects on central aortic pressures and hemodynamics compared with brachial BP. This may explain the greater beneficial effect provided by newer antihypertensive drugs beyond peripheral BP reduction. Although many methodological problems still hinder the wide clinical application of parameters of arterial stiffness, these will likely contribute to cardiovascular assessment and management in future clinical practice. Each of the abovementioned parameters reflects a different characteristic of the atherosclerotic process, involving functional and/or morphological changes in the vessel wall. Therefore, acquiring simultaneous measurements of different parameters of vascular function and structure could theoretically enhance the power to improve risk stratification. Continuous technological effort is necessary to refine our methods of investigation in order to detect early arterial abnormalities. Arterial stiffness and its consequences represent the great challenge of the twenty-first century for

  3. Fitness as a determinant of arterial stiffness in healthy adult men: a cross-sectional study.

    PubMed

    Chung, Jinwook; Kim, Milyang; Jin, Youngsoo; Kim, Yonghwan; Hong, Jeeyoung

    2018-01-01

    Fitness is known to influence arterial stiffness. This study aimed to assess differences in cardiorespiratory endurance, muscular strength, and flexibility according to arterial stiffness, based on sex and age. We enrolled 1590 healthy adults (men: 1242, women: 348) who were free of metabolic syndrome. We measured cardiorespiratory endurance in an exercise stress test on a treadmill, muscular strength by a grip test, and flexibility by upper body forward-bends from a standing position. The brachial-ankle pulse wave velocity test was performed to measure arterial stiffness before the fitness test. Cluster analysis was performed to divide the patients into groups with low (Cluster 1) and high (Cluster 2) arterial stiffness. According to the k-cluster analysis results, Cluster 1 included 624 men and 180 women, and Cluster 2 included 618 men and 168 women. Men in the middle-aged group with low arterial stiffness demonstrated higher cardiorespiratory endurance, muscular strength, and flexibility than those with high arterial stiffness. Similarly, among men in the old-aged group, the cardiorespiratory endurance and muscular strength, but not flexibility, differed significantly according to arterial stiffness. Women in both clusters showed similar cardiorespiratory endurance, muscular strength, and flexibility regardless of their arterial stiffness. Among healthy adults, arterial stiffness was inversely associated with fitness in men but not in women. Therefore, fitness seems to be a determinant for arterial stiffness in men. Additionally, regular exercise should be recommended for middle-aged men to prevent arterial stiffness.

  4. Ursodeoxycholic acid treatment is associated with improvement of liver stiffness in cystic fibrosis patients.

    PubMed

    van der Feen, Cathelijne; van der Doef, Hubert P J; van der Ent, Cornelis K; Houwen, Roderick H J

    2016-11-01

    Ursodeoxycholic acid (UDCA) might prevent progression of cystic fibrosis liver disease, but objective parameters for its effect are lacking. We used liver stiffness measurements to evaluate the effect of Ursodeoxycholic acid. Paired measurements of liver stiffness were done in 73 patients without UDCA and in 32 patients with UDCA. In the latter group, 6 patients had cirrhosis; in 15 patients, UDCA was started based on Colombo criteria, and in 11 patients for other reasons. In patients without UDCA, liver stiffness increased: 0.19 (-0.03 to 0.59)kPa/year. Liver stiffness also increased in patients with cirrhosis: 4.6 (0.67-12.4)kPa/year. In patients who had UDCA based on Colombo criteria, a decrease of liver stiffness was observed: 0.70 (-1.6 to 0.55)kPa/year (P=0.01). In patients on UDCA for other reasons, liver stiffness increased: 0.23 (-0.20 to 0.51)kPa/year. UDCA reduced liver stiffness in patients with well-defined, mild liver disease. Copyright © 2016 European Cystic Fibrosis Society. Published by Elsevier B.V. All rights reserved.

  5. Aortic propagation velocity does not correlate with classical aortic stiffness parameters in healthy individuals.

    PubMed

    Arı, Hatem; Kahraman, Fatih; Türker, Yasin; Güler, Serdar; Baş, Hasan Aydın; Erdoğan, Doğan

    2017-10-30

    Aortic stiffness is an important cardiovascular risk marker, which can be determined using different noninvasive techniques. Aortic propagation velocity (APV) has recently been established as a novel echocardiographic parameter of aortic stiffness. This study aimed to investigate the association between APV and the classical echocardiography-derived aortic stiffness parameters, aortic distensibility (AD) and aortic strain (AS), in a group of otherwise healthy individuals. In total, 97 consecutive healthy subjects were recruited in this observational study. APV was measured using color M-mode echocardiography from the suprasternal window in the descending aorta. AS and AD were calculated using clinical blood pressure and the M-mode echocardiography-derived aortic diameters. Correlation analyses were performed between cardiovascular risk factors related to increased aortic stiffness (age, obesity, and blood pressure) and measured stiffness parameters (APV, AS, and AD). Correlation analyses were also performed among the measured stiffness parameters. Good correlation of age, blood pressure, and BMI with AS and AD was observed. One-on-one correlation of age, blood pressure, and BMI with APV was not observed. No correlation was observed between APV and AS (r=-0.05, p=0.6) or between APV and AD (r=-0.17, p=0.8). Although APV has been proposed as a novel and practical echocardiographic parameter of aortic stiffness, especially in patients with coronary artery disease, correlations between classical stiffness parameters (AS and AD) and APV were absent in healthy individuals at low-intermediate risk. The clinical and research applicability of APV should be further evaluated.

  6. Acute pressure changes in the brain are correlated with MR elastography stiffness measurements: initial feasibility in an in vivo large animal model.

    PubMed

    Arani, Arvin; Min, Hoon-Ki; Fattahi, Nikoo; Wetjen, Nicholas M; Trzasko, Joshua D; Manduca, Armando; Jack, Clifford R; Lee, Kendall H; Ehman, Richard L; Huston, John

    2018-02-01

    The homeostasis of intracranial pressure (ICP) is of paramount importance for maintaining normal brain function. A noninvasive technique capable of making direct measurements of ICP currently does not exist. MR elastography (MRE) is capable of noninvasively measuring brain tissue stiffness in vivo, and may act as a surrogate to measure ICP. The objective of this study was to investigate the impact of changing ICP on brain stiffness using MRE in a swine model. Baseline MRE measurements were obtained, and then catheters were surgically placed into the left and right lateral ventricles of three animals. ICP was systematically increased over the range of 0 to 55 millimeters mercury (mmHg), and stiffness measurements were made using brain MRE at vibration frequencies of 60 hertz (Hz), 90 Hz, 120 Hz, and 150 Hz. A significant linear correlation between stiffness and ICP in the cross-subject comparison was observed for all tested vibrational frequencies (P ≤ 0.01). The 120 Hz (0.030 ± 0.004 kilopascal (kPa)/mmHg, P < 0.0001) and 150 Hz (0.031 ± 0.008 kPa/mmHg, P = 0.01) vibrational frequencies had nearly identical slopes, which were approximately two- to three-fold higher than the 90 Hz (0.017 ± 0.002 kPa/mmHg, P < 0.0001) and 60 Hz (0.009 ± 0.002 kPa/mmHg, P = 0.001) slopes, respectively. In this study, MRE demonstrated the potential for noninvasive measurement of changes in ICP. Magn Reson Med 79:1043-1051, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley

  7. PNPLA3 rs738409 polymorphism is associated with liver fibrosis progression in patients with chronic hepatitis C: A repeated measures study.

    PubMed

    Jiménez-Sousa, María Ángeles; Gómez-Moreno, Ana Zaida; Pineda-Tenor, Daniel; Sánchez-Ruano, Juan José; Fernández-Rodríguez, Amanda; Artaza-Varasa, Tomas; Gómez-Sanz, Alicia; Martín-Vicente, María; Vázquez-Morón, Sonia; Resino, Salvador

    2018-06-01

    Host genetic background has been associated with liver fibrosis progression. To analyze the association between the patatin-like phospholipase domain-containing 3 (PNPLA3) rs738409 polymorphism and liver fibrosis progression in hepatitis C virus (HCV)-infected patients. In this retrospective cohort study, 187 patients with chronic HCV infection were included, who had at least two liver stiffness measurements (LSM) by transient elastography during the follow-up. Results were expressed in kilopascals (kPa). The analysis of genetic association was carried out according to additive model by using Generalized Linear Models. No patients had advanced fibrosis/cirrhosis at baseline. During a median follow-up time of 47.9 months, 15 patients developed advanced fibrosis and 17 cirrhosis. In multivariate analysis adjusted by the main clinical and epidemiological covariates, the rs738409 G allele was related to higher increase of LSM values during the follow-up (adjusted arithmetic mean ratio (aAMR) = 1.16 (95%CI = 1.04; 1.29); p = .006) and higher odds of having progression to advanced fibrosis [aOR = 2.03 (95%CI = 1.01; 4.06); p = .045], and progression to cirrhosis [aOR = 3.03 (95%CI = 1.26; 7.30); p = .014]. PNPLA3 rs738409 polymorphism appears to be related to the increased progression of liver fibrosis in HCV infected patients. Copyright © 2018 Elsevier B.V. All rights reserved.

  8. Vertical stiffness is not related to anterior cruciate ligament elongation in professional rugby union players.

    PubMed

    Serpell, Benjamin G; Scarvell, Jennie M; Pickering, Mark R; Ball, Nick B; Perriman, Diana; Warmenhoven, John; Smith, Paul N

    2016-01-01

    Novel research surrounding anterior cruciate ligament (ACL) injury is necessary because ACL injury rates have remained unchanged for several decades. An area of ACL risk mitigation which has not been well researched relates to vertical stiffness. The relationship between increased vertical stiffness and increased ground reaction force suggests that vertical stiffness may be related to ACL injury risk. However, given that increased dynamic knee joint stability has been shown to be associated with vertical stiffness, it is possible that modification of vertical stiffness could help to protect against injury. We aimed to determine whether vertical stiffness is related to measures known to load, or which represent loading of, the ACL. This was a cross-sectional observational study of 11 professional Australian rugby players. Knee kinematics and ACL elongation were measured from a 4-dimensional model of a hopping task which simulated the change of direction manoeuvre typically observed when non-contact ACL injury occurs. The model was generated from a CT scan of the participant's knee registered frame by frame to fluoroscopy images of the hopping task. Vertical stiffness was calculated from force plate data. There was no association found between vertical stiffness and anterior tibial translation (ATT) or ACL elongation (r=-0.05; p=0.89, and r=-0.07; p=0.83, respectively). ATT was related to ACL elongation (r=0.93; p=0.0001). Vertical stiffness was not associated with ACL loading in this cohort of elite rugby players but a novel method for measuring ACL elongation in vivo was found to have good construct validity.

  9. Matrix Stiffness Corresponding to Strictured Bowel Induces a Fibrogenic Response in Human Colonic Fibroblasts

    PubMed Central

    Johnson, Laura A.; Rodansky, Eva S.; Sauder, Kay L.; Horowitz, Jeffrey C.; Mih, Justin D.; Tschumperlin, Daniel J.; Higgins, Peter D.

    2013-01-01

    Background Crohn’s disease is characterized by repeated cycles of inflammation and mucosal healing which ultimately progress to intestinal fibrosis. This inexorable progression towards fibrosis suggests that fibrosis becomes inflammation-independent and auto-propagative. We hypothesized that matrix stiffness regulates this auto-propagation of intestinal fibrosis. Methods The stiffness of fresh ex vivo samples from normal human small intestine, Crohn’s disease strictures, and the unaffected margin were measured with a microelastometer. Normal human colonic fibroblasts were cultured on physiologically normal or pathologically stiff matrices corresponding to the physiological stiffness of normal or fibrotic bowel. Cellular response was assayed for changes in cell morphology, α-smooth muscle actin (αSMA) staining, and gene expression. Results Microelastometer measurements revealed a significant increase in colonic tissue stiffness between normal human colon and Crohn’s strictures as well as between the stricture and adjacent tissue margin. In Ccd-18co cells grown on stiff matrices corresponding to Crohn’s strictures, cellular proliferation increased. Pathologic stiffness induced a marked change in cell morphology and increased αSMA protein expression. Growth on a stiff matrix induced fibrogenic gene expression, decreased matrix metalloproteinase and pro-inflammatory gene expression, and was associated with nuclear localization of the transcriptional cofactor MRTF-A. Conclusions Matrix stiffness, representative of the pathological stiffness of Crohn’s strictures, activates human colonic fibroblasts to a fibrogenic phenotype. Matrix stiffness affects multiple pathways suggesting the mechanical properties of the cellular environment are critical to fibroblast function and may contribute to autopropagation of intestinal fibrosis in the absence of inflammation, thereby contributing to the intractable intestinal fibrosis characteristic of Crohn’s disease. PMID

  10. Key Insights into Hand Biomechanics: Human Grip Stiffness Can Be Decoupled from Force by Cocontraction and Predicted from Electromyography

    PubMed Central

    Höppner, Hannes; Große-Dunker, Maximilian; Stillfried, Georg; Bayer, Justin; van der Smagt, Patrick

    2017-01-01

    We investigate the relation between grip force and grip stiffness for the human hand with and without voluntary cocontraction. Apart from gaining biomechanical insight, this issue is particularly relevant for variable-stiffness robotic systems, which can independently control the two parameters, but for which no clear methods exist to design or efficiently exploit them. Subjects were asked in one task to produce different levels of force, and stiffness was measured. As expected, this task reveals a linear coupling between force and stiffness. In a second task, subjects were then asked to additionally decouple stiffness from force at these force levels by using cocontraction. We measured the electromyogram from relevant groups of muscles and analyzed the possibility to predict stiffness and force. Optical tracking was used for avoiding wrist movements. We found that subjects were able to decouple grip stiffness from force when using cocontraction on average by about 20% of the maximum measured stiffness over all force levels, while this ability increased with the applied force. This result contradicts the force–stiffness behavior of most variable-stiffness actuators. Moreover, we found the thumb to be on average twice as stiff as the index finger and discovered that intrinsic hand muscles predominate our prediction of stiffness, but not of force. EMG activity and grip force allowed to explain 72 ± 12% of the measured variance in stiffness by simple linear regression, while only 33 ± 18% variance in force. Conclusively the high signal-to-noise ratio and the high correlation to stiffness of these muscles allow for a robust and reliable regression of stiffness, which can be used to continuously teleoperate compliance of modern robotic hands. PMID:28588472

  11. Finding trap stiffness of optical tweezers using digital filters.

    PubMed

    Almendarez-Rangel, Pedro; Morales-Cruzado, Beatriz; Sarmiento-Gómez, Erick; Pérez-Gutiérrez, Francisco G

    2018-02-01

    Obtaining trap stiffness and calibration of the position detection system is the basis of a force measurement using optical tweezers. Both calibration quantities can be calculated using several experimental methods available in the literature. In most cases, stiffness determination and detection system calibration are performed separately, often requiring procedures in very different conditions, and thus confidence of calibration methods is not assured due to possible changes in the environment. In this work, a new method to simultaneously obtain both the detection system calibration and trap stiffness is presented. The method is based on the calculation of the power spectral density of positions through digital filters to obtain the harmonic contributions of the position signal. This method has the advantage of calculating both trap stiffness and photodetector calibration factor from the same dataset in situ. It also provides a direct method to avoid unwanted frequencies that could greatly affect calibration procedure, such as electric noise, for example.

  12. Scaling of the flow-stiffness relationship in weakly correlated single fractures

    NASA Astrophysics Data System (ADS)

    Petrovitch, Christopher L.

    critical regime. From this, a scaling function was defined for the hydromechanical coupling. This scaling function provides the link between fluid flow and fracture specific stiffness so that seismic waves may be used to remotely probe the hydraulic properties of fractures. Then, the DG method is shown to be capable of measuring such fracture specific stiffnesses by numerically measuring the velocity of interface waves when propagated across laboratory measured fracture geometries of Austin Chalk.

  13. Lower Extremity Stiffness Changes following Concussion in Collegiate Football Players

    PubMed Central

    DuBose, Dominique F.; Herman, Daniel C.; Jones, Debi L.; Tillman, Susan M.; Clugston, James R.; Pass, Anthony; Hernandez, Jorge A.; Vasilopoulos, Terrie; Horodyski, MaryBeth; Chmielewski, Terese L.

    2016-01-01

    Purpose Recent research indicates that a concussion increases risk of musculoskeletal injury. Neuromuscular changes following concussion might contribute to the increased risk of injury. Many studies have examined gait post-concussion, but few studies have examined more demanding tasks. This study compared changes in stiffness across the lower extremity, a measure of neuromuscular function, during a jump-landing task in athletes with a concussion (CONC) to uninjured athletes (UNINJ). Methods Division I football players (13 CONC, 26 UNINJ) were tested pre- and post-season. A motion-capture system recorded subjects jumping on one limb from a 25.4 cm step onto a force plate. Hip, knee, and ankle joint stiffness were calculated from initial contact to peak joint flexion using the regression line slopes of the joint moment versus joint angle plots. Leg stiffness was (peak vertical ground reaction force (PVGRF)/lower extremity vertical displacement) from initial contact to PVGRF. All stiffness values were normalized to bodyweight. Values from both limbs were averaged. General linear models compared group (CONC, UNINJ) differences in the changes of pre- and post-season stiffness values. Results Average time from concussion to post-season testing was 49.9 days. The CONC group showed an increase in hip stiffness (p=0.03), a decrease in knee (p=0.03) and leg stiffness (p=0.03), but no change in ankle stiffness (p=0.65) from pre- to post-season. Conclusion Lower extremity stiffness is altered following concussion, which could contribute to an increased risk of lower extremity injury. These data provide further evidence of altered neuromuscular function after concussion. PMID:27501359

  14. Effects of substitution on the exchange stiffness and magnetization of Co films

    NASA Astrophysics Data System (ADS)

    Eyrich, C.; Zamani, A.; Huttema, W.; Arora, M.; Harrison, D.; Rashidi, F.; Broun, D.; Heinrich, B.; Mryasov, O.; Ahlberg, M.; Karis, O.; Jönsson, P. E.; From, M.; Zhu, X.; Girt, E.

    2014-12-01

    An antiferromagnetically coupled FM/NM/FM (FM = ferromagnet, NM = normal metal) trilayer structure responds to an external magnetic field by the formation of a magnetic-moment spring within the FM layers. We show that the exchange stiffness (Aex) of an FM layer can be determined by fitting the field-dependent magnetization, M (H ) , of the FM/NM/FM trilayer to a micromagnetic model. Using this method, we have measured the exchange stiffness of thin-film Co alloyed with Cr, Fe, Ni, Pd, Pt, and Ru. The results show that the rate at which a substituent element reduces the exchange stiffness is not directly related to its effect on the magnetization of the alloy. The observed trends have been understood by material-specific modeling based on density functional theory within the local density approximation. The stiffness measurements are in agreement with Brillouin light scattering carried out on thicker Co films.

  15. Comparative study of diastolic filling under varying left ventricular wall stiffness

    NASA Astrophysics Data System (ADS)

    Mekala, Pritam; Santhanakrishnan, Arvind

    2014-11-01

    Pathological remodeling of the human cardiac left ventricle (LV) is observed in hypertensive heart failure as a result of pressure overload. Myocardial stiffening occurs in these patients prior to chronic maladaptive changes, resulting in increased LV wall stiffness. The goal of this study was to investigate the change in intraventricular filling fluid dynamics inside a physical model of the LV as a function of wall stiffness. Three LV models of varying wall stiffness were incorporated into an in vitro flow circuit driven by a programmable piston pump. Windkessel elements were used to tune the inflow and systemic pressure in the model with least stiffness to match healthy conditions. Models with stiffer walls were comparatively tested maintaining circuit compliance, resistance and pump amplitude constant. 2D phase-locked PIV measurements along the central plane showed that with increase in wall stiffness, the peak velocity and cardiac output inside the LV decreased. Further, inflow vortex ring propagation toward the LV apex was reduced with increasing stiffness. The above findings indicate the importance of considering LV wall relaxation characteristics in pathological studies of filling fluid dynamics.

  16. Active stiffness and strength in people with unilateral anterior shoulder instability: a bilateral comparison.

    PubMed

    Olds, Margie; McNair, Peter; Nordez, Antoine; Cornu, Christophe

    2011-01-01

    Active muscle stiffness might protect the unstable shoulder from recurrent dislocation. To compare strength and active stiffness in participants with unilateral anterior shoulder instability and to examine the relationship between active stiffness and functional ability. Cross-sectional study. University research laboratory. Participants included 16 males (age range, 16-40 years; height = 179.4 ± 6.1 cm; mass = 79.1 ± 6.8 kg) with 2 or more episodes of unilateral traumatic anterior shoulder instability. Active stiffness and maximal voluntary strength were measured bilaterally in participants. In addition, quality of life, function, and perceived instability were measured using the Western Ontario Stability Index, American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, and Single Alpha Numeric Evaluation, respectively. We found less horizontal adduction strength (t(15) = -4.092, P = .001) and less stiffness at 30% (t(14) = -3.796, P = .002) and 50% (t(12) = -2.341, P = .04) maximal voluntary strength in the unstable than stable shoulder. Active stiffness was not correlated with quality of life, function, or perceived instability (r range, 0.0-0.25; P > .05). The observed reduction in stiffness in the unstable shoulder warrants inclusion of exercises in the rehabilitation program to protect the joint from perturbations that might lead to dislocation. The lack of association between active stiffness and quality of life, function, or perceived instability might indicate that stiffness plays a less direct role in shoulder stability.

  17. Musculoskeletal stiffness changes linearly in response to increasing load during walking gait.

    PubMed

    Caron, Robert R; Lewis, Cara L; Saltzman, Elliot; Wagenaar, Robert C; Holt, Kenneth G

    2015-04-13

    Development of biologically inspired exoskeletons to assist soldiers in carrying load is a rapidly expanding field. Understanding how the body modulates stiffness in response to changing loads may inform the development of these exoskeletons and is the purpose of the present study. Seventeen subjects walked on a treadmill at a constant preferred walking velocity while nine different backpack loading conditions ranging from 12.5% to 40% bodyweight (BW) were introduced in an ascending and then descending order. Kinematic data were collected using Optotrak, a 3D motion analysis system, and used to estimate the position of the center of mass (COM). Two different estimates of stiffness were computed for the stance phase of gait. Both measures of stiffness were positively and linearly related to load magnitudes, with the slopes of the relationships being larger for the descending than the ascending conditions. These results indicate that changes in mechanical stiffness brought about in the musculoskeletal system vary systematically during increases in load to ensure that critical kinematic variables measured in a previous publication remain invariant (Caron et al., 2013). Changes in stiffness and other kinematics measured at the 40% BW condition suggest a boundary in which gait stiffness control limit is reached and a new gait pattern is required. Since soldiers are now carrying up to 96% of body weight, the need for research with even heavier loads is warranted. These findings have implications on the development of exoskeletons to assist in carrying loads. Copyright © 2015 Elsevier Ltd. All rights reserved.

  18. Modifiable Risk Factors for Increased Arterial Stiffness in Outpatient Nephrology

    PubMed Central

    Elewa, Usama; Fernandez-Fernandez, Beatriz; Alegre, Raquel; Sanchez-Niño, Maria D.; Mahillo-Fernández, Ignacio; Perez-Gomez, Maria Vanessa; El-Fishawy, Hussein; Belal, Dawlat; Ortiz, Alberto

    2015-01-01

    Arterial stiffness, as measured by pulse wave velocity (PWV), is an independent predictor of cardiovascular events and mortality. Arterial stiffness increases with age. However, modifiable risk factors such as smoking, BP and salt intake also impact on PWV. The finding of modifiable risk factors may lead to the identification of treatable factors, and, thus, is of interest to practicing nephrologist. We have now studied the prevalence and correlates of arterial stiffness, assessed by PWV, in 191 patients from nephrology outpatient clinics in order to identify modifiable risk factors for arterial stiffness that may in the future guide therapeutic decision-making. PWV was above normal levels for age in 85/191 (44.5%) patients. Multivariate analysis showed that advanced age, systolic BP, diabetes mellitus, serum uric acid and calcium polystyrene sulfonate therapy or calcium-containing medication were independent predictors of PWV. A new parameter, Delta above upper limit of normal PWV (Delta PWV) was defined to decrease the weight of age on PWV values. Delta PWV was calculated as (measured PWV) - (upper limit of the age-adjusted PWV values for the general population). Mean±SD Delta PWV was 0.76±1.60 m/sec. In multivariate analysis, systolic blood pressure, active smoking and calcium polystyrene sulfonate therapy remained independent predictors of higher delta PWV, while age, urinary potassium and beta blocker therapy were independent predictors of lower delta PWV. In conclusion, arterial stiffness was frequent in nephrology outpatients. Systolic blood pressure, smoking, serum uric acid, calcium-containing medications, potassium metabolism and non-use of beta blockers are modifiable factors associated with increased arterial stiffness in Nephrology outpatients. PMID:25880081

  19. Improvement of arthroscopic cartilage stiffness probe using amorphous diamond coating.

    PubMed

    Töyräs, Juha; Korhonen, Rami K; Voutilainen, Tanja; Jurvelin, Jukka S; Lappalainen, Reijo

    2005-04-01

    During arthroscopic evaluation of articular cartilage unstable contact and even slipping of the measurement instrument on the tissue surface may degrade the reproducibility of the measurement. The main aim of the present study was to achieve more stable contact by controlling the friction between articular cartilage surface and the arthroscopic cartilage stiffness probe (Artscan 200, Artscan Oy, Helsinki, Finland) using amorphous diamond (AD) coating. In order to obtain surfaces with different average roughnesses (R(a)), polished stainless steel disks were coated with AD by using the filtered pulsed arc-discharge (FPAD) method. Dynamic coefficient of friction (mu) between the articular cartilage (n = 8) and the coated plates along one non-coated plate was then determined. The friction between AD and cartilage could be controlled over a wide range (mu = 0.027-0.728, p < 0.05, Wilcoxon test) by altering the roughness. Possible deterioration of cartilage was investigated by measuring surface roughness after friction tests and comparing it with the roughness of the adjacent, untested samples (n = 8). Importantly, even testing with the roughest AD (R(a) = 1250 nm) did not damage articular surface. On the basis of the friction measurements, a proper AD coating was selected for the stiffness probe. The performance of coated and non-coated probe was compared by measuring bovine osteochondral samples (n = 22) with both instruments. The reproducibility of the stiffness measurements was significantly better with the AD-coated probe (CV% = 4.7) than with the uncoated probe (CV% = 8.2). To conclude, AD coating can be used to safely control dynamic friction with articular surface. Sufficient friction between articular surface and reference plate of the arthroscopic probe improves significantly reproducibility of the stiffness measurements. (c) 2005 Wiley Periodicals, Inc.

  20. Evaluating the Significance of Viscoelasticity in Diagnosing Early-Stage Liver Fibrosis with Transient Elastography.

    PubMed

    Zhao, Jingxin; Zhai, Fei; Cheng, Jun; He, Qiong; Luo, Jianwen; Yang, Xueping; Shao, Jinhua; Xing, Huichun

    2017-01-01

    Transient elastography quantifies the propagation of a mechanically generated shear wave within a soft tissue, which can be used to characterize the elasticity and viscosity parameters of the tissue. The aim of our study was to combine numerical simulation and clinical assessment to define a viscoelastic index of liver tissue to improve the quality of early diagnosis of liver fibrosis. This is clinically relevant, as early fibrosis is reversible. We developed an idealized two-dimensional axisymmetric finite element model of the liver to evaluate the effects of different viscoelastic values on the propagation characteristics of the shear wave. The diagnostic value of the identified viscoelastic index was verified against the clinical data of 99 patients who had undergone biopsy and routine blood tests for staging of liver disease resulting from chronic hepatitis B infection. Liver stiffness measurement (LSM) and the shear wave attenuation fitting coefficient (AFC) were calculated from the ultrasound data obtained by performing transient elastography. Receiver operating curve analysis was used to evaluate the reliability and diagnostic accuracy of LSM and AFC. Compared to LSM, the AFC provided a higher diagnostic accuracy to differentiate early stages of liver fibrosis, namely F1 and F2 stages, with an overall specificity of 81.48%, sensitivity of 83.33% and diagnostic accuracy of 81.82%. AFC was influenced by the level of LSM, ALT. However, there are no correlation between AFC and Age, BMI, TBIL or DBIL. Quantification of the viscoelasticity of liver tissue provides reliable measurement to identify and differentiate early stages of liver fibrosis.

  1. Evaluating the Significance of Viscoelasticity in Diagnosing Early-Stage Liver Fibrosis with Transient Elastography

    PubMed Central

    Cheng, Jun; He, Qiong; Luo, Jianwen; Yang, Xueping; Shao, Jinhua; Xing, Huichun

    2017-01-01

    Transient elastography quantifies the propagation of a mechanically generated shear wave within a soft tissue, which can be used to characterize the elasticity and viscosity parameters of the tissue. The aim of our study was to combine numerical simulation and clinical assessment to define a viscoelastic index of liver tissue to improve the quality of early diagnosis of liver fibrosis. This is clinically relevant, as early fibrosis is reversible. We developed an idealized two-dimensional axisymmetric finite element model of the liver to evaluate the effects of different viscoelastic values on the propagation characteristics of the shear wave. The diagnostic value of the identified viscoelastic index was verified against the clinical data of 99 patients who had undergone biopsy and routine blood tests for staging of liver disease resulting from chronic hepatitis B infection. Liver stiffness measurement (LSM) and the shear wave attenuation fitting coefficient (AFC) were calculated from the ultrasound data obtained by performing transient elastography. Receiver operating curve analysis was used to evaluate the reliability and diagnostic accuracy of LSM and AFC. Compared to LSM, the AFC provided a higher diagnostic accuracy to differentiate early stages of liver fibrosis, namely F1 and F2 stages, with an overall specificity of 81.48%, sensitivity of 83.33% and diagnostic accuracy of 81.82%. AFC was influenced by the level of LSM, ALT. However, there are no correlation between AFC and Age, BMI, TBIL or DBIL. Quantification of the viscoelasticity of liver tissue provides reliable measurement to identify and differentiate early stages of liver fibrosis. PMID:28107385

  2. Vertical stiffness is not related to anterior cruciate ligament elongation in professional rugby union players

    PubMed Central

    Serpell, Benjamin G; Scarvell, Jennie M; Pickering, Mark R; Ball, Nick B; Perriman, Diana; Warmenhoven, John; Smith, Paul N

    2016-01-01

    Background Novel research surrounding anterior cruciate ligament (ACL) injury is necessary because ACL injury rates have remained unchanged for several decades. An area of ACL risk mitigation which has not been well researched relates to vertical stiffness. The relationship between increased vertical stiffness and increased ground reaction force suggests that vertical stiffness may be related to ACL injury risk. However, given that increased dynamic knee joint stability has been shown to be associated with vertical stiffness, it is possible that modification of vertical stiffness could help to protect against injury. We aimed to determine whether vertical stiffness is related to measures known to load, or which represent loading of, the ACL. Methods This was a cross-sectional observational study of 11 professional Australian rugby players. Knee kinematics and ACL elongation were measured from a 4-dimensional model of a hopping task which simulated the change of direction manoeuvre typically observed when non-contact ACL injury occurs. The model was generated from a CT scan of the participant's knee registered frame by frame to fluoroscopy images of the hopping task. Vertical stiffness was calculated from force plate data. Results There was no association found between vertical stiffness and anterior tibial translation (ATT) or ACL elongation (r=−0.05; p=0.89, and r=−0.07; p=0.83, respectively). ATT was related to ACL elongation (r=0.93; p=0.0001). Conclusions Vertical stiffness was not associated with ACL loading in this cohort of elite rugby players but a novel method for measuring ACL elongation in vivo was found to have good construct validity. PMID:27900192

  3. The effect of short-term isometric training on core/torso stiffness.

    PubMed

    Lee, Benjamin; McGill, Stuart

    2017-09-01

    "Core" exercise is a basic part of many physical training regimens with goals ranging from rehabilitation of spine and knee injuries to improving athletic performance. Core stiffness has been proposed to perform several functions including reducing pain by minimising joint micro-movements, and enhancing strength and speed performance. This study probes the links between a training approach and immediate but temporary changes in stiffness. Passive and active stiffness was measured on 24 participants; 12 having little to no experience in core training (inexperienced), and the other 12 being athletes experienced to core training methods; before and after a 15 min bout of isometric core exercises. Passive stiffness was assessed on a "frictionless" bending apparatus and active stiffness assessed via a quick release mechanism. Short-term isometric core training increased passive and active stiffness in most directions for both inexperienced and experienced participants, passive left lateral bend among experienced participants being the exception (P < 0.05). There was no difference between the inexperienced and experienced groups. The results confirm that the specific isometric training exercise approach tested here can induce immediate changes in core stiffness, in this case following a single session. This may influence performance and injury resilience for a brief period.

  4. Design and Testing of a Dynamically-Tuned Magnetostrictive Spring with Electrically-Controlled Stiffness

    NASA Technical Reports Server (NTRS)

    Scheidler, Justin; Asnani, Vivake M.; Dapino, Marcelo J.

    2015-01-01

    This paper details the development of an electrically-controlled, variable-stiffness spring based on magnetostrictive materials. The device, termed a magnetostrictive Varispring, can be applied as a semi-active vibration isolator or switched stiffness vibration controller for reducing transmitted vibrations. The Varispring is designed using 1D linear models that consider the coupled electrical response, mechanically-induced magnetic diffusion, and the effect of internal mass on dynamic stiffness. Modeling results illustrate that a Terfenol-D-based Varispring has a rise time almost an order of magnitude smaller and a magnetic diffusion cut-off frequency over two orders of magnitude greater than a Galfenol-based Varispring. The results motivate the use of laminated Terfenol-D rods for a greater stiffness tuning range and increased bandwidth. The behavior of a prototype Varispring is examined under vibratory excitation up to 6 MPa and 25 Hz using a dynamic load frame. For this prototype, stiffness is indirectly varied by controlling the excitation current. Preliminary measurements of continuous stiffness tuning via sinusoidal currents up to 1 kHz are presented. The measurements demonstrate that the Young's modulus of the Terfenol-D rod inside the Varispring can be continuously varied by up to 21.9 GPa. The observed stiffness tuning range is relatively constant up to 500 Hz, but significantly decreases thereafter. The stiffness tuning range can be greatly increased by improving the current and force control such that a more consistent current can be applied and the Varispring can be accurately tested at a more optimal bias stress.

  5. Real time shear wave elastography in chronic liver diseases: Accuracy for predicting liver fibrosis, in comparison with serum markers

    PubMed Central

    Jeong, Jae Yoon; Kim, Tae Yeob; Sohn, Joo Hyun; Kim, Yongsoo; Jeong, Woo Kyoung; Oh, Young-Ha; Yoo, Kyo-Sang

    2014-01-01

    AIM: To evaluate the correlation between liver stiffness measurement (LSM) by real-time shear wave elastography (SWE) and liver fibrosis stage and the accuracy of LSM for predicting significant and advanced fibrosis, in comparison with serum markers. METHODS: We consecutively analyzed 70 patients with various chronic liver diseases. Liver fibrosis was staged from F0 to F4 according to the Batts and Ludwig scoring system. Significant and advanced fibrosis was defined as stage F ≥ 2 and F ≥ 3, respectively. The accuracy of prediction for fibrosis was analyzed using receiver operating characteristic curves. RESULTS: Seventy patients, 15 were belonged to F0-F1 stage, 20 F2, 13 F3 and 22 F4. LSM was increased with progression of fibrosis stage (F0-F1: 6.77 ± 1.72, F2: 9.98 ± 3.99, F3: 15.80 ± 7.73, and F4: 22.09 ± 10.09, P < 0.001). Diagnostic accuracies of LSM for prediction of F ≥ 2 and F ≥ 3 were 0.915 (95%CI: 0.824-0.968, P < 0.001) and 0.913 (95%CI: 0.821-0.967, P < 0.001), respectively. The cut-off values of LSM for prediction of F ≥ 2 and F ≥ 3 were 8.6 kPa with 78.2% sensitivity and 93.3% specificity and 10.46 kPa with 88.6% sensitivity and 80.0% specificity, respectively. However, there were no significant differences between LSM and serum hyaluronic acid and type IV collagen in diagnostic accuracy. CONCLUSION: SWE showed a significant correlation with the severity of liver fibrosis and was useful and accurate to predict significant and advanced fibrosis, comparable with serum markers. PMID:25320528

  6. Serial combination of non-invasive tools improves the diagnostic accuracy of severe liver fibrosis in patients with NAFLD.

    PubMed

    Petta, S; Wong, V W-S; Cammà, C; Hiriart, J-B; Wong, G L-H; Vergniol, J; Chan, A W-H; Di Marco, V; Merrouche, W; Chan, H L-Y; Marra, F; Le-Bail, B; Arena, U; Craxì, A; de Ledinghen, V

    2017-09-01

    The accuracy of available non-invasive tools for staging severe fibrosis in patients with nonalcoholic fatty liver disease (NAFLD) is still limited. To assess the diagnostic performance of paired or serial combination of non-invasive tools in NAFLD patients. We analysed data from 741 patients with a histological diagnosis of NAFLD. The GGT/PLT, APRI, AST/ALT, BARD, FIB-4, and NAFLD Fibrosis Score (NFS) scores were calculated according to published algorithms. Liver stiffness measurement (LSM) was performed by FibroScan. LSM, NFS and FIB-4 were the best non-invasive tools for staging F3-F4 fibrosis (AUC 0.863, 0.774, and 0.792, respectively), with LSM having the highest sensitivity (90%), and the highest NPV (94%), and NFS and FIB-4 the highest specificity (97% and 93%, respectively), and the highest PPV (73% and 79%, respectively). The paired combination of LSM or NFS with FIB-4 strongly reduced the likelihood of wrongly classified patients (ranging from 2.7% to 2.6%), at the price of a high uncertainty area (ranging from 54.1% to 58.2%), and of a low overall accuracy (ranging from 43% to 39.1%). The serial combination with the second test used in patients in the grey area of the first test and in those with high LSM values (>9.6 KPa) or low NFS or FIB-4 values (<-1.455 and <1.30, respectively) overall increased the diagnostic performance generating an accuracy ranging from 69.8% to 70.1%, an uncertainty area ranging from 18.9% to 20.4% and a rate of wrong classification ranging from 9.2% to 11.3%. The serial combination of LSM with FIB-4/NFS has a good diagnostic accuracy for the non-invasive diagnosis of severe fibrosis in NAFLD. © 2017 John Wiley & Sons Ltd.

  7. Real time shear wave elastography in chronic liver diseases: accuracy for predicting liver fibrosis, in comparison with serum markers.

    PubMed

    Jeong, Jae Yoon; Kim, Tae Yeob; Sohn, Joo Hyun; Kim, Yongsoo; Jeong, Woo Kyoung; Oh, Young-Ha; Yoo, Kyo-Sang

    2014-10-14

    To evaluate the correlation between liver stiffness measurement (LSM) by real-time shear wave elastography (SWE) and liver fibrosis stage and the accuracy of LSM for predicting significant and advanced fibrosis, in comparison with serum markers. We consecutively analyzed 70 patients with various chronic liver diseases. Liver fibrosis was staged from F0 to F4 according to the Batts and Ludwig scoring system. Significant and advanced fibrosis was defined as stage F ≥ 2 and F ≥ 3, respectively. The accuracy of prediction for fibrosis was analyzed using receiver operating characteristic curves. Seventy patients, 15 were belonged to F0-F1 stage, 20 F2, 13 F3 and 22 F4. LSM was increased with progression of fibrosis stage (F0-F1: 6.77 ± 1.72, F2: 9.98 ± 3.99, F3: 15.80 ± 7.73, and F4: 22.09 ± 10.09, P < 0.001). Diagnostic accuracies of LSM for prediction of F ≥ 2 and F ≥ 3 were 0.915 (95%CI: 0.824-0.968, P < 0.001) and 0.913 (95%CI: 0.821-0.967, P < 0.001), respectively. The cut-off values of LSM for prediction of F ≥ 2 and F ≥ 3 were 8.6 kPa with 78.2% sensitivity and 93.3% specificity and 10.46 kPa with 88.6% sensitivity and 80.0% specificity, respectively. However, there were no significant differences between LSM and serum hyaluronic acid and type IV collagen in diagnostic accuracy. SWE showed a significant correlation with the severity of liver fibrosis and was useful and accurate to predict significant and advanced fibrosis, comparable with serum markers.

  8. Concurrent use of methotrexate and celecoxib increases risk of silent liver fibrosis in rheumatoid arthritis patients with subclinical reduced kidney function.

    PubMed

    Park, Jin Su; Park, Min-Chan; Park, Yong-Beom; Lee, Soo-Kon; Lee, Sang-Won

    2014-01-01

    We evaluated the effects of concurrent use of methotrexate and celecoxib on silent liver and kidney damages in rheumatoid arthritis (RA) patients. We enrolled 92 RA patients with normal laboratory results related to liver and kidney functions, who had received methotrexate and celecoxib concurrently over 6 months. Liver stiffness measurement (LSM) using transient elastography and ultrasonography were performed along with blood and urine tests. Estimated glomerular filtration rate (eGFR) was calculated by both the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and the Modification of Diet in Renal Disease (MDRD) equations. Initial eGFR represented kidney function at the time of the initiation of celecoxib. The cutoff for abnormal LSM values was adopted as 5.3 kPa. The optimal cutoff of each eGFR for abnormal LSM values was also calculated. The median age of patients was 55 years old (74 women). The median LSM was 4.4 kPa and the median eGFRs and median initial eGFRs ranged from 89 to 99 mL/min/1.73 m(2). The cumulative doses of methotrexate and celecoxib and their concurrent administration duration did not affect LSM values and eGFRs. Both eGFRs were significantly associated with LSM values. Patients with initial eGFR(CKD-EPI), initial eGFR(MDRD), and eGFR(CKD-EPI) below each optimal cutoff had significantly high risks for silent liver fibrosis (RR 9.4, 10.3, and 4.4, p < 0.001, respectively). Both initial eGFRs (CKD-EPI and MDRD) and eGFR (CKD-EPI) were significant predictors for the development of silent liver fibrosis in RA patients who had received methotrexate and celecoxib concurrently for at least 6 months.

  9. Structural stiffness identification of bridge superstructures : final report.

    DOT National Transportation Integrated Search

    1996-01-01

    Accurate measures of bridge stiffness are important when determining structural integrity. This information should be an integral part of any comprehensive bridge maintenance program, especially considering the nation's aging infrastructure. Informed...

  10. Gender differences in active musculoskeletal stiffness. Part II. Quantification of leg stiffness during functional hopping tasks.

    PubMed

    Granata, K P; Padua, D A; Wilson, S E

    2002-04-01

    Leg stiffness was compared between age-matched males and females during hopping at preferred and controlled frequencies. Stiffness was defined as the linear regression slope between the vertical center of mass (COM) displacement and ground-reaction forces recorded from a force plate during the stance phase of the hopping task. Results demonstrate that subjects modulated the vertical displacement of the COM during ground contact in relation to the square of hopping frequency. This supports the accuracy of the spring-mass oscillator as a representative model of hopping. It also maintained peak vertical ground-reaction load at approximately three times body weight. Leg stiffness values in males (33.9+/-8.7 kN/m) were significantly (p<0.01) greater than in females (26.3+/-6.5 kN/m) at each of three hopping frequencies, 3.0, 2.5 Hz, and a preferred hopping rate. In the spring-mass oscillator model leg stiffness and body mass are related to the frequency of motion. Thus male subjects necessarily recruited greater leg stiffness to drive their heavier body mass at the same frequency as the lighter female subjects during the controlled frequency trials. However, in the preferred hopping condition the stiffness was not constrained by the task because frequency was self-selected. Nonetheless, both male and female subjects hopped at statistically similar preferred frequencies (2.34+/-0.22 Hz), therefore, the females continued to demonstrate less leg stiffness. Recognizing the active muscle stiffness contributes to biomechanical stability as well as leg stiffness, these results may provide insight into the gender bias in risk of musculoskeletal knee injury.

  11. Sex differences in fat distribution influence the association between BMI and arterial stiffness.

    PubMed

    van den Munckhof, Inge C L; Holewijn, Suzanne; de Graaf, Jacqueline; Rutten, Joost H W

    2017-06-01

    The increase in arterial stiffness in patients with the metabolic syndrome is strongly related to the amount of visceral adipose tissue. In clinical practice, anthropometric measurements such as BMI and waist circumference are commonly used to assess general and abdominal adiposity. Waist circumference is a composite measure of subcutaneous and visceral abdominal adipose tissue. As the distribution of intra-abdominal fat differs between men and women, we investigated the sex-specific associations between different anthropometric measures for general and abdominal obesity with arterial stiffness. A cross-sectional descriptive study was performed in 1517 participants of the Nijmegen Biomedical Study, aged 50-70 years. After measurement of height, waist circumference and hip circumference, the following indices were calculated: BMI, waist-hip ratio and waist-height ratio (WHtR). Arterial stiffness was assessed by measurement of carotid-femoral pulse wave velocity (PWV). The association between the anthropometric indices and vascular stiffness was investigated by linear regression analysis adjusting for the traditional cardiovascular risk factors. BMI, waist circumference, waist-hip ratio and WHtR correlated positively with PWV in univariate analysis both in men and women (all P < 0.016). Hip circumference was only associated with PWV in women (P < 0.001). After adjustment for age and heart rate, waist circumference and WHtR (standardized beta of 0.142 and 0.141, respectively, both P < 0.001) showed the strongest associations with PWV in men, whereas in women only BMI was associated with PWV (standardized beta of 0.177, P < 0.001). In men, WHtR was independently related to increased arterial stiffness, after adjustment for BMI and traditional cardiovascular risk factors. In women, in multivariate analyses, BMI remained significantly positively associated with PWV, whereas WHtR became negatively associated with PWV. Sex-related differences in adipose

  12. Stiffness and force in activated frog skeletal muscle fibers.

    PubMed Central

    Cecchi, G.; Griffiths, P. J.; Taylor, S.

    1986-01-01

    Single fibers, isolated intact from frog skeletal muscles, were held firmly very near to each end by stiff metal clasps fastened to the tendons. The fibers were then placed horizontally between two steel hooks inserted in eyelets of the tendon clasps. One hook was attached to a capacitance gauge force transducer (resonance frequency up to approximately 50 kHz) and the other was attached to a moving-coil length changer. This allowed us to impose small, rapid releases (complete in less than 0.15 ms) and high frequency oscillations (up to 13 kHz) to one end of a resting or contracting fiber and measure the consequences at the other end with fast time resolution at 4 to 6 degrees C. The stiffness of short fibers (1.8-2.6 mm) was determined directly from the ratio of force to length variations produced by the length changer. The resonance frequency of short fibers was so high (approximately 40 kHz) that intrinsic oscillations were not detectably excited. The stiffness of long fibers, on the other hand, was calculated from measurement of the mechanical resonance frequency of a fiber. Using both short and long fibers, we measured the sinusoids of force at one end of a contracting fiber that were produced by relatively small sinusoidal length changes at the other end. The amplitudes of the sinusoidal length changes were small compared with the size of step changes that produce nonlinear force-extension relations. The sinusoids of force from long fibers changed amplitude and shifted phase with changes in oscillation frequency in a manner expected of a transmission line composed of mass, compliance, and viscosity, similar to that modelled by (Ford, L. E., A. F. Huxley, and R. M. Simmons, 1981, J. Physiol. (Lond.), 311:219-249). A rapid release during the plateau of tetanic tension in short fibers caused a fall in force and stiffness, a relative change in stiffness that putatively was much smaller than that of force. Our results are, for the most part, consistent with the

  13. The Myotonometer: Not a Valid Measurement Tool for Active Hamstring Musculotendinous Stiffness.

    PubMed

    Pamukoff, Derek N; Bell, Sarah E; Ryan, Eric D; Blackburn, J Troy

    2016-05-01

    Hamstring musculotendinous stiffness (MTS) is associated with lower-extremity injury risk (ie, hamstring strain, anterior cruciate ligament injury) and is commonly assessed using the damped oscillatory technique. However, despite a preponderance of studies that measure MTS reliably in laboratory settings, there are no valid clinical measurement tools. A valid clinical measurement technique is needed to assess MTS and permit identification of individuals at heightened risk of injury and track rehabilitation progress. To determine the validity and reliability of the Myotonometer for measuring active hamstring MTS. Descriptive laboratory study. Laboratory. 33 healthy participants (15 men, age 21.33 ± 2.94 y, height 172.03 ± 16.36 cm, mass 74.21 ± 16.36 kg). Hamstring MTS was assessed using the damped oscillatory technique and the Myotonometer. Intraclass correlations were used to determine the intrasession, intersession, and interrater reliability of the Myotonometer. Criterion validity was assessed via Pearson product-moment correlation between MTS measures obtained from the Myotonometer and from the damped oscillatory technique. The Myotonometer demonstrated good intrasession (ICC3,1 = .807) and interrater reliability (ICC2,k = .830) and moderate intersession reliability (ICC2,k = .693). However, it did not provide a valid measurement of MTS compared with the damped oscillatory technique (r = .346, P = .061). The Myotonometer does not provide a valid measure of active hamstring MTS. Although the Myotonometer does not measure active MTS, it possesses good reliability and portability and could be used clinically to measure tissue compliance, muscle tone, or spasticity associated with multiple musculoskeletal disorders. Future research should focus on portable and clinically applicable tools to measure active hamstring MTS in efforts to prevent and monitor injuries.

  14. Inverse relationship between physical activity and arterial stiffness in adults with hypertension.

    PubMed

    O'Donovan, Cuisle; Lithander, Fiona E; Raftery, Tara; Gormley, John; Mahmud, Azra; Hussey, Juliette

    2014-02-01

    Physical activity has beneficial effects on arterial stiffness among healthy adults. There is a lack of data on this relationship in adults with hypertension. The majority of studies which have examined physical activity and arterial stiffness have used subjective measures of activity. The aim of this study was to investigate the relationship between objectively measured habitual physical activity and arterial stiffness in individuals with newly diagnosed essential hypertension. Adults attending an outpatient hypertension clinic were recruited into this cross sectional study. Physical activity was measured using a triaxial accelerometer. Pulse wave velocity (PWV) and augmentation index (AIx) were measured using applanation tonometry. Participant's full lipid profile and glucose were determined through the collection of a fasting blood sample. Fifty-three adults [51(14) years, 26 male] participated, 16 of whom had the metabolic syndrome. Inactivity was positively correlated with PWV (r = .53, P < .001) and AIx (r = .48, P < .001). There were significant inverse associations between habitual physical activity of all intensities and both AIx and PWV. In stepwise regression, after adjusting for potential confounders, physical activity was a significant predictor of AIx and PWV. Habitual physical activity of all intensities is associated with reduced arterial stiffness among adults with hypertension.

  15. Feasibility of using 3D MR elastography to determine pancreatic stiffness in healthy volunteers.

    PubMed

    Shi, Yu; Glaser, Kevin J; Venkatesh, Sudhakar K; Ben-Abraham, Ephraim I; Ehman, Richard L

    2015-02-01

    To evaluate the feasibility of using three-dimensional (3D) MR elastography (MRE) to determine the stiffness of the pancreas in healthy volunteers. Twenty healthy volunteers underwent 1.5 Tesla MRE exams using an accelerated echo planar imaging (EPI) pulse sequence with low-frequency vibrations (40 and 60 Hz). Stiffness was calculated with a 3D direct inversion algorithm. The mean shear stiffness in five pancreatic subregions (uncinate, head, neck, body, and tail) and the corresponding liver stiffness were calculated. The intrasubject coefficient of variation (CV) was calculated as a measure of the reproducibility for each volunteer. The mean shear stiffness (average of values obtained in different pancreatic subregions) was (1.15 ± 0.17) kPa at 40 Hz, and (2.09 ± 0.33) kPa at 60 Hz. The corresponding liver stiffness was higher than the pancreas stiffness at 40 Hz ([1.60 ± 0.21] kPa, mean pancreas-to-liver stiffness ratio: 0.72), but similar at 60Hz ([2.12 ± 0.23) kPa, mean ratio: 0.95). The mean intrasubject CV for each pancreatic subregion was lower at 40 Hz than 60 Hz (P < 0.05 for all subregions, range: 11.9-15.7% at 40 Hz and 16.5-19.6% at 60 Hz). The 3D pancreatic MRE can provide promising and reproducible stiffness measurements throughout the pancreas, with more consistent data acquired at 40 Hz. © 2014 Wiley Periodicals, Inc.

  16. Testosterone deficiency: a determinant of aortic stiffness in men.

    PubMed

    Vlachopoulos, Charalambos; Ioakeimidis, Nikolaos; Miner, Martin; Aggelis, Athanassios; Pietri, Panagiota; Terentes-Printzios, Dimitrios; Tsekoura, Dorothea; Stefanadis, Christodoulos

    2014-03-01

    Low testosterone levels and increased aortic stiffness are predictors of cardiovascular events. The influence of androgen level on the age- and blood pressure-related increase in aortic stiffness is unknown. From January 2007 to June 2011 we enrolled 455 consecutive men with no evidence of cardiovascular disease from a large cohort followed in our Department for arterial function studies. Their total testosterone (TT) levels were measured and carotid-femoral pulse wave velocity (PWVc-f) was measured as an index of aortic stiffness. In multivariable analysis, PWVc-f values were inversely correlated to TT after adjustment for confounders (β = -0.365, P < 0.001). In younger age categories (<50 yrs and 50-59 yrs), patients with testosterone deficiency (TD) had higher blood pressure-adjusted PWVc-f (P < 0.001 and P = 0.005, respectively) compared to subjects with normal TT, indicating an "aging effect" of 10 years, whereas in older age categories such a difference was not observed. Furthermore, in men with a higher mean pressure (102-108 mmHg and >108 mmHg), patients with TD had higher age-adjusted PWVc-f (P < 0.001) compared to subjects with normal TT, indicating a synergistic unfavorable effect of testosterone deficiency and blood pressure on aortic stiffness. TT levels are independently associated with aortic stiffening. The effect of low testosterone concentration on aortic stiffness is more prominent in young men and in subjects with higher blood pressure levels. These findings identify testosterone as a marker of arterial damage with special emphasis on young and hypertensive individuals and support its role as predictor of events. Copyright © 2014. Published by Elsevier Ireland Ltd.

  17. Reduced prosthetic stiffness lowers the metabolic cost of running for athletes with bilateral transtibial amputations.

    PubMed

    Beck, Owen N; Taboga, Paolo; Grabowski, Alena M

    2017-04-01

    Inspired by the springlike action of biological legs, running-specific prostheses are designed to enable athletes with lower-limb amputations to run. However, manufacturer's recommendations for prosthetic stiffness and height may not optimize running performance. Therefore, we investigated the effects of using different prosthetic configurations on the metabolic cost and biomechanics of running. Five athletes with bilateral transtibial amputations each performed 15 trials on a force-measuring treadmill at 2.5 or 3.0 m/s. Athletes ran using each of 3 different prosthetic models (Freedom Innovations Catapult FX6, Össur Flex-Run, and Ottobock 1E90 Sprinter) with 5 combinations of stiffness categories (manufacturer's recommended and ± 1) and heights (International Paralympic Committee's maximum competition height and ± 2 cm) while we measured metabolic rates and ground reaction forces. Overall, prosthetic stiffness [fixed effect (β) = 0.036; P = 0.008] but not height ( P ≥ 0.089) affected the net metabolic cost of transport; less stiff prostheses reduced metabolic cost. While controlling for prosthetic stiffness (in kilonewtons per meter), using the Flex-Run (β = -0.139; P = 0.044) and 1E90 Sprinter prostheses (β = -0.176; P = 0.009) reduced net metabolic costs by 4.3-4.9% compared with using the Catapult prostheses. The metabolic cost of running improved when athletes used prosthetic configurations that decreased peak horizontal braking ground reaction forces (β = 2.786; P = 0.001), stride frequencies (β = 0.911; P < 0.001), and leg stiffness values (β = 0.053; P = 0.009). Remarkably, athletes did not maintain overall leg stiffness across prosthetic stiffness conditions. Rather, the in-series prosthetic stiffness governed overall leg stiffness. The metabolic cost of running in athletes with bilateral transtibial amputations is influenced by prosthetic model and stiffness but not height. NEW & NOTEWORTHY We measured the

  18. Stiffness is more than just duration and severity: a qualitative exploration in people with rheumatoid arthritis

    PubMed Central

    Dures, Emma; Kirwan, John; Pollock, Jon; Baker, Gill; Edmunds, Avis; Hewlett, Sarah

    2015-01-01

    Objective. Stiffness is internationally recognized as an important indicator of inflammatory activity in RA but is poorly understood and difficult to measure. The aim of this study was to explore the experience of stiffness from the patient perspective. Methods. Semi-structured interviews conducted with 16 RA patients were analysed independently by researchers and pat.ient partners using inductive thematic analysis. Results. Six themes were identified. Part of having RA identified stiffness as a normal consequence of RA, perceived as associated with disease-related aspects such as fluctuating disease activity, other RA symptoms and disease duration. Local and widespread highlighted stiffness occurring not only in joints, but also over the whole body, being more widespread during the morning or flare. Linked to behaviour and environment illustrated factors that influence stiffness, including movement, medications and weather. Highly variable captured the fluctuating nature of stiffness within and between patients and in relation to temporality, duration and intensity. Impacts on daily life emphasized the effect of stiffness on a range of domains, including physical function, quality of life, psychological well-being, activities of daily living and participation in work and leisure activities. Requires self-management detailed self-management strategies targeting both the symptom and its consequences. Conclusion. Patients’ experiences of stiffness were varied, complex and not exclusive to the morning period. Importantly, stiffness was reported in terms of impact rather than the traditional measurement concepts of severity or duration. Based on these findings, further research is needed to develop a patient-centred measure that adequately reflects inflammatory activity. PMID:25231178

  19. Hemodynamic and arterial stiffness differences between African-Americans and Caucasians after maximal exercise.

    PubMed

    Yan, Huimin; Ranadive, Sushant M; Heffernan, Kevin S; Lane, Abbi D; Kappus, Rebecca M; Cook, Marc D; Wu, Pei-Tzu; Sun, Peng; Harvey, Idethia S; Woods, Jeffrey A; Wilund, Kenneth R; Fernhall, Bo

    2014-01-01

    African-American (AA) men have higher arterial stiffness and augmentation index (AIx) than Caucasian-American (CA) men. Women have greater age-associated increases in arterial stiffness and AIx than men. This study examined racial and sex differences in arterial stiffness and central hemodynamics at rest and after an acute bout of maximal exercise in young healthy individuals. One hundred young, healthy individuals (28 AA men, 24 AA women, 25 CA men, and 23 CA women) underwent measurements of aortic blood pressure (BP) and arterial stiffness at rest and 15 and 30 min after an acute bout of graded maximal aerobic exercise. Aortic BP and AIx were derived from radial artery applanation tonometry. Aortic stiffness (carotid-femoral) was measured via pulse wave velocity. Aortic stiffness was increased in AA subjects but not in CA subjects (P < 0.05) after an acute bout of maximal cycling exercise, after controlling for body mass index. Aortic BP decreased after exercise in CA subjects but not in AA subjects (P < 0.05). Women exhibited greater reductions in AIx after maximal aerobic exercise compared with men (P < 0.05). In conclusion, race and sex impact vascular and central hemodynamic responses to exercise. Young AA and CA subjects exhibited differential responses in central stiffness and central BP after acute maximal exercise. Premenopausal women had greater augmented pressure at rest and after maximal aerobic exercise than men. Future research is needed to examine the potential mechanisms.

  20. Hemodynamic and arterial stiffness differences between African-Americans and Caucasians after maximal exercise

    PubMed Central

    Ranadive, Sushant M.; Heffernan, Kevin S.; Lane, Abbi D.; Kappus, Rebecca M.; Cook, Marc D.; Wu, Pei-Tzu; Sun, Peng; Harvey, Idethia S.; Woods, Jeffrey A.; Wilund, Kenneth R.; Fernhall, Bo

    2013-01-01

    African-American (AA) men have higher arterial stiffness and augmentation index (AIx) than Caucasian-American (CA) men. Women have greater age-associated increases in arterial stiffness and AIx than men. This study examined racial and sex differences in arterial stiffness and central hemodynamics at rest and after an acute bout of maximal exercise in young healthy individuals. One hundred young, healthy individuals (28 AA men, 24 AA women, 25 CA men, and 23 CA women) underwent measurements of aortic blood pressure (BP) and arterial stiffness at rest and 15 and 30 min after an acute bout of graded maximal aerobic exercise. Aortic BP and AIx were derived from radial artery applanation tonometry. Aortic stiffness (carotid-femoral) was measured via pulse wave velocity. Aortic stiffness was increased in AA subjects but not in CA subjects (P < 0.05) after an acute bout of maximal cycling exercise, after controlling for body mass index. Aortic BP decreased after exercise in CA subjects but not in AA subjects (P < 0.05). Women exhibited greater reductions in AIx after maximal aerobic exercise compared with men (P < 0.05). In conclusion, race and sex impact vascular and central hemodynamic responses to exercise. Young AA and CA subjects exhibited differential responses in central stiffness and central BP after acute maximal exercise. Premenopausal women had greater augmented pressure at rest and after maximal aerobic exercise than men. Future research is needed to examine the potential mechanisms. PMID:24186094

  1. The endogenous fluorescence of fibroblast in collagen gels as indicator of stiffness of the extracellular matrix

    NASA Astrophysics Data System (ADS)

    Padilla-Martinez, J. P.; Ortega-Martinez, A.; Franco, W.

    2016-03-01

    The stiffness or rigidity of the extracellular matrix (ECM) regulates cell response. Established mechanical tests to measure stiffness, such as indentation and tensile tests, are invasive and destructive to the sample. Endogenous or native molecules to cells and ECM components, like tryptophan and cross-links of collagen, display fluorescence upon irradiation with ultraviolet light. Most likely, the concentration of these endogenous fluorophores changes as the stiffness of the ECM changes. In this work we investigate the endogenous fluorescence of collagen gels containing fibroblasts as a non-invasive non-destructive method to measure stiffness of the ECM. Human fibroblast cells were cultured in three-dimensional gels of type I collagen (50,000 cells/ml). This construct is a simple model of tissue contraction. During contraction, changes in the excitation-emission matrix (a fluorescence map in the 240-520/290-530 nm range) of constructs were measured with a spectrofluoremeter, and changes in stiffness were measured with a standard indentation test over 16 days. Results show that a progressive increase in fluorescence of the 290/340 nm excitation-emission pair correlates with a progressive increase in stiffness (r=0.9, α=0.5). The fluorescence of this excitation-emission pair is ascribed to tryptophan and variations in the fluorescence of this pair correlate with cellular proliferation. In this tissue model, the endogenous functional fluorescence of proliferating fibroblast cells is a biomechanical marker of stiffness of the ECM.

  2. Determination of mechanical stiffness of bone by pQCT measurements: correlation with non-destructive mechanical four-point bending test data.

    PubMed

    Martin, Daniel E; Severns, Anne E; Kabo, J M J Michael

    2004-08-01

    Mechanical tests of bone provide valuable information about material and structural properties important for understanding bone pathology in both clinical and research settings, but no previous studies have produced applicable non-invasive, quantitative estimates of bending stiffness. The goal of this study was to evaluate the effectiveness of using peripheral quantitative computed tomography (pQCT) data to accurately compute the bending stiffness of bone. Normal rabbit humeri (N=8) were scanned at their mid-diaphyses using pQCT. The average bone mineral densities and the cross-sectional moments of inertia were computed from the pQCT cross-sections. Bending stiffness was determined as a function of the elastic modulus of compact bone (based on the local bone mineral density), cross-sectional moment of inertia, and simulated quasistatic strain rate. The actual bending stiffness of the bones was determined using four-point bending tests. Comparison of the bending stiffness estimated from the pQCT data and the mechanical bending stiffness revealed excellent correlation (R2=0.96). The bending stiffness from the pQCT data was on average 103% of that obtained from the four-point bending tests. The results indicate that pQCT data can be used to accurately determine the bending stiffness of normal bone. Possible applications include temporal quantification of fracture healing and risk management of osteoporosis or other bone pathologies.

  3. Leg stiffness and stride frequency in human running.

    PubMed

    Farley, C T; González, O

    1996-02-01

    When humans and other mammals run, the body's complex system of muscle, tendon and ligament springs behaves like a single linear spring ('leg spring'). A simple spring-mass model, consisting of a single linear leg spring and a mass equivalent to the animal's mass, has been shown to describe the mechanics of running remarkably well. Force platform measurements from running animals, including humans, have shown that the stiffness of the leg spring remains nearly the same at all speeds and that the spring-mass system is adjusted for higher speeds by increasing the angle swept by the leg spring. The goal of the present study is to determine the relative importance of changes to the leg spring stiffness and the angle swept by the leg spring when humans alter their stride frequency at a given running speed. Human subjects ran on treadmill-mounted force platform at 2.5ms-1 while using a range of stride frequencies from 26% below to 36% above the preferred stride frequency. Force platform measurements revealed that the stiffness of the leg spring increased by 2.3-fold from 7.0 to 16.3 kNm-1 between the lowest and highest stride frequencies. The angle swept by the leg spring decreased at higher stride frequencies, partially offsetting the effect of the increased leg spring stiffness on the mechanical behavior of the spring-mass system. We conclude that the most important adjustment to the body's spring system to accommodate higher stride frequencies is that leg spring becomes stiffer.

  4. Effects of passive muscle stiffness measured by Shear Wave Elastography, muscle thickness, and body mass index on athletic performance in adolescent female basketball players.

    PubMed

    Akkoc, Orkun; Caliskan, Emine; Bayramoglu, Zuhal

    2018-05-02

    Athletic performance in basketball comprises the contributions of anaerobic and aerobic performance. The aim was to investigate the effects of passive muscle stiffness, using shear wave elastography (SWE), as well as muscle thickness, and body mass index (BMI), on both aerobic and anaerobic performances in adolescent female basketball players.Material and methods: Anaerobic and aerobic (VO2max) performance was assessed using the vertical jump and shuttle run tests, respectively, in 24 volunteer adolescent female basketball players. Passive muscle stiffness of the rectus femoris (RF), gastrocnemius medialis (GM), gastrocnemius lateralis (GL) and soleus muscles were measured by SWE, and the thickness of each muscle was assessed by gray scale ultrasound. The BMI of each participant was also calculated. The relationship between vertical jump and VO2max values, and those of muscle stiffness, thickness, and BMI were investigated via Pearson's correlation and multivariate linear regression analysis. No significant correlation was observed between muscle stiffness and VO2max or vertical jump (p>0.05). There was significant negative correlation between GL thickness and VO2max (p=0.026), and soleus thickness and VO2max (p=0.046). There was also a significant negative correlation between BMI and VO2max (p=0.001). Conclusions: This preliminary work can be a reference for future research. Although our article indicates that passive muscle stiffness measured by SWE is not directly related to athletic performance, future comprehensive studies should be performed in order to illuminate the complex nature of muscles. The  maintenance of lower muscle thickness and optimal BMI may be associated with better aerobic performance.

  5. Gait training reduces ankle joint stiffness and facilitates heel strike in children with Cerebral Palsy.

    PubMed

    Willerslev-Olsen, Maria; Lorentzen, Jakob; Nielsen, Jens Bo

    2014-01-01

    Foot drop and toe walking are frequent concerns in children with cerebral palsy (CP). Increased stiffness of the ankle joint muscles may contribute to these problems. Does four weeks of daily home based treadmill training with incline reduce ankle joint stiffness and facilitate heel strike in children with CP? Seventeen children with CP (4-14 years) were recruited. Muscle stiffness and gait ability were measured twice before and twice after training with an interval of one month. Passive and reflex-mediated stiffness were measured by a dynamometer which applied stretches below and above reflex threshold. Gait kinematics were recorded by 3-D video-analysis during treadmill walking. Foot pressure was measured by force-sensitive foot soles during treadmill and over-ground walking. Children with increased passive stiffness showed a significant reduction in stiffness following training (P = 0.01). Toe lift in the swing phase (P = 0.014) and heel impact (P = 0.003) increased significantly following the training during both treadmill and over-ground walking. Daily intensive gait training may influence the elastic properties of ankle joint muscles and facilitate toe lift and heel strike in children with CP. Intensive gait training may be beneficial in preventing contractures and maintain gait ability in children with CP.

  6. In vivo distribution of spinal intervertebral stiffness based on clinical flexibility tests.

    PubMed

    Lafon, Yoann; Lafage, Virginie; Steib, Jean-Paul; Dubousset, Jean; Skalli, Wafa

    2010-01-15

    A numerical study was conducted to identify the intervertebral stiffness of scoliotic spines from spinal flexibility tests. To study the intervertebral 3-dimensional (3D) stiffness distribution along scoliotic spine. Few methods have been reported in literature to quantify the in vivo 3D intervertebral stiffness of the scoliotic spine. Based on the simulation of flexibility tests, these methods were operator-dependent and could yield to clinically irrelevant stiffnesses. This study included 30 patients surgically treated for severe idiopathic scoliosis. A previously validated trunk model, with patient-specific geometry, was used to simulate bending tests according to the in vivo displacements of T1 and L5 measured from bending test radiographs. Differences between in vivo and virtual spinal behaviors during bending tests (left and right) were computed in terms of vertebral rotations and translation. An automated method, driven by a priori knowledge, identified intervertebral stiffnesses in order to reproduce the in vivo spinal behavior. Because of the identification of intervertebral stiffnesses, differences between in vivo and virtual spinal displacements were drastically reduced (95% of the differences less than +/-3 mm for vertebral translation). Intervertebral stiffness distribution after identification was analyzed. On convex side test, the intervertebral stiffness of the compensatory curves increased in most cases, whereas the major curve became more flexible. Stiffness singularities were found in junctional zones: these specific levels were predominantly flexible, both in torsion and in lateral bending. The identification of in vivo intervertebral stiffness may improve our understanding of scoliotic spine and the relevance of patient-specific methods for surgical planning.

  7. Cardiovascular Health and Arterial Stiffness: The Maine Syracuse Longitudinal Study

    PubMed Central

    Crichton, Georgina E; Elias, Merrill F; Robbins, Michael A

    2014-01-01

    Ideal cardiovascular health is a recently defined construct by the American Heart Association (AHA) to promote cardiovascular disease reduction. Arterial stiffness is a major risk factor for cardiovascular disease. The extent to which the presence of multiple prevalent cardiovascular risk factors and health behaviors is associated with arterial stiffness is unknown. The aim of this study was to examine the association between the AHA construct of cardiovascular health and arterial stiffness, as indexed by pulse wave velocity and pulse pressure. The AHA health metrics, comprising of four health behaviors (smoking, body mass index, physical activity, and diet) and three health factors (total cholesterol, blood pressure, and fasting plasma glucose) were evaluated among 505 participants in the Maine-Syracuse Longitudinal Study. Outcome measures were carotid-femoral pulse wave velocity (PWV) and pulse pressure measured at 4 to 5-year follow-up. Better cardiovascular health, comprising both health factors and behaviors, was associated with lower arterial stiffness, as indexed by pulse wave velocity and pulse pressure. Those with at least five health metrics at ideal levels had significantly lower PWV (9.8 m/s) than those with two or less ideal health metrics (11.7 m/s) (P<0.001). This finding remained with the addition of demographic and PWV-related variables (P=0.004). PMID:24384629

  8. Cardiovascular health and arterial stiffness: the Maine-Syracuse Longitudinal Study.

    PubMed

    Crichton, G E; Elias, M F; Robbins, M A

    2014-07-01

    Ideal cardiovascular health is a recently defined construct by the American Heart Association (AHA) to promote cardiovascular disease reduction. Arterial stiffness is a major risk factor for cardiovascular disease. The extent to which the presence of multiple prevalent cardiovascular risk factors and health behaviors is associated with arterial stiffness is unknown. The aim of this study was to examine the association between the AHA construct of cardiovascular health and arterial stiffness, as indexed by pulse wave velocity (PWV) and pulse pressure. The AHA health metrics, comprising of four health behaviors (smoking, body mass index, physical activity and diet) and three health factors (total cholesterol, blood pressure and fasting plasma glucose), were evaluated among 505 participants in the Maine-Syracuse Longitudinal Study. Outcome measures were carotid-femoral PWV and pulse pressure measured at 4- to 5-year follow-up. Better cardiovascular health, comprising both health factors and behaviors, was associated with lower arterial stiffness, as indexed by PWV and pulse pressure. Those with at least five health metrics at ideal levels had significantly lower PWV (9.8 m s(-1)) than those with two or less ideal health metrics (11.7 m s(-1)) (P < 0.001). This finding remained with the addition of demographic and PWV-related variables (P = 0.004).

  9. [Odontoid bending stiffness after anterior fixation with a single lag screw: biomechanical study].

    PubMed

    Buchvald, P; Čapek, L; Barsa, P

    2015-01-01

    PURPOSE OF THE STUDY The aim of the experiment was to compare the bending stiffness of an intact odontoid process with bending stiffness after its simulated type II fracture was fixed with a single lag screw. The experiment was done with a desire to answer the question of whether a single osteosynthetic screw is sufficient for good fixation of a type II odontoid fracture. MATERIAL AND METHODS The C2 vertebrae of six cadavers were used. With simultaneous measurement of odontoid bending stiffness, the occurrence of a fracture (type IIA, Grauer's modification of the Anderson- D'Alonzo classification) was simulated using action exerted by a tearing machine in the direction perpendicular to the odontoid axis. Each odontoid fracture was subsequently treated by direct osteosynthesis with a single lag screw inserted in the axial direction by a standard surgical procedure in order to provide conditions similar to those achieved by routine surgical management. The treated odontoid process was subsequently subjected to the same tearing machine loading as applied to it at the start of the experiment. The bending stiffness measured was then compared with that found before the fracture occurred. The results were statistically evaluated by the t-test for paired samples at the level of significance α = 0.05. RESULTS The average value of bending stiffness for odontoid processes of intact vertebrae at the moment of fracture occurrence was 318.3 N/mm. After single axial lag screw fixation of the fracture, the average bending stiffness for the odontoid processes treated was 331.3 N/mm. DISCUSSION Higher values of bending stiffness after screw fixation were found in all specimens and, in comparison with the values recorded before simulated fractures, the increase was statistically significant. CONCLUSIONS The results of our measurements suggest that the single lag screw fixation of a type IIA odontoid fracture will provide better stability for the fracture fragment-C2 body complex on

  10. Linear Parameter Varying Identification of Dynamic Joint Stiffness during Time-Varying Voluntary Contractions

    PubMed Central

    Golkar, Mahsa A.; Sobhani Tehrani, Ehsan; Kearney, Robert E.

    2017-01-01

    Dynamic joint stiffness is a dynamic, nonlinear relationship between the position of a joint and the torque acting about it, which can be used to describe the biomechanics of the joint and associated limb(s). This paper models and quantifies changes in ankle dynamic stiffness and its individual elements, intrinsic and reflex stiffness, in healthy human subjects during isometric, time-varying (TV) contractions of the ankle plantarflexor muscles. A subspace, linear parameter varying, parallel-cascade (LPV-PC) algorithm was used to identify the model from measured input position perturbations and output torque data using voluntary torque as the LPV scheduling variable (SV). Monte-Carlo simulations demonstrated that the algorithm is accurate, precise, and robust to colored measurement noise. The algorithm was then used to examine stiffness changes associated with TV isometric contractions. The SV was estimated from the Soleus EMG using a Hammerstein model of EMG-torque dynamics identified from unperturbed trials. The LPV-PC algorithm identified (i) a non-parametric LPV impulse response function (LPV IRF) for intrinsic stiffness and (ii) a LPV-Hammerstein model for reflex stiffness consisting of a LPV static nonlinearity followed by a time-invariant state-space model of reflex dynamics. The results demonstrated that: (a) intrinsic stiffness, in particular ankle elasticity, increased significantly and monotonically with activation level; (b) the gain of the reflex pathway increased from rest to around 10–20% of subject's MVC and then declined; and (c) the reflex dynamics were second order. These findings suggest that in healthy human ankle, reflex stiffness contributes most at low muscle contraction levels, whereas, intrinsic contributions monotonically increase with activation level. PMID:28579954

  11. Aortic root dimension and arterial stiffness in arterial hypertension: the Campania Salute Network.

    PubMed

    Lønnebakken, Mai Tone; Izzo, Raffaele; Mancusi, Costantino; Losi, Maria Angela; Stabile, Eugenio; Rozza, Francesco; Gerdts, Eva; Trimarco, Bruno; de Luca, Nicola; de Simone, Giovanni

    2016-06-01

    The relation between aortic root dimension (ARD) and measures of arterial stiffness is uncertain. Accordingly, we studied the relation between ARD and an estimate of arterial stiffness in 12 392 hypertensive patients (age 53 ± 12 years, 43% women) free of prevalent cardiovascular disease and with ejection fraction at least 50%, from the Campania Salute Network Registry. Echocardiographic ARD was measured and compared with the value predicted by age, sex and height by using a z-score. Arterial stiffness was assessed by the pulse pressure/stroke index. The highest population tertile of pulse pressure/stroke index was considered 'high arterial stiffness'. High arterial stiffness was more common in women than in men (P < 0.001) and associated with older age, diabetes, longer duration of hypertension and less frequent smoking habit (all P less than 0.01). Patients with high arterial stiffness had smaller ARD, higher carotid intima-media thickness and plasma cholesterol, and lower BMI and glomerular filtration rate (all P less than 0.01). In multivariable logistic analysis, high arterial stiffness was associated with both lower ARD z-score [OR 0.83 (95% confidence interval 0.79-0.88)] and higher carotid intima-media thickness [OR 1.36 (95% confidence interval 1.26-1.47); both P less than 0.0001], independent of significant associations with age, female sex, body size, DBP, heart rate, duration of hypertension, diabetes and smoking habit. Small ARD, together with atherosclerotic modifications of conduit arteries, is associated with increased 2-element Windkessel model of arterial stiffness in hypertension, independently of the significant effect of confounders.

  12. Serum S100 calcium binding protein A4 improves the diagnostic accuracy of transient elastography for assessing liver fibrosis in hepatitis B.

    PubMed

    Yan, Li-Bo; Zhang, Qing-Bo; Zhu, Xia; He, Min; Tang, Hong

    2018-02-01

    The diagnostic performance of Fibroscan might be improved when combined with other serum fibrosis related markers. Previous study has demonstrated that S100A4 expression is associated with liver fibrosis in humans with hepatitis. This study aimed to clarify diagnostic accuracy of serum S100A4 levels for significant liver fibrosis in patients with chronic hepatitis B (CHB), and develop a combined algorithm of liver stiffness measurement (LSM) and S100A4 to predict significant liver fibrosis in CHB. One hundred and seventy-five CHB patients who had performed liver biopsy were consecutively included. We evaluated serum S100A4 levels, LSM values and other clinically-approved fibrosis scores. Serum S100A4 level was higher in CHB patients with significant fibrosis, compared to those without [199.58 (33.31-1971.96) vs. 107.15 (2.10-1038.94), P<0.001]. Using receiver-operating characteristic (ROC) analyses, the area under the curves (AUC), sensitivity, specificity and accuracy of S100A4 were found to be 0.749, 62.7%, 75.9% and 0.70 for significant fibrosis (≥Stage 2), respectively. Although not superior to LSM, these results were better than the fibrosis index based on the 4 factor (FIB-4) and the aspartate aminotransferase-to-platelet ratio index (APRI) for significant fibrosis detection. An algorithm consisting of S100A4 and LSM was derived. The AUC, sensitivity, specificity and accuracy of model based on serum S100A4 level and LSM were 0.866, 86.6%, 77.8% and 0.79 for significant fibrosis detection, superior to those based on LSM alone (0.834, 76.1%, 80.7% and 0.76, P=0.041). Serum S100A4 level was identified as a fibrosis marker of liver fibrosis in patients with CHB. Combining serum S100A4 with LSM improved the accuracy of transient elastography for hepatitis B significant fibrosis detection. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

  13. Potential Relationship between Passive Plantar Flexor Stiffness and Running Performance.

    PubMed

    Ueno, Hiromasa; Suga, Tadashi; Takao, Kenji; Tanaka, Takahiro; Misaki, Jun; Miyake, Yuto; Nagano, Akinori; Isaka, Tadao

    2018-02-01

    The present study aimed to determine the relationship between passive stiffness of the plantar flexors and running performance in endurance runners. Forty-eight well-trained male endurance runners and 24 untrained male control subjects participated in this study. Plantar flexor stiffness during passive dorsiflexion was calculated from the slope of the linear portion of the torque-angle curve. Of the endurance runners included in the present study, running economy in 28 endurance runners was evaluated by measuring energy cost during three 4-min trials (14, 16, and 18 km/h) of submaximal treadmill running. Passive stiffness of the plantar flexors was significantly higher in endurance runners than in untrained subjects. Moreover, passive plantar flexor stiffness in endurance runners was significantly correlated with a personal best 5000-m race time. Furthermore, passive plantar flexor stiffness in endurance runners was significantly correlated with energy cost during submaximal running at 16 km/h and 18 km/h, and a trend towards such significance was observed at 14 km/h. The present findings suggest that stiffer plantar flexors may help achieve better running performance, with greater running economy, in endurance runners. Therefore, in the clinical setting, passive stiffness of the plantar flexors may be a potential parameter for assessing running performance. © Georg Thieme Verlag KG Stuttgart · New York.

  14. Variable Stiffness Panel Structural Analyses With Material Nonlinearity and Correlation With Tests

    NASA Technical Reports Server (NTRS)

    Wu, K. Chauncey; Gurdal, Zafer

    2006-01-01

    Results from structural analyses of three tow-placed AS4/977-3 composite panels with both geometric and material nonlinearities are presented. Two of the panels have variable stiffness layups where the fiber orientation angle varies as a continuous function of location on the panel planform. One variable stiffness panel has overlapping tow bands of varying thickness, while the other has a theoretically uniform thickness. The third panel has a conventional uniform-thickness [plus or minus 45](sub 5s) layup with straight fibers, providing a baseline for comparing the performance of the variable stiffness panels. Parametric finite element analyses including nonlinear material shear are first compared with material characterization test results for two orthotropic layups. This nonlinear material model is incorporated into structural analysis models of the variable stiffness and baseline panels with applied end shortenings. Measured geometric imperfections and mechanical prestresses, generated by forcing the variable stiffness panels from their cured anticlastic shapes into their flatter test configurations, are also modeled. Results of these structural analyses are then compared to the measured panel structural response. Good correlation is observed between the analysis results and displacement test data throughout deep postbuckling up to global failure, suggesting that nonlinear material behavior is an important component of the actual panel structural response.

  15. Probing the stiffness of isolated nucleoli by atomic force microscopy.

    PubMed

    Louvet, Emilie; Yoshida, Aiko; Kumeta, Masahiro; Takeyasu, Kunio

    2014-04-01

    In eukaryotic cells, ribosome biogenesis occurs in the nucleolus, a membraneless nuclear compartment. Noticeably, the nucleolus is also involved in several nuclear functions, such as cell cycle regulation, non-ribosomal ribonucleoprotein complex assembly, aggresome formation and some virus assembly. The most intriguing question about the nucleolus is how such dynamics processes can occur in such a compact compartment. We hypothesized that its structure may be rather flexible. To investigate this, we used atomic force microscopy (AFM) on isolated nucleoli. Surface topography imaging revealed the beaded structure of the nucleolar surface. With the AFM's ability to measure forces, we were able to determine the stiffness of isolated nucleoli. We could establish that the nucleolar stiffness varies upon drastic morphological changes induced by transcription and proteasome inhibition. Furthermore, upon ribosomal proteins and LaminB1 knockdowns, the nucleolar stiffness was increased. This led us to propose a model where the nucleolus has steady-state stiffness dependent on ribosome biogenesis activity and requires LaminB1 for its flexibility.

  16. Model-Based Estimation of Ankle Joint Stiffness

    PubMed Central

    Misgeld, Berno J. E.; Zhang, Tony; Lüken, Markus J.; Leonhardt, Steffen

    2017-01-01

    We address the estimation of biomechanical parameters with wearable measurement technologies. In particular, we focus on the estimation of sagittal plane ankle joint stiffness in dorsiflexion/plantar flexion. For this estimation, a novel nonlinear biomechanical model of the lower leg was formulated that is driven by electromyographic signals. The model incorporates a two-dimensional kinematic description in the sagittal plane for the calculation of muscle lever arms and torques. To reduce estimation errors due to model uncertainties, a filtering algorithm is necessary that employs segmental orientation sensor measurements. Because of the model’s inherent nonlinearities and nonsmooth dynamics, a square-root cubature Kalman filter was developed. The performance of the novel estimation approach was evaluated in silico and in an experimental procedure. The experimental study was conducted with body-worn sensors and a test-bench that was specifically designed to obtain reference angle and torque measurements for a single joint. Results show that the filter is able to reconstruct joint angle positions, velocities and torque, as well as, joint stiffness during experimental test bench movements. PMID:28353683

  17. Spinal Stiffness in Prone and Upright Postures During 0-1.8 g Induced by Parabolic Flight.

    PubMed

    Swanenburg, Jaap; Meier, Michael L; Langenfeld, Anke; Schweinhardt, Petra; Humphreys, B Kim

    2018-06-01

    The purpose of this study was to analyze posterior-to-anterior spinal stiffness in Earth, hyper-, and microgravity conditions during both prone and upright postures. During parabolic flight, the spinal stiffness of the L3 vertebra of a healthy 37-yr-old man was measured in normal Earth gravity (1.0 g), hypergravity (1.8 g), and microgravity (0.0 g) conditions induced in the prone and upright positions. Differences in spinal stiffness were significant across all three gravity conditions in the prone and upright positions. Most effect sizes were large; however, in the upright posture, the effect size between Earth gravity and microgravity was medium. Significant differences in spinal stiffness between the prone and upright positions were found during Earth gravity and hypergravity conditions. No difference was found between the two postures during microgravity conditions. Based on repeated measurements of a single individual, our results showed detectable changes in posterior-to-anterior spinal stiffness. Spinal stiffness increased during microgravity and decreased during hypergravity conditions. In microgravity conditions, posture did not impact spinal stiffness. More data on spinal stiffness in variable gravitational conditions is needed to confirm these results.Swanenburg J, Meier ML, Langenfeld A, Schweinhardt P, Humphreys BK. Spinal stiffness in prone and upright postures during 0-1.8 g induced by parabolic flight. Aerosp Med Hum Perform. 2018; 89(6):563-567.

  18. Experimental confirmation of the atomic force microscope cantilever stiffness tilt correction

    NASA Astrophysics Data System (ADS)

    Gates, Richard S.

    2017-12-01

    The tilt angle (angle of repose) of an AFM cantilever relative to the surface it is interrogating affects the effective stiffness of the cantilever as it analyzes the surface. For typical AFMs and cantilevers that incline from 10° to 15° tilt, this is thought to be a 3%-7% stiffness increase correction. While the theoretical geometric analysis of this effect may have reached a consensus that it varies with cos-2 θ, there is very little experimental evidence to confirm this using AFM cantilevers. Recently, the laser Doppler vibrometry thermal calibration method utilized at NIST has demonstrated sufficient stiffness calibration accuracy, and precision to allow a definitive experimental confirmation of the particular trigonometric form of this tilt effect using a commercial microfabricated AFM cantilever specially modified to allow strongly tilted (up to 15°) effective cantilever stiffness measurements.

  19. Follow-up of ankle stiffness and electromechanical delay in immobilized children: three cases studies.

    PubMed

    Grosset, Jean-François; Lapole, Thomas; Mora, Isabelle; Verhaeghe, Martine; Doutrellot, Pierre-Louis; Pérot, Chantal

    2010-08-01

    Clinical manual tests refer to increased ankle stiffness in children immobilized due to hip osteochondritis. The aim of the present study was to investigate musculo-articular stiffness via different techniques in immobilized children to confirm or not and quantify these observations. Ankle stiffness was quantified monthly during the long immobilization period in three diseased children and compared to healthy age-matched children. Sinusoidal perturbations were used to evaluate musculo-articular (MA) stiffness of the ankle plantar-flexors. The stiffness index (SI(MA-EMG)) was the slope of the linear relationship between angular stiffness and plantar-flexion torque normalized with electromyographic activity of the triceps surae (TS). The stiffness of the ankle plantar-flexors was also indirectly evaluated using the TS electromechanical delay (EMD). SI(MA-EMG) was greater for diseased children, and this higher stiffness was confirmed by the higher EMD values found in these immobilized children. Furthermore, both parameters indicated that ankle stiffness continues to increase through immobilization period. This study gives a quantitative evaluation of ankle stiffness changes through the immobilization period imposed to children treated for hip osteochondritis. The use of EMD measurement to indirectly evaluate these stiffness changes is also validated. This study shed for the first time some light into the patterns of muscle modifications following immobilization in children. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

  20. Evaluation of Liver Stiffness After Radioembolization by Real-Time ShearWave™ Elastography: Preliminary Study

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bas, Ahmet, E-mail: dr.ahmetbas@hotmail.com; Samanci, Cesur, E-mail: cesursamanci@gmail.com; Gulsen, Fatih, E-mail: drfgulsen@yahoo.com

    2015-08-15

    PurposeTo evaluate the effect of ShearWave™ elastography (SWE) for the assessment of liver fibrosis after radioembolization (RE) in patients with liver malignancies.Materials and MethodsWe prospectively examined the effects of SWE before and after RE in 17 adult patients, from June 2012 to September 2013. All patients underwent SWE within 1 month before and 3 months (96.3 ± 22.9 days) after RE. Measurements were taken in segments III, IV, V, and VI (lateral/medial left lobe and anterior/posterior right lobe, respectively). Liver stiffness was studied in the 39 treated segments.ResultsThe mean stiffness of liver tissue according to the pre-RE SWE measurements was not different from the post-REmore » SWE measurements in the segments that did not undergo RE. Conversely, segments treated with RE were significantly stiffer according to the post-RE SWE measurements (mean SWE 17.4 kPa) than according to the baseline measurements (7.0 kPa) (p < 0.001). Patients with hepatocellular carcinoma and preexisting infection with hepatitis B and C viruses had higher pre-embolization stiffness, and the post-embolization stiffness of the treated segments in these patients was higher than that in the remainder of the study population.ConclusionThese data suggest that SWE measurements of liver stiffness increase as early as the third month after RE. SWE could be used as a noninvasive complementary imaging method for preliminary assessment of liver fibrosis before and after RE.« less

  1. Functionalized AFM probes for force spectroscopy: eigenmode shapes and stiffness calibration through thermal noise measurements.

    PubMed

    Laurent, Justine; Steinberger, Audrey; Bellon, Ludovic

    2013-06-07

    The functionalization of an atomic force microscope (AFM) cantilever with a colloidal bead is a widely used technique when the geometry between the probe and the sample must be controlled, particularly in force spectroscopy. But some questions remain: how does a bead glued at the end of a cantilever influence its mechanical response? And more importantly for quantitative measurements, can we still determine the stiffness of the AFM probe with traditional techniques?In this paper, the influence of the colloidal mass loading on the eigenmode shape and resonant frequency is investigated by measuring the thermal noise on rectangular AFM microcantilevers with and without beads attached at their extremities. The experiments are performed with a home-made ultra-sensitive AFM, based on differential interferometry. The focused beam from the interferometer probes the cantilever at different positions and the spatial shapes of the modes are determined up to the fifth resonance, without external excitation. The results clearly demonstrate that the first eigenmode is almost unchanged by mass loading. However the oscillation behavior of higher resonances presents a marked difference: with a particle glued at its extremity, the nodes of the modes are displaced towards the free end of the cantilever. These results are compared to an analytical model taking into account the mass and inertial moment of the load in an Euler-Bernoulli framework, where the normalization of the eigenmodes is explicitly worked out in order to allow a quantitative prediction of the thermal noise amplitude of each mode. A good agreement between the experimental results and the analytical model is demonstrated, allowing a clean calibration of the probe stiffness.

  2. Influence of inhaled nicotine source on arterial stiffness.

    PubMed

    Szołtysek-Bołdys, Izabela; Sobczak, Andrzej; Zielińska-Danch, Wioleta; Bartoń, Aleksandra; Koszowski, Bartosz; Kośmider, Leon

    2014-01-01

    Tobacco smoking leads to changes in hemodynamic parameters such as heart rate and systolic or diastolic blood pressure. It has a direct influence on the elasticity of blood vessels and increases arterial stiffness, which can result in development of atherosclerosis. Data show that the nicotine in tobacco smoke probably is responsible for these changes. Electronic cigarettes (e-cigarettes) were supposedly a healthier alternative to combustible cigarettes because they imitate a process of cigarettes smoking but generate nicotine aerosol without the toxic substances from tobacco combustion. However, the use of e-cigarettes is still controversial because their toxicity, safety and long term use health impact have not been sufficiently studied. The aim of this study was to evaluate changes in arterial stiffness parameters after smoking a cigarette or e-cigarette use. Fifteen healthy women, aged 19-25 years old, smoking ≥5 cigarettes per day for at least two years participated in the study. A non-invasive measurement of arterial stiffness parameters - Stiffness Index (SI) and Reflection Index (RI) - was conducted and systolic and diastolic blood pressure and heart rate were measured before and after smoking a conventional cigarette as well as use of an e-cigarette. Statistically significant changes in the SI and RI were observed before and after smoking of a conventional cigarette [SI: 6.75m/s (6.66 - 6.85, 95% CI) vs 6.56m/s (6.46 - 6.65. 95% CI), p=0.0056; RI: 54.0% (51.5 - 56.7, 95% CI) vs 49.6% (47.5 - 51.8, 95% CI), p=0.010]. The use of e-cigarettes resulted in no statistically significant changes in the SI and RI. After both product use systolic and diastolic blood pressure and heart rate increased but the changes were not statistically significant. In contrast to conventional cigarette use, the use of electronic cigarettes causes no changes in arterial stiffness. This may indicate lower bioavailability of nicotine from the e-cigarette or an additional effect of

  3. Control of paraplegic ankle joint stiffness using FES while standing.

    PubMed

    Hunt, K J; Gollee, H; Jaime, R P

    2001-10-01

    The goal of this work was to investigate the feasibility of ankle stiffness control using functional electrical stimulation (FES) while standing, as relevant to the development of feedback systems for balance control in paraplegia. The work was carried out using apparatus in which the subject stands with all joints above the ankles braced, and where ankle moment is provided via FES of the ankle flexor and extensor muscles. A feedback control strategy for ankle stiffness control is proposed in which the ankle moment is controlled to a reference value equal to the product of the desired stiffness and the measured ankle angle. Two subjects participated in the study: one neurologically-intact person, and one paraplegic person with a complete thoracic spinal cord lesion. The results show that during forward-leaning postures, when the plantarflexor muscles are stimulated, relatively high ankle moments of up to 60 Nm can be generated and accurate moment tracking is achieved. As a consequence, ankle stiffness is close to the desired value. During backward lean, on the other hand, the dorsiflexor muscles are stimulated. These muscles are relatively weak and only modest ankle moments of up to around 15 Nm can be produced. As a result, dorsiflexor stimulation readily saturates giving poor stiffness control. It was further observed that when the desired stiffness is higher more external force has to be applied to perturb the body away from the neutral (upright) position. We conclude that: (i) accurate ankle stiffness control, up to the fundamental strength limits of the muscles, can be achieved with controlled FES; (ii) ankle stiffness control using FES in paraplegia has the potential to ease the task of stabilising upright posture by application of additional upper-body forces.

  4. Magnetic Resonance Elastography: Measurement of Hepatic Stiffness Using Different Direct Inverse Problem Reconstruction Methods in Healthy Volunteers and Patients with Liver Disease.

    PubMed

    Saito, Shigeyoshi; Tanaka, Keiko; Hashido, Takashi

    2016-02-01

    The purpose of this study was to compare the mean hepatic stiffness values obtained by the application of two different direct inverse problem reconstruction methods to magnetic resonance elastography (MRE). Thirteen healthy men (23.2±2.1 years) and 16 patients with liver diseases (78.9±4.3 years; 12 men and 4 women) were examined for this study using a 3.0 T-MRI. The healthy volunteers underwent three consecutive scans, two 70-Hz waveform and a 50-Hz waveform scans. On the other hand, the patients with liver disease underwent scanning using the 70-Hz waveform only. The MRE data for each subject was processed twice for calculation of the mean hepatic stiffness (Pa), once using the multiscale direct inversion (MSDI) and once using the multimodel direct inversion (MMDI). There were no significant differences in the mean stiffness values among the scans obtained with two 70-Hz and different waveforms. However, the mean stiffness values obtained with the MSDI technique (with mask: 2895.3±255.8 Pa, without mask: 2940.6±265.4 Pa) were larger than those obtained with the MMDI technique (with mask: 2614.0±242.1 Pa, without mask: 2699.2±273.5 Pa). The reproducibility of measurements obtained using the two techniques was high for both the healthy volunteers [intraclass correlation coefficients (ICCs): 0.840-0.953] and the patients (ICC: 0.830-0.995). These results suggest that knowledge of the characteristics of different direct inversion algorithms is important for longitudinal liver stiffness assessments such as the comparison of different scanners and evaluation of the response to fibrosis therapy.

  5. Blood pressure and arterial stiffness in obese children and adolescents.

    PubMed

    Hvidt, Kristian Nebelin

    2015-03-01

    Obesity, elevated blood pressure (BP) and arterial stiffness are risk factors for cardiovascular disease. A strong relationship exists between obesity and elevated BP in both children and adults. Obesity and elevated BP in childhood track into adult life increasing the risk of cardiovascular disease in adulthood. Ambulatory BP is the most precise measure to evaluate the BP burden, whereas carotid-femoral pulse wave velocity (cfPWV) is regarded as the gold standard for evaluating arterial (i.e. aortic) stiffness. These measures might contribute to a better understanding of obesity's adverse impact on the cardiovascular system, and ultimately a better prevention and treatment of childhood obesity. The overall aim of the present PhD thesis is to investigate arterial stiffness and 24-hour BP in obese children and adolescents, and evaluate whether these measures are influenced by weight reduction. The present PhD thesis is based on four scientific papers.  In a cross-sectional design, 104 severe obese children and adolescents with an age of 10-18 years were recruited when newly referred to the Children's Obesity Clinic, Holbæk University Hospital, and compared to 50 normal weighted age and gender matched control individuals. Ambulatory BP was measured, and cfPWV was investigated in two ways in respect to the distance measure of aorta; the previously recommended length - the so called subtracted distance, and the currently recommended length - the direct distance. In a longitudinal design, the obese patients were re-investigated after one-year of lifestyle intervention at the Children's Obesity Clinic in purpose of reducing the degree of obesity. In the cross-sectional design, the obese group had higher measures of obesity, while matched for age, gender and height, when compared to the control group. In the longitudinal design, 74% of the 72 followed up obese patients experienced a significant weight reduction. CfPWV was dependent on the method used to measure the

  6. Augmented vascular smooth muscle cell stiffness and adhesion when hypertension is superimposed on aging.

    PubMed

    Sehgel, Nancy L; Sun, Zhe; Hong, Zhongkui; Hunter, William C; Hill, Michael A; Vatner, Dorothy E; Vatner, Stephen F; Meininger, Gerald A

    2015-02-01

    Hypertension and aging are both recognized to increase aortic stiffness, but their interactions are not completely understood. Most previous studies have attributed increased aortic stiffness to changes in extracellular matrix proteins that alter the mechanical properties of the vascular wall. Alternatively, we hypothesized that a significant component of increased vascular stiffness in hypertension is due to changes in the mechanical and adhesive properties of vascular smooth muscle cells, and that aging would augment the contribution from vascular smooth muscle cells when compared with the extracellular matrix. Accordingly, we studied aortic stiffness in young (16-week-old) and old (64-week-old) spontaneously hypertensive rats and Wistar-Kyoto wild-type controls. Systolic and pulse pressures were significantly increased in young spontaneously hypertensive rats when compared with young Wistar-Kyoto rats, and these continued to rise in old spontaneously hypertensive rats when compared with age-matched controls. Excised aortic ring segments exhibited significantly greater elastic moduli in both young and old spontaneously hypertensive rats versus Wistar-Kyoto rats. were isolated from the thoracic aorta, and stiffness and adhesion to fibronectin were measured by atomic force microscopy. Hypertension increased both vascular smooth muscle cell stiffness and vascular smooth muscle cell adhesion, and these increases were both augmented with aging. By contrast, hypertension did not affect histological measures of aortic collagen and elastin, which were predominantly changed by aging. These findings support the concept that stiffness and adhesive properties of vascular smooth muscle cells are novel mechanisms contributing to the increased aortic stiffness occurring with hypertension superimposed on aging. © 2014 American Heart Association, Inc.

  7. Differences in neutral foot positions when measured barefoot compared to in shoes with varying stiffnesses.

    PubMed

    Shultz, R; Birmingham, T B; Jenkyn, T R

    2011-12-01

    This study examined the absolute differences in neutral positions of the joints of the foot with different footwear. This addresses the question of whether separate static trials should be collected for each footwear condition to establish neutral positions. A multi-segment kinematic foot model and optical motion analysis system measured four inter-segmental joints of the foot: (1) hindfoot-to-midfoot in the frontal plane, (2) forefoot-to-midfoot in the frontal plane, (3) hallux-to-forefoot in the sagittal plane, and (4) the height-to-length ratio of the medial longitudinal arch. Barefoot was compared to three shoe condition using Nike Free trainers of varying longitudinal torsional stiffness in ten male volunteers. There was high variability both within subjects and shoe conditions. Shoes in general tended to raise the medial longitudinal arch and dorsiflex the hallux compared to barefoot condition. For the hallux, a minimum important difference of 5° or more was found between shoe conditions and the barefoot condition for majority of the subjects in all three shoe conditions (90% for control, 60% for least stiff, 50% for most stiff). This was less for the frontal plane inter-segmental joints of the foot where 50% of the subjects experience a change above 5° for at least one of the conditions. The choice of using condition-specific neutral trials versus a single common neutral trials should be considered carefully. A single common trial allows for differences in absolute joint angles to be compared between footwear conditions. This can be important clinically to determine whether a joint is approaching its end-of-range and therefore at risk of injury. Several condition-specific neutral trials allows for subtleties in kinematic waveforms to be better compared between conditions, since absolute shifts in joint angles due to changing neutral position are removed and the waveforms are better aligned. Copyright © 2011. Published by Elsevier Ltd.

  8. Is passive stiffness in human muscles related to the elasticity of tendon structures?

    PubMed

    Kubo, K; Kanehisa, H; Fukunaga, T

    2001-08-01

    The purpose of this study was to examine in vivo whether passive stiffness in human muscles was related to the elasticity of tendon structures and to performance during stretch-shortening cycle exercise. Passive torque of plantar flexor muscles was measured during passive stretch from 90 degrees (anatomical position) to 65 degrees of dorsiflexion at a constant velocity of 5 degrees.s-1. The slope of the linear portion of the passive torque-angle curve during stretching was defined as the passive stiffness of the muscle. The elongation of the tendon and aponeurosis of the medial gastrocnemius muscle (MG) was directly measured using ultrasonography during ramp isometric plantar flexion up to the voluntary maximum. The relationship between the estimated muscle force of MG and tendon elongation was fitted to a linear regression, the slope of which was defined as the stiffness of the tendon. In addition, the dynamic torques during maximal voluntary concentric plantar flexion with and without prior eccentric contraction were determined at a constant velocity of 120 degrees.s-1. There were no significant correlations between passive stiffness and either the tendon stiffness (r = 0.19, P > 0.05) or the relative increase in torque with prior eccentric contraction (r = -0.19, P > 0.05). However, tendon stiffness was negatively correlated to the relative increase in torque output (r = -0.42, P < 0.05). The present results suggested that passive stiffness was independent of the elasticity of tendon structures, and had no favourable effect on the muscle performance during stretch-shortening cycle exercise.

  9. Atomic Force Microscopy Study on the Stiffness of Nanosized Liposomes Containing Charged Lipids.

    PubMed

    Takechi-Haraya, Yuki; Goda, Yukihiro; Sakai-Kato, Kumiko

    2018-06-18

    It has recently been recognized that the mechanical properties of lipid nanoparticles play an important role during in vitro and in vivo behaviors such as cellular uptake, blood circulation, and biodistribution. However, there have been no quantitative investigations of the effect of commonly used charged lipids on the stiffness of nanosized liposomes. In this study, by means of atomic force microscopy (AFM), we quantified the stiffness of nanosized liposomes composed of neutrally charged lipids combined with positively or negatively charged lipids while simultaneously imaging the liposomes in aqueous medium. Our results showed that charged lipids, whether negatively or positively charged, have the effect of reducing the stiffness of nanosized liposomes, independently of the saturation degree of the lipid acyl chains; the measured stiffness values of liposomes containing charged lipids are 30-60% lower than those of their neutral counterpart liposomes. In addition, we demonstrated that the Laurdan generalized polarization values, which are related to the hydration degree of the liposomal membrane interface and often used as a qualitative indicator of liposomal membrane stiffness, do not directly correlate with the physical stiffness values of the liposomes prepared in this study. However, our results indicate that direct quantitative AFM measurement is a valuable method to gain molecular-scale information about how the hydration degree of liposomal interfaces reflects (or does not reflect) liposome stiffness as a macroscopic property. Our AFM method will contribute to the quantitative characterization of the nano-bio interaction of nanoparticles and to the optimization of the lipid composition of liposomes for clinical use.

  10. Supersonic shear imaging for the diagnosis of liver fibrosis and portal hypertension in liver diseases: a meta-analysis.

    PubMed

    Deng, Han; Qi, Xingshun; Zhang, Tiansong; Qi, Xiaolong; Yoshida, Eric M; Guo, Xiaozhong

    2018-01-01

    The meta-analysis aimed to summarize the technical success rate of supersonic shear imaging (SSI) and to evaluate the diagnostic performance of liver and spleen stiffness measurement (LSM and SSM) with SSI for the detection of liver fibrosis, portal hypertension, and gastroesophageal varices in liver diseases. PubMed, EMBASE, and Cochrane Library databases were searched. Technical success rate of SSI was pooled. Area under curve (AUC), sensitivity, and specificity with corresponding 95% confidence interval (CI) were calculated. Included studies regarding the diagnostic performance of SSI for liver fibrosis, portal hypertension, and esophageal varices numbered 28, 4, and 4 respectively. The pooled technical success rates of LSM and SSM were 95.3% and 75.5%, respectively. The AUC, sensitivity, and specificity of LSM/SSM for different stages of liver fibrosis were 0.85-0.94, 0.7-0.89, and 0.82-0.92, respectively. The AUC, sensitivity, and specificity of LSM were 0.84 (95%CI = 0.8-0.86), 0.79 (95%CI = 0.7-0.85), and 0.82 (95%CI = 0.72-0.88) for clinically significant portal hypertension, 0.85 (95%CI = 0.82-0.88), 0.8 (95%CI = 0.68-0.88), and 0.8 (95%CI = 0.6-0.92) for any varices, and 0.86 (95%CI = 0.83-0.89), 0.86 (95%CI = 0.76-0.92), and 0.61 (95%CI = 0.35-0.83) for high-risk varices, respectively. LSM with SSI had a high diagnostic accuracy for liver fibrosis, but a moderate diagnostic accuracy for portal hypertension and esophageal varices.

  11. A quantitative method for evaluating inferior glenohumeral joint stiffness using ultrasonography.

    PubMed

    Tsai, Wen-Wei; Lee, Ming-Yih; Yeh, Wen-Lin; Cheng, Shih-Chung; Soon, Kok-Soon; Lei, Kin Fong; Lin, Wen-Yen

    2013-02-01

    Subluxation of the affected shoulder in post-stroke patients is associated with nerve disorders and muscle fatigue. Clinicians must be able to accurately and reliably measure inferior glenohumeral subluxation in patients to provide appropriate treatment. However, quantitative methods for evaluating the laxity and stiffness of the glenohumeral joint (GHJ) are still being developed. The aim of this study was to develop a new protocol for evaluating the laxity and stiffness of the inferior GHJ using ultrasonography under optimal testing conditions and to investigate changes in the GHJ from a commercially available humerus brace and shoulder brace. Multistage inferior displacement forces were applied to create a glide between the most cephalad point on the visible anterosuperior surface of the humeral head and coracoid process in seven healthy volunteers. GHJ stiffness was defined as the slope of the linear regression line between the glides and different testing loads. The testing conditions were defined by different test loading mechanisms (n=2), shoulder constraining conditions (n=2), and loading modes (n=4). The optimal testing condition was defined as the condition with the least residual variance of measured laxity to the calculated stiffness under different testing loads. A paired t-test was used to compare the laxity and stiffness of the inferior GHJ using different braces. No significant difference was identified between the two test loading mechanisms (t=0.218, p=0.831) and two shoulder constraining conditions (t=-0.235, p=0.818). We concluded that ultrasonographic laxity measurements performed using a pulley set loading mechanism was as reliable as direct loading. Additionally, constraining the unloaded shoulder was proposed due to the lower mean residual variance value. Moreover, pulling the elbow downward with loading on the upper arm was suggested, as pulling the elbow downward with the elbow flexed and loading on the forearm may overestimate stiffness

  12. Transient elastography compared to liver biopsy and morphometry for predicting fibrosis in pediatric chronic liver disease: Does etiology matter?

    PubMed Central

    Behairy, Behairy El-Sayed; Sira, Mostafa Mohamed; Zalata, Khaled Refat; Salama, El-Sayed Ebrahem; Abd-Allah, Mohamed Ahmed

    2016-01-01

    AIM: To evaluate transient elastography (TE) as a noninvasive tool in staging liver fibrosis compared with liver biopsy and morphometry in children with different chronic liver diseases. METHODS: A total of 90 children [50 with chronic hepatitis C virus (HCV), 20 with autoimmune hepatitis (AIH) and 20 with Wilson disease] were included in the study and underwent liver stiffness measurement (LSM) using TE. Liver biopsies were evaluated for fibrosis, qualitatively, by Ishak score and quantitatively by fibrosis area fraction (FAF) using digital image analysis (morphometry). LSM was correlated with fibrosis and other studied variables using spearman correlation. A stepwise multiple regression analysis was also performed to examine independent factors associated with LSM. Different cut-off values of LSM were calculated for predicting individual fibrosis stages using receiver-operating characteristic curve. Cut-off values with optimal clinical performance (optimal sensitivity and specificity simultaneously) were selected. RESULTS: The majority of HCV group had minimal activity (80%) and no/mild fibrosis (72%). On the other hand, the majority of AIH group had mild to moderate activity (70%) and moderate to severe fibrosis (95%) and all Wilson disease group had mild to moderate activity (100%) and moderate to severe fibrosis (100%). LSM correlated significantly with both FAF and Ishak scores and the correlation appeared better with the latter (r = 0.839 vs 0.879, P < 0.0001 for both). LSM discriminated individual stages of fibrosis with high performance. Sensitivity ranged from 81.4% to 100% and specificity ranged from 75.0% to 97.2%. When we compared LSM values for the same stage of fibrosis, they varied according to the different etiologies. Higher values were in AIH (16.15 ± 7.23 kPa) compared to Wilson disease (8.30 ± 0.84 kPa) and HCV groups (7.43 ± 1.73 kPa). Multiple regression analysis revealed that Ishak fibrosis stage was the only independent variable

  13. A novel cell-stiffness-fingerprinting analysis by scanning atomic force microscopy: Comparison of fibroblasts and diverse cancer cell lines

    PubMed Central

    Zoellner, Hans; Paknejad, Navid; Manova, Katia; Moore, Malcolm

    2016-01-01

    Differing stimuli affect cell-stiffness while cancer metastasis further relates to cell-stiffness. Cell-stiffness determined by atomic Force Microscopy (AFM) has been limited by measurement over nuclei to avoid spurious substratum effects in thin cytoplasmic domains, and we sought to develop a more complete approach including cytoplasmic areas. 90 μm square fields were recorded from 10 sites of cultured Human Dermal Fibroblasts (HDF), and 3 sites each for melanoma (MM39, WM175, MeIRMu), osteosarcoma (SAOS-2, U2OS), and ovarian carcinoma (COLO316, PEO4) cell lines, each site providing 1,024 measurements as 32x32 square grids. Stiffness recorded below 0.8 μm height was occasionally influenced by substratum, so only stiffness recorded above 0.8 μm was analyzed, but all sites were included for height and volume analysis. COLO316 had the lowest cell height and volume, followed by HDF (p<0.0001), and then PEO4, SAOS-2, MeIRMu, WM175, U2OS, and MM39. HDF were more stiff than all other cells (p < 0.0001), while in descending order of stiffness were PEO4, COLO316, WM175, SAOS-2, U2OS, MM39, and MeIRMu (p < 0.02). Stiffness-fingerprints comprised scattergrams of stiffness values plotted against the height at which each stiffness value was recorded, and appeared unique for each cell type studied, although in most cases the overall form of fingerprints was similar, with maximum stiffness at low height measurements and a second lower peak occurring at high height levels. We suggest our stiffness-fingerprint analytical method provides a more nuanced description than previously reported, and will facilitate study of the stiffness response to cell stimulation. PMID:26357955

  14. Stiffness after total knee arthroplasty.

    PubMed

    Manrique, Jorge; Gomez, Miguel M; Parvizi, Javad

    2015-04-01

    Stiffness after total knee arthroplasty (TKA) adversely affects outcome and impacts patient function. Various risk factors for stiffness after TKA have been identified, including reduced preoperative knee range of motion, history of prior knee surgery, etiology of arthritis, incorrect positioning or oversizing of components, and incorrect gap balancing. Mechanical and associated causes, such as infection, arthrofibrosis, complex regional pain syndrome, and heterotopic ossification, secondary gain issues have also been identified. Management of stiffness following TKA can be challenging. The condition needs to be assessed and treated in a staged manner. A nonsurgical approach is the first step. Manipulation under anesthesia may be considered within the first 3 months after the index TKA, if physical therapy fails to improve the range of motion. Beyond this point, consideration should be given to surgical intervention such as lysis of adhesions, either arthroscopically or by open arthrotomy. If the cause of stiffness is deemed to be surgical error, such as component malpositioning, revision arthroplasty is indicated. The purpose of this article is to evaluate the various aspects of management of stiffness after TKA. Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.

  15. Functions of fish skin: flexural stiffness and steady swimming of longnose gar, Lepisosteus osseus

    PubMed

    Long; Hale; Mchenry; Westneat

    1996-01-01

    The functions of fish skin during swimming remain enigmatic. Does skin stiffen the body and alter the propagation of the axial undulatory wave? To address this question, we measured the skin's in situ flexural stiffness and in vivo mechanical role in the longnose gar Lepisosteus osseus. To measure flexural stiffness, dead gar were gripped and bent in a device that measured applied bending moment (N m) and the resulting midline curvature (m-1). From these values, the flexural stiffness of the body (EI in N m2) was calculated before and after sequential alterations of skin structure. Cutting of the dermis between two caudal scale rows significantly reduced the flexural stiffness of the body and increased the neutral zone of curvature, a region of bending without detectable stiffness. Neither bending property was significantly altered by the removal of a caudal scale row. These alterations in skin structure were also made in live gar and the kinematics of steady swimming was measured before and after each treatment. Cutting of the dermis between two caudal scale rows, performed under anesthesia, changed the swimming kinematics of the fish: tailbeat frequency (Hz) and propulsive wave speed (body lengths per second, L s-1) decreased, while the depth (in L) of the trailing edge of the tail increased. The decreases in tailbeat frequency and wave speed are consistent with predictions of the theory of forced, harmonic vibrations; wave speed, if equated with resonance frequency, is proportional to the square root of a structure's stiffness. While it did not significantly reduce the body's flexural stiffness, surgical removal of a caudal scale row resulted in increased tailbeat amplitude and the relative total hydrodynamic power. In an attempt to understand the specific function of the scale row, we propose a model in which a scale row resists medio-lateral force applied by a single myomere, thus functioning to enhance mechanical advantage for bending. Finally, surgical

  16. Comparison Between Neck and Shoulder Stiffness Determined by Shear Wave Ultrasound Elastography and a Muscle Hardness Meter.

    PubMed

    Akagi, Ryota; Kusama, Saki

    2015-08-01

    The goals of this study were to compare neck and shoulder stiffness values determined by shear wave ultrasound elastography with those obtained with a muscle hardness meter and to verify the correspondence between objective and subjective stiffness in the neck and shoulder. Twenty-four young men and women participated in the study. Their neck and shoulder stiffness was determined at six sites. Before the start of the measurements, patients rated their present subjective symptoms of neck and shoulder stiffness on a 6-point verbal scale. At all measurement sites, the correlation coefficients between the values of muscle hardness indices determined by the muscle hardness meter and shear wave ultrasound elastography were not significant. Furthermore, individuals' subjective neck and shoulder stiffness did not correspond to their objective symptoms. These results suggest that the use of shear wave ultrasound elastography is essential to more precisely assess neck and shoulder stiffness. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

  17. Effect of upper body position on arterial stiffness: influence of hydrostatic pressure and autonomic function.

    PubMed

    Schroeder, Elizabeth C; Rosenberg, Alexander J; Hilgenkamp, Thessa I M; White, Daniel W; Baynard, Tracy; Fernhall, Bo

    2017-12-01

    To evaluate changes in arterial stiffness with positional change and whether the stiffness changes are due to hydrostatic pressure alone or if physiological changes in vasoconstriction of the conduit arteries play a role in the modulation of arterial stiffness. Thirty participants' (male = 15, 24 ± 4 years) upper bodies were positioned at 0, 45, and 72° angles. Pulse wave velocity (PWV), cardio-ankle vascular index, carotid beta-stiffness index, carotid blood pressure (cBP), and carotid diameters were measured at each position. A gravitational height correction was determined using the vertical fluid column distance (mmHg) between the heart and carotid artery. Carotid beta-stiffness was calibrated using three methods: nonheight corrected cBP of each position, height corrected cBP of each position, and height corrected cBP of the supine position (theoretical model). Low frequency systolic blood pressure variability (LFSAP) was analyzed as a marker of sympathetic activity. PWV and cardio-ankle vascular index increased with position (P < 0.05). Carotid beta-stiffness did not increase if not corrected for hydrostatic pressure. Arterial stiffness indices based on Method 2 were not different from Method 3 (P = 0.65). LFSAP increased in more upright positions (P < 0.05) but diastolic diameter relative to diastolic pressure did not (P > 0.05). Arterial stiffness increases with a more upright body position. Carotid beta-stiffness needs to be calibrated accounting for hydrostatic effects of gravity if measured in a seated position. It is unclear why PWV increased as this increase was independent of blood pressure. No difference between Methods 2 and 3 presumably indicates that the beta-stiffness increases are only pressure dependent, despite the increase in vascular sympathetic modulation.

  18. Age and Sex Effects on the Active Stiffness of Vastus Intermedius under Isometric Contraction

    PubMed Central

    Wang, Cong-Zhi; Guo, Jing-Yi; Li, Tian-Jie; Shi, Wenxiu; Zheng, Yong-Ping

    2017-01-01

    Previously, a novel technique was proposed to quantify the relationship between the muscle stiffness and its nonfatigue contraction intensity. The method extended the measured range of isometric contraction to 100% maximum voluntary contraction (MVC) using an ultrasonic shear wave measurement setup. Yet, it has not been revealed how this relationship could be affected by factors like age or sex. To clarify these questions, vastus intermedius (VI) stiffness of 40 healthy subjects was assessed under 11 step levels of isometric contraction. The subjects were divided into four groups: young males, young females, elderly males, and elderly females (n = 10 for each). In a relaxed state, no significant difference was observed between the male and female subjects (p = 0.156) nor between the young and elderly subjects (p = 0.221). However, when performing isometric contraction, the VI stiffness of males was found to be significantly higher than that of females at the same level (p < 0.001), and that of the young was higher than the elderly (p < 0.001). Meanwhile, for two knee joint angles used, the stiffness measured at a 90° knee joint angle was always significantly larger than that measured at 60° (p < 0.001). Recognizing the active muscle stiffness of VI contributes to body stability, and these results may provide insight into the age and sex bias in musculoskeletal studies, such as those on fall risks. PMID:28473990

  19. Physical Fitness and Aortic Stiffness Explain the Reduced Cognitive Performance Associated with Increasing Age in Older People.

    PubMed

    Kennedy, Greg; Meyer, Denny; Hardman, Roy J; Macpherson, Helen; Scholey, Andrew B; Pipingas, Andrew

    2018-01-01

    Greater physical fitness is associated with reduced rates of cognitive decline in older people; however, the mechanisms by which this occurs are still unclear. One potential mechanism is aortic stiffness, with increased stiffness resulting in higher pulsatile pressures reaching the brain and possibly causing progressive micro-damage. There is limited evidence that those who regularly exercise may have lower aortic stiffness. To investigate whether greater fitness and lower aortic stiffness predict better cognitive performance in older people and, if so, whether aortic stiffness mediates the relationship between fitness and cognition. Residents of independent living facilities, aged 60-90, participated in the study (N = 102). Primary measures included a computerized cognitive assessment battery, pulse wave velocity analysis to measure aortic stiffness, and the Six-Minute Walk test to assess fitness. Based on hierarchical regression analyses, structural equation modelling was used to test the mediation hypothesis. Both fitness and aortic stiffness independently predicted Spatial Working Memory (SWM) performance, however no mediating relationship was found. Additionally, the derived structural equation model shows that, in conjunction with BMI and sex, fitness and aortic stiffness explain 33% of the overall variation in SWM, with age no longer directly predicting any variation. Greater fitness and lower aortic stiffness both independently predict better SWM in older people. The strong effect of age on cognitive performance is totally mediated by fitness and aortic stiffness. This suggests that addressing both physical fitness and aortic stiffness may be important to reduce the rate of age associated cognitive decline.

  20. Arterial stiffness in normotensive and hypertensive subjects: Frequency in community pharmacies.

    PubMed

    Rodilla Sala, Enrique; Adell Alegre, Manuel; Giner Galvañ, Vicente; Perseguer Torregrosa, Zeneida; Pascual Izuel, Jose Maria; Climent Catalá, María Teresa

    2017-12-07

    Arterial stiffness (AS) is a well-recognized target organ lesion. This study aims to determine: 1) the frequency of AS in community pharmacies; 2) if stiffened subjects identified by brachial oscillometry have more CV risk factors than normal subjects, and 3) the dependence of stiffness on using either age-adjusted values or a fixed threshold. Observational, cross-sectional study in 32 community pharmacies of the Valencia Community, between November/2015 and April/2016. Stiffness was as pulse wave velocity (PWV) measured with a semi-automatic, validated device (Mobil-O-Graph ® , IEM), followed by a 10-item questionnaire. Mean age of the 1,427 consecutive recruited patients was 56.6 years. Overall proportion of patients with AS was 17.4% with age-adjusted PWV (9.4% in normotensives, 28.3% in hypertensives). Multivariate logistic regression showed independent association of stiffness in normotensives with male gender, obesity, higher pulse pressure and heart rate, in hypertensives, with higher pulse pressure and lower age. AS was globally found in 20.5% of subjects, defining stiffness by PWV>10m/s (6.2% in normotensives, 40.2% in hypertensives). It was associated with higher age and pulse pressure in both groups. Concordance in classifying stiffness was 74.6%. Frequency of AS varied between 17.4-20.5%. Age-adjusted stiffness is associated in normotensives with male gender, pulse pressure, obesity and heart rate, in hypertensives with pulse pressure and inversely to age. Stiffness by 10m/s is determined by higher pulse pressure and higher age. Both definitions of PWV are not interchangeable. Copyright © 2017 Elsevier España, S.L.U. All rights reserved.

  1. A Comparison of Total and Intrinsic Muscle Stiffness Among Flexors and Extensors of the Ankle, Knee and Elbow

    NASA Technical Reports Server (NTRS)

    Lemoine, Sandra M.

    1997-01-01

    This study examined 3 methods that assessed muscle stiffness. Muscle stiffness has been quantified by tissue reactive force (transverse stiffness), vibration, and force (or torque) over displacement. Muscle stiffness also has two components: reflex (due to muscle sensor activity) and intrinsic (tonic firing of motor units, elastic nature of actin and myosin cross bridges, and connective tissue). This study compared three methods of measuring muscle stiffness of agonist-antagonist muscle pairs of the ankle, knee and elbow.

  2. Evaluation of stiffness feedback for hard nodule identification on a phantom silicone model

    PubMed Central

    Konstantinova, Jelizaveta; Xu, Guanghua; He, Bo; Aminzadeh, Vahid; Xie, Jun; Wurdemann, Helge; Althoefer, Kaspar

    2017-01-01

    Haptic information in robotic surgery can significantly improve clinical outcomes and help detect hard soft-tissue inclusions that indicate potential abnormalities. Visual representation of tissue stiffness information is a cost-effective technique. Meanwhile, direct force feedback, although considerably more expensive than visual representation, is an intuitive method of conveying information regarding tissue stiffness to surgeons. In this study, real-time visual stiffness feedback by sliding indentation palpation is proposed, validated, and compared with force feedback involving human subjects. In an experimental tele-manipulation environment, a dynamically updated color map depicting the stiffness of probed soft tissue is presented via a graphical interface. The force feedback is provided, aided by a master haptic device. The haptic device uses data acquired from an F/T sensor attached to the end-effector of a tele-manipulated robot. Hard nodule detection performance is evaluated for 2 modes (force feedback and visual stiffness feedback) of stiffness feedback on an artificial organ containing buried stiff nodules. From this artificial organ, a virtual-environment tissue model is generated based on sliding indentation measurements. Employing this virtual-environment tissue model, we compare the performance of human participants in distinguishing differently sized hard nodules by force feedback and visual stiffness feedback. Results indicate that the proposed distributed visual representation of tissue stiffness can be used effectively for hard nodule identification. The representation can also be used as a sufficient substitute for force feedback in tissue palpation. PMID:28248996

  3. Evaluation of stiffness feedback for hard nodule identification on a phantom silicone model.

    PubMed

    Li, Min; Konstantinova, Jelizaveta; Xu, Guanghua; He, Bo; Aminzadeh, Vahid; Xie, Jun; Wurdemann, Helge; Althoefer, Kaspar

    2017-01-01

    Haptic information in robotic surgery can significantly improve clinical outcomes and help detect hard soft-tissue inclusions that indicate potential abnormalities. Visual representation of tissue stiffness information is a cost-effective technique. Meanwhile, direct force feedback, although considerably more expensive than visual representation, is an intuitive method of conveying information regarding tissue stiffness to surgeons. In this study, real-time visual stiffness feedback by sliding indentation palpation is proposed, validated, and compared with force feedback involving human subjects. In an experimental tele-manipulation environment, a dynamically updated color map depicting the stiffness of probed soft tissue is presented via a graphical interface. The force feedback is provided, aided by a master haptic device. The haptic device uses data acquired from an F/T sensor attached to the end-effector of a tele-manipulated robot. Hard nodule detection performance is evaluated for 2 modes (force feedback and visual stiffness feedback) of stiffness feedback on an artificial organ containing buried stiff nodules. From this artificial organ, a virtual-environment tissue model is generated based on sliding indentation measurements. Employing this virtual-environment tissue model, we compare the performance of human participants in distinguishing differently sized hard nodules by force feedback and visual stiffness feedback. Results indicate that the proposed distributed visual representation of tissue stiffness can be used effectively for hard nodule identification. The representation can also be used as a sufficient substitute for force feedback in tissue palpation.

  4. The intrinsic stiffness of human trabecular meshwork cells increases with senescence

    PubMed Central

    Chang, Yow-Ren; Murphy, Christopher J.; Russell, Paul

    2015-01-01

    Dysfunction of the human trabecular meshwork (HTM) plays a central role in the age-associated disease glaucoma, a leading cause of irreversible blindness. The etiology remains poorly understood but cellular senescence, increased stiffness of the tissue, and the expression of Wnt antagonists such as secreted frizzled related protein-1 (SFRP1) have been implicated. However, it is not known if senescence is causally linked to either stiffness or SFRP1 expression. In this study, we utilized in vitro HTM senescence to determine the effect on cellular stiffening and SFRP1 expression. Stiffness of cultured cells was measured using atomic force microscopy and the morphology of the cytoskeleton was determined using immunofluorescent analysis. SFRP1 expression was measured using qPCR and immunofluorescent analysis. Senescent cell stiffness increased 1.88±0.14 or 2.57±0.14 fold in the presence or absence of serum, respectively. This was accompanied by increased vimentin expression, stress fiber formation, and SFRP1 expression. In aggregate, these data demonstrate that senescence may be a causal factor in HTM stiffening and elevated SFRP1 expression, and contribute towards disease progression. These findings provide insight into the etiology of glaucoma and, more broadly, suggest a causal link between senescence and altered tissue biomechanics in aging-associated diseases. PMID:25915531

  5. Arterial stiffness and cardiovascular events: the Framingham Heart Study.

    PubMed

    Mitchell, Gary F; Hwang, Shih-Jen; Vasan, Ramachandran S; Larson, Martin G; Pencina, Michael J; Hamburg, Naomi M; Vita, Joseph A; Levy, Daniel; Benjamin, Emelia J

    2010-02-02

    Various measures of arterial stiffness and wave reflection have been proposed as cardiovascular risk markers. Prior studies have not assessed relations of a comprehensive panel of stiffness measures to prognosis in the community. We used proportional hazards models to analyze first-onset major cardiovascular disease events (myocardial infarction, unstable angina, heart failure, or stroke) in relation to arterial stiffness (pulse wave velocity [PWV]), wave reflection (augmentation index, carotid-brachial pressure amplification), and central pulse pressure in 2232 participants (mean age, 63 years; 58% women) in the Framingham Heart Study. During median follow-up of 7.8 (range, 0.2 to 8.9) years, 151 of 2232 participants (6.8%) experienced an event. In multivariable models adjusted for age, sex, systolic blood pressure, use of antihypertensive therapy, total and high-density lipoprotein cholesterol concentrations, smoking, and presence of diabetes mellitus, higher aortic PWV was associated with a 48% increase in cardiovascular disease risk (95% confidence interval, 1.16 to 1.91 per SD; P=0.002). After PWV was added to a standard risk factor model, integrated discrimination improvement was 0.7% (95% confidence interval, 0.05% to 1.3%; P<0.05). In contrast, augmentation index, central pulse pressure, and pulse pressure amplification were not related to cardiovascular disease outcomes in multivariable models. Higher aortic stiffness assessed by PWV is associated with increased risk for a first cardiovascular event. Aortic PWV improves risk prediction when added to standard risk factors and may represent a valuable biomarker of cardiovascular disease risk in the community.

  6. MR Elastography Can Be Used to Measure Brain Stiffness Changes as a Result of Altered Cranial Venous Drainage During Jugular Compression.

    PubMed

    Hatt, A; Cheng, S; Tan, K; Sinkus, R; Bilston, L E

    2015-10-01

    Compressing the internal jugular veins can reverse ventriculomegaly in the syndrome of inappropriately low pressure acute hydrocephalus, and it has been suggested that this works by "stiffening" the brain tissue. Jugular compression may also alter blood and CSF flow in other conditions. We aimed to understand the effect of jugular compression on brain tissue stiffness and CSF flow. The head and neck of 9 healthy volunteers were studied with and without jugular compression. Brain stiffness (shear modulus) was measured by using MR elastography. Phase-contrast MR imaging was used to measure CSF flow in the cerebral aqueduct and blood flow in the neck. The shear moduli of the brain tissue increased with the percentage of blood draining through the internal jugular veins during venous compression. Peak velocity of caudally directed CSF in the aqueduct increased significantly with jugular compression (P < .001). The mean jugular venous flow rate, amplitude, and vessel area were significantly reduced with jugular compression, while cranial arterial flow parameters were unaffected. Jugular compression influences cerebral CSF hydrodynamics in healthy subjects and can increase brain tissue stiffness, but the magnitude of the stiffening depends on the percentage of cranial blood draining through the internal jugular veins during compression—that is, subjects who maintain venous drainage through the internal jugular veins during jugular compression have stiffer brains than those who divert venous blood through alternative pathways. These methods may be useful for studying this phenomenon in patients with the syndrome of inappropriately low-pressure acute hydrocephalus and other conditions. © 2015 by American Journal of Neuroradiology.

  7. Design and Analyze a New Measuring Lift Device for Fin Stabilizers Using Stiffness Matrix of Euler-Bernoulli Beam

    PubMed Central

    Liang, Lihua; Sun, Mingxiao; Shi, Hongyu; Luan, Tiantian

    2017-01-01

    Fin-angle feedback control is usually used in conventional fin stabilizers, and its actual anti-rolling effect is difficult to reach theoretical design requirements. Primarily, lift of control torque is a theoretical value calculated by static hydrodynamic characteristics of fin. However, hydrodynamic characteristics of fin are dynamic while fin is moving in waves. As a result, there is a large deviation between actual value and theoretical value of lift. Firstly, the reasons of deviation are analyzed theoretically, which could avoid a variety of interference factors and complex theoretical derivations. Secondly, a new device is designed for direct measurement of actual lift, which is composed of fin-shaft combined mechanism and sensors. This new device can make fin-shaft not only be the basic function of rotating fin, but also detect actual lift. Through analysis using stiffness matrix of Euler-Bernoulli beam, displacement of shaft-core end is measured instead of lift which is difficult to measure. Then quantitative relationship between lift and displacement is defined. Three main factors are analyzed with quantitative relationship. What is more, two installation modes of sensors and a removable shaft-end cover are proposed according to hydrodynamic characteristics of fin. Thus the new device contributes to maintenance and measurement. Lastly, the effectiveness and accuracy of device are verified by contrasting calculation and simulation on the basis of actual design parameters. And the new measuring lift method can be proved to be effective through experiments. The new device is achieved from conventional fin stabilizers. Accordingly, the reliability of original equipment is inherited. The alteration of fin stabilizers is minor, which is suitable for engineering application. In addition, the flexural properties of fin-shaft are digitized with analysis of stiffness matrix. This method provides theoretical support for engineering application by carrying out finite

  8. Vibration Control via Stiffness Switching of Magnetostrictive Transducers

    NASA Technical Reports Server (NTRS)

    Scheidler, Justin J.; Asnani, Vivake M.; Dapino, Marcelo J.

    2016-01-01

    This paper presents a computational study of structural vibration control that is realized by switching a magnetostrictive transducer between high and low stiffness states. Switching is accomplished by either changing the applied magnetic field with a voltage excitation or changing the shunt impedance on the transducer's coil (i.e., the magnetostrictive material's magnetic boundary condition). Switched-stiffness vibration control is simulated using a lumped mass supported by a damper and the magnetostrictive transducer (mount), which is represented by a nonlinear, electromechanical model. Free vibration of the mass is calculated while varying the mount's stiffness according to a reference switched-stiffness vibration control law. The results reveal that switching the magnetic field produces the desired change in stiffness, but also an undesired actuation force that can significantly degrade the vibration control. Hence, a modified switched-stiffness control law that accounts for the actuation force is proposed and implemented for voltage-controlled stiffness switching. The influence of the magnetomechanical bias condition is also discussed. Voltage-controlled stiffness switching is found to introduce damping equivalent to a viscous damping factor up to about 0.25; this is shown to primarily result from active vibration reduction caused by the actuation force. The merit of magnetostrictive switched-stiffness vibration control is then quantified by comparing the results of voltage- and shunt-controlled stiffness switching to the performance of optimal magnetostrictive shunt damping.

  9. Actin cytoskeleton stiffness grades metastatic potential of ovarian carcinoma Hey A8 cells via nanoindentation mapping.

    PubMed

    Zhou, Z L; Sun, X X; Ma, J; Tong, M H; To, S K Y; Wong, A S T; Ngan, A H W

    2017-07-26

    Recent studies have indicated that the nanoindentation measured stiffness of carcinoma adherent cells is in general lower than normal cells, thus suggesting that cell stiffness may serve as a bio-marker for carcinoma. However, the proper establishment of such a conclusion would require biophysical understanding of the underlying mechanism of the cell stiffness. In this work, we compared the elastic moduli of the actin cytoskeletons of Hey A8 ovarian carcinoma cells with and without metastasis (HM and NM), as measured by 2D atomic force microscopy (AFM) with low-depth nanoindentation via a rate-jump method. The results indicate clearly that HM cells showed lower actin cytoskeleton stiffness atop of their nucleus position and higher actin cytoskeleton stiffness at their rims, compared to NM cells, suggesting that the local stiffness on the cytoskeleton can reflect actin filament distribution. Immunofluorescence staining and scanning electron microscopy (SEM) also indicated that the difference in stiffness in Hey A8 cells with different metastasis is associated with their F-actin rearrangement. Finite-element modelling (FEM) shows that a migrating cell would have its actin filaments bundled together to form stress fibers, which would exhibit lower indentation stiffness than the less aligned arrangement of filaments in a non-migrating cell. The results here indicate that the actin cytoskeleton stiffness can serve as a reliable marker for grading the metastasis of adherent carcinoma cells due to their cytoskeleton change and potentially predicting the migration direction of the cells. Copyright © 2017 Elsevier Ltd. All rights reserved.

  10. Determinants of arterial stiffness in an apparently healthy population over 60 years.

    PubMed

    Alecu, C; Gueguen, R; Aubry, C; Salvi, P; Perret-Guillaume, C; Ducrocq, X; Vespignani, H; Benetos, A

    2006-10-01

    Arterial stiffness assessed by the pulse wave velocity (PWV), a non-invasive and reproducible method, predicts cardiovascular morbidity and mortality. The main determinants of arterial stiffness are well established in younger and middle-aged populations, but much less in the elderly. The aim of this study was to describe the determinants of arterial stiffness in elderly apparently healthy subjects. The study included 221 voluntary subjects born before 1944 (mean age 67.4+/-5.0 years), who had a standard health check-up at the 'Centre de Médecine Préventive' of Nancy. Arterial stiffness was evaluated by measuring the carotid-femoral PWV with the PulsePen automatic device. Clinical and biological parameters were evaluated at the same day. Measurements were valid and analysed in 207 subjects (94 women). Mean PWV was 9.39+/-2.64 m/s. Men showed higher PWV values than women (9.99+/-2.56 vs 8.66+/-2.56, P<0.001). In univariate analysis, PWV was correlated with age (r=0.26, P<0.001) and mean arterial pressure (MAP) (r=0.40, P<0.001), and these relationships were similar in men and women. Subjects with hypertension (P<0.001), diabetes mellitus (P<0.001) and obesity (P<0.01) had higher values of PWV. In multiple regression analysis, PWV correlated positively and independently with age, male gender, MAP and diabetes mellitus. In conclusion, in an apparently healthy elderly population, the main determinants of arterial stiffness are the age, MAP, diabetes and gender. Our study also shows that the gender-related differences in arterial stiffness observed in middle-aged subjects are maintained in the elderly.

  11. Acetabular shell deformation as a function of shell stiffness and bone strength.

    PubMed

    Dold, Philipp; Pandorf, Thomas; Flohr, Markus; Preuss, Roman; Bone, Martin C; Joyce, Tom J; Holland, James; Deehan, David

    2016-04-01

    Press-fit acetabular shells used for hip replacement rely upon an interference fit with the bone to provide initial stability. This process may result in deformation of the shell. This study aimed to model shell deformation as a process of shell stiffness and bone strength. A cohort of 32 shells with two different wall thicknesses (3 and 4 mm) and 10 different shell sizes (44- to 62-mm outer diameter) were implanted into eight cadavers. Shell deformation was then measured in the cadavers using a previously validated ATOS Triple Scan III optical system. The shell-bone interface was then considered as a spring system according to Hooke's law and from this the force exerted on the shell by the bone was calculated using a combined stiffness consisting of the measured shell stiffness and a calculated bone stiffness. The median radial stiffness for the 3-mm wall thickness was 4192 N/mm (range, 2920-6257 N/mm), while for the 4-mm wall thickness the median was 9633 N/mm (range, 6875-14,341 N/mm). The median deformation was 48 µm (range, 3-187 µm), while the median force was 256 N (range, 26-916 N). No statistically significant correlation was found between shell stiffness and deformation. Deformation was also found to be not fully symmetric (centres 180° apart), with a median angle discrepancy of 11.5° between the two maximum positive points of deformation. Further work is still required to understand how the bone influences acetabular shell deformation. © IMechE 2016.

  12. Quantifying the effects of hydration on corneal stiffness with optical coherence elastography

    NASA Astrophysics Data System (ADS)

    Singh, Manmohan; Li, Jiasong; Han, Zhaolong; Vantipalli, Srilatha; Aglyamov, Salavat R.; Twa, Michael D.; Larin, Kirill V.

    2018-02-01

    Several methods have been proposed to assess changes in corneal biomechanical properties due to various factors, such as degenerative diseases, intraocular pressure, and therapeutic interventions (e.g. corneal collagen crosslinking). However, the effect of the corneal tissue hydration state on corneal stiffness is not well understood. In this work, we induce low amplitude (< 10 μm) elastic waves with a focused micro air-pulse in fresh in situ rabbit corneas (n = 10) in the whole eye-globe configuration at an artificially controlled intraocular pressure. The waves were then detected with a phase-stabilized swept source optical coherence elastography system. Baseline measurements were taken every 20 minutes for an hour while the corneas were hydrated with 1X PBS. After the measurement at 60 minutes, a 20% dextran solution was topically instilled to dehydrate the corneas. The measurements were repeated every 20 minutes again for an hour. The results showed that the elastic wave velocity decreased as the corneal thickness decreased. Finite element modeling (FEM) was performed using the corneal geometry and elastic wave propagation speed to assess the stiffness of the samples. The results show that the stiffness increased from 430 kPa during hydration with PBS to 500 kPa after dehydration with dextran, demonstrating that corneal hydration state, apart from geometry and intraocular pressure, can change the stiffness of the cornea.

  13. Vibration Control via Stiffness Switching of Magnetostrictive Transducers

    NASA Technical Reports Server (NTRS)

    Scheidler, Justin J.; Asnani, Vivake M.; Dapino, Marcelo J.

    2016-01-01

    In this paper, a computational study is presented of structural vibration control that is realized by switching a magnetostrictive transducer between high and low stiffness states. Switching is accomplished by either changing the applied magnetic field with a voltage excitation or changing the shunt impedance on the transducer's coil (i.e., the magnetostrictive material's magnetic boundary condition). Switched-stiffness vibration control is simulated using a lumped mass supported by a damper and the magnetostrictive transducer (mount), which is represented by a nonlinear, electromechanical model. Free vibration of the mass is calculated while varying the mount's stiffness according to a reference switched-stiffness vibration control law. The results reveal that switching the magnetic field produces the desired change in stiffness, but also an undesired actuation force that can significantly degrade the vibration control. Hence, a modified switched-stiffness control law that accounts for the actuation force is proposed and implemented for voltage-controlled stiffness switching. The influence of the magneto-mechanical bias condition is also discussed. Voltage-controlled stiffness switching is found to introduce damping equivalent to a viscous damping factor up to about 0.13; this is shown to primarily result from active vibration reduction caused by the actuation force. The merit of magnetostrictive switched-stiffness vibration control is then quantified by comparing the results of voltage- and shunt-controlled stiffness switching to the performance of optimal magnetostrictive shunt damping. For the cases considered, optimal resistive shunt damping performed considerably better than both voltage- and shunt-controlled stiffness switching.

  14. Postural Changes in Measures of Arterial Stiffness in Hypertensive Subjects on Antihypertensive Drug Therapy: A Prospective, Pilot Study.

    PubMed

    Sule, Ashish Anil; Jun, Du Qi; Cheong, Chin Yee

    2017-06-01

    Prospective study with a controlled arm to know if there are variations of measures of arterial stiffness with posture in subjects with hypertension on antihypertensive medications. We studied postural variations of measures of arterial stiffness in 21 subjects with diagnosed hypertension on antihypertensive medications and compared them with 21 normotensive subjects. All subjects underwent pulse-wave analysis on SphygmoCor in the morning between 8 am to 10 am initially in supine and then in sitting position after 3 minutes. Summary measures on demographics, and blood pressure characteristics at sitting and supine positions are obtained. Differences between characteristics at supine and sitting position are compared using nonparametric paired test of Wilcoxon signed-rank test. A value of p  < 0.05 was accepted as statistically significant. Antihypertensive medications decreased the supine aortic augmentation pressure (AAP) and augmentation index (AI) but not significantly. When subgroups of patients with antihypertensive treatment were analyzed, it was noted that angiotensin-converting enzyme inhibitor and angiotensin receptor blocker group (12) decreased AAP and AI significantly in supine position compared with patients on other antihypertensive medications (9) ( p -value 0.034 and 0.038, respectively). There was no significant difference in other groups of calcium channel blockers, β-blockers, or diuretics. However, in normotensive control arm, there was an increase in AAP and AI in the supine position. In hypertensive subjects, on antihypertensive, there was reduction in AAP and AI in supine position compared with those of normotensives. The significance of the decrease in AAP and AI in supine position on antihypertensive needs to be studied further.

  15. The relationship between arterial wall stiffness and left ventricular dysfunction.

    PubMed

    Hu, Y; Li, L; Shen, L; Gao, H

    2013-05-01

    The purpose of this study was to explore the relationship between left ventricular (LV) dysfunction and arterial wall stiffening. A total of 218 patients over the age of 45 diagnosed with hypertension in Jinan City and hospitalised between 2010 and 2011 were included in this study. LV function was evaluated using echocardiography (ECHO). Blood pressure was monitored with an automated tonometric device, and the parameters of arterial wall stiffness were measured. In addition, the metabolic parameters of blood samples, such as glucose and lipids, were also determined using the Cobas E601 analyser. Stiffness parameter beta positively correlated with LV diastolic function (E/Em ratio) (r = 0.255, p < 0.001). LV end-diastolic diameter not only related to the E/Em ratio (r = 0.196, p = 0.009) but also with beta (r = 0.220, p = 0.002). The stiffness parameter beta was an early indicator of E/Em ratio as determined by multiple regression analysis (R (2) = 0.381, p < 0.01). Age, blood pressure and fasting blood glucose contributed to stiffness parameter beta (p < 0.05), as well as the E/Em ratio (p < 0.01). Our findings suggested that LV dysfunction may have a direct relationship to arterial stiffening, independently of having similar risk factors. In addition, arterial stiffness can be an independent predictor of LV diastolic function, suggesting that the severity of arterial stiffness directly correlates with the severity of LV dysfunction.

  16. Knee joint stiffness in individuals with and without knee osteoarthritis: a preliminary study.

    PubMed

    Oatis, Carol A; Wolff, Edward F; Lennon, Sandra K

    2006-12-01

    Descriptive, case-matched comparison. To compare the knee joint stiffness and damping coefficients of individuals with knee osteoarthritis (KOA) to those of age- and gender-matched individuals without KOA. A secondary purpose was to investigate relationships between these coefficients and complaints of stiffness in individuals with KOA. KOA is a leading cause of disability, and stiffness is a common complaint in individuals with KOA. Yet the most common method of assessing knee joint stiffness is through a self-report questionnaire. Stiffness and damping coefficients at the knee were calculated in 10 volunteers (mean age +/- SD, 64.1+/-15.5 years) with KOA and compared to coefficients from age-and gender-matched individuals without KOA, collected in a previous study (mean age +/- SD, 62.1+/-13.9 years). Stiffness and damping coefficients were calculated from the angular motion of the knee during a relaxed oscillation. Spearman correlation coefficients were calculated between stiffness and damping coefficients and WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) scores for subjects with KOA. Independent 2-tailed t tests revealed significantly larger damping coefficients (P = .035) among those with KOA (95% CI, 0.10-2.32 Nm s/rad). Spearman rank correlations revealed a significant positive relationship (r = .85, P = .003) between the damping coefficient and the stiffness subscore of the WOMAC. This study offers preliminary data demonstrating the feasibility of measuring stiffness and damping coefficients in individuals with KOA. Additionally, the damping coefficient is increased in people with KOA when compared to age- and gender-matched individuals without KOA. The damping coefficient appears to be associated with the complaints of stiffness reported by the WOMAC.

  17. Stiff Hands

    MedlinePlus

    ... Stiff Hands Find a hand surgeon near you. Videos Figures Figure 1: Hand splint to help straighten ... or "in." Also, avoid using media types like "video," "article," and "picture." Tip 4: Your results can ...

  18. Threshold value of home pulse pressure predicting arterial stiffness in patients with type 2 diabetes: KAMOGAWA-HBP study.

    PubMed

    Kitagawa, Noriyuki; Ushigome, Emi; Matsumoto, Shinobu; Oyabu, Chikako; Ushigome, Hidetaka; Yokota, Isao; Asano, Mai; Tanaka, Muhei; Yamazaki, Masahiro; Fukui, Michiaki

    2018-03-01

    This cross-sectional multicenter study was designed to evaluate the threshold value of home pulse pressure (PP) and home systolic blood pressure (SBP) predicting the arterial stiffness in 876 patients with type 2 diabetes. We measured the area under the receiver-operating characteristic curve (AUC) and estimated the ability of home PP to identify arterial stiffness using Youden-Index defined cut-off point. The arterial stiffness was measured using the brachial-ankle pulse wave velocity (baPWV). AUC for arterial stiffness in morning PP was significantly greater than that in morning SBP (P < .001). AUC for arterial stiffness in evening PP was also significantly greater than that in evening SBP (P < .001). The optimal cut-off points for morning PP and evening PP, which predicted arterial stiffness, were 54.6 and 56.9 mm Hg, respectively. Our findings indicate that we should pay more attention to increased home PP in patients with type 2 diabetes. ©2018 Wiley Periodicals, Inc.

  19. The effect of eccentric and concentric calf muscle training on Achilles tendon stiffness.

    PubMed

    Morrissey, Dylan; Roskilly, Anna; Twycross-Lewis, Richard; Isinkaye, Tomide; Screen, Hazel; Woledge, Roger; Bader, Dan

    2011-03-01

    To compare in vivo effects of eccentric and concentric calf muscle training on Achilles tendon stiffness, in subjects without tendinopathy. Thirty-eight recreational athletes completed 6 weeks eccentric (6 males, 13 females, 21.6  ±  2.2 years) or concentric training (8 males, 11 females, 21.1  ±  2.0 years). Achilles tendon stiffness, tendon modulus and single-leg jump height were measured before and after intervention. Exercise adherence was recorded using a diary. All data are reported as mean  ±  SD. Groups were matched for height and weight but the eccentric training group were more active at baseline (P < 0.05). Tendon stiffness was higher in the eccentrically trained group at baseline compared to the concentrically trained group (20.9  ±  7.3 N/mm v 13.38  ±  4.66 N/mm; P = 0.001) and decreased significantly after eccentric training (to 17.2 ( ±  5.9) N/mm (P = 0.035)). There was no stiffness change in the concentric group (P = 0.405). Stiffness modulus showed similar changes to stiffness. An inverse correlation was found between initial, and subsequent, reduction in stiffness (r = -0.66). Jump height did not change and no correlation between stiffness change and adherence was observed in either group (r = 0.01). Six weeks of eccentric training can alter Achilles tendon stiffness while a matched concentric programme shows no similar effects. Studies in patients with Achilles tendinopathy are warranted.

  20. Ultra-endurance sports have no negative impact on indices of arterial stiffness.

    PubMed

    Radtke, Thomas; Schmidt-Trucksäss, Arno; Brugger, Nicolas; Schäfer, Daniela; Saner, Hugo; Wilhelm, Matthias

    2014-01-01

    Marathon running has been linked with higher arterial stiffness. Blood pressure is a major contributor to pulse wave velocity (PWV). We examined indices of arterial stiffness with a blood pressure-independent method in marathon runners and ultra-endurance athletes. Male normotensive amateur runners were allocated to three groups according to former participation in competitions: group I (recreational athletes), group II (marathon runners) and group III (ultra-endurance athletes). Indices of arterial stiffness were measured with a non-invasive device (VaSera VS-1500N, Fukuda Denshi, Japan) to determine the cardio-ankle vascular index (CAVI, primary endpoint) and brachial-ankle PWV (baPWV). Lifetime training hours were calculated. Cumulative competitions were expressed as marathon equivalents. Linear regression analysis was performed to determine predictors for CAVI and baPWV. Measurements of arterial stiffness were performed in 51 subjects (mean age 44.6 ± 1.2 years): group I (n = 16), group II (n = 19) and group III (n = 16). No between-group differences existed in age, anthropometric characteristics and resting BP. CAVI and baPWV were comparable between all groups (P = 0.604 and P = 0.947, respectively). In linear regression analysis, age was the only independent predictor for CAVI (R(2) = 0.239, β = 0.455, P = 0.001). Systolic BP was significantly associated with baPWV (R(2) = 0.225, β = 0.403, P = 0.004). In middle-aged normotensive athletes marathon running and ultra-endurance sports had no negative impact on arterial stiffness.

  1. [Liver stiffness measured by acoustic radiation force impulse imaging in assessing hepatic functional reserve in patients with space-occupying lesions in the liver].

    PubMed

    Yan, Hui-tong; Luo, Yu-kun; Tang, Wen-bo; Jiao, Zi-yu; Yao, Chun-xiao; Lv, Fa-qin; Tang, Jie

    2013-04-01

    To investigate the value of liver stiffness measured by acoustic radiation force impulse imaging(ARFI) in assessing hepatic functional reserve in patients with space-occupying lesions in the liver. Sixty-three patients with space-occupying lesions in the liver were enrolled. Liver stiffness (LS) measurements with ARFI and indocyanine green(ICG) retention test were performed in the same day, and plasma clearance rate of indocyanine green(ICG-K), ICG retention at 15 minutes(ICGR15) as well as 10 effective values of LS were recorded. The correlation between Child-Pugh score, ICGR15, ICG-K, and LS were evaluated. The LS measurements with ARFI failed in one patient. A strong correlation between LS and ICGR15(r=0.789, P<0.01) and an inverse correlation between LS and ICG-K(r=-0.738, P<0.01) were observed. Besides, there was a significant correlation between LS measurements and Child-Pugh score(r=0.929, P<0.01) . The LS significantly differed among patients with Child-Pugh class A, B, and C(P<0.01) . ARFI is a simple, feasible and non-invasive method for assessing hepatic functional reserve in patients with space-occupying lesions in the liver.

  2. Constitutive Modelling of Resins in the Stiffness Domain

    NASA Astrophysics Data System (ADS)

    Klasztorny, M.

    2004-09-01

    An analytic method for inverting the constitutive compliance equations of viscoelasticity for resins is developed. These equations describe the HWKK/H rheological model, which makes it possible to simulate, with a good accuracy, short-, medium- and long-term viscoelastic processes in epoxy and polyester resins. These processes are of first-rank reversible isothermal type. The time histories of deviatoric stresses are simulated with three independent strain history functions of fractional and normal exponential types. The stiffness equations are described by two elastic and six viscoelastic constants having a clear physic meaning (three long-term relaxation coefficients and three relaxation times). The time histories of axiatoric stresses are simulated as perfectly elastic. The inversion method utilizes approximate constitutive stiffness equations of viscoelasticity for the HWKK/H model. The constitutive compliance equations for the model are a basis for determining the exact complex shear stiffness, whereas the approximate constitutive stiffness equations are used for determining the approximate complex shear stiffness. The viscoelastic constants in the stiffness domain are derived by equating the exact and approximate complex shear stiffnesses. The viscoelastic constants are obtained for Epidian 53 epoxy and Polimal 109 polyester resins. The accuracy of the approximate constitutive stiffness equations are assessed by comparing the approximate and exact complex shear stiffnesses. The constitutive stiffness equations for the HWKK/H model are presented in uncoupled (shear/bulk) and coupled forms. Formulae for converting the constants of shear viscoelasticity into the constants of coupled viscoelasticity are given as well.

  3. An infinitely-stiff elastic system via a tuned negative-stiffness component stabilized by rotation-produced gyroscopic forces

    NASA Astrophysics Data System (ADS)

    Kochmann, D. M.; Drugan, W. J.

    2016-06-01

    An elastic system containing a negative-stiffness element tuned to produce positive-infinite system stiffness, although statically unstable as is any such elastic system if unconstrained, is proved to be stabilized by rotation-produced gyroscopic forces at sufficiently high rotation rates. This is accomplished in possibly the simplest model of a composite structure (or solid) containing a negative-stiffness component that exhibits all these features, facilitating a conceptually and mathematically transparent, completely closed-form analysis.

  4. Particle numbers of lipoprotein subclasses and arterial stiffness among middle-aged men from the ERA JUMP study.

    PubMed

    Vishnu, A; Choo, J; Masaki, K H; Mackey, R H; Barinas-Mitchell, E; Shin, C; Willcox, B J; El-Saed, A; Seto, T B; Fujiyoshi, A; Miura, K; Lee, S; Sutton-Tyrrell, K; Kuller, L H; Ueshima, H; Sekikawa, A

    2014-02-01

    We examined the association between serum lipoprotein subclasses and the three measures of arterial stiffness, that is, (i) carotid-femoral pulse wave velocity (cfPWV), which is a gold standard measure of central arterial stiffness, (ii) brachial-ankle PWV (baPWV), which is emerging as a combined measure of central and peripheral arterial stiffness and (iii) femoral-ankle PWV (faPWV), which is a measure of peripheral arterial stiffness. Among a population-based sample of 701 apparently healthy Caucasian, Japanese American and Korean men aged 40-49 years, concentrations of lipoprotein particles were assessed by nuclear magnetic resonance (NMR) spectroscopy, and the PWV was assessed with an automated waveform analyzer (VP2000, Omron, Japan). Multiple linear regressions were performed to analyse the association between each NMR lipoprotein subclasses and PWV measures, after adjusting for cardiovascular risk factors and other confounders. A cutoff of P<0.01 was used for determining significance. All PWV measures had significant correlations with total and small low-density lipoprotein particle number (LDL-P) (all P<0.0001) but not LDL cholesterol (LDL-C) (all P>0.1), independent of race and age. In multivariate regression analysis, no NMR lipoprotein subclass was significantly associated with cfPWV (all P>0.01). However, most NMR lipoprotein subclasses had significant associations with both baPWV and faPWV (P<0.01). In this study of healthy middle-aged men, as compared with cfPWV, both baPWV and faPWV had stronger associations with particle numbers of lipoprotein subclasses. Our results may suggest that both baPWV and faPWV are related to arterial stiffness and atherosclerosis, whereas cfPWV may represent arterial stiffness alone.

  5. Early-time cosmology with stiff era from modified gravity

    NASA Astrophysics Data System (ADS)

    Odintsov, S. D.; Oikonomou, V. K.

    2017-11-01

    In this work, we shall incorporate a stiff era in the Universe's evolution in the context of F (R ) gravity. After deriving the vacuum F (R ) gravity, which may realize a stiff evolution, we combine the stiff F (R ) gravity with an R2 model, and we construct a qualitative model for the inflationary and stiff era, with the latter commencing after the end of the inflationary era. We assume that the baryogenesis occurs during the stiff era, and we calculate the baryon to entropy ratio, which effectively constraints the functional form of the stiff F (R ) gravity. Further constraints on the stiff F (R ) gravity may come from the primordial gravitational waves, and particularly their scalar mode, which is characteristic of the F (R ) gravity theory. The stiff era presence does not contradict the standard cosmology era, namely, inflation, and the radiation-matter domination eras. Furthermore, we investigate which F (R ) gravity may realize a dust and stiff matter dominated Einstein-Hilbert evolution.

  6. Analytical study of a quasi-zero stiffness coupling using a torsion magnetic spring with negative stiffness

    NASA Astrophysics Data System (ADS)

    Zheng, Yisheng; Zhang, Xinong; Luo, Yajun; Zhang, Yahong; Xie, Shilin

    2018-02-01

    By now, many translation quasi-zero stiffness (QZS) mechanisms have been proposed to overcome the restriction between the isolation frequency range and the load bearing capacity of linear isolators. The couplings of rotor systems undertake the functions of transmitting static driving torque and isolating disturbing torque simultaneously, which creates the demand of torsion QZS mechanisms. Hence a QZS coupling is presented in this paper, where a torsion magnetic spring (TMS) composed of two coaxial ring magnet arrangements in repulsive configuration is employed to produce negative torsion stiffness to counteract the positive stiffness of a rubber spring. In this paper, the expressions of magnetic torque and stiffness are given firstly and verified by finite element simulations; and the effect of geometric parameters of the TMS on its stiffness characteristic is analyzed in detail, which contributes to the optimal design of the TMS. Then dynamic analysis of the QZS coupling is performed and the analytical expression of the torque transmissibility is achieved based on the Harmonic Balance Method. Finally, simulation of the torque transmissibility is carried out to reveal how geometric parameters of the TMS affect the isolation performance.

  7. Association between triglyceride glucose index and arterial stiffness in Korean adults.

    PubMed

    Lee, Sang Bae; Ahn, Chul Woo; Lee, Byoung Kwon; Kang, Shinae; Nam, Ji Sun; You, Ji Hong; Kim, Min Jin; Kim, Min Kyung; Park, Jong Suk

    2018-03-21

    The triglyceride glucose (TyG) index has been suggested as a simple surrogate marker of insulin resistance. However, there are limited data regarding the association between the TyG index and arterial stiffness in adults. Therefore, we evaluated the relationship between the TyG index and arterial stiffness as measured based on brachial ankle pulse wave velocity (baPWV) in Korean adults. A total of 3587 subjects were enrolled in this study. Anthropometric and cardiovascular risk factors were measured. The TyG index was calculated as ln[fasting triglycerides(mg/dl) × fasting glucose(mg/dl)/2], and the insulin resistance index of homeostasis model assessment (HOMA-IR) was estimated. Arterial stiffness was determined by measuring baPWV. The subjects were stratified into four groups based on the TyG index. There were significant differences in cardiovascular parameters among the groups; the mean baPWV increased significantly with increasing TyG index. According to the logistic regression analysis after adjusting for multiple risk factors, the odds ratio (95% CI) for increased baPWV (> 75th percentile) for the highest and lowest quartiles of the TyG index was 2.92 (1.92-4.44) in men and 1.84 (1.15-2.96) in women, and the odds ratio for increased baPWV for the highest and lowest quartiles of the HOMA-IR was 1.80 (1.17-2.78) in men and 1.46 (1.06-2.47) in women, respectively. The TyG index is more independently associated with increased arterial stiffness than HOMA-IR in Korean adults.

  8. Dispersive Stiffness of Dzyaloshinskii Domain Walls

    NASA Astrophysics Data System (ADS)

    Pellegren, J. P.; Lau, D.; Sokalski, V.

    2017-07-01

    It is well documented that subjecting perpendicular magnetic films that exhibit the interfacial Dzyaloshinskii-Moriya interaction to an in-plane magnetic field results in a domain wall (DW) energy σ , which is highly anisotropic with respect to the orientation of the DW in the film plane Θ . We demonstrate that this anisotropy has a profound impact on the elastic response of the DW as characterized by the surface stiffness σ ˜ (Θ )=σ (Θ )+σ''(Θ ) and evaluate its dependence on the length scale of deformation. The influence of stiffness on DW mobility in the creep regime is assessed, with analytic and numerical calculations showing trends in σ ˜ that better represent experimental measurements of domain wall velocity in magnetic thin films compared to σ alone. Our treatment provides experimental support for theoretical models of the mobility of anisotropic elastic manifolds and makes progress toward a more complete understanding of magnetic domain wall creep.

  9. Biomechanical evaluation of primary stiffness of tibiotalocalcaneal fusion with intramedullary nails.

    PubMed

    Mückley, Thomas; Eichorn, Stephan; Hoffmeier, Konrad; von Oldenburg, Geert; Speitling, Andreas; Hoffmann, Gunther O; Bühren, Volker

    2007-02-01

    Intramedullary implants are being used with increasing frequency for tibiotalocalcaneal fusion (TTCF). Clinically, the question arises whether intramedullary (IM) nails should have a compression mode to enhance biomechanical stiffness and fusion-site compression. This biomechanical study compared the primary stability of TTCF constructs using compressed and uncompressed retrograde IM nails and a screw technique in a bone model. For each technique, three composite bone models were used. The implants were a Biomet nail (static locking mode and compressed mode), a T2 femoral nail (compressed mode); a prototype IM nail 1 (PT1, compressed mode), a prototype IM nail 2 (PT2, dynamic locking mode and compressed mode), and a three-screw construct. The compressed contact surface of each construct was measured with pressure-sensitive film and expressed as percent of the available fusion-site area. Stiffness was tested in dorsiflexion and plantarflexion (D/P), varus and valgus (V/V), and internal rotation and external rotation (I/E) (20 load cycles per loading mode). Mean contact surfaces were 84.0 +/- 6.0% for the Biomet nail, 84.0 +/- 13.0% for the T2 nail, 70.0 +/- 7.2% for the PTI nail, and 83.5 +/- 5.5% for the compressed PT2 nail. The greatest primary stiffness in D/P was obtained with the compressed PT2, followed by the compressed Biomet nail. The dynamically locked PT2 produced the least primary stiffness. In V/V, PT1 had the (significantly) greatest primary stiffness, followed by the compressed PT2. The statically locked Biomet nail and the dynamically locked PT2 had the least primary stiffness in V/V. In I/E, the compressed PT2 had the greatest primary stiffness, followed by the PT1 and the T2 nails, which did not differ significantly from each other. The dynamically locked PT2 produced the least primary stiffness. The screw construct's contact surface and stiffness were intermediate. The IM nails with compression used for TTCF produced good contact surfaces and

  10. Prognostic durability of liver fibrosis tests and improvement in predictive performance for mortality by combining tests.

    PubMed

    Bertrais, Sandrine; Boursier, Jérôme; Ducancelle, Alexandra; Oberti, Frédéric; Fouchard-Hubert, Isabelle; Moal, Valérie; Calès, Paul

    2017-06-01

    There is currently no recommended time interval between noninvasive fibrosis measurements for monitoring chronic liver diseases. We determined how long a single liver fibrosis evaluation may accurately predict mortality, and assessed whether combining tests improves prognostic performance. We included 1559 patients with chronic liver disease and available baseline liver stiffness measurement (LSM) by Fibroscan, aspartate aminotransferase to platelet ratio index (APRI), FIB-4, Hepascore, and FibroMeter V2G . Median follow-up was 2.8 years during which 262 (16.8%) patients died, with 115 liver-related deaths. All fibrosis tests were able to predict mortality, although APRI (and FIB-4 for liver-related mortality) showed lower overall discriminative ability than the other tests (differences in Harrell's C-index: P < 0.050). According to time-dependent AUROCs, the time period with optimal predictive performance was 2-3 years in patients with no/mild fibrosis, 1 year in patients with significant fibrosis, and <6 months in cirrhotic patients even in those with a model of end-stage liver disease (MELD) score <15. Patients were then randomly split in training/testing sets. In the training set, blood tests and LSM were independent predictors of all-cause mortality. The best-fit multivariate model included age, sex, LSM, and FibroMeter V2G with C-index = 0.834 (95% confidence interval, 0.803-0.862). The prognostic model for liver-related mortality included the same covariates with C-index = 0.868 (0.831-0.902). In the testing set, the multivariate models had higher prognostic accuracy than FibroMeter V2G or LSM alone for all-cause mortality and FibroMeter V2G alone for liver-related mortality. The prognostic durability of a single baseline fibrosis evaluation depends on the liver fibrosis level. Combining LSM with a blood fibrosis test improves mortality risk assessment. © 2016 Journal of Gastroenterology and Hepatology Foundation and John Wiley & Sons Australia

  11. Familial history of hypertension as a predictor of increased arterial stiffness in normotensive offspring.

    PubMed

    Youssef, Ghada; El Tebi, Ibrahim; Osama, Dina; Shehahta, Ahmed; Baligh, Essam; Ashour, Zeinab; Gamal, Hany

    2017-03-01

    Increased arterial stiffness can be used as a prognostic marker of arterial hypertension. The relationship between arterial stiffness and arterial hypertension seems to be reciprocal. Evaluation of changes of the arterial elastic prosperities in normotensive subjects, with and without parental history of hypertension. One hundred and ten normotensive individuals, aged 20-30 years, were divided into two groups: group-A ( n  = 57) and group-B ( n  = 53) subjects with positive and negative parental history of hypertension, respectively. Systolic, diastolic and pulse pressures were measured using mercury sphygmomanometer. The elastic properties of the ascending aorta and the common carotid arteries were assessed using M-mode echo and B-mode imaging, respectively. Stiffness index of the digital volume pulse (SIDVP) was measured in the right index finger using photoplethysmography. Group A subjects showed higher aortic stiffness index ( p  = 0.002), carotid stiffness index ( p  = 0.001), carotid pulse wave velocity ( p  ⩽ 0.001) and stiffness index of digital volume pulse ( p  = 0.001). Group A subjects showed lower aortic distensibility ( p  = 0.001), aortic strain ( p  = 0.004), changes in aortic diameter ( p  = 0.022), carotid distension ( p  = 0.026), carotid distensibility coefficient ( p  ⩽ 0.001) and carotid compliance coefficient ( p  = 0.002). The aortic and carotid stiffness parameters and SIDVP were higher in normotensive offspring of hypertensive parents. This finding could direct the attention towards the increased cardiovascular risk in this group and thus prompt earlier and tighter prevention of cardiovascular risk factors.

  12. Cone penetrometer equipped with piezoelectric sensors for measurement of soil stiffness in highway pavement.

    DOT National Transportation Integrated Search

    2005-11-01

    The stiffness (elastic modulus and shear modulus) and Poisson's ratio of the base and sublayers are important parameters in the design and quality assurance during construction of highway pavements. The new highway construction guide proposed by AASH...

  13. Research regarding stiffness optimization of wires used for joints actuation from an elephant's trunk robotic arm

    NASA Astrophysics Data System (ADS)

    Ciofu, C.; Stan, G.

    2016-11-01

    Elephant's trunk robotic arms driven by wires and pulley mechanisms have issues with wires stiffness because of the entailed elastic deformations that is causing errors of positioning. Static and dynamic loads from each joint of the robotic arm affect the stiffness of driving wires and precision positioning. The influence of wires elastic deformation on precision positioning decreases with the increasing of wires stiffness by using different pre-tensioning devices. In this paper, we analyze the variation of driving wires stiffness particularly to each wire driven joint. We obtain optimum wires stiffness variation by using an analytical method that highlights the efficiency of pre-tensioning mechanism. The analysis of driving wires stiffness is necessary for taking appropriate optimization measures of robotic arm dynamic behavior and, thus, for decreasing positioning errors of the elephant's trunk robotic arm with inner actuation through wires/cables.

  14. First results from the NEWS-G direct dark matter search experiment at the LSM

    NASA Astrophysics Data System (ADS)

    Arnaud, Q.; Asner, D.; Bard, J.-P.; Brossard, A.; Cai, B.; Chapellier, M.; Clark, M.; Corcoran, E. C.; Dandl, T.; Dastgheibi-Fard, A.; Dering, K.; Di Stefano, P.; Durnford, D.; Gerbier, G.; Giomataris, I.; Gorel, P.; Gros, M.; Guillaudin, O.; Hoppe, E. W.; Kamaha, A.; Katsioulas, I.; Kelly, D. G.; Martin, R. D.; McDonald, J.; Muraz, J.-F.; Mols, J.-P.; Navick, X.-F.; Papaevangelou, T.; Piquemal, F.; Roth, S.; Santos, D.; Savvidis, I.; Ulrich, A.; Vazquez de Sola Fernandez, F.; Zampaolo, M.

    2018-01-01

    New Experiments With Spheres-Gas (NEWS-G) is a direct dark matter detection experiment using Spherical Proportional Counters (SPCs) with light noble gases to search for low-mass Weakly Interacting Massive Particles (WIMPs). We report the results from the first physics run taken at the Laboratoire Souterrain de Modane (LSM) with SEDINE, a 60 cm diameter prototype SPC operated with a mixture of Ne + CH4 (0.7%) at 3.1 bars for a total exposure of 9.6 kg · days. New constraints are set on the spin-independent WIMP-nucleon scattering cross-section in the sub-GeV/c2 mass region. We exclude cross-sections above 4.4 ×10-37cm2 at 90% confidence level (C.L.) for a 0.5 GeV/c2 WIMP. The competitive results obtained with SEDINE are promising for the next phase of the NEWS-G experiment: a 140 cm diameter SPC to be installed at SNOLAB by summer 2018.

  15. Paraspinal Muscle Passive Stiffness Remodels in Direct Response to Spine Stiffness: A Study Using the ENT1-Deficient Mouse.

    PubMed

    Gsell, Kelsey Y; Zwambag, Derek P; Fournier, Dale E; Séguin, Cheryle A; Brown, Stephen H M

    2017-10-01

    Basic science study of the relationship between the structural properties of the spine and its surrounding musculature. To determine whether an increase in spine stiffness causes an inverse compensatory change in the passive stiffness of the adjacent paraspinal muscles. Intervertebral disc degeneration causes an increase in multifidus passive stiffness; this was hypothesized to compensate for a decrease in spine stiffness associated with disc degeneration. Mice lacking equilibrative nucleoside transporter 1 (ENT1) develop progressive ectopic calcification of the fibrous connective tissues of the spine, which affects the lumbar spine by 6 months of age and likely creates a mechanically stiffer spine. Experiments were conducted on four groups of mice (n = 8 mice/group): wild-type (WT) and ENT1 knockout (KO) at 2 or 8 months of age. Lumbar spines were removed and tested in cyclic axial compression to determine neutral zone length and stiffness. Single muscle fibers and bundles of fibers were isolated from lumbar multifidus and erector spinae, as well as tibialis anterior (a non-spine-related control) and tested to determine elastic modulus (passive stiffness). At 2 months of age, neither spine nor muscle stiffness was different between KO and WT. At 8 months of age, compared with WT the lumbar spines of ENT1 KO mice had a stiffer and shorter neutral zone, and the paraspinal muscle fibers were less stiff; however, fiber bundles were not different. In addition, tibialis anterior was not different between KO and WT. This work has confirmed that calcification of spinal connective tissues in the ENT1 KO mouse results in a stiffened spine, whereas the concurrent decrease in muscle fiber elastic modulus in the adjacent paraspinal muscles suggests a direct compensatory relationship between the stiffness of the spine and the muscles that are attached to it. N/A.

  16. Altered neuromuscular control of leg stiffness following soccer-specific exercise.

    PubMed

    Oliver, Jon L; De Ste Croix, Mark B A; Lloyd, Rhodri S; Williams, Craig A

    2014-11-01

    To examine changes to neuromuscular control of leg stiffness following 42 min of soccer-specific exercise. Ten youth soccer players, aged 15.8 ± 0.4 years, stature 1.73 ± 0.06 m and mass 59.8 ± 9.7 kg, hopped on a force plate at a self-selected frequency before and after simulated soccer exercise performed on a non-motorised treadmill. During hopping, muscle activity was measured using surface electromyography from four lower limb muscles and analysed to determine feedforward- and feedback-mediated activity, as well as co-contraction. There was a small, non-significant change in stiffness following exercise (26.6 ± 10.6 vs. 24.0 ± 7.0 kN m(-1), p > 0.05, ES = 0.25), with half the group increasing and half decreasing their stiffness. Changes in stiffness were significantly related to changes in centre of mass (CoM) displacement (r = 0.90, p < 0.01, extremely large correlation) but not changes in peak ground reaction force (r = 0.58, p > 0.05, large correlation). A number of significant relationships were observed between changes in stiffness and CoM displacement with changes in feedforward, feedback and eccentric muscle activity of the soleus and vastus lateralis muscles following exercise (r = 0.64-0.98, p < 0.05, large-extremely large correlations), but not with changes in co-contraction (r = 0.11-0.55, p > 0.05, small-large correlations). Following soccer-specific exercise individual changes in feedforward- and reflex-mediated activity of the soleus and vastus lateralis, and not co-contraction around the knee and ankle, modulate changes in CoM displacement and leg stiffness.

  17. Variation in within-bone stiffness measured by nanoindentation in mice bred for high levels of voluntary wheel running.

    PubMed

    Middleton, Kevin M; Goldstein, Beth D; Guduru, Pradeep R; Waters, Julie F; Kelly, Scott A; Swartz, Sharon M; Garland, T

    2010-01-01

    The hierarchical structure of bone, involving micro-scale organization and interaction of material components, is a critical determinant of macro-scale mechanics. Changes in whole-bone morphology in response to the actions of individual genes, physiological loading during life, or evolutionary processes, may be accompanied by alterations in underlying mineralization or architecture. Here, we used nanoindentation to precisely measure compressive stiffness in the femoral mid-diaphysis of mice that had experienced 37 generations of selective breeding for high levels of voluntary wheel running (HR). Mice (n = 48 total), half from HR lines and half from non-selected control (C) lines, were divided into two experimental groups, one with 13-14 weeks of access to a running wheel and one housed without wheels (n = 12 in each group). At the end of the experiment, gross and micro-computed tomography (microCT)-based morphometric traits were measured, and reduced elastic modulus (E(r)) was estimated separately for four anatomical quadrants of the femoral cortex: anterior, posterior, lateral, and medial. Two-way, mixed-model analysis of covariance (ancova) showed that body mass was a highly significant predictor of all morphometric traits and that structural change is more apparent at the microCT level than in conventional morphometrics of whole bones. Both line type (HR vs. C) and presence of the mini-muscle phenotype (caused by a Mendelian recessive allele and characterized by a approximately 50% reduction in mass of the gastrocnemius muscle complex) were significant predictors of femoral cortical cross-sectional anatomy. Measurement of reduced modulus obtained by nanoindentation was repeatable within a single quadrant and sensitive enough to detect inter-individual differences. Although we found no significant effects of line type (HR vs. C) or physical activity (wheel vs. no wheel) on mean stiffness, anterior and posterior quadrants were significantly stiffer (P < 0

  18. Does experimental low back pain change posteroanterior lumbar spinal stiffness and trunk muscle activity? A randomized crossover study.

    PubMed

    Wong, Arnold Y L; Parent, Eric C; Prasad, Narasimha; Huang, Christopher; Chan, K Ming; Kawchuk, Gregory N

    2016-05-01

    While some patients with low back pain demonstrate increased spinal stiffness that decreases as pain subsides, this observation is inconsistent. Currently, the relation between spinal stiffness and low back pain remains unclear. This study aimed to investigate the effects of experimental low back pain on temporal changes in posteroanterior spinal stiffness and concurrent trunk muscle activity. In separate sessions five days apart, nine asymptomatic participants received equal volume injections of hypertonic or isotonic saline in random order into the L3-L5 interspinous ligaments. Pain intensity, spinal stiffness (global and terminal stiffness) at the L3 level, and the surface electromyographic activity of six trunk muscles were measured before, immediately after, and 25-minute after injections. These outcome measures under different saline conditions were compared by generalized estimating equations. Compared to isotonic saline injections, hypertonic saline injections evoked significantly higher pain intensity (mean difference: 5.7/10), higher global (mean difference: 0.73N/mm) and terminal stiffness (mean difference: 0.58N/mm), and increased activity of four trunk muscles during indentation (P<0.05). Both spinal stiffness and trunk muscle activity returned to baseline levels as pain subsided. While previous clinical research reported inconsistent findings regarding the association between spinal stiffness and low back pain, our study revealed that experimental pain caused temporary increases in spinal stiffness and concurrent trunk muscle co-contraction during indentation, which helps explain the temporal relation between spinal stiffness and low back pain observed in some clinical studies. Our results substantiate the role of spinal stiffness assessments in monitoring back pain progression. Copyright © 2016 Elsevier Ltd. All rights reserved.

  19. Contact stiffness and damping of liquid films in dynamic atomic force microscope

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Xu, Rong-Guang; Leng, Yongsheng, E-mail: leng@gwu.edu

    2016-04-21

    The mechanical properties and dissipation behaviors of nanometers confined liquid films have been long-standing interests in surface force measurements. The correlation between the contact stiffness and damping of the nanoconfined film is still not well understood. We establish a novel computational framework through molecular dynamics (MD) simulation for the first time to study small-amplitude dynamic atomic force microscopy (dynamic AFM) in a simple nonpolar liquid. Through introducing a tip driven dynamics to mimic the mechanical oscillations of the dynamic AFM tip-cantilever assembly, we find that the contact stiffness and damping of the confined film exhibit distinct oscillations within 6-7 monolayermore » distances, and they are generally out-of-phase. For the solid-like film with integer monolayer thickness, further compression of the film before layering transition leads to higher stiffness and lower damping, while much lower stiffness and higher damping occur at non-integer monolayer distances. These two alternating mechanisms dominate the mechanical properties and dissipation behaviors of simple liquid films under cyclic elastic compression and inelastic squeeze-out. Our MD simulations provide a direct picture of correlations between the structural property, mechanical stiffness, and dissipation behavior of the nanoconfined film.« less

  20. Ultrasound shear wave elastography in the assessment of passive biceps brachii muscle stiffness: influences of sex and elbow position.

    PubMed

    Chen, Johnson; O'Dell, Michael; He, Wen; Du, Li-Juan; Li, Pai-Chi; Gao, Jing

    To assess differences in biceps brachii muscle (BBM) stiffness as evaluated by ultrasound shear wave elastography (SWE). The passive stiffness of the BBM was quantified with shear wave velocity (SWV) measurements obtained from 10 healthy volunteers (5 men and 5 women, mean age 50years, age range 42-63 years) with the elbow at full extension and 30° flexion in this IRB-approved study. Potential differences between two depths within the muscle, two elbow positions, the two arms, and sexes were assessed by using two-tailed t-test. The reproducibility of SWV measurements was tested by using intraclass correlation coefficient (ICC). Significantly higher passive BBM stiffness was found at full elbow extension compared to 30° of flexion (p≤0.00006 for both arms). Significantly higher passive stiffness in women was seen for the right arm (p=0.04 for both elbow positions). Good correlation of shear wave velocity measured at the different depths. The ICC for interobserver and intraobserver variation was high. SWE is a reliable quantitative tool for assessing BBM stiffness, with differences in stiffness based on elbow position demonstrated and based on sex suggested. Copyright © 2017 Elsevier Inc. All rights reserved.

  1. Comparison of stiffness and interface pressure during rest and exercise among various arm sleeves.

    PubMed

    Hirai, M; Niimi, K; Iwata, H; Sugimoto, I; Ishibashi, H; Ota, T; Nakamura, H

    2010-08-01

    To compare the interface pressure during rest and exercise among various kinds of arm sleeves. The interface pressure underneath nine different arm sleeves was measured during 10 maximal opening and closing movements of fingers using a pressure transducer (Air Pack Type Analyser) in 16 healthy volunteers. Furthermore, in order to evaluate the characteristics of each arm sleeve, the extensibility, stiffness and thickness were determined in vitro by several apparatuses. There was a significant correlation between stiffness and extensibility. The stiffness was significantly correlated with the pressure difference between muscle contraction and relaxation during exercise. The higher the value of stiffness, the greater the pressure amplitude during exercise. Short-stretch arm sleeves characterized with a high level stiffness, including thick round- and flat-knitted arm sleeves, are more beneficial for the augmentation of muscle pumping than long-stretch arm sleeves, in the same way as short-stretch bandages or stockings applied to the leg.

  2. A Stewart isolator with high-static-low-dynamic stiffness struts based on negative stiffness magnetic springs

    NASA Astrophysics Data System (ADS)

    Zheng, Yisheng; Li, Qingpin; Yan, Bo; Luo, Yajun; Zhang, Xinong

    2018-05-01

    In order to improve the isolation performance of passive Stewart platforms, the negative stiffness magnetic spring (NSMS) is employed to construct high static low dynamic stiffness (HSLDS) struts. With the NSMS, the resonance frequencies of the platform can be reduced effectively without deteriorating its load bearing capacity. The model of the Stewart isolation platform with HSLDS struts is presented and the stiffness characteristic of its struts is studied firstly. Then the nonlinear dynamic model of the platform including both geometry nonlinearity and stiffness nonlinearity is established; and its simplified dynamic model is derived under the condition of small vibration. The effect of nonlinearity on the isolation performance is also evaluated. Finally, a prototype is built and the isolation performance is tested. Both simulated and experimental results demonstrate that, by using the NSMS, the resonance frequencies of the Stewart isolator are reduced and the isolation performance in all six directions is improved: the isolation frequency band is increased and extended to a lower-frequency level.

  3. Laminar shear stress modulates endothelial luminal surface stiffness in a tissue-specific manner.

    PubMed

    Merna, Nick; Wong, Andrew K; Barahona, Victor; Llanos, Pierre; Kunar, Balvir; Palikuqi, Brisa; Ginsberg, Michael; Rafii, Shahin; Rabbany, Sina Y

    2018-04-17

    Endothelial cells form vascular beds in all organs and are exposed to a range of mechanical forces that regulate cellular phenotype. We sought to determine the role of endothelial luminal surface stiffness in tissue-specific mechanotransduction of laminar shear stress in microvascular mouse cells and the role of arachidonic acid in mediating this response. Microvascular mouse endothelial cells were subjected to laminar shear stress at 4 dynes/cm 2 for 12 hours in parallel plate flow chambers that enabled real-time optical microscopy and atomic force microscopy measurements of cell stiffness. Lung endothelial cells aligned parallel to flow, while cardiac endothelial cells did not. This rapid alignment was accompanied by increased cell stiffness. The addition of arachidonic acid to cardiac endothelial cells increased alignment and stiffness in response to shear stress. Inhibition of arachidonic acid in lung endothelial cells and embryonic stem cell-derived endothelial cells prevented cellular alignment and decreased cell stiffness. Our findings suggest that increased endothelial luminal surface stiffness in microvascular cells may facilitate mechanotransduction and alignment in response to laminar shear stress. Furthermore, the arachidonic acid pathway may mediate this tissue-specific process. An improved understanding of this response will aid in the treatment of organ-specific vascular disease. © 2018 John Wiley & Sons Ltd.

  4. Smed-SmB, a member of the LSm protein superfamily, is essential for chromatoid body organization and planarian stem cell proliferation.

    PubMed

    Fernandéz-Taboada, Enrique; Moritz, Sören; Zeuschner, Dagmar; Stehling, Martin; Schöler, Hans R; Saló, Emili; Gentile, Luca

    2010-04-01

    Planarians are an ideal model system to study in vivo the dynamics of adult pluripotent stem cells. However, our knowledge of the factors necessary for regulating the 'stemness' of the neoblasts, the adult stem cells of planarians, is sparse. Here, we report on the characterization of the first planarian member of the LSm protein superfamily, Smed-SmB, which is expressed in stem cells and neurons in Schmidtea mediterranea. LSm proteins are highly conserved key players of the splicing machinery. Our study shows that Smed-SmB protein, which is localized in the nucleus and the chromatoid body of stem cells, is required to safeguard the proliferative ability of the neoblasts. The chromatoid body, a cytoplasmatic ribonucleoprotein complex, is an essential regulator of the RNA metabolism required for the maintenance of metazoan germ cells. However, planarian neoblasts and neurons also rely on its functions. Remarkably, Smed-SmB dsRNA-mediated knockdown results in a rapid loss of organization of the chromatoid body, an impairment of the ability to post-transcriptionally process the transcripts of Smed-CycB, and a severe proliferative failure of the neoblasts. This chain of events leads to a quick depletion of the neoblast pool, resulting in a lethal phenotype for both regenerating and intact animals. In summary, our results suggest that Smed-SmB is an essential component of the chromatoid body, crucial to ensure a proper RNA metabolism and essential for stem cell proliferation.

  5. The relationship between latissimus dorsi stiffness and altered scapular kinematics among asymptomatic collegiate swimmers.

    PubMed

    Laudner, Kevin G; Williams, Jeffrey G

    2013-02-01

    To determine the strength of the relationship between latissimus dorsi stiffness and altered scapular kinematics among swimmers. Cross sectional. Laboratory. Nineteen NCAA Division III swimmers (7 male, 12 female) (age = 18.8 ± 0.9 years, height = 174.7 ± 8.9 cm, mass = 71.6 ± 11.9 kg) volunteered to participate. Subjects had no recent history of upper extremity pathology or any previous surgery. We measured latissimus dorsi stiffness of the dominant arm while in a lengthened position with a myotonometer. We used an electromagnetic tracking device with specialized software to measure scapular kinematics at humeral elevation angles of 30°, 60°, 90°, and 110° within the scapular plane. Latissimus dorsi stiffness and scapular upward/downward rotation, internal/external rotation, and anterior/posterior tilt. Latissimus dorsi stiffness showed moderate-to-good relationships with increased scapular upward rotation (r > -0.63, P < 0.002) and posterior tilt (r > -0.62, P < 0.004) at all four angles of humeral elevation. Increased latissimus dorsi stiffness also showed moderate-to-good relationships with decreased scapular internal rotation at humeral elevation angles of 60° (r = 0.47, P = 0.03) and 90° (r = 0.54, P = 0.01). Our results suggest there are several moderate-to-good relationships between increased latissimus dorsi stiffness in swimmers and altered scapular upward rotation, internal rotation, and posterior tilt at various angles of humeral elevation. If latissimus dorsi stiffness is not addressed subsequent scapular alterations, which have been associated with shoulder dysfunction, may occur. Published by Elsevier Ltd.

  6. Ambient Vibration Testing for Story Stiffness Estimation of a Heritage Timber Building

    PubMed Central

    Min, Kyung-Won; Kim, Junhee; Park, Sung-Ah; Park, Chan-Soo

    2013-01-01

    This paper investigates dynamic characteristics of a historic wooden structure by ambient vibration testing, presenting a novel estimation methodology of story stiffness for the purpose of vibration-based structural health monitoring. As for the ambient vibration testing, measured structural responses are analyzed by two output-only system identification methods (i.e., frequency domain decomposition and stochastic subspace identification) to estimate modal parameters. The proposed methodology of story stiffness is estimation based on an eigenvalue problem derived from a vibratory rigid body model. Using the identified natural frequencies, the eigenvalue problem is efficiently solved and uniquely yields story stiffness. It is noteworthy that application of the proposed methodology is not necessarily confined to the wooden structure exampled in the paper. PMID:24227999

  7. Rolling Element Bearing Stiffness Matrix Determination (Presentation)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Guo, Y.; Parker, R.

    2014-01-01

    Current theoretical bearing models differ in their stiffness estimates because of different model assumptions. In this study, a finite element/contact mechanics model is developed for rolling element bearings with the focus of obtaining accurate bearing stiffness for a wide range of bearing types and parameters. A combined surface integral and finite element method is used to solve for the contact mechanics between the rolling elements and races. This model captures the time-dependent characteristics of the bearing contact due to the orbital motion of the rolling elements. A numerical method is developed to determine the full bearing stiffness matrix corresponding tomore » two radial, one axial, and two angular coordinates; the rotation about the shaft axis is free by design. This proposed stiffness determination method is validated against experiments in the literature and compared to existing analytical models and widely used advanced computational methods. The fully-populated stiffness matrix demonstrates the coupling between bearing radial, axial, and tilting bearing deflections.« less

  8. Tuning the Stiffness Balance Using Characteristic Frequencies as a Criterion for a Superconducting Gravity Gradiometer.

    PubMed

    Liu, Xikai; Ma, Dong; Chen, Liang; Liu, Xiangdong

    2018-02-08

    Tuning the stiffness balance is crucial to full-band common-mode rejection for a superconducting gravity gradiometer (SGG). A reliable method to do so has been proposed and experimentally tested. In the tuning scheme, the frequency response functions of the displacement of individual test mass upon common-mode accelerations were measured and thus determined a characteristic frequency for each test mass. A reduced difference in characteristic frequencies between the two test masses was utilized as the criterion for an effective tuning. Since the measurement of the characteristic frequencies does not depend on the scale factors of displacement detection, stiffness tuning can be done independently. We have tested this new method on a single-component SGG and obtained a reduction of two orders of magnitude in stiffness mismatch.

  9. Non-crossbridge calcium-dependent stiffness in slow and fast skeletal fibres from mouse muscle.

    PubMed

    Nocella, Marta; Colombini, Barbara; Bagni, Maria Angela; Bruton, Joseph; Cecchi, Giovanni

    2012-03-01

    We showed previously that force development in frog and FDB mouse skeletal muscle fibres is preceded by an increase of fibre stiffness occurring well before crossbridge attachment and force generation. This stiffness increase, referred to as static stiffness, is due to a Ca(2+)-dependent stiffening of a non-crossbridge sarcomere structure which we suggested could be attributed to the titin filaments. To investigate further the role of titin in static stiffness, we measured static stiffness properties at 24 and 35°C in soleus and EDL mouse muscle fibres which are known to express different titin isoforms. We found that static stiffness was present in both soleus and EDL fibres, however, its value was about five times greater in EDL than in soleus fibres. The rate of development of static stiffness on stimulation increased with temperature and was slightly faster in EDL than in soleus in agreement with previously published data on the time course of the intracellular Ca(2+) transients in these muscles. The present results show that the presence of a non-crossbridge Ca(2+)-dependent stiffening of the muscle fibre is a physiological general characteristic of skeletal muscle. Static stiffness depends on fibre type, being greater and developing faster in fast than in slow fibres. Our observations are consistent with the idea that titin stiffening on contraction improves the sarcomere structure stability. Such an action in fact seems to be more important in EDL fast fibre than in soleus slow fibres.

  10. Effects of plyometric and isometric training on muscle and tendon stiffness in vivo.

    PubMed

    Kubo, Keitaro; Ishigaki, Tomonobu; Ikebukuro, Toshihiro

    2017-08-01

    The purpose of this study was to compare the effects of plyometric and isometric training on tendon properties during ramp and ballistic contractions and muscle stiffness under passive and active conditions. Eleven subjects completed 12 weeks (3 days/week) of a unilateral training program for the plantar flexors. They performed plyometric training on one side (PLY) and isometric training on the other side (ISO). Active muscle stiffness in the medial gastrocnemius muscle was calculated according to changes in estimated muscle force and fascicle length during fast stretching after submaximal isometric contractions. Passive muscle stiffness was also calculated from estimated passive muscle force and fascicle length during slow passive stretching. Stiffness and hysteresis of tendon structures were measured using ultrasonography during ramp and ballistic contractions. Passive muscle stiffness and tendon hysteresis did not change for PLY or ISO Active muscle stiffness significantly increased for PLY, but not for ISO Tendon stiffness during ramp and ballistic contractions increased significantly for ISO, but not for PLY In addition, tendon elongation values at force production levels beyond 100 N during ballistic contractions increased for PLY These results suggest that plyometric training (but not isometric training) enhances the extensibility of tendon structures during ballistic contractions and active muscle stiffness during fast stretching, and these changes may be related to improved performances during stretch-shortening cycle exercises. © 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

  11. Bending stiffness, torsional stability, and insertion force of cementless femoral stems.

    PubMed

    Incavo, S J; Johnson, C C; Churchill, D L; Beynnon, B D

    2001-04-01

    In cementless total hip arthroplasty, increased femoral stem flexibility and decreased fracture propensity are desirable characteristics. The slotting and tapering of the stem have been introduced to achieve this. These features should not, however, be allowed to interfere with the ability of the distal stem to provide initial mechanical stability, especially under rotation. This study was done to investigate the ability of slotted and tapered stem designs to reduce stiffness and insertion force while still maintaining adequate torsional strength. The torsional strength, maximum insertion force, and insertional work of straight, slotted, and taper stems were measured by inserting each type into rigid polyurethane foam and torque testing to failure. Bending stiffness of each stem design was calculated using numerical methods. When compared to a straight stem, a unislot stem has similar torsional strength, maximum insertional force, and work of insertion. The bending stiffness is decreased by 19% to 82% depending on the bending direction. A trislot design decreased torque strength by 29%, maximal insertion force by 36%, and work by 11%. Bending stiffness was decreased by 74% and was not dependent on bending direction. A 0.5-mm taper decreased torque strength by 11% and insertional work by 14%. No difference was seen in maximum insertional force. We conclude that the design features studied (slots and taper) are effective in decreasing stem stiffness and reducing fracture propensity.

  12. Stiffness-constant variation in nickel-based alloys: Experiment and theory

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hennion, M.; Hennion, B.

    1979-01-01

    Recent measurements of the spin-wave stiffness constant in several nickel alloys at various concentrations are interpreted within a random-phase approximation, coherent-potential approximation (RPA-CPA) band model which uses the Hartree-Fock approximation to treat the intraatomic correlations. We give a theoretical description of the possible impurity states in the Hartree-Fock approximation. This allows the determination of the Hartree-Fock solutions which can account for the stiffness-constant behavior and the magnetic moment on the impurity for all the investigated alloys. For alloys such as NiCr, NiV, NiMo, and NiRu, the magnetizations of which deviate from the Slater-Pauling curve, our determination does not correspond tomore » previous works and is consequently discussed. The limits of the model appear mainly due to local-environment effects; in the case of NiMn, it is found that a ternary-alloy model with some Mn atoms in the antiferromagnetic state can account for both stiffness-constant and magnetization behaviors.« less

  13. Normalized stiffness ratios for mechanical characterization of isotropic acoustic foams.

    PubMed

    Sahraoui, Sohbi; Brouard, Bruno; Benyahia, Lazhar; Parmentier, Damien; Geslain, Alan

    2013-12-01

    This paper presents a method for the mechanical characterization of isotropic foams at low frequency. The objective of this study is to determine the Young's modulus, the Poisson's ratio, and the loss factor of commercially available foam plates. The method is applied on porous samples having square and circular sections. The main idea of this work is to perform quasi-static compression tests of a single foam sample followed by two juxtaposed samples having the same dimensions. The load and displacement measurements lead to a direct extraction of the elastic constants by means of normalized stiffness and normalized stiffness ratio which depend on Poisson's ratio and shape factor. The normalized stiffness is calculated by the finite element method for different Poisson ratios. The no-slip boundary conditions imposed by the loading rigid plates create interfaces with a complex strain distribution. Beforehand, compression tests were performed by means of a standard tensile machine in order to determine the appropriate pre-compression rate for quasi-static tests.

  14. The interplay of stiffness and force anisotropies drives embryo elongation

    PubMed Central

    Vuong-Brender, Thanh Thi Kim; Ben Amar, Martine; Pontabry, Julien; Labouesse, Michel

    2017-01-01

    The morphogenesis of tissues, like the deformation of an object, results from the interplay between their material properties and the mechanical forces exerted on them. The importance of mechanical forces in influencing cell behaviour is widely recognized, whereas the importance of tissue material properties, in particular stiffness, has received much less attention. Using Caenorhabditis elegans as a model, we examine how both aspects contribute to embryonic elongation. Measuring the opening shape of the epidermal actin cortex after laser nano-ablation, we assess the spatiotemporal changes of actomyosin-dependent force and stiffness along the antero-posterior and dorso-ventral axis. Experimental data and analytical modelling show that myosin-II-dependent force anisotropy within the lateral epidermis, and stiffness anisotropy within the fiber-reinforced dorso-ventral epidermis are critical in driving embryonic elongation. Together, our results establish a quantitative link between cortical tension, material properties and morphogenesis of an entire embryo. DOI: http://dx.doi.org/10.7554/eLife.23866.001 PMID:28181905

  15. Effects of circumferential ankle pressure on ankle proprioception, stiffness, and postural stability: a preliminary investigation.

    PubMed

    You, Sung H; Granata, Kevin P; Bunker, Linda K

    2004-08-01

    Cross-sectional repeated-measures design. Determine the effects of circumferential ankle pressure (CAP) intervention on proprioceptive acuity, ankle stiffness, and postural stability. The application of CAP using braces, taping, and adaptive shoes or military boots is widely used to address chronic ankle instability (CAI). An underlying assumption is that the CAP intervention might improve ankle stability through increased proprioceptive acuity and stiffness in the ankle. METHOD AND MEASURES: A convenience sample of 10 subjects was recruited from the local university community and categorized according to proprioceptive acuity (high, low) and ankle stability (normal, CAI). Proprioceptive acuity was measured when blindfolded subjects were asked to accurately reproduce a self-selected target ankle position before and after the application of CAP. Proprioceptive acuity was determined in 5 different ankle joint position sense tests: neutral, inversion, eversion, plantar flexion, and dorsiflexion. Joint position angles were recorded electromechanically using a potentiometer. Passive ankle stiffness was computed from the ratio of applied static moment versus angular displacement. Active ankle stiffness was determined from biomechanical analyses of ankle motion following a mediolateral perturbation. Postural stability was quantified from the center of pressure displacement in the mediolateral and the anteroposterior directions in unipedal stance. All measurements were recorded with and without CAP applied by a pediatric blood pressure cuff. Data were analyzed using a separate mixed-model analysis of variance (ANOVA) for each dependent variable. Post hoc comparison using Tukey's honestly significant difference (HSD) test was performed if significant interactions were obtained. Significance level was set at P<.05 for all analyses. Significant group (high versus low proprioceptive acuity) x CAP interactions were identified for postural stability. Passive ankle stiffness was

  16. A novel variable stiffness mechanism for dielectric elastomer actuators

    NASA Astrophysics Data System (ADS)

    Li, Wen-Bo; Zhang, Wen-Ming; Zou, Hong-Xiang; Peng, Zhi-Ke; Meng, Guang

    2017-08-01

    In this paper, a novel variable stiffness mechanism is proposed for the design of a variable stiffness dielectric elastomer actuator (VSDEA) which combines a flexible strip with a DEA in a dielectric elastomer minimum energy structure. The DEA induces an analog tuning of the transverse curvature of the strip, thus conveniently providing a voltage-controllable flexural rigidity. The VSDEA tends to be a fully flexible and compact structure with the advantages of simplicity and fast response. Both experimental and theoretical investigations are carried out to reveal the variable stiffness performances of the VSDEA. The effect of the clamped location on the bending stiffness of the VSDEA is analyzed, and then effects of the lengths, the loading points and the applied voltages on the bending stiffness are experimentally investigated. An analytical model is developed to verify the availability of this variable stiffness mechanism, and the theoretical results demonstrate that the bending stiffness of the VSDEA decreases as the applied voltage increases, which agree well with the experimental data. Moreover, the experimental results show that the maximum change of the relative stiffness can reach about 88.80%. It can be useful for the design and optimization of active variable stiffness structures and DEAs for soft robots, vibration control, and morphing applications.

  17. Higher cell stiffness indicating lower metastatic potential in B16 melanoma cell variants and in (-)-epigallocatechin gallate-treated cells.

    PubMed

    Watanabe, Tatsuro; Kuramochi, Hiromi; Takahashi, Atsushi; Imai, Kazue; Katsuta, Naoko; Nakayama, Tomonobu; Fujiki, Hirota; Suganuma, Masami

    2012-05-01

    To understand how nanomechanical stiffness affects metastatic potential, we studied the relationship between cell migration, a characteristic of metastasis, and cell stiffness using atomic force microscopy (AFM), which can measure stiffness (elasticity) of individual living cells. Migration and cell stiffness of three metastatic B16 melanoma variants (B16-F10, B16-BL6, and B16-F1 cells), and also effects of (-)-epigallocatechin gallate (EGCG), were studied using Transwell assay and AFM. Migration of B16-F10 and B16-BL6 cells was 3 and 2 times higher than that of B16-F1 cells in Transwell assay, and cell stiffness determined by AFM was also different among the three variants, although they have similar morphologies and the same growth rates: Means of Young's modulus were 350.8 ± 4.8 Pa for B16-F10 cells, 661.9 ± 16.5 Pa for B16-BL6 cells, and 727.2 ± 13.0 Pa for B16-F1 cells. AFM measurements revealed that highly motile B16-F10 cells have low cell stiffness, and low motile and metastatic B16-F1 cells have high cell stiffness: Nanomechanical stiffness is inversely correlated with migration potential. Treatment of highly motile B16-F10 cells with EGCG increased cell stiffness 2-fold and inhibited migration of the cells. Our study with AFM clearly demonstrates that cell stiffness is a reliable quantitative indicator of migration potential, and very likely metastatic potential, even in morphologically similar cells. And increased cell stiffness may be a key nanomechanical feature in inhibition of metastasis.

  18. Biomechanical response to ankle-foot orthosis stiffness during running.

    PubMed

    Russell Esposito, Elizabeth; Choi, Harmony S; Owens, Johnny G; Blanck, Ryan V; Wilken, Jason M

    2015-12-01

    The Intrepid Dynamic Exoskeletal Orthosis (IDEO) is an ankle-foot orthosis developed to address the high rates of delayed amputation in the military. Its use has enabled many wounded Service Members to run again. During running, stiffness is thought to influence an orthosis' energy storage and return mechanical properties. This study examined the effect of orthosis stiffness on running biomechanics in patients with lower limb impairments who had undergone unilateral limb salvage. Ten patients with lower limb impairments underwent gait analysis at a self-selected running velocity. 1. Nominal (clinically-prescribed), 2. Stiff (20% stiffer than nominal), and 3. Compliant (20% less stiff than nominal) ankle-foot orthosis stiffnesses were tested. Ankle joint stiffness was greatest in the stiffest strut and lowest in the compliant strut, however ankle mechanical work remained unchanged. Speed, stride length, cycle time, joint angles, moments, powers, and ground reaction forces were not significantly different among stiffness conditions. Ankle joint kinematics and ankle, knee and hip kinetics were different between limbs. Ankle power, in particular, was lower in the injured limb. Ankle-foot orthosis stiffness affected ankle joint stiffness but did not influence other biomechanical parameters of running in individuals with unilateral limb salvage. Foot strike asymmetries may have influenced the kinetics of running. Therefore, a range of stiffness may be clinically appropriate when prescribing ankle-foot orthoses for active individuals with limb salvage. Published by Elsevier Ltd.

  19. Stiffness Corrections for the Vibration Frequency of a Stretched Wire

    ERIC Educational Resources Information Center

    Hornung, H. G.; Durie, M. J.

    1977-01-01

    Discusses the need of introducing corrections due to wire stiffness arising from end constraints and wire axis distribution curvature in the measurement of ac electrical frequency by exciting transverse standing waves in a stretched steel wire. (SL)

  20. Arterial stiffness and decline of renal function in a primary care population.

    PubMed

    van Varik, Bernard J; Vossen, Liv M; Rennenberg, Roger J; Stoffers, Henri E; Kessels, Alfons G; de Leeuw, Peter W; Kroon, Abraham A

    2017-01-01

    Arterial stiffness is an important pathophysiological factor linking cardiovascular disease and kidney disease. Controversy exists as to whether arterial stiffness causes renal function decline, or kidney dysfunction leads to stiffening or whether the association is mutual. We aimed to investigate the longitudinal association between arterial stiffness and annual rate of renal function decline. We prospectively investigated in a primary care population whether carotid-femoral pulse wave velocity (PWV) was associated with estimated glomerular filtration rate (eGFR) and annual decline in eGFR in participants aged ⩾40 years without overt kidney disease. Baseline data on PWV and eGFR were available for 587 participants; follow-up measurements with a mean duration of 5.6 years were available for 222 patients. PWV, female gender and mean arterial pressure were independently associated with eGFR at baseline, although age confounded this association. More importantly, baseline PWV, age and eGFR were independent predictors of renal function decline. Stratification for age showed that the effect of PWV on rate of eGFR decline was amplified with advancing age. On the other hand, baseline eGFR did not determine annual change in PWV, suggesting a unidirectional association between arterial stiffness and eGFR. Arterial stiffness amplifies age-related renal function decline, suggesting that arterial stiffness plays a causal role in the development of renal damage, at least at later stages of age-related renal function decline, possibly through impaired renal autoregulation and increased arterial blood pressure pulsatility.

  1. Topography compensation for haptization of a mesh object and its stiffness distribution.

    PubMed

    Yim, Sunghoon; Jeon, Seokhee; Choi, Seungmoon

    2015-01-01

    This work was motivated by the need for perceptualizing nano-scale scientific data, e.g., those acquired by a scanning probe microscope, where collocated topography and stiffness distribution of a surface can be measured. Previous research showed that when the topography of a surface with spatially varying stiffness is rendered using the conventional penalty-based haptic rendering method, the topography perceived by the user could be significantly distorted from its original model. In the worst case, a higher region with a smaller stiffness value can be perceived to be lower than a lower region with a larger stiffness value. This problem was explained by the theory of force constancy: the user tends to maintain an invariant contact force when s/he strokes the surface to perceive its topography. In this paper, we present a haptization algorithm that can render the shape of a mesh surface and its stiffness distribution with high perceptual accuracy. Our algorithm adaptively changes the surface topography on the basis of the force constancy theory to deliver adequate shape information to the user while preserving the stiffness perception. We also evaluated the performance of the proposed haptization algorithm in comparison to the constraint-based algorithm by examining relevant proximal stimuli and carrying out a user experiment. Results demonstrated that our algorithm could improve the perceptual accuracy of shape and reduce the exploration time, thereby leading to more accurate and efficient haptization.

  2. Aortic stiffness and calcification in men in a population-based international study.

    PubMed

    Sekikawa, Akira; Shin, Chol; Curb, J David; Barinas-Mitchell, Emma; Masaki, Kamal; El-Saed, Aiman; Seto, Todd B; Mackey, Rachel H; Choo, Jina; Fujiyoshi, Akira; Miura, Katsuyuki; Edmundowicz, Daniel; Kuller, Lewis H; Ueshima, Hirotsugu; Sutton-Tyrrell, Kim

    2012-06-01

    Aortic stiffness, a hallmark of vascular aging, is an independent risk factor of cardiovascular disease and all-cause mortality. The association of aortic stiffness with aortic calcification in middle-aged general population remains unknown although studies in patients with end-stage renal disease or elderly subjects suggest that aortic calcification is an important determinant of aortic stiffness. The goal of this study was to examine the association of aortic calcification and stiffness in multi-ethnic population-based samples of relatively young men. We examined the association in 906 men aged 40-49 (81 Black Americans, 276 Japanese Americans, 258 White Americans and 291 Koreans). Aortic stiffness was measured as carotid-femoral pulse wave velocity (cfPWV) using an automated waveform analyzer. Aortic calcification from aortic arch to iliac bifurcation was evaluated using electron-beam computed tomography. Aortic calcium score was calculated and was categorized into four groups: zero (n=303), 1-100 (n=411), 101-300 (n=110), and 401+ (n=82). Aortic calcification category had a significant positive association with cfPWV after adjusting for age, race, and mean arterial pressure (mean (standard error) of cfPWV (cm/s) from the lowest to highest categories: 836 (10), 850 (9), 877 (17) and 941 (19), P for trend <0.001). The significant positive association remained after further adjusting for other cardiovascular risk factors. The significant positive association was also observed in each race group. The results suggest that aortic calcification can be one mechanism for aortic stiffness and that the association of aortic calcification with stiffness starts as early as the 40s. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

  3. Aortic stiffness and calcification in men in a population-based international study

    PubMed Central

    Sekikawa, Akira; Shin, Chol; Curb, J. David; Barinas-Mitchell, Emma; Masaki, Kamal; El-Saed, Aiman; Seto, Todd B.; Mackey, Rachel H.; Choo, Jina; Fujiyoshi, Akira; Miura, Katsuyuki; Edmundowicz, Daniel; Kuller, Lewis H.; Ueshima, Hirotsugu; Sutton-Tyrrell, Kim

    2012-01-01

    Objectives Aortic stiffness, a hallmark of vascular aging, is an independent risk factor of cardiovascular disease and all-cause mortality. The association of aortic stiffness with aortic calcification in middle-aged general population remains unknown although studies in patients with end-stage renal disease or elderly subjects suggest that aortic calcification is an important determinant of aortic stiffness. The goal of this study was to examine the association of aortic calcification and stiffness in multi-ethnic population-based samples of relatively young men. Methods We examined the association in 906 men aged 40–49 (81 Black Americans, 276 Japanese Americans, 258 White Americans and 291 Koreans). Aortic stiffness was measured as carotid-femoral pulse wave velocity (cfPWV) using an automated waveform analyzer. Aortic calcification from aortic arch to iliac bifurcation was evaluated using electron-beam computed tomography. Results Aortic calcium score was calculated and was categorized into four groups: zero (n=303), 1–100 (n=411), 101–300 (n=110), and 401+ (n=82). Aortic calcification category had a significant positive association with cfPWV after adjusting for age, race, and mean arterial pressure (mean (standard error) of cfPWV (cm/second) from the lowest to highest categories: 836 (10), 850 (9), 877 (17) and 941 (19), p for trend <0.001). The significant positive association remained after further adjusting for other cardiovascular risk factors. The significant positive association was also observed in each race group. Conclusions The results suggest that aortic calcification can be one mechanism for aortic stiffness and that the association of aortic calcification with stiffness starts as early as the 40’s. PMID:22537531

  4. The effect of lifelong exercise frequency on arterial stiffness.

    PubMed

    Shibata, Shigeki; Fujimoto, Naoki; Hastings, Jeffrey L; Carrick-Ranson, Graeme; Bhella, Paul S; Hearon, Christopher; Levine, Benjamin D

    2018-05-20

    This study examined the effect of different 'doses' of lifelong (>25 years) exercise on arterial stiffening (a hallmark of vascular ageing) in older adults. There are clear dose-dependent effects of lifelong exercise training on human arterial stiffness that vary according to the site and size of the arteries. Similar to what we have observed previously with ventricular stiffening, 4-5 days week -1 of committed exercise over a lifetime are necessary to preserve 'youthful' vascular compliance, especially of the large central arteries. Casual exercise training of two to three times per week may be sufficient for middle-sized arteries like the carotid to minimize arterial stiffening with ageing. However, there is little effect of exercise training on the small-sized peripheral arteries at any dose. Central arterial stiffness increases with sedentary ageing. While near-daily, vigorous lifelong (>25 years) endurance exercise training prevents arterial stiffening with ageing, this rigorous routine of exercise training over a lifetime is impractical for most individuals. The aim was to examine whether a less frequent 'dose' of lifelong exercise training (four to five sessions per week for > 30 min) that is consistent with current physical activity recommendations elicits similar benefits on central arterial stiffening with ageing. A cross-sectional examination of 102 seniors (>60 years old) who had a consistent lifelong exercise history was performed. Subjects were stratified into four groups based on exercise frequency as an index of exercise 'dose': sedentary: fewer than two sessions per week; casual exercisers: two to three sessions per week; committed exercisers: four to five sessions per week; and Masters athletes: six to seven sessions per week plus regular competitions. Detailed measurements of arterial stiffness and left ventricular afterload were collected. Biological aortic age and central pulse wave velocity were younger in committed exercisers and

  5. Cell prestress. I. Stiffness and prestress are closely associated in adherent contractile cells

    NASA Technical Reports Server (NTRS)

    Wang, Ning; Tolic-Norrelykke, Iva Marija; Chen, Jianxin; Mijailovich, Srboljub M.; Butler, James P.; Fredberg, Jeffrey J.; Stamenovic, Dimitrije; Ingber, D. E. (Principal Investigator)

    2002-01-01

    The tensegrity hypothesis holds that the cytoskeleton is a structure whose shape is stabilized predominantly by the tensile stresses borne by filamentous structures. Accordingly, cell stiffness must increase in proportion with the level of the tensile stress, which is called the prestress. Here we have tested that prediction in adherent human airway smooth muscle (HASM) cells. Traction microscopy was used to measure the distribution of contractile stresses arising at the interface between each cell and its substrate; this distribution is called the traction field. Because the traction field must be balanced by tensile stresses within the cell body, the prestress could be computed. Cell stiffness (G) was measured by oscillatory magnetic twisting cytometry. As the contractile state of the cell was modulated with graded concentrations of relaxing or contracting agonists (isoproterenol or histamine, respectively), the mean prestress ((t)) ranged from 350 to 1,900 Pa. Over that range, cell stiffness increased linearly with the prestress: G (Pa) = 0.18(t) + 92. While this association does not necessarily preclude other interpretations, it is the hallmark of systems that secure shape stability mainly through the prestress. Regardless of mechanism, these data establish a strong association between stiffness of HASM cells and the level of tensile stress within the cytoskeleton.

  6. Damage detection on sudden stiffness reduction based on discrete wavelet transform.

    PubMed

    Chen, Bo; Chen, Zhi-wei; Wang, Gan-jun; Xie, Wei-ping

    2014-01-01

    The sudden stiffness reduction in a structure may cause the signal discontinuity in the acceleration responses close to the damage location at the damage time instant. To this end, the damage detection on sudden stiffness reduction of building structures has been actively investigated in this study. The signal discontinuity of the structural acceleration responses of an example building is extracted based on the discrete wavelet transform. It is proved that the variation of the first level detail coefficients of the wavelet transform at damage instant is linearly proportional to the magnitude of the stiffness reduction. A new damage index is proposed and implemented to detect the damage time instant, location, and severity of a structure due to a sudden change of structural stiffness. Numerical simulation using a five-story shear building under different types of excitation is carried out to assess the effectiveness and reliability of the proposed damage index for the building at different damage levels. The sensitivity of the damage index to the intensity and frequency range of measurement noise is also investigated. The made observations demonstrate that the proposed damage index can accurately identify the sudden damage events if the noise intensity is limited.

  7. Evaluation of urban surface parameterizations in the WRF model using measurements during the Texas Air Quality Study 2006 field campaign

    NASA Astrophysics Data System (ADS)

    Lee, S.-H.; Kim, S.-W.; Angevine, W. M.; Bianco, L.; McKeen, S. A.; Senff, C. J.; Trainer, M.; Tucker, S. C.; Zamora, R. J.

    2011-03-01

    The performance of different urban surface parameterizations in the WRF (Weather Research and Forecasting) in simulating urban boundary layer (UBL) was investigated using extensive measurements during the Texas Air Quality Study 2006 field campaign. The extensive field measurements collected on surface (meteorological, wind profiler, energy balance flux) sites, a research aircraft, and a research vessel characterized 3-dimensional atmospheric boundary layer structures over the Houston-Galveston Bay area, providing a unique opportunity for the evaluation of the physical parameterizations. The model simulations were performed over the Houston metropolitan area for a summertime period (12-17 August) using a bulk urban parameterization in the Noah land surface model (original LSM), a modified LSM, and a single-layer urban canopy model (UCM). The UCM simulation compared quite well with the observations over the Houston urban areas, reducing the systematic model biases in the original LSM simulation by 1-2 °C in near-surface air temperature and by 200-400 m in UBL height, on average. A more realistic turbulent (sensible and latent heat) energy partitioning contributed to the improvements in the UCM simulation. The original LSM significantly overestimated the sensible heat flux (~200 W m-2) over the urban areas, resulting in warmer and higher UBL. The modified LSM slightly reduced warm and high biases in near-surface air temperature (0.5-1 °C) and UBL height (~100 m) as a result of the effects of urban vegetation. The relatively strong thermal contrast between the Houston area and the water bodies (Galveston Bay and the Gulf of Mexico) in the LSM simulations enhanced the sea/bay breezes, but the model performance in predicting local wind fields was similar among the simulations in terms of statistical evaluations. These results suggest that a proper surface representation (e.g. urban vegetation, surface morphology) and explicit parameterizations of urban physical

  8. Management of the Stiff Finger: Evidence and Outcomes

    PubMed Central

    Yang, Guang; McGlinn, Evan P.; Chung, Kevin C.

    2014-01-01

    SYNOPSIS The term “stiff finger” refers to a reduction in the range of motion in the finger, and it is a condition that has many different causes and involves a number of different structures. Almost all injuries of the fingers and some diseases can cause finger stiffness. Hand surgeons often face difficulty treating stiff fingers that are affected by irreversible soft tissues fibrosis. Stiff fingers can be divided into flexion and extension deformities. They can also be sub-classified into four categories according to the involved tissues extending from the skin to the joint capsule. Prevention of stiff fingers by judicious mobilization of the joints is prudent to avoid more complicated treatment after established stiffness occurs. Static progressive and dynamic splints have been considered as effective non-operative interventions to treat stiff fingers. Most authors believe force of joint distraction and time duration of stretching are two important factors to consider while applying a splint or cast. We also introduce the concepts of capsulotomy and collateral ligament release and other soft tissue release of the MCP and PIP joint in this article. Future outcomes research is vital to assessing the effectiveness of these surgical procedures and guiding postoperative treatment recommendations. PMID:24996467

  9. Experimental Challenges to Stiffness as a Transport Paradigm

    NASA Astrophysics Data System (ADS)

    Luce, T. C.

    2017-10-01

    Transport in plasmas is treated experimentally as a relationship between gradients and fluxes in analogy to the random-walk problem. Gyrokinetic models often predict strong increases in local flux for small increases in local gradient when above a threshold, holding all other parameters fixed. This has been named `stiffness'. The radial scalelength is then expected to vary little with source strength as a result of high stiffness. To probe the role of ExB shearing on stiffness in the DIII-D tokamak, two neutral beam injection power scans in H-mode plasmas were specially crafted-one with constant, low torque and one with increasing torque. The ion heat, electron heat, and ion toroidal momentum transport do not show expected signatures of stiffness, while the ion particle transport does. The ion heat transport shows the clearest discrepancy; the normalized heat flux drops with increasing inverse ion temperature scalelength. ExB shearing affects the transport magnitude, but not the scalelength dependence. Linear gyrofluid (TGLF) and nonlinear gyrokinetic (GYRO) predictions show stiff ion heat transport around the experimental profiles. The ion temperature gradient required to match the ion heat flux with increasing auxiliary power is not correctly described by TGLF, even when parameters are varied within the experimental uncertainties. TGLF also underpredicts transport at smaller radii, but overpredicts transport at larger radii. Independent of the theory/experiment comparison, it is not clear that the theoretical definition of stiffness yields any prediction about parameter scans such as the power scans here, because the quantities that must be held fixed to quantify stiffness are varied. A survey of recent literature indicated that profile resilience is routinely attributed to stiffness, but simple model calculations show profile resilience does not imply stiffness. Taken together, these observations challenge the use of local stiffness as a paradigm for explaining

  10. Arterial stiffness in 10-year-old children: current and early determinants.

    PubMed

    Schack-Nielsen, Lene; Mølgaard, Christian; Larsen, Dorthe; Martyn, Christopher; Michaelsen, Kim Fleischer

    2005-12-01

    It has been suggested that CVD has its origins in early life. An impairment of fetal growth and early postnatal nutrition may have programming effects on cardiovascular physiology. In addition, traditional risk factors for CVD may initiate the atherosclerotic process during childhood. We explored the effect of fat intake, physical activity and lipid profile in childhood, and birth weight, growth during infancy and breast-feeding on arterial stiffness in a cohort study of ninety-three 10-year-old children followed during infancy and re-examined at the age of 10 years. Arterial stiffness in two arterial segments (aorto-radial and aorto-femoral) was measured as pulse wave velocity. Arterial stiffness was inversely associated with physical activity (a regression coefficient in cm/s (95 % CI) of -6.8 (-11.2, -2.4) and -3.9 (-6.9, -0.8) per h of high physical activity/d in the aorto-radial and aorto-femoral segments, respectively). Arterial stiffness was also positively associated with dietary fat energy percentage (3.1 (95 % CI 0.9, 5.2) and 1.8 (95 % CI 0.2, 3.2) per fat energy percentage in the aorto-radial and aorto-femoral segments, respectively) but was not related to body composition, insulin resistance or lipid profile. Arterial stiffness was also positively associated with duration of breast-feeding for the aorto-femoral segment only (2.1 (95 % CI 0.4, 3.7) per month) but was not associated with growth in early life. In conclusion, patterns of physical activity and diet, and history of breast-feeding in infancy, have an influence on the stiffness of the large arteries in children. The long-term effects of this are unknown.

  11. Does short-term whole-body vibration training affect arterial stiffness in chronic stroke? A preliminary study

    PubMed Central

    Yule, Christie E.; Stoner, Lee; Hodges, Lynette D.; Cochrane, Darryl J.

    2016-01-01

    [Purpose] Previous studies have shown that stroke is associated with increased arterial stiffness that can be diminished by a program of physical activity. A novel exercise intervention, whole-body vibration (WBV), is reported to significantly improve arterial stiffness in healthy men and older sedentary adults. However, little is known about its efficacy in reducing arterial stiffness in chronic stroke. [Subjects and Methods] Six participants with chronic stroke were randomly assigned to 4 weeks of WBV training or control followed by cross-over after a 2-week washout period. WBV intervention consisted of 3 sessions of 5 min intermittent WBV per week for 4 weeks. Arterial stiffness (carotid arterial stiffness, pulse wave velocity [PWV], pulse and wave analysis [PWA]) were measured before/after each intervention. [Results] No significant improvements were reported with respect to carotid arterial stiffness, PWV, and PWA between WBV and control. However, carotid arterial stiffness showed a decrease over time following WBV compared to control, but this was not significant. [Conclusion] Three days/week for 4 weeks of WBV seems too short to elicit appropriate changes in arterial stiffness in chronic stroke. However, no adverse effects were reported, indicating that WBV is a safe and acceptable exercise modality for people with chronic stroke. PMID:27134400

  12. Relations Between Aortic Stiffness and Left Ventricular Mechanical Function in the Community.

    PubMed

    Bell, Vanessa; McCabe, Elizabeth L; Larson, Martin G; Rong, Jian; Merz, Allison A; Osypiuk, Ewa; Lehman, Birgitta T; Stantchev, Plamen; Aragam, Jayashri; Benjamin, Emelia J; Hamburg, Naomi M; Vasan, Ramachandran S; Mitchell, Gary F; Cheng, Susan

    2017-01-09

    Aortic stiffness impairs optimal ventricular-vascular coupling and left ventricular systolic function, particularly in the long axis. Left ventricular global longitudinal strain (GLS) has recently emerged as a sensitive measure of early cardiac dysfunction. In this study, we investigated the relation between aortic stiffness and GLS in a large community-based sample. In 2495 participants (age 39-90 years, 57% women) of the Framingham Offspring and Omni cohorts, free of cardiovascular disease, we performed tonometry to measure arterial hemodynamics and echocardiography to assess cardiac function. Aortic stiffness was evaluated as carotid-femoral pulse wave velocity and as characteristic impedance, and GLS was calculated using speckle tracking-based measurements. In multivariable analyses adjusting for age, sex, height, systolic blood pressure, augmentation index, left ventricular structure, and additional cardiovascular risk factors, increased carotid-femoral pulse wave velocity (B±SE: 0.122±0.030% strain per SD, P<0.0001) and characteristic impedance (0.090±0.029, P=0.002) were both associated with worse GLS. We observed effect modification by sex on the relation between characteristic impedance and GLS (P=0.004); in sex-stratified multivariable analyses, the relation between greater characteristic impedance and worse GLS persisted in women (0.145±0.039, P=0.0003) but not in men (P=0.73). Multiple measures of increased aortic stiffness were cross-sectionally associated with worse GLS after adjusting for hemodynamic variables. Parallel reductions in left ventricular long axis shortening and proximal aortic longitudinal strain in individuals with a stiffened proximal aorta, from direct mechanical ventricular-vascular coupling, offers an alternative explanation for the observed relations. © 2017 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.

  13. Development of Stiff and Extendible Electromagnetic Sensors for Space Missions

    NASA Astrophysics Data System (ADS)

    Kasaba, Y.; Kumamoto, A.; Ishisaka, K.; Kojima, H.; Higuchi, K.; Watanabe, A.; Watanabe, K.

    2010-05-01

    We developed three types of stiff and extendible electromagnetic sensors in rigid monopole antenna, loop antenna, and Yagi-Uda antenna for future space missions. They are based on carbon fiber reinforced plastic (CFRP) technologies, in order to fulfill severe requirements, i.e. enough stiffness, light mass, compact storage, safe extension, and reasonable test efforts. One of them, rigid monopole antennas, coupled with an inflatable actuator system, was successfully used in the JAXA S-520-23 sounding rocket experiment in September 2007. Applications of those antennas are expected in space plasma missions including the SCOPE program, sounding rocket experiments, planetary radar remote sensing, and landing radio measurements.

  14. Probing the salt dependence of the torsional stiffness of DNA by multiplexed magnetic torque tweezers

    PubMed Central

    Kriegel, Franziska; Ermann, Niklas; Forbes, Ruaridh; Dulin, David; Dekker, Nynke H.

    2017-01-01

    Abstract The mechanical properties of DNA fundamentally constrain and enable the storage and transmission of genetic information and its use in DNA nanotechnology. Many properties of DNA depend on the ionic environment due to its highly charged backbone. In particular, both theoretical analyses and direct single-molecule experiments have shown its bending stiffness to depend on salt concentration. In contrast, the salt-dependence of the twist stiffness of DNA is much less explored. Here, we employ optimized multiplexed magnetic torque tweezers to study the torsional stiffness of DNA under varying salt conditions as a function of stretching force. At low forces (<3 pN), the effective torsional stiffness is ∼10% smaller for high salt conditions (500 mM NaCl or 10 mM MgCl2) compared to lower salt concentrations (20 mM NaCl and 100 mM NaCl). These differences, however, can be accounted for by taking into account the known salt dependence of the bending stiffness. In addition, the measured high-force (6.5 pN) torsional stiffness values of C = 103 ± 4 nm are identical, within experimental errors, for all tested salt concentration, suggesting that the intrinsic torsional stiffness of DNA does not depend on salt. PMID:28460037

  15. Virion stiffness regulates immature HIV-1 entry

    PubMed Central

    2013-01-01

    Background Human immunodeficiency virus type 1 (HIV-1) undergoes a protease-mediated maturation process that is required for its infectivity. Little is known about how the physical properties of viral particles change during maturation and how these changes affect the viral lifecycle. Using Atomic Force Microscopy (AFM), we previously discovered that HIV undergoes a “stiffness switch”, a dramatic reduction in particle stiffness during maturation that is mediated by the viral Envelope (Env) protein. Results In this study, we show that transmembrane-anchored Env cytoplasmic tail (CT) domain is sufficient to regulate the particle stiffness of immature HIV-1. Using this construct expressed in trans with viral Env lacking the CT domain, we show that increasing particle stiffness reduces viral entry activity in immature virions. A similar effect was also observed for immature HIV-1 pseudovirions containing Env from vesicular stomatitis virus. Conclusions This linkage between particle stiffness and viral entry activity illustrates a novel level of regulation for viral replication, providing the first evidence for a biological role of virion physical properties and suggesting a new inhibitory strategy. PMID:23305456

  16. Acute effects of static stretching on passive stiffness of the hamstring muscles calculated using different mathematical models.

    PubMed

    Nordez, Antoine; Cornu, Christophe; McNair, Peter

    2006-08-01

    The aim of this study was to assess the effects of static stretching on hamstring passive stiffness calculated using different data reduction methods. Subjects performed a maximal range of motion test, five cyclic stretching repetitions and a static stretching intervention that involved five 30-s static stretches. A computerised dynamometer allowed the measurement of torque and range of motion during passive knee extension. Stiffness was then calculated as the slope of the torque-angle relationship fitted using a second-order polynomial, a fourth-order polynomial, and an exponential model. The second-order polynomial and exponential models allowed the calculation of stiffness indices normalized to knee angle and passive torque, respectively. Prior to static stretching, stiffness levels were significantly different across the models. After stretching, while knee maximal joint range of motion increased, stiffness was shown to decrease. Stiffness decreased more at the extended knee joint angle, and the magnitude of change depended upon the model used. After stretching, the stiffness indices also varied according to the model used to fit data. Thus, the stiffness index normalized to knee angle was found to decrease whereas the stiffness index normalized to passive torque increased after static stretching. Stretching has significant effects on stiffness, but the findings highlight the need to carefully assess the effect of different models when analyzing such data.

  17. Tuning the Stiffness Balance Using Characteristic Frequencies as a Criterion for a Superconducting Gravity Gradiometer

    PubMed Central

    Liu, Xikai; Ma, Dong; Chen, Liang; Liu, Xiangdong

    2018-01-01

    Tuning the stiffness balance is crucial to full-band common-mode rejection for a superconducting gravity gradiometer (SGG). A reliable method to do so has been proposed and experimentally tested. In the tuning scheme, the frequency response functions of the displacement of individual test mass upon common-mode accelerations were measured and thus determined a characteristic frequency for each test mass. A reduced difference in characteristic frequencies between the two test masses was utilized as the criterion for an effective tuning. Since the measurement of the characteristic frequencies does not depend on the scale factors of displacement detection, stiffness tuning can be done independently. We have tested this new method on a single-component SGG and obtained a reduction of two orders of magnitude in stiffness mismatch. PMID:29419796

  18. Biphasic response of cell invasion to matrix stiffness in 3-dimensional biopolymer networks

    PubMed Central

    Lang, Nadine R.; Skodzek, Kai; Hurst, Sebastian; Mainka, Astrid; Steinwachs, Julian; Schneider, Julia; Aifantis, Katerina E.; Fabry, Ben

    2015-01-01

    When cells come in contact with an adhesive matrix, they begin to spread and migrate with a speed that depends on the stiffness of the extracellular matrix. On a flat surface, migration speed decreases with matrix stiffness mainly due to an increased stability of focal adhesions. In a 3-dimensional (3D) environment, cell migration is thought to be additionally impaired by the steric hindrance imposed by the surrounding matrix. For porous 3D biopolymer networks such as collagen gels, however, the effect of matrix stiffness on cell migration is difficult to separate from effects of matrix pore size and adhesive ligand density, and is therefore unknown. Here we used glutaraldehyde as a crosslinker to increase the stiffness of self-assembled collagen biopolymer networks independently of collagen concentration or pore size. Breast carcinoma cells were seeded onto the surface of 3D collagen gels, and the invasion depth was measured after 3 days of culture. Cell invasion in gels with pore sizes larger than 5 μm increased with higher gel stiffness, whereas invasion in gels with smaller pores decreased with higher gel stiffness. These data show that 3D cell invasion is enhanced by higher matrix stiffness, opposite to cell behavior in 2D, as long as the pore size does not fall below a critical value where it causes excessive steric hindrance. These findings may be important for optimizing the recellularization of soft tissue implants or for the design of 3D invasion models in cancer research. PMID:25462839

  19. Stress stiffened silicon nitride micro bridges array as substrate with tunable stiffness for cell culture.

    PubMed

    Chen, Jianfeng; Liu, Guangli; Ma, Chengfu; Zhao, Gang; Du, Wenqiang; Zhu, Wulin; Chu, Jiaru

    2017-06-01

    Recently, interactions between one-dimensional structural stiffness of physical micro environments and cell biological process have been widely studied. However in previous studies, the influence of structural stiffness on biological process was coupled with the influence of micro fiber curvature. Therefore decoupling the influences of fiber curvature and structural stiffness on cell biological process is of prime importance. In this study, we proposed a novel cell culture substrate comprised of silicon nitride bridges whose structure stiffness can be regulated by altering the axial residual stress without changing material and geometry properties. Both theoretical calculations and finite element simulations were performed to study the influence of residual stress on structure stiffness of bridges. Then multi-positions AFM bending tests were implemented to measure local stiffness of a single micro bridge so as to verify our predictions. NIH/3T3 mouse fibroblast cells were cultured on our substrates to examine the feasibility of the substrate application for investigating cellular response to microenvironment with variable stiffness. The results showed that cells on the edge region near bridge ends were more spread, elongated and better aligned along the bridge axial direction than those on the bridge center region. The results suggest that cells can sense and respond to the differences of stiffness and stiffness gradient between the edge and the center region of the bridges, which makes this kind of substrates can be applied in some biomedical fields, such as cell migration and wound healing. Copyright © 2017 Elsevier B.V. All rights reserved.

  20. In vivo tibial stiffness is maintained by whole bone morphology and cross-sectional geometry in growing female mice

    PubMed Central

    Main, Russell P.; Lynch, Maureen E.; van der Meulen, Marjolein C.H.

    2010-01-01

    Whole bone morphology, cortical geometry, and tissue material properties modulate skeletal stresses and strains that in turn influence skeletal physiology and remodeling. Understanding how bone stiffness, the relationship between applied load and tissue strain, is regulated by developmental changes in bone structure and tissue material properties is important in implementing biophysical strategies for promoting healthy bone growth and preventing bone loss. The goal of this study was to relate developmental patterns of in vivo whole bone stiffness to whole bone morphology, cross-sectional geometry, and tissue properties using a mouse axial loading model. We measured in vivo tibial stiffness in three age groups (6wks, 10wks, 16wks old) of female C57Bl/6 mice during cyclic tibial compression. Tibial stiffness was then related to cortical geometry, longitudinal bone curvature, and tissue mineral density using microcomputed tomography (microCT). Tibial stiffness and the stresses induced by axial compression were generally maintained from 6 to 16wks of age. Growth-related increases in cortical cross-sectional geometry and longitudinal bone curvature had counteracting effects on induced bone stresses and, therefore, maintained tibial stiffness similarly with growth. Tissue mineral density increased slightly from 6 to 16wks of age, and although the effects of this increase on tibial stiffness were not directly measured, its role in the modulation of whole bone stiffness was likely minor over the age range examined. Thus, whole bone morphology, as characterized by longitudinal curvature, along with cortical geometry, plays an important role in modulating bone stiffness during development and should be considered when evaluating and designing in vivo loading studies and biophysical skeletal therapies. PMID:20673665

  1. Transient micro-elastography: A novel non-invasive approach to measure liver stiffness in mice

    PubMed Central

    Bastard, Cécile; Bosisio, Matteo R; Chabert, Michèle; Kalopissis, Athina D; Mahrouf-Yorgov, Meriem; Gilgenkrantz, Hélène; Mueller, Sebastian; Sandrin, Laurent

    2011-01-01

    AIM: To develop and validate a transient micro-elastography device to measure liver stiffness (LS) in mice. METHODS: A novel transient micro-elastography (TME) device, dedicated to LS measurements in mice with a range of measurement from 1-170 kPa, was developed using an optimized vibration frequency of 300 Hz and a 2 mm piston. The novel probe was validated in a classical fibrosis model (CCl4) and in a transgenic murine model of systemic amyloidosis. RESULTS: TME could be successfully performed in control mice below the xiphoid cartilage, with a mean LS of 4.4 ± 1.3 kPa, a mean success rate of 88%, and an excellent intra-observer agreement (0.98). Treatment with CCl4 over seven weeks drastically increased LS as compared to controls (18.2 ± 3.7 kPa vs 3.6 ± 1.2 kPa). Moreover, fibrosis stage was highly correlated with LS (Spearman coefficient = 0.88, P < 0.01). In the amyloidosis model, much higher LS values were obtained, reaching maximum values of > 150 kPa. LS significantly correlated with the amyloidosis index (0.93, P < 0.0001) and the plasma concentration of mutant hapoA-II (0.62, P < 0.005). CONCLUSION: Here, we have established the first non-invasive approach to measure LS in mice, and have successfully validated it in two murine models of high LS. PMID:21448348

  2. Energy cost of running and Achilles tendon stiffness in man and woman trained runners

    PubMed Central

    Fletcher, Jared R.; Pfister, Ted R.; MacIntosh, Brian R.

    2013-01-01

    Abstract The energy cost of running (Erun), a key determinant of distance running performance, is influenced by several factors. Although it is important to express Erun as energy cost, no study has used this approach to compare similarly trained men and women. Furthermore, the relationship between Achilles tendon (AT) stiffness and Erun has not been compared between men and women. Therefore, our purpose was to determine if sex‐specific differences in Erun and/or AT stiffness existed. Erun (kcal kg−1 km−1) was determined by indirect calorimetry at 75%, 85%, and 95% of the speed at lactate threshold (sLT) on 11 man (mean ± SEM, 35 ± 1 years, 177 ± 1 cm, 78 ± 1 kg, 1 = 56 ± 1 mL kg−1 min−1) and 18 woman (33 ± 1 years, 165 ± 1 cm, 58 ± 1 kg, 2 = 50 ± 0.3 mL kg−1 min−1) runners. AT stiffness was measured using ultrasound with dynamometry. Man Erun was 1.01 ± 0.06, 1.04 ± 0.07, and 1.07 ± 0.07 kcal kg−1 km−1. Woman Erun was 1.05 ± 0.10, 1.07 ± 0.09, and 1.09 ± 0.10 kcal kg−1 km−1. There was no significant sex effect for Erun or RER, but both increased with speed (P < 0.01) expressed relative to sLT. High‐range AT stiffness was 191 ± 5.1 N mm−1 for men and 125 ± 5.5 N mm−1, for women (P < 0.001). The relationship between low‐range AT stiffness and Erun was significant at all measured speeds for women (r2 = 0.198, P < 0.05), but not for the men. These results indicate that when Erun is measured at the same relative intensity, there are no sex‐specific differences in Erun or substrate use. Furthermore, differences in Erun cannot be explained solely by differences in AT stiffness. PMID:24744857

  3. Anterior Glenohumeral Laxity and Stiffness After a Shoulder-Strengthening Program in Collegiate Cheerleaders

    PubMed Central

    Laudner, Kevin G; Metz, Betsy; Thomas, David Q

    2013-01-01

    Context Approximately 62% of all cheerleaders sustain some type of orthopaedic injury during their cheerleading careers. Furthermore, the occurrence of such injuries has led to inquiry regarding optimal prevention techniques. One possible cause of these injuries may be related to inadequate conditioning in cheerleaders. Objective To determine whether a strength and conditioning program produces quantifiable improvements in anterior glenohumeral (GH) laxity and stiffness. Design Descriptive laboratory study. Setting University laboratory. Patients or Other Participants A sample of 41 collegiate cheerleaders (24 experimental and 17 control participants) volunteered. No participants had a recent history (in the past 6 months) of upper extremity injury or any history of upper extremity surgery. Intervention(s) The experimental group completed a 6-week strength and conditioning program between the pretest and posttest measurements; the control group did not perform any strength training between tests. Main Outcome Measure(s) We measured anterior GH laxity and stiffness with an instrumented arthrometer. We conducted a group × time analysis of variance with repeated measures on time (P < .05) to determine differences between groups. Results A significant interaction was demonstrated, with the control group having more anterior GH laxity at the posttest session than the strengthening group (P = .03, partial η2 = 0.11). However, no main effect for time (P = .92) or group (P = .97) was observed. In another significant interaction, the control group had less anterior GH stiffness at the posttest session than the strengthening group (P = .03, partial η2 = 0.12). Main effects for time (P = .02) and group (P = .004) were also significant. Conclusions Cheerleaders who participate in a shoulder-strengthening program developed less anterior GH laxity and more stiffness than cheerleaders in the control group. PMID:23672322

  4. Massage induces an immediate, albeit short-term, reduction in muscle stiffness.

    PubMed

    Eriksson Crommert, M; Lacourpaille, L; Heales, L J; Tucker, K; Hug, F

    2015-10-01

    Using ultrasound shear wave elastography, the aims of this study were: (a) to evaluate the effect of massage on stiffness of the medial gastrocnemius (MG) muscle and (b) to determine whether this effect (if any) persists over a short period of rest. A 7-min massage protocol was performed unilaterally on MG in 18 healthy volunteers. Measurements of muscle shear elastic modulus (stiffness) were performed bilaterally (control and massaged leg) in a moderately stretched position at three time points: before massage (baseline), directly after massage (follow-up 1), and following 3 min of rest (follow-up 2). Directly after massage, participants rated pain experienced during the massage. MG shear elastic modulus of the massaged leg decreased significantly at follow-up 1 (-5.2 ± 8.8%, P = 0.019, d = -0.66). There was no difference between follow-up 2 and baseline for the massaged leg (P = 0.83) indicating that muscle stiffness returned to baseline values. Shear elastic modulus was not different between time points in the control leg. There was no association between perceived pain during the massage and stiffness reduction (r = 0.035; P = 0.89). This is the first study to provide evidence that massage reduces muscle stiffness. However, this effect is short lived and returns to baseline values quickly after cessation of the massage. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  5. The differential effects of gender, anthropometry, and prior hormonal state on frontal plane knee joint stiffness

    PubMed Central

    Cammarata, Martha L.; Dhaher, Yasin Y.

    2012-01-01

    Background Gender differences in passive frontal plane knee stiffness may contribute to the increased anterior cruciate ligament injury rate in females. Gender-based stiffness differences have been attributed to anthropometric variations, but little data exist describing this relationship. Furthermore, sex hormone levels appear to influence joint stiffness, but the differential effects of instantaneous and prior hormonal concentrations remain unknown. This study sought to explore the effect of gender, prior hormonal status, and anthropometry on passive frontal plane knee joint stiffness. Methods Twelve males and 31 females participated. Females were grouped by hormonal contraceptive use (non users [n=11], monophasic contraceptive users [n=11], and triphasic contraceptive users [n=9]) and tested at the same point in the menstrual cycle. Subjects’ right knee was passively stretched ±7° in the frontal plane at 3°/s. Stiffness was estimated at three loading levels and normalized by body size to minimize anthropometric biases. A 4 (group) × 3 (load) repeated measures analysis of variance was performed for both raw and normalized stiffness. Linear regression analyses were preformed between stiffness estimates and knee diameter and quadriceps femoris angle. Findings Males displayed significantly greater (P<0.05) frontal plane stiffness than females. When normalized, males displayed significantly greater stiffness in valgus (P<0.05), but not varus (P>0.05) than females. No significant effect (P>0.05) of prior hormonal state was found; however, when normalized, varus stiffness was significantly less for triphasic contraceptive users than the other female groups (P<0.05). Quadriceps femoris angle was negatively correlated and knee diameter was positively correlated to knee stiffness. Interpretation Consistent with earlier in vitro findings, our data may indicate that ligament material properties are gender specific. A deficit in passive knee joint stiffness may place a

  6. Sciatic nerve stiffness is not changed immediately after a slump neurodynamics technique.

    PubMed

    Neto, Tiago; Freitas, Sandro R; Andrade, Ricardo J; Gomes, João; Vaz, João; Mendes, Bruno; Firmino, Telmo; Nordez, Antoine; Oliveira, Raúl

    2017-01-01

    Neurodynamics techniques aim to assess and improve neural mechanosensitivity. However, there is no in vivo evidence regarding the mechanical effects of these techniques in the nerve stiffness. This study examined the immediate effects of a slump neurodynamics technique in the sciatic nerve shear wave velocity (SWV. i.e. an index of stiffness) using ultrasound-based elastography. Fourteen healthy participants were included in this experiment. Sciatic SWV and ankle passive torque were measured during a passive ankle dorsiflexion motion (2°/s), before and immediately after 3 minutes of slump neurodynamics technique, randomly applied to one lower limb. The contralateral limb served as control. The slump intervention did not change the sciatic SWV (P=0.78), nor the dorsiflexion passive torque (P=0.14), throughout the ankle dorsiflexion motion. Excellent values of intra-rater repeatability (ICC=0.88, 0.68-0.96), and low values of standard error of measurement (0.59 m/s, 0.35-1.15m/s), were observed for the SWV measurements. The sciatic nerve stiffness of healthy participants did not change immediately after a slump neurodynamics technique, suggesting a compliance of the neural tissue to tensile loads. However, these results ought to be confirmed using other neurodynamics techniques and in other populations (e.g. peripheral neuropathies). III.

  7. Regular Exercise Reduces Endothelial Cortical Stiffness in Western Diet-Fed Female Mice.

    PubMed

    Padilla, Jaume; Ramirez-Perez, Francisco I; Habibi, Javad; Bostick, Brian; Aroor, Annayya R; Hayden, Melvin R; Jia, Guanghong; Garro, Mona; DeMarco, Vincent G; Manrique, Camila; Booth, Frank W; Martinez-Lemus, Luis A; Sowers, James R

    2016-11-01

    We recently showed that Western diet-induced obesity and insulin resistance promotes endothelial cortical stiffness in young female mice. Herein, we tested the hypothesis that regular aerobic exercise would attenuate the development of endothelial and whole artery stiffness in female Western diet-fed mice. Four-week-old C57BL/6 mice were randomized into sedentary (ie, caged confined, n=6) or regular exercise (ie, access to running wheels, n=7) conditions for 16 weeks. Exercise training improved glucose tolerance in the absence of changes in body weight and body composition. Compared with sedentary mice, exercise-trained mice exhibited reduced endothelial cortical stiffness in aortic explants (sedentary 11.9±1.7 kPa versus exercise 5.5±1.0 kPa; P<0.05), as assessed by atomic force microscopy. This effect of exercise was not accompanied by changes in aortic pulse wave velocity (P>0.05), an in vivo measure of aortic stiffness. In comparison, exercise reduced femoral artery stiffness in isolated pressurized arteries and led to an increase in femoral internal artery diameter and wall cross-sectional area (P<0.05), indicative of outward hypertrophic remodeling. These effects of exercise were associated with an increase in femoral artery elastin content and increased number of fenestrae in the internal elastic lamina (P<0.05). Collectively, these data demonstrate for the first time that the aortic endothelium is highly plastic and, thus, amenable to reductions in stiffness with regular aerobic exercise in the absence of changes in in vivo whole aortic stiffness. Comparatively, the same level of exercise caused destiffening effects in peripheral muscular arteries, such as the femoral artery, that perfuse the working limbs. © 2016 American Heart Association, Inc.

  8. The effects of resistance exercise training on arterial stiffness in metabolic syndrome.

    PubMed

    DeVallance, E; Fournier, S; Lemaster, K; Moore, C; Asano, S; Bonner, D; Donley, D; Olfert, I M; Chantler, P D

    2016-05-01

    Arterial stiffness is a strong independent risk factor for cardiovascular disease and is elevated in individuals with metabolic syndrome (MetS). Resistance training is a popular form of exercise that has beneficial effects on muscle mass, strength, balance and glucose control. However, it is unknown whether resistance exercise training (RT) can lower arterial stiffness in patients with MetS. Thus, the aim of this study was to examine whether a progressive RT program would improve arterial stiffness in MetS. A total of 57 subjects (28 healthy sedentary subjects; 29 MetS) were evaluated for arterial structure and function, including pulse wave velocity (cfPWV: arterial stiffness), before and after an 8-week period of RT or continuation of sedentary lifestyle. We found that 8 weeks of progressive RT increased skeletal muscle strength in both Con and MetS, but did not change arterial stiffness in either MetS (cfPWV; Pre 7.9 ± 0.4 m/s vs. Post 7.7 ± 0.4 m/s) or healthy controls (cfPWV; Pre 6.9 ± 0.3 m/s vs. Post 7.0 ± 0.3 m/s). However, when cfPWV is considered as a continuous variable, high baseline measures of cfPWV tended to show a decrease in cfPWV following RT. Eight weeks of progressive RT did not decrease the group mean values of arterial stiffness in individuals with MetS or healthy controls.

  9. Assessment of passive knee stiffness and viscosity in individuals with spinal cord injury using pendulum test

    PubMed Central

    Joghtaei, Mahmoud; Arab, Amir Massoud; Hashemi-Nasl, Hamed; Joghataei, Mohammad Taghi; Tokhi, Mohammad Osman

    2015-01-01

    Objective Stiffness and viscosity represent passive resistances to joint motion related with the structural properties of the joint tissue and of the musculotendinous complex. Both parameters can be affected in patients with spinal cord injury (SCI). The purpose of this study was to measure passive knee stiffness and viscosity in patients with SCI with paraplegia and healthy subjects using Wartenberg pendulum test. Design Non-experimental, cross-sectional, case–control design. Setting An outpatient physical therapy clinic, University of social welfare and Rehabilitation Science, Iran. Patients A sample of convenience sample of 30 subjects participated in the study. Subjects were categorized into two groups: individuals with paraplegic SCI (n = 15, age: 34.60 ± 9.18 years) and 15 able-bodied individuals as control group (n = 15, age: 30.66 ± 11.13 years). Interventions Not applicable. Main measures Passive pendulum test of Wartenberg was used to measure passive viscous-elastic parameters of the knee (stiffness, viscosity) in all subjects. Results Statistical analysis (independent t-test) revealed significant difference in the joint stiffness between healthy subjects and those with paraplegic SCI (P = 0.01). However, no significant difference was found in the viscosity between two groups (P = 0.17). Except for first peak flexion angle, all other displacement kinematic parameters exhibited no statistically significant difference between normal subjects and subjects with SCI. Conclusions Patients with SCI have significantly greater joint stiffness compared to able-bodied subjects. PMID:25437824

  10. A novel method of measuring leaf epidermis and mesophyll stiffness shows the ubiquitous nature of the sandwich structure of leaf laminas in broad-leaved angiosperm species

    PubMed Central

    Onoda, Yusuke; Schieving, Feike; Anten, Niels P. R.

    2015-01-01

    Plant leaves commonly exhibit a thin, flat structure that facilitates a high light interception per unit mass, but may increase risks of mechanical failure when subjected to gravity, wind and herbivory as well as other stresses. Leaf laminas are composed of thin epidermis layers and thicker intervening mesophyll layers, which resemble a composite material, i.e. sandwich structure, used in engineering constructions (e.g. airplane wings) where high bending stiffness with minimum weight is important. Yet, to what extent leaf laminas are mechanically designed and behave as a sandwich structure remains unclear. To resolve this issue, we developed and applied a novel method to estimate stiffness of epidermis- and mesophyll layers without separating the layers. Across a phylogenetically diverse range of 36 angiosperm species, the estimated Young’s moduli (a measure of stiffness) of mesophyll layers were much lower than those of the epidermis layers, indicating that leaf laminas behaved similarly to efficient sandwich structures. The stiffness of epidermis layers was higher in evergreen species than in deciduous species, and strongly associated with cuticle thickness. The ubiquitous nature of sandwich structures in leaves across studied species suggests that the sandwich structure has evolutionary advantages as it enables leaves to be simultaneously thin and flat, efficiently capturing light and maintaining mechanical stability under various stresses. PMID:25675956

  11. A novel method of measuring leaf epidermis and mesophyll stiffness shows the ubiquitous nature of the sandwich structure of leaf laminas in broad-leaved angiosperm species.

    PubMed

    Onoda, Yusuke; Schieving, Feike; Anten, Niels P R

    2015-05-01

    Plant leaves commonly exhibit a thin, flat structure that facilitates a high light interception per unit mass, but may increase risks of mechanical failure when subjected to gravity, wind and herbivory as well as other stresses. Leaf laminas are composed of thin epidermis layers and thicker intervening mesophyll layers, which resemble a composite material, i.e. sandwich structure, used in engineering constructions (e.g. airplane wings) where high bending stiffness with minimum weight is important. Yet, to what extent leaf laminas are mechanically designed and behave as a sandwich structure remains unclear. To resolve this issue, we developed and applied a novel method to estimate stiffness of epidermis- and mesophyll layers without separating the layers. Across a phylogenetically diverse range of 36 angiosperm species, the estimated Young's moduli (a measure of stiffness) of mesophyll layers were much lower than those of the epidermis layers, indicating that leaf laminas behaved similarly to efficient sandwich structures. The stiffness of epidermis layers was higher in evergreen species than in deciduous species, and strongly associated with cuticle thickness. The ubiquitous nature of sandwich structures in leaves across studied species suggests that the sandwich structure has evolutionary advantages as it enables leaves to be simultaneously thin and flat, efficiently capturing light and maintaining mechanical stability under various stresses. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.

  12. Relationships between central arterial stiffness, lean body mass, and absolute and relative strength in young and older men and women.

    PubMed

    Fahs, Christopher A; Thiebaud, Robert S; Rossow, Lindy M; Loenneke, Jeremy P; Bemben, Debra A; Bemben, Michael G

    2017-08-16

    Relationships between muscular strength and arterial stiffness as well as between muscle mass and arterial stiffness have been observed suggesting a link between the neuromuscular system and vascular health. However, the relationship between central arterial stiffness and absolute and relative strength along with muscle mass has not been investigated in both sexes across a broad age range. The purpose of this study was to examine the relationship between central arterial stiffness and absolute and relative strength as well as between central arterial stiffness and lean body mass (LBM) in men and women across a broad age range. LBM, central arterial stiffness and strength were measured on 36 men and 35 women between the ages of 18 and 75 years. Strength was measured on five machine resistance exercises and summed as one measure of overall strength (absolute strength). Relative strength was calculated as total strength divided by LBM (relative strength). Central arterial stiffness was inversely related to both absolute (r = -0·230; P = 0·029) and relative strength (r = -0·484; P < 0·001) but not LBM (r = 0·097; P = 0·213). The relationship between central arterial stiffness and relative strength was attenuated but still present when controlling for either age, per cent body fat, LBM or mean arterial pressure. These results suggest that, across a wide age range, the expression of relative muscular strength has a stronger relationship with central arterial stiffness compared to either LBM or absolute strength. This suggests that muscle function more than muscle mass may be coupled with vascular health. © 2017 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.

  13. A novel device for measuring arterial stiffness using finger-toe pulse wave velocity: Validation study of the pOpmètre®.

    PubMed

    Alivon, Maureen; Vo-Duc Phuong, Thao; Vignon, Virginie; Bozec, Erwan; Khettab, Hakim; Hanon, Olivier; Briet, Marie; Halimi, Jean-Michel; Hallab, Magid; Plichart, Matthieu; Mohammedi, Kamel; Marre, Michel; Boutouyrie, Pierre; Laurent, Stéphane

    2015-04-01

    The finger-toe pathway could be a good alternative for assessing arterial stiffness conveniently. To evaluate the accuracy of the pOpmètre®--a new device that measures finger-toe pulse wave velocity (ft-PWV). The pOpmètre has two photodiode sensors, positioned on the finger and the toe. Pulse waves are recorded continuously for 20 seconds, and the difference in pulse wave transit time between toe and finger (ft-TT) is calculated. The travelled distance is estimated using subject height. Study 1 compared ft-PWV with carotid-femoral PWV (cf-PWV) obtained by the reference method (SphygmoCor®) in 86 subjects (mean age 53±20 years), including 69 patients with various pathologies and 17 healthy normotensives. Study 2 compared changes in ft-PWV and cf-PWV during a cold pressor test in 10 healthy subjects. Study 3 assessed repeatability in 45 patients. ft-PWV correlated significantly with cf-PWV (R2=0.43; P<0.0001). A better correlation was found in terms of transit time (R2=0.61; P<0.0001). The discrepancy between transit times was related to age. The cold pressor test induced parallel changes in cf-PWV and ft-PWV, with increased aortic stiffness that was reversible during recovery. Intra-session repeatability was very good, with a coefficient of variation of 4.52%. The pOpmètre® allows measurement of arterial stiffness in routine clinical practice. The greatest advantages of ft-PWV are simplicity, rapidity, feasibility, acceptability by patients and correct agreement with the reference technique. Further studies are needed to adjust for bias and to validate the pOpmètre in larger populations. Copyright © 2015 Elsevier Masson SAS. All rights reserved.

  14. Steady-state stiffness of utricular hair cells depends on macular location and hair bundle structure.

    PubMed

    Spoon, Corrie; Moravec, W J; Rowe, M H; Grant, J W; Peterson, E H

    2011-12-01

    Spatial and temporal properties of head movement are encoded by vestibular hair cells in the inner ear. One of the most striking features of these receptors is the orderly structural variation in their mechanoreceptive hair bundles, but the functional significance of this diversity is poorly understood. We tested the hypothesis that hair bundle structure is a significant contributor to hair bundle mechanics by comparing structure and steady-state stiffness of 73 hair bundles at varying locations on the utricular macula. Our first major finding is that stiffness of utricular hair bundles varies systematically with macular locus. Stiffness values are highest in the striola, near the line of hair bundle polarity reversal, and decline exponentially toward the medial extrastriola. Striolar bundles are significantly more stiff than those in medial (median: 8.9 μN/m) and lateral (2.0 μN/m) extrastriolae. Within the striola, bundle stiffness is greatest in zone 2 (106.4 μN/m), a band of type II hair cells, and significantly less in zone 3 (30.6 μN/m), which contains the only type I hair cells in the macula. Bathing bundles in media that break interciliary links produced changes in bundle stiffness with predictable time course and magnitude, suggesting that links were intact in our standard media and contributed normally to bundle stiffness during measurements. Our second major finding is that bundle structure is a significant predictor of steady-state stiffness: the heights of kinocilia and the tallest stereocilia are the most important determinants of bundle stiffness. Our results suggest 1) a functional interpretation of bundle height variability in vertebrate vestibular organs, 2) a role for the striola in detecting onset of head movement, and 3) the hypothesis that differences in bundle stiffness contribute to diversity in afferent response dynamics.

  15. Steady-state stiffness of utricular hair cells depends on macular location and hair bundle structure

    PubMed Central

    Spoon, Corrie; Moravec, W. J.; Rowe, M. H.; Grant, J. W.

    2011-01-01

    Spatial and temporal properties of head movement are encoded by vestibular hair cells in the inner ear. One of the most striking features of these receptors is the orderly structural variation in their mechanoreceptive hair bundles, but the functional significance of this diversity is poorly understood. We tested the hypothesis that hair bundle structure is a significant contributor to hair bundle mechanics by comparing structure and steady-state stiffness of 73 hair bundles at varying locations on the utricular macula. Our first major finding is that stiffness of utricular hair bundles varies systematically with macular locus. Stiffness values are highest in the striola, near the line of hair bundle polarity reversal, and decline exponentially toward the medial extrastriola. Striolar bundles are significantly more stiff than those in medial (median: 8.9 μN/m) and lateral (2.0 μN/m) extrastriolae. Within the striola, bundle stiffness is greatest in zone 2 (106.4 μN/m), a band of type II hair cells, and significantly less in zone 3 (30.6 μN/m), which contains the only type I hair cells in the macula. Bathing bundles in media that break interciliary links produced changes in bundle stiffness with predictable time course and magnitude, suggesting that links were intact in our standard media and contributed normally to bundle stiffness during measurements. Our second major finding is that bundle structure is a significant predictor of steady-state stiffness: the heights of kinocilia and the tallest stereocilia are the most important determinants of bundle stiffness. Our results suggest 1) a functional interpretation of bundle height variability in vertebrate vestibular organs, 2) a role for the striola in detecting onset of head movement, and 3) the hypothesis that differences in bundle stiffness contribute to diversity in afferent response dynamics. PMID:21918003

  16. Intrinsic ankle stiffness during standing increases with ankle torque and passive stretch of the Achilles tendon

    PubMed Central

    Gill, Jaspret

    2018-01-01

    Individuals may stand with a range of ankle angles. Furthermore, shoes or floor surfaces may elevate or depress their heels. Here we ask how these situations impact ankle stiffness and balance. We performed two studies (each with 10 participants) in which the triceps surae, Achilles tendon and aponeurosis were stretched either passively, by rotating the support surface, or actively by leaning forward. Participants stood freely on footplates which could rotate around the ankle joint axis. Brief, small stiffness-measuring perturbations (<0.7 deg; 140 ms) were applied at intervals of 4–5 s. In study 1, participants stood at selected angles of forward lean. In study 2, normal standing was compared with passive dorsiflexion induced by 15 deg toes-up tilt of the support surface. Smaller perturbations produced higher stiffness estimates, but for all perturbation sizes stiffness increased with active torque or passive stretch. Sway was minimally affected by stretch or lean, suggesting that this did not underlie the alterations in stiffness. In quiet stance, maximum ankle stiffness is limited by the tendon. As tendon strain increases, it becomes stiffer, causing an increase in overall ankle stiffness, which would explain the effects of leaning. However, stiffness also increased considerably with passive stretch, despite a modest torque increase. We discuss possible explanations for this increase. PMID:29558469

  17. Differentiation between non-neural and neural contributors to ankle joint stiffness in cerebral palsy

    PubMed Central

    2013-01-01

    Background Spastic paresis in cerebral palsy (CP) is characterized by increased joint stiffness that may be of neural origin, i.e. improper muscle activation caused by e.g. hyperreflexia or non-neural origin, i.e. altered tissue viscoelastic properties (clinically: “spasticity” vs. “contracture”). Differentiation between these components is hard to achieve by common manual tests. We applied an assessment instrument to obtain quantitative measures of neural and non-neural contributions to ankle joint stiffness in CP. Methods Twenty-three adolescents with CP and eleven healthy subjects were seated with their foot fixated to an electrically powered single axis footplate. Passive ramp-and-hold rotations were applied over full ankle range of motion (RoM) at low and high velocities. Subject specific tissue stiffness, viscosity and reflexive torque were estimated from ankle angle, torque and triceps surae EMG activity using a neuromuscular model. Results In CP, triceps surae reflexive torque was on average 5.7 times larger (p = .002) and tissue stiffness 2.1 times larger (p = .018) compared to controls. High tissue stiffness was associated with reduced RoM (p < .001). Ratio between neural and non-neural contributors varied substantially within adolescents with CP. Significant associations of SPAT (spasticity test) score with both tissue stiffness and reflexive torque show agreement with clinical phenotype. Conclusions Using an instrumented and model based approach, increased joint stiffness in CP could be mainly attributed to higher reflexive torque compared to control subjects. Ratios between contributors varied substantially within adolescents with CP. Quantitative differentiation of neural and non-neural stiffness contributors in CP allows for assessment of individual patient characteristics and tailoring of therapy. PMID:23880287

  18. Differentiation between non-neural and neural contributors to ankle joint stiffness in cerebral palsy.

    PubMed

    de Gooijer-van de Groep, Karin L; de Vlugt, Erwin; de Groot, Jurriaan H; van der Heijden-Maessen, Hélène C M; Wielheesen, Dennis H M; van Wijlen-Hempel, Rietje M S; Arendzen, J Hans; Meskers, Carel G M

    2013-07-23

    Spastic paresis in cerebral palsy (CP) is characterized by increased joint stiffness that may be of neural origin, i.e. improper muscle activation caused by e.g. hyperreflexia or non-neural origin, i.e. altered tissue viscoelastic properties (clinically: "spasticity" vs. "contracture"). Differentiation between these components is hard to achieve by common manual tests. We applied an assessment instrument to obtain quantitative measures of neural and non-neural contributions to ankle joint stiffness in CP. Twenty-three adolescents with CP and eleven healthy subjects were seated with their foot fixated to an electrically powered single axis footplate. Passive ramp-and-hold rotations were applied over full ankle range of motion (RoM) at low and high velocities. Subject specific tissue stiffness, viscosity and reflexive torque were estimated from ankle angle, torque and triceps surae EMG activity using a neuromuscular model. In CP, triceps surae reflexive torque was on average 5.7 times larger (p = .002) and tissue stiffness 2.1 times larger (p = .018) compared to controls. High tissue stiffness was associated with reduced RoM (p < .001). Ratio between neural and non-neural contributors varied substantially within adolescents with CP. Significant associations of SPAT (spasticity test) score with both tissue stiffness and reflexive torque show agreement with clinical phenotype. Using an instrumented and model based approach, increased joint stiffness in CP could be mainly attributed to higher reflexive torque compared to control subjects. Ratios between contributors varied substantially within adolescents with CP. Quantitative differentiation of neural and non-neural stiffness contributors in CP allows for assessment of individual patient characteristics and tailoring of therapy.

  19. Biomechanical constraints on the feedforward regulation of endpoint stiffness.

    PubMed

    Hu, Xiao; Murray, Wendy M; Perreault, Eric J

    2012-10-01

    Although many daily tasks tend to destabilize arm posture, it is still possible to have stable interactions with the environment by regulating the multijoint mechanics of the arm in a task-appropriate manner. For postural tasks, this regulation involves the appropriate control of endpoint stiffness, which represents the stiffness of the arm at the hand. Although experimental studies have been used to evaluate endpoint stiffness control, including the orientation of maximal stiffness, the underlying neural strategies remain unknown. Specifically, the relative importance of feedforward and feedback mechanisms has yet to be determined due to the difficulty separately identifying the contributions of these mechanisms in human experiments. This study used a previously validated three-dimensional musculoskeletal model of the arm to quantify the degree to which the orientation of maximal endpoint stiffness could be changed using only steady-state muscle activations, used to represent feedforward motor commands. Our hypothesis was that the feedforward control of endpoint stiffness orientation would be significantly constrained by the biomechanical properties of the musculoskeletal system. Our results supported this hypothesis, demonstrating substantial biomechanical constraints on the ability to regulate endpoint stiffness throughout the workspace. The ability to regulate stiffness orientation was further constrained by additional task requirements, such as the need to support the arm against gravity or exert forces on the environment. Together, these results bound the degree to which slowly varying feedforward motor commands can be used to regulate the orientation of maximum arm stiffness and provide a context for better understanding conditions in which feedback control may be needed.

  20. Probing the salt dependence of the torsional stiffness of DNA by multiplexed magnetic torque tweezers.

    PubMed

    Kriegel, Franziska; Ermann, Niklas; Forbes, Ruaridh; Dulin, David; Dekker, Nynke H; Lipfert, Jan

    2017-06-02

    The mechanical properties of DNA fundamentally constrain and enable the storage and transmission of genetic information and its use in DNA nanotechnology. Many properties of DNA depend on the ionic environment due to its highly charged backbone. In particular, both theoretical analyses and direct single-molecule experiments have shown its bending stiffness to depend on salt concentration. In contrast, the salt-dependence of the twist stiffness of DNA is much less explored. Here, we employ optimized multiplexed magnetic torque tweezers to study the torsional stiffness of DNA under varying salt conditions as a function of stretching force. At low forces (<3 pN), the effective torsional stiffness is ∼10% smaller for high salt conditions (500 mM NaCl or 10 mM MgCl2) compared to lower salt concentrations (20 mM NaCl and 100 mM NaCl). These differences, however, can be accounted for by taking into account the known salt dependence of the bending stiffness. In addition, the measured high-force (6.5 pN) torsional stiffness values of C = 103 ± 4 nm are identical, within experimental errors, for all tested salt concentration, suggesting that the intrinsic torsional stiffness of DNA does not depend on salt. © The Author(s) 2017. Published by Oxford University Press on behalf of Nucleic Acids Research.

  1. Relative stiffness of flat conductor cables

    NASA Technical Reports Server (NTRS)

    Hankins, J. D.

    1976-01-01

    The measurement of the bending moment required to obtain a given deflection in short lengths of flat conductor cable (FCC) is presented in this report. Experimental data were taken on 10 different samples of FCC and normalized to express all bending moments (relative stiffness factor) in terms of a cable 5.1 cm (2.0 in.) in width. Data are presented in tabular and graphical form for the covenience of designers who may be interested in finding torques exerted on critical components by short lengths of FCC.

  2. In vivo quantification of liver stiffness in a rat model of hepatic fibrosis with acoustic radiation force.

    PubMed

    Wang, Michael H; Palmeri, Mark L; Guy, Cynthia D; Yang, Liu; Hedlund, Laurence W; Diehl, Anna Mae; Nightingale, Kathryn R

    2009-10-01

    Liver fibrosis is currently staged using needle biopsy, a highly invasive procedure with a number of disadvantages. Measurement of liver stiffness changes that accompany progression of the disease may provide a quantitative and noninvasive method to assess the health of the liver. The purpose of this study is to investigate the correlation between liver stiffness measured by radiation force induced shear waves and disease related changes in the liver. An additional aim is to present initial findings on the effects of liver viscosity on radiation force induced shear wave morphology. Liver fibrosis was induced in 10 rats using carbon tetrachloride (CCl(4)), while five rats acted as controls. Liver stiffness was measured in vivo in all rats after a treatment period of 8 weeks using a modified Siemens SONOLINE Antares scanner (Siemens Medical Solutions USA, Ultrasound Division, Issaquah, WA, USA). The spatial coherence of radiation force induced shear waves propagating in the viscoelastic rat liver decreased significantly with propagation distance, compared with shear waves in an elastic phantom and a finite element model of a purely elastic medium. Animals were sacrificed after imaging and liver samples were taken for histopathologic analysis and collagen quantification using picrosirius red staining and hydroxyproline assay. At the end of the treatment period, five rats had healthy livers (stage F0), while six had severe fibrosis (F3) and the rest had light to moderate fibrosis (F1 and F2). The measured liver stiffness for the F0 group was 1.5+/-0.1 kPa (mean+/-95% confidence interval) and for F3 livers was 1.8+/-0.2 kPa. In this study, liver stiffness was found to be linearly correlated with the amount of collagen in the liver measured by picrosirius red staining (r(2)=0.43, p=0.008). In addition, stiffness spatial heterogeneity was also linearly correlated with liver collagen content (r(2)=0.58, p=0.001) by picrosirius red staining. These results are consistent

  3. Spatial distributions of pericellular stiffness in natural extracellular matrices are dependent on cell-mediated proteolysis and contractility.

    PubMed

    Keating, M; Kurup, A; Alvarez-Elizondo, M; Levine, A J; Botvinick, E

    2017-07-15

    instruct cells, which can in turn modify their ECM, as has been shown in the study of cancer and regenerative medicine. Here we measure the stiffness of the collagen microenvironment surrounding cells and quantitatively measure the dependence of pericellular stiffness on MMP activity and cytoskeletal contractility. Competent cell-mediated stiffening results in a wildly heterogeneous micromechanical topography, with values spanning orders of magnitude around a single cell. We speculate studies must consider this notable heterogeneity generated by cells when testing theories regarding the role of ECM mechanics in health and disease. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  4. Implant material and design alter construct stiffness in distal femur locking plate fixation: a pilot study.

    PubMed

    Schmidt, Ulf; Penzkofer, Rainer; Bachmaier, Samuel; Augat, Peter

    2013-09-01

    Construct stiffness affects healing of bones fixed with locking plates. However, variable construct stiffness reported in the literature may be attributable to differing test configurations and direct comparisons may clarify these differences. We therefore asked whether different distal femur locking plate systems and constructs will lead to different (1) axial and rotational stiffness and (2) fatigue under cyclic loading. We investigated four plate systems for distal femur fixation (AxSOS, LCP, PERI-LOC, POLYAX) of differing designs and materials using bone substitutes in a distal femur fracture model (OTA/AO 33-A3). We created six constructs of each of the four plating systems. Stiffness under static and cyclic loading and fatigue under cyclic loading were measured. Mean construct stiffness under axial loading was highest for AxSOS (100.8 N/mm) followed by PERI-LOC (80.8 N/mm) and LCP (62.6 N/mm). POLYAX construct stiffness testing showed the lowest stiffness (51.7 N/mm) with 50% stiffness of AxSOS construct testing. Mean construct stiffness under torsional loading was similar in the group of AxSOS and PERI-LOC (3.40 Nm/degree versus 3.15 Nm/degree) and in the group of LCP and POLYAX (2.63 Nm/degree versus 2.56 Nm/degree). The fourth load level of > 75,000 cycles was reached by three of six AxSOS, three of six POLYAX, and two of six PERI-LOC constructs. All others including all LCP constructs failed earlier. Implant design and material of new-generation distal femur locking plate systems leads to a wide range of differences in construct stiffness. Assuming construct stiffness affects fracture healing, these data may influence surgical decision-making in choosing an implant system.

  5. Endoscopic add-on stiffness probe for real-time soft surface characterisation in MIS.

    PubMed

    Faragasso, A; Stilli, A; Bimbo, J; Noh, Y; Liu, H; Nanayakkara, T; Dasgupta, P; Wurdemann, H A; Althoefer, K

    2014-01-01

    This paper explores a novel stiffness sensor which is mounted on the tip of a laparoscopic camera. The proposed device is able to compute stiffness when interacting with soft surfaces. The sensor can be used in Minimally Invasive Surgery, for instance, to localise tumor tissue which commonly has a higher stiffness when compared to healthy tissue. The purely mechanical sensor structure utilizes the functionality of an endoscopic camera to the maximum by visually analyzing the behavior of trackers within the field of view. Two pairs of spheres (used as easily identifiable features in the camera images) are connected to two springs with known but different spring constants. Four individual indenters attached to the spheres are used to palpate the surface. During palpation, the spheres move linearly towards the objective lens (i.e. the distance between lens and spheres is changing) resulting in variations of their diameters in the camera images. Relating the measured diameters to the different spring constants, a developed mathematical model is able to determine the surface stiffness in real-time. Tests were performed using a surgical endoscope to palpate silicon phantoms presenting different stiffness. Results show that the accuracy of the sensing system developed increases with the softness of the examined tissue.

  6. Arterial stiffness is associated with age-related differences in cerebrovascular conductance.

    PubMed

    Jaruchart, Tussana; Suwanwela, Nijasri C; Tanaka, Hirofumi; Suksom, Daroonwan

    2016-01-01

    To determine if arterial stiffness is associated with age-related differences in cerebrovascular conductance and reactivity, twenty-eight apparently healthy sedentary young (25±1 years; n=15) and older (67±1 years; n=13) adults were studied. Brachial-ankle pulse wave velocity (baPWV) was measured as an index of arterial stiffness. Cerebrovascular reactivity was determined by measuring changes in mean blood velocity in the middle cerebral artery under normocapnic, hypocapnic and hypercapnic conditions. Mean baPWV was greater (p<0.05) in older compared with young adults. At baseline, mean cerebral blood flow velocity and cerebrovascular conductance index were lower (p<0.05) in older compared with young adults under normocapnic, hypocapnic and hypercapnic conditions. There were no significant group differences in cerebrovascular reactivity when they were adjusted for stimuli (i.e., end-tidal CO2 concentrations) in most perturbation conditions except for the normocapnia to hypercapnia condition. baPWV was negatively associated with cerebrovascular conductance index at all conditions (all p<0.05). We concluded that arterial stiffness was associated with age-related differences in cerebrovascular conductance and that there were no apparent age-associated differences in cerebrovascular reactivity. Copyright © 2015 Elsevier Inc. All rights reserved.

  7. Mass and stiffness estimation using mobile devices for structural health monitoring

    NASA Astrophysics Data System (ADS)

    Le, Viet; Yu, Tzuyang

    2015-04-01

    In the structural health monitoring (SHM) of civil infrastructure, dynamic methods using mass, damping, and stiffness for characterizing structural health have been a traditional and widely used approach. Changes in these system parameters over time indicate the progress of structural degradation or deterioration. In these methods, capability of predicting system parameters is essential to their success. In this paper, research work on the development of a dynamic SHM method based on perturbation analysis is reported. The concept is to use externally applied mass to perturb an unknown system and measure the natural frequency of the system. Derived theoretical expressions for mass and stiffness prediction are experimentally verified by a building model. Dynamic responses of the building model perturbed by various masses in free vibration were experimentally measured by a mobile device (cell phone) to extract the natural frequency of the building model. Single-degreeof- freedom (SDOF) modeling approach was adopted for the sake of using a cell phone. From the experimental result, it is shown that the percentage error of predicted mass increases when the mass ratio increases, while the percentage error of predicted stiffness decreases when the mass ratio increases. This work also demonstrated the potential use of mobile devices in the health monitoring of civil infrastructure.

  8. A recursive Bayesian updating model of haptic stiffness perception.

    PubMed

    Wu, Bing; Klatzky, Roberta L

    2018-06-01

    Stiffness of many materials follows Hooke's Law, but the mechanism underlying the haptic perception of stiffness is not as simple as it seems in the physical definition. The present experiments support a model by which stiffness perception is adaptively updated during dynamic interaction. Participants actively explored virtual springs and estimated their stiffness relative to a reference. The stimuli were simulations of linear springs or nonlinear springs created by modulating a linear counterpart with low-amplitude, half-cycle (Experiment 1) or full-cycle (Experiment 2) sinusoidal force. Experiment 1 showed that subjective stiffness increased (decreased) as a linear spring was positively (negatively) modulated by a half-sinewave force. In Experiment 2, an opposite pattern was observed for full-sinewave modulations. Modeling showed that the results were best described by an adaptive process that sequentially and recursively updated an estimate of stiffness using the force and displacement information sampled over trajectory and time. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

  9. Passive stiffness of pressure-induced hypertrophied cat myocardium.

    PubMed

    Williams, J F; Potter, R D

    1981-07-01

    The effect of myocardial hypertrophy on passive stiffness was determined from the stress (sigma)-strain relationship of right ventricular papillary muscles from 18 pulmonary artery-banded and 21 non-banded cats. By use of Lagrangian strain, (1-lo)lo is initial muscle length, and instantaneous stress elastic constants beta and alpha were calculated from the equation sigma = alpha(ebeta epsilon - 1). Elastic stiffness (d sigma/d epsilon) was determined from the formula d sigma/d epsilon = beta alpha + alpha beta. Banding produced an average increase in RV mass of 70%. Beta averaged 14.2 +/- 0.9 (SEM) and 16.0 +/- 0.8 in the non-hypertrophied and hypertrophied muscles, respectively (NS). However, elastic stiffness was significantly greater in hypertrophied muscles over the entire stress range. Contractile function varied widely among hypertrophied muscles but was not related to changes in stiffness. Thus, moderate degrees of pressure-induced hypertrophy are associated with a modest increase in the passive stiffness properties of the muscle, independent of changes in contractile function.

  10. Liver stiffness measurements with supersonic shear wave elastography in the diagnosis of biliary atresia: a comparative study with grey-scale US.

    PubMed

    Zhou, Lu-Yao; Jiang, Hong; Shan, Quan-Yuan; Chen, Dong; Lin, Xiao-Na; Liu, Bao-Xian; Xie, Xiao-Yan

    2017-08-01

    To prospectively assess the diagnostic performance of supersonic shear wave elastography (SSWE) in identifying biliary atresia (BA) among infants with conjugated hyperbilirubinaemia by comparing this approach with grey-scale ultrasonography (US). Forty infants were analysed as the control group to determine normal liver stiffness values. The use of SSWE values for identifying BA was investigated in 172 infants suspected of having BA, and results were compared with the results obtained by grey-scale US. The Mann-Whitney U test, unpaired t-test, Spearman correlation and linear regression were also performed. The success rates of SSWE measurements in the control and study group were 100% (40/40) and 96.4% (244/253), respectively. Age, direct bilirubin, and indirect bilirubin all significantly correlated with SSWE in the liver (all P < 0.001). Linear regression showed that age had a greater effect on SSWE values than direct or indirect bilirubin. The diagnostic performance of liver stiffness values in identifying BA was lower than that of grey-scale US (area under the receiver operating characteristic curve [AUC], 0.790 vs 0.893, P < 0.001). SSWE is feasible and valuable in differentiating BA from non-BA. However, its diagnostic performance does not exceed that of grey-scale US. • SSWE could be successfully performed in an infant population. • For infants, the liver stiffness will increase as age increases. • SSWE is potentially useful in assessing infants suspected of biliary atresia. • SSWE is inferior to grey-scale US in identifying biliary atresia.

  11. Serum ferritin levels are associated with arterial stiffness in healthy Korean adults.

    PubMed

    Ha, Ji Yoon; Kim, Min Kyung; Kang, Shinae; Nam, Ji Sun; Ahn, Chul Woo; Kim, Kyung Rae; Park, Jong Suk

    2016-08-01

    Although an association between serum ferritin and atherosclerosis has been suggested, limited epidemiologic data are available regarding the association between ferritin and arterial stiffness in healthy adults. A total of 2932 healthy subjects were enrolled in this study. Anthropometric and biochemical profiles including ferritin were measured. The arterial stiffness was measured using brachial-ankle pulse wave velocity (baPWV). Serum ferritin levels were classified into quartiles and baPWV values gradually increased with each ferritin quartile. Multiple regression analysis showed that ferritin levels were independently correlated with baPWV. After adjusting for multiple risk factors, as compared with the lowest quartile, the odds ratios for high baPWV (>75(th) percentile) were 1.15 (0.84-1.56), 1.37 (0.97-1.73), and 1.46 (1.29-2.17) among men (p for trend < 0.05) and 1.24 (0.87-1.79), 1.53 (1.09-2.16), and 1.80 (1.25-2.82) among women (p for trend < 0.05), for the second, third, and fourth quartiles of ferritin, respectively. In conclusion, serum ferritin levels are independently associated with arterial stiffness in healthy Korean adults. © The Author(s) 2016.

  12. Analysis and Design of Variable Stiffness Composite Cylinders

    NASA Technical Reports Server (NTRS)

    Tatting, Brian F.; Guerdal, Zafer

    1998-01-01

    An investigation of the possible performance improvements of thin circular cylindrical shells through the use of the variable stiffness concept is presented. The variable stiffness concept implies that the stiffness parameters change spatially throughout the structure. This situation is achieved mainly through the use of curvilinear fibers within a fiber-reinforced composite laminate, though the possibility of thickness variations and discrete stiffening elements is also allowed. These three mechanisms are incorporated into the constitutive laws for thin shells through the use of Classical Lamination Theory. The existence of stiffness variation within the structure warrants a formulation of the static equilibrium equations from the most basic principles. The governing equations include sufficient detail to correctly model several types of nonlinearity, including the formation of a nonlinear shell boundary layer as well as the Brazier effect due to nonlinear bending of long cylinders. Stress analysis and initial buckling estimates are formulated for a general variable stiffness cylinder. Results and comparisons for several simplifications of these highly complex governing equations are presented so that the ensuing numerical solutions are considered reliable and efficient enough for in-depth optimization studies. Four distinct cases of loading and stiffness variation are chosen to investigate possible areas of improvement that the variable stiffness concept may offer over traditional constant stiffness and/or stiffened structures. The initial investigation deals with the simplest solution for cylindrical shells in which all quantities are constant around the circumference of the cylinder. This axisymmetric case includes a stiffness variation exclusively in the axial direction, and the only pertinent loading scenarios include constant loads of axial compression, pressure, and torsion. The results for these cases indicate that little improvement over traditional

  13. The influence of artificially increased trunk stiffness on the balance recovery after a trip.

    PubMed

    van der Burg, J C E; Pijnappels, M; van Dieën, J H

    2007-07-01

    Falls occur frequently in the growing population of elderly. Since trunk control is critical for maintaining balance, the higher trunk stiffness in elderly people compared to the general population has been associated with their increased fall-risk. Theoretically, trunk stiffness may be beneficial for balance recovery in walking, i.e. after a trip. A stiff joint may provide a torque that restricts the perturbation effects and thereby reduces the probability of a fall. The aim of this study was to test whether trunk stiffness impaired or assisted balance recovery after a trip during walking. An orthopedic corset was used to simulate trunk stiffness in 11 young male adults. Subjects walked over a platform, with or without the corset on, and were occasionally tripped over a hidden obstacle. Kinematics of the tripping reaction were measured. Initial trunk accelerations were significantly attenuated by the corset, which indicates a positive effect of the stiffening corset. However, no subsequent effects on peak trunk inclination and on the peak moment arm of gravity on the trunk were found. The pattern of trunk motion allowed ample time for triggered or voluntary muscle responses to be generated, before a substantial inclination occurred. It appears that such active responses were sufficient in the young subjects tested to obtain a similar net effect with or without the increased trunk stiffness induced by the corset.

  14. Spleen Stiffness Is Superior to Liver Stiffness for Predicting Esophageal Varices in Chronic Liver Disease: A Meta-Analysis.

    PubMed

    Ma, Xiaowen; Wang, Le; Wu, Hao; Feng, Yuemin; Han, Xibiao; Bu, Haoran; Zhu, Qiang

    2016-01-01

    Liver stiffness (LS) and spleen stiffness (SS) are two most widely accessible non-invasive parameters for predicting esophageal varices (EV), but the reported accuracy of the two predictors have been inconsistent across studies. This meta-analysis aims to evaluate the diagnostic performance of LS and SS measurement for detecting EV in patients with chronic liver disease (CLD), and compare their accuracy. Pubmed/Medline, Embase, Cochrane Library and Ovid were searched for all studies assessing SS and LS simultaneously in EV diagnosis. A total of 16 studies including 1892 patients were included in this meta-analysis, and the pooled statistical parameters were calculated using the bivariate mixed effects models. In detection of any EV, for LS measurement, the summary sensitivity was 0.83 (95% confidence interval [CI]: 0.78-0.87), and the specificity was 0.66 (95% CI: 0.60-0.72). While for SS measurement, the pooled sensitivity and specificity was 0.88 (95% CI: 0.83-0.92) and 0.78 (95% CI: 0.73-0.83). The summary receiver operating characteristic (SROC) curve values of LS and SS were 0.81 (95% CI: 0.77-0.84) and 0.88 (95% CI: 0.85-0.91) respectively, and the results had statistical significance (P<0.01). The diagnostic odds ratio (DOR) of SS (25.73) was significantly higher than that of LS (9.54), with the relative DOR value was 2.48 (95%CI: 1.10-5.60), P<0.05. Under current techniques, SS is significantly superior to LS for identifying the presence of EV in patients with CLD. SS measurement may help to select patients for endoscopic screening.

  15. The contribution of quasi-joint stiffness of the ankle joint to gait in patients with hemiparesis.

    PubMed

    Sekiguchi, Yusuke; Muraki, Takayuki; Kuramatsu, Yuko; Furusawa, Yoshihito; Izumi, Shin-Ichi

    2012-06-01

    The role of ankle joint stiffness during gait in patients with hemiparesis has not been clarified. The purpose of this study was to determine the contribution of quasi-joint stiffness of the ankle joint to spatiotemporal and kinetic parameters regarding gait in patients with hemiparesis due to brain tumor or stroke and healthy individuals. Spatiotemporal and kinetic parameters regarding gait in twelve patients with hemiparesis due to brain tumor or stroke and nine healthy individuals were measured with a 3-dimensional motion analysis system. Quasi-joint stiffness was calculated from the slope of the linear regression of the moment-angle curve of the ankle joint during the second rocker. There was no significant difference in quasi-joint stiffness among both sides of patients and the right side of controls. Quasi-joint stiffness on the paretic side of patients with hemiparesis positively correlated with maximal ankle power (r=0.73, P<0.01) and gait speed (r=0.66, P<0.05). In contrast, quasi-joint stiffness in controls negatively correlated with maximal ankle power (r=-0.73, P<0.05) and gait speed (r=-0.76, P<0.05). Our findings suggested that ankle power during gait might be generated by increasing quasi-joint stiffness in patients with hemiparesis. In contrast, healthy individuals might decrease quasi-joint stiffness to avoid deceleration of forward tilt of the tibia. Our findings might be useful for selecting treatment for increased ankle stiffness due to contracture and spasticity in patients with hemiparesis. Copyright © 2011 Elsevier Ltd. All rights reserved.

  16. Leg stiffness and expertise in men jumping.

    PubMed

    Laffaye, Guillaume; Bardy, Benoît G; Durey, Alain

    2005-04-01

    The aim of the present study is to investigate: a) the leg spring behavior in the one-leg vertical jump, b) the contribution of impulse parameters to this behavior, and c) the effect of jumping expertise on leg stiffness. Four categories of experts (handball, basketball, volleyball players, and Fosbury athletes), as well as novice subjects performed a run-and-jump test to touch a ball with the head. Five experimental conditions were tested from 55 to 95% of the maximum jump height. Kinematic and kinetic data were collected using six cameras and a force plate. The mechanical behavior of the musculoskeleton component of the human body can be modeled as a simple mass-spring system, from which leg stiffness values can be extracted to better understand energy transfer during running or jumping. The results indicate that leg stiffness (mean value of 11.5 kN.m) decreased with jumping height. Leg shortening at takeoff also increased with jumping height, whereas contact time decreased (-18%). No difference was found between experts and novices for leg stiffness. However, a principal components analysis (PCA) indicated the contribution of two main factors to the performance. The first factor emerged out of vertical force, stiffness, and duration of impulse. The second factor included leg shortening and jumping height. Differences between experts and novices were observed in terms of the contribution of leg stiffness to jump height, and more importantly, clear differences existed between experts in jumping parameters. The analysis performed on the sport categories indeed revealed different jumping profiles, characterized by specific, sport-related impulse parameters.

  17. Estimation of Time-Varying, Intrinsic and Reflex Dynamic Joint Stiffness during Movement. Application to the Ankle Joint

    PubMed Central

    Guarín, Diego L.; Kearney, Robert E.

    2017-01-01

    Dynamic joint stiffness determines the relation between joint position and torque, and plays a vital role in the control of posture and movement. Dynamic joint stiffness can be quantified during quasi-stationary conditions using disturbance experiments, where small position perturbations are applied to the joint and the torque response is recorded. Dynamic joint stiffness is composed of intrinsic and reflex mechanisms that act and change together, so that nonlinear, mathematical models and specialized system identification techniques are necessary to estimate their relative contributions to overall joint stiffness. Quasi-stationary experiments have demonstrated that dynamic joint stiffness is heavily modulated by joint position and voluntary torque. Consequently, during movement, when joint position and torque change rapidly, dynamic joint stiffness will be Time-Varying (TV). This paper introduces a new method to quantify the TV intrinsic and reflex components of dynamic joint stiffness during movement. The algorithm combines ensemble and deterministic approaches for estimation of TV systems; and uses a TV, parallel-cascade, nonlinear system identification technique to separate overall dynamic joint stiffness into intrinsic and reflex components from position and torque records. Simulation studies of a stiffness model, whose parameters varied with time as is expected during walking, demonstrated that the new algorithm accurately tracked the changes in dynamic joint stiffness using as little as 40 gait cycles. The method was also used to estimate the intrinsic and reflex dynamic ankle stiffness from an experiment with a healthy subject during which ankle movements were imposed while the subject maintained a constant muscle contraction. The method identified TV stiffness model parameters that predicted the measured torque very well, accounting for more than 95% of its variance. Moreover, both intrinsic and reflex dynamic stiffness were heavily modulated through the

  18. Effect of postprandial insulinemia and insulin resistance on measurement of arterial stiffness (augmentation index).

    PubMed

    Greenfield, Jerry R; Samaras, Katherine; Chisholm, Donald J; Campbell, Lesley V

    2007-01-02

    Arterial stiffness, specifically augmentation index (AIx), is an independent predictor of cardiovascular risk. Previous studies suggest that insulin infusion decreases AIx and that this response is attenuated in insulin resistance. Whether physiological postprandial insulinemia similarly affects AIx measurements, and whether insulin resistance modifies this response, has not been studied. Seven relatively insulin-resistant and seven insulin-sensitive postmenopausal women received low-carbohydrate and high-carbohydrate high-fat meals on separate days. Glucose and insulin levels were measured for 360-min following meal consumption. AIx was measured by radial artery applanation tonometry at regular intervals postprandially. Postprandial increases in glucose and insulin were greater following the high-carbohydrate high-fat meal in both insulin-sensitive and insulin-resistant subjects. AIx decreased in both groups following both meals. In insulin-sensitive subjects, the postprandial reduction (incremental area above the curve) in AIx was greater following the high-carbohydrate vs. low-carbohydrate high-fat meal (-6821+/-1089 vs. -3797+/-1171% x min, respectively, P=0.009). In contrast, in insulin-resistant subjects, postprandial AIx responses were similar following the meals, suggesting that insulin resistance is associated with impaired postprandial arterial relaxation. This study demonstrates that the carbohydrate content of a meal, and, hence, the magnitude of the postprandial glucose and insulin responses it elicits, are important determinants of postprandial AIx measurements. The further observation that insulin resistance modified this effect raises the possibility that this phenomenon is a contributor to increased cardiovascular risk in insulin resistance. The results indicate that future studies of AIx need to control for the effects of these potentially confounding variables and that measurement of AIx should be standardized with respect to meals.

  19. A New Method for Cerebral Arterial Stiffness by Measuring Pulse Wave Velocity Using Transcranial Doppler.

    PubMed

    Fu, Xian; Huang, Chuming; Wong, Ka Sing; Chen, Xiangyan; Gao, Qingchun

    2016-08-01

    Pulse wave velocity (PWV) has been regarded as the "gold standard" measurement of arterial stiffness (AS), but it is still only used in the assessment of central and peripheral arteries. We constructed a new method to evaluate cerebral AS by measuring PWV using transcranial Doppler (TCD). In all, 90 healthy subjects who received annual health screening were consecutively enrolled in this study between January 2011 and June 2013. Data on clinical characteristics, brachium-ankle (ba) PWV, and carotid-cerebral (cc) PWV measured with our newly constructed method by two experienced operators were recorded. cc PWV was calculated as the distance between two points in the common carotid artery and proximal part of ipsilateral middle cerebral artery, which was divided by the pulse transit time between these two points where the pulse was measured using TCD. The value of cc PWV was 499.3±78.6 cm/s. Correlation between cc PWV and ba PWV in the assessment of AS was r=0.794 (P<0.001). The concordance between both the above mentioned methods was good. Interobserver and intraobserver reliability using interclass correlation for measuring cc PWV were 0.815 (P<0.001) and 0.939 (P<0.001), respectively. In multivariable analysis, older age (β=4.51, P<0.001) and increased diastolic blood pressure (β=2.39, P<0.001) were independently associated with higher cc PWV. cc PWV measured using TCD may be a promising method for the assessment of human cerebral AS, which is independently associated with age and diastolic blood pressure.

  20. Estimation of arterial baroreflex sensitivity in relation to carotid artery stiffness.

    PubMed

    Lipponen, Jukka A; Tarvainen, Mika P; Laitinen, Tomi; Karjalainen, Pasi A; Vanninen, Joonas; Koponen, Timo; Lyyra-Laitinen, Tiina

    2012-01-01

    Arterial baroreflex has a significant role in regulating blood pressure. It is known that increased stiffness of the carotid sinus affects mecanotransduction of baroreceptors and therefore limits baroreceptors capability to detect changes in blood pressure. By using high resolution ultrasound video signal and continuous measurement of electrocardiogram (ECG) and blood pressure, it is possible to define elastic properties of artery simultaneously with baroreflex sensitivity parameters. In this paper dataset which consist 38 subjects, 11 diabetics and 27 healthy controls was analyzed. Use of diabetic and healthy test subjects gives wide scale of arteries with different elasticity properties, which provide opportunity to validate baroreflex and artery stiffness estimation methods.

  1. Stiffness of hyaluronic acid gels containing liver extracellular matrix supports human hepatocyte function and alters cell morphology.

    PubMed

    Deegan, Daniel B; Zimmerman, Cynthia; Skardal, Aleksander; Atala, Anthony; Shupe, Thomas D

    2015-03-01

    Tissue engineering and cell based liver therapies have utilized primary hepatocytes with limited success due to the failure of hepatocytes to maintain their phenotype in vitro. In order to overcome this challenge, hyaluronic acid (HA) cell culture substrates were formulated to closely mimic the composition and stiffness of the normal liver cellular microenvironment. The stiffness of the substrate was modulated by adjusting HA hydrogel crosslinking. Additionally, the repertoire of bioactive molecules within the HA substrate was bolstered by supplementation with normal liver extracellular matrix (ECM). Primary human hepatocyte viability and phenotype were determined over a narrow physiologically relevant range of substrate stiffnesses from 600 to 4600Pa in both the presence and absence of liver ECM. Cell attachment, viability, and organization of the actin cytoskeleton improved with increased stiffness up to 4600Pa. These differences were not evident in earlier time points or substrates containing only HA. However, gene expression for the hepatocyte markers hepatocyte nuclear factor 4 alpha (HNF4α) and albumin significantly decreased on the 4600Pa stiffness at day 7 indicating that cells may not have maintained their phenotype long-term at this stiffness. Function, as measured by albumin secretion, varied with both stiffness and time in culture and peaked at day 7 at the 1200Pa stiffness, slightly below the stiffness of normal liver ECM at 3000Pa. Overall, gel stiffness affected primary human hepatocyte cell adhesion, functional marker expression, and morphological characteristics dependent on both the presence of liver ECM in gel substrates and time in culture. Copyright © 2015 Elsevier Ltd. All rights reserved.

  2. Sciatic nerve stiffness is not changed immediately after a slump neurodynamics technique

    PubMed Central

    Neto, Tiago; Freitas, Sandro R; Andrade, Ricardo J; Gomes, João; Vaz, João; Mendes, Bruno; Firmino, Telmo; Nordez, Antoine; Oliveira, Raúl

    2017-01-01

    Summary Background Neurodynamics techniques aim to assess and improve neural mechanosensitivity. However, there is no in vivo evidence regarding the mechanical effects of these techniques in the nerve stiffness. This study examined the immediate effects of a slump neurodynamics technique in the sciatic nerve shear wave velocity (SWV. i.e. an index of stiffness) using ultrasound-based elastography. Methods Fourteen healthy participants were included in this experiment. Sciatic SWV and ankle passive torque were measured during a passive ankle dorsiflexion motion (2°/s), before and immediately after 3 minutes of slump neurodynamics technique, randomly applied to one lower limb. The contralateral limb served as control. Results The slump intervention did not change the sciatic SWV (P=0.78), nor the dorsiflexion passive torque (P=0.14), throughout the ankle dorsiflexion motion. Excellent values of intra-rater repeatability (ICC=0.88, 0.68–0.96), and low values of standard error of measurement (0.59 m/s, 0.35–1.15m/s), were observed for the SWV measurements. Conclusions The sciatic nerve stiffness of healthy participants did not change immediately after a slump neurodynamics technique, suggesting a compliance of the neural tissue to tensile loads. However, these results ought to be confirmed using other neurodynamics techniques and in other populations (e.g. peripheral neuropathies). Level of evidence III. PMID:29387655

  3. An acoustic startle alters knee joint stiffness and neuromuscular control.

    PubMed

    DeAngelis, A I; Needle, A R; Kaminski, T W; Royer, T R; Knight, C A; Swanik, C B

    2015-08-01

    Growing evidence suggests that the nervous system contributes to non-contact knee ligament injury, but limited evidence has measured the effect of extrinsic events on joint stability. Following unanticipated events, the startle reflex leads to universal stiffening of the limbs, but no studies have investigated how an acoustic startle influences knee stiffness and muscle activation during a dynamic knee perturbation. Thirty-six individuals were tested for knee stiffness and muscle activation of the quadriceps and hamstrings. Subjects were seated and instructed to resist a 40-degree knee flexion perturbation from a relaxed state. During some trials, an acoustic startle (50 ms, 1000 Hz, 100 dB) was applied 100 ms prior to the perturbation. Knee stiffness, muscle amplitude, and timing were quantified across time, muscle, and startle conditions. The acoustic startle increased short-range (no startle: 0.044 ± 0.011 N·m/deg/kg; average startle: 0.047 ± 0.01 N·m/deg/kg) and total knee stiffness (no startle: 0.036 ± 0.01 N·m/deg/kg; first startle 0.027 ± 0.02 N·m/deg/kg). Additionally, the startle contributed to decreased [vastus medialis (VM): 13.76 ± 33.6%; vastus lateralis (VL): 6.72 ± 37.4%] but earlier (VM: 0.133 ± 0.17 s; VL: 0.124 ± 0.17 s) activation of the quadriceps muscles. The results of this study indicate that the startle response can significantly disrupt knee stiffness regulation required to maintain joint stability. Further studies should explore the role of unanticipated events on unintentional injury. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  4. Extracellular Matrix Disarray as A Mechanism for Greater Abdominal vs. Thoracic Aortic Stiffness with Aging in Primates

    PubMed Central

    Zhang, Jie; Zhao, Xin; Vatner, Dorothy E; McNulty, Tara; Bishop, Sanford; Sun, Zhe; Shen, You-Tang; Chen, Li; Meininger, Gerald A; Vatner, Stephen F

    2016-01-01

    Objective Increased vascular stiffness is central to the pathophysiology of aging, hypertension, diabetes and atherosclerosis. However, relatively few studies have examined vascular stiffness in both the thoracic and abdominal aorta with aging, despite major differences in anatomy, embryological origin and relation to aortic aneurysm. Approach and Results The two other unique features of this study were 1) to study young (9±1 years) and old (26±1 years) male monkeys, and 2) to study direct and continuous measurements of aortic pressure and thoracic and abdominal aortic diameters in conscious monkeys. As expected, aortic stiffness, β, was increased p<0.05, 2–3 fold, in old vs. young thoracic aorta, and augmented further with superimposition of acute hypertension with phenylephrine. Surprisingly, stiffness was not greater in old thoracic aorta than young abdominal aorta. These results can be explained in part by the collagen/elastin ratio, but more importantly, by disarray of collagen and elastin, which correlated best with vascular stiffness. However, vascular smooth muscle cell stiffness, was not different in thoracic vs. abdominal aorta in either young or old monkeys. Conclusions Thus, aortic stiffness increases with aging as expected, but the most severe increases in aortic stiffness observed in the abdominal aorta is novel, where values in young monkeys equaled, or even exceeded, values of thoracic aortic stiffness in old monkeys. These results can be explained by alterations in collagen/elastin ratio, but even more importantly by collagen and elastin disarray. PMID:26891739

  5. Assessment of passive knee stiffness and viscosity in individuals with spinal cord injury using pendulum test.

    PubMed

    Joghtaei, Mahmoud; Arab, Amir Massoud; Hashemi-Nasl, Hamed; Joghataei, Mohammad Taghi; Tokhi, Mohammad Osman

    2015-03-01

    Stiffness and viscosity represent passive resistances to joint motion related with the structural properties of the joint tissue and of the musculotendinous complex. Both parameters can be affected in patients with spinal cord injury (SCI). The purpose of this study was to measure passive knee stiffness and viscosity in patients with SCI with paraplegia and healthy subjects using Wartenberg pendulum test. Non-experimental, cross-sectional, case-control design. An outpatient physical therapy clinic, University of social welfare and Rehabilitation Science, Iran. A sample of convenience sample of 30 subjects participated in the study. Subjects were categorized into two groups: individuals with paraplegic SCI (n = 15, age: 34.60 ± 9.18 years) and 15 able-bodied individuals as control group (n = 15, age: 30.66 ± 11.13 years). Not applicable. Passive pendulum test of Wartenberg was used to measure passive viscous-elastic parameters of the knee (stiffness, viscosity) in all subjects. Statistical analysis (independent t-test) revealed significant difference in the joint stiffness between healthy subjects and those with paraplegic SCI (P = 0.01). However, no significant difference was found in the viscosity between two groups (P = 0.17). Except for first peak flexion angle, all other displacement kinematic parameters exhibited no statistically significant difference between normal subjects and subjects with SCI. Patients with SCI have significantly greater joint stiffness compared to able-bodied subjects.

  6. Multifunctional Stiff Carbon Foam Derived from Bread.

    PubMed

    Yuan, Ye; Ding, Yujie; Wang, Chunhui; Xu, Fan; Lin, Zaishan; Qin, Yuyang; Li, Ying; Yang, Minglong; He, Xiaodong; Peng, Qingyu; Li, Yibin

    2016-07-06

    The creation of stiff yet multifunctional three-dimensional porous carbon architecture at very low cost is still challenging. In this work, lightweight and stiff carbon foam (CF) with adjustable pore structure was prepared by using flour as the basic element via a simple fermentation and carbonization process. The compressive strength of CF exhibits a high value of 3.6 MPa whereas its density is 0.29 g/cm(3) (compressive modulus can be 121 MPa). The electromagnetic interference (EMI) shielding effectiveness measurements (specific EMI shielding effectiveness can be 78.18 dB·cm(3)·g(-1)) indicate that CF can be used as lightweight, effective shielding material. Unlike ordinary foam structure materials, the low thermal conductivity (lowest is 0.06 W/m·K) with high resistance to fire makes CF a good candidate for commercial thermal insulation material. These results demonstrate a promising method to fabricate an economical, robust carbon material for applications in industry as well as topics regarding environmental protection and improvement of energy efficiency.

  7. Knee joint laxity and passive stiffness in meniscectomized patients compared with healthy controls.

    PubMed

    Thorlund, Jonas B; Creaby, Mark W; Wrigley, Tim V; Metcalf, Ben R; Bennell, Kim L

    2014-10-01

    Passive mechanical behavior of the knee in the frontal plane, measured as angular laxity and mechanical stiffness, may play an important role in the pathogenesis of knee osteoarthritis (OA). Little is known about knee laxity and stiffness prior to knee OA onset. We investigated knee joint angular laxity and passive stiffness in meniscectomized patients at high risk of knee OA compared with healthy controls. Sixty patients meniscectomized for a medial meniscal tear (52 men, 41.4 ± 5.5 years, 175.3 ± 7.9 cm, 83.6 ± 12.8 kg, mean ± SD) and 21 healthy controls (18 men, 42.0 ± 6.7 years, 176.8 ± 5.7 cm, 77.8 ± 13.4 kg) had their knee joint angular laxity and passive stiffness assessed twice ~2.3 years apart. Linear regression models including age, sex, height and body mass as covariates in the adjusted model were used to assess differences between groups. Greater knee joint varus (-10.1 vs. -7.3°, p<0.001), valgus (7.1 vs. 5.6°, p=0.001) and total (17.2 vs. 12.9°, p<0.001) angular laxity together with reduced midrange passive stiffness (1.71 vs. 2.36 Nm/°, p<0.001) were observed in patients vs. healthy controls. No differences were observed in change in stiffness over time between patients and controls, however a tendency towards increased laxity in patients was seen. Meniscectomized patients showed increased knee joint angular laxity and reduced passive stiffness ~3 months post surgery compared with controls. In addition, the results indicated that knee joint laxity may increase over time in meniscectomized patients. Copyright © 2014 Elsevier B.V. All rights reserved.

  8. Interplay between arterial stiffness and diastolic function: a marker of ventricular-vascular coupling.

    PubMed

    Zito, Concetta; Mohammed, Moemen; Todaro, Maria Chiara; Khandheria, Bijoy K; Cusmà-Piccione, Maurizio; Oreto, Giuseppe; Pugliatti, Pietro; Abusalima, Mohamed; Antonini-Canterin, Francesco; Vriz, Olga; Carerj, Scipione

    2014-11-01

    We evaluated the interplay between left ventricular diastolic function and large-artery stiffness in asymptomatic patients at increased risk of heart failure and no structural heart disease (Stage A). We divided 127 consecutive patients (mean age 49 ± 17 years) with risk factors for heart failure who were referred to our laboratory to rule out structural heart disease into two groups according to presence (Group 1, n = 35) or absence (Group 2, n = 92) of grade I left ventricular diastolic dysfunction. Doppler imaging with high-resolution echo-tracking software was used to measure intima-media thickness (IMT) and stiffness of carotid arteries. Group 1 had significantly higher mean age, blood pressure, left ventricular mass index, carotid IMT and arterial stiffness than Group 2 (P < 0.05). Overall, carotid stiffness indices (β-stiffness index, augmentation index and elastic modulus) and 'one-point' pulse wave velocity each showed inverse correlation with E-wave velocity, E' velocity and E/A ratio, and direct correlation with A-wave velocity, E-wave deceleration time and E/E' ratio (P < 0.05). Arterial compliance showed negative correlations with the echocardiographic indices of left ventricular diastolic function (P < 0.05). On logistic regression analysis, age, hypertension, SBP, pulse pressure, left ventricular mass index, carotid IMT and stiffness parameters were associated with grade I left ventricular diastolic dysfunction (P < 0.05 for each). However, on multivariate logistic analysis, only 'one-point' pulse wave velocity and age were independent predictors (P = 0.038 and P = 0.016, respectively). An independent association between grade I left ventricular diastolic dysfunction and increased arterial stiffness is demonstrated at the earliest stage of heart failure. Hence, assessment of vascular function, beyond cardiac function, should be included in a comprehensive clinical evaluation of these patients.

  9. Cryotherapy induces an increase in muscle stiffness.

    PubMed

    Point, M; Guilhem, G; Hug, F; Nordez, A; Frey, A; Lacourpaille, L

    2018-01-01

    Although cold application (ie, cryotherapy) may be useful to treat sports injuries and to prevent muscle damage, it is unclear whether it has adverse effects on muscle mechanical properties. This study aimed to determine the effect of air-pulsed cryotherapy on muscle stiffness estimated using ultrasound shear wave elastography. Myoelectrical activity, ankle passive torque, shear modulus (an index of stiffness), and muscle temperature of the gastrocnemius medialis were measured before, during an air-pulsed cryotherapy (-30°C) treatment of four sets of 4 minutes with 1-minute recovery in between and during a 40 minutes postcryotherapy period. Muscle temperature significantly decreased after the second set of treatment (10 minutes: 32.3±2.5°C; P<.001), peaked at 29 minutes (27.9±2.2°C; P<.001) and remained below baseline values at 60 minutes (29.5±2.0°C; P<.001). Shear modulus increased by +11.5±11.8% after the second set (10 minutes; P=.011), peaked at 30 minutes (+34.7±42.6%; P<.001), and remained elevated until the end of the post-treatment period (+25.4±17.1%; P<.001). These findings provide evidence that cryotherapy induces an increase in muscle stiffness. This acute change in muscle mechanical properties may lower the amount of stretch that the muscle tissue is able to sustain without subsequent injury. This should be considered when using cryotherapy in athletic practice. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  10. Stiffness mapping prostate biopsy samples using a tactile sensor.

    PubMed

    Peng, Qiyu; Omata, Sadao; Peehl, Donna M; Constantinou, Chris E

    2011-01-01

    Previous studies have demonstrated that the stiffness of cancerous cells reflects their pathological stage and progression rates, with increased cancerous cell stiffness associated with increased aggressiveness. Therefore, the elasticity of the cancerous cells has the potential to be used as an indicator of the cancer's aggressiveness. However, the sensitivity and resolution of current palpation and imaging techniques are not sufficient to detect small cancerous tissues. In previous studies, we developed a tactile-based device to map with high resolution the stiffness of a tissue section. The purpose of this study is to evaluate this device using different tissues (BPH, Cancer and PZ) collected from human prostates. The preliminary results show that the tactile device is sensitive enough to tell the differences of the stiffness of different tissues. The results also disclosed the factors (humidity, temperature and tissue degradation) which could dramatically affect the results of stiffness mapping. The tactile technology described in this paper has the potential to help disclose the underlying mechanical mechanisms that lead to increased stiffness in prostate tumors.

  11. Anterior glenohumeral laxity and stiffness after a shoulder-strengthening program in collegiate cheerleaders.

    PubMed

    Laudner, Kevin G; Metz, Betsy; Thomas, David Q

    2013-01-01

    Approximately 62% of all cheerleaders sustain some type of orthopaedic injury during their cheerleading careers. Furthermore, the occurrence of such injuries has led to inquiry regarding optimal prevention techniques. One possible cause of these injuries may be related to inadequate conditioning in cheerleaders. To determine whether a strength and conditioning program produces quantifiable improvements in anterior glenohumeral (GH) laxity and stiffness. Descriptive laboratory study. University laboratory. A sample of 41 collegiate cheerleaders (24 experimental and 17 control participants) volunteered. No participants had a recent history (in the past 6 months) of upper extremity injury or any history of upper extremity surgery. The experimental group completed a 6-week strength and conditioning program between the pretest and posttest measurements; the control group did not perform any strength training between tests. We measured anterior GH laxity and stiffness with an instrumented arthrometer. We conducted a group × time analysis of variance with repeated measures on time (P < .05) to determine differences between groups. A significant interaction was demonstrated, with the control group having more anterior GH laxity at the posttest session than the strengthening group (P = .03, partial η2 = 0.11). However, no main effect for time (P = .92) or group (P = .97) was observed. In another significant interaction, the control group had less anterior GH stiffness at the posttest session than the strengthening group (P = .03, partial η2 = 0.12). Main effects for time (P = .02) and group (P = .004) were also significant. Cheerleaders who participate in a shoulder-strengthening program developed less anterior GH laxity and more stiffness than cheerleaders in the control group.

  12. Conformational Analysis of Stiff Chiral Polymers with End-Constraints

    PubMed Central

    Kim, Jin Seob; Chirikjian, Gregory S.

    2010-01-01

    We present a Lie-group-theoretic method for the kinematic and dynamic analysis of chiral semi-flexible polymers with end constraints. The first is to determine the minimum energy conformations of semi-flexible polymers with end constraints, and the second is to perform normal mode analysis based on the determined minimum energy conformations. In this paper, we use concepts from the theory of Lie groups and principles of variational calculus to model such polymers as inextensible or extensible chiral elastic rods with coupling between twisting and bending stiffnesses, and/or between twisting and extension stiffnesses. This method is general enough to include any stiffness and chirality parameters in the context of elastic filament models with the quadratic elastic potential energy function. As an application of this formulation, the analysis of DNA conformations is discussed. We demonstrate our method with examples of DNA conformations in which topological properties such as writhe, twist, and linking number are calculated from the results of the proposed method. Given these minimum energy conformations, we describe how to perform the normal mode analysis. The results presented here build both on recent experimental work in which DNA mechanical properties have been measured, and theoretical work in which the mechanics of non-chiral elastic rods has been studied. PMID:20198114

  13. Quantification of change in vocal fold tissue stiffness relative to depth of artificial damage.

    PubMed

    Rohlfs, Anna-Katharina; Schmolke, Sebastian; Clauditz, Till; Hess, Markus; Müller, Frank; Püschel, Klaus; Roemer, Frank W; Schumacher, Udo; Goodyer, Eric

    2017-10-01

    To quantify changes in the biomechanical properties of human excised vocal folds with defined artificial damage. The linear skin rheometer (LSR) was used to obtain a series of rheological measurements of shear modulus from the surface of 30 human cadaver vocal folds. The tissue samples were initially measured in a native condition and then following varying intensities of thermal damage. Histological examination of each vocal fold was used to determine the depth of artificial alteration. The measured changes in stiffness were correlated with the depth of cell damage. For vocal folds in a pre-damage state the shear modulus values ranged from 537 Pa to 1,651 Pa (female) and from 583 Pa to 1,193 Pa (male). With increasing depth of damage from the intermediate layer of the lamina propria (LP), tissue stiffness increased consistently (compared with native values) following application of thermal damage to the vocal folds. The measurement showed an increase of tissue stiffness when the depth of tissue damage was extending from the intermediate LP layer downwards. Changes in the elastic characteristics of human vocal fold tissue following damage at defined depths were demonstrated in an in vitro experiment. In future, reproducible in vivo measurements of elastic vocal fold tissue alterations may enable phonosurgeons to infer the extent of subepithelial damage from changes in surface elasticity.

  14. Estimation of joint stiffness with a compliant load.

    PubMed

    Ludvig, Daniel; Kearney, Robert E

    2009-01-01

    Joint stiffness defines the dynamic relationship between the position of the joint and the torque acting about it. It consists of two components: intrinsic and reflex stiffness. Many previous studies have investigated joint stiffness in an open-loop environment, because the current algorithm in use is an open-loop algorithm. This paper explores issues related to the estimation of joint stiffness when subjects interact with compliant loads. First, we show analytically how the bias in closed-loop estimates of joint stiffness depends on the properties of the load, the noise power, and length of the estimated impulse response functions (IRF). We then demonstrate with simulations that the open-loop analysis will fail completely for an elastic load but may succeed for an inertial load. We further show that the open-loop analysis can yield unbiased results with an inertial load and document IRF length, signal-to-noise ratio needed, and minimum inertia needed for the analysis to succeed. Thus, by using a load with a properly selected inertia, open-loop analysis can be used under closed-loop conditions.

  15. Variable stiffness sandwich panels using electrostatic interlocking core

    NASA Astrophysics Data System (ADS)

    Heath, Callum J. C.; Bond, Ian P.; Potter, Kevin D.

    2016-04-01

    Structural topology has a large impact on the flexural stiffness of a beam structure. Reversible attachment between discrete substructures allows for control of shear stress transfer between structural elements, thus stiffness modulation. Electrostatic adhesion has shown promise for providing a reversible latching mechanism for controllable internal connectivity. Building on previous research, a thin film copper polyimide laminate has been used to incorporate high voltage electrodes to Fibre Reinforced Polymer (FRP) sandwich structures. The level of electrostatic holding force across the electrode interface is key to the achievable level of stiffness modulation. The use of non-flat interlocking core structures can allow for a significant increase in electrode contact area for a given core geometry, thus a greater electrostatic holding force. Interlocking core geometries based on cosine waves can be Computer Numerical Control (CNC) machined from Rohacell IGF 110 Foam core. These Interlocking Core structures could allow for enhanced variable stiffness functionality compared to basic planar electrodes. This novel concept could open up potential new applications for electrostatically induced variable stiffness structures.

  16. Rotational and peak torque stiffness of rugby shoes.

    PubMed

    Ballal, Moez S; Usuelli, Federico Giuseppe; Montrasio, Umberto Alfieri; Molloy, Andy; La Barbera, Luigi; Villa, Tomaso; Banfi, Giuseppe

    2014-09-01

    Sports people always strive to avoid injury. Sports shoe designs in many sports have been shown to affect traction and injury rates. The aim of this study is to demonstrate the differing stiffness and torque in rugby boots that are designed for the same effect. Five different types of rugby shoes commonly worn by scrum forwards were laboratory tested for rotational stiffness and peak torque on a natural playing surface generating force patterns that would be consistent with a rugby scrum. The overall internal rotation peak torque was 57.75±6.26 Nm while that of external rotation was 56.55±4.36 Nm. The Peak internal and external rotational stiffness were 0.696±0.1 and 0.708±0.06 Nm/deg respectively. Our results, when compared to rotational stiffness and peak torques of football shoes published in the literature, show that shoes worn by rugby players exert higher rotational and peak torque stiffness compared to football shoes when tested on the same natural surfaces. There was significant difference between the tested rugby shoes brands. In our opinion, to maximize potential performance and lower the potential of non-contact injury, care should be taken in choosing boots with stiffness appropriate to the players main playing role. Copyright © 2014 Elsevier Ltd. All rights reserved.

  17. Ambulatory Aortic Stiffness Is Associated With Narrow Retinal Arteriolar Caliber in Hypertensives: The SAFAR Study.

    PubMed

    Aissopou, Evaggelia K; Argyris, Antoniοs A; Nasothimiou, Efthimia G; Konstantonis, George D; Tampakis, Kostas; Tentolouris, Nikolaos; Papathanassiou, Miltiadis; Theodossiadis, Panagiotis G; Papaioannou, Theodoros G; Stehouwer, Coen D A; Sfikakis, Petros P; Protogerou, Athanassios D

    2016-05-01

    Arterial stiffness measured under static conditions reclassifies significantly cardiovascular (CV) risk and associates with narrower retinal arterioles. However, arterial stiffness exhibits circadian variation, thus single static stiffness recordings do not correspond to the "usual" 24 hr, awake, and asleep average arterial stiffness. We aimed to test the hypothesis that ambulatory 24 hr, awake, and asleep aortic (a) pulse wave velocity (PWV) associate with retinal vessel calibers, independently of confounders and of static arterial stiffness, in hypertensive individuals free from diabetes and CV disease. Digital retinal images were obtained (181 individuals, age: 53.9±10.7 years, 55.2% men) and retinal vessel calibers were measured with validated software to determine central retinal arteriolar and venular equivalents (CRAE and CRVE, respectively); ambulatory (24 hr, awake, asleep) and static office aPWV were estimated by Mobil-O-Graph; and static office carotid to femoral (cf) PWV by SphygmoCor. Regression analysis performed in 320 gradable retinal images showed that, after adjustment for confounders: (i) ambulatory aPWV was significantly associated with narrower retinal arterioles but not with venules; (ii) asleep aPWV had stronger associations with CRAE than awake aPWV; (iii) both ambulatory aPWV and cfPWV were associated mutually independently with narrower retinal arterioles; aPWV introduction in the model of cfPWV, improved model's R2 (P = 0.012). Similar discriminatory ability of 24 hr aPWV and of cfPWV to detect the presence of retinal arteriolar narrowing was found. Ambulatory aPWV, estimated by an operator-independent method, provides additional information to cfPWV regarding the associations of arterial stiffness with the retinal vessel calibers. © American Journal of Hypertension, Ltd 2015. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  18. Characterization of the bending stiffness of large space structure joints

    NASA Technical Reports Server (NTRS)

    Wu, K. Chauncey

    1989-01-01

    A technique for estimating the bending stiffness of large space structure joints is developed and demonstrated for an erectable joint concept. Experimental load-deflection data from a three-point bending test was used as input to solve a closed-form expression for the joint bending stiffness which was derived from linear beam theory. Potential error sources in both the experimental and analytical procedures are identified and discussed. The bending stiffness of a mechanically preloaded erectable joint is studied at three applied moments and seven joint orientations. Using this technique, the joint bending stiffness was bounded between 6 and 17 percent of the bending stiffness of the graphite/epoxy strut member.

  19. Age, arterial stiffness, and components of blood pressure in Chinese adults.

    PubMed

    Zheng, Meili; Xu, Xiping; Wang, Xiaobin; Huo, Yong; Xu, Xin; Qin, Xianhui; Tang, Genfu; Xing, Houxun; Fan, Fangfang; Cui, Wei; Yang, Xinchun

    2014-12-01

    Blood pressure (BP) changes with age. We conducted a cross-sectional study in rural Chinese adults to investigate: (1) what is the relationship between age, arterial stiffness, and BP in Chinese men and women; and (2) to what degree can the age-BP relationship be explained by arterial stiffness, controlling for other covariables. These analyses included a total of 1688 subjects (males/females: 623/1065), aged 40 to 88 years. Among them, 353 (20.9%) had hypertension (defined as systolic blood pressure (SBP) ≥ 140 mm Hg or diastolic blood pressure (DBP) ≥ 90 mm Hg). Arterial stiffness was measured by brachial-ankle pulse wave velocity (baPWV). baPWV appeared to be more strongly correlated with BP (including SBP, DBP, mean arterial pressure [MAP], pulse pressure [PP]) than age (P < 0.001 for comparisons between Spearman correlation coefficients). Furthermore, baPWV was associated with BP (including SBP, DBP, MAP, and PP) and risk of hypertension in a dose-response fashion, independent of age; in contrast, the age-BP associations were either attenuated or became negative after adjusting for baPWV. Arterial stiffness appears to be an independent contributor to hypertension, even after adjusting for age and other covariables. In contrast, age-BP associations became attenuated or negative after adjusting for baPWV. The utility of baPWV as a diagnostic, prognostic, and therapeutic indicator for hypertension warrants further investigation.

  20. Hyperglycemia and Arterial Stiffness: the Atherosclerosis Risk in the Communities Study

    PubMed Central

    Rubin, Jonathan; Nambi, Vijay; Chambless, Lloyd E.; Steffes, Michael W.; Juraschek, Stephen P.; Coresh, Josef; Sharrett, A. Richey; Selvin, Elizabeth

    2014-01-01

    Objectives Hyperglycemia has been associated with an increased risk of cardiovascular morbidity and mortality. Although numerous studies have demonstrated that hyperglycemia is associated with the atherosis component of atherosclerosis, limited studies have addressed the independent role of hyperglycemia in the pathophysiology of sclerotic vascular disease. We hypothesized that hyperglycemia, as assessed by hemoglobin A1c (HbA1c), would be independently associated two common indices of arterial stiffness (pressure-strain elastic modulus (Ep) and Young’s elastic modulus (YEM)). Methods We examined the cross-sectional association between HbA1c and arterial stiffness using B-mode ultrasound examination of the carotid artery in 9,050 participants from the community-based Atherosclerosis Risk in Communities (ARIC) Study. We used multivariable linear and logistic regression models to characterize the association between HbA1c and increased Ep and YEM. Results Higher values of HbA1c were associated in a graded fashion with increased arterial stiffness (P-trend <0.001 for both EP and YEM). After adjusting for traditional risk factors, increasing HbA1c deciles were significantly associated with elevated EP (OR for the highest decile of HbA1c compared to the lowest, 2.01, 95% CI 1.30, 3.11) and YEM (OR = 1.71, 95% CI 1.15, 2.55). Conclusion Elevated HbA1c is associated with measures of increased arterial stiffness, even after accounting for arterial wall thickness. This is consistent with the hypothesis that hyperglycemia contributes to arterial stiffness beyond its effects on atherosis and suggests that hyperglycemia is associated with altered material within the arterial wall. PMID:23031361

  1. Estrogen receptor-alpha genotype affects exercise-related reduction of arterial stiffness.

    PubMed

    Hayashi, Koichiro; Maeda, Seiji; Iemitsu, Motoyuki; Otsuki, Takeshi; Sugawara, Jun; Tanabe, Takumi; Miyauchi, Takashi; Kuno, Shinya; Ajisaka, Ryuichi; Matsuda, Mitsuo

    2008-02-01

    Arterial stiffness, an independent risk factor for cardiovascular disease, increases with advancing age. Arterial stiffness is improved by regular exercise, but individual responses to exercise training are variable. Given that estrogen and estrogen receptor-alpha (ER-alpha) can induce vasodilation and can exert an antiatherosclerotic effect in vessels, we hypothesized that gene polymorphisms of ER-alpha might influence the ability of regular exercise to improve arterial stiffness in postmenopausal women. One hundred ninety-five healthy postmenopausal women (62 +/- 6 yr, mean +/- SD) participated in our cross-sectional study. We determined the genotype of single-nucleotide polymorphisms (SNP) at -401T/C of intron 1 of the ER-alpha gene. Arterial stiffness was measured by brachial-ankle pulse wave velocity (baPWV), and daily physical activity was estimated by a uniaxial accelerometer. Subjects were divided into active and inactive groups according to the median value (200 kcal.d(-1)) of energy expenditure. baPWV in individuals with the TT variant of -401T/C genotype were significantly higher than for individuals with the TC+CC genotype. No significant differences in mean baPWV values were found between the active group and the inactive group (P = 0.09). A significant reduction of baPWV secondary to increased daily physical activity was observed in individuals with the TC+CC genotype but not in individuals with the TT genotype (TT/active: 1470 +/- 36 cm.s(-1); TT/inactive: 1457 +/- 34 cm.s(-1); TC+CC/active: 1359 +/- 21 cm.s(-1); TC+CC/inactive: 1433 +/- 24 cm.s(-1)). These results suggest that ER-alpha polymorphism affects the regular exercise-related reduction in arterial stiffness in healthy postmenopausal women.

  2. Fear of Movement Is Related to Trunk Stiffness in Low Back Pain

    PubMed Central

    Karayannis, Nicholas V.; Smeets, Rob J. E. M.; van den Hoorn, Wolbert; Hodges, Paul W.

    2013-01-01

    Background Psychological features have been related to trunk muscle activation patterns in low back pain (LBP). We hypothesised higher pain-related fear would relate to changes in trunk mechanical properties, such as higher trunk stiffness. Objectives To evaluate the relationship between trunk mechanical properties and psychological features in people with recurrent LBP. Methods The relationship between pain-related fear (Tampa Scale for Kinesiophobia, TSK; Photograph Series of Daily Activities, PHODA-SeV; Fear Avoidance Beliefs Questionnaire, FABQ; Pain Catastrophizing Scale, PCS) and trunk mechanical properties (estimated from the response of the trunk to a sudden sagittal plane forwards or backwards perturbation by unpredictable release of a load) was explored in a case-controlled study of 14 LBP participants. Regression analysis (r 2) tested the linear relationships between pain-related fear and trunk mechanical properties (trunk stiffness and damping). Mechanical properties were also compared with t-tests between groups based on stratification according to high/low scores based on median values for each psychological measure. Results Fear of movement (TSK) was positively associated with trunk stiffness (but not damping) in response to a forward perturbation (r2 = 0.33, P = 0.03), but not backward perturbation (r2 = 0.22, P = 0.09). Other pain-related fear constructs (PHODA-SeV, FABQ, PCS) were not associated with trunk stiffness or damping. Trunk stiffness was greater for individuals with high kinesiophobia (TSK) for forward (P = 0.03) perturbations, and greater with forward perturbation for those with high fear avoidance scores (FABQ-W, P = 0.01). Conclusions Fear of movement is positively (but weakly) associated with trunk stiffness. This provides preliminary support an interaction between biological and psychological features of LBP, suggesting this condition may be best understood if these domains are not considered in isolation

  3. Clinical appraisal of arterial stiffness: the Argonauts in front of the Golden Fleece

    PubMed Central

    Vlachopoulos, C; Aznaouridis, K; Stefanadis, C

    2006-01-01

    Interest in evaluating arterial elastic properties has grown in parallel with the widespread availability of non‐invasive methods for assessing arterial stiffness. A clinically useful diagnostic index must be pathophysiologically relevant, must be readily measurable, and must indicate the severity of the disease and predict the corresponding risk. Interventional modification of this index must parallel disease regression and benefit prognosis. The current evidence for the clinical value of estimating arterial stiffness (mainly of large, elastic‐type arteries, such as the aorta and the carotids) in the contemporary era of cardiovascular medicine is reviewed. PMID:16339817

  4. Proximal pulmonary vascular stiffness as a prognostic factor in children with pulmonary arterial hypertension.

    PubMed

    Friesen, Richard M; Schäfer, Michal; Ivy, D Dunbar; Abman, Steven H; Stenmark, Kurt; Browne, Lorna P; Barker, Alex J; Hunter, Kendall S; Truong, Uyen

    2018-05-16

    Main pulmonary artery (MPA) stiffness and abnormal flow haemodynamics in pulmonary arterial hypertension (PAH) are strongly associated with elevated right ventricular (RV) afterload and associated with disease severity and poor clinical outcomes in adults with PAH. However, the long-term effects of MPA stiffness on RV function in children with PAH remain poorly understood. This study is the first comprehensive evaluation of MPA stiffness in children with PAH, delineating the mechanistic relationship between flow haemodynamics and MPA stiffness as well as the prognostic ability of these measures regarding clinical outcomes. Fifty-six children diagnosed with PAH underwent baseline cardiac magnetic resonance (CMR) acquisition and were compared with 23 control subjects. MPA stiffness and wall shear stress (WSS) were evaluated using phase contrast CMR and were evaluated for prognostic potential along with standard RV volumetric and functional indices. Pulse wave velocity (PWV) was significantly increased (2.8 m/s vs. 1.4 m/s, P < 0.0001) and relative area change (RAC) was decreased (25% vs. 37%, P < 0.0001) in the PAH group, correlating with metrics of RV performance. Decreased WSS was associated with a decrease in RAC over time (r = 0.679, P < 0.001). For each unit increase in PWV, there was approximately a 3.2-fold increase in having a moderate clinical event. MPA stiffness assessed by non-invasive CMR was increased in children with PAH and correlated with RV performance, suggesting that MPA stiffness is a major contribution to RV dysfunction. PWV is predictive of moderate clinical outcomes, and may be a useful prognostic marker of disease activity in children with PAH.

  5. Contributions of Hamstring Stiffness to Straight-Leg-Raise and Sit-and-Reach Test Scores.

    PubMed

    Miyamoto, Naokazu; Hirata, Kosuke; Kimura, Noriko; Miyamoto-Mikami, Eri

    2018-02-01

    The passive straight-leg-raise (PSLR) and the sit-and-reach (SR) tests have been widely used to assess hamstring extensibility. However, it remains unclear to what extent hamstring stiffness (a measure of material properties) contributes to PSLR and SR test scores. Therefore, we aimed to clarify the relationship between hamstring stiffness and PSLR and SR scores using ultrasound shear wave elastography. Ninety-eight healthy subjects completed the study. Each subject completed PSLR testing, and classic and modified SR testing of the right leg. Muscle shear modulus of the biceps femoris, semitendinosus, and semimembranosus was quantified as an index of muscle stiffness. The relationships between shear modulus of each muscle and PSLR or SR scores were calculated using Pearson's product-moment correlation coefficients. Shear modulus of the semitendinosus and semimembranosus showed negative correlations with the two PSLR and two SR scores (absolute r value≤0.484). Shear modulus of the biceps femoris was significantly correlated with the PSLR score determined by the examiner and the modified SR score (absolute r value≤0.308). The present findings suggest that PSLR and SR test scores are strongly influenced by factors other than hamstring stiffness and therefore might not accurately evaluate hamstring stiffness. © Georg Thieme Verlag KG Stuttgart · New York.

  6. Maps and models of density and stiffness within individual Douglas-fir trees

    Treesearch

    Christine L. Todoroki; Eini C. Lowell; Dennis P. Dykstra; David G. Briggs

    2012-01-01

    Spatial maps of density and stiffness patterns within individual trees were developed using two methods: (1) measured wood properties of veneer sheets; and (2) mixed effects models, to test the hypothesis that within-tree patterns could be predicted from easily measurable tree variables (height, taper, breast-height diameter, and acoustic velocity). Sample trees...

  7. Substrate stiffness regulates cadherin-dependent collective migration through myosin-II contractility

    PubMed Central

    Ng, Mei Rosa; Besser, Achim

    2012-01-01

    The mechanical microenvironment is known to influence single-cell migration; however, the extent to which mechanical cues affect collective migration of adherent cells is not well understood. We measured the effects of varying substrate compliance on individual cell migratory properties in an epithelial wound-healing assay. Increasing substrate stiffness increased collective cell migration speed, persistence, and directionality as well as the coordination of cell movements. Dynamic analysis revealed that wounding initiated a wave of motion coordination from the wound edge into the sheet. This was accompanied by a front-to-back gradient of myosin-II activation and establishment of cell polarity. The propagation was faster and farther reaching on stiff substrates, indicating that substrate stiffness affects the transmission of directional cues. Manipulation of myosin-II activity and cadherin–catenin complexes revealed that this transmission is mediated by coupling of contractile forces between neighboring cells. Thus, our findings suggest that the mechanical environment integrates in a feedback with cell contractility and cell–cell adhesion to regulate collective migration. PMID:23091067

  8. Non-invasive assessment of muscle stiffness in patients with Duchenne muscular dystrophy.

    PubMed

    Lacourpaille, Lilian; Hug, François; Guével, Arnaud; Péréon, Yann; Magot, Armelle; Hogrel, Jean-Yves; Nordez, Antoine

    2015-02-01

    Assessment of muscle mechanical properties may provide clinically valuable information for follow-up of patients with Duchenne muscular dystrophy (DMD) through the course of their disease. In this study we aimed to assess the effect of DMD on stiffness of relaxed muscles using elastography (supersonic shear imaging). Fourteen DMD patients and 13 control subjects were studied. Six muscles were measured at 2 muscle lengths (shortened and stretched): gastrocnemius medialis (GM); tibialis anterior (TA); vastus lateralis (VL); biceps brachii (BB); triceps brachii (TB); and abductor digiti minimi (ADM). Stiffness was significantly higher in DMD patients compared with controls for all the muscles (main effect for population, P < 0.033 in all cases), except for ADM. The effect size was small (d = 0.33 for ADM at both muscle lengths) to large (d = 0.86 for BB/stretched). Supersonic shear imaging is a sensitive non-invasive technique to assess the increase in muscle stiffness associated with DMD. © 2014 Wiley Periodicals, Inc.

  9. Accounting for spatial variation of trabecular anisotropy with subject-specific finite element modeling moderately improves predictions of local subchondral bone stiffness at the proximal tibia.

    PubMed

    Nazemi, S Majid; Kalajahi, S Mehrdad Hosseini; Cooper, David M L; Kontulainen, Saija A; Holdsworth, David W; Masri, Bassam A; Wilson, David R; Johnston, James D

    2017-07-05

    Previously, a finite element (FE) model of the proximal tibia was developed and validated against experimentally measured local subchondral stiffness. This model indicated modest predictions of stiffness (R 2 =0.77, normalized root mean squared error (RMSE%)=16.6%). Trabecular bone though was modeled with isotropic material properties despite its orthotropic anisotropy. The objective of this study was to identify the anisotropic FE modeling approach which best predicted (with largest explained variance and least amount of error) local subchondral bone stiffness at the proximal tibia. Local stiffness was measured at the subchondral surface of 13 medial/lateral tibial compartments using in situ macro indentation testing. An FE model of each specimen was generated assuming uniform anisotropy with 14 different combinations of cortical- and tibial-specific density-modulus relationships taken from the literature. Two FE models of each specimen were also generated which accounted for the spatial variation of trabecular bone anisotropy directly from clinical CT images using grey-level structure tensor and Cowin's fabric-elasticity equations. Stiffness was calculated using FE and compared to measured stiffness in terms of R 2 and RMSE%. The uniform anisotropic FE model explained 53-74% of the measured stiffness variance, with RMSE% ranging from 12.4 to 245.3%. The models which accounted for spatial variation of trabecular bone anisotropy predicted 76-79% of the variance in stiffness with RMSE% being 11.2-11.5%. Of the 16 evaluated finite element models in this study, the combination of Synder and Schneider (for cortical bone) and Cowin's fabric-elasticity equations (for trabecular bone) best predicted local subchondral bone stiffness. Copyright © 2017 Elsevier Ltd. All rights reserved.

  10. The effect of subthalamic stimulation on viscoelastic stiffness of skeletal muscles in patients with Parkinson's disease.

    PubMed

    Rätsep, Tõnu; Asser, Toomas

    2017-05-01

    Myotonometric evaluation of viscoelastic stiffness of skeletal muscles has been proposed to document the effect of surgical or pharmacological treatment on rigidity in patients with Parkinson's disease. The aim of the study was to analyze the changes of viscoelastic stiffness induced by deep brain stimulation. Fifteen patients in an advanced stage of Parkinson's disease participated in the study. The study took place in the off-medication conditions after one night of drug withdrawal. The Unified Parkinson's Disease Rating Scale was used for clinical assessment of the disease. Myotonometry was used to measure viscoelastic stiffness in the resting muscles before and directly after passive wrist movements, commonly used for clinical evaluation of rigidity. The measurements were repeated during the stimulation-on and stimulation-off periods and compared with fifteen healthy control persons. The clinical scores for wrist rigidity improved from 3.0 (1-4) to 0.93 (0-2) (P<0.05) due to brain stimulation. The mean values of viscoelastic stiffness were similar before and after passive wrist movements, but the differences between the patients with high vs. low rigidity values (354.9 vs 310.2N/m; P<0.05) and in stimulation-off vs. stimulation-on conditions (342.7 vs 310.5N/m; P<0.05) were significant only if the measurements had been performed after passive wrist movements. Effective deep brain stimulation and increased rigidity can significantly change viscoelastic stiffness in the resting muscles in patients with Parkinson's disease, especially if evaluated after passive wrist movements. This paper supports the use of myotonometry for objective quantification of parkinsonian rigidity at rest. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. Impact of hypertension severity on arterial stiffness, cerebral vasoreactivity, and cognitive performance.

    PubMed

    Muela, Henrique Cotchi Simbo; Costa-Hong, Valeria A; Yassuda, Monica Sanches; Machado, Michel Ferreira; Nogueira, Ricardo de Carvalho; Moraes, Natalia C; Memória, Claudia Maia; Macedo, Thiago A; Bor-Seng-Shu, Edson; Massaro, Ayrton Roberto; Nitrini, Ricardo; Bortolotto, Luiz A

    2017-01-01

    Aging, hypertension (HTN), and other cardiovascular risk factors contribute to structural and functional changes of the arterial wall. To evaluate whether arterial stiffness (AS) is related to cerebral blood flow changes and its association with cognitive function in patients with hypertension. 211 patients (69 normotensive and 142 hypertensive) were included. Patients with hypertension were divided into 2 stages: HTN stage-1 and HTN stage-2. The mini-mental state examination (MMSE), Montreal Cognitive Assessment (MoCA) and a battery of neuropsychological (NPE) tests were used to determine cognitive function. Pulse wave velocity was measured using the Complior ® . Carotid properties were assessed by radiofrequency ultrasound. Central arterial pressure and augmentation index were obtained using applanation tonometry. Middle cerebral artery flow velocity was measured by transcranial Doppler ultrasonography. Both arterial stiffness parameters and cerebral vasoreactivity worsened in line with HTN severity. There was a negative correlation between breath holding index (BHI) and arterial stiffness parameters. Cognitive performance worsened in line with HTN severity, with statistical difference occurring mainly between the HTN-2 and normotension groups on both the MMSE and MoCA. The same tendency was observed on the NPE tests. Hypertension severity was associated with higher AS, worse BHI, and lower cognitive performance.

  12. Impact of hypertension severity on arterial stiffness, cerebral vasoreactivity, and cognitive performance

    PubMed Central

    Muela, Henrique Cotchi Simbo; Costa-Hong, Valeria A.; Yassuda, Monica Sanches; Machado, Michel Ferreira; Nogueira, Ricardo de Carvalho; Moraes, Natalia C.; Memória, Claudia Maia; Macedo, Thiago A.; Bor-Seng-Shu, Edson; Massaro, Ayrton Roberto; Nitrini, Ricardo; Bortolotto, Luiz A.

    2017-01-01

    ABSTRACT. Aging, hypertension (HTN), and other cardiovascular risk factors contribute to structural and functional changes of the arterial wall. Objective: To evaluate whether arterial stiffness (AS) is related to cerebral blood flow changes and its association with cognitive function in patients with hypertension. Methods: 211 patients (69 normotensive and 142 hypertensive) were included. Patients with hypertension were divided into 2 stages: HTN stage-1 and HTN stage-2. The mini-mental state examination (MMSE), Montreal Cognitive Assessment (MoCA) and a battery of neuropsychological (NPE) tests were used to determine cognitive function. Pulse wave velocity was measured using the Complior®. Carotid properties were assessed by radiofrequency ultrasound. Central arterial pressure and augmentation index were obtained using applanation tonometry. Middle cerebral artery flow velocity was measured by transcranial Doppler ultrasonography. Results: Both arterial stiffness parameters and cerebral vasoreactivity worsened in line with HTN severity. There was a negative correlation between breath holding index (BHI) and arterial stiffness parameters. Cognitive performance worsened in line with HTN severity, with statistical difference occurring mainly between the HTN-2 and normotension groups on both the MMSE and MoCA. The same tendency was observed on the NPE tests. Conclusion: Hypertension severity was associated with higher AS, worse BHI, and lower cognitive performance. PMID:29354219

  13. Effect of acute aerobic exercise and histamine receptor blockade on arterial stiffness in African Americans and Caucasians

    PubMed Central

    Ranadive, Sushant M.; Lane-Cordova, Abbi D.; Kappus, Rebecca M.; Behun, Michael A.; Cook, Marc D.; Woods, Jeffrey A.; Wilund, Kenneth R.; Baynard, Tracy; Fernhall, Bo

    2017-01-01

    African Americans (AA) exhibit exaggerated central blood pressure (BP) and arterial stiffness measured by pulse wave velocity (PWV) in response to an acute bout of maximal exercise compared with Caucasians (CA). However, whether potential racial differences exist in central BP, elastic, or muscular arterial distensibility after submaximal aerobic exercise remains unknown. Histamine receptor activation mediates sustained postexercise hyperemia in CA but the effect on arterial stiffness is unknown. This study sought to determine the effects of an acute bout of aerobic exercise on central BP and arterial stiffness and the role of histamine receptors, in AA and CA. Forty-nine (22 AA, 27 CA) young and healthy subjects completed the study. Subjects were randomly assigned to take either histamine receptor antagonist or control placebo. Central blood BP and arterial stiffness measurements were obtained at baseline, and at 30, 60, and 90 min after 45 min of moderate treadmill exercise. AA exhibited greater central diastolic BP, elevated brachial PWV, and local carotid arterial stiffness after an acute bout of submaximal exercise compared with CA, which may contribute to their higher risk of cardiovascular disease. Unexpectedly, histamine receptor blockade did not affect central BP or PWV in AA or CA after exercise, but it may play a role in mediating local carotid arterial stiffness. Furthermore, histamine may mediate postexercise carotid arterial dilation in CA but not in AA. These observations provide evidence that young and healthy AA exhibit an exaggerated hemodynamic response to exercise and attenuated vasodilator response compared with CA. NEW & NOTEWORTHY African Americans are at greater risk for developing cardiovascular disease than Caucasians. We are the first to show that young and healthy African Americans exhibit greater central blood pressure, elevated brachial stiffness, and local carotid arterial stiffness following an acute bout of submaximal exercise

  14. Effect of acute aerobic exercise and histamine receptor blockade on arterial stiffness in African Americans and Caucasians.

    PubMed

    Yan, Huimin; Ranadive, Sushant M; Lane-Cordova, Abbi D; Kappus, Rebecca M; Behun, Michael A; Cook, Marc D; Woods, Jeffrey A; Wilund, Kenneth R; Baynard, Tracy; Halliwill, John R; Fernhall, Bo

    2017-02-01

    African Americans (AA) exhibit exaggerated central blood pressure (BP) and arterial stiffness measured by pulse wave velocity (PWV) in response to an acute bout of maximal exercise compared with Caucasians (CA). However, whether potential racial differences exist in central BP, elastic, or muscular arterial distensibility after submaximal aerobic exercise remains unknown. Histamine receptor activation mediates sustained postexercise hyperemia in CA but the effect on arterial stiffness is unknown. This study sought to determine the effects of an acute bout of aerobic exercise on central BP and arterial stiffness and the role of histamine receptors, in AA and CA. Forty-nine (22 AA, 27 CA) young and healthy subjects completed the study. Subjects were randomly assigned to take either histamine receptor antagonist or control placebo. Central blood BP and arterial stiffness measurements were obtained at baseline, and at 30, 60, and 90 min after 45 min of moderate treadmill exercise. AA exhibited greater central diastolic BP, elevated brachial PWV, and local carotid arterial stiffness after an acute bout of submaximal exercise compared with CA, which may contribute to their higher risk of cardiovascular disease. Unexpectedly, histamine receptor blockade did not affect central BP or PWV in AA or CA after exercise, but it may play a role in mediating local carotid arterial stiffness. Furthermore, histamine may mediate postexercise carotid arterial dilation in CA but not in AA. These observations provide evidence that young and healthy AA exhibit an exaggerated hemodynamic response to exercise and attenuated vasodilator response compared with CA. NEW & NOTEWORTHY African Americans are at greater risk for developing cardiovascular disease than Caucasians. We are the first to show that young and healthy African Americans exhibit greater central blood pressure, elevated brachial stiffness, and local carotid arterial stiffness following an acute bout of submaximal exercise

  15. An Investigation of the Immediate Effect of Static Stretching on the Morphology and Stiffness of Achilles Tendon in Dominant and Non-Dominant Legs

    PubMed Central

    Chiu, Tsz-chun Roxy; Ngo, Hiu-ching; Lau, Lai-wa; Leung, King-wah; Lo, Man-him; Yu, Ho-fai; Ying, Michael

    2016-01-01

    Aims This study was undertaken to investigate the immediate effect of static stretching on normal Achilles tendon morphology and stiffness, and the different effect on dominant and non-dominant legs; and to evaluate inter-operator and intra-operator reliability of using shear-wave elastography in measuring Achilles tendon stiffness. Methods 20 healthy subjects (13 males, 7 females) were included in the study. Thickness, cross-sectional area and stiffness of Achilles tendons in both legs were measured before and after 5-min static stretching using grey-scale ultrasound and shear-wave elastography. Inter-operator and intra-operator reliability of tendon stiffness measurements of six operators were evaluated. Results Result showed that there was no significant change in the thickness and cross-sectional area of Achilles tendon after static stretching in both dominant and non-dominant legs (p > 0.05). Tendon stiffness showed a significant increase in non-dominant leg (p < 0.05) but not in dominant leg (p > 0.05). The inter-operator reliability of shear-wave elastography measurements was 0.749 and the intra-operator reliability ranged from 0.751 to 0.941. Conclusion Shear-wave elastography is a useful and non-invasive imaging tool to assess the immediate stiffness change of Achilles tendon in response to static stretching with high intra-operator and inter-operator reliability. PMID:27120097

  16. Effect of CPAP on arterial stiffness in severely obese patients with obstructive sleep apnoea.

    PubMed

    Seetho, Ian W; Asher, Rebecca; Parker, Robert J; Craig, Sonya; Duffy, Nick; Hardy, Kevin J; Wilding, John P H

    2015-12-01

    Obstructive sleep apnoea (OSA) may independently increase cardiovascular risk in obesity. Although there is evidence that arterial stiffness is altered in OSA, knowledge of these effects with continuous positive airway pressure (CPAP) in severe obesity (body mass index (BMI) ≥ 35 kg/m(2)) is limited. This study aimed to explore how arterial stiffness, as measured by the augmentation index (Aix), changed in severely obese patients with OSA who were treated with CPAP and in patients without OSA. Forty-two patients with severe obesity-22 with OSA, 20 without OSA-were recruited at baseline and followed-up after a median of 13.5 months. Pulse wave analysis (PWA) was performed using applanation tonometry at the radial artery to measure augmentation index (Aix), augmentation pressure (AP) and subendocardial viability ratio (SEVR). Cardiovascular parameters and body composition were also measured. There were significant improvements in Aix, AP (both P < 0.001) and SEVR (P = 0.021) in OSA patients on CPAP compared with subjects without OSA. Epworth scores (P < 0.001), systolic (P < 0.001) and mean arterial pressures (P = 0.002) improved with CPAP. Regression showed that CPAP was significantly associated with change in arterial stiffness from baseline. However, patients with OSA on CPAP continued to have increased arterial stiffness (Aix) (P < 0.001), AP (P = 0.028) and reduced SEVR (P = 0.002) relative to non-OSA patients. Although sleepiness and blood pressure improve with CPAP in severe obesity, CPAP alone is not sufficient to modify PWA measures to levels comparable with non-OSA patients. This supports a need for a multifaceted approach when managing cardiovascular risk in patients with severe obesity and obstructive sleep apnoea receiving CPAP therapy.

  17. Lesion stiffness measured by shear-wave elastography: Preoperative predictor of the histologic underestimation of US-guided core needle breast biopsy.

    PubMed

    Park, Ah Young; Son, Eun Ju; Kim, Jeong-Ah; Han, Kyunghwa; Youk, Ji Hyun

    2015-12-01

    To determine whether lesion stiffness measured by shear-wave elastography (SWE) can be used to predict the histologic underestimation of ultrasound (US)-guided 14-gauge core needle biopsy (CNB) for breast masses. This retrospective study enrolled 99 breast masses from 93 patients, including 40 high-risk lesions and 59 ductal carcinoma in situ (DCIS), which were diagnosed by US-guided 14-gauge CNB. SWE was performed for all breast masses to measure quantitative elasticity values before US-guided CNB. To identify the preoperative factors associated with histologic underestimation, patients' age, symptoms, lesion size, B-mode US findings, and quantitative SWE parameters were compared according to the histologic upgrade after surgery using the chi-square test, Fisher's exact test, or independent t-test. The independent factors for predicting histologic upgrade were evaluated using multivariate logistic regression analysis. The underestimation rate was 28.3% (28/99) in total, 25.0% (10/40) in high-risk lesions, and 30.5% (18/59) in DCIS. All elasticity values of the upgrade group were significantly higher than those of the non-upgrade group (P<0.001). On multivariate analysis, the mean (Odds ratio [OR]=1.021, P=0.001), maximum (OR=1.015, P=0.008), and minimum (OR=1.028, P=0.001) elasticity values were independently associated with histologic underestimation. The patients' age, lesion size, and final assessment category on US of the upgrade group were higher than those of the non-upgrade group (P=0.046 for age; P=0.021 for lesion size; P=0.030 for US category), but these were not independent predictors of histologic underestimation on multivariate analysis. Breast lesion stiffness quantitatively measured by SWE could be helpful to predict the underestimation of malignancy in US-guided 14-gauge CNB. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  18. Contact stiffness of regularly patterned multi-asperity interfaces

    NASA Astrophysics Data System (ADS)

    Li, Shen; Yao, Quanzhou; Li, Qunyang; Feng, Xi-Qiao; Gao, Huajian

    2018-02-01

    Contact stiffness is a fundamental mechanical index of solid surfaces and relevant to a wide range of applications. Although the correlation between contact stiffness, contact size and load has long been explored for single-asperity contacts, our understanding of the contact stiffness of rough interfaces is less clear. In this work, the contact stiffness of hexagonally patterned multi-asperity interfaces is studied using a discrete asperity model. We confirm that the elastic interaction among asperities is critical in determining the mechanical behavior of rough contact interfaces. More importantly, in contrast to the common wisdom that the interplay of asperities is solely dictated by the inter-asperity spacing, we show that the number of asperities in contact (or equivalently, the apparent size of contact) also plays an indispensable role. Based on the theoretical analysis, we propose a new parameter for gauging the closeness of asperities. Our theoretical model is validated by a set of experiments. To facilitate the application of the discrete asperity model, we present a general equation for contact stiffness estimation of regularly rough interfaces, which is further proved to be applicable for interfaces with single-scale random roughness.

  19. Spleen stiffness is positively correlated with HVPG and decreases significantly after TIPS implantation.

    PubMed

    Buechter, Matthias; Manka, Paul; Theysohn, Jens M; Reinboldt, Marcus; Canbay, Ali; Kahraman, Alisan

    2018-01-01

    Transjugular intrahepatic portosystemic shunt (TIPS) is indicated in patients with decompensated portal hypertension (PH). Hepatic venous pressure gradient (HVPG) is considered gold standard for assessment of PH. Because HVPG measurement is invasive, non-invasive methods for evaluating severity of PH are warranted. We retrospectively correlated spleen stiffness as measured by FibroScan with HVPG in patients who underwent TIPS. Twenty-four patients with spleen stiffness measurement (SSM) one day before (D-1), one day after (D+1) and 28 days after TIPS (D+28) were included. SSM was positively correlated with pre-TIPS HVPG (HVPG <13mmHg, median SSM: 19.7±8.6kPa; HVPG 13-24mmHg, median SSM: 45.0±15.7kPa; HVPG >24mmHg, median SSM: 75.0±6.2kPa; p<0.05]; r 2 =0.72; p<0.001) and decreased significantly after TIPS implantation (D-1, median SSM: 67.1±17.3kPa; D+1, median SSM: 44.7±18.5kPa; D+28, median SSM: 35.6±17.0kPa; p<0.05), while liver stiffness measurement decrease was not statistically significant. Our study highlights the utility of SSM as non-invasive tool in patients with chronic liver disease in evaluating degree of PH potentially offering a confirmable additional parameter in surveillance of patients undergoing TIPS procedure. Copyright © 2017 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd. All rights reserved.

  20. Strain sonoelastographic evaluation of biceps muscle intrinsic stiffness after botulinum toxin-A injection.

    PubMed

    Aşkın, Ayhan; Kalaycı, Özlem Tuğçe; Bayram, Korhan Barış; Tosun, Aliye; Demirdal, Ümit Seçil; Atar, Emel; İnci, Mehmet Fatih

    2017-01-01

    The most commonly used clinical tools for measuring spasticity are modified Ashworth scale (MAS) and Tardieu scale but both yield subjective rather than objective results. Ultrasound elastography (EUS) provides information on tissue stiffness and allows the qualitative or quantitative measurements of the mechanical properties of tissues. To assess the stiffness of biceps brachialis muscles in stroke patients by strain EUS and to investigate the sonoelastographic changes and its correlations with clinical evaluation parameters after botulinum toxin-A (BTA) injections. This is a prospective study. A total of 48 chronic stroke patients requiring BTA injections to biceps brachialis muscles were included in the study. All patients received injections with BTA to biceps brachialis muscles under ultrasound guidance. MAS, goniometric measurements, and strain EUS assessments were performed at preintervention and at 4-week postintervention. Strain index values of biceps muscle on the affected side were significantly increased compared with those on the unaffected side (p < 0.01). At 4 weeks after BTA injection, significant improvements were observed in MAS grades and goniometric measurements (p < 0.05). Statistically significant differences were also found between the MAS grades and strain index values in both pre-/postintervention period (p < 0.01). No significant correlations were observed between clinical parameters and strain EUS findings. Strain EUS is a promising diagnostic tool for assessing stiffness in spastic muscles, in establishing the treatment plan and monitoring the effectiveness of the therapeutic modality.

  1. Arterial Stiffness and Autonomic Modulation After Free-Weight Resistance Exercises in Resistance Trained Individuals.

    PubMed

    Kingsley, J Derek; Mayo, Xián; Tai, Yu Lun; Fennell, Curtis

    2016-12-01

    Kingsley, JD, Mayo, X, Tai, YL, and Fennell, C. Arterial stiffness and autonomic modulation after free-weight resistance exercises in resistance trained individuals. J Strength Cond Res 30(12): 3373-3380, 2016-We investigated the effects of an acute bout of free-weight, whole-body resistance exercise consisting of the squat, bench press, and deadlift on arterial stiffness and cardiac autonomic modulation in 16 (aged 23 ± 3 years; mean ± SD) resistance-trained individuals. Arterial stiffness, autonomic modulation, and baroreflex sensitivity (BRS) were assessed at rest and after 3 sets of 10 repetitions at 75% 1-repetition maximum on each exercise with 2 minutes of rest between sets and exercises. Arterial stiffness was analyzed using carotid-femoral pulse wave velocity (cf-PWV). Linear heart rate variability (log transformed [ln] absolute and normalized units [nu] of low-frequency [LF] and high-frequency [HF] power) and nonlinear heart rate complexity (Sample Entropy [SampEn], Lempel-Ziv Entropy [LZEn]) were measured to determine autonomic modulation. BRS was measured by the sequence method. A 2 × 2 repeated measures analysis of variance (ANOVA) was used to analyze time (rest, recovery) across condition (acute resistance exercise, control). There were significant increases in cf-PWV (p = 0.05), heart rate (p = 0.0001), normalized LF (LFnu; p = 0.001), and the LF/HF ratio (p = 0.0001). Interactions were also noted for ln HF (p = 0.006), HFnu (p = 0.0001), SampEn (p = 0.001), LZEn (p = 0.005), and BRS (p = 0.0001) such that they significantly decreased during recovery from the resistance exercise compared with rest and the control. There was no effect on ln total power, or ln LF. These data suggest that a bout of resistance exercise using free-weights increases arterial stiffness and reduces vagal activity and BRS in comparison with a control session. Vagal tone may not be fully recovered up to 30 minutes after a resistance exercise bout.

  2. Numerical Simulation of Callus Healing for Optimization of Fracture Fixation Stiffness

    PubMed Central

    Steiner, Malte; Claes, Lutz; Ignatius, Anita; Simon, Ulrich; Wehner, Tim

    2014-01-01

    The stiffness of fracture fixation devices together with musculoskeletal loading defines the mechanical environment within a long bone fracture, and can be quantified by the interfragmentary movement. In vivo results suggested that this can have acceleratory or inhibitory influences, depending on direction and magnitude of motion, indicating that some complications in fracture treatment could be avoided by optimizing the fixation stiffness. However, general statements are difficult to make due to the limited number of experimental findings. The aim of this study was therefore to numerically investigate healing outcomes under various combinations of shear and axial fixation stiffness, and to detect the optimal configuration. A calibrated and established numerical model was used to predict fracture healing for numerous combinations of axial and shear fixation stiffness under physiological, superimposed, axial compressive and translational shear loading in sheep. Characteristic maps of healing outcome versus fixation stiffness (axial and shear) were created. The results suggest that delayed healing of 3 mm transversal fracture gaps will occur for highly flexible or very rigid axial fixation, which was corroborated by in vivo findings. The optimal fixation stiffness for ovine long bone fractures was predicted to be 1000–2500 N/mm in the axial and >300 N/mm in the shear direction. In summary, an optimized, moderate axial stiffness together with certain shear stiffness enhances fracture healing processes. The negative influence of one improper stiffness can be compensated by adjustment of the stiffness in the other direction. PMID:24991809

  3. Numerical simulation of callus healing for optimization of fracture fixation stiffness.

    PubMed

    Steiner, Malte; Claes, Lutz; Ignatius, Anita; Simon, Ulrich; Wehner, Tim

    2014-01-01

    The stiffness of fracture fixation devices together with musculoskeletal loading defines the mechanical environment within a long bone fracture, and can be quantified by the interfragmentary movement. In vivo results suggested that this can have acceleratory or inhibitory influences, depending on direction and magnitude of motion, indicating that some complications in fracture treatment could be avoided by optimizing the fixation stiffness. However, general statements are difficult to make due to the limited number of experimental findings. The aim of this study was therefore to numerically investigate healing outcomes under various combinations of shear and axial fixation stiffness, and to detect the optimal configuration. A calibrated and established numerical model was used to predict fracture healing for numerous combinations of axial and shear fixation stiffness under physiological, superimposed, axial compressive and translational shear loading in sheep. Characteristic maps of healing outcome versus fixation stiffness (axial and shear) were created. The results suggest that delayed healing of 3 mm transversal fracture gaps will occur for highly flexible or very rigid axial fixation, which was corroborated by in vivo findings. The optimal fixation stiffness for ovine long bone fractures was predicted to be 1000-2500 N/mm in the axial and >300 N/mm in the shear direction. In summary, an optimized, moderate axial stiffness together with certain shear stiffness enhances fracture healing processes. The negative influence of one improper stiffness can be compensated by adjustment of the stiffness in the other direction.

  4. Effects of Static Stretching Exercise on Lumbar Flexibility and Central Arterial Stiffness.

    PubMed

    Logan, Jeongok G; Kim, Suk-Sun; Lee, Mijung; Byon, Ha Do; Yeo, SeonAe

    Previous studies have demonstrated that arterial stiffness is associated with lumbar flexibility (LF). Stretching exercise targeted to improve LF may have a beneficial effect on reducing arterial stiffness. We examined the effects of a single bout of a structured, static stretching exercise on arterial stiffness, LF, peripheral and central blood pressure (BP), and heart rate (HR) and tested the association between LF and central arterial stiffness. The study had a pretest-posttest design without a control group. Thirty healthy women followed a video demonstration of a 30-minute whole-body stretching exercise. Carotid-femoral pulse wave velocity (cf-PWV), augmentation index, LF, peripheral and central BP, and HR were measured before and after the stretching exercise. One bout of a static stretching exercise significantly reduced cf-PWV (t29 = 2.708, P = .011) and HR (t29 = 7.160, P = .000) and increased LF (t29 = 12.248, P < .000). Augmentation index and peripheral and central BP also decreased but did not reach statistical significance. Despite no association found between cf-PWV and LF, the larger increase in LF the subjects had, the larger decrease in cf-PWV they had after exercise (r = 0.500, P = .005). Study findings highlight the potential benefit of a static stretching exercise on central arterial stiffness, an independent predictor of cardiovascular morbidity. Static stretching exercise conducted in the sitting position may be used as an effective intervention to reduce cardiovascular risk after a cardiac event or for patients whose sympathetic function should not be overly activated or whose gaits are not stable.

  5. Arterial stiffness and stroke: de-stiffening strategy, a therapeutic target for stroke

    PubMed Central

    Chen, Yajing; Shen, Fanxia; Liu, Jianrong; Yang, Guo-Yuan

    2017-01-01

    Stroke is the second leading cause of mortality and morbidity worldwide. Early intervention is of great importance in reducing disease burden. Since the conventional risk factors cannot fully account for the pathogenesis of stroke, it is extremely important to detect useful biomarkers of the vascular disorder for appropriate intervention. Arterial stiffness, a newly recognised reliable feature of arterial structure and function, is demonstrated to be associated with stroke onset and serve as an independent predictor of stroke incidence and poststroke functional outcomes. In this review article, different measurements of arterial stiffness, especially pressure wave velocity, were discussed. We explained the association between arterial stiffness and stroke occurrence by discussing the secondary haemodynamic changes. We reviewed clinical data that support the prediction role of arterial stiffness on stroke. Despite the lack of long-term randomised double-blind controlled therapeutic trials, it is high potential to reduce stroke prevalence through a significant reduction of arterial stiffness (which is called de-stiffening therapy). Pharmacological interventions or lifestyle modification that can influence blood pressure, arterial function or structure in either the short or long term are promising de-stiffening therapies. Here, we summarised different de-stiffening strategies including antihypertension drugs, antihyperlipidaemic agents, chemicals that target arterial remodelling and exercise training. Large and well-designed clinical trials on de-stiffening strategy are needed to testify the prevention effect for stroke. Novel techniques such as modern microscopic imaging and reliable animal models would facilitate the mechanistic analyses in pathophysiology, pharmacology and therapeutics. PMID:28959494

  6. Passive stiffness of rat skeletal muscle undernourished during fetal development

    PubMed Central

    Toscano, Ana Elisa; Ferraz, Karla Mônica; de Castro, Raul Manhães; Canon, Francis

    2010-01-01

    OBJECTIVES: The aim of the study was to investigate the effect of fetal undernutrition on the passive mechanical properties of skeletal muscle of weaned and young adult rats. INTRODUCTION: A poor nutrition supply during fetal development affects physiological functions of the fetus. From a mechanical point of view, skeletal muscle can be also characterized by its resistance to passive stretch. METHODS: Male Wistar rats were divided into two groups according to their mother's diet during pregnancy: a control group (mothers fed a 17% protein diet) and an isocaloric low‐protein group (mothers fed a 7.8% protein diet). At birth, all mothers received a standardized meal ad libitum. At the age of 25 and 90 days, the soleus muscle and extensor digitorum longus (EDL) muscles were removed in order to test the passive mechanical properties. A first mechanical test consisted of an incremental stepwise extension test using fast velocity stretching (500 mm/s) enabling us to measure, for each extension stepwise, the dynamic stress (σd) and the steady stress (σs). A second test consisted of a slow velocity stretch in order to calculate normalized stiffness and tangent modulus from the stress–strain relationship. RESULTS: The results for the mechanical properties showed an important increase in passive stiffness in both the soleus and EDL muscles in weaned rat. In contrast, no modification was observed in young adult rats. CONCLUSIONS: The increase in passive stiffness in skeletal muscle of weaned rat submitted to intrauterine undernutrition it is most likely due to changes in muscle passive stiffness. PMID:21340228

  7. Pressing movements and perceived force and displacement are influenced by object stiffness.

    PubMed

    Endo, Hiroshi

    2016-09-01

    Despite many previous studies on stiffness perception, few have investigated the exploratory procedures involved. This study evaluated whether stiffness range influences pressing movements and perception of force and displacement during stiffness discrimination tasks. Force and displacement data were obtained from 30 participants. Peak values of force and displacement, pressing duration and number of presses were analyzed. Two kinds of subjective evaluations were also recorded: perceived difference in force/displacement used to discriminate between specimens, and perceived effort. Although the number of presses and pressing duration were constant across a wide stiffness range, pressing strength was adjusted for the stiffness of objects, with harder specimens pressed more strongly. Further, even if the stiffnesses of two compared specimens were different, the pressing forces applied to the specimens approached the same magnitude at a higher stiffness range. Differences in force were most easily perceived at lower stiffness ranges, while displacement differences were perceived more readily at higher stiffness ranges. These results were consistent with those of previous studies. Finally, the reasons why stiffness range influenced pressing movements and perceived differences in force/displacement are discussed. Copyright © 2016 Elsevier Inc. All rights reserved.

  8. Carotid and aortic stiffness in essential hypertension and their relation with target organ damage: the CATOD study

    PubMed Central

    Bruno, Rosa Maria; Cartoni, Giulia; Stea, Francesco; Armenia, Sabina; Bianchini, Elisabetta; Buralli, Simona; Giannarelli, Chiara; Taddei, Stefano; Ghiadoni, Lorenzo

    2017-01-01

    Objective The objective of the study is to investigate in the hypertensive population the possible differential association between increased aortic and/or carotid stiffness and organ damage in multiple districts, such as the kidney, the vessels, and the heart. Methods In 314 essential hypertensive patients, carotid–femoral pulse wave velocity (cfPWV, by applanation tonometry) and carotid stiffness (from ultrasound images analysis), together with left ventricular hypertrophy, carotid intima–media thickness, urinary albumin–creatinin ratio, and glomerular filtration rate were measured. Increased cfPWV and carotid stiffness were defined according to either international reference values or the 90th percentile of a local control group (110 age and sex-matched healthy individuals). Results When considering the 90th percentile of a local control group, increased cfPWV was associated with reduced glomerular filtration rate, either when carotid stiffness was increased [odds ratio (OR) 13.27 (confidence limits (CL) 95% 3.86–45.58)] or not [OR 7.39 (CL95% 2.25–24.28)], whereas increased carotid stiffness was associated with left ventricular hypertrophy, either when cfPWV was increased [OR 2.86 (CL95% 1.15–7.09)] or not [OR 2.81 (CL95% 1.13–6.97)]. No association between increased cfPWV or carotid stiffness and target organ damage was found when cutoffs obtained by international reference values were used. The concomitance of both increased cfPWV and carotid stiffness did not have an additive effect on organ damage. Conclusion Aortic and carotid stiffness are differentially associated with target organ damage in hypertensive patients. Regional arterial stiffness as assessed by cfPWV is associated with renal organ damage and local carotid stiffness with cardiac organ damage. PMID:27841779

  9. Muscle 'contractures' and the 'stiff-man' syndrome.

    PubMed

    Slater, J D

    1986-12-01

    The aetiology of the clinical stiff-man syndrome is likely to be heterogenous, but until we have more precise methods of identifying an individual cause the need will continue for this rather flippant appellation in patients whose condition cannot be described in any other way. It is also important because patients may otherwise become labelled as suffering from a psychiatric disorder and may even be falsely accused of abusing diazepam (Westblom, 1978). The reverse is also true, and patients may masquerade as stiff men or women (Price and Allott, 1958; Casati and Rossi, 1969). The endocrine dimension remains and should be tested for carefully, particularly in patients with predominantly lower-limb rigidity whose spasms are a relatively minor aspect of their clinical syndrome. Clearly those patients described by George et al (1984) and Slater (1960) as suffering from the stiff-man syndrome need to be reclassified as examples of the hormonal stiff muscle syndrome, and there may be others so misclassified. An endocrine aetiology may easily be missed in a patient with relatively minor muscle stiffness, pain and cramps, such as the man described by Yunus et al (1981) whose myalgia, 'arthralgia' and muscle tenderness vanished completely within four days of taking physiological replacement doses of cortisone acetate as treatment for his hypopituitarism. The rarity of the stiff-man syndrome makes prospective studies of its aetiology and treatment impossible, yet the dramatic and devastating nature of the syndrome suggests that such cases may be extreme examples of a much more common condition. On the other hand, it is possible to argue that once the psychiatric, the overtly neurological and the endocrine cases are omitted we are left with nothing. However, this is just where Moersch and Woltman came in; they could not explain 14 of their cases. Despite modern technology, despite refinements of diagnosis and despite the increasing recognition of the stiff-man syndrome as a

  10. Ultrasonographic vascular mechanics to assess arterial stiffness: a review.

    PubMed

    Teixeira, Rogério; Vieira, Maria João; Gonçalves, Alexandra; Cardim, Nuno; Gonçalves, Lino

    2016-03-01

    In recent years, the role of arterial stiffness in the development of cardiovascular diseases has been explored more extensively. Local arterial stiffness may be gauged via ultrasound, measuring pulse transit time relative to changing vessel diameters and distending pressures. Recently, direct vessel-wall tracking systems have been devised based on new ultrasonographic methodologies, such as tissue Doppler imaging and speckle-tracking analysis--vascular mechanics. These advances have been evaluated in varying arterial distributions, are proved surrogates of pulse wave velocity, and are ascending in clinical importance. In the course of this review, we describe fundamental concepts and methodologies involved in ultrasound assessment of vascular mechanics. We also present relevant clinical studies and discuss the potential clinical utility of such diagnostic pursuits. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2015. For permissions please email: journals.permissions@oup.com.

  11. Dynamic Stiffness and Damping Characteristics of a High-Temperature Air Foil Journal Bearing

    NASA Technical Reports Server (NTRS)

    Howard, Samuel A.; DellaCorte, Christopher; Valco, Mark J.; Prahl, Joseph M.; Heshmat, Hooshang

    2001-01-01

    Using a high-temperature optically based displacement measurement system, a foil air bearing's stiffness and damping characteristics were experimentally determined. Results were obtained over a range of modified Sommerfeld Number from 1.5E6 to 1.5E7, and at temperatures from 25 to 538 C. An Experimental procedure was developed comparing the error in two curve fitting functions to reveal different modes of physical behavior throughout the operating domain. The maximum change in dimensionless stiffness was 3.0E-2 to 6.5E-2 over the Sommerfeld Number range tested. Stiffness decreased with temperature by as much as a factor of two from 25 to 538 C. Dimensionless damping was a stronger function of Sommerfeld Number ranging from 20 to 300. The temperature effect on damping being more qualitative, showed the damping mechanism shifted from viscous type damping to frictional type as temperature increased.

  12. Linear parameter varying identification of ankle joint intrinsic stiffness during imposed walking movements.

    PubMed

    Sobhani Tehrani, Ehsan; Jalaleddini, Kian; Kearney, Robert E

    2013-01-01

    This paper describes a novel model structure and identification method for the time-varying, intrinsic stiffness of human ankle joint during imposed walking (IW) movements. The model structure is based on the superposition of a large signal, linear, time-invariant (LTI) model and a small signal linear-parameter varying (LPV) model. The methodology is based on a two-step algorithm; the LTI model is first estimated using data from an unperturbed IW trial. Then, the LPV model is identified using data from a perturbed IW trial with the output predictions of the LTI model removed from the measured torque. Experimental results demonstrate that the method accurately tracks the continuous-time variation of normal ankle intrinsic stiffness when the joint position changes during the IW movement. Intrinsic stiffness gain decreases from full plantarflexion to near the mid-point of plantarflexion and then increases substantially as the ankle is dosriflexed.

  13. Monolithic superelastic rods with variable flexural stiffness for spinal fusion: modeling of the processing-properties relationship.

    PubMed

    Facchinello, Yann; Brailovski, Vladimir; Petit, Yvan; Mac-Thiong, Jean-Marc

    2014-11-01

    The concept of a monolithic Ti-Ni spinal rod with variable flexural stiffness is proposed to reduce the risks associated with spinal fusion. The variable stiffness is conferred to the rod using the Joule-heating local annealing technique. The annealing temperature and the mechanical properties' distributions resulted from this thermal treatment are numerically modeled and experimentally measured. To illustrate the possible applications of such a modeling approach, two case studies are presented: (a) optimization of the Joule-heating strategy to reduce annealing time, and (b) modulation of the rod's overall flexural stiffness using partial annealing. A numerical model of a human spine coupled with the model of the variable flexural stiffness spinal rod developed in this work can ultimately be used to maximize the stabilization capability of spinal instrumentation, while simultaneously decreasing the risks associated with spinal fusion. Copyright © 2014 IPEM. Published by Elsevier Ltd. All rights reserved.

  14. Finite element based nonlinear normalization of human lumbar intervertebral disc stiffness to account for its morphology.

    PubMed

    Maquer, Ghislain; Laurent, Marc; Brandejsky, Vaclav; Pretterklieber, Michael L; Zysset, Philippe K

    2014-06-01

    Disc degeneration, usually associated with low back pain and changes of intervertebral stiffness, represents a major health issue. As the intervertebral disc (IVD) morphology influences its stiffness, the link between mechanical properties and degenerative grade is partially lost without an efficient normalization of the stiffness with respect to the morphology. Moreover, although the behavior of soft tissues is highly nonlinear, only linear normalization protocols have been defined so far for the disc stiffness. Thus, the aim of this work is to propose a nonlinear normalization based on finite elements (FE) simulations and evaluate its impact on the stiffness of human anatomical specimens of lumbar IVD. First, a parameter study involving simulations of biomechanical tests (compression, flexion/extension, bilateral torsion and bending) on 20 FE models of IVDs with various dimensions was carried out to evaluate the effect of the disc's geometry on its compliance and establish stiffness/morphology relations necessary to the nonlinear normalization. The computed stiffness was then normalized by height (H), cross-sectional area (CSA), polar moment of inertia (J) or moments of inertia (Ixx, Iyy) to quantify the effect of both linear and nonlinear normalizations. In the second part of the study, T1-weighted MRI images were acquired to determine H, CSA, J, Ixx and Iyy of 14 human lumbar IVDs. Based on the measured morphology and pre-established relation with stiffness, linear and nonlinear normalization routines were then applied to the compliance of the specimens for each quasi-static biomechanical test. The variability of the stiffness prior to and after normalization was assessed via coefficient of variation (CV). The FE study confirmed that larger and thinner IVDs were stiffer while the normalization strongly attenuated the effect of the disc geometry on its stiffness. Yet, notwithstanding the results of the FE study, the experimental stiffness showed consistently

  15. Impact of skin capsular distance on the performance of controlled attenuation parameter in patients with chronic liver disease.

    PubMed

    Shen, Feng; Zheng, Rui-Dan; Shi, Jun-Ping; Mi, Yu-Qiang; Chen, Guo-Feng; Hu, Xiqi; Liu, Yong-Gang; Wang, Xiao-Ying; Pan, Qin; Chen, Guang-Yu; Chen, Jian-Neng; Xu, Liang; Zhang, Rui-Nan; Xu, Lei-Ming; Fan, Jian-Gao

    2015-11-01

    Controlled attenuation parameter (CAP) is a non-invasive method for evaluating hepatic steatosis. However, larger skin capsular distance (SCD) can affect the accuracy. The aim of this study was to investigate the impact of SCD on the diagnostic performance of CAP and liver stiffness measurement (LSM). Of 101 patients with non-alcoholic fatty liver disease (NAFLD) and 280 patients with chronic hepatitis B (CHB) who underwent liver biopsy were prospectively recruited. CAP, LSM and SCD were performed using FibroScan with M probe. The areas under receiver operating characteristics curves (AUROCs) were calculated to determine the diagnostic efficacy. The optimal thresholds were defined by the maximum Youden index. SCD (B 30.34, P < 0.001) and hepatic steatosis (B 23.04, P < 0.001) were independently associated with CAP by multivariate analysis. The AUROCs were slightly higher for SCD <25 mm compared to those for SCD ≥25 mm for steatosis ≥5% (0.88 vs. 0.81), >33% (0.90 vs. 0.85) and >66% (0.84 vs. 0.72). For SCD <25 mm, the optimal CAP cut-offs for differentiating steatosis ≥5%, >33% and >66% were 255.0 dB/m, 283.5 dB/m and 293.5 dB/m. However, cut-offs were elevated by approximately 60-70 dB/m for SCD ≥25 mm. When stratified by fibrosis grade, LSM was significantly affected by SCD ≥25 mm for advanced fibrosis (≥F3) in NAFLD, but not in CHB. CAP is a promising tool for detecting and quantifying hepatic steatosis. SCD ≥25 mm may cause overestimation of steatosis. Similarly, SCD ≥25 mm affects the detection of advanced fibrosis by LSM in NAFLD patients. © 2015 The Authors. Liver International Published by John Wiley & Sons Ltd.

  16. Stiffness distribution in insect cuticle: a continuous or a discontinuous profile?

    PubMed

    Rajabi, H; Jafarpour, M; Darvizeh, A; Dirks, J-H; Gorb, S N

    2017-07-01

    Insect cuticle is a biological composite with a high degree of complexity in terms of both architecture and material composition. Given the complex morphology of many insect body parts, finite-element (FE) models play an important role in the analysis and interpretation of biomechanical measurements, taken by either macroscopic or nanoscopic techniques. Many previous studies show that the interpretation of nanoindentation measurements of this layered composite material is very challenging. To develop accurate FE models, it is of particular interest to understand more about the variations in the stiffness through the thickness of the cuticle. Considering the difficulties of making direct measurements, in this study, we use the FE method to analyse previously published data and address this issue numerically. For this purpose, sets of continuous or discontinuous stiffness profiles through the thickness of the cuticle were mathematically described. The obtained profiles were assigned to models developed based on the cuticle of three insect species with different geometries and layer configurations. The models were then used to simulate the mechanical behaviour of insect cuticles subjected to nanoindentation experiments. Our results show that FE models with discontinuous exponential stiffness gradients along their thickness were able to predict the stress and deformation states in insect cuticle very well. Our results further suggest that, for more accurate measurements and interpretation of nanoindentation test data, the ratio of the indentation depth to cuticle thickness should be limited to 7% rather than the traditional '10% rule'. The results of this study thus might be useful to provide a deeper insight into the biomechanical consequences of the distinct material distribution in insect cuticle and also to form a basis for more realistic modelling of this complex natural composite. © 2017 The Author(s).

  17. A Novel Echocardiographic Method for Assessing Arterial Stiffness in Obstructive Sleep Apnea Syndrome

    PubMed Central

    Akyol, Aytac; Cakmak, Huseyin Altug; Gunbatar, Hulya; Asker, Muntecep; Babat, Naci; Tosu, Aydin Rodi; Yaman, Mehmet; Gumrukcuoglu, Hasan Ali

    2015-01-01

    Background and Objectives Obstructive sleep apnea syndrome (OSAS) is associated with increased arterial stiffness and cardiovascular complications. The objective of this study was to assess whether the color M-mode-derived propagation velocity of the descending thoracic aorta (aortic velocity propagation, AVP) was an echocardiographic marker for arterial stiffness in OSAS. Subjects and Methods The study population included 116 patients with OSAS and 90 age and gender-matched control subjects. The patients with OSAS were categorized according to their apnea hypopnea index (AHI) as follows: mild to moderate degree (AHI 5-30) and severe degree (AHI≥30). Aortofemoral pulse wave velocity (PWV), carotid intima-media thickness (CIMT), brachial artery flow-mediated dilatation (FMD), and AVP were measured to assess arterial stiffness. Results AVP and FMD were significantly decreased in patients with OSAS compared to controls (p<0.001). PWV and CIMT were increased in the OSAS group compared to controls (p<0.001). Moreover, AVP and FMD were significantly decreased in the severe OSAS group compared to the mild to moderate OSAS group (p<0.001). PWV and CIMT were significantly increased in the severe group compared to the mild to moderate group (p<0.001). AVP was significantly positively correlated with FMD (r=0.564, p<0.001). However, it was found to be significantly inversely related to PWV (r=-0.580, p<0.001) and CIMT (r=-0.251, p<0.001). Conclusion The measurement of AVP is a novel and practical echocardiographic method, which may be used to identify arterial stiffness in OSAS. PMID:26617653

  18. The effect of Nordic hamstring strength training on muscle architecture, stiffness, and strength.

    PubMed

    Seymore, Kayla D; Domire, Zachary J; DeVita, Paul; Rider, Patrick M; Kulas, Anthony S

    2017-05-01

    Hamstring strain injury is a frequent and serious injury in competitive and recreational sports. While Nordic hamstring (NH) eccentric strength training is an effective hamstring injury-prevention method, the protective mechanism of this exercise is not understood. Strength training increases muscle strength, but also alters muscle architecture and stiffness; all three factors may be associated with reducing muscle injuries. The purpose of this study was to examine the effects of NH eccentric strength training on hamstring muscle architecture, stiffness, and strength. Twenty healthy participants were randomly assigned to an eccentric training group or control group. Control participants performed static stretching, while experimental participants performed static stretching and NH training for 6 weeks. Pre- and post-intervention measurements included: hamstring muscle architecture and stiffness using ultrasound imaging and elastography, and maximal hamstring strength measured on a dynamometer. The experimental group, but not the control group, increased volume (131.5 vs. 145.2 cm 3 , p < 0.001) and physiological cross-sectional area (16.1 vs. 18.1 cm 2 , p = 0.032). There were no significant changes to muscle fascicle length, stiffness, or eccentric hamstring strength. The NH intervention was an effective training method for muscle hypertrophy, but, contrary to common literature findings for other modes of eccentric training, did not increase fascicle length. The data suggest that the mechanism behind NH eccentric strength training mitigating hamstring injury risk could be increasing volume rather than increasing muscle length. Future research is, therefore, warranted to determine if muscle hypertrophy induced by NH training lowers future hamstring strain injury risk.

  19. Saxagliptin Prevents Increased Coronary Vascular Stiffness in Aortic-Banded Mini Swine.

    PubMed

    Fleenor, Bradley S; Ouyang, An; Olver, T Dylan; Hiemstra, Jessica A; Cobb, Melissa S; Minervini, Gianmaria; Emter, Craig A

    2018-06-11

    Increased peripheral conduit artery stiffness has been shown in patients with heart failure (HF) with preserved ejection fraction. However, it is unknown whether this phenomenon extends to the coronary vasculature. HF with preserved ejection fraction may be driven, in part, by coronary inflammation, and inhibition of the enzyme DPP-4 (dipeptidyl-peptidase 4) reduces inflammation and oxidative stress. The purpose of this study was to determine the effect of saxagliptin-a DPP-4 inhibitor-on coronary stiffness in aortic-banded mini swine. We hypothesized saxagliptin would prevent increased coronary artery stiffness in a translational swine model with cardiac features of HF with preserved ejection fraction by inhibiting perivascular adipose tissue inflammation. Yucatan mini swine were divided into 3 groups: control, aortic-banded untreated HF, and aortic-banded saxagliptin-treated HF. Ex vivo mechanical testing was performed on the left circumflex and right coronary arteries, and advanced glycation end product, NF-κB (nuclear factor-κB), and nitrotyrosine levels were measured. An increase in the coronary elastic modulus of HF animals was associated with increased vascular advanced glycation end products, NF-κB, and nitrotyrosine levels compared with control and prevented by saxagliptin treatment. Aortas from healthy mice were treated with media from swine perivascular adipose tissue culture to assess its role on vascular stiffening. Conditioned media from HF and saxagliptin-treated HF animals increased mouse aortic stiffness; however, only perivascular adipose tissue from the HF group showed increased advanced glycation end products and NF-κB levels. In conclusion, our data show increased coronary conduit vascular stiffness was prevented by saxagliptin and associated with decreased advanced glycation end products, NF-κB, and nitrotyrosine levels in a swine model with potential relevance to HF with preserved ejection fraction. © 2018 American Heart Association

  20. Brain tissue stiffness is a sensitive marker for acidosis.

    PubMed

    Holtzmann, Kathrin; Gautier, Hélène O B; Christ, Andreas F; Guck, Jochen; Káradóttir, Ragnhildur Thóra; Franze, Kristian

    2016-09-15

    Carbon dioxide overdose is frequently used to cull rodents for tissue harvesting. However, this treatment may lead to respiratory acidosis, which potentially could change the properties of the investigated tissue. Mechanical tissue properties often change in pathological conditions and may thus offer a sensitive generic readout for changes in biological tissues with clinical relevance. In this study, we performed force-indentation measurements with an atomic force microscope on acute cerebellar slices from adult rats to test if brain tissue undergoes changes following overexposure to CO2 compared to other methods of euthanasia. The pH significantly decreased in brain tissue of animals exposed to CO2. Concomitant with the drop in pH, cerebellar grey matter significantly stiffened. Tissue stiffening was reproduced by incubation of acute cerebellar slices in acidic medium. Tissue stiffness provides an early, generic indicator for pathophysiological changes in the CNS. Atomic force microscopy offers unprecedented high spatial resolution to detect such changes. Our results indicate that the stiffness particularly of grey matter strongly correlates with changes of the pH in the cerebellum. Furthermore, the method of tissue harvesting and preparation may not only change tissue stiffness but very likely also other physiologically relevant parameters, highlighting the importance of appropriate sample preparation. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.