Numerical analysis of the effect of turbulence transition on the hemodynamic parameters in human coronary arteries.

PubMed

Mahalingam, Arun; Gawandalkar, Udhav Ulhas; Kini, Girish; Buradi, Abdulrajak; Araki, Tadashi; Ikeda, Nobutaka; Nicolaides, Andrew; Laird, John R; Saba, Luca; Suri, Jasjit S

2016-06-01

Local hemodynamics plays an important role in atherogenesis and the progression of coronary atherosclerosis disease (CAD). The primary biological effect due to blood turbulence is the change in wall shear stress (WSS) on the endothelial cell membrane, while the local oscillatory nature of the blood flow affects the physiological changes in the coronary artery. In coronary arteries, the blood flow Reynolds number ranges from few tens to several hundreds and hence it is generally assumed to be laminar while calculating the WSS calculations. However, the pulsatile blood flow through coronary arteries under stenotic condition could result in transition from laminar to turbulent flow condition. In the present work, the onset of turbulent transition during pulsatile flow through coronary arteries for varying degree of stenosis (i.e., 0%, 30%, 50% and 70%) is quantitatively analyzed by calculating the turbulent parameters distal to the stenosis. Also, the effect of turbulence transition on hemodynamic parameters such as WSS and oscillatory shear index (OSI) for varying degree of stenosis is quantified. The validated transitional shear stress transport (SST) k-ω model used in the present investigation is the best suited Reynolds averaged Navier-Stokes turbulence model to capture the turbulent transition. The arterial wall is assumed to be rigid and the dynamic curvature effect due to myocardial contraction on the blood flow has been neglected. Our observations shows that for stenosis 50% and above, the WSSavg, WSSmax and OSI calculated using turbulence model deviates from laminar by more than 10% and the flow disturbances seems to significantly increase only after 70% stenosis. Our model shows reliability and completely validated. Blood flow through stenosed coronary arteries seems to be turbulent in nature for area stenosis above 70% and the transition to turbulent flow begins from 50% stenosis.

Three-dimensional whole-brain perfusion quantification using pseudo-continuous arterial spin labeling MRI at multiple post-labeling delays: accounting for both arterial transit time and impulse response function.

PubMed

Qin, Qin; Huang, Alan J; Hua, Jun; Desmond, John E; Stevens, Robert D; van Zijl, Peter C M

2014-02-01

Measurement of the cerebral blood flow (CBF) with whole-brain coverage is challenging in terms of both acquisition and quantitative analysis. In order to fit arterial spin labeling-based perfusion kinetic curves, an empirical three-parameter model which characterizes the effective impulse response function (IRF) is introduced, which allows the determination of CBF, the arterial transit time (ATT) and T(1,eff). The accuracy and precision of the proposed model were compared with those of more complicated models with four or five parameters through Monte Carlo simulations. Pseudo-continuous arterial spin labeling images were acquired on a clinical 3-T scanner in 10 normal volunteers using a three-dimensional multi-shot gradient and spin echo scheme at multiple post-labeling delays to sample the kinetic curves. Voxel-wise fitting was performed using the three-parameter model and other models that contain two, four or five unknown parameters. For the two-parameter model, T(1,eff) values close to tissue and blood were assumed separately. Standard statistical analysis was conducted to compare these fitting models in various brain regions. The fitted results indicated that: (i) the estimated CBF values using the two-parameter model show appreciable dependence on the assumed T(1,eff) values; (ii) the proposed three-parameter model achieves the optimal balance between the goodness of fit and model complexity when compared among the models with explicit IRF fitting; (iii) both the two-parameter model using fixed blood T1 values for T(1,eff) and the three-parameter model provide reasonable fitting results. Using the proposed three-parameter model, the estimated CBF (46 ± 14 mL/100 g/min) and ATT (1.4 ± 0.3 s) values averaged from different brain regions are close to the literature reports; the estimated T(1,eff) values (1.9 ± 0.4 s) are higher than the tissue T1 values, possibly reflecting a contribution from the microvascular arterial blood compartment

Modeling and optimization of Look-Locker spin labeling for measuring perfusion and transit time changes in activation studies taking into account arterial blood volume.

PubMed

Francis, S T; Bowtell, R; Gowland, P A

2008-02-01

This work describes a new compartmental model with step-wise temporal analysis for a Look-Locker (LL)-flow-sensitive alternating inversion-recovery (FAIR) sequence, which combines the FAIR arterial spin labeling (ASL) scheme with a LL echo planar imaging (EPI) measurement, using a multireadout EPI sequence for simultaneous perfusion and T*(2) measurements. The new model highlights the importance of accounting for the transit time of blood through the arteriolar compartment, delta, in the quantification of perfusion. The signal expected is calculated in a step-wise manner to avoid discontinuities between different compartments. The optimal LL-FAIR pulse sequence timings for the measurement of perfusion with high signal-to-noise ratio (SNR), and high temporal resolution at 1.5, 3, and 7T are presented. LL-FAIR is shown to provide better SNR per unit time compared to standard FAIR. The sequence has been used experimentally for simultaneous monitoring of perfusion, transit time, and T*(2) changes in response to a visual stimulus in four subjects. It was found that perfusion increased by 83 +/- 4% on brain activation from a resting state value of 94 +/- 13 ml/100 g/min, while T*(2) increased by 3.5 +/- 0.5%. (c) 2008 Wiley-Liss, Inc.

Pulsatility index variations using two different transit-time flowmeters in coronary artery bypass surgery.

PubMed

Nordgaard, Håvard B; Vitale, Nicola; Astudillo, Rafael; Renzulli, Attilio; Romundstad, Pål; Haaverstad, Rune

2010-05-01

Transit-time flow measurement is widely accepted as an intra-operative assessment in coronary artery bypass grafting (CABG). However, the two most commonly applied flowmeters, manufactured by MediStim ASA and Transonic Inc., have different default filter settings of 20 and 10 Hz, respectively. This may cause different flow measurements, which will influence the reported results. The aim was to compare pulsatility index (PI) values recorded by the MediStim and Transonic flowmeters in two different clinical settings: (1) analysis of the flow patterns recorded simultaneously by both flowmeters in the same CABGs; and (2) evaluation of flow patterns under different levels of filter settings in the same grafts. Graft flow and PI were measured using the two different flowmeters simultaneously in 19 bypass grafts. Finally, eight grafts were assessed under different digital filter settings at 5, 10, 20, 30, 50 and 100 Hz. The Transonic flowmeter provided substantially lower PI as compared with the MediStim flowmeter. By increasing the filter setting in the flowmeter, PI increased considerably. The Transonic flowmeter displayed a lower PI than the MediStim, due to a lower filter setting. In the Transonic,flow signals are filtered at a lower level, rendering a 'smoother' pattern of flow curves. Because different filter settings determine different PIs, caution must be taken when flow values and flowmeters are compared. The type of flowmeter should be indicated whenever graft flow measurements and derived indexes are provided [corrected]. Copyright 2009 European Association for Cardio-Thoracic Surgery. All rights reserved.

Blood Pressure Estimation Using Pulse Transit Time From Bioimpedance and Continuous Wave Radar.

PubMed

Buxi, Dilpreet; Redout, Jean-Michel; Yuce, Mehmet Rasit

2017-04-01

We have developed and tested a new architecture for pulse transit time (PTT) estimation at the central arteries using electrical bioimpedance, electrocardiogram, and continuous wave radar to estimate cuffless blood pressure. A transmitter and receiver antenna are placed at the sternum to acquire the arterial pulsation at the aortic arch. A four-electrode arrangement across the shoulders acquires arterial pulse across the carotid and subclavian arteries from bioimpedance as well as a bipolar lead I electrocardiogram. The PTT and pulse arrival times (PATs) are measured on six healthy male subjects during exercise on a bicycle ergometer. Using linear regression, the estimated PAT and PTT values are calibrated to the systolic and mean as well as diastolic blood pressure from an oscillometric device. For all subjects, the Pearson correlation coefficients for PAT-SBP and PTT-SBP are -0.66 (p = 0.001) and -0.48 (p = 0.0029), respectively. Correlation coefficients for individual subjects ranged from -0.54 to -0.9 and -0.37 to -0.95, respectively. The proposed system architecture is promising in estimating cuffless arterial blood pressure at the central, proximal arteries, which obey the Moens-Korteweg equation more closely when compared to peripheral arteries. An important advantage of PTT from the carotid and subclavian arteries is that the PTT over the central elastic arteries is measured instead of the peripheral arteries, which potentially reduces the changes in PTT due to vasomotion. Furthermore, the sensors can be completely hidden under a patients clothes, making them more acceptable by the patient for ambulatory monitoring.

Global versus local linear beat-to-beat analysis of the relationship between arterial pressure and pulse transit time during dynamic exercise.

PubMed

Porta, A; Gasperi, C; Nollo, G; Lucini, D; Pizzinelli, P; Antolini, R; Pagani, M

2006-04-01

Global linear analysis has been traditionally performed to verify the relationship between pulse transit time (PTT) and systolic arterial pressure (SAP) at the level of their spontaneous beat-to-beat variabilities: PTT and SAP have been plotted in the plane (PTT,SAP) and a significant linear correlation has been found. However, this relationship is weak and in specific individuals cannot be found. This result prevents the utilization of the SAP-PTT relationship to derive arterial pressure changes from PTT measures on an individual basis. We propose a local linear approach to study the SAP-PTT relationship. This approach is based on the definition of short SAP-PTT sequences characterized by SAP increase (decrease) and PTT decrease (increase) and on their search in the SAP and PTT beat-to-beat series. This local approach was applied to PTT and SAP series derived from 13 healthy humans during incremental supine dynamic exercise (at 10, 20 and 30% of the nominal individual maximum effort) and compared to the global approach. While global approach failed in some subjects, local analysis allowed the extraction of the gain of the SAP-PTT relationship in all subjects both at rest and during exercise. When both local and global analyses were successful, the local SAP-PTT gain is more negative than the global one as a likely result of noise reduction.

Correlation between reduction in microvascular transit time after superficial temporal artery-middle cerebral artery bypass surgery for moyamoya disease and the development of postoperative hyperperfusion syndrome.

PubMed

Yang, Tao; Higashino, Yoshifumi; Kataoka, Hiroharu; Hamano, Eika; Maruyama, Daisuke; Iihara, Koji; Takahashi, Jun C

2018-05-01

OBJECTIVE Hyperperfusion syndrome (HPS) is a notable complication that causes various neurological symptoms after superficial temporal artery (STA)-middle cerebral artery (MCA) bypass surgery for moyamoya disease (MMD). The authors used intraoperative indocyanine green (ICG) videoangiography to measure the change in microvascular transit time (MVTT) after bypass surgery. An analysis was then conducted to identify the correlation between change in MVTT and presence of postoperative HPS. METHODS This study included 105 hemispheres of 81 patients with MMD who underwent STA-MCA single bypass surgery between January 2010 and January 2015. Intraoperative ICG videoangiography was performed before and after bypass surgery. The MVTT was calculated from the ICG time intensity curve recorded in the pial arterioles and venules. Multivariate logistic regression analysis was conducted to test the effect of multiple variables, including the change in MVTT after bypass surgery, on postoperative HPS. RESULTS Postoperative HPS developed in 28 (26.7%) of the 105 hemispheres operated on. MVTT was reduced significantly after bypass surgery (prebypass 5.34 ± 2.00 sec vs postbypass 4.12 ± 1.60 sec; p < 0.001). The difference between prebypass and postbypass MVTT values, defined as ΔMVTT, was significantly greater in the HPS group than in the non-HPS group (2.55 ± 2.66 sec vs 0.75 ± 1.78 sec; p < 0.001). Receiver operating characteristic curve analysis revealed that the optimal cutoff point of ΔMVTT was 2.6 seconds (sensitivity 46.4% and specificity 85.7% as a predictor of postoperative HPS). A ΔMVTT > 2.6 seconds was an independent predictor of HPS in multivariate analysis (hazard ratio 4.88, 95% CI 1.76-13.57; p = 0.002). CONCLUSIONS MVTT in patients with MMD was reduced significantly after bypass surgery. Patients with a ΔMVTT > 2.6 seconds tended to develop postoperative HPS. Because ΔMVTT can be easily measured during surgery, it is a useful diagnostic tool for identifying

Pulse Transit Time Measurement Using Seismocardiogram, Photoplethysmogram, and Acoustic Recordings: Evaluation and Comparison.

PubMed

Yang, Chenxi; Tavassolian, Negar

2018-05-01

This work proposes a novel method of pulse transit time (PTT) measurement. The proximal arterial location data are collected from seismocardiogram (SCG) recordings by placing a micro-electromechanical accelerometer on the chest wall. The distal arterial location data are recorded using an acoustic sensor placed inside the ear. The performance of distal location recordings is evaluated by comparing SCG-acoustic and SCG-photoplethysmogram (PPG) measurements. PPG and acoustic performances under motion noise are also compared. Experimental results suggest comparable performances for the acoustic-based and PPG-based devices. The feasibility of each PTT measurement method is validated for blood pressure evaluations and its limitations are analyzed.

Transition path time distributions

NASA Astrophysics Data System (ADS)

Laleman, M.; Carlon, E.; Orland, H.

2017-12-01

Biomolecular folding, at least in simple systems, can be described as a two state transition in a free energy landscape with two deep wells separated by a high barrier. Transition paths are the short part of the trajectories that cross the barrier. Average transition path times and, recently, their full probability distribution have been measured for several biomolecular systems, e.g., in the folding of nucleic acids or proteins. Motivated by these experiments, we have calculated the full transition path time distribution for a single stochastic particle crossing a parabolic barrier, including inertial terms which were neglected in previous studies. These terms influence the short time scale dynamics of a stochastic system and can be of experimental relevance in view of the short duration of transition paths. We derive the full transition path time distribution as well as the average transition path times and discuss the similarities and differences with the high friction limit.

Arterial Blood Flow Measurement Using Digital Subtraction Angiography (DSA)

NASA Astrophysics Data System (ADS)

Swanson, David K.; Myerowitz, P. David; Van Lysel, Michael S.; Peppler, Walter W.; Fields, Barry L.; Watson, Kim M.; O'Connor, Julia

1984-08-01

Standard angiography demonstrates the anatomy of arterial occlusive disease but not its physiological signficance. Using intravenous digital subtraction angiography (DSA), we investigated transit-time videodensitometric techniques in measuring femoral arterial flows in dogs. These methods have been successfully applied to intraarterial DSA but not to intravenous DSA. Eight 20 kg dogs were instrumented with an electromagnetic flow probe and a balloon occluder above an imaged segment of femoral artery. 20 cc of Renografin 76 was power injected at 15 cc/sec into the right atrium. Flow in the femoral artery was varied by partial balloon occlusion or peripheral dilatation following induced ischemia resulting in 51 flow measurements varying from 15 to 270 cc/min. Three different transit-time techniques were studied: crosscorrelation, mean square error, and two leading edge methods. Correlation between videodensitometry and flowmeter measurements using these different techniques ranged from 0.78 to 0.88 with a mean square error of 29 to 37 cc/min. Blood flow information using several different transit-time techniques can be obtained with intravenous DSA.

Improved Pulse Transit Time Estimation by System Identification Analysis of Proximal and Distal Arterial Waveforms

DTIC Science & Technology

2011-10-01

response; pulse wave velocity ACCORDING TO THE MOENS-KORTEWEG equation, pulse wave ve- locity ( PWV ) increases as the arteries stiffen. Indeed, PWV is the...and mortality in hypertensive patients (2, 4, 12, 14). In addition, because arterial stiffness increases with arterial blood pressure (ABP), PWV and...ABP often show positive correlation, suggesting that PWV could provide a means to achieve continuous, noninvasive, and cuffless ABP monitoring (18

Plasma Indicator Dispersion in Arteries of the Human Leg

PubMed Central

Bassingthwaighte, James B.

2010-01-01

Indicator-dilution curves were recorded from the femoral and dorsalis pedis arteries of five normal men after injections of indocyanine green into the superior vena cava or thoracic aorta. By considering the femoral curves as inputs to a mathematically linear system and the dorsalis pedis curves as outputs, transfer functions (the distribution of transit times) for the arterial segment between these sites were obtained in terms of a four-parameter model, the lagged normal density curve, over a sixfold range of flow rates. The parameters of the spread (dispersion) of 57 transfer functions were proportional to the mean transit time. The mean difference between transit time and appearance time was 0.30 t̄; the square root of the variances was 0.18 t̄. These linear relationships suggest that flow rate has no significant influence on dispersion and that, since no transition from laminar to turbulent flow was apparent, arterial flow characteristics were not significantly changed over a wide range of flow rates. The secondary implication is that the rate of spatial longitudinal spreading of indicator with distance traveled is primarily a function of the geometry of the arterial system, not of the rate of flow, and, therefore, that the spatial distribution at any instant is a function of this rate and of the distance traveled through the system. PMID:5330717

Increased pulse wave transit time after percutaneous coronary intervention procedure in CAD patients.

PubMed

Ji, Lizhen; Liu, Chengyu; Li, Peng; Wang, Xinpei; Liu, Changchun; Hou, Yinglong

2018-01-08

Pulse wave transit time (PWTT) has been widely used as an index in assessing arterial stiffness. Percutaneous coronary intervention (PCI) is usually applied to the treatment of coronary artery disease (CAD). Research on the changes in PWTT caused by PCI is helpful for understanding the impact of the PCI procedure. In addition, effects of stent sites and access sites on the changes in PWTT have not been explored. Consequently, this study aimed to provide this information. The results showed that PWTT significantly increased after PCI (p < 0.01) while the standard deviation (SD) of PWTT time series had no statistically significant changes (p = 0.60) between before and after PCI. Significantly increased PWTT was found in the radial access group (p < 0.01), while there were no significant changes in the femoral access group (p > 0.4). Additionally, PWTT in the left anterior descending (LAD) group significantly increased after PCI (p < 0.01), but the increase that was found in the right coronary artery (RCA) group was not significant (p > 0.1). Our study indicates that arterial elasticity and left ventricular functions can benefit from a successful PCI procedure, and the increase of peripheral PWTT after PCI can help to better understand the effectiveness of the procedure.

Analyses of some exoplanets' transits and transit timing variations

NASA Astrophysics Data System (ADS)

Püsküllü, ćaǧlar; Soydugan, Faruk

2017-02-01

We present solutions of the transit light curves and transit timing variations (TTVs) analyses of the exoplanets HAT-P-5b, HAT-P-9b and HAT-P-25b. Transit light curves were collected at Çanakkale Onsekiz Mart University Observatory and TUBITAK National Observatory. The models were produced by WINFITTER program and stellar, planetary and orbital properties were obtained and discussed. We gave new transit times and generated TTVs with them by appending additional data based on Exoplanet Transit Database (ETD). Significant signals at the TTVs were also investigated.

Pulse transit time as a measure of inspiratory effort in children.

PubMed

Pagani, Jacopo; Villa, Maria Pia; Calcagnini, Giovanni; Alterio, Arianna; Ambrosio, Rosa; Censi, Federica; Ronchetti, Roberto

2003-10-01

The current criterion standard for measuring inspiratory effort, esophageal manometry, is an invasive procedure that young patients find intolerable. Inspiratory effort can also be assessed noninvasively by measuring the pulse transit time (PTT). PTT is the time the pulse wave (PW) takes to travel between two arterial sites (normally heart to finger). The speed at which the PW travels is directly proportional to arterial BP. When BP rises, PTT shortens. Conversely, when BP falls, PTT lengthens. In this study, we investigated PTT as a measure for evaluating inspiratory effort in children. We studied 15 healthy children (age range, 5 to 12 years; mean age [+/- SD], 8.3 +/- 2.74; 9 male children) selected from patients referred to our pediatric center for routine assessment. We assessed changes in the PTT during breathing against known resistances in awake children. Resistance was applied to the nose and mouth with a modified, two-way, nonrebreathing facemask. Our data show a good correlation between the induced inspiratory effort and the amplitude of PTT variations. PTT should be a useful method for quantifying changes in inspiratory effort due to augmented upper airway resistance in awake children.

Distribution of capillary transit times in isolated lungs of oxygen-tolerant rats.

PubMed

Ramakrishna, Madhavi; Gan, Zhuohui; Clough, Anne V; Molthen, Robert C; Roerig, David L; Audi, Said H

2010-11-01

Rats pre-exposed to 85% O₂ for 5-7 days tolerate the otherwise lethal effects of 100% O₂. The objective was to evaluate the effect of rat exposure to 85% O₂ for 7 days on lung capillary mean transit time t(c) and distribution of capillary transit times (h(c)(t)). This information is important for subsequent evaluation of the effect of this hyperoxia model on the redox metabolic functions of the pulmonary capillary endothelium. The venous concentration vs. time outflow curves of fluorescein isothiocyanate labeled dextran (FITC-dex), an intravascular indicator, and coenzyme Q₁ hydroquinone (CoQ₁H₂), a compound which rapidly equilibrates between blood and tissue on passage through the pulmonary circulation, were measured following their bolus injection into the pulmonary artery of isolated perfused lungs from rats exposed to room air (normoxic) or 85% O₂ for 7 days (hyperoxic). The moments (mean transit time and variance) of the measured FITC-dex and CoQ₁H₂ outflow curves were determined for each lung, and were then used in a mathematical model [Audi et al. J. Appl. Physiol. 77: 332-351, 1994] to estimate t(c) and the relative dispersion (RD(c)) of h (c)(t). Data analysis reveals that exposure to hyperoxia decreases lung t(c) by 42% and increases RD(c), a measure h(c)(t) heterogeneity, by 40%.

Transition Time: Make It a Learning Time.

ERIC Educational Resources Information Center

Baker, Betty Ruth

Teacher selection and planning of appropriate transition activities for preschool age children is discussed in this paper. Teachers are encouraged to use transition time to provide an opportunity for imaginative and creative thinking and to avoid tedious waiting and chaos. Transition activities can be used as a teaching technique to prepare…

Measurements Of Coronary Mean Transit Time And Myocardial Tissue Blood Flow By Deconvolution Of Intravasal Tracer Dilution Curves

NASA Astrophysics Data System (ADS)

Korb, H.; Hoeft, A.; Hellige, G.

1984-10-01

Previous studies have shown that intramyocardial blood volume does not vary to a major extent even during extreme variation of hemodynamics and coronary vascular tone. Based on a constant intramyocardial blood volume it is therefore possible to calculate tissue blood flow from the mean transit time of an intravascular tracer. The purpose of this study was to develop a clinically applicable method for measurement of coronary blood flow. The new method was based on indocyanine green, a dye which is bound to albumin and intravasally detectable by means of a fiberoptic catheter device. One fiberoptic catheter was placed in the aortic root and another in the coronary sinus. After central venous dye injection the resulting arterial and coronary venous dye dilution curves were processed on-line by a micro-computer. The mean transit time as well as myocardial blood flow were calculated from the step response function of the deconvoluted arterial and coronary venous signals. Reference flow was determined with an extracorporeal electromagnetic flowprobe within a coronary sinus bypass system. 38 steady states with coronary blood flow ranging from 49 - 333 ml/min*100g were analysed in 5 dogs. Mean transit times varied from 2.9 to 16.6 sec. An average intracoronary blood volume of 13.9 -7 1.8 m1/100g was calculated. The correlation between flow determined by the dye dilution technique and flow measured with the reference method was 0.98. According to these results determination of coronary blood flow with a double fiberoptic system and indocyanine green should be possible even under clinical conditions. Furthermore, the arterial and coronary venous oxygen saturation can be monitored continuously by the fiberoptic catheters. Therefore, additional information about the performance of the heart such as myocardial oxygen consumption and myocardial efficiency is available with the same equipment.

Evaluation of transit-time and electromagnetic flow measurement in a chronically instrumented nonhuman primate model.

PubMed

Koenig, S C; Reister, C A; Schaub, J; Swope, R D; Ewert, D; Fanton, J W

1996-01-01

The Physiology Research Branch at Brooks AFB conducts both human and nonhuman primate experiments to determine the effects of microgravity and hypergravity on the cardiovascular system and to identify the particular mechanisms that invoke these responses. Primary investigative efforts in our nonhuman primate model require the determination of total peripheral resistance, systemic arterial compliance, and pressure-volume loop characteristics. These calculations require beat-to-beat measurement of aortic flow. This study evaluated accuracy, linearity, biocompatability, and anatomical features of commercially available electromagnetic (EMF) and transit-time flow measurement techniques. Five rhesus monkeys were instrumented with either EMF (3 subjects) or transit-time (2 subjects) flow sensors encircling the proximal ascending aorta. Cardiac outputs computed from these transducers taken over ranges of 0.5 to 2.0 L/min were compared to values obtained using thermodilution. In vivo experiments demonstrated that the EMF probe produced an average error of 15% (r = .896) and 8.6% average linearity per reading, and the transit-time flow probe produced an average error of 6% (r = .955) and 5.3% average linearity per reading. Postoperative performance and biocompatability of the probes were maintained throughout the study. The transit-time sensors provided the advantages of greater accuracy, smaller size, and lighter weight than the EMF probes. In conclusion, the characteristic features and performance of the transit-time sensors were superior to those of the EMF sensors in this study.

Evaluation of transit-time and electromagnetic flow measurement in a chronically instrumented nonhuman primate model

NASA Technical Reports Server (NTRS)

Koenig, S. C.; Reister, C. A.; Schaub, J.; Swope, R. D.; Ewert, D.; Fanton, J. W.; Convertino, V. A. (Principal Investigator)

1996-01-01

The Physiology Research Branch at Brooks AFB conducts both human and nonhuman primate experiments to determine the effects of microgravity and hypergravity on the cardiovascular system and to identify the particular mechanisms that invoke these responses. Primary investigative efforts in our nonhuman primate model require the determination of total peripheral resistance, systemic arterial compliance, and pressure-volume loop characteristics. These calculations require beat-to-beat measurement of aortic flow. This study evaluated accuracy, linearity, biocompatability, and anatomical features of commercially available electromagnetic (EMF) and transit-time flow measurement techniques. Five rhesus monkeys were instrumented with either EMF (3 subjects) or transit-time (2 subjects) flow sensors encircling the proximal ascending aorta. Cardiac outputs computed from these transducers taken over ranges of 0.5 to 2.0 L/min were compared to values obtained using thermodilution. In vivo experiments demonstrated that the EMF probe produced an average error of 15% (r = .896) and 8.6% average linearity per reading, and the transit-time flow probe produced an average error of 6% (r = .955) and 5.3% average linearity per reading. Postoperative performance and biocompatability of the probes were maintained throughout the study. The transit-time sensors provided the advantages of greater accuracy, smaller size, and lighter weight than the EMF probes. In conclusion, the characteristic features and performance of the transit-time sensors were superior to those of the EMF sensors in this study.

Comparison of noninvasive pulse transit time estimates as markers of blood pressure using invasive pulse transit time measurements as a reference.

PubMed

Gao, Mingwu; Olivier, N Bari; Mukkamala, Ramakrishna

2016-05-01

Pulse transit time (PTT) measured as the time delay between invasive proximal and distal blood pressure (BP) or flow waveforms (invasive PTT [I-PTT]) tightly correlates with BP PTT estimated as the time delay between noninvasive proximal and distal arterial waveforms could therefore permit cuff-less BP monitoring. A popular noninvasive PTT estimate for this application is the time delay between ECG and photoplethysmography (PPG) waveforms (pulse arrival time [PAT]). Another estimate is the time delay between proximal and distal PPG waveforms (PPG-PTT). PAT and PPG-PTT were assessed as markers of BP over a wide physiologic range using I-PTT as a reference. Waveforms for determining I-PTT, PAT, and PPG-PTT through central arteries were measured from swine during baseline conditions and infusions of various hemodynamic drugs. Diastolic, mean, and systolic BP varied widely in each subject (group average (mean ± SE) standard deviation between 25 ± 2 and 36 ± 2 mmHg). I-PTT correlated well with all BP levels (group average R(2) values between 0.86 ± 0.03 and 0.91 ± 0.03). PPG-PTT also correlated well with all BP levels (group average R(2) values between 0.81 ± 0.03 and 0.85 ± 0.02), and its R(2) values were not significantly different from those of I-PTT PAT correlated best with systolic BP (group average R(2) value of 0.70 ± 0.04), but its R(2) values for all BP levels were significantly lower than those of I-PTT (P < 0.005) and PPG-PTT (P < 0.02). The pre-ejection period component of PAT was responsible for its inferior correlation with BP In sum, PPG-PTT was not different from I-PTT and superior to the popular PAT as a marker of BP. © 2016 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.

Analysis of tracer transit in rat brain after carotid artery and femoral vein administrations using linear system theory.

PubMed

Rudin, M; Beckmann, N; Sauter, A

1997-01-01

Determination of tissue perfusion rates by MRI bolus tracking methods relies on the central volume principle which states that tissue blood flow is given by the tissue blood volume divided by the mean tracer transit time (MTT). Accurate determination of the MTT requires knowledge of the arterial input function which in MRI experiments is usually not known, especially when using small animals. The problem of unknown arterial input can be circumvented in animal experiments by directly injecting the contrast agent into a feeding artery of the tissue of interest. In the present article the passage of magnetite nanoparticles through the rat cerebral cortex is analyzed after injection into the internal carotid artery. The results are discussed in the framework of linear system theory using a one-compartment model for brain tissue and by using the well characterized gamma-variate function to describe the tissue concentration profile of the contrast agent. The results obtained from the intra-arterial tracer administration experiments are then compared with the commonly used intra-venous injection of the contrast agent in order to estimate the contribution of the peripheral circulation to the MTT values in the latter case. The experiments were analyzed using a two-compartment model and the gamma-variate function. As an application perfusion rates in normal and ischemic cerebral cortex of hypertensive rats were estimated in a model of focal cerebral ischemia. The results indicate that peripheral circulation has a significant influence on the MTT values and thus on the perfusion rates, which cannot be neglected.

Distribution of Capillary Transit Times in Isolated Lungs of Oxygen-Tolerant Rats

PubMed Central

Ramakrishna, Madhavi; Gan, Zhuohui; Clough, Anne V.; Molthen, Robert C.; Roerig, David L.; Audi, Said H.

2014-01-01

Rats pre-exposed to 85% O2 for 5–7 days tolerate the otherwise lethal effects of 100% O2. The objective was to evaluate the effect of rat exposure to 85% O2 for 7 days on lung capillary mean transit time (t̄c) and distribution of capillary transit times (hc(t)). This information is important for subsequent evaluation of the effect of this hyperoxia model on the redox metabolic functions of the pulmonary capillary endothelium. The venous concentration vs. time outflow curves of fluorescein isothiocyanate labeled dextran (FITC-dex), an intravascular indicator, and coenzyme Q1 hydroquinone (CoQ1H2), a compound which rapidly equilibrates between blood and tissue on passage through the pulmonary circulation, were measured following their bolus injection into the pulmonary artery of isolated perfused lungs from rats exposed to room air (normoxic) or 85% O2 for 7 days (hyperoxic). The moments (mean transit time and variance) of the measured FITC-dex and CoQ1H2 outflow curves were determined for each lung, and were then used in a mathematical model [Audi et al. J. Appl. Physiol. 77: 332–351, 1994] to estimate t̄c and the relative dispersion (RDc) of hc(t). Data analysis reveals that exposure to hyperoxia decreases lung t̄c by 42% and increases RDc, a measure hc(t) heterogeneity, by 40%. PMID:20552277

Transition path time distribution and the transition path free energy barrier.

PubMed

Pollak, Eli

2016-10-19

The recent experimental measurement of the transition path time distributions of proteins presents several challenges to theory. Firstly, why do the fits of the experimental data to a theoretical expression lead to barrier heights which are much lower than the free energies of activation of the observed transitions? Secondly, there is the theoretical question of determining the transition path time distribution, without invoking the Smoluchowski limit. In this paper, we derive an exact expression for a transition path time distribution which is valid for arbitrary memory friction using the normal mode transformation which underlies Kramers' rate theory. We then recall that for low barriers, there is a noticeable difference between the transition path time distribution obtained with absorbing boundary conditions and free boundary conditions. For the former, the transition times are shorter, since recrossings of the boundaries are disallowed. As a result, if one uses the distribution based on absorbing boundary conditions to fit the experimental data, one will find that the transition path barrier will be larger than the values found based on a theory with free boundary conditions. We then introduce the paradigm of a transition path barrier height, and show that one should always expect it to be much smaller than the activation energy.

Coordinating Transit Transfers in Real Time

DOT National Transportation Integrated Search

2016-05-06

Transfers are a major source of travel time variability for transit passengers. Coordinating transfers between transit routes in real time can reduce passenger waiting times and travel time variability, but these benefits need to be contrasted with t...

Arterial endothelial function measurement method and apparatus

DOEpatents

Maltz, Jonathan S; Budinger, Thomas F

2014-03-04

A "relaxoscope" (100) detects the degree of arterial endothelial function. Impairment of arterial endothelial function is an early event in atherosclerosis and correlates with the major risk factors for cardiovascular disease. An artery (115), such as the brachial artery (BA) is measured for diameter before and after several minutes of either vasoconstriction or vasorelaxation. The change in arterial diameter is a measure of flow-mediated vasomodification (FMVM). The relaxoscope induces an artificial pulse (128) at a superficial radial artery (115) via a linear actuator (120). An ultrasonic Doppler stethoscope (130) detects this pulse 10-20 cm proximal to the point of pulse induction (125). The delay between pulse application and detection provides the pulse transit time (PTT). By measuring PTT before (160) and after arterial diameter change (170), FMVM may be measured based on the changes in PTT caused by changes in vessel caliber, smooth muscle tone and wall thickness.

Weighing Scale-Based Pulse Transit Time is a Superior Marker of Blood Pressure than Conventional Pulse Arrival Time

NASA Astrophysics Data System (ADS)

Martin, Stephanie L.-O.; Carek, Andrew M.; Kim, Chang-Sei; Ashouri, Hazar; Inan, Omer T.; Hahn, Jin-Oh; Mukkamala, Ramakrishna

2016-12-01

Pulse transit time (PTT) is being widely pursued for cuff-less blood pressure (BP) monitoring. Most efforts have employed the time delay between ECG and finger photoplethysmography (PPG) waveforms as a convenient surrogate of PTT. However, these conventional pulse arrival time (PAT) measurements include the pre-ejection period (PEP) and the time delay through small, muscular arteries and may thus be an unreliable marker of BP. We assessed a bathroom weighing scale-like system for convenient measurement of ballistocardiography and foot PPG waveforms - and thus PTT through larger, more elastic arteries - in terms of its ability to improve tracking of BP in individual subjects. We measured “scale PTT”, conventional PAT, and cuff BP in humans during interventions that increased BP but changed PEP and smooth muscle contraction differently. Scale PTT tracked the diastolic BP changes well, with correlation coefficient of -0.80 ± 0.02 (mean ± SE) and root-mean-squared-error of 7.6 ± 0.5 mmHg after a best-case calibration. Conventional PAT was significantly inferior in tracking these changes, with correlation coefficient of -0.60 ± 0.04 and root-mean-squared-error of 14.6 ± 1.5 mmHg (p < 0.05). Scale PTT also tracked the systolic BP changes better than conventional PAT but not to an acceptable level. With further development, scale PTT may permit reliable, convenient measurement of BP.

Weighing Scale-Based Pulse Transit Time is a Superior Marker of Blood Pressure than Conventional Pulse Arrival Time.

PubMed

Martin, Stephanie L-O; Carek, Andrew M; Kim, Chang-Sei; Ashouri, Hazar; Inan, Omer T; Hahn, Jin-Oh; Mukkamala, Ramakrishna

2016-12-15

Pulse transit time (PTT) is being widely pursued for cuff-less blood pressure (BP) monitoring. Most efforts have employed the time delay between ECG and finger photoplethysmography (PPG) waveforms as a convenient surrogate of PTT. However, these conventional pulse arrival time (PAT) measurements include the pre-ejection period (PEP) and the time delay through small, muscular arteries and may thus be an unreliable marker of BP. We assessed a bathroom weighing scale-like system for convenient measurement of ballistocardiography and foot PPG waveforms - and thus PTT through larger, more elastic arteries - in terms of its ability to improve tracking of BP in individual subjects. We measured "scale PTT", conventional PAT, and cuff BP in humans during interventions that increased BP but changed PEP and smooth muscle contraction differently. Scale PTT tracked the diastolic BP changes well, with correlation coefficient of -0.80 ± 0.02 (mean ± SE) and root-mean-squared-error of 7.6 ± 0.5 mmHg after a best-case calibration. Conventional PAT was significantly inferior in tracking these changes, with correlation coefficient of -0.60 ± 0.04 and root-mean-squared-error of 14.6 ± 1.5 mmHg (p < 0.05). Scale PTT also tracked the systolic BP changes better than conventional PAT but not to an acceptable level. With further development, scale PTT may permit reliable, convenient measurement of BP.

Arterial pressure transfer characteristics: effects of travel time.

PubMed

Westerhof, Berend E; Guelen, Ilja; Stok, Wim J; Wesseling, Karel H; Spaan, Jos A E; Westerhof, Nico; Bos, Willem Jan; Stergiopulos, Nikos

2007-02-01

We investigated the quantitative contribution of all local conduit arterial, blood, and distal load properties to the pressure transfer function from brachial artery to aorta. The model was based on anatomical data, Young's modulus, wall viscosity, blood viscosity, and blood density. A three-element windkessel represented the distal arterial tree. Sensitivity analysis was performed in terms of frequency and magnitude of the peak of the transfer function and in terms of systolic, diastolic, and pulse pressure in the aorta. The root mean square error (RMSE) described the accuracy in wave-shape prediction. The percent change of these variables for a 25% alteration of each of the model parameters was calculated. Vessel length and diameter are found to be the most important parameters determining pressure transfer. Systolic and diastolic pressure changed <3% and RMSE <1.8 mmHg for a 25% change in vessel length and diameter. To investigate how arterial tapering influences the pressure transfer, a single uniform lossless tube was modeled. This simplification introduced only small errors in systolic and diastolic pressures (1% and 0%, respectively), and wave shape was less well described (RMSE, approximately 2.1 mmHg). Local (arm) vasodilation affects the transfer function little, because it has limited effect on the reflection coefficient. Since vessel length and diameter translate into travel time, this parameter can describe the transfer accurately. We suggest that with a, preferably, noninvasively measured travel time, an accurate individualized description of pressure transfer can be obtained.

Late-time cosmological phase transitions

NASA Technical Reports Server (NTRS)

Schramm, David N.

1991-01-01

It is shown that the potential galaxy formation and large scale structure problems of objects existing at high redshifts (Z approx. greater than 5), structures existing on scales of 100 M pc as well as velocity flows on such scales, and minimal microwave anisotropies ((Delta)T/T) (approx. less than 10(exp -5)) can be solved if the seeds needed to generate structure form in a vacuum phase transition after decoupling. It is argued that the basic physics of such a phase transition is no more exotic than that utilized in the more traditional GUT scale phase transitions, and that, just as in the GUT case, significant random Gaussian fluctuations and/or topological defects can form. Scale lengths of approx. 100 M pc for large scale structure as well as approx. 1 M pc for galaxy formation occur naturally. Possible support for new physics that might be associated with such a late-time transition comes from the preliminary results of the SAGE solar neutrino experiment, implying neutrino flavor mixing with values similar to those required for a late-time transition. It is also noted that a see-saw model for the neutrino masses might also imply a tau neutrino mass that is an ideal hot dark matter candidate. However, in general either hot or cold dark matter can be consistent with a late-time transition.

FTA real-time transit information assessment : white paper on literature review of real-time transit information systems.

DOT National Transportation Integrated Search

Real-time transit information systems are key technology applications within the transit industry designed to provide better customer service by disseminating timely and accurate information. Riders use this information to make various decisions abou...

Measurement of arterial transit time and renal blood flow using pseudocontinuous ASL MRI with multiple post-labeling delays: Feasibility, reproducibility, and variation.

PubMed

Kim, Dong Won; Shim, Woo Hyun; Yoon, Seong Kuk; Oh, Jong Yeong; Kim, Jeong Kon; Jung, Hoesu; Matsuda, Tsuyoshi; Kim, Dongeun

2017-09-01

To evaluate the feasibility, reproducibility, and variation of renal perfusion and arterial transit time (ATT) using pseudocontinuous arterial spin labeling magnetic resonance imaging (PCASL MRI) in healthy volunteers. PCASL MRI at 3T was performed in 25 healthy volunteers on two different occasions. The ATT and ATT-corrected renal blood flow (ATT-cRBF) were calculated at four different post-labeling delay points (0.5, 1.0, 1.5, and 2.0 s) and evaluated for each kidney and subject. The intraclass correlation (ICC) and Bland-Altman plot were used to assess the reproducibility of the PCASL MRI technique. The within-subject coefficient of variance was determined. Results were obtained for 46 kidneys of 23 subjects with a mean age of 38.6 ± 9.8 years and estimated glomerular filtration rate (eGFR) of 89.1 ± 21.2 ml/min/1.73 m 2 . Two subjects failed in the ASL MRI examination. The mean cortical and medullary ATT-cRBF for the subjects were 215 ± 65 and 81 ± 21 ml/min/100 g, respectively, and the mean cortical and medullary ATT were 1141 ± 262 and 1123 ± 245 msec, correspondingly. The ICC for the cortical ATT-cRBF was 0.927 and the within-subject coefficient of variance was 14.4%. The ICCs for the medullary ATT-cRBF and the cortical and medullary ATT were poor. The Bland-Altman plot for cortical RBF showed good agreement between the two measurements. PCASL MRI is a feasible and reproducible method for measuring renal cortical perfusion. In contrast, ATT for the renal cortex and medulla has poor reproducibility and high variation. 2 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:813-819. © 2017 International Society for Magnetic Resonance in Medicine.

Intraoperative left subclavian artery occlusion with left hand ischaemia and steal syndrome in the left internal thoracic artery

PubMed Central

Jelenc, Matija; Kneževič, Ivan; Stankovič, Milenko; Geršak, Borut

2012-01-01

We present a case of a 62-year old man with a left main stenosis, left coronary artery dominance, normal ejection fraction and no valvular pathology, and status post right carotid artery stenting, who was scheduled for elective coronary revascularization. We performed off-pump coronary revascularization, anastomosing the left internal thoracic artery to the left anterior descending artery, and three separate saphenous vein grafts to the intermediate artery and the first and second obtuse marginals, respectively. Proximally, the right internal thoracic artery was used as the inflow for all three venous grafts due to a heavily calcified ascending aorta. During the construction of the distal anastomoses to the obtuse marginals, the arterial pressure in the left radial artery suddenly dropped. The left hand was found to be pale and pulseless. A femoral artery catheter was placed for pressure monitoring and the anastomoses were completed as planned. Intraoperative transit-time graft flow measurement showed a reversed flow in the left internal thoracic artery. Postoperatively, angiography was performed showing a subtotal stenosis of the proximal left subclavian artery. The artery was dilated and stented. The postoperative course was uneventful and the patient was discharged on the 12th postoperative day. PMID:22767542

Reconstruction of the replaced right hepatic artery at the time of pancreaticoduodenectomy.

PubMed

Allendorf, John D; Bellemare, Sarah

2009-03-01

The arterial anatomy supplying the liver is highly variable. One of the most common variants is a completely replaced right hepatic artery which is seen in about 11% of the population. Interruption of arterial flow to the right hepatic artery at the time of pancreaticoduodenectomy has been associated with biliary fistula and the consequent complications, as well as stenosis of the biliary enteric anastomosis. Malignancies of the posterior aspect of the head of the pancreas can encase a replaced right hepatic artery without involvement of other vascular structures. In this situation, it is possible to resect and reconstruct the replaced right hepatic artery to maintain oxygen delivery to the biliary enteric anastomosis. Herein we describe a technique to reconstruct a replaced right hepatic artery following resection of the vessel en bloc with the tumor during a pancreaticoduodenectomy, using inflow from the gastroduodenal artery.

Transition path time distributions for Lévy flights

NASA Astrophysics Data System (ADS)

Janakiraman, Deepika

2018-07-01

This paper presents a study of transition path time distributions for Lévy noise-induced barrier crossing. Transition paths are short segments of the reactive trajectories and span the barrier region of the potential without spilling into the reactant/product wells. The time taken to traverse this segment is referred to as the transition path time. Since the transition path is devoid of excursions in the minimum, the corresponding time will give the exclusive barrier crossing time, unlike . This work explores the distribution of transition path times for superdiffusive barrier crossing, analytically. This is made possible by approximating the barrier by an inverted parabola. Using this approximation, the distributions are evaluated in both over- and under-damped limits of friction. The short-time behaviour of the distributions, provide analytical evidence for single-step transition events—a feature in Lévy-barrier crossing as observed in prior simulation studies. The average transition path time is calculated as a function of the Lévy index (α), and the optimal value of α leading to minimum average transition path time is discussed, in both the limits of friction. Langevin dynamics simulations corroborating with the analytical results are also presented.

Weighing Scale-Based Pulse Transit Time is a Superior Marker of Blood Pressure than Conventional Pulse Arrival Time

PubMed Central

Martin, Stephanie L.-O.; Carek, Andrew M.; Kim, Chang-Sei; Ashouri, Hazar; Inan, Omer T.; Hahn, Jin-Oh; Mukkamala, Ramakrishna

2016-01-01

Pulse transit time (PTT) is being widely pursued for cuff-less blood pressure (BP) monitoring. Most efforts have employed the time delay between ECG and finger photoplethysmography (PPG) waveforms as a convenient surrogate of PTT. However, these conventional pulse arrival time (PAT) measurements include the pre-ejection period (PEP) and the time delay through small, muscular arteries and may thus be an unreliable marker of BP. We assessed a bathroom weighing scale-like system for convenient measurement of ballistocardiography and foot PPG waveforms – and thus PTT through larger, more elastic arteries – in terms of its ability to improve tracking of BP in individual subjects. We measured “scale PTT”, conventional PAT, and cuff BP in humans during interventions that increased BP but changed PEP and smooth muscle contraction differently. Scale PTT tracked the diastolic BP changes well, with correlation coefficient of −0.80 ± 0.02 (mean ± SE) and root-mean-squared-error of 7.6 ± 0.5 mmHg after a best-case calibration. Conventional PAT was significantly inferior in tracking these changes, with correlation coefficient of −0.60 ± 0.04 and root-mean-squared-error of 14.6 ± 1.5 mmHg (p < 0.05). Scale PTT also tracked the systolic BP changes better than conventional PAT but not to an acceptable level. With further development, scale PTT may permit reliable, convenient measurement of BP. PMID:27976741

Smartphone-based Continuous Blood Pressure Measurement Using Pulse Transit Time.

PubMed

Gholamhosseini, Hamid; Meintjes, Andries; Baig, Mirza; Linden, Maria

2016-01-01

The increasing availability of low cost and easy to use personalized medical monitoring devices has opened the door for new and innovative methods of health monitoring to emerge. Cuff-less and continuous methods of measuring blood pressure are particularly attractive as blood pressure is one of the most important measurements of long term cardiovascular health. Current methods of noninvasive blood pressure measurement are based on inflation and deflation of a cuff with some effects on arteries where blood pressure is being measured. This inflation can also cause patient discomfort and alter the measurement results. In this work, a mobile application was developed to collate the PhotoPlethysmoGramm (PPG) waveform provided by a pulse oximeter and the electrocardiogram (ECG) for calculating the pulse transit time. This information is then indirectly related to the user's systolic blood pressure. The developed application successfully connects to the PPG and ECG monitoring devices using Bluetooth wireless connection and stores the data onto an online server. The pulse transit time is estimated in real time and the user's systolic blood pressure can be estimated after the system has been calibrated. The synchronization between the two devices was found to pose a challenge to this method of continuous blood pressure monitoring. However, the implemented continuous blood pressure monitoring system effectively serves as a proof of concept. This combined with the massive benefits that an accurate and robust continuous blood pressure monitoring system would provide indicates that it is certainly worthwhile to further develop this system.

The relationship between heart-carotid pulse transit time and carotid intima-media thickness in hypertensive patients.

PubMed

Li, C; Xiong, H; Wu, W; Tian, X; Wang, Y; Wu, D; Lin, W-H; Miao, F; Zhang, H; Huang, W; Zhang, Y-T

2015-11-01

The study aimed to investigate the relationship between heart-carotid pulse transit time and carotid intima-media thickness (CIMT) in hypertensive patients, and whether including the pre-ejection period (PEP) in heart-carotid pulse transit time would affect this correlation. A total of 62 hypertensive patients were included in this study. They were divided into the normal CIMT group (n=33, CIMT⩽0.8 mm) and the thickened CIMT group (n=29, CIMT>0.8 mm). The noninvasive ultrasound method was used to measure CIMT, electrocardiogram R-wave-based heart-carotid pulse transit time (rcPTT) and PEP. Aortic valve-carotid artery pulse transit time (acPTT) was calculated by subtracting PEP from rcPTT. Simple linear analysis showed that CIMT was negatively associated with rcPTT and acPTT (r=-0.57, P<0.0001; r=-0.41, P=0.016) in the normal CIMT group as well as in the thickened CIMT group (r=-0.50, P=0.0053; r=-0.59, P=0.001). These relationships were eliminated in the normal CIMT group after adjusting for age, gender, smoking behaviour, systolic blood pressure, diastolic blood pressure and cholesterol levels. However, rcPTT and acPTT still showed significant correlations with CIMT in the thickened CIMT group. In conclusion, rcPTT and acPTT were associated with CIMT, independent of well-known clinical confounders in thickened CIMT hypertensive patients. Therefore, rcPTT and acPTT might be useful markers for atherosclerosis evaluation.

A Catalog of Transit Timing Posterior Distributions for all Kepler Planet Candidate Transit Events

NASA Astrophysics Data System (ADS)

Montet, Benjamin Tyler; Becker, Juliette C.; Johnson, John Asher

2015-12-01

Kepler has ushered in a new era of planetary dynamics, enabling the detection of interactions between multiple planets in transiting systems for hundreds of systems. These interactions, observed as transit timing variations (TTVs), have been used to find non-transiting companions to transiting systems and to measure masses, eccentricities, and inclinations of transiting planets. Often, physical parameters are inferred by comparing the observed light curve to the result of a photodynamical model, a time-intensive process that often ignores the effects of correlated noise in the light curve. Catalogs of transit timing observations have previously neglected non-Gaussian uncertainties in the times of transit, uncertainties in the transit shape, and short cadence data. Here, I present a catalog of not only times of transit centers, but also posterior distributions on the time of transit for every planet candidate transit event in the Kepler data, developed through importance sampling of each transit. This catalog allows one to marginalize over uncertainties in the transit shape and incorporate short cadence data, the effects of correlated noise, and non-Gaussian posteriors. Our catalog will enable dynamical studies that reflect accurately the precision of Kepler and its limitations without requiring the computational power to model the light curve completely with every integration. I will also present our open-source N-body photodynamical modeling code, which integrates planetary and stellar orbits accounting for the effects of GR, tidal effects, and Doppler beaming.

Validation and augmentation of Inrix arterial travel time data using independent sources : [research summary].

DOT National Transportation Integrated Search

2015-02-01

Although the freeway travel time data has been validated extensively in recent : years, the quality of arterial travel time data is not well known. This project : presents a comprehensive validation scheme for arterial travel time data based : on GPS...

Renal contrast-enhanced MR angiography: timing errors and accurate depiction of renal artery origins.

PubMed

Schmidt, Maria A; Morgan, Robert

2008-10-01

To investigate bolus timing artifacts that impair depiction of renal arteries at contrast material-enhanced magnetic resonance (MR) angiography and to determine the effect of contrast agent infusion rates on artifact generation. Renal contrast-enhanced MR angiography was simulated for a variety of infusion schemes, assuming both correct and incorrect timing between data acquisition and contrast agent injection. In addition, the ethics committee approved the retrospective evaluation of clinical breath-hold renal contrast-enhanced MR angiographic studies obtained with automated detection of contrast agent arrival. Twenty-two studies were evaluated for their ability to depict the origin of renal arteries in patent vessels and for any signs of timing errors. Simulations showed that a completely artifactual stenosis or an artifactual overestimation of an existing stenosis at the renal artery origin can be caused by timing errors of the order of 5 seconds in examinations performed with contrast agent infusion rates compatible with or higher than those of hand injections. Lower infusion rates make the studies more likely to accurately depict the origin of the renal arteries. In approximately one-third of all clinical examinations, different contrast agent uptake rates were detected on the left and right sides of the body, and thus allowed us to confirm that it is often impossible to optimize depiction of both renal arteries. In three renal arteries, a signal void was found at the origin in a patent vessel, and delayed contrast agent arrival was confirmed. Computer simulations and clinical examinations showed that timing errors impair the accurate depiction of renal artery origins. (c) RSNA, 2008.

Occipital Artery to Middle Cerebral Artery Bypass in Cases of Unavailable Superficial Temporal Artery.

PubMed

Hirano, Tsukasa; Mikami, Takeshi; Suzuki, Hime; Hirano, Toru; Kimura, Yusuke; Komatsu, Katusya; Akiyama, Yukinori; Wanibuchi, Masahiko; Mikuni, Nobuhiro

2018-04-01

In neurosurgery, extracranial-to-intracranial (EC-IC) bypass surgery is necessary for patients who have undergone surgery in which the superficial temporal artery (STA) was already used for a different bypass procedure or was damaged. Here we report our experience with EC-IC bypass using the occipital artery (OA) in patients in whom the STA was unavailable, and discuss the technical considerations and pitfalls. Five patients with ischemic-onset moyamoya disease and atherosclerotic disease were included. Two patterns of skin incisions were planned according to the OA pathway and recipient artery location. In one of these methods, a skin incision is made above the OA, and a craniotomy is performed under this incision after OA dissection. In the other method, a skin incision is made above the OA to enable its dissection, and a craniotomy is performed via a separate skin incision. No major perioperative complications developed in any of the 5 cases, and bypass patency was confirmed in all patients. There was a significant difference between the preoperative and postoperative asymmetry ratios of the mean transit time values. Our findings suggest that OA-to-middle cerebral artery (MCA) bypass is a simple and effective technique in patients in whom the STA was already used or was damaged by previous intracranial revascularization or craniotomy. This procedure could be an alternative to STA-MCA bypass in patients without an available STA. Copyright © 2018 Elsevier Inc. All rights reserved.

Segmentation features and structural organization of the intrapulmonary artery of the yak.

PubMed

Zhou, Jinxing; Yu, Sijiu; He, Junfeng; Cui, Yan

2013-11-01

This study aims to systematically investigate intrapulmonary artery segmentation, blood vessel wall characteristics and structure organization, and the interrelation between intrapulmonary artery structure and plateau hypoxia adaptation in yak. The normal intrapulmonary artery structure of the yak had been studied using histological methods and transmission electron microscopy. The intrapulmonary artery of the yak was also examined using morphometric analysis and angiography. Results showed that the elastic intrapulmonary artery is divided into two types, namely, classical and transitional elastic segments. The muscular intrapulmonary artery is divided into three types, namely, transitional, classical muscular, and muscular arteriole segments. In the transitional elastic artery, elastic fibers and smooth muscles are linked through three models of ends, lateral branches, and branch tops. Two phenomena are possible for the transition from the elastic intrapulmonary artery to the muscular artery. One phenomenon postulates that a less elastic membrane is first increased and then suddenly decreased, and another supposes that the elastic membrane is gradually reduced and assembled in one to two layers before entering the transitional muscular artery. The smooth muscle of the intrapulmonary artery tunica media had more apophysis; it was physically connected with elastic membrane or fiber and composed of functionally resilient unit of the intrapulmonary arterial wall. Glycogenosomes increased in the muscular intrapulmonary artery smooth muscle cells. It exist one to two layers intact smooth muscle in intrapulmonary arteriole, the presence of intact smooth muscle in the intrapulmonary arteriole of the yak is a kind of structure adaptation to low-oxygen environment. Copyright © 2013 Wiley Periodicals, Inc.

Access to destinations : arterial data acquisition and network-wide travel time estimation (phase II).

DOT National Transportation Integrated Search

2010-03-01

The objectives of this project were to (a) produce historic estimates of travel times on Twin-Cities arterials : for 1995 and 2005, and (b) develop an initial architecture and database that could, in the future, produce timely : estimates of arterial...

Modeling, implementation, and validation of arterial travel time reliability.

DOT National Transportation Integrated Search

2013-11-01

Previous research funded by Florida Department of Transportation (FDOT) developed a method for estimating : travel time reliability for arterials. This method was not initially implemented or validated using field data. This : project evaluated and r...

Graft flow assessment using a transit time flow meter in fractional flow reserve-guided coronary artery bypass surgery.

PubMed

Honda, Kentaro; Okamura, Yoshitaka; Nishimura, Yoshiharu; Uchita, Shunji; Yuzaki, Mitsuru; Kaneko, Masahiro; Yamamoto, Nobuko; Kubo, Takashi; Akasaka, Takashi

2015-06-01

To evaluate the relationship between preoperative severity of coronary stenosis occurring with fractional flow reserve (FFR), and the intraoperative bypass graft flow pattern. In all, 72 patients were enrolled in this retrospective study. The FFR value of the left anterior descending artery was evaluated, and data on "in situ" bypass grafting from the internal thoracic artery to the left anterior descending artery were assessed. Patients were divided into 3 groups according to preoperative FFR values (Group S: FFR < 0.70; group M: 0.70 ≤ FFR < 0.75; and group N: FFR ≥ 0.75). In groups S, M, and N, respectively, mean graft flow was 24.7 ± 10.6 mL/minute, 19.2 ± 14.0 mL/minute, and 16.0 ± 9.7 mL mL/minute; pulsatility index was 2.35 ± 0.6, 3.02 ± 1.1, and 5.51 ± 8.20; and number of patients with systolic reverse flow was 3 (6.8%), 5 (35.7%), and 4 (28.6%). Significant differences were observed in graft flow (P = .009), pulsatility index (P = .038), and proportion of systolic reverse flow (P = .023) among the 3 groups. In all patients, graft patency was confirmed with intraoperative fluorescence imaging; postoperative graft patency was confirmed with multislice computed tomography or coronary angiography in 69 patients (follow-up interval: 213 days). Early graft failure occurred in 1 patient. As coronary stenosis severity increased, graft flow increased, pulsatility index decreased, and proportion of patients with systolic reverse flow increased. In mild coronary artery stenosis, the chance of flow competition between the native coronary artery and the bypass graft increased. Copyright © 2015 The American Association for Thoracic Surgery. Published by Elsevier Inc. All rights reserved.

Daylight Saving Time Transitions and Road Traffic Accidents

PubMed Central

Lahti, Tuuli; Nysten, Esa; Haukka, Jari; Sulander, Pekka; Partonen, Timo

2010-01-01

Circadian rhythm disruptions may have harmful impacts on health. Circadian rhythm disruptions caused by jet lag compromise the quality and amount of sleep and may lead to a variety of symptoms such as fatigue, headache, and loss of attention and alertness. Even a minor change in time schedule may cause considerable stress for the body. Transitions into and out of daylight saving time alter the social and environmental timing twice a year. According to earlier studies, this change in time-schedule leads to sleep disruption and fragmentation of the circadian rhythm. Since sleep deprivation decreases motivation, attention, and alertness, transitions into and out of daylight saving time may increase the amount of accidents during the following days after the transition. We studied the amount of road traffic accidents one week before and one week after transitions into and out of daylight saving time during years from 1981 to 2006. Our results demonstrated that transitions into and out of daylight saving time did not increase the number of traffic road accidents. PMID:20652036

DNS of flow in stenosed carotid artery

NASA Astrophysics Data System (ADS)

Grinberg, Leopold; Yakhot, Alexander; Karniadakis, George

2006-11-01

Direct numerical simulation (DNS) of a three-dimensional flow through a stenosed carotid artery has been performed. Onset of turbulence downstream of the occlusion has been observed. The developing turbulence is characterized by an alternating spatio-temporal transitional regime. The transition to turbulence occurs during the systolic phase approximately five throat-diameters downstream of the throat, while laminarization occurs during the diastolic phase. Transition in space is first enhanced and subsequently decays downstream. The wall shear stress increases in the stenosed internal carotid artery due to the vessel occlusion and as the result of turbulence.

Central retinal artery occlusion - rethinking retinal survival time.

PubMed

Tobalem, Stephan; Schutz, James S; Chronopoulos, Argyrios

2018-04-18

The critical time from onset of complete occlusion of the central retinal artery (CRA) to functionally significant inner retinal infarction represents a window of opportunity for treatment and also has medical-legal implications, particularly when central retinal artery occlusion (CRAO) complicates therapeutic interventions. Here, we review the evidence for time to infarction from complete CRAO and discuss the implications of our findings. A Medline search was performed using each of the terms "central retinal artery occlusion", "retinal infarction", "retinal ischemia", and "cherry red spot" from 1970 to the present including articles in French and German. All retrieved references as well as their reference lists were screened for relevance. An Internet search using these terms was also performed to look for additional references. We find that the experimental evidence showing that inner retinal infarction occurs after 90-240 min of total CRAO, which is the interval generally accepted in the medical literature and practice guidelines, is flawed in important ways. Moreover, the retinal ganglion cells, supplied by the CRA, are part of the central nervous system which undergoes infarction after non-perfusion of 12-15 min or less. Retinal infarction is most likely to occur after only 12-15 min of complete CRAO. This helps to explain why therapeutic maneuvers for CRAO are often ineffective. Nevertheless, many CRAOs are incomplete and may benefit from therapy after longer intervals. To try to avoid retinal infarcton from inadvertent ocular compression by a headrest during prone anesthesia, the eyes should be checked at intervals of less than 15'.

Dynamical quantum phase transitions in discrete time crystals

NASA Astrophysics Data System (ADS)

Kosior, Arkadiusz; Sacha, Krzysztof

2018-05-01

Discrete time crystals are related to nonequilibrium dynamics of periodically driven quantum many-body systems where the discrete time-translation symmetry of the Hamiltonian is spontaneously broken into another discrete symmetry. Recently, the concept of phase transitions has been extended to nonequilibrium dynamics of time-independent systems induced by a quantum quench, i.e., a sudden change of some parameter of the Hamiltonian. There, the return probability of a system to the ground state reveals singularities in time which are dubbed dynamical quantum phase transitions. We show that the quantum quench in a discrete time crystal leads to dynamical quantum phase transitions where the return probability of a periodically driven system to a Floquet eigenstate before the quench reveals singularities in time. It indicates that dynamical quantum phase transitions are not restricted to time-independent systems and can be also observed in systems that are periodically driven. We discuss how the phenomenon can be observed in ultracold atomic gases.

Transit satellite system timing capabilities

NASA Technical Reports Server (NTRS)

Finsod, T. D.

1978-01-01

Current time transfer capabilities of the Transit Satellite System are reviewed. Potential improvements in the changes in equipment and operational procedures using operational satellites are discussed.

Detection of artery interfaces: a real-time system and its clinical applications

NASA Astrophysics Data System (ADS)

Faita, Francesco; Gemignani, Vincenzo; Bianchini, Elisabetta; Giannarelli, Chiara; Ghiadoni, Lorenzo; Demi, Marcello

2008-03-01

Analyzing the artery mechanics is a crucial issue because of its close relationship with several cardiovascular risk factors, such as hypertension and diabetes. Moreover, most of the work can be carried out by analyzing image sequences obtained with ultrasounds, that is with a non-invasive technique which allows a real-time visualization of the observed structures. For this reason, therefore, an accurate temporal localization of the main vessel interfaces becomes a central task for which the manual approach should be avoided since such a method is rather unreliable and time consuming. Real-time automatic systems are advantageously used to automatically locate the arterial interfaces. The automatic measurement reduces the inter/intra-observer variability with respect to the manual measurement which unavoidably depends on the experience of the operator. The real-time visual feedback, moreover, guides physicians when looking for the best position of the ultrasound probe, thus increasing the global robustness of the system. The automatic system which we developed is a stand-alone video processing system which acquires the analog video signal from the ultrasound equipment, performs all the measurements and shows the results in real-time. The localization algorithm of the artery tunics is based on a new mathematical operator (the first order absolute moment) and on a pattern recognition approach. Various clinical applications have been developed on board and validated through a comparison with gold-standard techniques: the assessment of intima-media thickness, the arterial distension, the flow-mediated dilation and the pulse wave velocity. With this paper, the results obtained on clinical trials are presented.

Assessment of umbilical artery flow and fetal heart rate to predict delivery time in bitches.

PubMed

Giannico, Amália Turner; Garcia, Daniela Aparecida Ayres; Gil, Elaine Mayumi Ueno; Sousa, Marlos Gonçalves; Froes, Tilde Rodrigues

2016-10-15

The aim of this study was to quantitatively investigate the oscillation of the fetal heart rate (HR) in advance of normal delivery and whether this index could be used to indicate impending delivery. In addition, fetal HR oscillation and umbilical artery resistive index (RI) were correlated to determine if the combination of these parameters provided a more accurate prediction of the time of delivery. Sonographic evaluation was performed in 11 pregnant bitches to evaluate the fetal HR and umbilical artery RI at the following antepartum times: 120 to 96 hours, 72 to 48 hours, 24 to 12 hours, and 12 to 1 hours. Statistical analysis indicated a correlation between the oscillation of fetal HR and the umbilical artery RI. As delivery approached a considerable reduction in the umbilical artery RI was documented and greater oscillations between maximum and minimum HRs occurred. We conclude that the quantitative analysis of fetal HR oscillations may be used to predict the time of delivery in bitches. The combination of fetal HR and umbilical artery RI together may provide more accurate predictions of time of delivery. Copyright © 2016 Elsevier Inc. All rights reserved.

Cerebral arterial bolus arrival time is prolonged in multiple sclerosis and associated with disability

PubMed Central

Paling, David; Thade Petersen, Esben; Tozer, Daniel J; Altmann, Daniel R; Wheeler-Kingshott, Claudia AM; Kapoor, Raju; Miller, David H; Golay, Xavier

2014-01-01

Alterations in the overall cerebral hemodynamics have been reported in multiple sclerosis (MS); however, their cause and significance is unknown. While potential venous causes have been examined, arterial causes have not. In this study, a multiple delay time arterial spin labeling magnetic resonance imaging sequence at 3T was used to quantify the arterial hemodynamic parameter bolus arrival time (BAT) and cerebral blood flow (CBF) in normal-appearing white matter (NAWM) and deep gray matter in 33 controls and 35 patients with relapsing–remitting MS. Bolus arrival time was prolonged in MS in NAWM (1.0±0.2 versus 0.9±0.2 seconds, P=0.031) and deep gray matter (0.90±0.18 versus 0.80±0.14 seconds, P=0.001) and CBF was increased in NAWM (14±4 versus 10±2 mL/100 g/min, P=0.001). Prolonged BAT in NAWM (P=0.042) and deep gray matter (P=0.01) were associated with higher expanded disability status score. This study demonstrates alteration in cerebral arterial hemodynamics in MS. One possible cause may be widespread inflammation. Bolus arrival time was longer in patients with greater disability independent of atrophy and T2 lesion load, suggesting alterations in cerebral arterial hemodynamics may be a marker of clinically relevant pathology. PMID:24045400

Improved hemodynamic parameters in middle cerebral artery infarction after decompressive craniectomy.

PubMed

Amorim, Robson Luis; de Andrade, Almir Ferreira; Gattás, Gabriel S; Paiva, Wellingson Silva; Menezes, Marcos; Teixeira, Manoel Jacobsen; Bor-Seng-Shu, Edson

2014-05-01

Decompressive craniectomy (DC) reduces mortality and improves functional outcome in patients with malignant middle cerebral artery infarction. However, little is known regarding the impact of DC on cerebral hemodynamics. Therefore, our goal was to study the hemodynamic changes that may occur in patients with malignant middle cerebral artery infarction after DC and to assess their relationship with outcomes. Twenty-seven patients with malignant middle cerebral artery infarction who were treated with DC were studied. The perfusion CT hemodynamic parameters, mean transit time, cerebral blood flow, and cerebral blood volume were evaluated preoperatively and within the first 24 hours after DC. There was a global trend toward improved cerebral hemodynamics after DC. Preoperative and postoperative absolute mean transit times were associated with mortality at 6 months, and the ratio of post- and preoperative cerebral blood flow was significantly higher in patients with favorable outcomes than those with unfavorable outcomes. Patients who underwent surgery 48 hours after stroke, those with midline brain shift>10 mm, and those who were >55 years showed no significant improvement in any perfusion CT parameters. DC improves cerebral hemodynamics in patients with malignant middle cerebral artery infarction, and the level of improvement is related to outcome. However, some patients did not seem to experience any additional hemodynamic benefit, suggesting that perfusion CT may play a role as a prognostic tool in patients undergoing DC after ischemic stroke.

Transit light curves with finite integration time: Fisher information analysis

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

Price, Ellen M.; Rogers, Leslie A.

2014-10-10

Kepler has revolutionized the study of transiting planets with its unprecedented photometric precision on more than 150,000 target stars. Most of the transiting planet candidates detected by Kepler have been observed as long-cadence targets with 30 minute integration times, and the upcoming Transiting Exoplanet Survey Satellite will record full frame images with a similar integration time. Integrations of 30 minutes affect the transit shape, particularly for small planets and in cases of low signal to noise. Using the Fisher information matrix technique, we derive analytic approximations for the variances and covariances on the transit parameters obtained from fitting light curvemore » photometry collected with a finite integration time. We find that binning the light curve can significantly increase the uncertainties and covariances on the inferred parameters when comparing scenarios with constant total signal to noise (constant total integration time in the absence of read noise). Uncertainties on the transit ingress/egress time increase by a factor of 34 for Earth-size planets and 3.4 for Jupiter-size planets around Sun-like stars for integration times of 30 minutes compared to instantaneously sampled light curves. Similarly, uncertainties on the mid-transit time for Earth and Jupiter-size planets increase by factors of 3.9 and 1.4. Uncertainties on the transit depth are largely unaffected by finite integration times. While correlations among the transit depth, ingress duration, and transit duration all increase in magnitude with longer integration times, the mid-transit time remains uncorrelated with the other parameters. We provide code in Python and Mathematica for predicting the variances and covariances at www.its.caltech.edu/∼eprice.« less

Real-time subway information for improving transit ridership.

DOT National Transportation Integrated Search

2016-08-01

In recent years, the standardization of transit schedule information has yielded a dramatic increase in the accessibility of computerized transit schedules and given rise to real-time service schedules. Two such real-time service schedules are the Ge...

Pulse transit time reveals drug kinetics on vascular changes affected by propofol.

PubMed

Lan, Yuan-Chun; Shen, Ching-Hui; Kang, Hsung-Ming; Chong, Fok-Ching

2012-01-01

Pulse transit time (PTT) is the duration in which a pulse wave travels between two arterial sites within the same cardiac cycle. The aim of our study is to use PTT to examine propofol's effects on the vascular system. Methods. We collected data from 50 healthy women, between 28 and 51 years old, who underwent gynaecological surgery under general anaesthesia. The general anaesthesia was induced with propofol injection (2 mg/kg). PTT measurements were obtained from the R-wave of electrocardiogram and the pulse wave of photoplethysmograph. Two PTT values were obtained; one before (the control) and the other after propofol injection. The results were analysed by Student's t-test. Results. After propofol injection, the PTT was prolonged. The change in the PTT value from that of baseline was significant statistically (P < 0.05, by Student's t-test). The PTT change over time correlated with the degree of vasodilatation over time. Monitoring of PTT not only revealed the magnitude of vascular changes but also demonstrated the onset of vascular dilation, its peak and duration. We conclude that PTT is a useful guide in monitoring the drug kinetics of propofol.

Transition Icons for Time-Series Visualization and Exploratory Analysis.

PubMed

Nickerson, Paul V; Baharloo, Raheleh; Wanigatunga, Amal A; Manini, Todd M; Tighe, Patrick J; Rashidi, Parisa

2018-03-01

The modern healthcare landscape has seen the rapid emergence of techniques and devices that temporally monitor and record physiological signals. The prevalence of time-series data within the healthcare field necessitates the development of methods that can analyze the data in order to draw meaningful conclusions. Time-series behavior is notoriously difficult to intuitively understand due to its intrinsic high-dimensionality, which is compounded in the case of analyzing groups of time series collected from different patients. Our framework, which we call transition icons, renders common patterns in a visual format useful for understanding the shared behavior within groups of time series. Transition icons are adept at detecting and displaying subtle differences and similarities, e.g., between measurements taken from patients receiving different treatment strategies or stratified by demographics. We introduce various methods that collectively allow for exploratory analysis of groups of time series, while being free of distribution assumptions and including simple heuristics for parameter determination. Our technique extracts discrete transition patterns from symbolic aggregate approXimation representations, and compiles transition frequencies into a bag of patterns constructed for each group. These transition frequencies are normalized and aligned in icon form to intuitively display the underlying patterns. We demonstrate the transition icon technique for two time-series datasets-postoperative pain scores, and hip-worn accelerometer activity counts. We believe transition icons can be an important tool for researchers approaching time-series data, as they give rich and intuitive information about collective time-series behaviors.

Dynamic Flow Velocity Mapping from Fluorescent Dye Transit Times in the Brain Surface Microcirculation of Anesthetized Rats and Mice.

PubMed

Hoshikawa, Ryo; Kawaguchi, Hiroshi; Takuwa, Hiroyuki; Ikoma, Yoko; Tomita, Yutaka; Unekawa, Miyuki; Suzuki, Norihiro; Kanno, Iwao; Masamoto, Kazuto

2016-08-01

This study aimed to develop a new method for mapping blood flow velocity based on the spatial evolution of fluorescent dye transit times captured with CLSFM in the cerebral microcirculation of anesthetized rodents. The animals were anesthetized with isoflurane, and a small amount of fluorescent dye was intravenously injected to label blood plasma. The CLSFM was conducted through a closed cranial window to capture propagation of the dye in the cortical vessels. The transit time of the dye over a certain distance in a single vessel was determined with automated image analyses, and average flow velocity was mapped in each vessel. The average flow velocity measured in the rat pial artery and vein was 4.4 ± 1.2 and 2.4 ± 0.5 mm/sec, respectively. A similar range of flow velocity to those of the rats was observed in the mice; 4.9 ± 1.4 and 2.0 ± 0.9 mm/sec, respectively, although the vessel diameter in the mice was about half of that in the rats. Flow velocity in the cerebral microcirculation can be mapped based on fluorescent dye transit time measurements with conventional CLSFM in experimental animals. © 2016 John Wiley & Sons Ltd.

Analysis of flow disturbance in a stenosed carotid artery bifurcation using two-equation transitional and turbulence models.

PubMed

Tan, F P P; Soloperto, G; Bashford, S; Wood, N B; Thom, S; Hughes, A; Xu, X Y

2008-12-01

In this study, newly developed two-equation turbulence models and transitional variants are employed for the prediction of blood flow patterns in a diseased carotid artery where the growth, progression, and structure of the plaque at rupture are closely linked to low and oscillating wall shear stresses. Moreover, the laminar-turbulent transition in the poststenotic zone can alter the separation zone length, wall shear stress, and pressure distribution over the plaque, with potential implications for stresses within the plaque. Following the validation with well established experimental measurements and numerical studies, a magnetic-resonance (MR) image-based model of the carotid bifurcation with 70% stenosis was reconstructed and simulated using realistic patient-specific conditions. Laminar flow, a correlation-based transitional version of Menter's hybrid k-epsilon/k-omega shear stress transport (SST) model and its "scale adaptive simulation" (SAS) variant were implemented in pulsatile simulations from which analyses of velocity profiles, wall shear stress, and turbulence intensity were conducted. In general, the transitional version of SST and its SAS variant are shown to give a better overall agreement than their standard counterparts with experimental data for pulsatile flow in an axisymmetric stenosed tube. For the patient-specific case reported, the wall shear stress analysis showed discernable differences between the laminar flow and SST transitional models but virtually no difference between the SST transitional model and its SAS variant.

Quantitative cerebral perfusion assessment using microscope-integrated analysis of intraoperative indocyanine green fluorescence angiography versus positron emission tomography in superficial temporal artery to middle cerebral artery anastomosis.

PubMed

Kobayashi, Shinya; Ishikawa, Tatsuya; Tanabe, Jun; Moroi, Junta; Suzuki, Akifumi

2014-01-01

Intraoperative qualitative indocyanine green (ICG) angiography has been used in cerebrovascular surgery. Hyperperfusion may lead to neurological complications after superficial temporal artery to middle cerebral artery (STA-MCA) anastomosis. The purpose of this study is to quantitatively evaluate intraoperative cerebral perfusion using microscope-integrated dynamic ICG fluorescence analysis, and to assess whether this value predicts hyperperfusion syndrome (HPS) after STA-MCA anastomosis. Ten patients undergoing STA-MCA anastomosis due to unilateral major cerebral artery occlusive disease were included. Ten patients with normal cerebral perfusion served as controls. The ICG transit curve from six regions of interest (ROIs) on the cortex, corresponding to ROIs on positron emission tomography (PET) study, was recorded. Maximum intensity (IMAX), cerebral blood flow index (CBFi), rise time (RT), and time to peak (TTP) were evaluated. RT/TTP, but not IMAX or CBFi, could differentiate between control and study subjects. RT/TTP correlated (|r| = 0.534-0.807; P < 0.01) with mean transit time (MTT)/MTT ratio in the ipsilateral to contralateral hemisphere by PET study. Bland-Altman analysis showed a wide limit of agreement between RT and MTT and between TTP and MTT. The ratio of RT before and after bypass procedures was significantly lower in patients with postoperative HPS than in patients without postoperative HPS (0.60 ± 0.032 and 0.80 ± 0.056, respectively; P = 0.017). The ratio of TTP was also significantly lower in patients with postoperative HPS than in patients without postoperative HPS (0.64 ± 0.081 and 0.85 ± 0.095, respectively; P = 0.017). Time-dependent intraoperative parameters from the ICG transit curve provide quantitative information regarding cerebral circulation time with quality and utility comparable to information obtained by PET. These parameters may help predict the occurrence of postoperative HPS.

Effects of cuff inflation and deflation on pulse transit time measured from ECG and multi-wavelength PPG.

PubMed

Liu, Jing; Li, Yao; Ding, Xiao-Rong; Dai, Wen-Xuan; Zhang, Yuan-Ting

2015-01-01

Pulse transit time (PTT), which refers to the time it takes a pulse wave to travel between two arterial sites is a promising index for cuff-less blood pressure (BP) estimation, as well as non-invasive assessment of arterial functions. However, it has not been investigated whether PTTs measured from ECG and different wavelength PPG are equally affected by the arterial status. Furthermore, comparison between the changes of different PTTs can provide enlightenment on the hardware implementation of the PTT-based BP estimation method. This work mainly studied the changes of PTTs calculated from electrocardiogram (ECG) and multi-wavelength photoplethysmogram (PPG) after exerting cuff pressure on the upper arm. A four-channel PPG acquisition system was developed to collect the multi-wavelength PPG signals of red, yellow, green and blue light at the fingertip simultaneously. Ten subjects participated in the experiment and their PTTs measured from different PPG and ECG signals before and after exerting cuff pressure were compared. This study found that within one minute after the four-minute cuff inflation and deflation process, the PTT measured from ECG and yellow PPG experienced a significant increase (p<;0.05) while the PTT from ECG and blue PPG had no statistical difference (p>0.9) compared with that before exerting cuff pressure. This indicates that PTTs calculated from different wavelength PPG have different recoverability from smooth muscle relaxation. Another interesting finding is that the PTT calculated from ECG and yellow PPG had a strong correlation (|r|>0.7) with the time difference between yellow PPG and other PPG signals, which implies the potential of the time difference between yellow PPG and other PPGs as a complementary to PTT-based model for blood pressure estimation.

Stiffness Indices and Fractal Dimension relationship in Arterial Pressure and Diameter Time Series in-Vitro

NASA Astrophysics Data System (ADS)

Cymberknop, L.; Legnani, W.; Pessana, F.; Bia, D.; Zócalo, Y.; Armentano, R. L.

2011-12-01

The advent of vascular diseases, such as hypertension and atherosclerosis, is associated to significant alterations in the physical properties of arterial vessels. Evaluation of arterial biomechanical behaviour is related to the assessment of three representative indices: arterial compliance, arterial distensibility and arterial stiffness index. Elasticity is the most important mechanical property of the arterial wall, whose natures is strictly non-linear. Intervention of elastin and collagen fibres, passive constituent elements of the arterial wall, is related to the applied wall stress level. Concerning this, appropriate tools are required to analyse the temporal dynamics of the signals involved, in order to characterize the whole phenomenon. Fractal geometry can be mentioned as one of those techniques. The aim of this study consisted on arterial pressure and diameter signals processing, by means of nonlinear techniques based on fractal geometry. Time series morphology was related to different arterial stiffness states, generated by means of blood flow variations, during experiences performed in vitro.

Transition amplitude for two-time physics

NASA Astrophysics Data System (ADS)

Frederico, João E.; Rivelles, Victor O.

2010-07-01

We present the transition amplitude for a particle moving in a space with two times and D space dimensions having an Sp(2,R) local symmetry and an SO(D,2) rigid symmetry. It was obtained from the BRST-BFV quantization with a unique gauge choice. We show that by constraining the initial and final points of this amplitude to lie on some hypersurface of the D+2 space the resulting amplitude reproduces well-known systems in lower dimensions. This work provides an alternative way to derive the effects of two-time physics where all the results come from a single transition amplitude.

Transition amplitude for two-time physics

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

Frederico, Joao E.; Rivelles, Victor O.; Instituto de Fisica, Universidade de Sao Paulo, Caixa Postal 66318, 05314-970, Sao Paulo, SP

2010-07-15

We present the transition amplitude for a particle moving in a space with two times and D space dimensions having an Sp(2,R) local symmetry and an SO(D,2) rigid symmetry. It was obtained from the BRST-BFV quantization with a unique gauge choice. We show that by constraining the initial and final points of this amplitude to lie on some hypersurface of the D+2 space the resulting amplitude reproduces well-known systems in lower dimensions. This work provides an alternative way to derive the effects of two-time physics where all the results come from a single transition amplitude.

Temporal dynamics of catchment transit times from stable isotope data

NASA Astrophysics Data System (ADS)

Klaus, Julian; Chun, Kwok P.; McGuire, Kevin J.; McDonnell, Jeffrey J.

2015-06-01

Time variant catchment transit time distributions are fundamental descriptors of catchment function but yet not fully understood, characterized, and modeled. Here we present a new approach for use with standard runoff and tracer data sets that is based on tracking of tracer and age information and time variant catchment mixing. Our new approach is able to deal with nonstationarity of flow paths and catchment mixing, and an irregular shape of the transit time distribution. The approach extracts information on catchment mixing from the stable isotope time series instead of prior assumptions of mixing or the shape of transit time distribution. We first demonstrate proof of concept of the approach with artificial data; the Nash-Sutcliffe efficiencies in tracer and instantaneous transit times were >0.9. The model provides very accurate estimates of time variant transit times when the boundary conditions and fluxes are fully known. We then tested the model with real rainfall-runoff flow and isotope tracer time series from the H.J. Andrews Watershed 10 (WS10) in Oregon. Model efficiencies were 0.37 for the 18O modeling for a 2 year time series; the efficiencies increased to 0.86 for the second year underlying the need of long time tracer time series with a long overlap of tracer input and output. The approach was able to determine time variant transit time of WS10 with field data and showed how it follows the storage dynamics and related changes in flow paths where wet periods with high flows resulted in clearly shorter transit times compared to dry low flow periods.

Time Domain Estimation of Arterial Parameters using the Windkessel Model and the Monte Carlo Method

NASA Astrophysics Data System (ADS)

Gostuski, Vladimir; Pastore, Ignacio; Rodriguez Palacios, Gaspar; Vaca Diez, Gustavo; Moscoso-Vasquez, H. Marcela; Risk, Marcelo

2016-04-01

Numerous parameter estimation techniques exist for characterizing the arterial system using electrical circuit analogs. However, they are often limited by their requirements and usually high computational burdain. Therefore, a new method for estimating arterial parameters based on Monte Carlo simulation is proposed. A three element Windkessel model was used to represent the arterial system. The approach was to reduce the error between the calculated and physiological aortic pressure by randomly generating arterial parameter values, while keeping constant the arterial resistance. This last value was obtained for each subject using the arterial flow, and was a necessary consideration in order to obtain a unique set of values for the arterial compliance and peripheral resistance. The estimation technique was applied to in vivo data containing steady beats in mongrel dogs, and it reliably estimated Windkessel arterial parameters. Further, this method appears to be computationally efficient for on-line time-domain estimation of these parameters.

Domain wall formation in late-time phase transitions

NASA Technical Reports Server (NTRS)

Kolb, Edward W.; Wang, Yun

1992-01-01

We examine domain wall formulation in late time phase transitions. We find that in the invisible axion domain wall phenomenon, thermal effects alone are insufficient to drive different parts of the disconnected vacuum manifold. This suggests that domain walls do not form unless either there is some supplemental (but perhaps not unreasonable) dynamics to localize the scalar field responsible for the phase transition to the low temperature maximum (to an extraordinary precision) before the onset of the phase transition, or there is some non-thermal mechanism to produce large fluctuations in the scalar field. The fact that domain wall production is not a robust prediction of late time transitions may suggest future directions in model building.

Cuff-Free Blood Pressure Estimation Using Pulse Transit Time and Heart Rate.

PubMed

Wang, Ruiping; Jia, Wenyan; Mao, Zhi-Hong; Sclabassi, Robert J; Sun, Mingui

2014-10-01

It has been reported that the pulse transit time (PTT), the interval between the peak of the R-wave in electrocardiogram (ECG) and the fingertip photoplethysmogram (PPG), is related to arterial stiffness, and can be used to estimate the systolic blood pressure (SBP) and diastolic blood pressure (DBP). This phenomenon has been used as the basis to design portable systems for continuously cuff-less blood pressure measurement, benefiting numerous people with heart conditions. However, the PTT-based blood pressure estimation may not be sufficiently accurate because the regulation of blood pressure within the human body is a complex, multivariate physiological process. Considering the negative feedback mechanism in the blood pressure control, we introduce the heart rate (HR) and the blood pressure estimate in the previous step to obtain the current estimate. We validate this method using a clinical database. Our results show that the PTT, HR and previous estimate reduce the estimated error significantly when compared to the conventional PTT estimation approach (p<0.05).

It's Time to Transition to Production, Now What?

NASA Technical Reports Server (NTRS)

Jansma, P. A.; Montgomery, Marc; Werntz, David; Payne, Michael

1999-01-01

When it's time to transition to production, it's easy to be too focused on the application itself and to overlook some areas crucial to your success. Learn about the 10 transition tasks that will ensure a smooth transition, and will prepare your organization to operate and use your system effectively.

Characteristics of time-varying intracranial pressure on blood flow through cerebral artery: A fluid-structure interaction approach.

PubMed

Syed, Hasson; Unnikrishnan, Vinu U; Olcmen, Semih

2016-02-01

Elevated intracranial pressure is a major contributor to morbidity and mortality in severe head injuries. Wall shear stresses in the artery can be affected by increased intracranial pressures and may lead to the formation of cerebral aneurysms. Earlier research on cerebral arteries and aneurysms involves using constant mean intracranial pressure values. Recent advancements in intracranial pressure monitoring techniques have led to measurement of the intracranial pressure waveform. By incorporating a time-varying intracranial pressure waveform in place of constant intracranial pressures in the analysis of cerebral arteries helps in understanding their effects on arterial deformation and wall shear stress. To date, such a robust computational study on the effect of increasing intracranial pressures on the cerebral arterial wall has not been attempted to the best of our knowledge. In this work, fully coupled fluid-structure interaction simulations are carried out to investigate the effect of the variation in intracranial pressure waveforms on the cerebral arterial wall. Three different time-varying intracranial pressure waveforms and three constant intracranial pressure profiles acting on the cerebral arterial wall are analyzed and compared with specified inlet velocity and outlet pressure conditions. It has been found that the arterial wall experiences deformation depending on the time-varying intracranial pressure waveforms, while the wall shear stress changes at peak systole for all the intracranial pressure profiles. © IMechE 2015.

The Timing of School Transitions and Early Adolescent Problem Behavior

PubMed Central

Lippold, Melissa A.; Powers, Christopher J.; Syvertsen, Amy K.; Feinberg, Mark E.; Greenberg, Mark T.

2013-01-01

This longitudinal study investigates whether rural adolescents who transition to a new school in sixth grade have higher levels of risky behavior than adolescents who transition in seventh grade. Our findings indicate that later school transitions had little effect on problem behavior between sixth and ninth grades. Cross-sectional analyses found a small number of temporary effects of transition timing on problem behavior: Spending an additional year in elementary school was associated with higher levels of deviant behavior in the Fall of Grade 6 and higher levels of antisocial peer associations in Grade 8. However, transition effects were not consistent across waves and latent growth curve models found no effects of transition timing on the trajectory of problem behavior. We discuss policy implications and compare our findings with other research on transition timing. PMID:24089584

Esophageal transit time in patients with chagasic megaesophagus

PubMed Central

Martins, Paula; Ferreira, Cid Sergio; Cunha-Melo, José Renan

2018-01-01

Abstract The aim of this study was to determine the esophageal transit time in control individuals and in chagasic patients with or without megaesophagus. A total of 148 patients were allocated in 6 groups according to serological diagnostic of Chagas disease and the degree of esophageal dilatation: A, control healthy individuals (n = 34, 22.9%); B, indeterminate form (n = 23, 15.5%); C, megaesophagus I (n = 37, 25.0%); D, megaesophagus II (n = 19, 12.8%); E, megaesophagus III (n = 21, 14.2%); and F, megaesophagus IV (n = 14, 9.5%). After 8-hour fasting, patients were asked to swallow 75 mL of barium sulfate solution. x-Rays were obtained after 8, 30, 60, and 90 seconds, 5, 10, 30, 60, and 90 minutes, 2, 6, 12, 24 hours, and at every 12 hours until no more contrast was seen in the esophagus. This was the transit time. The transit time varied from 8 seconds to 36 hours (median = 90 seconds). A linear correlation was observed between transit time and megaesophagus grade: 8 seconds in groups A and B, 5 minutes in C, 30 minutes in D, 2 hours in E, and 9:15 hours in F. Dysphagia was not reported by 60 of 114 (52.6%) patients with positive serological tests for Chagas disease (37/91—40.7%—of patients with megaesophagus I–IV grades). The esophageal transit time increased with the grade of megaesophagus. The esophageal transit time has a direct correlation with the grade of megaesophagus; dysphagia complaint correlates with the grade of megaesophagus. However, many patients with megaesophagus do not report dysphagia. PMID:29517674

Transit time of optical pulses propagating through a finite length medium.

PubMed

Bloemer, Mark; Myneni, Krishna; Centini, Marco; Scalora, Michael; D'Aguanno, Giuseppe

2002-05-01

We present experimental and theoretical results on the transit time of optical pulses propagating through bulk media of finite length, specifically GaAs and silica. The transit time of the peak of the pulse varies with the central wavelength due to the étalon effects caused by the reflectivity at the air/medium boundaries. For transform limited optical pulses, the transit time as a function of wavelength follows the transmittance spectrum, that is, the longest transit time occurs at the transmittance maxima where the cavity dwell time is the longest and the shortest transit time occurs at the transmittance minima. The results are dramatically different for chirped pulses obtained by modulating the injection current of a diode laser. The range in the transit times for chirped pulses is a factor of four times larger compared with transform limited pulses. In addition, the transit time for chirped pulses propagating through the GaAs sample is negative at certain wavelengths. Also, the transmitted pulse is not distorted. Although modulating the injection current of a diode laser is the most common method for generating optical pulses, to our knowledge this is the first reported observation of the transit time of these chirped optical pulses propagating through a simple étalon structure.

Effects of diabetes and gender on mechanical properties of the arterial system in rats: aortic impedance analysis.

PubMed

Chang, Kuo-Chu; Hsu, Kwan-Lih; Tseng, Yung-Zu

2003-01-01

We determined the effects of diabetes and gender on the physical properties of the vasculature in streptozotocin (STZ)-treated rats based on the aortic input impedance analysis. Rats given STZ 65 mg/kg i.v. were compared with untreated age-matched controls. Pulsatile aortic pressure and flow signals were measured and were then subjected to Fourier transformation for the analysis of aortic input impedance. Wave transit time was determined using the impulse response function of the filtered aortic input impedance spectra. Male but not female diabetic rats exhibited an increase in cardiac output in the absence of any significant changes in arterial blood pressure, resulting in a decline in total peripheral resistance. However, in each gender group, diabetes contributed to an increase in wave reflection factor, from 0.47 +/- 0.04 to 0.84 +/- 0.03 in males and from 0.46 +/- 0.03 to 0.81 +/- 0.03 in females. Diabetic rats had reduced wave transit time, at 18.82 +/- 0.60 vs 21.34 +/- 0.51 msec in males and at 19.63 +/- 0.37 vs 22.74 +/- 0.57 msec in females. Changes in wave transit time and reflection factor indicate that diabetes can modify the timing and magnitude of the wave reflection in the rat arterial system. Meanwhile, diabetes produced a fall in aortic characteristic impedance from 0.023 +/- 0.002 to 0.009 +/- 0.001 mmHg/min/kg/ml in males and from 0.028 +/- 0.002 to 0.014 +/- 0.001 mmHg/min/kg/ml in females. With unaltered aortic pressure, both the diminished aortic characteristic impedance and wave transit time suggest that the muscle inactivation in diabetes may occur in aortas and large arteries and may cause a detriment to the aortic distensibility in rats with either sex. We conclude that only rats with male gender diabetes produce a detriment to the physical properties of the resistance arterioles. In spite of male or female gender, diabetes decreases the aortic distensibility and impairs the wave reflection phenomenon in the rat arterial system.

Self-Powered Real-Time Arterial Pulse Monitoring Using Ultrathin Epidermal Piezoelectric Sensors.

PubMed

Park, Dae Yong; Joe, Daniel J; Kim, Dong Hyun; Park, Hyewon; Han, Jae Hyun; Jeong, Chang Kyu; Park, Hyelim; Park, Jung Gyu; Joung, Boyoung; Lee, Keon Jae

2017-10-01

Continuous monitoring of an arterial pulse using a pressure sensor attached on the epidermis is an important technology for detecting the early onset of cardiovascular disease and assessing personal health status. Conventional pulse sensors have the capability of detecting human biosignals, but have significant drawbacks of power consumption issues that limit sustainable operation of wearable medical devices. Here, a self-powered piezoelectric pulse sensor is demonstrated to enable in vivo measurement of radial/carotid pulse signals in near-surface arteries. The inorganic piezoelectric sensor on an ultrathin plastic achieves conformal contact with the complex texture of the rugged skin, which allows to respond to the tiny pulse changes arising on the surface of epidermis. Experimental studies provide characteristics of the sensor with a sensitivity (≈0.018 kPa -1 ), response time (≈60 ms), and good mechanical stability. Wireless transmission of detected arterial pressure signals to a smart phone demonstrates the possibility of self-powered and real-time pulse monitoring system. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

State transition model: vorapaxar added to standard antiplatelet therapy to prevent thrombosis post myocardial infarction or peripheral artery disease.

PubMed

Du, Mark; Chase, Monica; Oguz, Mustafa; Davies, Glenn

2017-09-01

To evaluate long-term health benefits and risks of adding vorapaxar (VOR) to the standard care antiplatelet therapy (SC) of aspirin and/or clopidogrel, among a population with a recent myocardial infarction (MI) and/or peripheral artery disease (PAD). In a state-transition model, patients transition between health states (event-free, recurrent MI, stroke, death), while at risk of experiencing non-transition-related revascularization and non-fatal bleeding events. Risk equations developed from the TRA 2°P-TIMI 50 trial's patient-level data were used to predict cardiovascular (CV) outcomes over longer time horizons. Additional sources, including trials and US-based observational studies, informed the inputs for short-term CV risk, non-CV death, and health-related quality of life. Survival and quality-adjusted life-years (QALYs) were estimated over a lifetime horizon, discounted at 3% per year. Within a cohort of 7361 patients with recent MI and/or PAD, VOR + SC relative to SC alone yielded 176 fewer CV events (MIs, strokes, or CV deaths), but 27 more major bleeding events. VOR + SC was associated with increased life expectancy and health benefits (19.93 undiscounted life-years [LYs], 9.57 discounted QALYs vs. 19.61 undiscounted LYs, 9.41 discounted QALYs). The results were most sensitive to scenarios varying time of vorapaxar initiation, and the assumptions in the 90 day period post-MI. Additional analyses showed that add-on vorapaxar provides consistent incremental benefits in high-risk subgroups. This study contributes to the growing literature on secondary prevention add-on therapy, as results from these modeling analyses suggest that adding vorapaxar to SC for patients at high atherothrombotic risk can provide long-term health benefits.

Myocardial blood flow and its transit time, oxygen utilization, and efficiency of highly endurance-trained human heart.

PubMed

Heinonen, Ilkka; Kudomi, Nobuyuki; Kemppainen, Jukka; Kiviniemi, Antti; Noponen, Tommi; Luotolahti, Matti; Luoto, Pauliina; Oikonen, Vesa; Sipilä, Hannu T; Kopra, Jaakko; Mononen, Ilkka; Duncker, Dirk J; Knuuti, Juhani; Kalliokoski, Kari K

2014-07-01

Highly endurance-trained athlete's heart represents the most extreme form of cardiac adaptation to physical stress, but its circulatory alterations remain obscure. In the present study, myocardial blood flow (MBF), blood mean transit time (MTT), oxygen extraction fraction (OEF) and consumption (MVO2), and efficiency of cardiac work were quantified in highly trained male endurance athletes and control subjects at rest and during supine cycling exercise using [(15)O]-labeled radiotracers and positron emission tomography. Heart rate and MBF were lower in athletes both at rest and during exercise. OEF increased in response to exercise in both groups, but was higher in athletes (70 ± 21 vs. 63 ± 11 % at rest and 86 ± 13 vs. 73 ± 10 % during exercise). MTT was longer and vascular resistance higher in athletes both at rest and during exercise, but arterial content of 2,3-diphosphoglycerate (oxygen affinity) was unchanged. MVO2 per gram of myocardium trended (p = 0.08) lower in athletes both at rest and during exercise, while myocardial efficiency of work and MVO2 per beat were not different between groups. Arterial levels of free fatty acids were ~twofold higher in athletes likely leading to higher myocardial fatty acid oxidation and hence oxygen cost, which may have blunted the bradycardia-induced decrease in MVO2. Finally, the observed group differences in MBF, OEF, MTT and vascular resistance remained significant also after they were controlled for differences in MVO2. In conclusion, in highly endurance-trained human heart, increased myocardial blood transition time enables higher oxygen extraction levels with a lower myocardial blood flow and higher vascular resistance. These physiological adaptations to exercise training occur independently of the level of oxygen consumption and together with training-induced bradycardia may serve as mechanisms to increase functional reserve of the human heart.

Transit-time and age distributions for nonlinear time-dependent compartmental systems.

PubMed

Metzler, Holger; Müller, Markus; Sierra, Carlos A

2018-02-06

Many processes in nature are modeled using compartmental systems (reservoir/pool/box systems). Usually, they are expressed as a set of first-order differential equations describing the transfer of matter across a network of compartments. The concepts of age of matter in compartments and the time required for particles to transit the system are important diagnostics of these models with applications to a wide range of scientific questions. Until now, explicit formulas for transit-time and age distributions of nonlinear time-dependent compartmental systems were not available. We compute densities for these types of systems under the assumption of well-mixed compartments. Assuming that a solution of the nonlinear system is available at least numerically, we show how to construct a linear time-dependent system with the same solution trajectory. We demonstrate how to exploit this solution to compute transit-time and age distributions in dependence on given start values and initial age distributions. Furthermore, we derive equations for the time evolution of quantiles and moments of the age distributions. Our results generalize available density formulas for the linear time-independent case and mean-age formulas for the linear time-dependent case. As an example, we apply our formulas to a nonlinear and a linear version of a simple global carbon cycle model driven by a time-dependent input signal which represents fossil fuel additions. We derive time-dependent age distributions for all compartments and calculate the time it takes to remove fossil carbon in a business-as-usual scenario.

Carotid artery distensibility and hormone therapy and menopause: the Los Angeles Atherosclerosis Study.

PubMed

Shufelt, Chrisandra; Elboudwarej, Omeed; Johnson, B Delia; Mehta, Puja; Bittner, Vera; Braunstein, Glenn; Berga, Sarah; Stanczyk, Frank; Dwyer, Kathleen; Merz, C Noel Bairey

2016-02-01

Observational studies have suggested that arterial distensibility decreases during menopause; however, its relationship with hormone therapy use remains controversial. We prospectively studied distensibility and hormone therapy use at different menopause stages. One hundred sixty-one women (aged between 42 and 61 y) without cardiovascular disease underwent carotid artery measurements by ultrasound to calculate distensibility index at baseline and 3 years later. Menopause stage was classified at each visit as premenopausal, perimenopausal, and postmenopausal. Across 3 years of prospective observation, women were classified as remaining premenopausal, remaining postmenopausal, or transitioning (defined as change from premenopausal to perimenopausal, from premenopausal to postmenopausal, from perimenopausal to perimenopausal, or from perimenopausal to postmenopausal). Distensibility declined across time at all menopause stages (P < 0.0001). Compared with postmenopausal women, premenopausal and transitioning/no hormone therapy women had more than twice the decline in distensibility index (P = 0.06 and P = 0.016, respectively), whereas transitioning/hormone therapy women did not differ in distensibility decline (P = 0.28). In a multivariate model, change in systolic blood pressure (P < 0.0001) and change in pulse pressure (P = 0.004) were independent predictors of distensibility index change and served as effect modulators. In an adjusted model, women in the premenopausal and transitioning/no hormone therapy groups had a significantly faster decline in distensibility index (P = 0.002 and P = 0.001, respectively) compared with postmenopausal women, whereas the transitioning/hormone therapy group did not (P = 0.21). These findings confirm that the menopausal transition is associated with reduced vascular compliance. Hormone therapy is associated with better arterial distensibility only during the menopausal transition. Additional prospective studies are needed to confirm

Superficial Femoral Artery Intervention by Single Transpedal Arterial Access.

PubMed

Amoroso, Nicholas S; Shah, Sooraj; Liou, Michael; Ratcliffe, Justin; Lala, Moinakhtar; Diwan, Ravi; Huang, Yili; Rosero, Hugo; Coppola, John; Bertrand, Olivier F; Kwan, Tak W

2015-11-01

Atherosclerotic disease of the superficial femoral artery (SFA) is frequently seen and can be treated with percutaneous interventions, traditionally via femoral artery access. There are limited reports of transpedal artery access for peripheral artery interventions, but none to date describing routine primary transpedal artery approach for SFA stenting. In this preliminary study, we report 4 patients who underwent successful endovascular SFA stenting using a single transpedal artery access via a new ultra-low profile 6 Fr sheath (Glidesheath Slender; Terumo Corporation). All patients underwent successful SFA stenting without complication. Procedure time varied from 51 to 72 minutes. The mean contrast amount used was 56 mL; mean fluoroscopy time was 21 minutes; mean radiation dose was 91 mGy. At 1-month follow-up, duplex ultrasonography showed that all pedal arteries had remained patent. Transpedal artery approach as a primary approach to SFA stenting appears feasible and safe. Comparative trials with standard percutaneous femoral approach are warranted.

Transition fronts of time periodic bistable reaction-diffusion equations in RN

NASA Astrophysics Data System (ADS)

Sheng, Wei-Jie; Guo, Hong-Jun

2018-09-01

This paper is concerned with the existence and qualitative properties of transition fronts for time periodic bistable reaction-diffusion equations in RN. We first show that any almost-planar transition front is actually planar, regardless of the number of transition layers. Then we prove that all transition fronts admit a global mean speed γ and it holds γ = | c |, where c is the speed of the planar traveling front. Finally we establish the existence of a transition front in RN that is not a standard traveling front. Such a front behaves like three moving time periodic planar fronts as time goes to -∞ and like a time periodic V-shaped traveling front as time goes to ∞.

Transitional Leadership: Leadership During Times of Transition, Key Principles, and Considerations for Success.

PubMed

Norbash, Alexander

2017-06-01

To suggest a methodical approach for refining transitional management abilities, including empowerment of a growing leader, leading in an unfamiliar organization or leading in an organization that is changing. Management approaches based on the body of work dealing with leadership studies and transitions and dealing with leadership during times of transition and change management were consolidated and categorized. Transitional leaders can benefit from effective leadership training including defining and prospectively accruing necessary experiences and skills; strengthening information gathering skills; effectively self-assessing; valuing and implementing mentoring; formulating strategy; and communicating. A categorical approach to transitional leadership may be implemented through a systems-based and methodical approach to gaining the definable, and distinct sets of skills and abilities necessary for transitional leadership success. Copyright © 2017 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.

Oral transit time: a critical review of the literature

PubMed Central

SOARES, Thais Jacóe; MORAES, Danielle Pedroni; de MEDEIROS, Gisele Chagas; SASSI, Fernanda Chiarion; ZILBERSTEIN, Bruno; de ANDRADE, Claudia Regina Furquim

2015-01-01

Introduction Oral transit time is one of the parameters observed during the clinical assessment of the swallowing function. The importance of this parameter is due to its impact on the total duration of a meal, whose consequence can be an unfavorable nutritional prognostic. Objective To document scientific papers that measure oral transit time in healthy subjects. Method The review followed the steps proposed by the Cochrane Handbook. The search was done via the PubMed database through the use of descriptors related to the oral phase of swallowing, as well as to types of food consistency. Results The articles on the theme had different definitions for oral transit time, as well as heterogeneity of tested volumes, age and gender of the participants. The times found varied from 0.35 s to 1.54 s for liquids, from 0.39 s to 1.05 s for pasty foods and from 1 s to 12.8 s for solid foods. Also, regardless of volume or consistency, oral transit time in elderly people is significantly longer than in adults. Conclusion There's no consensus in the literature about oral transit time in healthy subjects. However, this parameter should be valued during the assessment of the swallowing function due to its negative impact on the dynamics of swallowing, which can cause high energy expenditure during feeding. PMID:26176255

Optimal wrist angulation shortens time needed for radial artery catheterization: a prospective, randomized, and blinded study.

PubMed

Pandey, R; Ashraf, H; Bhalla, A P; Garg, R

2012-01-01

Optimal wrist position is essential for successful catheterization of the radial artery. We planned to study the success rate of radial artery catheterization at various degrees of wrist extension angulations. This prospective, randomized study was performed in 60 consenting patients aged between 18-65 years and undergoing variable surgeries where the anesthetic management required an arterial catheterization. All patients were randomized into three groups of 20 patients each, according to wrist angulation during radial artery catheterization : either 30 degrees (Group 30), 45 degrees (Group 45), or 60 degrees (Group 60). Three metallic angulated wrist boards with angles of 30 degrees, 45 degrees, and 60 degrees (angle measured with calipers) were prepared, on which patient's wrist was kept at the above-mentioned angles of extension. Radial artery catheterization success rate, catheterization time, and numbers of attempts were recorded. The catheterization time was minimal in group 45 (30.50 +/- 16.82 sec) as compared to 36.00 +/- 14.19 sec and 43.50 +/- 13.80 sec in group 30 and 60, respectively. Radial artery was catheterized at first attempt in 60% of Group 45 and Group 60 patients, and in 50% of Group 30 patients. The arterial catheterization was successful in 14/20 patients in Group 30, 19/20 patients in group 45, and 16/20 patients in group 60. We conclude that a wrist extension of 450 appears to be the optimal wrist joint extension for a successful radial artery cannula insertion.

Immediate flow reserve of Y thoracic artery grafts: an intraoperative flowmetric study.

PubMed

Gaudino, Mario; Di Mauro, Michele; Iacò, Angela Lorena; Canosa, Carlo; Vitolla, Giuseppe; Calafiore, Antonio Maria

2003-10-01

Use of both internal thoracic arteries in a Y graft configuration can raise concerns about the possibility of the single left internal thoracic artery being able to meet the flow requirements of two or three distal territories. We evaluated intraoperatively the flow reserve of a Y thoracic artery graft distally anastomosed to the anterior and lateral territories. In 21 patients who had Y thoracic artery grafts, the flow was measured in the main stem of the left internal thoracic artery, in the left internal thoracic artery branch, and in the right internal thoracic artery. A transit time Doppler flowmeter was used. Measurements were repeated after the injection of a bolus of 20 mug/kg dobutamine. At baseline condition, the mean blood flow was 44.8 +/- 24.2, 23.4 +/- 11.5, and 21.4 +/- 15.3 mL/min in the main stem of the left internal thoracic artery, in the left internal thoracic artery branch, and in the right internal thoracic artery, respectively. After dobutamine injection, these values increased to 93.2 +/- 49.8, 46.1 +/- 22.6, and 42.5 +/- 31.2 mL/min, respectively. Flow reserve was 2.1 +/- 0.6, 2.2 +/- 0.9, and 2.1 +/- 0.9 mL/min, respectively. Intraoperative injection of dobutamine increases the flow in the Y thoracic graft by more than two times, not only in the main stem but also in each branch. This finding attests to the safety of Y thoracic conduits in terms of hemodynamic potential.

Carotid Artery Distensibility and Hormone Therapy and Menopause: The Los Angeles Atherosclerosis Study (LAAS)

PubMed Central

Shufelt, Chrisandra; Elboudwarej, Omeed; Johnson, B. Delia; Mehta, Puja; Bittner, Vera; Braunstein, Glenn; Berga, Sarah; Stanczyk, Frank; Dwyer, Kathleen; Merz, C. Noel Bairey

2015-01-01

Objective Observational studies suggest that arterial distensibility decreases during menopause; however, the relation to hormone therapy use is controversial. We prospectively studied distensibility and hormone therapy use during different menopause stages. Methods 161 women between 42–61 years of age without cardiovascular disease had carotid artery measurements by ultrasound to calculate the distensibility index at baseline and 3 years later. Menopause stage was classified at each visit as premenopausal, perimenopausal, and postmenopausal. Over 3 years of prospective observation, women were classified as remaining premenopausal, remaining postmenopausal, or transitioning, defined as change from premenopausal-to-perimenopausal, premenopausal-to-postmenopausal, perimenopausal-to-perimenopausal, or perimenopausal-to-postmenopausal. Results Distensibility declined over time in all menopause stages (p<0.0001). Compared to postmenopausal women, premenopausal and transitioning/no hormone therapy women had over twice the decline in distensibility index (p=0.06 and p=0.016, respectively), whereas transitioning/hormone therapy did not differ in distensibility decline (p=0.28). In a multivariate model, change in systolic blood pressure (p<0.0001) and change in pulse pressure (p=0.004) were independent predictors of distensibility index change and served as effect modulators. In the adjusted model, women in the premenopausal and transitioning/no hormone therapy groups had a significantly faster distensibility index decline (p=0.002 and 0.001, respectively) than postmenopausal women, while the transitioning/hormone therapy group did not (p=0.21) Conclusions These findings confirm that menopause transition is associated with reduced vascular compliance. Hormone therapy is associated with better arterial distensibility only during menopause transition. Additional prospective studies are needed to confirm these findings and to determine if hormone therapy use beyond menopause

No variations in transit times for Qatar-1 b

NASA Astrophysics Data System (ADS)

Maciejewski, G.; Fernández, M.; Aceituno, F. J.; Ohlert, J.; Puchalski, D.; Dimitrov, D.; Seeliger, M.; Kitze, M.; Raetz, St.; Errmann, R.; Gilbert, H.; Pannicke, A.; Schmidt, J.-G.; Neuhäuser, R.

2015-05-01

Aims: The transiting hot-Jupiter planet Qatar-1 b exhibits variations in transit times that could be perturbative. A hot Jupiter with a planetary companion on a nearby orbit would constitute an unprecedented planetary configuration, which is important for theories of the formation and evolution of planetary systems. We performed a photometric follow-up campaign to confirm or refute transit timing variations. Methods: We extend the baseline of transit observations by acquiring 18 new transit light curves acquired with 0.6-2.0 m telescopes. These photometric time series, together with data available in the literature, were analyzed in a homogenous way to derive reliable transit parameters and their uncertainties. Results: We show that the dataset of transit times is consistent with a linear ephemeris leaving no hint of any periodic variations with a range of 1 min. We find no compelling evidence of a close-in planetary companion to Qatar-1 b. This finding is in line with a paradigm that hot Jupiters are not components of compact multiplanetary systems. Based on dynamical simulations, we place tighter constraints on the mass of any fictitious nearby planet in the system. Furthermore, new transit light curves allowed us to redetermine system parameters with better precision than reported in previous studies. Our values generally agree with previous determinations. Partly based on (1) data collected with telescopes at the Rozhen National Astronomical Observatory and (2) observations obtained with telescopes of the University Observatory Jena, which is operated by the Astrophysical Institute of the Friedrich-Schiller-University.Tables of light curve data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/577/A109

Photometric Analysis and Transit Times of TRAPPIST-1 B and C

NASA Astrophysics Data System (ADS)

Morris, Brett M.; Agol, Eric; Hawley, Suzanne L.

2018-01-01

TRAPPIST-1 hosts seven Earth-sized planets transiting an M8 star. We observed mid-transit times of each of the inner two planets with the Astrophysical Research Consortium (ARC) 3.5 m Telescope at Apache Point Observatory (APO) to help constrain the planet masses with transit timing variations, and we outline a procedure for analyzing transit observations of late-M stars with APO. The transit times of TRAPPIST-1 b and c are $\\mathrm{BJD}_{\\mathrm{TDB}} = 2457580.87634^{+0.00034}_{-0.00034}$ and $2457558.89477^{+0.00080}_{-0.00085}$, respectively, which will help constrain the planet masses.

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.

Tube-Load Model Parameter Estimation for Monitoring Arterial Hemodynamics

PubMed Central

Zhang, Guanqun; Hahn, Jin-Oh; Mukkamala, Ramakrishna

2011-01-01

A useful model of the arterial system is the uniform, lossless tube with parametric load. This tube-load model is able to account for wave propagation and reflection (unlike lumped-parameter models such as the Windkessel) while being defined by only a few parameters (unlike comprehensive distributed-parameter models). As a result, the parameters may be readily estimated by accurate fitting of the model to available arterial pressure and flow waveforms so as to permit improved monitoring of arterial hemodynamics. In this paper, we review tube-load model parameter estimation techniques that have appeared in the literature for monitoring wave reflection, large artery compliance, pulse transit time, and central aortic pressure. We begin by motivating the use of the tube-load model for parameter estimation. We then describe the tube-load model, its assumptions and validity, and approaches for estimating its parameters. We next summarize the various techniques and their experimental results while highlighting their advantages over conventional techniques. We conclude the review by suggesting future research directions and describing potential applications. PMID:22053157

The Effect of Static Stretch on Elastin Degradation in Arteries

PubMed Central

Chow, Ming-Jay; Choi, Myunghwan; Yun, Seok Hyun; Zhang, Yanhang

2013-01-01

Previously we have shown that gradual changes in the structure of elastin during an elastase treatment can lead to important transition stages in the mechanical behavior of arteries [1]. However, in vivo arteries are constantly being loaded due to systolic and diastolic pressures and so understanding the effects of loading on the enzymatic degradation of elastin in arteries is important. With biaxial tensile testing, we measured the mechanical behavior of porcine thoracic aortas digested with a mild solution of purified elastase (5 U/mL) in the presence of a static stretch. Arterial mechanical properties and biochemical composition were analyzed to assess the effects of mechanical stretch on elastin degradation. As elastin is being removed, the dimensions of the artery increase by more than 20% in both the longitude and circumference directions. Elastin assays indicate a faster rate of degradation when stretch was present during the digestion. A simple exponential decay fitting confirms the time constant for digestion with stretch (0.11±0.04 h−1) is almost twice that of digestion without stretch (0.069±0.028 h−1). The transition from J-shaped to S-shaped stress vs. strain behavior in the longitudinal direction generally occurs when elastin content is reduced by about 60%. Multiphoton image analysis confirms the removal/fragmentation of elastin and also shows that the collagen fibers are closely intertwined with the elastin lamellae in the medial layer. After removal of elastin, the collagen fibers are no longer constrained and become disordered. Release of amorphous elastin during the fragmentation of the lamellae layers is observed and provides insights into the process of elastin degradation. Overall this study reveals several interesting microstructural changes in the extracellular matrix that could explain the resulting mechanical behavior of arteries with elastin degradation. PMID:24358135

Hepatic vein transit time of second-generation ultrasound contrast agent: new tool in the assessment of portal hypertension.

PubMed

Luisa, Siciliani; Vitale, Giovanna; Sorbo, Anna Rita; Maurizio, Pompili; Lodovico, Rapaccini Gian

2017-03-01

It has been demonstrated that Doppler waveform of the hepatic vein (normally triphasic) is transformed into a biphasic or monophasic waveform in cirrhotic patients. The compressive mechanism of liver tissue has been considered up till now the cause of this change. Moreover, cirrhotics show, after USCA injection, a much earlier HVTT due to intrahepatic shunts. Our aim was to prospectively evaluate the correlation between Doppler pattern of hepatic vein and HVTT of a second-generation USCA; we also correlated HVTT with the most common indexes of portal hypertension. We enrolled 38 participants: 33 cirrhotics and 5 healthy controls. Doppler shift signals were obtained from the right hepatic vein. To characterize the hepatic vein pattern, we used the hepatic vein waveform index (HVWI). This index becomes >1 with the appearance of the triphasic waveform. We recorded a clip from 20 s before to 2 min after a peripheral intravenous bolus injection of 2.4 ml of USCA (sulfur hexafluoride).The time employed by USCA to cross the liver from the hepatic artery and portal vein to the hepatic vein was defined as HA-HVTT and PV-HVTT, respectively. Cirrhotics with low HVWI showed an earlier transit time; participants with higher HVWI had a longer transit time ( p  < 0.001). HVTT was earlier as MELD, Child-Pugh score and spleen diameter increased. Patients with ascites and varices of large size had significantly shorter transit times. Abnormal hepatic vein Doppler waveform in cirrhotic patients could be due to intrahepatic shunts. HVTT could be useful in the non-invasive evaluation of portal hypertension.

Quantitative Real-Time Fluoroscopy Analysis on Measurement of the Hepatic Arterial Flow During Transcatheter Arterial Chemoembolization of Hepatocellular Carcinoma: Comparison with Quantitative Digital Subtraction Angiography Analysis

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

Lin, Yi-Yang; Lee, Rheun-Chuan, E-mail: rclee@vghtpe.gov.tw; Guo, Wan-Yuo, E-mail: wyguo@vghtpe.gov.tw

PurposeTo quantify the arterial flow change during transcatheter arterial chemoembolization (TACE) for hepatocellular carcinoma (HCC) using digital subtraction angiography, quantitative color-coding analysis (d-QCA), and real-time subtraction fluoroscopy QCA (f-QCA).Materials and MethodsThis prospective study enrolled 20 consecutive patients with HCC who had undergone TACE via a subsegmental approach between February 2014 and April 2015. The TACE endpoint was a sluggish antegrade tumor-feeding arterial flow. d-QCA and f-QCA were used for determining the relative maximal density time (rT{sub max}) of the selected arteries. The rT{sub max} of the selected arteries was analyzed in d-QCA and f-QCA before and after TACE, and itsmore » correlation in both analyses was evaluated.ResultsThe pre- and post-TACE rT{sub max} of the embolized segmental artery in d-QCA and f-QCA were 1.59 ± 0.81 and 2.97 ± 1.80 s (P < 0.001) and 1.44 ± 0.52 and 2.28 ± 1.02 s (P < 0.01), respectively. The rT{sub max} of the proximal hepatic artery did not significantly change during TACE in d-QCA and f-QCA. The Spearman correlation coefficients of the pre- and post-TACE rT{sub max} of the embolized segmental artery between d-QCA and f-QCA were 0.46 (P < 0.05) and 0.80 (P < 0.001). Radiation doses in one series of d-QCA and f-QCA were 140.7 ± 51.5 milligray (mGy) and 2.5 ± 0.7 mGy, respectively.Conclusionsf-QCA can quantify arterial flow changes with a higher temporal resolution and lower radiation dose. Flow quantification of the embolized segmental artery using f-QCA and d-QCA is highly correlated.« less

[Determination of total and segmental colonic transit time in constipated children].

PubMed

Zhang, Shu-cheng; Wang, Wei-lin; Bai, Yu-zuo; Yuan, Zheng-wei; Wang, Wei

2003-03-01

To determine the total and segmental colonic transit time of normal Chinese children and to explore its value in constipation in children. The subjects involved in this study were divided into 2 groups. One group was control, which had 33 healthy children (21 males and 12 females) aged 2 - 13 years (mean 5 years). The other was constipation group, which had 25 patients (15 males and 10 females) aged 3 - 14 years (mean 7 years) with constipation according to Benninga's criteria. Written informed consent was obtained from the parents of each subject. In this study the simplified method of radio opaque markers was used to determine the total gastrointestinal transit time and segmental colonic transit time of the normal and constipated children, and in part of these patients X-ray defecography was also used. The total gastrointestinal transit time (TGITT), right colonic transit time (RCTT), left colonic transit time (LCTT) and rectosigmoid colonic transit time (RSTT) of the normal children were 28.7 +/- 7.7 h, 7.5 +/- 3.2 h, 6.5 +/- 3.8 h and 13.4 +/- 5.6 h, respectively. In the constipated children, the TGITT, LCTT and RSTT were significantly longer than those in controls (92.2 +/- 55.5 h vs 28.7 +/- 7.7 h, P < 0.001; 16.9 +/- 12.6 h vs 6.5 +/- 3.8 h, P < 0.01; 61.5 +/- 29.0 h vs 13.4 +/- 5.6 h, P < 0.001), while the RCTT had no significant difference. X-ray defecography demonstrated one rectocele, one perineal descent syndrome and one puborectal muscle syndrome, respectively. The TGITT, RCTT, LCTT and RSTT of the normal children were 28.7 +/- 7.7 h, 7.5 +/- 3.2 h, 6.5 +/- 3.8 h and 13.4 +/- 5.6 h, respectively. With the segmental colonic transit time, constipation can be divided into four types: slow-transit constipation, outlet obstruction, mixed type and normal transit constipation. X-ray defecography can demonstrate the anatomical or dynamic abnormalities within the anorectal area, with which constipation can be further divided into different subtypes, and

Viscoelastic dynamic arterial response.

PubMed

Charalambous, Haralambia P; Roussis, Panayiotis C; Giannakopoulos, Antonios E

2017-10-01

Arteries undergo large deformations under applied intraluminal pressure and may exhibit small hysteresis due to creep or relaxation process. The mechanical response of arteries depends, among others, on their topology along the arterial tree. Viscoelasticity of arterial tissues, which is the topic investigated in this study, is mainly a characteristic mechanical response of arteries that are located away from the heart and have increased smooth muscle cells content. The arterial wall viscosity is simulated by adopting a generalized Maxwell model and the method of internal variables, as proposed by Bonet and Holzapfel et al. The total stresses consist of elastic long-term stresses and viscoelastic stresses, requiring an iterative procedure for their calculation. The cross-section of the artery is modeled as a circular ring, consisting of a single homogenized layer, under a time-varying blood pressure. Two different loading approximations for the aortic pressure vs time are considered. A novel numerical method is developed in order to solve the controlling integro-differential equation. A large number of numerical investigations are performed and typical response time-profiles are presented in pictorial form. Results suggest that the viscoelastic arterial response is mainly affected by the ratio of the relaxation time to the characteristic time of the response and by the pressure-time approximation. Numerical examples, based on data available in the literature, are conducted. The investigation presented in this study reveals the effect of each material parameter on the viscoelastic arterial response. Thus, a better understanding of the behavior of viscoelastic arteries is achieved. Copyright © 2017 Elsevier Ltd. All rights reserved.

A Catalog of Transit Timing Posterior Distributions for all Kepler Planet Candidate Events

NASA Astrophysics Data System (ADS)

Montet, Benjamin Tyler; Becker, Juliette C.; Johnson, John

2015-08-01

Kepler has ushered in a new era of planetary dynamics, enabling the detection of interactions between multiple planets in transiting systems for hundreds of systems. These interactions, observed as transit timing variations (TTVs), have been used to find non-transiting companions to transiting systems and to measure masses, eccentricities, and inclinations of transiting planets. Often, physical parameters are inferred by comparing the observed light curve to the result of a photodynamical model, a time-intensive process that often ignores the effects of correlated noise in the light curve. Catalogs of transit timing observations have previously neglected non-Gaussian uncertainties in the times of transit, uncertainties in the transit shape, and short cadence data. Here, we present a catalog of not only times of transit centers, but also posterior distributions on the time of transit for every planet candidate transit event in the Kepler data, developed through importance sampling of each transit. This catalog allows us to marginalize over uncertainties in the transit shape and incorporate short cadence data, the effects of correlated noise, and non-Gaussian posteriors. Our catalog will enable dynamical studies that reflect accurately the precision of Kepler and its limitations without requiring the computational power to model the light curve completely with every integration.

Arterial stiffness in obstructive sleep apnoea: Is there a difference between daytime and night-time?

PubMed

Sarinc Ulasli, Sevinc; Sariaydin, Muzaffer; Ozkececi, Gulay; Gunay, Ersin; Halici, Bilal; Unlu, Mehmet

2016-11-01

Obstructive sleep apnoea syndrome (OSAS) is a common chronic systemic disease in the general population, with known associated cardiovascular outcomes. We aimed to investigate arterial stiffness in OSAS patients and compare daytime and night-time values with control subjects. A total of 104 patients undergoing investigation for OSAS with polysomnography also underwent pulse wave velocity (PWV) and augmentation index (AIx) measurements with Mobil-O-Graph for 24 h. Eighty-two patients were found to have OSAS and 22 did not have OSAS and acted as controls. PWV values of the 82 OSAS patients during the 24-h period, both daytime and night-time, were significantly higher than that of the control subjects. Moreover, night-time levels of AIx were significantly higher in OSAS patients than control subjects (P = 0.025). PWV during night-time was higher than daytime measurements in OSAS patients (P = 0.012). Apnoea hypopnoea index (AHI) was significantly correlated with PWV and AIx over 24 h (P = 0.0001, r = 0.412; P = 0.002, r = 0.333, respectively). Positive correlations were also found between oxygen desaturation index (ODI) with PWV and AIx during the night (P = 0.0001, r = 0.480; P = 0.002, r = 0.325, respectively). However, daytime AIx was not significantly correlated with ODI (P = 0.052, r = 0.205). OSAS patients, without known cardiovascular disease, have increased PWV, indicating an increased arterial stiffness, compared with control subjects and correlations between AHI and arterial stiffness indices suggest increased arterial stiffness with increased disease severity. Therefore, arterial stiffness should be considered as a possible cause for cardiovascular complications in OSAS patients. © 2016 Asian Pacific Society of Respirology.

Daylight Savings Time Transitions and the Incidence Rate of Unipolar Depressive Episodes.

PubMed

Hansen, Bertel T; Sønderskov, Kim M; Hageman, Ida; Dinesen, Peter T; Østergaard, Søren D

2017-05-01

Daylight savings time transitions affect approximately 1.6 billion people worldwide. Prior studies have documented associations between daylight savings time transitions and adverse health outcomes, but it remains unknown whether they also cause an increase in the incidence rate of depressive episodes. This seems likely because daylight savings time transitions affect circadian rhythms, which are implicated in the etiology of depressive disorder. Therefore, we investigated the effects of daylight savings time transitions on the incidence rate of unipolar depressive episodes. Using time series intervention analysis of nationwide data from the Danish Psychiatric Central Research Register from 1995 to 2012, we compared the observed trend in the incidence rate of hospital contacts for unipolar depressive episodes after the transitions to and from summer time to the predicted trend in the incidence rate. The analyses were based on 185,419 hospital contacts for unipolar depression and showed that the transition from summer time to standard time were associated with an 11% increase (95% CI = 7%, 15%) in the incidence rate of unipolar depressive episodes that dissipated over approximately 10 weeks. The transition from standard time to summer time was not associated with a parallel change in the incidence rate of unipolar depressive episodes. This study shows that the transition from summer time to standard time was associated with an increase in the incidence rate of unipolar depressive episodes. Distress associated with the sudden advancement of sunset, marking the coming of a long period of short days, may explain this finding. See video abstract at, http://links.lww.com/EDE/B179.

Novel blood pressure and pulse pressure estimation based on pulse transit time and stroke volume approximation.

PubMed

Lee, Joonnyong; Sohn, JangJay; Park, Jonghyun; Yang, SeungMan; Lee, Saram; Kim, Hee Chan

2018-06-18

Non-invasive continuous blood pressure monitors are of great interest to the medical community due to their value in hypertension management. Recently, studies have shown the potential of pulse pressure as a therapeutic target for hypertension, but not enough attention has been given to non-invasive continuous monitoring of pulse pressure. Although accurate pulse pressure estimation can be of direct value to hypertension management and indirectly to the estimation of systolic blood pressure, as it is the sum of pulse pressure and diastolic blood pressure, only a few inadequate methods of pulse pressure estimation have been proposed. We present a novel, non-invasive blood pressure and pulse pressure estimation method based on pulse transit time and pre-ejection period. Pre-ejection period and pulse transit time were measured non-invasively using electrocardiogram, seismocardiogram, and photoplethysmogram measured from the torso. The proposed method used the 2-element Windkessel model to model pulse pressure with the ratio of stroke volume, approximated by pre-ejection period, and arterial compliance, estimated by pulse transit time. Diastolic blood pressure was estimated using pulse transit time, and systolic blood pressure was estimated as the sum of the two estimates. The estimation method was verified in 11 subjects in two separate conditions with induced cardiovascular response and the results were compared against a reference measurement and values obtained from a previously proposed method. The proposed method yielded high agreement with the reference (pulse pressure correlation with reference R ≥ 0.927, diastolic blood pressure correlation with reference R ≥ 0.854, systolic blood pressure correlation with reference R ≥ 0.914) and high estimation accuracy in pulse pressure (mean root-mean-squared error ≤ 3.46 mmHg) and blood pressure (mean root-mean-squared error ≤ 6.31 mmHg for diastolic blood pressure and ≤ 8.41�

Qatar-1: indications for possible transit timing variations

NASA Astrophysics Data System (ADS)

von Essen, C.; Schröter, S.; Agol, E.; Schmitt, J. H. M. M.

2013-07-01

Aims: Variations in the timing of transiting exoplanets provide a powerful tool for detecting additional planets in the system. Thus, the aim of this paper is to discuss the plausibility of transit timing variations (TTVs) on the Qatar-1 system by means of primary transit light curves analysis. Furthermore, we provide an interpretation of the timing variation. Methods: We observed Qatar-1 between March 2011 and October 2012 using the 1.2 m OLT telescope in Germany and the 0.6 m PTST telescope in Spain. We present 26 primary transits of the hot Jupiter Qatar-1b. In total, our light curves cover a baseline of 18 months. Results: We report on indications for possible long-term TTVs. Assuming that these TTVs are true, we present two different scenarios that could explain them. Our reported ~190 days TTV signal can be reproduced by either a weak perturber in resonance with Qatar-1b, or by a massive body in the brown dwarf regime. More observations and radial velocity monitoring are required to better constrain the perturber's characteristics. We also refine the ephemeris of Qatar-1b, which we find to be T0 = 2456157.42204 ± 0.0001 BJDTDB and P = 1.4200246 ± 0.0000007 days, and improve the system orbital parameters. Tables of the transit observations are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A92

[Doppler ultrasound evaluation of aortic insufficiency using half-pressure time. Absence of arterial rigidity influence].

PubMed

Kalotka-Bratek, H; Drobinski, G; Klimczak, K; Busquet, P; Fraysse, J B; Bejean-Lebuisson, A; Grosgogeat, Y

1989-02-01

In 20 patients with pure aortic regurgitation we studied the relationship between the severity of regurgitation, as assessed haemodynamically by the percentage of leakage (%L), and the half-pressure (T 1/2 P) and half-velocity (T 1/2 V) times, as obtained from doppler aortic blood velocity curves, taking into account the rigidity of the systemic vascular circuit characterized by the pressure wave propagation velocity (PWPV). The systemic arterial circuit was supple in 14 patients (PWPV less than 7.5 m/sec) and rigid in 6 patients (PWPV greater than 7.5 m/sec). The regression slopes between %L and T 1/2 P and between %L and T 1/2 V were calculated with their confidence limits in the 14 patients with supple arteries. The 6 patients with rigid arteries fitted into this nomogram, thus demonstrating that systemic arterial rigidity makes no difference in the relationship between %L and doppler indices. The half-velocity and half-pressure times measured by doppler ultrasound were acquired from a velocity signal directly determined by the aortic regurgitation, without any detectable effect of vascular circuit rigidity. Being equivalent by nature to the signal decrease time constant, they are independent of the absolute protodiastolic value of diastolic pressure gradient or blood flow velocity. For this reason these two doppler parameters are reliable to evaluate the severity of aortic regurgitation.

Carotid Artery Stenting and Blood-Brain Barrier Permeability in Subjects with Chronic Carotid Artery Stenosis.

PubMed

Szarmach, Arkadiusz; Halena, Grzegorz; Kaszubowski, Mariusz; Piskunowicz, Maciej; Studniarek, Michal; Lass, Piotr; Szurowska, Edyta; Winklewski, Pawel J

2017-05-08

Failure of the blood-brain barrier (BBB) is a critical event in the development and progression of diseases such as acute ischemic stroke, chronic ischemia or small vessels disease that affect the central nervous system. It is not known whether BBB breakdown in subjects with chronic carotid artery stenosis can be restrained with postoperative recovery of cerebral perfusion. The aim of the study was to assess the short-term effect of internal carotid artery stenting on basic perfusion parameters and permeability surface area-product (PS) in such a population. Forty subjects (23 males) with stenosis of >70% within a single internal carotid artery and neurological symptoms who underwent a carotid artery stenting procedure were investigated. Differences in the following computed tomography perfusion (CTP) parameters were compared before and after surgery: global cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), time to peak (TTP) and PS. PS acquired by CTP is used to measure the permeability of the BBB to contrast material. In all baseline cases, the CBF and CBV values were low, while MTT and TTP were high on both the ipsi- and contralateral sides compared to reference values. PS was approximately twice the normal value. CBF was higher (+6.14%), while MTT was lower (-9.34%) on the contralateral than on the ipsilateral side. All perfusion parameters improved after stenting on both the ipsilateral (CBF +22.66%; CBV +18.98%; MTT -16.09%, TTP -7.62%) and contralateral (CBF +22.27%, CBV +19.72%, MTT -14.65%, TTP -7.46%) sides. PS decreased by almost half: ipsilateral -48.11%, contralateral -45.19%. The decline in BBB permeability was symmetrical on the ipsi- and contralateral sides to the stenosis. Augmented BBB permeability can be controlled by surgical intervention in humans.

Time-of-Flight MR Angiography for Detection of Cerebral Hyperperfusion Syndrome after Superficial Temporal Artery-Middle Cerebral Artery Anastomosis in Moyamoya Disease.

PubMed

Sato, K; Yamada, M; Kuroda, H; Yamamoto, D; Asano, Y; Inoue, Y; Fujii, K; Kumabe, T

2016-07-01

Cerebral hyperperfusion syndrome is a potential complication of superficial temporal artery-MCA anastomosis for Moyamoya disease. In this study, we evaluated whether TOF-MRA could assess cerebral hyperperfusion syndrome after superficial temporal artery-MCA anastomosis for this disease. This retrospective study included patients with Moyamoya disease who underwent superficial temporal artery-MCA single anastomosis. TOF-MRA and SPECT were performed before and 1-6 days after anastomosis. Bilateral ROIs on the source image of TOF-MRA were manually placed directly on the parietal branch of the superficial temporal artery just after branching the frontal branch of the superficial temporal artery and on the contralateral superficial temporal artery on the same axial image, respectively. The change ratio of the maximum signal intensity of the superficial temporal artery on TOF-MRA was calculated by using the following formula: (Postoperative Ipsilateral/Postoperative Contralateral)/(Preoperative Ipsilateral/Preoperative Contralateral). Of 23 patients (26 sides) who underwent the operation, 5 sides showed cerebral hyperperfusion syndrome postoperatively. There was a significant difference in the change ratio of signal intensity on TOF-MRA observed between the cerebral hyperperfusion syndrome and non-cerebral hyperperfusion syndrome groups (cerebral hyperperfusion syndrome group: 1.88 ± 0.32; non-cerebral hyperperfusion syndrome group: 1.03 ± 0.20; P = .0009). The minimum ratio value for the cerebral hyperperfusion syndrome group was 1.63, and the maximum ratio value for the non-cerebral hyperperfusion syndrome group was 1.30. Thus, no overlap was observed between the 2 groups for the change ratio of signal intensity on TOF-MRA. Diagnosis of cerebral hyperperfusion syndrome is indicated by an increase in the change ratio of signal intensity on TOF-MRA by more than approximately 1.5 times the preoperative levels. © 2016 by American Journal of Neuroradiology.

Three-Dimensional Localized-Delocalized Anderson Transition in the Time Domain

NASA Astrophysics Data System (ADS)

Delande, Dominique; Morales-Molina, Luis; Sacha, Krzysztof

2017-12-01

Systems which can spontaneously reveal periodic evolution are dubbed time crystals. This is in analogy with space crystals that display periodic behavior in configuration space. While space crystals are modeled with the help of space periodic potentials, crystalline phenomena in time can be modeled by periodically driven systems. Disorder in the periodic driving can lead to Anderson localization in time: the probability for detecting a system at a fixed point of configuration space becomes exponentially localized around a certain moment in time. We here show that a three-dimensional system exposed to a properly disordered pseudoperiodic driving may display a localized-delocalized Anderson transition in the time domain, in strong analogy with the usual three-dimensional Anderson transition in disordered systems. Such a transition could be experimentally observed with ultracold atomic gases.

Instantaneous frequency time analysis of physiology signals: The application of pregnant women’s radial artery pulse signals

NASA Astrophysics Data System (ADS)

Su, Zhi-Yuan; Wang, Chuan-Chen; Wu, Tzuyin; Wang, Yeng-Tseng; Tang, Feng-Cheng

2008-01-01

This study used the Hilbert-Huang transform, a recently developed, instantaneous frequency-time analysis, to analyze radial artery pulse signals taken from women in their 36th week of pregnancy and after pregnancy. The acquired instantaneous frequency-time spectrum (Hilbert spectrum) is further compared with the Morlet wavelet spectrum. Results indicate that the Hilbert spectrum is especially suitable for analyzing the time series of non-stationary radial artery pulse signals since, in the Hilbert-Huang transform, signals are decomposed into different mode functions in accordance with signal’s local time scale. Therefore, the Hilbert spectrum contains more detailed information than the Morlet wavelet spectrum. From the Hilbert spectrum, we can see that radial artery pulse signals taken from women in their 36th week of pregnancy and after pregnancy have different patterns. This approach could be applied to facilitate non-invasive diagnosis of fetus’ physiological signals in the future.

Arterial spin labelling reveals prolonged arterial arrival time in idiopathic Parkinson's disease.

PubMed

Al-Bachari, Sarah; Parkes, Laura M; Vidyasagar, Rishma; Hanby, Martha F; Tharaken, Vivek; Leroi, Iracema; Emsley, Hedley C A

2014-01-01

Idiopathic Parkinson's disease (IPD) is the second most common neurodegenerative disease, yet effective disease modifying treatments are still lacking. Neurodegeneration involves multiple interacting pathological pathways. The extent to which neurovascular mechanisms are involved is not well defined in IPD. We aimed to determine whether novel magnetic resonance imaging (MRI) techniques, including arterial spin labelling (ASL) quantification of cerebral perfusion, can reveal altered neurovascular status (NVS) in IPD. Fourteen participants with IPD (mean ± SD age 65.1 ± 5.9 years) and 14 age and cardiovascular risk factor matched control participants (mean ± SD age 64.6 ± 4.2 years) underwent a 3T MRI scan protocol. ASL images were collected before, during and after a 6 minute hypercapnic challenge. FLAIR images were used to determine white matter lesion score. Quantitative images of cerebral blood flow (CBF) and arterial arrival time (AAT) were calculated from the ASL data both at rest and during hypercapnia. Cerebrovascular reactivity (CVR) images were calculated, depicting the change in CBF and AAT relative to the change in end-tidal CO2. A significant (p = 0.005) increase in whole brain averaged baseline AAT was observed in IPD participants (mean ± SD age 1532 ± 138 ms) compared to controls (mean ± SD age 1335 ± 165 ms). Voxel-wise analysis revealed this to be widespread across the brain. However, there were no statistically significant differences in white matter lesion score, CBF, or CVR between patients and controls. Regional CBF, but not AAT, in the IPD group was found to correlate positively with Montreal cognitive assessment (MoCA) scores. These findings provide further evidence of alterations in NVS in IPD.

Does the transition into daylight saving time really cause partial sleep deprivation?

PubMed

Toth Quintilham, Manoel Carlos; Adamowicz, Taísa; Pereira, Erico Felden; Pedrazzoli, Mario; Louzada, Fernando Mazzilli

2014-01-01

To identify possible changes in the sleep patterns according to chronotype in undergraduate students during the daylight saving time (DST) transition. A total of 378 students answered the Morningness-Eveningness Questionnaire (MEQ) to determine their chronotype and kept a diary about sleep-wake schedules 1 week before and after the DST transition. Oral mucosal cell samples were collected for genetic analysis. After the DST transition, intermediate types (I-types) delayed bedtime and increased their time in bed and all groups delayed their wake-up time. All groups presented a shorter phase angle between sunset and the bedtime after the DST transition. On the other hand, only E-types showed a tendency to reduce the phase angle between sunrise and wake-up time, while I-types and M-types kept the same phase angles between sunrise and wake-up time after the DST transition. The polymorphisms in the human genes CLOCK and PER3 were not associated with individual differences in sleep patterns, nor were they associated with an adjustment to the DST transition. Under the new set of social times determined by DST, the adjustment was only partial. I-types delayed bedtime and all groups delayed their wake-up times after the beginning of DST. Consequently, the time in bed after the DST transition was not reduced; Morning (M-types) and Evening-types (E-types) kept the same time in bed and I-types showed an increase on it.

Linking age, survival, and transit time distributions

NASA Astrophysics Data System (ADS)

Calabrese, Salvatore; Porporato, Amilcare

2015-10-01

Although the concepts of age, survival, and transit time have been widely used in many fields, including population dynamics, chemical engineering, and hydrology, a comprehensive mathematical framework is still missing. Here we discuss several relationships among these quantities by starting from the evolution equation for the joint distribution of age and survival, from which the equations for age and survival time readily follow. It also becomes apparent how the statistical dependence between age and survival is directly related to either the age dependence of the loss function or the survival-time dependence of the input function. The solution of the joint distribution equation also allows us to obtain the relationships between the age at exit (or death) and the survival time at input (or birth), as well as to stress the symmetries of the various distributions under time reversal. The transit time is then obtained as a sum of the age and survival time, and its properties are discussed along with the general relationships between their mean values. The special case of steady state case is analyzed in detail. Some examples, inspired by hydrologic applications, are presented to illustrate the theory with the specific results. This article was corrected on 11 Nov 2015. See the end of the full text for details.

Taste and Temperature in Swallowing Transit Time after Stroke

PubMed Central

Cola, Paula C.; Gatto, Ana R.; da Silva, Roberta G.; Spadotto, André A.; Ribeiro, Priscila W.; Schelp, Arthur O.; Carvalho, Lidia R.; Henry, Maria A.C.A.

2012-01-01

Background Oropharyngeal dysphagia is common in individuals after stroke. Taste and temperature are used in dysphagia rehabilitation. The influence of stimuli, such as taste and temperature, on swallowing biomechanics has been investigated in both healthy individuals and in individuals with neurological disease. However, some questions still remain unanswered, such as how the sequence of offered stimuli influences the pharyngeal response. The goal of the present study was to determine the influence of the sequence of stimuli, sour taste and cold temperature, on pharyngeal transit time during deglutition in individuals after stroke. Methods The study included 60 individuals with unilateral ischemic stroke, 29 males and 31 females, aged 41–88 years (mean age: 66.2 years) examined 0–50 days after ictus (median: 6 days), with mild to moderate oropharyngeal dysphagia. Exclusion criteria were hemorrhagic stroke patients, patients with decreased level of consciousness, and clinically unstable patients, as confirmed by medical evaluation. The individuals were divided into two groups of 30 individuals each. Group 1 received a nonrandomized sequence of stimuli (i.e. natural, cold, sour, and sour-cold) and group 2 received a randomized sequence of stimuli. A videofluoroscopic swallowing study was performed to analyze the pharyngeal transit time. Four different stimuli (natural, cold, sour, and sour-cold) were offered. The images were digitalized and specific software was used to measure the pharyngeal transit time. Since the values did not present regular distribution and uniform variances, nonparametric tests were performed. Results Individuals in group 1 presented a significantly shorter pharyngeal transit time with the sour-cold stimulus than with the other stimuli. Individuals in group 2 did not show a significant difference in pharyngeal transit time between stimuli. Conclusions The results showed that the sequence of offered stimuli influences the pharyngeal transit

Clinical utility of time-resolved imaging of contrast kinetics (TRICKS) magnetic resonance angiography for infrageniculate arterial occlusive disease.

PubMed

Mell, Matthew; Tefera, Girma; Thornton, Frank; Siepman, David; Turnipseed, William

2007-03-01

The diagnostic accuracy of magnetic resonance angiography (MRA) in the infrapopliteal arterial segment is not well defined. This study evaluated the clinical utility and diagnostic accuracy of time-resolved imaging of contrast kinetics (TRICKS) MRA compared with digital subtraction contrast angiography (DSA) in planning for percutaneous interventions of popliteal and infrapopliteal arterial occlusive disease. Patients who underwent percutaneous lower extremity interventions for popliteal or tibial occlusive disease were identified for this study. Preprocedural TRICKS MRA was performed with 1.5 Tesla (GE Healthcare, Waukesha, Wis) magnetic resonance imaging scanners with a flexible peripheral vascular coil, using the TRICKS technique with gadodiamide injection. DSA was performed using standard techniques in angiography suite with a 15-inch image intensifier. DSA was considered the gold standard. The MRA and DSA were then evaluated in a blinded fashion by a radiologist and a vascular surgeon. The popliteal artery and tibioperoneal trunk were evaluated separately, and the tibial arteries were divided into proximal, mid, and distal segments. Each segment was interpreted as normal (0% to 49% stenosis), stenotic (50% to 99% stenosis), or occluded (100%). Lesion morphology was classified according to the TransAtlantic Inter-Society Consensus (TASC). We calculated concordance between the imaging studies and the sensitivity and specificity of MRA. The clinical utility of MRA was also assessed in terms of identifying arterial access site as well as predicting technical success of the percutaneous treatment. Comparisons were done on 150 arterial segments in 30 limbs of 27 patients. When evaluated by TASC classification, TRICKS MRA correlated with DSA in 83% of the popliteal and in 88% of the infrapopliteal segments. MRA correctly identified significant disease of the popliteal artery with a sensitivity of 94% and a specificity of 92%, and of the tibial arteries with a

Development and Application of the Transit Timing Planet Detection Technique

NASA Astrophysics Data System (ADS)

Steffen, J. H.; Agol, E.

2005-12-01

We present the development and application of a new planet detection technique that uses the transit timing of a known, transiting planet. The transits of a solitary planet orbiting a star occur at equally spaced intervals in time. If a second planet is present, then dynamical interactions within the system will cause the time interval between transits to vary. These transit time variations (TTV) can be used to infer the orbital elements and mass of the unseen, perturbing planet. In some cases, particularly near mean-motion resonances, this technique could detect planets with masses less than the mass of the Earth---a capability not yet achieved by other planet detection schemes. We present an analysis of the set of transit times of the TrES-1 system given by Charbonneau et al. (2005). While no convincing evidence for a second planet in the TrES-1 system was found from that data, we constrain the mass that a perturbing planet could have as a function of the semi-major axis ratio of the two planets and the eccentricity of the perturbing planet. Near low-order, mean-motion resonances (within about 1% fractional deviation), we find that a secondary planet must generally have a mass comparable to or less than the mass of the Earth--showing that this data is the first to have sensitivity to sub Earth-mass planets. We present results from our studies that use simulated data and from an ongoing analysis of the HD209458 system. These results show that TTV will be an important tool in the detection and characterization of extrasolar planetary systems.

A turbulence model for pulsatile arterial flows.

PubMed

Younis, B A; Berger, S A

2004-10-01

Difficulties in predicting the behavior of some high Reynolds number flows in the circulatory system stem in part from the severe requirements placed on the turbulence model chosen to close the time-averaged equations of fluid motion. In particular, the successful turbulence model is required to (a) correctly capture the "nonequilibrium" effects wrought by the interactions of the organized mean-flow unsteadiness with the random turbulence, (b) correctly reproduce the effects of the laminar-turbulent transitional behavior that occurs at various phases of the cardiac cycle, and (c) yield good predictions of the near-wall flow behavior in conditions where the universal logarithmic law of the wall is known to be not valid. These requirements are not immediately met by standard models of turbulence that have been developed largely with reference to data from steady, fully turbulent flows in approximate local equilibrium. The purpose of this paper is to report on the development of a turbulence model suited for use in arterial flows. The model is of the two-equation eddy-viscosity variety with dependent variables that are zero-valued at a solid wall and vary linearly with distance from it. The effects of transition are introduced by coupling this model to the local value of the intermittency and obtaining the latter from the solution of a modeled transport equation. Comparisons with measurements obtained in oscillatory transitional flows in circular tubes show that the model produces substantial improvements over existing closures. Further pulsatile-flow predictions, driven by a mean-flow wave form obtained in a diseased human carotid artery, indicate that the intermittency-modified model yields much reduced levels of wall shear stress compared to the original, unmodified model. This result, which is attributed to the rapid growth in the thickness of the viscous sublayer arising from the severe acceleration of systole, argues in favor of the use of the model for the

Development of an Experimental and Digital Cardiovascular Arterial Model for Transient Hemodynamic and Postural Change Studies: "A Preliminary Framework Analysis".

PubMed

Hewlin, Rodward L; Kizito, John P

2018-03-01

specific geometries, a MATLAB code was written to upload the CTA scans of each artery, calculate the centroids, and produce surface splines at each discrete cross section along the lumen centerline to create the patient specific arterial geometries. The MATLAB code worked in conjunction with computer aided software (CAD) Solidworks to produce solid models of the patient specific geometries and united them with the simplified geometries to produce the full arterial model (CAD model). The CAD model was also used as a blueprint to fabricate the experimental model which was used for flow visualization via particle imaging velocimetry (PIV) and postural change studies. A custom pulse duplicator (pulsatile pump) was also designed and developed for the present work. The pulse duplicator is capable of producing patient-specific volumetric waveforms for inlet flow to the experimental arterial model. A simple fluid structure interaction (FSI) study was also conducted via optical techniques to establish the magnitude of vessel diameter change due to the pulsatile flow. A medical drug delivery (dye dispersion and tracing) case was simulated via a dye being dispersed into the pulsatile flow stream to measure the transit time of the dye front. Pressure waveforms for diseased cases (hypertension & stenotic cases) were also obtained from the experimental arterial model during postural changes from bedrest (0°) to upright position (90°). The postural changes were simulated via attaching the experimental model to a tile table the can transition from 0° to 90°. The PIV results obtained from the experimental model provided parametric data such as velocity and wall shear stress data. The medical drug delivery simulations (experimental and numerical) studies produce time dependent data which is useful for predicting flow trajectory and transit time of medical drug dispersion. In the case of postural change studies, pressure waveforms were obtained from the common carotid artery and the

Time-Variable Transit Time Distributions in the Hyporheic Zone of a Headwater Mountain Stream

NASA Astrophysics Data System (ADS)

Ward, Adam S.; Schmadel, Noah M.; Wondzell, Steven M.

2018-03-01

Exchange of water between streams and their hyporheic zones is known to be dynamic in response to hydrologic forcing, variable in space, and to exist in a framework with nested flow cells. The expected result of heterogeneous geomorphic setting, hydrologic forcing, and between-feature interaction is hyporheic transit times that are highly variable in both space and time. Transit time distributions (TTDs) are important as they reflect the potential for hyporheic processes to impact biogeochemical transformations and ecosystems. In this study we simulate time-variable transit time distributions based on dynamic vertical exchange in a headwater mountain stream with observed, heterogeneous step-pool morphology. Our simulations include hyporheic exchange over a 600 m river corridor reach driven by continuously observed, time-variable hydrologic conditions for more than 1 year. We found that spatial variability at an instance in time is typically larger than temporal variation for the reach. Furthermore, we found reach-scale TTDs were marginally variable under all but the most extreme hydrologic conditions, indicating that TTDs are highly transferable in time. Finally, we found that aggregation of annual variation in space and time into a "master TTD" reasonably represents most of the hydrologic dynamics simulated, suggesting that this aggregation approach may provide a relevant basis for scaling from features or short reaches to entire networks.

A time-dependent order parameter for ultrafast photoinduced phase transitions.

PubMed

Beaud, P; Caviezel, A; Mariager, S O; Rettig, L; Ingold, G; Dornes, C; Huang, S-W; Johnson, J A; Radovic, M; Huber, T; Kubacka, T; Ferrer, A; Lemke, H T; Chollet, M; Zhu, D; Glownia, J M; Sikorski, M; Robert, A; Wadati, H; Nakamura, M; Kawasaki, M; Tokura, Y; Johnson, S L; Staub, U

2014-10-01

Strongly correlated electron systems often exhibit very strong interactions between structural and electronic degrees of freedom that lead to complex and interesting phase diagrams. For technological applications of these materials it is important to learn how to drive transitions from one phase to another. A key question here is the ultimate speed of such phase transitions, and to understand how a phase transition evolves in the time domain. Here we apply time-resolved X-ray diffraction to directly measure the changes in long-range order during ultrafast melting of the charge and orbitally ordered phase in a perovskite manganite. We find that although the actual change in crystal symmetry associated with this transition occurs over different timescales characteristic of the many electronic and vibrational coordinates of the system, the dynamics of the phase transformation can be well described using a single time-dependent 'order parameter' that depends exclusively on the electronic excitation.

TTVFaster: First order eccentricity transit timing variations (TTVs)

NASA Astrophysics Data System (ADS)

Agol, Eric; Deck, Katherine

2016-04-01

TTVFaster implements analytic formulae for transit time variations (TTVs) that are accurate to first order in the planet-star mass ratios and in the orbital eccentricities; the implementations are available in several languages, including IDL, Julia, Python and C. These formulae compare well with more computationally expensive N-body integrations in the low-eccentricity, low mass-ratio regime when applied to simulated and to actual multi-transiting Kepler planet systems.

Calculating ground water transit time of horizontal flow through leaky aquifers.

PubMed

Braunsfurth, Angelika C; Schneider, Wilfried

2008-01-01

The calculation of ground water transit times is one important factor in ground water protection. In this paper, we present an analytical solution for the transit time for a Dupuit-type flow system applicable to saturated flow through a horizontal leaky aquifer discharging to a downgradient fixed-head boundary under steady-state conditions. We investigate the influence of leakage when comparing the resulting travel times of our model based on head-dependent leakage with the commonly used model with no leakage and a simplified model with constant leakage. The results show significant differences in the position of the water divide and transit time, suggesting that leakage cannot be ignored.

Stabilisation times after transitions to standing from different working postures.

PubMed

DiDomenico, Angela; McGorry, Raymond W; Banks, Jacob J

2016-10-01

Transitioning to standing after maintaining working postures may result in imbalance and could elicit a fall. The objective of this study was to quantify the magnitude of imbalance using a stabilisation time metric. Forty-five male participants completed three replications of conditions created by one of four working postures (bent at waist, squat, forward kneel, reclined kneel) and three durations within posture. Participants transitioned to quiet standing at a self-selected pace. Stabilisation time, based on changes in centre of pressure velocity, was used to indicate the initiation of steady state while standing. Stabilisation time was significantly affected by static postures but not duration within posture. The largest stabilisation times resulted from transitions initiated from a bent at waist posture. The smallest were associated with the kneeling postures, which were not significantly different from each other. Findings may lead to recommendations for redesign of tasks, particularly in high-risk environments such as construction. Statement of Relevance: Task performance on the jobsite often requires individuals to maintain non-erect postures. This study suggests that working posture affects stabilisation during transition to a standing position. Bending at the waist and squatting resulted in longer stabilisation times, whereas both kneeling postures evaluated resulted in greater imbalance but for a shorter duration.

EPITOME-2: An open-label study assessing the transition to a new formulation of intravenous epoprostenol in patients with pulmonary arterial hypertension.

PubMed

Sitbon, Olivier; Delcroix, Marion; Bergot, Emmanuel; Boonstra, Anco B; Granton, John; Langleben, David; Subías, Pilar Escribano; Galiè, Nazzareno; Pfister, Thomas; Lemarié, Jean-Christophe; Simonneau, Gérald

2014-02-01

Continuous infusion of epoprostenol is the treatment of choice in patients with pulmonary arterial hypertension in functional classes III to IV. However, this treatment's limitations include instability at room temperature. A new epoprostenol formulation offers improved storage conditions and patient convenience. The EPITOME-2 trial was an open-label, prospective, multicenter, single-arm, phase IIIb study. Patients with pulmonary arterial hypertension on long-term, stable epoprostenol therapy were transitioned from epoprostenol with glycine and mannitol excipients (Flolan; GlaxoSmithKline, Durham, NC) to epoprostenol with arginine and sucrose excipients (Veletri; Actelion Pharmaceuticals Ltd, Allschwil, Switzerland). Patients were followed up for 3 months, and dose adjustments were recorded. Efficacy measures included the 6-minute walk distance, hemodynamics assessed by right heart catheterization, and New York Heart Association functional class. Safety and tolerability of the transition were also evaluated. Quality of life was assessed using the Treatment Satisfaction Questionnaire for Medication. Forty-two patients enrolled in the study, and 1 patient withdrew consent before treatment; thus, 41 patients received treatment and completed the study. Six patients required dose adjustments. There were no clinically relevant changes from baseline to month 3 in any of the efficacy end points. Adverse events were those previously described with intravenous prostacyclin therapy. Treatment Satisfaction Questionnaire for Medication scores showed an improvement from baseline to month 3 in the domain of treatment convenience. Transition from epoprostenol with glycine and mannitol excipients to epoprostenol with arginine and sucrose excipients did not affect treatment efficacy, raised no new safety or tolerability concerns, and provided patients with an increased sense of treatment convenience. © 2014.

Retinal artery occlusion during carotid artery stenting with distal embolic protection device.

PubMed

Kohara, Kotaro; Ishikawa, Tatsuya; Kobayashi, Tomonori; Kawamata, Takakazu

2018-01-01

Retinal artery occlusion associated with carotid artery stenosis is well known. Although it can also occur at the time of carotid artery stenting, retinal artery occlusion via the collateral circulation of the external carotid artery is rare. We encountered two cases of retinal artery occlusion that were thought to be caused by an embolus from the external carotid artery during carotid artery stenting with a distal embolic protection device for the internal carotid artery. A 71-year-old man presented with central retinal artery occlusion after carotid artery stenting using the Carotid Guardwire PS and a 77-year-old man presented with branch retinal artery occlusion after carotid artery stenting using the FilterWire EZ. Because additional new cerebral ischaemic lesions were not detected in either case by postoperative diffusion-weighted magnetic resonance imaging, it was highly likely that the debris that caused retinal artery occlusion passed through not the internal carotid artery but collaterals to retinal arteries from the external carotid artery, which was not protected by a distal embolic protection device. It is suggested that a distal protection device for the internal carotid artery alone cannot prevent retinal artery embolisation during carotid artery stenting and protection of the external carotid artery is important to avoid retinal artery occlusion.

Safety and feasibility audit of a home-based drug-transitioning approach for patients with pulmonary arterial hypertension: an observational study.

PubMed

Dawson, A; Reddecliffe, S; Coghlan, C; Schreiber, B E; Coghlan, J G

2018-04-01

Newer endothelin receptor antagonists (ERAs) used to treat patients with pulmonary arterial hypertension (PAH) are associated with fewer drug-drug interactions than bosentan and require less monitoring. This, combined with a pharmacokinetic basis for improved efficacy, means there may be a clinical rationale for changing therapies. However, this can be challenging and few data on its safety in patients with PAH are available. At the Royal Free Hospital in London, UK, home-based medication transitioning has been standard practice since 2009 to avoid unnecessary hospital visits for patients, unless there is a clinical imperative. In this audit of standard practice we evaluated the consequences of adopting such a strategy when transitioning PAH patients between ERA therapies. Using a Clinical Nurse Specialist-led, home-based transitioning strategy, 92 patients with PAH were transitioned from bosentan to macitentan or ambrisentan. Observational data were analysed retrospectively. The majority of patients were female with PAH associated with connective tissue disease and their ERA was changed in the hope of improving efficacy. The process was well tolerated with no adverse events associated with the process. Seventeen patients died during the study (macitentan, n = 5; ambrisentan, n = 12). None of the deaths was considered related to ERA treatment. The majority of patients remained clinically stable, based on WHO functional class and exercise capacity. An established home-based transitioning strategy can be adopted safely for patients with PAH changing ERA therapies. Most patients remained stable and the therapy change was well tolerated.

Using Dielectric Relaxation Spectroscopy to Characterize the Glass Transition Time of Polydextrose.

PubMed

Buehler, Martin G; Kindle, Michael L; Carter, Brady P

2015-06-01

Dielectric relaxation spectroscopy was used to characterize the glass transition time, tg , of polydextrose, where the glass transition temperature, Tg , and water activity, aw (relative humidity), were held constant during polydextrose relaxation. The tg was determined from a shift in the peak frequency of the imaginary capacitance spectrum with time. It was found that when the peak frequency reaches 30 mHz, polydextrose undergoes glass transition. Glass transition time, tg , is the time for polydextrose to undergo glass transition at a specific Tg and aw . Results lead to a modified state diagram, where Tg is depressed with increasing aw . This curve forms a boundary: (a) below the boundary, polydextrose does not undergo glass transition and (b) above the boundary, polydextrose rapidly undergoes glass transition. As the boundary curve is specified by a tg value, it can assist in the selection of storage conditions. An important point on the boundary curve is at aw = 0, where Tg0 = 115 °C. The methodology can also be used to calculate the stress-relaxation viscosity of polydextrose as a function of Tg and aw , which is important when characterizing the flow properties of polydextrose initially in powder form. © 2015 Institute of Food Technologists®

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.

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

Real-Time Elastography Visualization and Histopathological Characterization of Rabbit Atherosclerotic Carotid Arteries.

PubMed

Wang, ZhenZhen; Liu, NaNa; Zhang, LiFeng; Li, XiaoYing; Han, XueSong; Peng, YanQing; Dang, MeiZheng; Sun, LiTao; Tian, JiaWei

2016-01-01

To evaluate the feasibility of non-invasive vascular real-time elastography imaging (RTE) in visualizing the composition of rabbit carotid atherosclerotic plaque as determined by histopathology, a rabbit model of accelerated carotid atherosclerosis was used. Thirty rabbits were randomly divided into two groups of 15 rabbits each. The first group was fed a cholesterol-rich diet and received balloon-induced injury the left common carotid artery endothelium, whereas the second group only received a cholesterol-rich diet. The rabbits were all examined in vivo with HITACHI non-invasive vascular real-time elastography (Hi-RTE) at baseline and 12 wk, and results from the elastography were compared with American Heart Association histologic classifications. Hi-RTE and the American Heart Association histologic classifications had good agreement, with weighted Cohen's kappa (95% confidence internal) of 0.785 (0.649-0.920). Strains of segmented plaques that were stained in different colors were statistically different (p < 0.0001). The sensitivity and specificity of elastograms for detecting a lipid core were 95.5% and 61.5%, respectively, and the area under the receiver operating characteristic curve was 0.789, with a 95% confidence interval of 0.679 to 0.876. This study is the first to indicate the feasibility of utilizing Hi-RTE in visualizing normal and atherosclerotic rabbit carotid arteries non-invasively. This affordable and reliable method can be widely applied in research of both animal and human peripheral artery atherosclerosis. Copyright © 2016 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

A simple on-line arterial time-activity curve detector for [O-15] water PET studies

NASA Astrophysics Data System (ADS)

Wollenweber, S. D.; Hichwa, R. D.; Ponto, L. L. B.

1997-08-01

A simple, automated on-line detector system has been fabricated and implemented to detect the arterial time-activity curve (TAG) for bolus-injection [O-15] water PET studies. This system offers two significant improvements over existing systems: a pump mechanism is not required to control arterial blood flow through the detector and dispersion correction of the time-activity curve for dispersion in external tubing is unnecessary. The [O-15] positrons emanating from blood within a thin-walled, 0.134 cm inner-diameter plastic tube are detected by a 0.5 cm wide by 1.0 cm long by 0.1 cm thick plastic scintillator mounted to a miniature PMT. Photon background is reduced to insignificant levels by a 2.0 cm thick cylindrical lead shield. Mean cerebral blood flow (mCBF) determined from an autoradiographic model and from the TAC measured by 1-second automated sampling was compared to that calculated from a TAC acquired using 5-second integrated manual samples. Improvements in timing resolution (1-sec vs. 5-sec) cause small but significant differences between the two sampling methods. Dispersion is minimized due to small tubing diameters, short lengths of tubing between the radial arterial sampling site and the detector and the presence of a 3-way valve 10 cm proximal to the detector.

The time-course of red blood cell intracellular pH recovery following short-circuiting in relation to venous transit times in rainbow trout, Oncorhynchus mykiss.

PubMed

Harter, Till Sebastian; May, Alexandra G; Federspiel, William J; Supuran, Claudiu T; Brauner, Colin J

2018-04-11

Accumulating evidence is highlighting the importance of a system of enhanced hemoglobin-oxygen (Hb-O 2 ) unloading for cardiovascular O 2 transport in teleosts. Adrenergically stimulated sodium-proton-exchangers (β-NHE) create H + gradients across the red blood cell (RBC) membrane that are short-circuited in the presence of plasma-accessible carbonic anhydrase (paCA) at the tissues; the result is a large arterial-venous pH shift that greatly enhances O 2 unloading from pH-sensitive Hb. However, RBC intracellular pH (pH i ) must recover during venous transit (31-90 s), to enable O 2 -loading at the gills. The halftimes (t 1/2 ) and magnitudes of RBC β-adrenergic stimulation, short-circuiting with paCA and recovery of RBC pH i , were assessed in vitro, on rainbow trout whole blood, and using changes in closed-system PO 2 as a sensitive indicator for changes in RBC pH i . In addition, the recovery rate of RBC pH i was assessed in a continuous-flow apparatus that more closely mimics RBC transit though the circulation. Results indicate that: i) the t 1/2 of CA short-circuiting is likely within the residence time of blood in the capillaries; ii) the t 1/2 of RBC pH i recovery is 17 s and within the time of RBC venous transit; and iii) after short-circuiting RBCs re-establish the initial H + gradient across the membrane and can potentially undergo repeated cycles of short-circuiting and recovery. Thus, teleosts have evolved a system that greatly enhances O 2 unloading from pH-sensitive Hb at the tissues, while protecting O 2 loading at the gills; the resulting increase in O 2 transport per unit of blood flow may enable the tremendous athletic ability of salmonids.

Assessing the controls and uncertainties on mean transit times in contrasting headwater catchments

NASA Astrophysics Data System (ADS)

Cartwright, Ian; Irvine, Dylan; Burton, Chad; Morgenstern, Uwe

2018-02-01

Estimating the time required for water to travel through headwater catchments from where it recharges to where it discharges into streams (the transit time) is important for understanding catchment behaviour. This study uses tritium (3H) activities of stream water to estimate the mean transit times of water in the upper Latrobe and Yarra catchments, southeast Australia, at different flow conditions. The 3H activities of the stream water were between 1.26 and 1.99 TU, which are lower than those of local rainfall (2.6 to 3.0 TU). 3H activities in individual subcatchments are almost invariably lowest at low streamflows. Mean transit times calculated from the 3H activities using a range of lumped parameter models are between 7 and 62 years and are longest during low streamflows. Uncertainties in the estimated mean transit times result from uncertainties in the geometry of the flow systems, uncertainties in the 3H input, and macroscopic mixing. In addition, simulation of 3H activities in FEFLOW indicates that heterogeneous hydraulic conductivities increase the range of mean transit times corresponding to a specific 3H activity. The absolute uncertainties in the mean transit times may be up to ±30 years. However, differences between mean transit times at different streamflows in the same catchment or between different subcatchments in the same area are more reliably estimated. Despite the uncertainties, the conclusions that the mean transit times are years to decades and decrease with increasing streamflow are robust. The seasonal variation in major ion geochemistry and 3H activities indicate that the higher general streamflows in winter are sustained by water displaced from shallower younger stores (e.g., soils or regolith). Poor correlations between 3H activities and catchment area, drainage density, mean slope, distance to stream, and landuse, imply that mean transit times are controlled by a variety of factors including the hydraulic properties of the soils and

Novel MRI tests of orocecal transit time and whole gut transit time: studies in normal subjects

PubMed Central

Chaddock, G; Lam, C; Hoad, C L; Costigan, C; Cox, E F; Placidi, E; Thexton, I; Wright, J; Blackshaw, P E; Perkins, A C; Marciani, L; Gowland, P A; Spiller, R C

2014-01-01

Background Colonic transit tests are used to manage patients with Functional Gastrointestinal Disorders. Some tests used expose patients to ionizing radiation. The aim of this study was to compare novel magnetic resonance imaging (MRI) tests for measuring orocecal transit time (OCTT) and whole gut transit time (WGT), which also provide data on colonic volumes. Methods 21 healthy volunteers participated. Study 1: OCTT was determined from the arrival of the head of a meal into the cecum using MRI and the Lactose Ureide breath test (LUBT), performed concurrently. Study 2: WGT was assessed using novel MRI marker capsules and radio-opaque markers (ROMs), taken on the same morning. Studies were repeated 1 week later. Key Results OCTT measured using MRI and LUBT was 225 min (IQR 180–270) and 225 min (IQR 165–278), respectively, correlation rs = 0.28 (ns). WGT measured using MRI marker capsules and ROMs was 28 h (IQR 4–50) and 31 h ± 3 (SEM), respectively, correlation rs = 0.85 (p < 0.0001). Repeatability assessed using the intraclass correlation coefficient (ICC) was 0.45 (p = 0.017) and 0.35 (p = 0.058) for MRI and LUBT OCTT tests. Better repeatability was observed for the WGT tests, ICC being 0.61 for the MRI marker capsules (p = 0.001) and 0.69 for the ROM method (p < 0.001) respectively. Conclusions & Inferences The MRI WGT method is simple, convenient, does not use X-ray and compares well with the widely used ROM method. Both OCTT measurements showed modest reproducibility and the MRI method showed modest inter-observer agreement. PMID:24165044

A system for real-time measurement of the brachial artery diameter in B-mode ultrasound images.

PubMed

Gemignani, Vincenzo; Faita, Francesco; Ghiadoni, Lorenzo; Poggianti, Elisa; Demi, Marcello

2007-03-01

The measurement of the brachial artery diameter is frequently used in clinical studies for evaluating the flow-mediated dilation and, in conjunction with the blood pressure value, for assessing arterial stiffness. This paper presents a system for computing the brachial artery diameter in real-time by analyzing B-mode ultrasound images. The method is based on a robust edge detection algorithm which is used to automatically locate the two walls of the vessel. The measure of the diameter is obtained with subpixel precision and with a temporal resolution of 25 samples/s, so that the small dilations induced by the cardiac cycle can also be retrieved. The algorithm is implemented on a standalone video processing board which acquires the analog video signal from the ultrasound equipment. Results are shown in real-time on a graphical user interface. The system was tested both on synthetic ultrasound images and in clinical studies of flow-mediated dilation. Accuracy, robustness, and intra/inter observer variability of the method were evaluated.

Cardiac surgery during pregnancy: continuous fetal monitoring using umbilical artery Doppler flow velocity indices.

PubMed

Mishra, Manisha; Sawhney, Ravindra; Kumar, Anil; Bapna, Kumar Ramesh; Kohli, Vijay; Wasir, Harpreet; Trehan, Naresh

2014-01-01

The fetal death rate associated with cardiac surgery with cardiopulmonary bypass (CPB) is as high as 9.5-29%. We report continuous monitoring of fetal heart rate and umbilical artery flow-velocity waveforms by transvaginal ultrasonography and their analyses in relation to events of the CPB in two cases in second trimester of pregnancy undergoing mitral valve replacement. Our findings suggest that the transition of circulation from corporeal to extracorporeal is the most important event during surgery; the associated decrease in mean arterial pressure (MAP) at this stage potentially has deleterious effects on the fetus, which get aggravated with the use of vasopressors. We suggest careful management of CPB at this stage, which include partial controlled CPB at initiation and gradual transition to full CPB; this strategy maintains high MAP and avoids the use of vasopressors. Maternal and fetal monitoring can timely recognize the potential problems and provide window for the required treatment.

Using a physically-based transit time distribution function to estimate the hydraulic parameters and hydraulic transit times of an unconfined aquifer from tritium measurements

NASA Astrophysics Data System (ADS)

Farlin, Julien; Maloszewski, Piotr; Schneider, Wilfried; Gallé, Tom

2014-05-01

Groundwater transit time is of interest in environmental studies pertaining to the transport of pollutants from its source to the aquifer outlet (spring or pumping well) or to an observation well. Different models have been proposed to describe the distribution of transit times within groundwatersheds, the most common being the dispersion model, the exponential-piston-flow model (EPM) both proposed by Maloszewski and Zuber (Maloszewski and Zuber, 1982) and the (two or three parameter) gamma model (Amin and Campana, 1996; Kirchner et al., 1999). Choosing which function applies best is a recurrent and controversial problem in hydrogeology. The object of this study is to revisit the applicability of the EPM for unconfined aquifers, and to introduce an alternative model based explicitly on groundwater hydraulics. The alternative model is based on the transit time of water from any point at the groundwater table to the aquifer outlet, and is used to calculate inversely the hydraulic parameters of a fractured unconfined sandstone aquifer from tritium measurements made in a series of contact springs. This model is compared to the EPM, which is usually adopted to describe the transit time distribution of confined and unconfined aquifers alike. Both models are tested against observations, and it is shown that the EPM fails the test for some of the springs, and generally seems to overestimate the older water component. Amin, I. E., and M. E. Campana (1996), A general lumped parameter model for the interpretation of tracer data and transit time calculation in hydrologic systems, Journal of Hydrology, 179, 1-21, doi: 10.1016/0022-1694(95)02880-3. Kirchner, J. W., X. H. Feng, and C. Neal (1999), Fractal stream chemistry and its implications for contaminant transport in catchments, Nature physics, 403, 524-527, doi: 10.1038/35000537. Maloszewski, P., and A. Zuber (1982), Determining the turnover time of groundwater systems with the aid of environmental tracers, Journal of

Measurement of pulmonary transit time in healthy cats by use of ultrasound contrast media "Sonovue®": feasibility, reproducibility, and values in 42 cats.

PubMed

Streitberger, Andrea; Hocke, Verena; Modler, Peter

2013-09-01

To evaluate the feasibility of measuring pulmonary transit time (PTT) in healthy cats by transthoracic echocardiography using the ultrasound contrast agent Sonovue(®). To determine normalized PTT (nPTT) values in 42 healthy cats and to estimate the interobserver variability and the within-day repeatability of nPTT measurements. Forty-two privately owned healthy cats of different breeds, gender and age presented for cardiac examination. A bolus injection of contrast agent (Sonovue(®)) was administered intravenously. The right parasternal short axis echocardiographic view was used to record the contrast agent's transit time from the pulmonary artery to the left atrium. Pulmonary transit time and nPTT were determined independently by three examiners with different levels of experience. Normalized PTT was 4.12 ± 1.0 (mean ± SD) in our population. The median interobserver variability across our population was 6.8%, the median within-day variability for the three observers were 13.1%, 12.7% and 13%. No effect of the observer's experience on nPTT measurement was identified. Age, sex and body weight did not significantly influence nPTT. This study demonstrates that nPTT measurement is feasible in cats using ultrasound and the blood pool contrast media Sonovue(®). Measurements of nPTT can be performed in a clinical setting. Normalized PTT values in healthy cats are comparable with those reported in healthy dogs. Copyright © 2013 Elsevier B.V. All rights reserved.

Changes in the bilateral pulse transit time difference with a moving arm.

PubMed

Jiang, Xinge; Wei, Shoushui; Zheng, Dingchang; Huang, Peng; Liu, Chengyu

2018-04-20

Changes of pulse transit time (PTT) induced by arm position were studied for unilateral arm. However, consistency of the PTT changes was not validated for both arm sides. We aimed to quantify the PTT changes between horizontal and non-horizontal positions from right arm and left arm in order to explore the consistency of both arms. Twenty-four normal subjects aged between 21 and 50 (14 male and 10 female) years were enrolled. Left and right radial artery pulses were synchronously recorded from 24 healthy subjects with one arm (left or right) at five angles (90∘, 45∘, 0∘, -45∘ and -90∘) and the other arm at the horizontal level (0∘) for reference. The overall mean PTT changes at the five angles (from 90∘ to -90∘) in the left arm (right as reference) were 16.1, 12.3, -0.5, -2.5 and -2.6 ms, respectively, and in the right arm (left as reference) were 18.0, 12.6, 1.6, -1.6 and -2.0 ms, respectively. Obvious differences were not found in the PTT changes between the two arms (left arm moving or right arm moving) under each of the five different positions (all P> 0.05).

Intraoperative transit-time flow measurement is not altered in venous bypass grafts covered by the eSVS mesh.

PubMed

Emery, Robert W; Solien, Eric

2013-01-01

The aim of this study was to determine whether the eSVS Mesh interferes with transit-time flow measurement (TTFM) assessing intraoperative coronary vein graft patency. In four swine undergoing off-pump bypass grafting to the anterior descending coronary artery, five TTFMs were sequentially obtained on meshed and bare grafts at baseline and under Dobutamine stress at five separate locations on the graft in each animal. The Medistim VeriQ was used for TTFM. The grafts were examined for patency after the swine were killed. There was no difference in hemodynamics or TTFM either at baseline or under Dobutamine stress between the eSVS Mesh covered and uncovered grafts. Dobutamine, however, significantly increased hemodynamics and graft flow parameters measured from baseline. The eSVS Mesh does not interfere with Doppler flow measurement in covered coronary vein grafts.

Intra-Aortic Balloon Pump Malposition Reduces Visceral Artery Perfusion in an Acute Animal Model.

PubMed

Vondran, Maximilian; Rastan, Ardawan J; Tillmann, Eugen; Seeburger, Jörg; Schröter, Thomas; Dhein, Stefan; Bakhtiary, Farhad; Mohr, Friedrich-Wilhelm

2016-04-01

Visceral artery perfusion can be potentially affected by intra-aortic balloon pump (IABP) catheters. We utilized an animal model to quantify the acute impact of a low balloon position on mesenteric artery perfusion. In six pigs (78 ± 7 kg), a 30-cc IABP was placed in the descending aorta in a transfemoral procedure. The celiac artery (CA) and the cranial mesenteric artery (CMA) were surgically dissected. Transit time blood flow was measured for (i) baseline, (ii) 1:1 augmentation with the balloon proximal to the visceral arteries, and (iii) 1:1 augmentation with the balloon covering the visceral arteries. Blood flow in the CMA and CA was reduced by 17 and 24%, respectively, when the balloon compromised visceral arteries compared with a position above the visceral arteries (flow in mL/min: CMA: (i) 1281 ± 512, (ii) 1389 ± 287, (iii) 1064 ± 276, P < 0.05 for 3 vs. 1 and 3 vs. 2; CA: (i) 885 ± 370, (ii) 819 ± 297, (iii) 673 ± 315; P < 0.05 for 3 vs. 1). The covering of visceral arteries by an IABP balloon causes a significant reduction of visceral artery perfusion; thus, the positioning of this device during implantation is critical for obtaining a satisfactory outcome. Copyright © 2015 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

NASA's SDO Captures Mercury Transit Time-lapses SDO Captures Mercury Transit Time-lapse

NASA Image and Video Library

2017-12-08

Less than once per decade, Mercury passes between the Earth and the sun in a rare astronomical event known as a planetary transit. The 2016 Mercury transit occurred on May 9th, between roughly 7:12 a.m. and 2:42 p.m. EDT. The images in this video are from NASA’s Solar Dynamics Observatory Music: Encompass by Mark Petrie For more info on the Mercury transit go to: www.nasa.gov/transit This video is public domain and may be downloaded at: svs.gsfc.nasa.gov/12235 NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Improvements in Low-cost Ultrasonic Measurements of Blood Flow in "by-passes" Using Narrow & Broad Band Transit-time Procedures

NASA Astrophysics Data System (ADS)

Ramos, A.; Calas, H.; Diez, L.; Moreno, E.; Prohías, J.; Villar, A.; Carrillo, E.; Jiménez, A.; Pereira, W. C. A.; Von Krüger, M. A.

The cardio-pathology by ischemia is an important cause of death, but the re-vascularization of coronary arteries (by-pass operation) is an useful solution to reduce associated morbidity improving quality of life in patients. During these surgeries, the flow in coronary vessels must be measured, using non-invasive ultrasonic methods, known as transit time flow measurements (TTFM), which are the most accurate option nowadays. TTFM is a common intra-operative tool, in conjunction with classic Doppler velocimetry, to check the quality of these surgery processes for implanting grafts in parallel with the coronary arteries. This work shows important improvements achieved in flow-metering, obtained in our research laboratories (CSIC, ICIMAF, COPPE) and tested under real surgical conditions in Cardiocentro-HHA, for both narrowband NB and broadband BB regimes, by applying results of a CYTED multinational project (Ultrasonic & computational systems for cardiovascular diagnostics). mathematical models and phantoms were created to evaluate accurately flow measurements, in laboratory conditions, before our new electronic designs and low-cost implementations, improving previous ttfm systems, which include analogic detection, acquisition & post-processing, and a portable PC. Both regimes (NB and BB), with complementary performances for different conditions, were considered. Finally, specific software was developed to offer facilities to surgeons in their interventions.

Time synchronization via the transit satellite at Mizusawa

NASA Technical Reports Server (NTRS)

Hara, J.; Sato, K. H.

1978-01-01

Time signals emitted from Transit satellites and received by the NAVICODE type receiver at Mizusawa, Japan are presented. The International Latitude Observatory of Mizusawa and the U. S. Naval Observatory were compared using the time signals. Propagation delays, a receiver delay, effects of relative motion of satellites, and effects of the ionosphere are discussed.

Real-Time MRI-Guided Endovascular Recanalization of Chronic Total Arterial Occlusion in a Swine Model

PubMed Central

Raval, Amish N.; Karmarkar, Parag V.; Guttman, Michael A.; Ozturk, Cengizhan; Sampath, Smita; DeSilva, Ranil; Aviles, Ronnier J.; Xu, Minnan; Wright, Victor J.; Schenke, William H.; Kocaturk, Ozgur; Dick, Alexander J.; Raman, Venkatesh K.; Atalar, Ergin; McVeigh, Elliot R.; Lederman, Robert J.

2006-01-01

Background Endovascular recanalization (guidewire traversal) of peripheral artery chronic total occlusion (CTO) can be challenging. X-Ray angiography resolves CTO poorly. Virtually “blind” device advancement during X-ray-guided interventions can lead to procedure failure, perforation and hemorrhage. Alternatively, magnetic resonance imaging (MRI) may delineate the artery within the occluded segment to enhance procedural safety and success. We hypothesized that real-time MRI (rtMRI) guided CTO recanalization can be accomplished in an animal model. Methods and Results Carotid artery CTO was created by balloon injury in 19 lipid overfed swine. After 6–8 weeks, two underwent direct necropsy analysis for histology, three underwent primary X-ray-guided CTO recanalization attempts, and the remaining 14 underwent rtMRI-guided recanalization attempts in a 1.5T interventional MRI system. rtMRI intervention used custom CTO catheters and guidewires that incorporated MRI receiver antennae to enhance device visibility. The mean length of the occluded segments was 13.3 ± 1.6cm. rtMRI-guided CTO recanalization was successful in 11/14 swine and only 1/3 swine using X-ray alone. After unsuccessful rtMRI (n = 3), X-ray-guided attempts also were all unsuccessful. Conclusions Recanalization of long CTO is feasible entirely using rtMRI guidance. Low profile clinical-grade devices will be required to translate this experience to humans. Endovascular recanalization of chronic total arterial occlusion (CTO) is challenging under conventional X-ray guidance because devices are advanced almost blindly. MRI can image CTO borders and luminal contents, and could potentially guide these procedures. We test the feasibility of real-time MRI guided wire traversal in a swine model of peripheral artery CTO using custom active MRI catheters. PMID:16490819

In vivo measurement of the longitudinal relaxation time of arterial blood (T1a) in the mouse using a pulsed arterial spin labeling approach.

PubMed

Thomas, David L; Lythgoe, Mark F; Gadian, David G; Ordidge, Roger J

2006-04-01

A novel method for measuring the longitudinal relaxation time of arterial blood (T1a) is presented. Knowledge of T1a is essential for accurately quantifying cerebral perfusion using arterial spin labeling (ASL) techniques. The method is based on the flow-sensitive alternating inversion recovery (FAIR) pulsed ASL (PASL) approach. We modified the standard FAIR acquisition scheme by incorporating a global saturation pulse at the beginning of the recovery period. With this approach the FAIR tissue signal difference has a simple monoexponential dependence on the recovery time, with T1a as the time constant. Therefore, FAIR measurements performed over a range of recovery times can be fitted to a monoexponential recovery curve and T1a can be calculated directly. This eliminates many of the difficulties associated with the measurement of T1a. Experiments performed in vivo in the mouse at 2.35T produced a mean value of 1.51 s for T1a, consistent with previously published values. (c) 2006 Wiley-Liss, Inc.

Colonic transit time is related to bacterial metabolism and mucosal turnover in the gut.

PubMed

Roager, Henrik M; Hansen, Lea B S; Bahl, Martin I; Frandsen, Henrik L; Carvalho, Vera; Gøbel, Rikke J; Dalgaard, Marlene D; Plichta, Damian R; Sparholt, Morten H; Vestergaard, Henrik; Hansen, Torben; Sicheritz-Pontén, Thomas; Nielsen, H Bjørn; Pedersen, Oluf; Lauritzen, Lotte; Kristensen, Mette; Gupta, Ramneek; Licht, Tine R

2016-06-27

Little is known about how colonic transit time relates to human colonic metabolism and its importance for host health, although a firm stool consistency, a proxy for a long colonic transit time, has recently been positively associated with gut microbial richness. Here, we show that colonic transit time in humans, assessed using radio-opaque markers, is associated with overall gut microbial composition, diversity and metabolism. We find that a long colonic transit time associates with high microbial richness and is accompanied by a shift in colonic metabolism from carbohydrate fermentation to protein catabolism as reflected by higher urinary levels of potentially deleterious protein-derived metabolites. Additionally, shorter colonic transit time correlates with metabolites possibly reflecting increased renewal of the colonic mucosa. Together, this suggests that a high gut microbial richness does not per se imply a healthy gut microbial ecosystem and points at colonic transit time as a highly important factor to consider in microbiome and metabolomics studies.

Pulmonary Arterial Hypertension and Neonatal Arterial Switch Surgery for Correction of Transposition of the Great Arteries.

PubMed

Domínguez Manzano, Paula; Mendoza Soto, Alberto; Román Barba, Violeta; Moreno Galdó, Antonio; Galindo Izquierdo, Alberto

2016-09-01

There are few reports of the appearance of pulmonary arterial hypertension following arterial switch surgery in the neonatal period to correct transposition of the great arteries. We assessed the frequency and clinical pattern of this complication in our series of patients. Our database was reviewed to select patients with transposition of the great arteries corrected by neonatal arterial switch at our hospital and who developed pulmonary hypertension over time. We identified 2 (1.3%) patients with transposition of the great arteries successfully repaired in the first week of life who later experienced pulmonary arterial hypertension. The first patient was a 7-year-old girl diagnosed with severe pulmonary hypertension at age 8 months who did not respond to medical treatment and required lung transplantation. The anatomic pathology findings were consistent with severe pulmonary arterial hypertension. The second patient was a 24-month-old boy diagnosed with severe pulmonary hypertension at age 13 months who did not respond to medical therapy. Pulmonary hypertension is a rare but very severe complication that should be investigated in all patients with transposition of the great arteries who have undergone neonatal arterial switch, in order to start early aggressive therapy for affected patients, given the poor therapeutic response and poor prognosis involved. Copyright © 2016 Sociedad Española de Cardiología. Published by Elsevier España, S.L.U. All rights reserved.

Lesions Responsible for Delayed Oral Transit Time in Post-stroke Dysphagia.

PubMed

Moon, Hyun Im; Yoon, Seo Yeon; Yi, Tae Im; Jeong, Yoon Jeong; Cho, Tae Hwan

2018-06-01

Some stroke patients show oral phase dysphagia, characterized by a markedly prolonged oral transit time that hinders oral feeding. The aim of this study was to clarify the clinical characteristics and lesions responsible for delayed swallowing. We reviewed 90 patients with stroke. The oral processing time plus the postfaucial aggregation time required to swallow semisolid food was assessed. The patients were divided into two groups according to oral transit time, and we analyzed the differences in characteristics such as demographic factors, lesion factors, and cognitive function. Logistic regression analyses were performed to examine the predictors of delayed oral transit time. Lesion location and volume were measured on brain magnetic resonance images. We generated statistic maps of lesions related to delayed oral phase in swallowing using voxel-based lesion symptom mapping (VLSM). The group of patients who showed delayed oral transit time had significantly low cognitive function. Also, in a regression model, delayed oral phase was predicted with low K-MMSE (Korean version of the Mini Mental Status Exam). Using VLSM, we found the lesion location to be associated with delayed oral phase after adjusting for K-MMSE score. Although these results did not reach statistical significance, they showed the lesion pattern with predominant distribution in the left frontal lobe. Delayed oral phase in post-stroke patients was not negligible clinically. Patients' cognitive impairments affect the oral transit time. When adjusting it, we found a trend that the lesion responsible for delayed oral phase was located in the left frontal lobe, though the association did not reach significance. The delay might be related to praxis function.

Comparing Intra-Arterial Chemotherapy Combined With Intravesical Chemotherapy Versus Intravesical Chemotherapy Alone: A Randomised Prospective Pilot Study for T1G3 Bladder Transitional Cell Carcinoma After Bladder-Preserving Surgery

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

Chen, Junxing, E-mail: Junxingchen@hotmail.com; Yao, Zhijun, E-mail: yaozhijun1985@qq.com; Qiu, Shaopeng, E-mail: qiushp@mail.sysu.edu.cn

Purpose: To compare the efficacy of intra-arterial chemotherapy combined with intravesical chemotherapy versus intravesical chemotherapy alone for T1G3 bladder transitional cell carcinoma (BTCC) followed by bladder-preserving surgery. Materials and Methods: Sixty patients with T1G3 BTCC were randomly divided into two groups. After bladder-preserving surgery, 29 patients (age 30-80 years, 24 male and 5 female) received intra-arterial chemotherapy in combination with intravesical chemotherapy (group A), whereas 31 patients (age 29-83 years, 26 male and 5 female) were treated with intravesical chemotherapy alone (group B). Twenty-nine patients were treated with intra-arterial epirubicin (50 mg/m{sup 2}) + cisplatin (60 mg/m{sup 2}) chemotherapy 2-3more » weeks after bladder-preserving surgery once every 4-6 weeks. All of the patients received the same intravesical chemotherapy: An immediate prophylactic was administered in the first 6 h. After that, therapy was administered one time per week for 8 weeks and then one time per month for 8 months. The instillation drug was epirubicin (50 mg/m{sup 2}) and lasted for 30-40 min each time. The end points were tumour recurrence (stage Ta, T1), tumour progression (to T2 or greater), and disease-specific survival. During median follow-up of 22 months, the overall survival rate, tumour-specific death rate, recurrence rate, progression rate, time to first recurrence, and adverse reactions were compared between groups. Results: The recurrence rates were 10.3 % (3 of 29) in group A and 45.2 % (14 of 31) in group B, and the progression rates were 0 % (0 of 29) in group A and 22.6 % (7 of 31) in group B. There was a significant difference between the two groups regarding recurrence (p = 0.004) and progression rates (p = 0.011). Median times to first recurrence in the two groups were 15 and 6.5 months, respectively. The overall survival rates were 96.6 and 87.1 %, and the tumour-specific death rates were 0 % (0 of 29) and 13.5 % (4

Children and Transition Time.

ERIC Educational Resources Information Center

Baker, Betty Ruth

Daily transitions in early childhood centers and classrooms include periods when children are completing one activity, preparing to begin a new activity, and moving from place to place in a room or building. Transition activities involve teaching techniques that prepare learners to listen, relax, sit down, move between locations or activities, and…

[Ultrasonographic study of blood flow in the renal arteries of patients with arterial hypertension].

PubMed

Makarenko, E S; Dombrovskiĭ, V I; Nelasov, N Iu

2012-01-01

Vascular duplex ultrasound duplex with simultaneous ECG registration was made to estimate the quantitative and time parameters of blood flow in the renal arteries with grade 1-2 arterial hypertension. There were increases in vascular resistance indices and acceleration phase index and a reduction in systolic phase index. There were correlations of the time parameters of blood flow in the renal arteries with age and lipidogram values.

Transit times and mean ages for nonautonomous and autonomous compartmental systems

DOE PAGES

Rasmussen, Martin; Hastings, Alan; Smith, Matthew J.; ...

2016-04-01

In this study, we develop a theory for transit times and mean ages for nonautonomous compartmental systems. Using the McKendrick–von Förster equation, we show that the mean ages of mass in a compartmental system satisfy a linear nonautonomous ordinary differential equation that is exponentially stable. We then define a nonautonomous version of transit time as the mean age of mass leaving the compartmental system at a particular time and show that our nonautonomous theory generalises the autonomous case. We apply these results to study a nine-dimensional nonautonomous compartmental system modeling the terrestrial carbon cycle, which is a modification of themore » Carnegie–Ames–Stanford approach model, and we demonstrate that the nonautonomous versions of transit time and mean age differ significantly from the autonomous quantities when calculated for that model.« less

Watching excitons move: the time-dependent transition density matrix

NASA Astrophysics Data System (ADS)

Ullrich, Carsten

2012-02-01

Time-dependent density-functional theory allows one to calculate excitation energies and the associated transition densities in principle exactly. The transition density matrix (TDM) provides additional information on electron-hole localization and coherence of specific excitations of the many-body system. We have extended the TDM concept into the real-time domain in order to visualize the excited-state dynamics in conjugated molecules. The time-dependent TDM is defined as an implicit density functional, and can be approximately obtained from the time-dependent Kohn-Sham orbitals. The quality of this approximation is assessed in simple model systems. A computational scheme for real molecular systems is presented: the time-dependent Kohn-Sham equations are solved with the OCTOPUS code and the time-dependent Kohn-Sham TDM is calculated using a spatial partitioning scheme. The method is applied to show in real time how locally created electron-hole pairs spread out over neighboring conjugated molecular chains. The coupling mechanism, electron-hole coherence, and the possibility of charge separation are discussed.

Determination of Gastrointestinal Transit Times in Barred Owls ( Strix varia ) by Contrast Fluoroscopy.

PubMed

Doss, Grayson A; Williams, Jackie M; Mans, Christoph

2017-06-01

Contrast imaging studies are routinely performed in avian patients when an underlying abnormality of the gastrointestinal (GI) tract is suspected. Fluoroscopy offers several advantages over traditional radiography and can be performed in conscious animals with minimal stress and restraint. Although birds of prey are commonly encountered as patients, little is known about GI transit times and contrast imaging studies in these species, especially owls. Owls are commonly encountered in zoological, educational, and wildlife settings. In this study, 12 adult barred owls ( Strix varia ) were gavage fed a 30% weight-by-volume barium suspension (25 mL/kg body weight). Fluoroscopic exposures were recorded at 5, 15, 30, 60, 120, 180, 240, and 300 minutes after administration. Overall GI transit time and transit times of various GI organs were recorded. Median (interquartile range [IQR]) overall GI transit time was 60 minutes (IQR: 19-60 minutes) and ranged from 5-120 minutes. Ventricular and small intestinal contrast filling was rapid. Ventricular emptying was complete by a median of 60 minutes (IQR: 30-120 minutes; range: 30-240 minutes), whereas small intestinal emptying was not complete in 9/12 birds by 300 minutes. Median small intestinal contraction rate was 15 per minute (IQR: 13-16 minutes; range: 10-19 minutes). Median overall GI transit time in barred owls is more rapid than mean transit times reported for psittacine birds and red-tailed hawks ( Buteo jamaicensis ). Fluoroscopy is a safe, suitable method for investigating GI motility and transit in this species.

Contrast-enhanced time-resolved MRA for pre-angiographic evaluation of suspected spinal dural arterial venous fistulas.

PubMed

Saindane, Amit M; Boddu, Srikanth R; Tong, Frank C; Dehkharghani, Seena; Dion, Jacques E

2015-02-01

Spinal digital subtraction angiography (DSA) is the gold standard for diagnosis of spinal dural arterial venous fistulas (SDAVFs), but can require extensive time, radiation exposure and contrast dose. We hypothesize that contrast-enhanced time-resolved MR angiography (CE-TR MRA) will have utility for the non-invasive diagnosis and pre-angiographic localization of SDAVFs. Eighteen patients underwent both CE-TR MRA and DSA for suspected SDAVFs, with DSA performed a median of 11 days (range 0-41) after MRA. CE-TR MRA was performed on a 1.5 T GE unit using Time Resolved Imaging of Contrast Kinetics (TRICKS). CE-TR MRA and DSA images were evaluated for the presence of SDAVFs and location of the feeding arterial supply, with DSA as the reference standard. DSA was also evaluated for the number of vessels catheterized, contrast volume and fluoroscopic and procedure times. Eight of the 18 patients were positive for SDAVF on DSA. Sensitivity, specificity, positive predictive value and negative predictive value for the 18 CE-TR MRAs were 88%, 90%, 88% and 90%, respectively. Localization of the SDAVF arterial supply on CE-TR MRA was within one vertebral level from DSA for 6/7 SDAVFs. Compared with patients with a SDAVF and feeding artery identified on CE-TR MRA, patients with negative or suboptimal CE-TR MRA had a significantly increased number of vessels catheterized (p=0.027) and larger contrast volumes (p=0.022). CE-TR MRA is a useful initial examination for the diagnosis and localization of SDAVFs, with a high concordance rate with DSA. When CE-TR MRA demonstrates a SDAVF, the number of catheterized vessels and contrast dose can be decreased during DSA. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

The Transit-Time Distribution from the Northern Hemisphere Midlatitude Surface

NASA Technical Reports Server (NTRS)

Orbe, Clara; Waugh, Darryn W.; Newman, Paul A.; Strahan, Susan; Steenrod, Stephen

2015-01-01

The distribution of transit times from the Northern Hemisphere (NH) midlatitude surface is a fundamental property of tropospheric transport. Here we present an analysis of the transit time distribution (TTD) since air last contacted the northern midlatitude surface layer, as simulated by the NASA Global Modeling Initiative Chemistry Transport Model. We find that throughout the troposphere the TTD is characterized by long flat tails that reflect the recirculation of old air from the Southern Hemisphere and results in mean ages that are significantly larger than the modal age. Key aspects of the TTD -- its mode, mean and spectral width -- are interpreted in terms of tropospheric dynamics, including seasonal shifts in the location and strength of tropical convection and variations in quasi-isentropic transport out of the northern midlatitude surface layer. Our results indicate that current diagnostics of tropospheric transport are insufficient for comparing model transport and that the full distribution of transit times is a more appropriate constraint.

No Timing Variations Observed in Third Transit of Snow-line Exoplanet Kepler-421b

NASA Astrophysics Data System (ADS)

Dalba, Paul A.; Muirhead, Philip S.

2016-07-01

We observed Kepler-421 during the anticipated third transit of the snow-line exoplanet Kepler-421b in order to constrain the existence and extent of transit timing variations (TTVs). Previously, the Kepler spacecraft only observed two transits of Kepler-421b, leaving the planet’s transit ephemeris unconstrained. Our visible light, time-series observations from the 4.3 m Discovery Channel Telescope were designed to capture pre-transit baseline and the partial transit of Kepler-421b, barring significant TTVs. We use the light curves to assess the probabilities of various transit models using both the posterior odds ratio and the Bayesian Information Criterion, and find that a transit model with no TTVs is favored to 3.6σ confidence. These observations suggest that Kepler-421b is either alone in its system or is only experiencing minor dynamic interactions with an unseen companion. With the Kepler-421b ephemeris constrained, we calculate future transit times and discuss the opportunity to characterize the atmosphere of this cold, long-period exoplanet via transmission spectroscopy. Our investigation emphasizes the difficulties associated with observing long-period exoplanet transits and the consequences that arise from failing to refine transit ephemerides.

Adolescents’ Changing Future Expectations Predict the Timing of Adult Role Transitions

PubMed Central

Beal, Sarah J.; Crockett, Lisa J.; Peugh, James

2016-01-01

Individual differences in the transition to adulthood are well established. This study examines the extent to which heterogeneity in pathways to adulthood that have been observed in the broader U.S. population are mirrored in adolescents’ expectations regarding when they will experience key adult role transitions (e.g., marriage). Patterns of change in adolescents’ expectations and the relations between their expectations and subsequent role transitions are also explored. Data from 626 youth in Grade 11 (M age = 16), Grade 12, and early adulthood (M age = 23) are analyzed using mover-stayer latent transition analysis. Results indicate three profiles of expected timing, corresponding to youth who anticipate early role entry (i.e., early starters), youth who anticipate earlier entry into employment but no other roles (i.e., employment-focused), and youth who anticipate delays in role transitions favoring increased education (i.e., education-focused). Two-thirds of youths changed their expectations from Grade 11 to 12. Grade 11 and 12 profile membership predicted role transitions in early adulthood. These findings highlight the importance of adolescents’ expectations and changes in expectations across time in shaping entry into adulthood. PMID:27548390

Daylight saving time transitions and hospital treatments due to accidents or manic episodes

PubMed Central

Lahti, Tuuli A; Haukka, Jari; Lönnqvist, Jouko; Partonen, Timo

2008-01-01

Background Daylight saving time affects millions of people annually but its impacts are still widely unknown. Sleep deprivation and the change of circadian rhythm can trigger mental illness and cause higher accident rates. Transitions into and out of daylight saving time changes the circadian rhythm and may cause sleep deprivation. Thus it seems plausible that the prevalence of accidents and/or manic episodes may be higher after transition into and out of daylight saving time. The aim of this study was to explore the effects of transitions into and out of daylight saving time on the incidence of accidents and manic episodes in the Finnish population during the years of 1987 to 2003. Methods The nationwide data were derived from the Finnish Hospital Discharge Register. From the register we obtained the information about the hospital-treated accidents and manic episodes during two weeks before and two weeks after the transitions in 1987–2003. Results The results were negative, as the transitions into or out of daylight saving time had no significant effect on the incidence of accidents or manic episodes. Conclusion One-hour transitions do not increase the incidence of manic episodes or accidents which require hospital treatment. PMID:18302734

Dallas integrated corridor management (ICM) transit vehicle real-time data demonstration.

DOT National Transportation Integrated Search

2015-01-01

This project demonstrated and evaluated the ability to collect and transmit transit location and passenger loading data to a transit management center(s) and/or Integrated Corridor Management (ICM) system in real time. It also demonstrated and evalua...

Hemodynamic transition driven by stent porosity in sidewall aneurysms.

PubMed

Bouillot, Pierre; Brina, Olivier; Ouared, Rafik; Lovblad, Karl-Olof; Farhat, Mohamed; Pereira, Vitor Mendes

2015-05-01

The healing process of intracranial aneurysms (IAs) treated with flow diverter stents (FDSs) depends on the IA flow modifications and on the epithelization process over the neck. In sidewall IA models with straight parent artery, two main hemodynamic regimes with different flow patterns and IA flow magnitude were broadly observed for unstented and high porosity stented IA on one side, and low porosity stented IA on the other side. The hemodynamic transition between these two regimes is potentially involved in thrombosis formation. In the present study, CFD simulations and multi-time lag (MTL) particle imaging velocimetry (PIV) measurements were combined to investigate the physical nature of this transition. Measurable velocity fields and non-measurable shear stress and pressure fields were assessed experimentally and numerically in the aneurysm volume in the presence of stents with various porosities. The two main regimes observed in both PIV and CFD showed typical flow features of shear and pressure driven regimes. In particular, the waveform of the averaged IA velocities was matching both the shear stress waveform at IA neck or the pressure gradient waveform in parent artery. Moreover, the transition between the two regimes was controlled by stent porosity: a decrease of stent porosity leads to an increase (decrease) of pressure differential (shear stress) through IA neck. Finally, a good PIV-CFD agreement was found except in transitional regimes and low motion eddies due to small mismatch of PIV-CFD running conditions. Copyright © 2015 Elsevier Ltd. All rights reserved.

Children and Adolescent Obesity Associates with Pressure-Dependent and Age-Related Increase in Carotid and Femoral Arteries' Stiffness and Not in Brachial Artery, Indicative of Nonintrinsic Arterial Wall Alteration

PubMed Central

García-Espinosa, Victoria; Curcio, Santiago; Castro, Juan Manuel; Arana, Maite; Giachetto, Gustavo; Chiesa, Pedro; Zócalo, Yanina

2016-01-01

Aim. To analyze if childhood obesity associates with changes in elastic, transitional, and/or muscular arteries' stiffness. Methods. 221 subjects (4–15 years, 92 females) were assigned to normal weight (NW, n = 137) or obesity (OB, n = 84) groups, considering their body mass index z-score. Age groups were defined: 4–8; 8–12; 12–15 years old. Carotid, femoral, and brachial artery local stiffness was determined through systodiastolic pressure-diameter and stress-strain relationships. To this end, arterial diameter and peripheral and aortic blood pressure (BP) levels and waveforms were recorded. Carotid-femoral, femoropedal, and carotid-radial pulse wave velocities were determined to evaluate aortic, lower-limb, and upper-limb regional arterial stiffness, respectively. Correlation analysis between stiffness parameters and BP was done. Results. Compared to NW, OB subjects showed higher peripheral and central BP and carotid and femoral stiffness, reaching statistical significance in subjects aged 12 and older. Arterial stiffness differences disappeared when levels were normalized for BP. There were no differences in intrinsic arterial wall stiffness (elastic modulus), BP stiffness relationships, and regional stiffness parameters. Conclusion. OB associates with BP-dependent and age-related increase in carotid and femoral (but not brachial) stiffness. Stiffness changes would not be explained by intrinsic arterial wall alterations but could be associated with the higher BP levels observed in obese children. PMID:27066273

Takeover Time in Highly Automated Vehicles: Noncritical Transitions to and From Manual Control.

PubMed

Eriksson, Alexander; Stanton, Neville A

2017-06-01

The aim of this study was to review existing research into driver control transitions and to determine the time it takes drivers to resume control from a highly automated vehicle in noncritical scenarios. Contemporary research has moved from an inclusive design approach to adhering only to mean/median values when designing control transitions in automated driving. Research into control transitions in highly automated driving has focused on urgent scenarios where drivers are given a relatively short time span to respond to a request to resume manual control. We found a paucity in research into more frequent scenarios for control transitions, such as planned exits from highway systems. Twenty-six drivers drove two scenarios with an automated driving feature activated. Drivers were asked to read a newspaper, or to monitor the system, and to relinquish, or resume, control from the automation when prompted by vehicle systems. Significantly longer control transition times were found between driving with and without secondary tasks. Control transition times were substantially longer than those reported in the peer-reviewed literature. We found that drivers take longer to resume control when under no time pressure compared with that reported in the literature. Moreover, we found that drivers occupied by a secondary task exhibit larger variance and slower responses to requests to resume control. Workload scores implied optimal workload. Intra- and interindividual differences need to be accommodated by vehicle manufacturers and policy makers alike to ensure inclusive design of contemporary systems and safety during control transitions.

Time-Varying Transition Probability Matrix Estimation and Its Application to Brand Share Analysis.

PubMed

Chiba, Tomoaki; Hino, Hideitsu; Akaho, Shotaro; Murata, Noboru

2017-01-01

In a product market or stock market, different products or stocks compete for the same consumers or purchasers. We propose a method to estimate the time-varying transition matrix of the product share using a multivariate time series of the product share. The method is based on the assumption that each of the observed time series of shares is a stationary distribution of the underlying Markov processes characterized by transition probability matrices. We estimate transition probability matrices for every observation under natural assumptions. We demonstrate, on a real-world dataset of the share of automobiles, that the proposed method can find intrinsic transition of shares. The resulting transition matrices reveal interesting phenomena, for example, the change in flows between TOYOTA group and GM group for the fiscal year where TOYOTA group's sales beat GM's sales, which is a reasonable scenario.

Perforating arteries originating from the posterior communicating artery: a 7.0-Tesla MRI study.

PubMed

Conijn, Mandy M A; Hendrikse, Jeroen; Zwanenburg, Jaco J M; Takahara, Taro; Geerlings, Mirjam I; Mali, Willem P Th M; Luijten, Peter R

2009-12-01

The aim of this study was to investigate the ability of time-of-flight (TOF) magnetic resonance (MR) angiography at 7.0 Tesla to show the perforating branches of the posterior communicating artery (PCoA), and to investigate the presence of such visible perforating branches in relation to the size of the feeding PCoA. The secondary aim was to visualise and describe the anterior choroidal artery and the perforating branches of the P1-segment of posterior cerebral artery (P1). Forty-six healthy volunteers underwent TOF MR angiography at 7.0 Tesla. With 7.0-Tesla imaging, we visualised for the first time perforating arteries originating from the PCoA in vivo without the use of contrast agents. A perforating artery from the PCoA was found in a large proportion of the PCoAs (64%). The presence was associated with a larger diameter of the underlying PCoA (1.23 versus 1.06 mm, P = 0.03). The anterior choroidal artery was visible bilaterally in all participants. In 83% of all P1s, one or two perforating branches were visible. Non-invasive assessment of the perforating arteries of the PCoA together with the anterior choroidal artery and the perforating arteries of the P1 may increase our understanding of infarcts in the deep brain structures supplied by these arteries.

Electric dipole transitions for four-times ionized cerium (Ce V)

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

Usta, Betül Karaçoban, E-mail: bkaracoban@sakarya.edu.tr; Akgün, Elif, E-mail: elif.akgun@ogr.sakarya.edu.tr; Alparslan, Büşra, E-mail: busra.alparslan1@ogr.sakarya.edu.tr

2016-03-25

We have calculated the transition parameters, such as wavelengths, oscillator strengths, and transition probabilities (or rates), for the electric dipole (E1) transitions in four-times ionized cerium (Ce V, Z = 58) by using the multiconfiguration Hartree-Fock method within the framework of Breit-Pauli (MCHF+BP) relativistic corrections and the relativistic Hartree-Fock (HFR) method. The obtained results have been compared with other works available in literature. A discussion of these calculations for Ce V in this study has also been in view of the MCHF+BP and HFR methods.

NO TIMING VARIATIONS OBSERVED IN THIRD TRANSIT OF SNOW-LINE EXOPLANET KEPLER-421b

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

Dalba, Paul A.; Muirhead, Philip S., E-mail: pdalba@bu.edu

2016-07-20

We observed Kepler-421 during the anticipated third transit of the snow-line exoplanet Kepler-421b in order to constrain the existence and extent of transit timing variations (TTVs). Previously, the Kepler spacecraft only observed two transits of Kepler-421b, leaving the planet’s transit ephemeris unconstrained. Our visible light, time-series observations from the 4.3 m Discovery Channel Telescope were designed to capture pre-transit baseline and the partial transit of Kepler-421b, barring significant TTVs. We use the light curves to assess the probabilities of various transit models using both the posterior odds ratio and the Bayesian Information Criterion, and find that a transit model withmore » no TTVs is favored to 3.6 σ confidence. These observations suggest that Kepler-421b is either alone in its system or is only experiencing minor dynamic interactions with an unseen companion. With the Kepler-421b ephemeris constrained, we calculate future transit times and discuss the opportunity to characterize the atmosphere of this cold, long-period exoplanet via transmission spectroscopy. Our investigation emphasizes the difficulties associated with observing long-period exoplanet transits and the consequences that arise from failing to refine transit ephemerides.« less

A Gaussian Model-Based Probabilistic Approach for Pulse Transit Time Estimation.

PubMed

Jang, Dae-Geun; Park, Seung-Hun; Hahn, Minsoo

2016-01-01

In this paper, we propose a new probabilistic approach to pulse transit time (PTT) estimation using a Gaussian distribution model. It is motivated basically by the hypothesis that PTTs normalized by RR intervals follow the Gaussian distribution. To verify the hypothesis, we demonstrate the effects of arterial compliance on the normalized PTTs using the Moens-Korteweg equation. Furthermore, we observe a Gaussian distribution of the normalized PTTs on real data. In order to estimate the PTT using the hypothesis, we first assumed that R-waves in the electrocardiogram (ECG) can be correctly identified. The R-waves limit searching ranges to detect pulse peaks in the photoplethysmogram (PPG) and to synchronize the results with cardiac beats--i.e., the peaks of the PPG are extracted within the corresponding RR interval of the ECG as pulse peak candidates. Their probabilities of being the actual pulse peak are then calculated using a Gaussian probability function. The parameters of the Gaussian function are automatically updated when a new pulse peak is identified. This update makes the probability function adaptive to variations of cardiac cycles. Finally, the pulse peak is identified as the candidate with the highest probability. The proposed approach is tested on a database where ECG and PPG waveforms are collected simultaneously during the submaximal bicycle ergometer exercise test. The results are promising, suggesting that the method provides a simple but more accurate PTT estimation in real applications.

[Fiber intake and colonic transit time in functional constipated patients].

PubMed

Lopes, Adriana Cruz; Victoria, Carlos Roberto

2008-01-01

Patients with functional constipation presenting no response to treatment using fibers supplement represents important clinical issue. To evaluate the relations among the amount of ingested fiber, the constipation intensity and the colonic transit time in patients with functional constipation. We evaluated 30 patients, presenting no response to treatment using fibers supplement, and 18 healthy volunteers conducting individual inquiry into fibers intake, constipation intensity and the total and segmental colonic transit evaluation using radiopaque markers. In the constipated, despite the good level of fiber intake (26.3 +/- 12.9 g, constipated x 9.3 +/- 5,2 g, control), the symptoms of constipation was serious (score = 21.3 +/- 4.07). Mean total colonic transit was 58.8h. The colonic transit was slower in the constipated group (41.0 +/- 22.8 hours, constipated x 21.8 +/- 18.5h, control). In constipated patients with slow colonic transit (>58.8h) there were colonic inertia (eight), outlet constipation (one) and slow transit in left colon (one), and among constipated patients with normal colonic transit (<58.8h), there were isolated slow transit, in the right colon (nine), left colon (three) and in the rectosigmoid segment (eight). There were no relation among the amount of ingested fiber, constipation intensity and the colon transit. In the functional constipation the gravity of symptoms does not depend only on the dietary fibers intake, which is not the only responsible for the differences in the colonic transit. The colonic transit can differentiate normal from constipated patients and, among them, those with altered transit that demand approaches distinct of fiber supplementation.

Transiting Exoplanet Monitoring Project (TEMP). IV. Refined System Parameters, Transit Timing Variations, and Orbital Stability of the Transiting Planetary System HAT-P-25

NASA Astrophysics Data System (ADS)

Wang, Xian-Yu; Wang, Songhu; Hinse, Tobias C.; Li, Kai; Wang, Yong-Hao; Laughlin, Gregory; Liu, Hui-Gen; Zhang, Hui; Wu, Zhen-Yu; Zhou, Xu; Zhou, Ji-Lin; Hu, Shao-Ming; Wu, Dong-Hong; Peng, Xi-Yan; Chen, Yuan-Yuan

2018-06-01

We present eight new light curves of the transiting extra-solar planet HAT-P-25b obtained from 2013 to 2016 with three telescopes at two observatories. We use the new light curves, along with recent literature material, to estimate the physical and orbital parameters of the transiting planet. Specifically, we determine the mid-transit times (T C ) and update the linear ephemeris, T C[0] = 2456418.80996 ± 0.00025 [BJDTDB] and P = 3.65281572 ± 0.00000095 days. We carry out a search for transit timing variations (TTVs), and find no significant TTV signal at the ΔT = 80 s-level, placing a limit on the possible strength of planet–planet interactions (TTVG). In the course of our analysis, we calculate the upper mass-limits of the potential nearby perturbers. Near the 1:2, 2:1, and 3:1 resonances with HAT-P-25b, perturbers with masses greater than 0.5, 0.3, and 0.5 M ⊕ respectively, can be excluded. Furthermore, based on the analysis of TTVs caused by light travel time effect (LTTE) we also eliminate the possibility that a long-period perturber exists with M p > 3000 MJ within a = 11.2 au of the parent star.

Time-Varying Transition Probability Matrix Estimation and Its Application to Brand Share Analysis

PubMed Central

Chiba, Tomoaki; Akaho, Shotaro; Murata, Noboru

2017-01-01

In a product market or stock market, different products or stocks compete for the same consumers or purchasers. We propose a method to estimate the time-varying transition matrix of the product share using a multivariate time series of the product share. The method is based on the assumption that each of the observed time series of shares is a stationary distribution of the underlying Markov processes characterized by transition probability matrices. We estimate transition probability matrices for every observation under natural assumptions. We demonstrate, on a real-world dataset of the share of automobiles, that the proposed method can find intrinsic transition of shares. The resulting transition matrices reveal interesting phenomena, for example, the change in flows between TOYOTA group and GM group for the fiscal year where TOYOTA group’s sales beat GM’s sales, which is a reasonable scenario. PMID:28076383

Changes in Sleep Duration and Sleep Timing Associated with Retirement Transitions

PubMed Central

Hagen, Erika W.; Barnet, Jodi H.; Hale, Lauren; Peppard, Paul E.

2016-01-01

Study Objectives: Investigate whether retirement transitions are associated with changes in sleep duration and sleep timing, and whether these associations are modified by age, sex, mental health, or circadian preference. Methods: The Retirement and Sleep Trajectories (REST) study is a longitudinal study consisting of four annual mailed surveys that collected information about employment, sleep, and health. Differences in reported sleep duration, bedtime and wake time between successive surveys were calculated to estimate change over 1, 2, and 3 y. Linear regression models were used to estimate changes in these sleep parameters associated with retirement 1, 2, and 3 y posttransition. Results: Retiring from full-time work was associated with bedtimes that were 30, 31, and 36 min later 1, 2, and 3 y postretirement; wake times that were 63, 69, and 78 min later; and sleep durations that were 15, 16, and 22 min longer 1, 2, and 3 y postretirement. These associations did not differ by sex or mental health status. Age and circadian preference modified the associations between retirement and change in sleep parameters; the increase in sleep duration was shorter and the wake time extension was lesser with advancing retirement age; those with evening preference had longer wake time extensions than those with morning preference. Conclusion: Transitioning to retirement is associated with longer sleep duration, later bedtimes, and later wake times. These changes were detectable about 1 y postwork transition and were persistent up to 3 y later. Citation: Hagen EW, Barnet JH, Hale L, Peppard PE. Changes in sleep duration and sleep timing associated with retirement transitions. SLEEP 2016;39(3):665–673. PMID:26564125

Part-time Labor, Work Rules, and Transit Costs

DOT National Transportation Integrated Search

1981-01-01

This report examines two major issues: (1)the impact of labor union work rules : on bus transit operating costs and (2)the magnitude of cost savings that can be : expected from the use of part-time drivers. These issues are examined within : the cont...

Firing patterns transition and desynchronization induced by time delay in neural networks

NASA Astrophysics Data System (ADS)

Huang, Shoufang; Zhang, Jiqian; Wang, Maosheng; Hu, Chin-Kun

2018-06-01

We used the Hindmarsh-Rose (HR) model (Hindmarsh and Rose, 1984) to study the effect of time delay on the transition of firing behaviors and desynchronization in neural networks. As time delay is increased, neural networks exhibit diversity of firing behaviors, including regular spiking or bursting and firing patterns transitions (FPTs). Meanwhile, the desynchronization of firing and unstable bursting with decreasing amplitude in neural system, are also increasingly enhanced with the increase of time delay. Furthermore, we also studied the effect of coupling strength and network randomness on these phenomena. Our results imply that time delays can induce transition and desynchronization of firing behaviors in neural networks. These findings provide new insight into the role of time delay in the firing activities of neural networks, and can help to better understand the firing phenomena in complex systems of neural networks. A possible mechanism in brain that can cause the increase of time delay is discussed.

Transit timing at Toruń Center for Astronomy

NASA Astrophysics Data System (ADS)

Bykowski, W.; Maciejewski, G.

2011-01-01

The transit monitoring is one of well-known methods for discovering and observing new extrasolar planets. Among various advantages, this way of searching other worlds does not require complex and expensive equipment -- it can be performed with a relatively small telescope and high-quality CCD camera. At the Center for Astronomy of Nicolaus Copernicus University in Toruń, Poland, we collect observational data using the 60-cm Cassegrain telescope hoping that it would be possible to discover new objects in already known planetary systems using the transit timing variation method. Our observations are a part of a bigger cooperation between observatories from many countries.

TRANSIT TIMING OBSERVATIONS FROM KEPLER. I. STATISTICAL ANALYSIS OF THE FIRST FOUR MONTHS

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

Ford, Eric B.; Rowe, Jason F.; Caldwell, Douglas A.

The architectures of multiple planet systems can provide valuable constraints on models of planet formation, including orbital migration, and excitation of orbital eccentricities and inclinations. NASA's Kepler mission has identified 1235 transiting planet candidates. The method of transit timing variations (TTVs) has already confirmed seven planets in two planetary systems. We perform a transit timing analysis of the Kepler planet candidates. We find that at least {approx}11% of planet candidates currently suitable for TTV analysis show evidence suggestive of TTVs, representing at least {approx}65 TTV candidates. In all cases, the time span of observations must increase for TTVs to providemore » strong constraints on planet masses and/or orbits, as expected based on N-body integrations of multiple transiting planet candidate systems (assuming circular and coplanar orbits). We find the fraction of planet candidates showing TTVs in this data set does not vary significantly with the number of transiting planet candidates per star, suggesting significant mutual inclinations and that many stars with a single transiting planet should host additional non-transiting planets. We anticipate that Kepler could confirm (or reject) at least {approx}12 systems with multiple transiting planet candidates via TTVs. Thus, TTVs will provide a powerful tool for confirming transiting planets and characterizing the orbital dynamics of low-mass planets. If Kepler observations were extended to at least seven years, then TTVs would provide much more precise constraints on the dynamics of systems with multiple transiting planets and would become sensitive to planets with orbital periods extending into the habitable zone of solar-type stars.« less

Transitioning from parenteral to inhaled prostacyclin therapy in pulmonary arterial hypertension.

PubMed

Ataya, Ali; Somoracki, Angelina; Cope, Jessica; Alnuaimat, Hassan

2016-10-01

Parenteral prostacyclin therapy for PAH has allowed for improvements in functional status, quality of life and mortality. Parenteral therapies however carry an increased risk of line-associated complications. Inhaled prostacyclins are an attractive alternative therapy; however, limited data exists supporting the safety and outcomes after transition. We describe a retrospective observational analysis of adults with PAH who were transitioned from a parenteral prostacyclin to inhaled treprostinil at our institution. Endpoints include duration of transition, hospital length of stay, adverse effects during transition, and cardiopulmonary function post transition. Eight patients were included, all of which were on triple therapy. Seven patients receiving intravenous prostacyclin therapy were transitioned in an ICU setting, while one patient was transitioned from subcutaneous treprostinil as an outpatient. The average ICU and hospital length of stay was 4.1 ± 0.7 days. Patient preference was the most common reason for transition (n = 5), followed by line complication (n = 2), and intolerance to parenteral therapy (n = 1). One adverse event was observed while initiating inhaled treprostinil that only required slowing of the transition process. On follow-up (19.6 ± 11.1 months) functional class did not change, and non-parametric test showed no change in 6MWD after transition (p = 0.62). One patient failed inhaled therapy necessitating transition back to intravenous therapy. Transitioning patients from parenteral to inhaled prostacyclin therapy can be safely accomplished in specialized centers over a 48-72 h period. Patient preference was overwhelming the most prevalent reason for transition. Copyright © 2016 Elsevier Ltd. All rights reserved.

Biomagnetic techniques for evaluating gastric emptying, peristaltic contraction and transit time

PubMed Central

la Roca-Chiapas, Jose María De; Cordova-Fraga, Teodoro

2011-01-01

Biomagnetic techniques were used to measure motility in various parts of the gastrointestinal (GI) tract, particularly a new technique for detecting magnetic markers and tracers. A coil was used to enhance the signal from a magnetic tracer in the GI tract and the signal was detected using a fluxgate magnetometer or a magnetoresistor in an unshielded room. Estimates of esophageal transit time were affected by the position of the subject. The reproducibility of estimates derived using the new biomagnetic technique was greater than 85% and it yielded estimates similar to those obtained using scintigraphy. This technique is suitable for studying the effect of emotional state on GI physiology and for measuring GI transit time. The biomagnetic technique can be used to evaluate digesta transit time in the esophagus, stomach and colon, peristaltic frequency and gastric emptying and is easy to use in the hospital setting. PMID:22025978

Biomagnetic techniques for evaluating gastric emptying, peristaltic contraction and transit time.

PubMed

la Roca-Chiapas, Jose María De; Cordova-Fraga, Teodoro

2011-10-15

Biomagnetic techniques were used to measure motility in various parts of the gastrointestinal (GI) tract, particularly a new technique for detecting magnetic markers and tracers. A coil was used to enhance the signal from a magnetic tracer in the GI tract and the signal was detected using a fluxgate magnetometer or a magnetoresistor in an unshielded room. Estimates of esophageal transit time were affected by the position of the subject. The reproducibility of estimates derived using the new biomagnetic technique was greater than 85% and it yielded estimates similar to those obtained using scintigraphy. This technique is suitable for studying the effect of emotional state on GI physiology and for measuring GI transit time. The biomagnetic technique can be used to evaluate digesta transit time in the esophagus, stomach and colon, peristaltic frequency and gastric emptying and is easy to use in the hospital setting.

Channel Noise-Enhanced Synchronization Transitions Induced by Time Delay in Adaptive Neuronal Networks with Spike-Timing-Dependent Plasticity

NASA Astrophysics Data System (ADS)

Xie, Huijuan; Gong, Yubing; Wang, Baoying

In this paper, we numerically study the effect of channel noise on synchronization transitions induced by time delay in adaptive scale-free Hodgkin-Huxley neuronal networks with spike-timing-dependent plasticity (STDP). It is found that synchronization transitions by time delay vary as channel noise intensity is changed and become most pronounced when channel noise intensity is optimal. This phenomenon depends on STDP and network average degree, and it can be either enhanced or suppressed as network average degree increases depending on channel noise intensity. These results show that there are optimal channel noise and network average degree that can enhance the synchronization transitions by time delay in the adaptive neuronal networks. These findings could be helpful for better understanding of the regulation effect of channel noise on synchronization of neuronal networks. They could find potential implications for information transmission in neural systems.

Medical management and leadership: a time of transition?

PubMed

Dickinson, Helen; Phelps, Grant; Loh, Erwin; Bismark, Marie

2017-07-01

Perspectives on medical management and leadership are in a time of transition, but there is much we still need to understand better. This paper explores some of the tensions and dilemmas inherent in understandings of medical management and leadership. © 2017 Royal Australasian College of Physicians.

Solid volume fraction estimation of bone:marrow replica models using ultrasound transit time spectroscopy.

PubMed

Wille, Marie-Luise; Langton, Christian M

2016-02-01

The acceptance of broadband ultrasound attenuation (BUA) for the assessment of osteoporosis suffers from a limited understanding of both ultrasound wave propagation through cancellous bone and its exact dependence upon the material and structural properties. It has recently been proposed that ultrasound wave propagation in cancellous bone may be described by a concept of parallel sonic rays; the transit time of each ray defined by the proportion of bone and marrow propagated. A Transit Time Spectrum (TTS) describes the proportion of sonic rays having a particular transit time, effectively describing the lateral inhomogeneity of transit times over the surface aperture of the receive ultrasound transducer. The aim of this study was to test the hypothesis that the solid volume fraction (SVF) of simplified bone:marrow replica models may be reliably estimated from the corresponding ultrasound transit time spectrum. Transit time spectra were derived via digital deconvolution of the experimentally measured input and output ultrasonic signals, and compared to predicted TTS based on the parallel sonic ray concept, demonstrating agreement in both position and amplitude of spectral peaks. Solid volume fraction was calculated from the TTS; agreement between true (geometric calculation) with predicted (computer simulation) and experimentally-derived values were R(2)=99.9% and R(2)=97.3% respectively. It is therefore envisaged that ultrasound transit time spectroscopy (UTTS) offers the potential to reliably estimate bone mineral density and hence the established T-score parameter for clinical osteoporosis assessment. Copyright © 2015 Elsevier B.V. All rights reserved.

Pulse wave analysis in a 180-degree curved artery model: Implications under physiological and non-physiological inflows

NASA Astrophysics Data System (ADS)

Bulusu, Kartik V.; Plesniak, Michael W.

2013-11-01

Systolic and diastolic blood pressures, pulse pressures, and left ventricular hypertrophy contribute to cardiovascular risks. Increase of arterial stiffness due to aging and hypertension is an important factor in cardiovascular, chronic kidney and end-stage-renal-diseases. Pulse wave analysis (PWA) based on arterial pressure wave characteristics, is well established in clinical practice for evaluation of arterial distensibility and hypertension. The objective of our exploratory study in a rigid 180-degree curved artery model was to evaluate arterial pressure waveforms. Bend upstream conditions were measured using a two-component, two-dimensional, particle image velocimeter (2C-2D PIV). An ultrasonic transit-time flow meter and a catheter with a MEMS-based solid state pressure sensor, capable of measuring up to 20 harmonics of the observed pressure waveform, monitored flow conditions downstream of the bend. Our novel continuous wavelet transform algorithm (PIVlet 1.2), in addition to detecting coherent secondary flow structures is used to evaluate arterial pulse wave characteristics subjected to physiological and non-physiological inflows. Results of this study will elucidate the utility of wavelet transforms in arterial function evaluation and pulse wave speed. Supported by NSF Grant No. CBET- 0828903 and GW Center for Biomimetics and Bioinspired Engineering.

Automatic location of L/H transition times for physical studies with a large statistical basis

NASA Astrophysics Data System (ADS)

González, S.; Vega, J.; Murari, A.; Pereira, A.; Dormido-Canto, S.; Ramírez, J. M.; contributors, JET-EFDA

2012-06-01

Completely automatic techniques to estimate and validate L/H transition times can be essential in L/H transition analyses. The generation of databases with hundreds of transition times and without human intervention is an important step to accomplish (a) L/H transition physics analysis, (b) validation of L/H theoretical models and (c) creation of L/H scaling laws. An entirely unattended methodology is presented in this paper to build large databases of transition times in JET using time series. The proposed technique has been applied to a dataset of 551 JET discharges between campaigns C21 and C26. A prediction with discharges that show a clear signature in time series is made through the locating properties of the wavelet transform. It is an accurate prediction and the uncertainty interval is ±3.2 ms. The discharges with a non-clear pattern in the time series use an L/H mode classifier based on discharges with a clear signature. In this case, the estimation error shows a distribution with mean and standard deviation of 27.9 ms and 37.62 ms, respectively. Two different regression methods have been applied to the measurements acquired at the transition times identified by the automatic system. The obtained scaling laws for the threshold power are not significantly different from those obtained using the data at the transition times determined manually by the experts. The automatic methods allow performing physical studies with a large number of discharges, showing, for example, that there are statistically different types of transitions characterized by different scaling laws.

Time evolution and dynamical phase transitions at a critical time in a system of one-dimensional bosons after a quantum quench.

PubMed

Mitra, Aditi

2012-12-28

A renormalization group approach is used to show that a one-dimensional system of bosons subject to a lattice quench exhibits a finite-time dynamical phase transition where an order parameter within a light cone increases as a nonanalytic function of time after a critical time. Such a transition is also found for a simultaneous lattice and interaction quench where the effective scaling dimension of the lattice becomes time dependent, crucially affecting the time evolution of the system. Explicit results are presented for the time evolution of the boson interaction parameter and the order parameter for the dynamical transition as well as for more general quenches.

Improving Pedestrian Access to Transit: City of Gresham's Ped-to-MAX Program

DOT National Transportation Integrated Search

1999-01-01

Accommodating multi-modal travel on high speed arterials is a challenge, : particularly in Gresham where numerous arterials transect the city, creating : barriers to pedestrians, bicyclists, and transit users. The "Ped-to-MAX" : program was created t...

Ultrasonic Transit Time Flowmetry in Robotic Totally Endoscopic CABG

PubMed Central

Chaikhouni, Amer; Almulla, Abdulwahid

2011-01-01

Successful use of transit time flowmetry in robotic totally endoscopic coronary bypass operation is reported to demonstrate its applicability and ease of use in evaluating the function of grafts in such operations. PMID:22121466

Time-delayed transition of normal-to-abnormal glow in pin-to-water discharge

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

Yoon, S.-Y.; Byeon, Y.-S.; Yoo, S.

2016-08-15

Time-delayed transition of normal-to-abnormal glow was investigated in discharge between spoke-like pins and ultrapure water by applying AC-driven power at a frequency of 14.3 kHz at atmospheric pressure. The normal-to-abnormal transition can be recognized from the slope changes of current density, gas temperature, electrode temperature, and OH density. The slope changes took place in tens of minutes rather than just after discharge, in other words, the transition was delayed. The time-delay of the transition was caused by the interaction between the plasma and water. The plasma affected water properties, and then the water affected plasma properties.

Left Ventricular Retraining and Late Arterial Switch for D-Transposition of the Great Arteries.

PubMed

Watanabe, Naruhito; Mainwaring, Richard D; Carrillo, Sergio A; Lui, George K; Reddy, V Mohan; Hanley, Frank L

2015-05-01

For many decades, patients with d-transposition of the great arteries underwent an atrial switch procedure. Although many of these patients have continued to do well, a subset experience profound right ventricular failure. Some may be candidates for left ventricular (LV) retraining and late arterial switch. The purpose of this study was to review our experience with LV retraining and late arterial switch. This was a retrospective review of 32 patients with d-transposition. Thirty patients underwent a previous atrial switch and subsequently experienced right ventricular failure, whereas 2 presented late (8 months and 6 years) without previous intervention. The median age at the time of enrollment in this program was 15 years. Seven patients proceeded directly to late arterial switch owing to systemic LV pressures. The remaining 25 underwent a pulmonary artery band for LV retraining. Twenty of the 32 (63%) patients enrolled in this program were able to undergo a late arterial switch. There were 2 operative mortalities (10%). Two additional patients survived surgery but died in the early outpatient time period. There has been no late mortality after the arterial switch with a median follow-up of 5 years. Twelve patients underwent one or more pulmonary artery band procedures without evidence of effective LV retraining. There have been 2 early and 3 late (42%) deaths in this subgroup. The outcomes after arterial switch are encouraging and suggest that LV retraining and late arterial switch provide a viable option for this complex group of patients. Copyright © 2015 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.

Selective transarterial embolization with n-butyl-2-cyanoacrylate for the treatment of arterial hemorrhage after third molar extraction.

PubMed

Sagara, Yoshiko; Kiyosue, Hiro; Tanoue, Shuichi; Shimada, Ryuichi; Hongo, Norio; Kohno, Tatsuyuki; Kawano, Kenji; Mori, Hiromu

2013-06-01

Comprehensive reports concerning selective embolization for arterial bleeding from third molar removal have not been published. We analyzed cases of arterial bleeding from third molar extraction that required transarterial embolization, and we demonstrate representative cases. Five consecutive patients (three men and two women, aged 24 to 37 years) who underwent transarterial embolization at our institution were included in this study. Four of them showed postoperative bleeding after lower third molar removal, and one suffered bleeding after upper third molar extraction. The period of time from extraction to embolization varied from 5 h to 5 weeks. Angiography revealed pseudoaneurysms at the inferior alveolar artery in four cases and at the superior alveolar artery in one case. The pseudoaneurysms were selectively embolized using 25-33 % n-butyl-2-cyanoacrylate (NBCA)-lipiodol. All of the cases showed good results angiographically and clinically. Transit hypoesthesia at the region of the mental nerve was observed in one patient. Selective transarterial embolization is an effective technique for arterial bleeding from third molar removal when it is difficult to obtain hemostasis by dental procedures. Injection of NBCA can be useful when the alveolar artery is too small to embolize with coils.

Impact of timing of cranioplasty on hydrocephalus after decompressive hemicraniectomy in malignant middle cerebral artery infarction.

PubMed

Finger, Tobias; Prinz, Vincent; Schreck, Evelyn; Pinczolits, Alexandra; Bayerl, Simon; Liman, Thomas; Woitzik, Johannes; Vajkoczy, Peter

2017-02-01

Patients with malignant middle cerebral artery infarction frequently develop hydrocephalus after decompressive hemicraniectomy. Hydrocephalus itself and known shunt related complications after ventriculo-peritoneal shunt implantation may negatively impact patientś outcome. Here, we aimed to identify factors associated with the development of hydrocephalus after decompressive hemicraniectomy in malignant middle cerebral artery infarction. A total of 99 consecutive patients with the diagnosis of large hemispheric infarctions and the indication for decompressive hemicraniectomy were included. We retrospectively evaluated patient characteristics (gender, age and selected preoperative risk factors), stroke characteristics (side, stroke volume and existing mass effect) and surgical characteristics (size of the bone flap, initial complication rate, time to cranioplasty, complication rate following cranioplasty, type of implant, number of revision surgeries and mortality). Frequency of hydrocephalus development was 10% in our cohort. Patients who developed a hydrocephalus had an earlier time point of bone flap reimplantation compared to the control group (no hydrocephalus=164±104days, hydrocephalus=108±52days, p<0.05). Additionally, numbers of revision surgeries after cranioplasty was associated with hydrocephalus with a trend towards significance (p=0.08). Communicating hydrocephalus is frequent in patients with malignant middle cerebral artery infarction after decompressive hemicraniectomy. A later time point of cranioplasty might lead to a lower incidence of required shunting procedures in general as we could show in our patient cohort. Copyright © 2016 Elsevier B.V. All rights reserved.

Observer-based robust finite time H∞ sliding mode control for Markovian switching systems with mode-dependent time-varying delay and incomplete transition rate.

PubMed

Gao, Lijun; Jiang, Xiaoxiao; Wang, Dandan

2016-03-01

This paper investigates the problem of robust finite time H∞ sliding mode control for a class of Markovian switching systems. The system is subjected to the mode-dependent time-varying delay, partly unknown transition rate and unmeasurable state. The main difficulty is that, a sliding mode surface cannot be designed based on the unknown transition rate and unmeasurable state directly. To overcome this obstacle, the set of modes is firstly divided into two subsets standing for known transition rate subset and unknown one, based on which a state observer is established. A component robust finite-time sliding mode controller is also designed to cope with the effect of partially unknown transition rate. It is illustrated that the reachability, finite-time stability, finite-time boundedness, finite-time H∞ state feedback stabilization of sliding mode dynamics can be ensured despite the unknown transition rate. Finally, the simulation results verify the effectiveness of robust finite time control problem. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.

Where does the Occluded Artery Trial leave the late open artery hypothesis?

PubMed Central

Lamas, Gervasio A; Hochman, Judith S

2007-01-01

As of April 2007 the early open artery hypothesis is alive and well, but the late open artery hypothesis is adrift. For the foreseeable future, stable patients with persistent occlusion of the infarct artery late after myocardial infarction, and without severe ischaemia or uncontrollable angina, should be managed initially with optimal medical treatment alone, and not with percutaneous coronary intervention. Efforts should focus on establishing reperfusion earlier, including reducing the time to patient presentation. PMID:17933981

Transitions: Times of Change and Accommodation.

ERIC Educational Resources Information Center

Rice, Mabel L.; O'Brien, Marion

1990-01-01

The research literature is reviewed for transitions from birth to eight years. A model describes transition as a change in ecocultural niche, requiring accommodations in daily routines for a child, family, and service providers and transition impact measures the number of accommodations required and the sustainability of daily routines.…

Prompting technologies: A comparison of time-based and context-aware transition-based prompting

PubMed Central

Robertson, Kayela; Rosasco, Cody; Feuz, Kyle; Schmitter-Edgecombe, Maureen; Cook, Diane

2016-01-01

BACKGROUND While advancements in technology have encouraged the development of novel prompting systems to support cognitive interventions, little research has evaluated the best time to deliver prompts, which may impact the effectiveness of these interventions. OBJECTIVE This study examined whether transition-based context prompting (prompting an individual during task transitions) is more effective than traditional fixed time-based prompting. METHODS Participants were 42 healthy adults who completed 12 different everyday activities, each lasting 1–7 minutes, in an experimental smart home testbed and received prompts to record the completed activities from an electronic memory notebook. Half of the participants were delivered prompts during activity transitions, while the other half received prompts every 5 minutes. Participants also completed Likert-scale ratings regarding their perceptions of the prompting system. RESULTS Results revealed that participants in the transition-based context prompting condition responded to the first prompt more frequently and rated the system as more convenient, natural, and appropriate compared to participants in the time-based condition. CONCLUSIONS Our findings suggest that prompting during activity transitions produces higher adherence to the first prompt and more positive perceptions of the prompting system. This is an important finding given the benefits of prompting technology and the possibility of improving cognitive interventions by using context-aware transition prompting. PMID:26409520

The detection and characterization of a nontransiting planet by transit timing variations.

PubMed

Nesvorný, David; Kipping, David M; Buchhave, Lars A; Bakos, Gáspár Á; Hartman, Joel; Schmitt, Allan R

2012-06-01

The Kepler mission is monitoring the brightness of ~150,000 stars, searching for evidence of planetary transits. As part of the Hunt for Exomoons with Kepler (HEK) project, we report a planetary system with two confirmed planets and one candidate planet discovered with the publicly available data for KOI-872. Planet b transits the host star with a period P(b) = 33.6 days and exhibits large transit timing variations indicative of a perturber. Dynamical modeling uniquely detects an outer nontransiting planet c near the 5:3 resonance (P(c) = 57.0 days) with a mass 0.37 times that of Jupiter. Transits of a third planetary candidate are also found: a 1.7-Earth radius super-Earth with a 6.8-day period. Our analysis indicates a system with nearly coplanar and circular orbits, reminiscent of the orderly arrangement within the solar system.

Unconventional Topological Phase Transition in Two-Dimensional Systems with Space-Time Inversion Symmetry

NASA Astrophysics Data System (ADS)

Ahn, Junyeong; Yang, Bohm-Jung

2017-04-01

We study a topological phase transition between a normal insulator and a quantum spin Hall insulator in two-dimensional (2D) systems with time-reversal and twofold rotation symmetries. Contrary to the case of ordinary time-reversal invariant systems, where a direct transition between two insulators is generally predicted, we find that the topological phase transition in systems with an additional twofold rotation symmetry is mediated by an emergent stable 2D Weyl semimetal phase between two insulators. Here the central role is played by the so-called space-time inversion symmetry, the combination of time-reversal and twofold rotation symmetries, which guarantees the quantization of the Berry phase around a 2D Weyl point even in the presence of strong spin-orbit coupling. Pair creation and pair annihilation of Weyl points accompanying partner exchange between different pairs induces a jump of a 2D Z2 topological invariant leading to a topological phase transition. According to our theory, the topological phase transition in HgTe /CdTe quantum well structure is mediated by a stable 2D Weyl semimetal phase because the quantum well, lacking inversion symmetry intrinsically, has twofold rotation about the growth direction. Namely, the HgTe /CdTe quantum well can show 2D Weyl semimetallic behavior within a small but finite interval in the thickness of HgTe layers between a normal insulator and a quantum spin Hall insulator. We also propose that few-layer black phosphorus under perpendicular electric field is another candidate system to observe the unconventional topological phase transition mechanism accompanied by the emerging 2D Weyl semimetal phase protected by space-time inversion symmetry.

Masses of Kepler-46b, c from Transit Timing Variations

NASA Astrophysics Data System (ADS)

Saad-Olivera, Ximena; Nesvorný, David; Kipping, David M.; Roig, Fernando

2017-04-01

We use 16 quarters of the Kepler mission data to analyze the transit timing variations (TTVs) of the extrasolar planet Kepler-46b (KOI-872). Our dynamical fits confirm that the TTVs of this planet (period P={33.648}-0.005+0.004 days) are produced by a non-transiting planet Kepler-46c (P={57.325}-0.098+0.116 days). The Bayesian inference tool MultiNest is used to infer the dynamical parameters of Kepler-46b and Kepler-46c. We find that the two planets have nearly coplanar and circular orbits, with eccentricities ≃ 0.03 somewhat higher than previously estimated. The masses of the two planets are found to be {M}b={0.885}-0.343+0.374 and {M}c={0.362}-0.016+0.016 Jupiter masses, with M b being determined here from TTVs for the first time. Due to the precession of its orbital plane, Kepler-46c should start transiting its host star a few decades from now.

How old is streamwater? Open questions in catchment transit time conceptualization, modeling and analysis

Treesearch

J.J. McDonnell; K. McGuire; P. Aggarwal; K.J. Beven; D. Biondi; G. Destouni; S. Dunn; A. James; J. Kirchner; P. Kraft; S. Lyon; P. Maloszewski; B. Newman; L. Pfister; A. Rinaldo; A. Rodhe; T. Sayama; J. Seibert; K. Solomon; C. Soulsby; M. Stewart; D. Tetzlaff; C. Tobin; P. Troch; M. Weiler; A. Western; A. Wörman; S. Wrede

2010-01-01

The time water spends travelling subsurface through a catchment to the stream network (i.e. the catchment water transit time) fundamentally describes the storage, flow pathway heterogeneity and sources of water in a catchment. The distribution of transit times reflects how catchments retain and release water and solutes that in turn set biogeochemical conditions and...

Space-time thermodynamics of the glass transition

NASA Astrophysics Data System (ADS)

Merolle, Mauro; Garrahan, Juan P.; Chandler, David

2005-08-01

We consider the probability distribution for fluctuations in dynamical action and similar quantities related to dynamic heterogeneity. We argue that the so-called “glass transition” is a manifestation of low action tails in these distributions where the entropy of trajectory space is subextensive in time. These low action tails are a consequence of dynamic heterogeneity and an indication of phase coexistence in trajectory space. The glass transition, where the system falls out of equilibrium, is then an order-disorder phenomenon in space-time occurring at a temperature Tg, which is a weak function of measurement time. We illustrate our perspective ideas with facilitated lattice models and note how these ideas apply more generally. Author contributions: M.M., J.P.G., and D.C. performed research and wrote the paper.

Methods of blood flow measurement in the arterial circulatory system.

PubMed

Tabrizchi, R; Pugsley, M K

2000-01-01

The most commonly employed techniques for the in vivo measurement of arterial blood flow to individual organs involve the use of flow probes or sensors. Commercially available systems for the measurement of in vivo blood flow can be divided into two categories: ultrasonic and electromagnetic. Two types of ultrasonic probes are used. The first type of flow probe measures blood flow-mediated Doppler shifts (Doppler flowmetry) in a vessel. The second type of flow probe measures the "transit time" required by an emitted ultrasound wave to traverse the vessel and are transit-time volume flow sensors. Measurement of blood flow in any vessel requires that the flow probe or sensor be highly accurate and exhibit signal linearity over the flow range in the vessel of interest. Moreover, additional desirable features include compact design, size, and weight. An additional important feature for flow probes is that they exhibit good biocompatability; it is imperative for the sensor to behave in an inert manner towards the biological system. A sensitive and reliable method to assess blood flow in individual organs in the body, other than by the use of probes/sensors, is the reference sample method that utilizes hematogeneously delivered microspheres. This method has been utilized to a large extend to assess regional blood flow in the entire body. Obviously, the purpose of measuring blood flow is to determine the amount of blood delivered to a given region per unit time (milliliters per minute) and it is desirable to achieve this goal by noninvasive methodologies. This, however, is not always possible. This review attempts to offer an overview of some of the techniques available for the assessment of regional blood flow in the arterial circulatory system and discusses advantages and disadvantages of these common techniques.

Time-resolved PIV measurements of the flow field in a stenosed, compliant arterial model

NASA Astrophysics Data System (ADS)

Geoghegan, P. H.; Buchmann, N. A.; Soria, J.; Jermy, M. C.

2013-05-01

Compliant (flexible) structures play an important role in several biological flows including the lungs, heart and arteries. Coronary heart disease is caused by a constriction in the artery due to a build-up of atherosclerotic plaque. This plaque is also of major concern in the carotid artery which supplies blood to the brain. Blood flow within these arteries is strongly influenced by the movement of the wall. To study these problems experimentally in vitro, especially using flow visualisation techniques, can be expensive due to the high-intensity and high-repetition rate light sources required. In this work, time-resolved particle image velocimetry using a relatively low-cost light-emitting diode illumination system was applied to the study of a compliant flow phantom representing a stenosed (constricted) carotid artery experiencing a physiologically realistic flow wave. Dynamic similarity between in vivo and in vitro conditions was ensured in phantom construction by matching the distensibility and the elastic wave propagation wavelength and in the fluid system through matching Reynolds ( Re) and Womersley number ( α) with a maximum, minimum and mean Re of 939, 379 and 632, respectively, and a α of 4.54. The stenosis had a symmetric constriction of 50 % by diameter (75 % by area). Once the flow rate reached a critical value, Kelvin-Helmholtz instabilities were observed to occur in the shear layer between the main jet exiting the stenosis and a reverse flow region that occurred at a radial distance of 0.34 D from the axis of symmetry in the region on interest 0-2.5 D longitudinally downstream from the stenosis exit. The instability had an axis-symmetric nature, but as peak flow rate was approached this symmetry breaks down producing instability in the flow field. The characteristics of the vortex train were sensitive not only to the instantaneous flow rate, but also to whether the flow was accelerating or decelerating globally.

Hydroclimatic influences on non-stationary transit time distributions in a boreal headwater catchment

NASA Astrophysics Data System (ADS)

Peralta-Tapia, A.; Soulsby, C.; Tetzlaff, D.; Sponseller, R.; Bishop, K.; Laudon, H.

2016-12-01

Understanding how water moves through catchments - from the time it enters as precipitation to when it exits via streamflow - is of fundamental importance to understanding hydrological and biogeochemical processes. A basic descriptor of this routing is the Transit Time Distribution (TTD) which is derived from the input-output behavior of conservative tracers, the mean of which represents the average time elapsed between water molecules entering and exiting a flow system. In recent decades, many transit time studies have been conducted, but few of these have focused on snow-dominated catchments. We assembled a 10-year time series of isotopic data (δ18O and δ2H) for precipitation and stream water to estimate the characteristics of the transit time distribution in a boreal catchment in northern Sweden. We applied lumped parameter models using a gamma distribution to calculate the Mean Transit Time (MTT) of water over the entire period of record and to evaluate how inter-annual differences in transit times relate to hydroclimatic variability. The best fit MTT for the complete 10-year period was 650 days (Nash-Sutcliff Efficiency = 0.65), while the best fit inter-annual MTT ranged from 300 days up to 1200 days. Whilst there was a weak negative correlation between mean annual total precipitation and the annual MTT, this relationship was stronger (r2 = 0.53, p = 0.02) for the annual rain water input. This strong connection between the MTT and annual rainfall, rather than snowmelt, has strong implications for understanding future hydrological and biogeochemical processes in boreal regions, given that predicted warmer winters would translate into a greater proportion of precipitation falling as rain and thus shorter MTT in catchments. Such a change could have direct implications for the export of solutes and pollutants.

Cold-Induced Changes in Arterial Sensitivity

DTIC Science & Technology

1991-05-01

muscle contraction . The in vitro exposure of femoral arteries from rabbits and pigs to cold resulted in a progressive loss of sensitivity to agonist. Femoral arteries isolated from hypothermic pigs (core temp = 25 C for 2 hours) were no more sensitive to NEPI in vitro than arteries from normothermic animals. However, the in situ hind limb arterial bed of the hypothermic pig was ten times more sensitive to arterial injection of NEPI than the arterial bed of the normothermic pig. The sensitivity of porcine vascular smooth muscle to NEPI does not appear to be affected by

Time delay between cardiac and brain activity during sleep transitions

NASA Astrophysics Data System (ADS)

Long, Xi; Arends, Johan B.; Aarts, Ronald M.; Haakma, Reinder; Fonseca, Pedro; Rolink, Jérôme

2015-04-01

Human sleep consists of wake, rapid-eye-movement (REM) sleep, and non-REM (NREM) sleep that includes light and deep sleep stages. This work investigated the time delay between changes of cardiac and brain activity for sleep transitions. Here, the brain activity was quantified by electroencephalographic (EEG) mean frequency and the cardiac parameters included heart rate, standard deviation of heartbeat intervals, and their low- and high-frequency spectral powers. Using a cross-correlation analysis, we found that the cardiac variations during wake-sleep and NREM sleep transitions preceded the EEG changes by 1-3 min but this was not the case for REM sleep transitions. These important findings can be further used to predict the onset and ending of some sleep stages in an early manner.

Dynamics of transit times and StorAge Selection functions in four forested catchments from stable isotope data

NASA Astrophysics Data System (ADS)

Rodriguez, Nicolas B.; McGuire, Kevin J.; Klaus, Julian

2017-04-01

Transit time distributions, residence time distributions and StorAge Selection functions are fundamental integrated descriptors of water storage, mixing, and release in catchments. In this contribution, we determined these time-variant functions in four neighboring forested catchments in H.J. Andrews Experimental Forest, Oregon, USA by employing a two year time series of 18O in precipitation and discharge. Previous studies in these catchments assumed stationary, exponentially distributed transit times, and complete mixing/random sampling to explore the influence of various catchment properties on the mean transit time. Here we relaxed such assumptions to relate transit time dynamics and the variability of StoreAge Selection functions to catchment characteristics, catchment storage, and meteorological forcing seasonality. Conceptual models of the catchments, consisting of two reservoirs combined in series-parallel, were calibrated to discharge and stable isotope tracer data. We assumed randomly sampled/fully mixed conditions for each reservoir, which resulted in an incompletely mixed system overall. Based on the results we solved the Master Equation, which describes the dynamics of water ages in storage and in catchment outflows Consistent between all catchments, we found that transit times were generally shorter during wet periods, indicating the contribution of shallow storage (soil, saprolite) to discharge. During extended dry periods, transit times increased significantly indicating the contribution of deeper storage (bedrock) to discharge. Our work indicated that the strong seasonality of precipitation impacted transit times by leading to a dynamic selection of stored water ages, whereas catchment size was not a control on transit times. In general this work showed the usefulness of using time-variant transit times with conceptual models and confirmed the existence of the catchment age mixing behaviors emerging from other similar studies.

Influence of Convective Effect of Solar Winds on the CME Transit Time

NASA Astrophysics Data System (ADS)

Sun, Lu-yuan

2017-10-01

Based on an empirical model for predicting the transit time of coronal mass ejections (CMEs) proposed by Gopalswamy, 52 CME events which are related to the geomagnetic storms of Dst < -50 nT, and 10 CME events which caused extremely strong geomagnetic storms (Dst < -200 nT) in 1996- 2007 are selected, and combined with the observational data of the interplanetary solar winds that collected by the ACE satellite at 1AU, to analyze the influence of convective effect of ambient solar winds on the prediction of the CME transit time when it arrives at a place of 1 AU. After taking the convective effect of ambient solar winds into account, the standard deviation of predictions is reduced from 16.5 to 11.4 hours for the 52 CME events, and the prediction error is less than 15 hours for 68% of these events; while the standard deviation of predictions is reduced from 10.6 to 6.5 hours for the 10 CME events that caused extremely strong geomagnetic storms, and the prediction error is less than 5 hours for 6 of the 10 events. These results show that taking the convective effect of ambient solar winds into account can reduce the standard deviation of the predicted CME transit time, hence the convective effect of solar winds plays an important role for predicting the transit times of CME events.

Gastrointestinal Transit Time, Glucose Homeostasis and Metabolic Health: Modulation by Dietary Fibers

PubMed Central

Müller, Mattea; Canfora, Emanuel E.; Blaak, Ellen E.

2018-01-01

Gastrointestinal transit time may be an important determinant of glucose homeostasis and metabolic health through effects on nutrient absorption and microbial composition, among other mechanisms. Modulation of gastrointestinal transit may be one of the mechanisms underlying the beneficial health effects of dietary fibers. These effects include improved glucose homeostasis and a reduced risk of developing metabolic diseases such as obesity and type 2 diabetes mellitus. In this review, we first discuss the regulation of gastric emptying rate, small intestinal transit and colonic transit as well as their relation to glucose homeostasis and metabolic health. Subsequently, we briefly address the reported health effects of different dietary fibers and discuss to what extent the fiber-induced health benefits may be mediated through modulation of gastrointestinal transit. PMID:29495569

Proper time regularization and the QCD chiral phase transition

PubMed Central

Cui, Zhu-Fang; Zhang, Jin-Li; Zong, Hong-Shi

2017-01-01

We study the QCD chiral phase transition at finite temperature and finite quark chemical potential within the two flavor Nambu–Jona-Lasinio (NJL) model, where a generalization of the proper-time regularization scheme is motivated and implemented. We find that in the chiral limit the whole transition line in the phase diagram is of second order, whereas for finite quark masses a crossover is observed. Moreover, if we take into account the influence of quark condensate to the coupling strength (which also provides a possible way of how the effective coupling varies with temperature and quark chemical potential), it is found that a CEP may appear. These findings differ substantially from other NJL results which use alternative regularization schemes, some explanation and discussion are given at the end. This indicates that the regularization scheme can have a dramatic impact on the study of the QCD phase transition within the NJL model. PMID:28401889

Recanalization of Splenic Artery Aneurysm After Transcatheter Arterial Embolization Using N-Butyl Cyanoacrylate

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

Matsumoto, Keiji; Ushijima, Yasuhiro, E-mail: ushijima@radiol.med.kyushu-u.ac.jp; Tajima, Tsuyoshi

2010-02-15

A 65-year-old woman who had been diagnosed as having microscopic polyangiitis developed sudden abdominal pain and entered a state of shock. Abdominal CT showed massive hemoperitoneum, and emergent angiography revealed a ruptured splenic artery aneurysm. After direct catheterization attempts failed due to tortuous vessels and angiospasm, transcatheter arterial embolization using an n-butyl cyanoacrylate (NBCA)-lipiodol mixture was successfully performed. Fifty days later, the patient developed sudden abdominal pain again. Repeated angiography demonstrated recanalization of the splenic artery and splenic artery aneurysm. This time, the recanalized aneurysm was embolized using metallic coils with the isolation method. Physicians should keep in mind thatmore » recanalization can occur after transcatheter arterial embolization using N-butyl cyanoacrylate, which has been used as a permanent embolic agent.« less

Numerical modeling of dynamics of heart rate and arterial pressure during passive orthostatic test

NASA Astrophysics Data System (ADS)

Ishbulatov, Yu. M.; Kiselev, A. R.; Karavaev, A. S.

2018-04-01

A model of human cardiovascular system is proposed to describe the main heart rhythm, influence of autonomous regulation on frequency and strength of heart contractions and resistance of arterial vessels; process of formation of arterial pressure during systolic and diastolic phases; influence of respiration; synchronization between loops of autonomous regulation. The proposed model is used to simulate the dynamics of heart rate and arterial pressure during passive transition from supine to upright position. Results of mathematical modeling are compared to original experimental data.

Out-of-equilibrium dynamics driven by localized time-dependent perturbations at quantum phase transitions

NASA Astrophysics Data System (ADS)

Pelissetto, Andrea; Rossini, Davide; Vicari, Ettore

2018-03-01

We investigate the quantum dynamics of many-body systems subject to local (i.e., restricted to a limited space region) time-dependent perturbations. If the system crosses a quantum phase transition, an off-equilibrium behavior is observed, even for a very slow driving. We show that, close to the transition, time-dependent quantities obey scaling laws. In first-order transitions, the scaling behavior is universal, and some scaling functions can be computed exactly. For continuous transitions, the scaling laws are controlled by the standard critical exponents and by the renormalization-group dimension of the perturbation at the transition. Our protocol can be implemented in existing relatively small quantum simulators, paving the way for a quantitative probe of the universal off-equilibrium scaling behavior, without the need to manipulate systems close to the thermodynamic limit.

Finite-time scaling at the Anderson transition for vibrations in solids

NASA Astrophysics Data System (ADS)

Beltukov, Y. M.; Skipetrov, S. E.

2017-11-01

A model in which a three-dimensional elastic medium is represented by a network of identical masses connected by springs of random strengths and allowed to vibrate only along a selected axis of the reference frame exhibits an Anderson localization transition. To study this transition, we assume that the dynamical matrix of the network is given by a product of a sparse random matrix with real, independent, Gaussian-distributed nonzero entries and its transpose. A finite-time scaling analysis of the system's response to an initial excitation allows us to estimate the critical parameters of the localization transition. The critical exponent is found to be ν =1.57 ±0.02 , in agreement with previous studies of the Anderson transition belonging to the three-dimensional orthogonal universality class.

Relations between transit time, fermentation products, and hydrogen consuming flora in healthy humans.

PubMed

El Oufir, L; Flourié, B; Bruley des Varannes, S; Barry, J L; Cloarec, D; Bornet, F; Galmiche, J P

1996-06-01

To investigate whether transit time could influence H2 consuming flora and certain indices of colonic bacterial fermentation. Eight healthy volunteers (four methane excretors and four non-methane excretors) were studied for three, three week periods during which they received a controlled diet alone (control period), and then the same diet with cisapride or loperamide. At the end of each period, mean transit time (MTT) was estimated, an H2 lactulose breath test was performed, and stools were analysed. In the control period, transit time was inversely related to faecal weight, sulphate reducing bacteria counts, concentrations of total short chain fatty acids (SCFAs), propionic and butyric acids, and H2 excreted in breath after lactulose ingestion. Conversely, transit time was positively related to faecal pH and tended to be related to methanogen counts. Methanogenic bacteria counts were inversely related to those of sulphate reducing bacteria and methane excretors had slower MTT and lower sulphate reducing bacteria counts than non-methane excretors. Compared with the control period, MTT was significantly shortened (p < 0.05) by cisapride and prolonged (p < 0.05) by loperamide (73 (11) hours, 47 (5) hours and 147 (12) hours for control, cisapride, and loperamide, respectively, mean (SD)). Cisapride reduced transit time was associated with (a) a significant rise in faecal weight, sulphate reducing bacteria, concentrations of total SCFAs, and propionic and butyric acids and breath H2 as well as (b) a significant fall in faecal pH and breath CH4 excretion, and (c) a non-significant decrease in the counts of methanogenic bacteria. Reverse relations were roughly the same during the loperamide period including a significant rise in the counts of methanogenic bacteria and a significant fall in those of sulphate reducing bacteria. Transit time differences between healthy volunteers are associated with differences in H2 consuming flora and certain indices of colonic

Relations between transit time, fermentation products, and hydrogen consuming flora in healthy humans.

PubMed Central

El Oufir, L; Flourié, B; Bruley des Varannes, S; Barry, J L; Cloarec, D; Bornet, F; Galmiche, J P

1996-01-01

BACKGROUND/AIMS: To investigate whether transit time could influence H2 consuming flora and certain indices of colonic bacterial fermentation. METHODS: Eight healthy volunteers (four methane excretors and four non-methane excretors) were studied for three, three week periods during which they received a controlled diet alone (control period), and then the same diet with cisapride or loperamide. At the end of each period, mean transit time (MTT) was estimated, an H2 lactulose breath test was performed, and stools were analysed. RESULTS: In the control period, transit time was inversely related to faecal weight, sulphate reducing bacteria counts, concentrations of total short chain fatty acids (SCFAs), propionic and butyric acids, and H2 excreted in breath after lactulose ingestion. Conversely, transit time was positively related to faecal pH and tended to be related to methanogen counts. Methanogenic bacteria counts were inversely related to those of sulphate reducing bacteria and methane excretors had slower MTT and lower sulphate reducing bacteria counts than non-methane excretors. Compared with the control period, MTT was significantly shortened (p < 0.05) by cisapride and prolonged (p < 0.05) by loperamide (73 (11) hours, 47 (5) hours and 147 (12) hours for control, cisapride, and loperamide, respectively, mean (SD)). Cisapride reduced transit time was associated with (a) a significant rise in faecal weight, sulphate reducing bacteria, concentrations of total SCFAs, and propionic and butyric acids and breath H2 as well as (b) a significant fall in faecal pH and breath CH4 excretion, and (c) a non-significant decrease in the counts of methanogenic bacteria. Reverse relations were roughly the same during the loperamide period including a significant rise in the counts of methanogenic bacteria and a significant fall in those of sulphate reducing bacteria. CONCLUSIONS: Transit time differences between healthy volunteers are associated with differences in H2

Biomechanics of Ergometric Stress Test: regional and local effects on elastic, transitional and muscular human arteries

NASA Astrophysics Data System (ADS)

Valls, G.; Torrado, J.; Farro, I.; Bia, D.; Zócalo, Y.; Lluberas, S.; Craiem, D.; Armentano, Rl

2011-09-01

Ergometric exercise stress tests (EST) give important information about the cardiovascular (CV) response to increased demands. The expected EST-related changes in variables like blood pressure and heart rate are known, but those in the arterial biomechanics are controversial and incompletely characterized. In this context, this work aims were to characterize the regional and local arterial biomechanical behaviour in response to EST; to evaluate its temporal profile in the post-EST recovery phase; and to compare the biomechanical response of different to EST. Methods: In 16 non-trained healthy young subjects the carotid-femoral pulse wave velocity and the carotid, femoral and brachial arterial distensibility were non-invasively evaluated before (Rest) and after EST. Main results: The EST resulted in an early increase in the arterial stiffness, evidenced by both, regional and local parameters (pulse wave velocity increase and distensibility reduction). When analyzing conjunctly the different post-EST recovery stages there were quali-quantitative differences among the arterial local stiffness response to EST. The biomechanical changes could not be explained only by blood pressure variations.

Predictable Patterns in Planetary Transit Timing Variations and Transit Duration Variations Due to Exomoons

NASA Technical Reports Server (NTRS)

Heller, Rene; Hippke, Michael; Placek, Ben; Angerhausen, Daniel; Agol, Eric

2016-01-01

We present new ways to identify single and multiple moons around extrasolar planets using planetary transit timing variations (TTVs) and transit duration variations (TDVs). For planets with one moon, measurements from successive transits exhibit a hitherto undescribed pattern in the TTV-TDV diagram, originating from the stroboscopic sampling of the planet's orbit around the planet-moon barycenter. This pattern is fully determined and analytically predictable after three consecutive transits. The more measurements become available, the more the TTV-TDV diagram approaches an ellipse. For planets with multiple moons in orbital mean motion resonance (MMR), like the Galilean moon system, the pattern is much more complex and addressed numerically in this report. Exomoons in MMR can also form closed, predictable TTV-TDV figures, as long as the drift of the moons' pericenters is suciently slow.We find that MMR exomoons produce loops in the TTV-TDV diagram and that the number of these loops is equal to the order of the MMR, or the largest integer in the MMR ratio.We use a Bayesian model and Monte Carlo simulations to test the discoverability of exomoons using TTV-TDV diagrams with current and near-future technology. In a blind test, two of us (BP, DA) successfully retrieved a large moon from simulated TTV-TDV by co-authors MH and RH, which resembled data from a known Kepler planet candidate. Single exomoons with a 10 percent moon-to-planet mass ratio, like to Pluto-Charon binary, can be detectable in the archival data of the Kepler primary mission. Multi-exomoon systems, however, require either larger telescopes or brighter target stars. Complementary detection methods invoking a moon's own photometric transit or its orbital sampling effect can be used for validation or falsification. A combination of TESS, CHEOPS, and PLATO data would offer a compelling opportunity for an exomoon discovery around a bright star.

The Influence of Unpaid Work on the Transition Out of Full-Time Paid Work

PubMed Central

Carr, Dawn C.

2013-01-01

Purpose: Continued employment after retirement and engagement in unpaid work are both important ways of diminishing the negative economic effects of the retirement of baby boomer cohorts on society. Little research, however, examines the relationship between paid and unpaid work at the transition from full-time work. Using a resource perspective framework this study examines how engagement in unpaid work prior to and at the transition from full-time work influences whether individuals partially or fully retire. Design and Methods: This study used a sample of 2,236 Americans between the ages 50 and 68, who were interviewed between 1998 and 2008. Logistic regression was used to estimate transitioning into partial retirement (relative to full retirement) after leaving full-time work. Results: We found that the odds of transitioning into part-time work were increased by continuous volunteering (78%) and reduced by starting parental (84%), grandchild (41%), and spousal (90%) caregiving and unaffected by all other patterns of engagement in unpaid work. Implications: Our findings suggest that volunteering is complementary with a transition to part-time work, and starting a new caregiving role at this transitioncreates a barrier to continued employment. In order to provide workers the opportunity to engage in the work force longer at the brink of retirement, it may be necessary to increase the support mechanisms for those who experience new caregiving responsibilities. PMID:22859436

Radial electron-beam-breakup transit-time oscillator

DOEpatents

Kwan, Thomas J. T.; Mostrom, Michael A.

1998-01-01

A radial electron-beam-breakup transit-time oscillator (RBTO) provides a compact high power microwave generator. The RBTO includes a coaxial vacuum transmission line having an outer conductor and an inner conductor. The inner conductor defines an annular cavity with dimensions effective to support an electromagnetic field in a TEM.sub.00m mode. A radial field emission cathode is formed on the outer conductor for providing an electron beam directed toward the annular cavity electrode. Microwave energy is then extracted from the annular cavity electrode.

Effect of erythromycin on image quality and transit time of capsule endoscopy: A two-center study

PubMed Central

Niv, Eva; Bogner, Ido; Barkay, Olga; Halpern, Zamir; Mahajna, Elisabeth; Depsames, Roman; Kopelman, Yael; Fireman, Zvi

2008-01-01

AIM: To compare the effect of oral erythromycin vs no preparation with prokinetics on the transit time and the image quality of capsule endoscopy (CE) in evaluating small bowel (SB) pathology. METHODS: We conducted a retrospective, blinded (to the type of preparation) review of 100 CE studies, 50 with no preparation with prokinetics from one medical center (Group A) and 50 from another center with administration of a single dose of 200 mg oral erythromycin 1 h prior to CE (Group B). Gastric, SB and total transit times were calculated, the presence of bile in the duodenum was scored, as was cleanliness within the proximal, middle and distal intestine. RESULTS: The erythromycin group had a slightly shorter gastric transit time (21 min vs 28 min, with no statistical significance). SB transit time was similar for both groups (all P > 0.05). Total transit time was almost identical in both groups. The rate of incomplete examination was 16% for Group A and 10% for Group B (P = 0.37). Bile and cleanliness scores in different parts of the intestine were similar for the two groups (P > 0.05). CONCLUSION: Preparation for capsule endoscopy with erythromycin does not affect SB or total transit time. It tends to reduce gastric transit time, but it does not increase the cecum-reaching rate. Erythromycin does not adversely affect image quality. We consider the routine use of oral erythromycin preparation as being unjustified, although it might be considered in patients with known prolonged gastric emptying time. PMID:18442206

The use of the inferior epigastric artery for accessory lower polar artery revascularization in live donor renal transplantation.

PubMed

El-Sherbiny, M; Abou-Elela, A; Morsy, A; Salah, M; Foda, A

2008-01-01

This study describes the surgical technique and outcomes of live donor renal allografts with multiple arteries in which the lower polar artery was anastomosed to the inferior epigastric artery after declamping. Between 1988 and 2004, 477 consecutive live donor renal transplants were performed, including 429 with single and 48 with multiple arteries. Anastomosis of the lower polar artery to the inferior epigastric artery was used for 15 grafts with multiple arteries. Successful revascularization of all areas of the transplanted graft was confirmed by Doppler ultrasonography in most patients and radionuclide renal scanning +/- MRA in some patients. In live donor renal transplantation with multiple arteries, the anastomosis of the lower polar artery to the inferior epigastric artery after declamping avoids prolongation of the ischemia time that occurs with other surgical and microsurgical techniques of intracorporeal and ex vivo surgeries.

Proof of Concept: Design and Initial Evaluation of a Device to Measure Gastrointestinal Transit Time.

PubMed

Wagner, Robert H; Savir-Baruch, Bital; Halama, James R; Venu, Mukund; Gabriel, Medhat S; Bova, Davide

2017-09-01

Chronic constipation and gastrointestinal motility disorders constitute a large part of a gastroenterology practice and have a significant impact on a patient's quality of life and lifestyle. In most cases, medications are prescribed to alleviate symptoms without there being an objective measurement of response. Commonly used investigations of gastrointestinal transit times are currently limited to radiopaque markers or electronic capsules. Repeated use of these techniques is limited because of the radiation exposure and the significant cost of the devices. We present the proof of concept for a new device to measure gastrointestinal transit time using commonly available and inexpensive materials with only a small amount of radiotracer. Methods: We assembled gelatin capsules containing a 67 Ga-citrate-radiolabeled grain of rice embedded in paraffin for use as a point-source transit device. It was tested for stability in vitro and subsequently was given orally to 4 healthy volunteers and 10 patients with constipation or diarrhea. Imaging was performed at regular intervals until the device was excreted. Results: The device remained intact and visible as a point source in all subjects until excretion. When used along with a diary of bowel movement times and dates, the device could determine the total transit time. The device could be visualized either alone or in combination with a barium small-bowel follow-through study or a gastric emptying study. Conclusion: The use of a point-source transit device for the determination of gastrointestinal transit time is a feasible alternative to other methods. The device is inexpensive and easy to assemble, requires only a small amount of radiotracer, and remains inert throughout the gastrointestinal tract, allowing for accurate determination of gastrointestinal transit time. Further investigation of the device is required to establish optimum imaging parameters and reference values. Measurements of gastrointestinal transit time

Pulsatile spiral blood flow through arterial stenosis.

PubMed

Linge, Fabian; Hye, Md Abdul; Paul, Manosh C

2014-11-01

Pulsatile spiral blood flow in a modelled three-dimensional arterial stenosis, with a 75% cross-sectional area reduction, is investigated by using numerical fluid dynamics. Two-equation k-ω model is used for the simulation of the transitional flow with Reynolds numbers 500 and 1000. It is found that the spiral component increases the static pressure in the vessel during the deceleration phase of the flow pulse. In addition, the spiral component reduces the turbulence intensity and wall shear stress found in the post-stenosis region of the vessel in the early stages of the flow pulse. Hence, the findings agree with the results of Stonebridge et al. (2004). In addition, the results of the effects of a spiral component on time-varying flow are presented and discussed along with the relevant pathological issues.

A new model of arterial hemodynamics.

PubMed

Branzan, M; Sundri, G

1983-01-01

The determination of arterial blood flow parameters on the basis of ultrasound investigation requires a new hydrodynamic model of arterial circulation. Unlike previous research (Womersley, Bergel) considering the arterial pressure of its gradients to be known, the present model uses blood flow velocity and arterial radius magnitude easily obtained by ultrasound (Doppler effect). Processing these data requires the thorough analysis of rheological characteristics of blood flow and of arterial wall behaviour (elastic deformability). It has been assumed that: a) blood is a homogeneous and isotropic fluid; b) the artery has a cylindrical symmetry of a circular cross-section at any time moment; c) the pressure in the artery cross-section is constant. Because arterial dynamics has an undulatory character the Fourier analysis of the modified Navier-Stokes equations has been used. Finally, a simplified relation for blood pressure determination has been obtained.

Transit Timing Observations from Kepler. IX. Catalog of the Full Long-cadence Data Set

NASA Astrophysics Data System (ADS)

Holczer, Tomer; Mazeh, Tsevi; Nachmani, Gil; Jontof-Hutter, Daniel; Ford, Eric B.; Fabrycky, Daniel; Ragozzine, Darin; Kane, Mackenzie; Steffen, Jason H.

2016-07-01

We present a new transit timing catalog of 2599 Kepler Objects of Interest (KOIs), using the PDC-MAP long-cadence light curves that include the full 17 quarters of the mission (ftp://wise-ftp.tau.ac.il/pub/tauttv/TTV/ver_112). The goal is to produce an easy-to-use catalog that can stimulate further analyses of interesting systems. For 779 KOIs with high enough S/N, we derived the timing, duration, and depth of 69,914 transits. For 1820 KOIs with lower SNR, we derived only the timing of 225,273 transits. After removal of outlier timings, we derived various statistics for each KOI that were used to indicate significant variations. Including systems found by previous works, we have detected 260 KOIs that showed significant TTVs with long-term variations (>100 days), and another 14 KOIs with periodic modulations shorter than 100 days and small amplitudes. For five of those, the periodicity is probably due to the crossing of rotating stellar spots by the transiting planets.

Coronary artery to pulmonary artery fistula.

PubMed

Dadkhah-Tirani, Heidar; Salari, Arsalan; Shafighnia, Shora; Hosseini, Seyed Fazel; Naghdipoor, Misa

2013-01-01

Male, 69 FINAL DIAGNOSIS: Coronary artery to pulmonary artery fistula Symptoms: Chest pain Medication: - Clinical Procedure: Echocardiography • angiography • surgical intervention Specialty: Cardiology • Cardiac Surgery. Rare disease. A coronary artery fistula is an abnormal communication between a coronary artery and one of the cardiac chambers or a great vessel, so bypassing the myocardial capillary network. They are usually discovered incidentally upon coronary angiography. Clinical manifestations are variable depending on the type of fistula, the severity of shunt, site of shunt, and presence of other cardiac condition. We report a 69-year-old man without any previous medical history, who was admitted to our hospital with chest pain. The electrocardiogram (ECG) showed a sinus rhythm with ST depression in V2 to V6 precordial leads. Coronary angiography revealed a coronary artery fistula from left anterior descending coronary artery (LAD) to the main pulmonary artery, right coronary artery blockage and significant stenoses on the LAD and left circumflex artery (LCX). Surgical treatment was chosen because of the total occlusion of the right coronary artery and to relieve of pain to improve quality of life.

Dual-modality arterial pulse monitoring system for continuous blood pressure measurement.

PubMed

Wen-Xuan Dai; Yuan-Ting Zhang; Jing Liu; Xiao-Rong Ding; Ni Zhao

2016-08-01

Accurate and ambulatory measurement of blood pressure (BP) is essential for efficient diagnosis, management and prevention of cardiovascular diseases (CVDs). However, traditional cuff-based BP measurement methods provide only intermittent BP readings and can cause discomfort with the occlusive cuff. Although pulse transit time (PTT) method is promising for cuffless and continuous BP measurement, its pervasive use is restricted by its limited accuracy and requirement of placing sensors on multiple body sites. To tackle these issues, we propose a novel dual-modality arterial pulse monitoring system for continuous blood pressure measurement, which simultaneously records the pressure and photoplethysmography (PPG) signals of radial artery. The obtained signals can be used to generate a pressure-volume curve, from which the elasticity index (EI) and viscosity index (VI) can be extracted. Experiments were carried out among 7 healthy subjects with their PPG, ECG, arterial pressure wave and reference BP collected to examine the effectiveness of the proposed indexes. The results of this study demonstrate that a linear regression model combining EI and VI has significantly higher BP tracking correlation coefficient as compared to the PTT method. This suggests that the proposed system and method can potentially be used for convenient and continuous blood pressure estimation with higher accuracy.

Tunnel transit-time (TUNNETT) devices for terahertz sources

NASA Technical Reports Server (NTRS)

Haddad, G. I.; East, J. R.; Kidner, C.

1991-01-01

The potential and capabilities of tunnel transit-time (TUNNETT) devices for power generation in the 100-1000 GHz range are presented. The basic properties of these devices and the important material parameters which determine their properties are discussed and criteria for designing such devices are presented. It is shown from a first-order model that significant amounts of power can be obtained from these devices in the terahertz frequency range.

Magnetic resonance imaging and clinical outcome in patients with symptomatic carotid artery stenosis after carotid artery revascularization

PubMed Central

Badacz, Rafał; Urbańczyk-Zawadzka, Małgorzata; Banyś, Robert P.; Musiałek, Piotr; Odrowąż-Pieniążek, Piotr; Trystuła, Mariusz; Ścigalski, Jan; Żmudka, Krzysztof; Przewłocki, Tadeusz

2017-01-01

Introduction About 30% of patients with carotid artery stenosis (CAS) develop dementia after a cerebral ischemic event (CIE), and 20–50% suffer from CIE recurrence during 6 months. Carotid artery revascularization (CAR) may prevent CIE recurrence, at the cost of new microembolic lesions (MES). The impact of CAR on cognitive function is debatable. Aim To assess functional and cognitive outcome, cerebral flow on transcranial Doppler (TCD) and brain magnetic resonance imaging (MRI) in patients with symptomatic CAS referred for CAR. Material and methods Twenty-two patients (aged 69.0 ±7.2 y.o., 15 male) with recent CIE (21.9 ±20.9 days to CAR) related to CAS of mean 89.8 ±3.9% lumen reduction were prospectively evaluated with TCD, diffusion and perfusion MRI, Montreal Cognitive Assessment (MoCA), Mini Mental State Examination (MMSE), modified Rankin Scale (mRS) and the National Institutes of Health Stroke Scale (NIHSS) 24 h before, at 24–48 h and 1 month following CAR. Results New MES were found in 11 (50%) subjects following CAR. CAR resulted in a significant increase of cerebral flow velocity in the middle and anterior cerebral arteries (p < 0.002 and p = 0.003; respectively) and cerebral perfusion measured by time to peak (TTP) and mean transit time (MTT) (p = 0.0009 and p = 0.0002; respectively). Neurologic tests showed improvement in NIHSS (2.4 ±1.6 to 1.5 ±1.2, p = 0.003), mRS (from 1.3 ±0.9 to 0.7 ±0.9, p = 0.005), and MMSE (26.7 ±2.2 to 27.6 ±2.3, p = 0.019) at 1 month, while similar MoCA scores were observed before and 1 month after CAR (23.4 ±3.3 vs. 24.1 ±3.7, p = 0.136). Conclusions Improvement of cerebral flow and perfusion and functional outcome, as well as at least no cognitive decline, is observed after CAR for symptomatic CAS. PMID:29056995

Time-dependent reflection at the localization transition

NASA Astrophysics Data System (ADS)

Skipetrov, Sergey E.; Sinha, Aritra

2018-03-01

A short quasimonochromatic wave packet incident on a semi-infinite disordered medium gives rise to a reflected wave. The intensity of the latter decays as a power law, 1 /tα , in the long-time limit. Using the one-dimensional Aubry-André model, we show that in the vicinity of the critical point of Anderson localization transition, the decay slows down, and the power-law exponent α becomes smaller than both α =2 found in the Anderson localization regime and α =3 /2 expected for a one-dimensional random walk of classical particles.

Estimation of liquid volume fraction using ultrasound transit time spectroscopy

NASA Astrophysics Data System (ADS)

Al-Qahtani, Saeed M.; Langton, Christian M.

2016-12-01

It has recently been proposed that the propagation of an ultrasound wave through complex structures, consisting of two-materials of differing ultrasound velocity, may be considered as an array of parallel ‘sonic rays’, the transit time of each determined by their relative proportion; being a minimum (t min) in entire higher velocity material, and a maximum (t max) in entire lower velocity material. An ultrasound transit time spectrum (UTTS) describes the proportion of sonic rays at an individual transit time. It has previously been demonstrated that the solid volume fraction of a solid:liquid composite, specifically acrylic step-wedges immersed in water, may be reliably estimated from the UTTS. The aim of this research was to investigate the hypothesis that the volume fraction of a two-component liquid mixture, of unequal ultrasound velocity, may also be estimated by UTTS. A through-transmission technique incorporating two 1 MHz ultrasound transducers within a horizontally-aligned cylindrical tube-housing was utilised, the proportion of silicone oil to water being varied from 0% to 100%. The liquid volume fraction was estimated from the UTTS at each composition, the coefficient of determination (R 2%) being 98.9  ±  0.7%. The analysis incorporated a novel signal amplitude normalisation technique to compensate for absorption within the silicone oil. It is therefore envisaged that the parallel sonic ray concept and the derived UTTS may be further applied to the quantification of liquid mixture composition assessment.

Excellent Long-Term Outcomes of the Arterial Switch Operation in Patients With Intramural Coronary Arteries.

PubMed

Fricke, Tyson A; Bulstra, Anne Eva; Naimo, Phillip S; Bullock, Andrew; Robertson, Terry; d'Udekem, Yves; Brizard, Christian P; Konstantinov, Igor E

2016-02-01

Intramural coronary arteries may complicate coronary artery transfer during the arterial switch operation. We sought to determine the long-term outcomes of 28 patients with intramural coronary arteries who underwent an arterial switch operation at a single institution. All patients who had intramural coronary arteries and underwent an arterial switch operation were identified from the hospital database and retrospectively reviewed. From 1983 to 2009, 720 patients underwent an arterial switch operation at our institution. Twenty-eight (3.9%, 28 of 720) had intramural coronary arteries. Patients with intramural coronary arteries had transposition of the great arteries (96%, n = 27) or Taussig-Bing anomaly (4%, n = 1). There were no deaths. Follow-up was 100% complete. Mean follow-up was 16.3 years (median, 15.5 years; range, 5.6 to 26.9 years). No patient required reoperation or catheter reintervention on the coronary arteries. Freedom from reoperation was 93% at 10 years. No patient had more than mild aortic regurgitation at last follow-up. Nine (32%, 9 of 28) patients had coronary angiograms at median 16 months (range, 14 months to 17 years) after arterial switch operation. All patients were asymptomatic at the time of angiogram. One patient had mild stenosis of the circumflex coronary artery demonstrated on a routine coronary angiogram 14 months postoperatively. All 28 patients were asymptomatic and in New York Heart Association functional class I at last follow-up. Patients with intramural coronary arteries are not at increased risk of death or coronary reinterventions and have excellent late outcomes after the arterial switch operation. Copyright © 2016 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.

Decreased femoral arterial flow during simulated microgravity in the rat

NASA Technical Reports Server (NTRS)

Roer, Robert D.; Dillaman, Richard M.

1994-01-01

To determine whether the blood supply to the hindlimbs of rats is altered by the tail-suspension model of weightlessness, rats were chronically instrumented for the measurement of femoral artery flow. Ultrasonic transit-time flow probes were implanted into 8-wk-old Wistar-Furth rats under ketamine-xylazine anesthesia, and, after 24 h of recovery, flow was measured in the normal ambulatory posture. Next, rats were suspended and flow was measured immediately and then daily over the next 4-7 days. Rats were subsequently returned to normal posture, and flow was monitored daily for 1-3 days. Mean arterial flow decreased immediately on the rats being suspensed and continued to decrease until a new steady state of approximately 60% of control values was attained at 5 days. On the rats returning to normal posture, flow increased to levels observed before suspension. Quantile-quantile plots of blood flow data revealed a decrease in flow during both systole and diastole. The observed decrease in hindlimb blood flow during suspension suggests a possible role in the etiology of muscular atrophy and bone loss in microgravity.

A search for transit timing variations and orbital decay in WASP-46b

NASA Astrophysics Data System (ADS)

Petrucci, R.; Jofré, E.; Ferrero, L. V.; Cúneo, V.; Saker, L.; Lovos, F.; Gómez, M.; Mauas, P.

2018-02-01

We present 12 new transit observations of the exoplanet WASP-46b obtained with the 1.54-m telescope at Estación Astrofísica de Bosque Alegre (EABA, Argentina) and the 0.40-m Horacio Ghielmetti and 2.15-m Jorge Sahade telescopes at Complejo Astronómico El Leoncito (CASLEO, Argentina). We analyse them together with 37 light curves from the literature to re-determine the physical parameters and search for additional planets via transit timing variations (TTVs). We consider the 31 transits with uncertainties in their mid-transit times (e_T0) < 1 min, to perform the first homogeneous study of TTVs for the system, finding a dispersion of σ = 1.66 min over a 6 yr baseline. Since no periodic variations are found, our interpretation for this relatively high value of σ is that the stellar activity could be affecting the measured mid-transit times. This value of dispersion allows us to rule out the presence of additional bodies with masses larger than 2.3, 4.6, 7 and 9.3 M_{\\oplus} at the first-order mean-motion resonances 2:1, 3:2, 4:3 and 5:4 with the transiting planet, respectively. Despite the 6 yr baseline and a typical light-curve precision of 2 × 10-3, we find that we cannot significantly demonstrate a slow decrease of the orbital period of WASP-46b. We place a lower limit of Q⋆ > 7 × 103 on the tidal quality factor and determine that an additional 6 yr baseline is required to rule out Q⋆ < 105.

Use of Caval Subtraction 2D Phase-Contrast MR Imaging to Measure Total Liver and Hepatic Arterial Blood Flow: Preclinical Validation and Initial Clinical Translation.

PubMed

Chouhan, Manil D; Mookerjee, Rajeshwar P; Bainbridge, Alan; Walker-Samuel, Simon; Davies, Nathan; Halligan, Steve; Lythgoe, Mark F; Taylor, Stuart A

2016-09-01

Purpose To validate caval subtraction two-dimensional (2D) phase-contrast magnetic resonance (MR) imaging measurements of total liver blood flow (TLBF) and hepatic arterial fraction in an animal model and evaluate consistency and reproducibility in humans. Materials and Methods Approval from the institutional ethical committee for animal care and research ethics was obtained. Fifteen Sprague-Dawley rats underwent 2D phase-contrast MR imaging of the portal vein (PV) and infrahepatic and suprahepatic inferior vena cava (IVC). TLBF and hepatic arterial flow were estimated by subtracting infrahepatic from suprahepatic IVC flow and PV flow from estimated TLBF, respectively. Direct PV transit-time ultrasonography (US) and fluorescent microsphere measurements of hepatic arterial fraction were the standards of reference. Thereafter, consistency of caval subtraction phase-contrast MR imaging-derived TLBF and hepatic arterial flow was assessed in 13 volunteers (mean age, 28.3 years ± 1.4) against directly measured phase-contrast MR imaging PV and proper hepatic arterial inflow; reproducibility was measured after 7 days. Bland-Altman analysis of agreement and coefficient of variation comparisons were undertaken. Results There was good agreement between PV flow measured with phase-contrast MR imaging and that measured with transit-time US (mean difference, -3.5 mL/min/100 g; 95% limits of agreement [LOA], ±61.3 mL/min/100 g). Hepatic arterial fraction obtained with caval subtraction agreed well with those with fluorescent microspheres (mean difference, 4.2%; 95% LOA, ±20.5%). Good consistency was demonstrated between TLBF in humans measured with caval subtraction and direct inflow phase-contrast MR imaging (mean difference, -1.3 mL/min/100 g; 95% LOA, ±23.1 mL/min/100 g). TLBF reproducibility at 7 days was similar between the two methods (95% LOA, ±31.6 mL/min/100 g vs ±29.6 mL/min/100 g). Conclusion Caval subtraction phase-contrast MR imaging is a simple and clinically

The effects of capillary transit time heterogeneity (CTH) on brain oxygenation

PubMed Central

Angleys, Hugo; Østergaard, Leif; Jespersen, Sune N

2015-01-01

We recently extended the classic flow–diffusion equation, which relates blood flow to tissue oxygenation, to take capillary transit time heterogeneity (CTH) into account. Realizing that cerebral oxygen availability depends on both cerebral blood flow (CBF) and capillary flow patterns, we have speculated that CTH may be actively regulated and that changes in the capillary morphology and function, as well as in blood rheology, may be involved in the pathogenesis of conditions such as dementia and ischemia-reperfusion injury. The first extended flow–diffusion equation involved simplifying assumptions which may not hold in tissue. Here, we explicitly incorporate the effects of oxygen metabolism on tissue oxygen tension and extraction efficacy, and assess the extent to which the type of capillary transit time distribution affects the overall effects of CTH on flow–metabolism coupling reported earlier. After incorporating tissue oxygen metabolism, our model predicts changes in oxygen consumption and tissue oxygen tension during functional activation in accordance with literature reports. We find that, for large CTH values, a blood flow increase fails to cause significant improvements in oxygen delivery, and can even decrease it; a condition of malignant CTH. These results are found to be largely insensitive to the choice of the transit time distribution. PMID:25669911

Dynamic contrast–enhanced magnetic resonance imaging in patients with pulmonary arterial hypertension

PubMed Central

Condliffe, Robin; Marshall, Helen; Elliot, Charlie; Kiely, David G.; Wild, Jim M.

2014-01-01

Abstract Dynamic contrast–enhanced (DCE) time-resolved magnetic resonance (MR) imaging is a technique whereby the passage of an intravenous contrast bolus can be tracked through the pulmonary vascular system. The aim of this study was to investigate the prognostic significance of DCE-MR pulmonary blood transit times in patients with pulmonary arterial hypertension (PAH). Seventy-nine patients diagnosed with PAH underwent pulmonary DCE imaging at 1.5 T using a time-resolved three-dimensional spoiled gradient echo sequence. The prognostic significance of two DCE parameters, full width at half maximum (FWHM) of the first-pass clearance curve and pulmonary transit time (PTT), along with demographic and invasive catheter measurements, was evaluated by univariate and bivariate Cox proportional hazards regression and Kaplan-Meier analysis. DCE-MR transit times were most closely correlated with cardiac index (CI) and pulmonary vascular resistance index (PVRI) and were both found to be accurate for detecting reduced CI (FWHM area under the curve [AUC] at receiver operating characteristic analysis = 0.91 and PTT AUC = 0.92, respectively) and for detecting elevated PVRI (FWHM AUC = 0.88 and PTT AUC = 0.84, respectively). During the follow-up period, 25 patients died. Patients with longer measurements of FWHM (P = 0.0014) and PTT (P = 0.004) were associated with poor outcome at Kaplan-Meier analysis, and both parameters were strong predictors of adverse outcome from Cox proportional hazards analysis (P = 0.013 and 0.010, respectively). At bivariate analysis, DCE measurements predicted mortality independent of age, gender, and World Health Organization functional class; however, invasive hemodynamic indexes CI, PVRI, and DCE measurements were not independent of one another. In conclusion, DCE-MR transit times predict mortality in patients with PAH and are closely associated with clinical gold standards CI and PVRI. PMID:25006422

Dynamic contrast-enhanced magnetic resonance imaging in patients with pulmonary arterial hypertension.

PubMed

Swift, Andrew J; Telfer, Adam; Rajaram, Smitha; Condliffe, Robin; Marshall, Helen; Capener, Dave; Hurdman, Judith; Elliot, Charlie; Kiely, David G; Wild, Jim M

2014-03-01

Dynamic contrast-enhanced (DCE) time-resolved magnetic resonance (MR) imaging is a technique whereby the passage of an intravenous contrast bolus can be tracked through the pulmonary vascular system. The aim of this study was to investigate the prognostic significance of DCE-MR pulmonary blood transit times in patients with pulmonary arterial hypertension (PAH). Seventy-nine patients diagnosed with PAH underwent pulmonary DCE imaging at 1.5 T using a time-resolved three-dimensional spoiled gradient echo sequence. The prognostic significance of two DCE parameters, full width at half maximum (FWHM) of the first-pass clearance curve and pulmonary transit time (PTT), along with demographic and invasive catheter measurements, was evaluated by univariate and bivariate Cox proportional hazards regression and Kaplan-Meier analysis. DCE-MR transit times were most closely correlated with cardiac index (CI) and pulmonary vascular resistance index (PVRI) and were both found to be accurate for detecting reduced CI (FWHM area under the curve [AUC] at receiver operating characteristic analysis = 0.91 and PTT AUC = 0.92, respectively) and for detecting elevated PVRI (FWHM AUC = 0.88 and PTT AUC = 0.84, respectively). During the follow-up period, 25 patients died. Patients with longer measurements of FWHM (P = 0.0014) and PTT (P = 0.004) were associated with poor outcome at Kaplan-Meier analysis, and both parameters were strong predictors of adverse outcome from Cox proportional hazards analysis (P = 0.013 and 0.010, respectively). At bivariate analysis, DCE measurements predicted mortality independent of age, gender, and World Health Organization functional class; however, invasive hemodynamic indexes CI, PVRI, and DCE measurements were not independent of one another. In conclusion, DCE-MR transit times predict mortality in patients with PAH and are closely associated with clinical gold standards CI and PVRI.

Transit timing variations for planets co-orbiting in the horseshoe regime

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

Vokrouhlický, David; Nesvorný, David, E-mail: vokrouhl@cesnet.cz, E-mail: davidn@boulder.swri.edu

2014-08-10

Although not yet detected, pairs of exoplanets in 1:1 mean motion resonance probably exist. Low eccentricity, near-planar orbits, which in the comoving frame follow horseshoe trajectories, are one of the possible stable configurations. Here we study transit timing variations (TTVs) produced by mutual gravitational interaction of planets in this orbital architecture, with the goal to develop methods that can be used to recognize this case in observational data. In particular, we use a semi-analytic model to derive parametric constraints that should facilitate data analysis. We show that characteristic traits of the TTVs can directly constrain the (1) ratio of planetarymore » masses and (2) their total mass (divided by that of the central star) as a function of the minimum angular separation as seen from the star. In an ideal case, when transits of both planets are observed and well characterized, the minimum angular separation can also be inferred from the data. As a result, parameters derived from the observed transit timing series alone can directly provide both planetary masses scaled to the central star mass.« less

An analysis of the transit times of TrES-1b

NASA Astrophysics Data System (ADS)

Steffen, Jason H.; Agol, Eric

2005-11-01

The presence of a second planet in a known, transiting-planet system will cause the time between transits to vary. These variations can be used to constrain the orbital elements and mass of the perturbing planet. We analyse the set of transit times of the TrES-1 system given in Charbonneau et al. We find no convincing evidence for a second planet in the TrES-1 system from those data. By further analysis, we constrain the mass that a perturbing planet could have as a function of the semi-major axis ratio of the two planets and the eccentricity of the perturbing planet. Near low-order, mean-motion resonances (within ~1 per cent fractional deviation), we find that a secondary planet must generally have a mass comparable to or less than the mass of the Earth - showing that these data are the first to have sensitivity to sub-Earth-mass planets. We compare the sensitivity of this technique to the mass of the perturbing planet with future, high-precision radial velocity measurements.

Relation between digital peripheral arterial tonometry and brachial artery ultrasound measures of vascular function in patients with coronary artery disease and in healthy volunteers.

PubMed

Lee, Craig R; Bass, Almasa; Ellis, Kyle; Tran, Bryant; Steele, Savanna; Caughey, Melissa; Stouffer, George A; Hinderliter, Alan L

2012-03-01

Digital peripheral arterial tonometry (PAT) is an emerging, noninvasive method to assess vascular function. The physiology underlying this phenotype, however, remains unclear. Therefore, we evaluated the relation between digital PAT and established brachial artery ultrasound measures of vascular function under basal conditions and after reactive hyperemia. Using a cross-sectional study design, digital PAT and brachial artery ultrasonography with pulsed wave Doppler were simultaneously completed at baseline and after reactive hyperemia in both those with established coronary artery disease (n = 99) and healthy volunteers with low cardiovascular disease risk (n = 40). Under basal conditions, the digital pulse volume amplitude demonstrated a significant positive correlation with the brachial artery velocity-time integral that was independent of the arterial diameter, in both the healthy volunteer (r(s) = 0.64, p <0.001) and coronary artery disease (r(s) = 0.63, p <0.001) cohorts. Similar positive relations were observed with the baseline brachial artery blood flow velocity and blood flow. In contrast, no relation between the reactive hyperemia-evoked digital PAT ratio and either brachial artery flow-mediated dilation or shear stress was observed in either cohort (p = NS). In conclusion, these findings demonstrate that the digital PAT measures of vascular function more closely reflect basal blood flow in the brachial artery than reactive hyperemia-induced changes in the arterial diameter or flow velocity, and the presence of vascular disease does not modify the physiology underlying the digital PAT phenotype. Copyright © 2012 Elsevier Inc. All rights reserved.

Caregivers' Playfulness and Infants' Emotional Stress during Transitional Time

ERIC Educational Resources Information Center

Jung, Jeesun

2011-01-01

The purpose of this study is to explore the playfulness of the teachers of infants and its relations to infants' emotional distress during the transitional time at a child care centre. The study used a qualitative case study. Two infant caregivers in a university-based child care centre participated in this study. For the three-month research…

[Topographico-anatomic data on the testicular artery, ductus deferens artery and cremaster artery in the stallion].

PubMed

Jantosovicová, J; Jantosovic, J

1983-01-01

To study the vascularization of the testis of stallions we used 96 testes. We examined its topography and anatomy by roentgenography, stereoroentgenography, by the corosive method, and by means of gel and China ink injections. To make the roentgeno-arteriograms we used minimum emulsified in glycerine as contrast medium. The branching off of the Aa. testiculares from the Aorta abdominalis is variable in stallions. We observed also a peculiar age-dependent arrangement of the loops of the convolution. In the adult stallion, the shape of the convolution is either cylindrical or conical, spindle-shaped, or irregular. Bifurcation of the A. testicularis before entering the testis did not occur. The epididymical arteries arise either from the convolution or from the Pars recta a. testicularis. They may ramify from a common branch near the origine of A. testicularis. We found regular, direct anastomoses between A. epididymidis cranialis and the branches from the Rr. testiculares. Pars marginalis a. testicularis bifurcates at the transition plane of Margo epididymidis and Margo liber, eventually in the middle 1/3 of Margo epididymidis. Rr. testiculares run parallelly along the Margo liber and give off a number of verically arising branches. The Aa. radiatae centripetales run to the Mediastinum testis without giving off branches. We have not found any anstomoses between the centripetal arteries or the centripetal and centrifugal ones. The A. ductus deferentis is just as thick as the branches from the A. epididymidis caudalis. The lumina of the A. cremasterica is 0.5 to 1 mm. We did not succeed in filling it up reversely through the A. epididymidis caudalis. The artery anastomoses with A. ductus deferentis and A. epididymidis caudalis.

Transit time spreads in biased paracentric hemispherical deflection analyzers

NASA Astrophysics Data System (ADS)

Sise, Omer; Zouros, Theo J. M.

2016-02-01

The biased paracentric hemispherical deflection analyzers (HDAs) are an alternative to conventional (centric) HDAs maintaining greater dispersion, lower angular aberrations, and hence better energy resolution without the use of any additional fringing field correctors. In the present work, the transit time spread of the biased paracentric HDA is computed over a wide range of analyzer parameters. The combination of high energy resolution with good time resolution and simplicity of design makes the biased paracentric analyzers very promising for both coincidence and singles spectroscopy applications.

Lifetime measurements in transitional nuclei by fast electronic scintillation timing

NASA Astrophysics Data System (ADS)

Caprio, M. A.; Zamfir, N. V.; Casten, R. F.; Amro, H.; Barton, C. J.; Beausang, C. W.; Cooper, J. R.; Gürdal, G.; Hecht, A. A.; Hutter, C.; Krücken, R.; McCutchan, E. A.; Meyer, D. A.; Novak, J. R.; Pietralla, N.; Ressler, J. J.; Berant, Z.; Brenner, D. S.; Gill, R. L.; Regan, P. H.

2002-10-01

A new generation of experiments studying nuclei in spherical-deformed transition regions has been motivated by the introduction of innovative theoretical approaches to the treatment of these nuclei. The important structural signatures in the transition regions, beyond the basic yrast level properties, involve γ-ray transitions between low-spin, non-yrast levels, and so information on γ-ray branching ratios and absolute matrix elements (or level lifetimes) for these transitions is crucial. A fast electronic scintillation timing (FEST) system [H. Mach, R. L. Gill, and M. Moszyński, Nucl. Instrum. Methods A 280, 49 (1989)], making use of BaF2 and plastic scintillation detectors, has been implemented at the Yale Moving Tape Collector for the measurement of lifetimes of states populated in β^ decay. Experiments in the A100 (Pd, Ru) and A150 (Dy, Yb) regions have been carried out, and a few examples will be presented. Supported by the US DOE under grants and contracts DE-FG02-91ER-40609, DE-FG02-88ER-40417, and DE-AC02-98CH10886 and by the German DFG under grant Pi 393/1.

Radial mean arterial pressure reliably reflects femoral mean arterial pressure in uncomplicated pediatric cardiac surgery.

PubMed

Cetin, Secil; Pirat, Arash; Kundakci, Aycan; Camkiran, Aynur; Zeyneloglu, Pinar; Ozkan, Murat; Arslan, Gulnaz

2014-02-01

To see if radial mean arterial pressure reliably reflects femoral mean arterial pressure in uncomplicated pediatric cardiac surgery. An ethics committee-approved prospective interventional study. Operating room of a tertiary care hospital. Forty-five children aged 3 months to 4 years who underwent pediatric cardiac surgery with hypothermic cardiopulmonary bypass. Simultaneous femoral and radial arterial pressures were recorded at 10-minute intervals intraoperatively. A pressure gradient>5mmHg was considered to be clinically significant. The patients' mean age was 14±11 months and and mean weight was 8.0±3.0kg. A total of 1,816 simultaneous measurements of arterial pressure from the radial and femoral arteries were recorded during the pre-cardiopulmonary bypass, cardiopulmonary bypass, and post-cardiopulmonary bypass periods, including 520 (29%) systolic arterial pressures, 520 (29%) diastolic arterial pressures, and 776 (43%) mean arterial pressures. The paired mean arterial pressure measurements across the 3 periods were significantly and strongly correlated, and this was true for systolic arterial pressures and diastolic arterial pressures as well (r>0.93 and p<0.001 for all). Bland-Altman plots demonstrated good agreement between femoral and radial mean arterial pressures during the pre-cardiopulmonary bypass, cardiopulmonary bypass, and post-cardiopulmonary bypass periods. A significant radial-to-femoral pressure gradient was observed in 150 (8%) of the total 1,816 measurements. These gradients occurred most frequently between pairs of systolic arterial pressure measurements (n = 113, 22% of all systolic arterial pressures), followed by mean arterial pressure measurements (n = 28, 4% of all mean arterial pressures) and diastolic arterial pressures measurements (n = 9, 2% of all diastolic arterial pressures). These significant gradients were not sustained (ie, were not recorded at 2 or more successive time points). The results suggested that radial mean

Influence of pregnancy and smoking on brachial artery flow-mediated dilation values and time until maximum response.

PubMed

Nicolau, Luis G C; Martins, Wellington P; Gallarreta, Francisco M P; Lima, Jailson C; Filho, Francisco Mauad

2011-08-01

To evaluate the effect of pregnancy and smoking on endothelial function using brachial artery flow-mediated dilation (FMD) and to determine the time necessary until the occurrence of maximum brachial artery dilation after stimulus. This study was an observational study evaluating 133 women, who were grouped as follows: non-smoking pregnant women (N = 47), smoking pregnant women (N = 33), non-smoking women (N = 34), and smoking pregnant women (N = 19). The diameter of the brachial artery was measured at baseline and at 30, 60, 90 and 120 s after stimulus. The relative change of brachial artery was determined for each of these four moments. FMD measured at 60 s after stimulus was compared between the groups. The maximum FMD was observed at 60 s after cuff release in all groups. FMD was greater among non-smoking pregnant women compared to smoking pregnant women (11.50 ± 5.77 vs. 8.74 ± 4.83; p = 0.03) and also between non-smoking non-pregnant women compared to smoking non-pregnant women (10.52 ± 4.76 vs. 7.21 ± 5.57; p = 0.03). Maximum FMD was observed approximately 60 s after stimulus in all groups regardless of smoking and pregnancy status. The smoking habit seems to lead to endothelial dysfunction both in pregnant and non-pregnant women, as demonstrated by the lower FMD in smokers.

Lack of benefit from percutaneous intervention of persistently occluded infarct arteries after the acute phase of myocardial infarction is time independent: insights from Occluded Artery Trial

PubMed Central

Menon, Venu; Pearte, Camille A.; Buller, Christopher E.; Steg, Ph.Gabriel; Forman, Sandra A.; White, Harvey D.; Marino, Paolo N.; Katritsis, Demosthenes G.; Caramori, Paulo; Lasevitch, Ricardo; Loboz-Grudzien, Krystyna; Zurakowski, Aleksander; Lamas, Gervasio A.; Hochman, Judith S.

2009-01-01

Aims The Occluded Artery Trial (OAT) (n = 2201) showed no benefit for routine percutaneous intervention (PCI) (n = 1101) over medical therapy (MED) (n = 1100) on the combined endpoint of death, myocardial infarction (MI), and class IV heart failure (congestive heart failure) in stable post-MI patients with late occluded infarct-related arteries (IRAs). We evaluated the potential for selective benefit with PCI over MED for patients enrolled early in OAT. Methods and results We explored outcomes with PCI over MED in patients randomized to the ≤3 calendar days and ≤7 calendar days post-MI time windows. Earlier, times to randomization in OAT were associated with higher rates of the combined endpoint (adjusted HR 1.04/day: 99% CI 1.01–1.06; P < 0.001). The 48-month event rates for ≤3 days, ≤7 days post-MI enrolled patients were similar for PCI vs. MED for the combined and individual endpoints. There was no interaction between time to randomization defined as a continuous (P = 0.55) or categorical variable with a cut-point of 3 days (P = 0.98) or 7 days (P = 0.64) post-MI and treatment effect. Conclusion Consistent with overall OAT findings, patients enrolled in the ≤3 day and ≤7 day post-MI time windows derived no benefit with PCI over MED with no interaction between time to randomization and treatment effect. Our findings do not support routine PCI of the occluded IRA in trial-eligible patients even in the earliest 24–72 h time window. PMID:19028780

User-guided automated segmentation of time-series ultrasound images for measuring vasoreactivity of the brachial artery induced by flow mediation

NASA Astrophysics Data System (ADS)

Sehgal, Chandra M.; Kao, Yen H.; Cary, Ted W.; Arger, Peter H.; Mohler, Emile R.

2005-04-01

Endothelial dysfunction in response to vasoactive stimuli is closely associated with diseases such as atherosclerosis, hypertension and congestive heart failure. The current method of using ultrasound to image the brachial artery along the longitudinal axis is insensitive for measuring the small vasodilatation that occurs in response to flow mediation. The goal of this study is to overcome this limitation by using cross-sectional imaging of the brachial artery in conjunction with the User-Guided Automated Boundary Detection (UGABD) algorithm for extracting arterial boundaries. High-resolution ultrasound imaging was performed on rigid plastic tubing, on elastic rubber tubing phantoms with steady and pulsatile flow, and on the brachial artery of a healthy volunteer undergoing reactive hyperemia. The area of cross section of time-series images was analyzed by UGABD by propagating the boundary from one frame to the next. The UGABD results were compared by linear correlation with those obtained by manual tracing. UGABD measured the cross-sectional area of the phantom tubing to within 5% of the true area. The algorithm correctly detected pulsatile vasomotion in phantoms and in the brachial artery. A comparison of area measurements made using UGABD with those made by manual tracings yielded a correlation of 0.9 and 0.8 for phantoms and arteries, respectively. The peak vasodilatation due to reactive hyperemia was two orders of magnitude greater in pixel count than that measured by longitudinal imaging. Cross-sectional imaging is more sensitive than longitudinal imaging for measuring flow-mediated dilatation of brachial artery, and thus may be more suitable for evaluating endothelial dysfunction.

Understanding and Improving Arterial Roads to Support Public Health and Transportation Goals.

PubMed

McAndrews, Carolyn; Pollack, Keshia M; Berrigan, David; Dannenberg, Andrew L; Christopher, Ed J

2017-08-01

Arterials are types of roads designed to carry high volumes of motorized traffic. They are an integral part of transportation systems worldwide and exposure to them is ubiquitous, especially in urban areas. Arterials provide access to diverse commercial and cultural resources, which can positively influence community health by supporting social cohesion as well as economic and cultural opportunities. They can negatively influence health via safety issues, noise, air pollution, and lack of economic development. The aims of public health and transportation partially overlap; efforts to improve arterials can meet goals of both professions. Two trends in arterial design show promise. First, transportation professionals increasingly define the performance of arterials via metrics accounting for pedestrians, cyclists, transit riders, and nearby residents in addition to motor vehicle users. Second, applying traffic engineering and design can generate safety, air quality, and livability benefits, but we need evidence to support these interventions. We describe the importance of arterials (including exposures, health behaviors, effects on equity, and resulting health outcomes) and make the case for public health collaborations with the transportation sector.

Methods for Detecting Early Warnings of Critical Transitions in Time Series Illustrated Using Simulated Ecological Data

PubMed Central

Dakos, Vasilis; Carpenter, Stephen R.; Brock, William A.; Ellison, Aaron M.; Guttal, Vishwesha; Ives, Anthony R.; Kéfi, Sonia; Livina, Valerie; Seekell, David A.; van Nes, Egbert H.; Scheffer, Marten

2012-01-01

Many dynamical systems, including lakes, organisms, ocean circulation patterns, or financial markets, are now thought to have tipping points where critical transitions to a contrasting state can happen. Because critical transitions can occur unexpectedly and are difficult to manage, there is a need for methods that can be used to identify when a critical transition is approaching. Recent theory shows that we can identify the proximity of a system to a critical transition using a variety of so-called ‘early warning signals’, and successful empirical examples suggest a potential for practical applicability. However, while the range of proposed methods for predicting critical transitions is rapidly expanding, opinions on their practical use differ widely, and there is no comparative study that tests the limitations of the different methods to identify approaching critical transitions using time-series data. Here, we summarize a range of currently available early warning methods and apply them to two simulated time series that are typical of systems undergoing a critical transition. In addition to a methodological guide, our work offers a practical toolbox that may be used in a wide range of fields to help detect early warning signals of critical transitions in time series data. PMID:22815897

The Ebb and Flow of Filipino First-Time Fatherhood Transition Space: A Grounded Theory Study.

PubMed

Villamor, Neil Jupiter E; de Guzman, Allan B; Matienzo, Evangeline T

2016-11-01

Fatherhood, as a developmental process, is both a human experience and a text that needs to be read. For developing nations like the Philippines, little is known about the process undergone by first-time fathers on their transition to fatherhood, and how nurses can play a significant role in assisting them. This grounded theory study purported to conceptualize the multifaceted process of transition from the lens of Filipino first-time fathers' lived experiences. A total of 20 first-time fathers from Metro Manila, Philippines, were purposively selected to take part in an individual, semistructured, and in-depth interview. The Glaserian (classical) method of analysis was specifically used, and field texts were inductively analyzed using a repertory grid. Member checking and correspondence were done to validate the findings of the study. Six surfacing stages emerged relative to the process of transition. Interestingly, The B.R.I.D.G.E. Theory of First-Time Fatherhood Transition Space describes how these fathers progress from the beholding, reorganizing, inhibiting, delivering, grasping, and embracing phases toward successful transition. This emerged theoretical model can be used in framing health care programs where the needs of fathers during this period are met and addressed. Finally, it can also be used in guiding nurses in their provision of a more empathetic care for first-time fathers. © The Author(s) 2015.

Effects of three postexercice recovery treatments on femoral artery blood flow kinetics.

PubMed

Ménétrier, A; Mourot, L; Degano, B; Bouhaddi, M; Walther, G; Regnard, J; Tordi, N

2015-04-01

This study aimed to compare the kinetics of muscle leg blood flow during three recovery treatments following a prolonged exercise: contrast water therapy (CWT), compression stockings (CS) or passive recovery (PR). Fifteen men came to the laboratory three times to perform a 45-min exercise followed 5 min after by a standardized 12-min recovery treatment in upright position, alternating between two vats every 2 min: CWT (cold: ~12 °C to warm: 36 °C), CS (~20 mmHg) or PR. The order of treatments was randomized. Blood flow was measured using Doppler ultrasound during the recovery treatments (i.e., min 3, 5, 7 and 9) in the superficial femoral artery distally to the common bifurcation (~3 cm) (above the water and stocking). Blood flow was significantly higher during CWT (P<0.01; +22.91%) and CS (P<0.05; +15.26%) than during PR. Although no statistical difference between CWT and CS was observed, effect sizes were larger during CWT (large) than during CS (moderate). No changes in blood flow occurred in the femoral artery between hot and cold transitions of CWT. During immediate recovery of a high intensity exercise, CWT and CS trigger higher femoral artery blood flow than PR. Moreover, effect sizes were greater during CWT than during CS.

Withdrawal of long-term epoprostenol therapy in pulmonary arterial hypertension (PAH).

PubMed

Calcaianu, George; Calcaianu, Mihaela; Canuet, Matthieu; Enache, Irina; Kessler, Romain

2017-01-01

Once initiated for pulmonary arterial hypertension (PAH), epoprostenol treatment usually needs to be delivered for an indefinite duration. It is possible that some participants could be transitioned from epoprostenol to oral therapies. We retrospectively evaluated eight PAH participants transitioned from epoprostenol to PAH oral drugs. The criteria for epoprostenol withdrawal were: (1) persistent improvement of clinic and hemodynamic status; (2) stable dose of epoprostenol for the last three months; and (3) the participant's preference for oral therapy after evaluation of risk-benefit. We evaluated the clinical, functional, and hemodynamic status at baseline, at withdrawal, and after the transition to oral PAH therapy. The transition was completed in all eight participants. Four participants had a complete successful transition (CT) with a stable clinical and hemodynamic course and four participants had a partial successful transition (PT) remaining stable clinically, with a mild hemodynamic worsening, but without need to re-initiate epoprostenol therapy. The four CT participants were treated with epoprostenol for a shorter period of time (CT group: 35 ± 30 versus PT group: 79 ± 49 months, P = 0.08). Mean epoprostenol dosage was lower in the CT group (CT group: 15 ± 1.5 ng/kg/min versus PT group: 24 ± 11 ng/kg/min, P = 0.09). Safe withdrawal of epoprostenol treatment and transition to oral PAH therapy was possible in a small and highly selected group of participants. The majority of these participants had a porto-pulmonary PAH or PAH associated to HIV infection.

Wigner time-delay distribution in chaotic cavities and freezing transition.

PubMed

Texier, Christophe; Majumdar, Satya N

2013-06-21

Using the joint distribution for proper time delays of a chaotic cavity derived by Brouwer, Frahm, and Beenakker [Phys. Rev. Lett. 78, 4737 (1997)], we obtain, in the limit of the large number of channels N, the large deviation function for the distribution of the Wigner time delay (the sum of proper times) by a Coulomb gas method. We show that the existence of a power law tail originates from narrow resonance contributions, related to a (second order) freezing transition in the Coulomb gas.

Traumatic Axillary Artery Dissection with Radial Artery Embolism

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

Chung, Hwan-Hoon; Cha, Sang Hoon, E-mail: shcha123@naver.com; Cho, Sung Bum

This report describes a case of pathologically proven traumatic arterial dissection, presenting as complete occlusion of the axillary artery with radial artery embolism. Occlusion of the axillary artery by traumatic dissection mimicked transection and radial artery embolism mimicked congenital absence of the radial artery on the initial angiogram, but these were correctly diagnosed with the following sonogram.

Temporal and Spatial Variances in Arterial Spin-Labeling Are Inversely Related to Large-Artery Blood Velocity.

PubMed

Robertson, A D; Matta, G; Basile, V S; Black, S E; Macgowan, C K; Detre, J A; MacIntosh, B J

2017-08-01

The relationship between extracranial large-artery characteristics and arterial spin-labeling MR imaging may influence the quality of arterial spin-labeling-CBF images for older adults with and without vascular pathology. We hypothesized that extracranial arterial blood velocity can explain between-person differences in arterial spin-labeling data systematically across clinical populations. We performed consecutive pseudocontinuous arterial spin-labeling and phase-contrast MR imaging on 82 individuals (20-88 years of age, 50% women), including healthy young adults, healthy older adults, and older adults with cerebral small vessel disease or chronic stroke infarcts. We examined associations between extracranial phase-contrast hemodynamics and intracranial arterial spin-labeling characteristics, which were defined by labeling efficiency, temporal signal-to-noise ratio, and spatial coefficient of variation. Large-artery blood velocity was inversely associated with labeling efficiency ( P = .007), temporal SNR ( P < .001), and spatial coefficient of variation ( P = .05) of arterial spin-labeling, after accounting for age, sex, and group. Correction for labeling efficiency on an individual basis led to additional group differences in GM-CBF compared to correction using a constant labeling efficiency. Between-subject arterial spin-labeling variance was partially explained by extracranial velocity but not cross-sectional area. Choosing arterial spin-labeling timing parameters with on-line knowledge of blood velocity may improve CBF quantification. © 2017 by American Journal of Neuroradiology.

Transition to complete synchronization and global intermittent synchronization in an array of time-delay systems.

PubMed

Suresh, R; Senthilkumar, D V; Lakshmanan, M; Kurths, J

2012-07-01

We report the nature of transitions from the nonsynchronous to a complete synchronization (CS) state in arrays of time-delay systems, where the systems are coupled with instantaneous diffusive coupling. We demonstrate that the transition to CS occurs distinctly for different coupling configurations. In particular, for unidirectional coupling, locally (microscopically) synchronization transition occurs in a very narrow range of coupling strength but for a global one (macroscopically) it occurs sequentially in a broad range of coupling strength preceded by an intermittent synchronization. On the other hand, in the case of mutual coupling, a very large value of coupling strength is required for local synchronization and, consequently, all the local subsystems synchronize immediately for the same value of the coupling strength and, hence, globally, synchronization also occurs in a narrow range of the coupling strength. In the transition regime, we observe a type of synchronization transition where long intervals of high-quality synchronization which are interrupted at irregular times by intermittent chaotic bursts simultaneously in all the systems and which we designate as global intermittent synchronization. We also relate our synchronization transition results to the above specific types using unstable periodic orbit theory. The above studies are carried out in a well-known piecewise linear time-delay system.

Fast carotid artery MR angiography with compressed sensing based three-dimensional time-of-flight sequence.

PubMed

Li, Bo; Li, Hao; Dong, Li; Huang, Guofu

2017-11-01

In this study, we sought to investigate the feasibility of fast carotid artery MR angiography (MRA) by combining three-dimensional time-of-flight (3D TOF) with compressed sensing method (CS-3D TOF). A pseudo-sequential phase encoding order was developed for CS-3D TOF to generate hyper-intense vessel and suppress background tissues in under-sampled 3D k-space. Seven healthy volunteers and one patient with carotid artery stenosis were recruited for this study. Five sequential CS-3D TOF scans were implemented at 1, 2, 3, 4 and 5-fold acceleration factors for carotid artery MRA. Blood signal-to-tissue ratio (BTR) values for fully-sampled and under-sampled acquisitions were calculated and compared in seven subjects. Blood area (BA) was measured and compared between fully sampled acquisition and each under-sampled one. There were no significant differences between the fully-sampled dataset and each under-sampled in BTR comparisons (P>0.05 for all comparisons). The carotid vessel BAs measured from the images of CS-3D TOF sequences with 2, 3, 4 and 5-fold acceleration scans were all highly correlated with that of the fully-sampled acquisition. The contrast between blood vessels and background tissues of the images at 2 to 5-fold acceleration is comparable to that of fully sampled images. The images at 2× to 5× exhibit the comparable lumen definition to the corresponding images at 1×. By combining the pseudo-sequential phase encoding order, CS reconstruction, and 3D TOF sequence, this technique provides excellent visualizations for carotid vessel and calcifications in a short scan time. It has the potential to be integrated into current multiple blood contrast imaging protocol. Copyright © 2017. Published by Elsevier Inc.

A multivariate time-frequency method to characterize the influence of respiration over heart period and arterial pressure

NASA Astrophysics Data System (ADS)

Orini, Michele; Bailón, Raquel; Laguna, Pablo; Mainardi, Luca T.; Barbieri, Riccardo

2012-12-01

Respiratory activity introduces oscillations both in arterial pressure and heart period, through mechanical and autonomic mechanisms. Respiration, arterial pressure, and heart period are, generally, non-stationary processes and the interactions between them are dynamic. In this study we present a methodology to robustly estimate the time course of cross spectral indices to characterize dynamic interactions between respiratory oscillations of heart period and blood pressure, as well as their interactions with respiratory activity. Time-frequency distributions belonging to Cohen's class are used to estimate time-frequency (TF) representations of coherence, partial coherence and phase difference. The characterization is based on the estimation of the time course of cross spectral indices estimated in specific TF regions around the respiratory frequency. We used this methodology to describe the interactions between respiration, heart period variability (HPV) and systolic arterial pressure variability (SAPV) during tilt table test with both spontaneous and controlled respiratory patterns. The effect of selective autonomic blockade was also studied. Results suggest the presence of common underling mechanisms of regulation between cardiovascular signals, whose interactions are time-varying. SAPV changes followed respiratory flow both in supine and standing positions and even after selective autonomic blockade. During head-up tilt, phase differences between respiration and SAPV increased. Phase differences between respiration and HPV were comparable to those between respiration and SAPV during supine position, and significantly increased during standing. As a result, respiratory oscillations in SAPV preceded respiratory oscillations in HPV during standing. Partial coherence was the most sensitive index to orthostatic stress. Phase difference estimates were consistent among spontaneous and controlled breathing patterns, whereas coherence was higher in spontaneous breathing

A Novel External Carotid Arterial Sheath System for Intra-arterial Infusion Chemotherapy of Head and Neck Cancer.

PubMed

Ii, Noriko; Fuwa, Nobukazu; Toyomasu, Yutaka; Takada, Akinori; Nomura, Miwako; Kawamura, Tomoko; Sakuma, Hajime; Nomoto, Yoshihito

2017-07-01

The purpose of this study was to describe a novel system for treating advanced head and neck cancer consisting of an external carotid arterial sheath (ECAS) and a microcatheter to inject drugs retrogradely into multiple feeding arteries through the superficial temporal artery (STA). Four consecutive patients with head and neck cancer that had more than one feeding artery were enrolled in this study. The ECAS was made of polyurethane and surface-coated with heparin resin to prevent thrombus formation, allowing it to remain in place for a prolonged period of time. The ECAS was inserted through the STA, and its tip was placed between the maxillary artery and facial artery. The tumor-feeding arteries were selected using a hooked-shaped microcatheter through the ECAS. A total of 13 target arteries were selected in the four patients. The microcatheter inserted via the ECAS was used to catheterize ten arteries (five lingual arteries and five facial arteries). The remaining three lingual arteries were directly selected by the catheter without ECAS. All of the target arteries were able to be catheterized superselectively. The technical success rate was 100%. Vascular occlusion, which might have been caused by the ECAS, was observed in one patient. No neurologic toxicities occurred. This ECAS system is a new approach for retrograde superselective intra-arterial chemotherapy that covers the entire tumor with anticancer drugs. It has the potential to increase the effectiveness of therapy for advanced head and neck cancer. Level 4, Case Series.

TRANSIT TIMING OBSERVATIONS FROM KEPLER. VI. POTENTIALLY INTERESTING CANDIDATE SYSTEMS FROM FOURIER-BASED STATISTICAL TESTS

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

Steffen, Jason H.; Ford, Eric B.; Rowe, Jason F.

2012-09-10

We analyze the deviations of transit times from a linear ephemeris for the Kepler Objects of Interest (KOI) through quarter six of science data. We conduct two statistical tests for all KOIs and a related statistical test for all pairs of KOIs in multi-transiting systems. These tests identify several systems which show potentially interesting transit timing variations (TTVs). Strong TTV systems have been valuable for the confirmation of planets and their mass measurements. Many of the systems identified in this study should prove fruitful for detailed TTV studies.

Transit Timing Observations from Kepler: VII. Potentially interesting candidate systems from Fourier-based statistical tests

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

Steffen, Jason H.; /Fermilab; Ford, Eric B.

2012-01-01

We analyze the deviations of transit times from a linear ephemeris for the Kepler Objects of Interest (KOI) through Quarter six (Q6) of science data. We conduct two statistical tests for all KOIs and a related statistical test for all pairs of KOIs in multi-transiting systems. These tests identify several systems which show potentially interesting transit timing variations (TTVs). Strong TTV systems have been valuable for the confirmation of planets and their mass measurements. Many of the systems identified in this study should prove fruitful for detailed TTV studies.

A deconvolution method for deriving the transit time spectrum for ultrasound propagation through cancellous bone replica models.

PubMed

Langton, Christian M; Wille, Marie-Luise; Flegg, Mark B

2014-04-01

The acceptance of broadband ultrasound attenuation for the assessment of osteoporosis suffers from a limited understanding of ultrasound wave propagation through cancellous bone. It has recently been proposed that the ultrasound wave propagation can be described by a concept of parallel sonic rays. This concept approximates the detected transmission signal to be the superposition of all sonic rays that travel directly from transmitting to receiving transducer. The transit time of each ray is defined by the proportion of bone and marrow propagated. An ultrasound transit time spectrum describes the proportion of sonic rays having a particular transit time, effectively describing lateral inhomogeneity of transit times over the surface of the receiving ultrasound transducer. The aim of this study was to provide a proof of concept that a transit time spectrum may be derived from digital deconvolution of input and output ultrasound signals. We have applied the active-set method deconvolution algorithm to determine the ultrasound transit time spectra in the three orthogonal directions of four cancellous bone replica samples and have compared experimental data with the prediction from the computer simulation. The agreement between experimental and predicted ultrasound transit time spectrum analyses derived from Bland-Altman analysis ranged from 92% to 99%, thereby supporting the concept of parallel sonic rays for ultrasound propagation in cancellous bone. In addition to further validation of the parallel sonic ray concept, this technique offers the opportunity to consider quantitative characterisation of the material and structural properties of cancellous bone, not previously available utilising ultrasound.

Possible Transit Timing Variations of the TrES-3 Planetary System

NASA Astrophysics Data System (ADS)

Jiang, Ing-Guey; Yeh, Li-Chin; Thakur, Parijat; Wu, Yu-Ting; Chien, Ping; Lin, Yi-Ling; Chen, Hong-Yu; Hu, Juei-Hwa; Sun, Zhao; Ji, Jianghui

2013-03-01

Five newly observed transit light curves of the TrES-3 planetary system are presented. Together with other light-curve data from the literature, 23 transit light curves in total, which cover an overall timescale of 911 epochs, have been analyzed through a standard procedure. From these observational data, the system's orbital parameters are determined and possible transit timing variations (TTVs) are investigated. Given that a null TTV produces a fit with reduced χ2 = 1.52, our results agree with previous work, that TTVs might not exist in these data. However, a one-frequency oscillating TTV model, giving a fit with a reduced χ2 = 0.93, does possess a statistically higher probability. It is thus concluded that future observations and dynamical simulations for this planetary system will be very important.

The Effects of Barycentric and Asymmetric Transverse Velocities on Eclipse and Transit Times

NASA Astrophysics Data System (ADS)

Conroy, Kyle E.; Prša, Andrej; Horvat, Martin; Stassun, Keivan G.

2018-02-01

It has long been recognized that the finite speed of light can affect the observed time of an event. For example, as a source moves radially toward or away from an observer, the path length and therefore the light travel time to the observer decreases or increases, causing the event to appear earlier or later than otherwise expected, respectively. This light travel time effect has been applied to transits and eclipses for a variety of purposes, including studies of eclipse timing variations and transit timing variations that reveal the presence of additional bodies in the system. Here we highlight another non-relativistic effect on eclipse or transit times arising from the finite speed of light—caused by an asymmetry in the transverse velocity of the two eclipsing objects, relative to the observer. This asymmetry can be due to a non-unity mass ratio or to the presence of external barycentric motion. Although usually constant, this barycentric and asymmetric transverse velocity (BATV) effect can vary between sequential eclipses if either the path length between the two objects or the barycentric transverse velocity varies in time. We discuss this BATV effect and estimate its magnitude for both time-dependent and time-independent cases. For the time-dependent cases, we consider binaries that experience a change in orbital inclination, eccentric systems with and without apsidal motion, and hierarchical triple systems. We also consider the time-independent case which, by affecting the primary and secondary eclipses differently, can influence the inferred system parameters, such as the orbital eccentricity.

Direct simulation of groundwater transit-time distributions using the reservoir theory

NASA Astrophysics Data System (ADS)

Etcheverry, David; Perrochet, Pierre

Groundwater transit times are of interest for the management of water resources, assessment of pollution from non-point sources, and quantitative dating of groundwaters by the use of environmental isotopes. The age of water is the time water has spent in an aquifer since it has entered the system, whereas the transit time is the age of water as it exits the system. Water at the outlet of an aquifer is a mixture of water elements with different transit times, as a consequence of the different flow-line lengths. In this paper, transit-time distributions are calculated by coupling two existing methods, the reservoir theory and a recent age-simulation method. Based on the derivation of the cumulative age distribution over the whole domain, the approach accounts for the whole hydrogeological framework. The method is tested using an analytical example and its applicability illustrated for a regional layered aquifer. Results show the asymmetry and multimodality of the transit-time distribution even in advection-only conditions, due to the aquifer geometry and to the velocity-field heterogeneity. Résumé Les temps de transit des eaux souterraines sont intéressants à connaître pour gérer l'évaluation des ressources en eau dans le cas de pollution à partir de sources non ponctuelles, et aussi pour dater quantitativement les eaux souterraines au moyen des isotopes du milieu. L'âge de l'eau est le temps qu'elle a passé dans un aquifère depuis qu'elle est entrée dans le système, alors que le temps de transit est l'âge de l'eau au moment où elle quitte le système. L'eau à la sortie d'un aquifère est un mélange d'eaux possédant différents temps de transit, du fait des longueurs différentes des lignes de courant suivies. Dans ce papier, les distributions des temps de transit sont calculées en couplant deux méthodes, la théorie du réservoir et une méthode récente de simulation des âges. Basée sur la dérivation de la distribution cumulées des âges sur

Relationship between longitudinal stress wave transit time and moisture content of lumber during kiln-drying

Treesearch

William T. Simpson; Xiping. Wang

2001-01-01

The relationship between longitudinal stress wave transit time and wood moisture content (MC) was examined as a potential means of estimating MC control points in dry kiln schedules for lumber. A linear relationship was found between the relative transit time and the average MC of sugar maple and ponderosa pine boards dried according to typical kiln schedules.

Identifying transit corridors for elephant using a long time-series

NASA Astrophysics Data System (ADS)

Pittiglio, Claudia; Skidmore, Andrew K.; van Gils, Hein A. M. J.; Prins, Herbert H. T.

2012-02-01

The role of corridors in mitigating the effects of landscape fragmentation on biodiversity is controversial. Recent studies have highlighted the need for new approaches in corridor design using long-term datasets. We present a method to identify transit corridors for elephant at a population scale over a large area and an extended period of time using long-term aerial surveys. We investigated environmental and anthropogenic factors directly and indirectly related to the wet versus dry season distribution of elephant and its transit corridors. Four environmental variables predicted the presence of elephant at the landscape scale in both seasons: distance from permanent water, protected areas and settlements and vegetation structure. Path analysis revealed that altitude and monthly average NDVI, and distance from temporary water had a significant indirect effect on elephant distribution at local scale in dry and wet seasons respectively. Five transit corridors connecting Tarangire National Park and the northern as well as south-eastern wet season dispersal areas were identified and matched the wildlife migration routes described in the 1960s. The corridors are stable over the decades, providing landscape connectivity for elephant. Our approach yielded insights how advanced spatial analysis can be integrated with biological data available from long-term datasets to identify actual transit corridors and predictors of species distribution.

Surgical problems and complex procedures: issues for operative time in robotic totally endoscopic coronary artery bypass grafting.

PubMed

Wiedemann, Dominik; Bonaros, Nikolaos; Schachner, Thomas; Weidinger, Felix; Lehr, Eric J; Vesely, Mark; Bonatti, Johannes

2012-03-01

Robotically assisted totally endoscopic coronary artery bypass grafting (TECAB) is a viable option for closed chest coronary surgery, but it requires learning curves and longer operative times. This study evaluated the effect of extended operation times on the outcome of patients undergoing TECAB. From 2001 to 2009, 325 patients underwent TECAB with the da Vinci telemanipulation system. Correlations between operative times and preoperative, intraoperative, and early postoperative parameters were investigated. Receiver operating characteristic analysis was used to define the threshold of the procedure duration above which intensive care unit stay and ventilation time were prolonged. Demographic data, intraoperative and postoperative parameters, and survival data were compared. Patients with prolonged operative times more often underwent multivessel revascularization (P < .001) and beating-heart TECAB (P =.023). Other preoperative parameters were not associated with longer operative times. Incidences of technical difficulties and conversions (P < .001) were higher among patients with longer operative times. Prolonged intensive care unit stay, mechanical ventilation, hospital stay, and with requirement of blood products were associated with longer operative times. Receiver operating characteristic analysis showed operative times >445 minutes and >478 minutes to predict prolonged (>48 hours) intensive care unit stay and mechanical ventilation, respectively. Patients with procedures >478 minutes had longer hospital stays and higher perioperative morbidity and mortality. Kaplan-Meier analysis revealed decreased survival among patients with operative times >478 minutes. Multivessel revascularization and conversions lead to prolonged operative times in totally endoscopic coronary artery bypass grafting. Longer operative times significantly influence early postoperative and midterm outcomes. Copyright © 2012 The American Association for Thoracic Surgery. Published by

Arterial Wall Perfusion Measured with Photon Counting Spectral X-ray CT.

PubMed

Jorgensen, Steven M; Korinek, Mark J; Vercnocke, Andrew J; Anderson, Jill L; Halaweish, Ahmed; Leng, Shuai; McCollough, Cynthia H; Ritman, Erik L

2016-08-28

Early atherosclerosis changes perfusion of the arterial wall due to localized proliferation of the vasa vasorum. When contrast agent passes through the artery, some enters the vasa vasorum and increases radiopacity of the arterial wall. Technical challenges to detecting changes in vasa vasorum density include the thin arterial wall, partial volume averaging at the arterial lumen/wall interface and calcification within the wall. We used a photon-counting spectral CT scanner to study carotid arteries of anesthetized pigs and micro-CT of these arteries to quantify vasa vasorum density. The left carotid artery wall was injected with autologous blood to stimulate vasa vasorum angiogenesis. The scans were performed at 25-120 keV; the tube-current-time product was 550 mAs. A 60 mL bolus of iodine contrast agent was injected into the femoral vein at 5mL/s. Two seconds post injection, an axial scan was acquired at every 3 s over 60 s (i.e., 20 time points). Each time point acquired 28 contiguous transaxial slices with reconstructed voxels 0.16 × 0.16 × 1 mm 3 . Regions-of-interest in the outer 2/3 of the arterial wall and in the middle 2/3 of the lumen were drawn and their enhancements plotted versus time. Lumenal CT values peaked several seconds after injection and then returned towards baseline. Arterial wall CT values peaked concurrent to the lumen. The peak arterial wall enhancement in the left carotid arterial wall correlated with increased vasa vasorum density observed in micro-CT images of the isolated arteries.

Arterial wall perfusion measured with photon counting spectral x-ray CT

NASA Astrophysics Data System (ADS)

Jorgensen, Steven M.; Korinek, Mark J.; Vercnocke, Andrew J.; Anderson, Jill L.; Halaweish, Ahmed; Leng, Shuai; McCollough, Cynthia H.; Ritman, Erik L.

2016-10-01

Early atherosclerosis changes perfusion of the arterial wall due to localized proliferation of the vasa vasorum. When contrast agent passes through the artery, some enters the vasa vasorum and increases radiopacity of the arterial wall. Technical challenges to detecting changes in vasa vasorum density include the thin arterial wall, partial volume averaging at the arterial lumen/wall interface and calcification within the wall. We used a photon-counting spectral CT scanner to study carotid arteries of anesthetized pigs and micro-CT of these arteries to quantify vasa vasorum density. The left carotid artery wall was injected with autologous blood to stimulate vasa vasorum angiogenesis. The scans were performed at 25-120 keV; the tube-current-time product was 550 mAs. A 60 mL bolus of iodine contrast agent was injected into the femoral vein at 5mL/s. Two seconds post injection, an axial scan was acquired at every 3 s over 60 s (i.e., 20 time points). Each time point acquired 28 contiguous transaxial slices with reconstructed voxels 0.16 x 0.16 x 1 mm3. Regions-of-interest in the outer 2/3 of the arterial wall and in the middle 2/3 of the lumen were drawn and their enhancements plotted versus time. Lumenal CT values peaked several seconds after injection and then returned towards baseline. Arterial wall CT values peaked concurrent to the lumen. The peak arterial wall enhancement in the left carotid arterial wall correlated with increased vasa vasorum density observed in micro-CT images of the isolated arteries.

Validation of thermal techniques for measurement of pelvic organ blood flows in the nonpregnant sheep: comparison with transit-time ultrasonic and microsphere measurements of blood flow

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

Randall, N.J.; Beard, R.W.; Sutherland, I.A.

1988-03-01

Data obtained from a thermal system capable of measuring changes in organ temperature as well as tissue thermal clearance in the uterus and vagina have been compared with blood flow measured continuously with a transit-time ultrasound volume-flow sensor placed around the common internal iliac artery and intermittently with radioactive microspheres in the chronically instrumented nonpregnant sheep. Temperature changes in both the uterus and the vagina correlated well with blood flow changes measured by both techniques after intravenous administration of estradiol or norepinephrine. Thermal clearance did not correlate well with blood flow in the vagina or uterus. These methods may havemore » value in the investigation of blood flow patterns in various clinical situations such as the pelvic pain syndrome and early pregnancy.« less

[Effect of ambulatory supervised cardiac training on arterial hypertension in patients with coronary artery disease and arterial hypertension].

PubMed

Kałka, Dariusz; Sobieszczańska, Małgorzata; Marciniak, Wojciech; Popielewicz-Kautz, Aleksandra; Markuszewski, Leszek; Chorebała, Arkadiusz; Korzeniowska, Joanna; Janczak, Jacek; Adamus, Jerzy

2007-01-01

Arterial hypertension is one of the most common health problems occurring in highly developed countries. It was proved that long-term and regular physical activity results in hypotensive effect. A goal of the present study was to assess an influence of six-month ambulatory cardiac rehabilitation on arterial pressure level in patients with coronary artery disease and hypertension as well as analysis of correlation between pressure values alterations and intensity of cardiac training. A study group comprised 103 patients (mean age: 61.2 +/- 0.8 years) manifesting coronary artery disease accompanied by arterial hypertension. A control group constituted 39 normotensive patients with coronary artery disease (mean age: 59.4 +/- 1.3 years). The both observed groups differ from each other only with values of left ventricle mass index and drug regimen established at least three months prior to the follow-up onset. During the rehabilitation cycle, no treatment corrections were made and no new preparations were added. The all patients were enrolled to the six-month cardiac rehabilitation program. The program comprised 45-minute training with cycle ergometer, three times a week, and generally improving gym exercises, two times a week. The analyses concerned systolic and diastolic pressure values, measured just before each training (resting pressure) and just after peak exercise interval (peak pressure), at the beginning and at the end of the rehabilitation cycle. At the initial stage, the patient group with hypertension demonstrated the higher pressure values (resting and peak), as compared with the control group. Cardiac rehabilitation performed in the examined patients caused a statistically significant reduction of the mean resting pressure, both systolic (p < 0.01) and diastolic (p < 0.01). As to the mean peak pressure in this group, systolic diminished slightly (NS), but diastolic was reduced significantly (p < 0.01). In the control group, after six-month rehabilitation

Dating violence, bullying, and sexual harassment: longitudinal profiles and transitions over time.

PubMed

Miller, Shari; Williams, Jason; Cutbush, Stacey; Gibbs, Deborah; Clinton-Sherrod, Monique; Jones, Sarah

2013-04-01

Although there is growing recognition of the problem of dating violence, little is known about how it unfolds among young adolescents who are just beginning to date. This study examined classes (subgroups) and transitions between classes over three time points based on dating violence, bullying, and sexual harassment perpetration and victimization experienced by youth. The sample was ethnically diverse, consisting of 795 seventh-grade students from schools that were part of a multi-site, longitudinal evaluation of a dating violence initiative (50 % female; 27 % White, 32 % African American, 25 % Latino, 16 % other or multiple races). Results from latent transition analyses revealed five classes of students with distinct behavioral profiles: multi-problem (victimization and perpetration), bullying and sexual harassment (victimization and perpetration), bullying (victimization and perpetration) and sexual harassment (victimization only), bullying (victimization and perpetration), and a least problem group. The majority of classes were characterized by reports of both perpetration and victimization for at least one behavior. Girls were more likely to be in the less problematic classes. Class membership was fairly stable across the three time points. When students transitioned to a different class, the shift was most often from a more problematic to a less problematic class, particularly for girls. The findings support understanding dating violence within a dynamic, developmental process that recognizes related behaviors within and across individuals. Overall, the findings highlight the utility of person-oriented approaches to enhance our understanding of longitudinal profiles and transitions over time for dating violence and related behaviors.

The Time Course of the Probability of Transition Into and Out of REM Sleep

PubMed Central

Bassi, Alejandro; Vivaldi, Ennio A.; Ocampo-Garcés, Adrián

2009-01-01

Study Objectives: A model of rapid eye movement (REM) sleep expression is proposed that assumes underlying regulatory mechanisms operating as inhomogenous Poisson processes, the overt results of which are the transitions into and out of REM sleep. Design: Based on spontaneously occurring REM sleep episodes (“Episode”) and intervals without REM sleep (“Interval”), 3 variables are defined and evaluated over discrete 15-second epochs using a nonlinear logistic regression method: “Propensity” is the instantaneous rate of into-REM transition occurrence throughout an Interval, “Volatility” is the instantaneous rate of out-of-REM transition occurrence throughout an Episode, and “Opportunity” is the probability of being in non-REM (NREM) sleep at a given time throughout an Interval, a requisite for transition. Setting: 12:12 light:dark cycle, isolated boxes. Participants: Sixteen male Sprague-Dawley rats Interventions: None. Spontaneous sleep cycles. Measurements and Results: The highest levels of volatility and propensity occur, respectively, at the very beginning of Episodes and Intervals. The new condition stabilizes rapidly, and variables reach nadirs at minute 1.25 and 2.50, respectively. Afterward, volatility increases markedly, reaching values close to the initial level. Propensity increases moderately, the increment being stronger through NREM sleep bouts occurring at the end of long Intervals. Short-term homeostasis is evidenced by longer REM sleep episodes lowering propensity in the following Interval. Conclusions: The stabilization after transitions into Episodes or Intervals and the destabilization after remaining for some time in either condition may be described as resulting from continuous processes building up during Episodes and Intervals. These processes underlie the overt occurrence of transitions. Citation: Bassi A; Vivaldi EA; Ocampo-Garcées A. The time course of the probability of transition into and out of REM sleep. SLEEP 2009

Comparison of active-set method deconvolution and matched-filtering for derivation of an ultrasound transit time spectrum.

PubMed

Wille, M-L; Zapf, M; Ruiter, N V; Gemmeke, H; Langton, C M

2015-06-21

The quality of ultrasound computed tomography imaging is primarily determined by the accuracy of ultrasound transit time measurement. A major problem in analysis is the overlap of signals making it difficult to detect the correct transit time. The current standard is to apply a matched-filtering approach to the input and output signals. This study compares the matched-filtering technique with active set deconvolution to derive a transit time spectrum from a coded excitation chirp signal and the measured output signal. The ultrasound wave travels in a direct and a reflected path to the receiver, resulting in an overlap in the recorded output signal. The matched-filtering and deconvolution techniques were applied to determine the transit times associated with the two signal paths. Both techniques were able to detect the two different transit times; while matched-filtering has a better accuracy (0.13 μs versus 0.18 μs standard deviations), deconvolution has a 3.5 times improved side-lobe to main-lobe ratio. A higher side-lobe suppression is important to further improve image fidelity. These results suggest that a future combination of both techniques would provide improved signal detection and hence improved image fidelity.

Combination of rare right arterial variation with anomalous origins of the vertebral artery, aberrant subclavian artery and persistent trigeminal artery. A case report.

PubMed

Ishihara, H; San Millán Ruíz, D; Abdo, G; Asakura, F; Yilmaz, H; Lovblad, K O; Rüfenacht, D A

2011-09-01

A 32-year-old woman hospitalized for subarachnoid hemorrhage showed rare arterial variation on the right side with anomalous origins of the vertebral artery, aberrant subclavian artery and persistent trigeminal artery. Angiography showed the right vertebral artery to originate from the right common carotid artery, the right subclavian artery to arise separately from the descending aorta, and persistent trigeminal artery on the right side. The possible embryonic mechanism of this previously unreported variant combination is discussed.

Laminar microvascular transit time distribution in the mouse somatosensory cortex revealed by Dynamic Contrast Optical Coherence Tomography

PubMed Central

Merkle, Conrad W.; Srinivasan, Vivek J.

2015-01-01

The transit time distribution of blood through the cerebral microvasculature both constrains oxygen delivery and governs the kinetics of neuroimaging signals such as blood-oxygen-level-dependent functional Magnetic Resonance Imaging (BOLD fMRI). However, in spite of its importance, capillary transit time distribution has been challenging to quantify comprehensively and efficiently at the microscopic level. Here, we introduce a method, called Dynamic Contrast Optical Coherence Tomography (DyC-OCT), based on dynamic cross-sectional OCT imaging of an intravascular tracer as it passes through the field-of-view. Quantitative transit time metrics are derived from temporal analysis of the dynamic scattering signal, closely related to tracer concentration. Since DyC-OCT does not require calibration of the optical focus, quantitative accuracy is achieved even deep in highly scattering brain tissue where the focal spot degrades. After direct validation of DyC-OCT against dilution curves measured using a fluorescent plasma label in surface pial vessels, we used DyC-OCT to investigate the transit time distribution in microvasculature across the entire depth of the mouse somatosensory cortex. Laminar trends were identified, with earlier transit times and less heterogeneity in the middle cortical layers. The early transit times in the middle cortical layers may explain, at least in part, the early BOLD fMRI onset times observed in these layers. The layer-dependencies in heterogeneity may help explain how a single vascular supply manages to deliver oxygen to individual cortical layers with diverse metabolic needs. PMID:26477654

POSSIBLE TRANSIT TIMING VARIATIONS OF THE TrES-3 PLANETARY SYSTEM

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

Jiang, Ing-Guey; Wu, Yu-Ting; Chien, Ping

2013-03-15

Five newly observed transit light curves of the TrES-3 planetary system are presented. Together with other light-curve data from the literature, 23 transit light curves in total, which cover an overall timescale of 911 epochs, have been analyzed through a standard procedure. From these observational data, the system's orbital parameters are determined and possible transit timing variations (TTVs) are investigated. Given that a null TTV produces a fit with reduced {chi}{sup 2} = 1.52, our results agree with previous work, that TTVs might not exist in these data. However, a one-frequency oscillating TTV model, giving a fit with a reducedmore » {chi}{sup 2} = 0.93, does possess a statistically higher probability. It is thus concluded that future observations and dynamical simulations for this planetary system will be very important.« less

Space and time renormalization in phase transition dynamics

DOE PAGES

Francuz, Anna; Dziarmaga, Jacek; Gardas, Bartłomiej; ...

2016-02-18

Here, when a system is driven across a quantum critical point at a constant rate, its evolution must become nonadiabatic as the relaxation time τ diverges at the critical point. According to the Kibble-Zurek mechanism (KZM), the emerging post-transition excited state is characterized by a finite correlation length ξˆ set at the time tˆ=τˆ when the critical slowing down makes it impossible for the system to relax to the equilibrium defined by changing parameters. This observation naturally suggests a dynamical scaling similar to renormalization familiar from the equilibrium critical phenomena. We provide evidence for such KZM-inspired spatiotemporal scaling by investigatingmore » an exact solution of the transverse field quantum Ising chain in the thermodynamic limit.« less

Incorporating real-time traffic and weather data to explore road accident likelihood and severity in urban arterials.

PubMed

Theofilatos, Athanasios

2017-06-01

The effective treatment of road accidents and thus the enhancement of road safety is a major concern to societies due to the losses in human lives and the economic and social costs. The investigation of road accident likelihood and severity by utilizing real-time traffic and weather data has recently received significant attention by researchers. However, collected data mainly stem from freeways and expressways. Consequently, the aim of the present paper is to add to the current knowledge by investigating accident likelihood and severity by exploiting real-time traffic and weather data collected from urban arterials in Athens, Greece. Random Forests (RF) are firstly applied for preliminary analysis purposes. More specifically, it is aimed to rank candidate variables according to their relevant importance and provide a first insight on the potential significant variables. Then, Bayesian logistic regression as well finite mixture and mixed effects logit models are applied to further explore factors associated with accident likelihood and severity respectively. Regarding accident likelihood, the Bayesian logistic regression showed that variations in traffic significantly influence accident occurrence. On the other hand, accident severity analysis revealed a generally mixed influence of traffic variations on accident severity, although international literature states that traffic variations increase severity. Lastly, weather parameters did not find to have a direct influence on accident likelihood or severity. The study added to the current knowledge by incorporating real-time traffic and weather data from urban arterials to investigate accident occurrence and accident severity mechanisms. The identification of risk factors can lead to the development of effective traffic management strategies to reduce accident occurrence and severity of injuries in urban arterials. Copyright © 2017 Elsevier Ltd and National Safety Council. All rights reserved.

Advances in arterial spin labelling MRI methods for measuring perfusion and collateral flow.

PubMed

van Osch, Matthias Jp; Teeuwisse, Wouter M; Chen, Zhensen; Suzuki, Yuriko; Helle, Michael; Schmid, Sophie

2017-01-01

With the publication in 2015 of the consensus statement by the perfusion study group of the International Society for Magnetic Resonance in Medicine (ISMRM) and the EU-COST action 'ASL in dementia' on the implementation of arterial spin labelling MRI (ASL) in a clinical setting, the development of ASL can be considered to have become mature and ready for clinical prime-time. In this review article new developments and remaining issues will be discussed, especially focusing on quantification of ASL as well as on new technological developments of ASL for perfusion imaging and flow territory mapping. Uncertainty of the achieved labelling efficiency in pseudo-continuous ASL (pCASL) as well as the presence of arterial transit time artefacts, can be considered the main remaining challenges for the use of quantitative cerebral blood flow (CBF) values. New developments in ASL centre around time-efficient acquisition of dynamic ASL-images by means of time-encoded pCASL and diversification of information content, for example by combined 4D-angiography with perfusion imaging. Current vessel-encoded and super-selective pCASL-methodology have developed into easily applied flow-territory mapping methods providing relevant clinical information with highly similar information content as digital subtraction angiography (DSA), the current clinical standard. Both approaches seem therefore to be ready for clinical use.

Aggregation in environmental systems - Part 2: Catchment mean transit times and young water fractions under hydrologic nonstationarity

NASA Astrophysics Data System (ADS)

Kirchner, J. W.

2016-01-01

Methods for estimating mean transit times from chemical or isotopic tracers (such as Cl-, δ18O, or δ2H) commonly assume that catchments are stationary (i.e., time-invariant) and homogeneous. Real catchments are neither. In a companion paper, I showed that catchment mean transit times estimated from seasonal tracer cycles are highly vulnerable to aggregation error, exhibiting strong bias and large scatter in spatially heterogeneous catchments. I proposed the young water fraction, which is virtually immune to aggregation error under spatial heterogeneity, as a better measure of transit times. Here I extend this analysis by exploring how nonstationarity affects mean transit times and young water fractions estimated from seasonal tracer cycles, using benchmark tests based on a simple two-box model. The model exhibits complex nonstationary behavior, with striking volatility in tracer concentrations, young water fractions, and mean transit times, driven by rapid shifts in the mixing ratios of fluxes from the upper and lower boxes. The transit-time distribution in streamflow becomes increasingly skewed at higher discharges, with marked increases in the young water fraction and decreases in the mean water age, reflecting the increased dominance of the upper box at higher flows. This simple two-box model exhibits strong equifinality, which can be partly resolved by simple parameter transformations. However, transit times are primarily determined by residual storage, which cannot be constrained through hydrograph calibration and must instead be estimated by tracer behavior. Seasonal tracer cycles in the two-box model are very poor predictors of mean transit times, with typical errors of several hundred percent. However, the same tracer cycles predict time-averaged young water fractions (Fyw) within a few percent, even in model catchments that are both nonstationary and spatially heterogeneous (although they may be biased by roughly 0.1-0.2 at sites where strong

Transit-Time Damping, Landau Damping, and Perturbed Orbits

NASA Astrophysics Data System (ADS)

Simon, A.; Short, R. W.

1997-11-01

Transit-time damping(G.J. Morales and Y.C. Lee, Phys. Rev. Lett. 33), 1534 (1974).*^,*(P.A. Robinson, Phys. Fluids B 3), 545 (1991).** has traditionally been obtained by calculating the net energy gain of transiting electrons, of velocity v, to order E^2* in the amplitude of a localized electric field. This necessarily requires inclusion of the perturbed orbits in the equation of motion. A similar method has been used by others(D.R. Nicholson, Introduction to Plasma Theory) (Wiley, 1983).*^,*(E.M. Lifshitz and L.P. Pitaevskifi, Physical Kinetics) (Pergamon, 1981).** to obtain a ``physical'' picture of Landau damping in a nonlocalized field. The use of perturbed orbits seems odd since the original derivation of Landau (and that of Dawson) never went beyond a linear picture of the dynamics. We introduce a novel method that takes advantage of the time-reversal invariance of the Vlasov equation and requires only the unperturbed orbits to obtain the result. Obviously, there is much reduction in complexity. Application to finite slab geometry yields a simple expression for the damping rate. Equivalence to much more complicated results^2* is demonstrated. This method allows us to calculate damping in more complicated geometries and more complex electric fields, such as occur in SRS in filaments. See accompanying talk.(R.W. Short and A. Simon, this conference.) This work was supported by the U.S. DOE Office of Inertial Confinement Fusion under Co-op Agreement No. DE-FC03-92SF19460.

Arterial switch: translocation of the intramural coronary artery.

PubMed

Asou, T; Karl, T R; Pawade, A; Mee, R B

1994-02-01

Translocation of an intramural coronary artery is one of the most challenging problems in anatomic correction of transposition of the great arteries. Of 259 patients undergoing arterial switch procedure for transposition of the great arteries in our hospital, 12 (4.6%) were found to have intramural coronary arteries. The diagnosis was made intraoperatively in all patients. There were five different types of intramural coronary anatomy noted, with ostial stenosis present in half. The operative technique consisted of detachment of the posterior commissure of the aortic valve and unroofing of the intramural segment of the coronary artery by excision of a triangular portion of internal aortic wall. The coronary arteries were excised as a single disc, which was divided into two cuffs. The arterial switch was then performed in the usual fashion. The posterior commissure of the aortic valve was resuspended to the pericardial patch used to reconstruct the neopulmonary artery sinus. There were no operative or late deaths over a follow-up of 328 patient-months. Postoperatively, no patient showed ischemic changes on electrocardiogram or abnormal wall motion on echocardiogram. We believe that intramural coronary arteries can be managed satisfactorily with this technique, and that arterial switch will be possible in all cases.

A Gain-Programmable Transit-Time-Stable and Temperature-Stable PMT Voltage Divider

NASA Astrophysics Data System (ADS)

Liu, Yaqiang; Li, Hongdi; Wang, Yu; Xing, Tao; Xie, Shuping; Uribe, J.; Baghaei, H.; Ramirez, R.; Kim, Soonseok; Wong, Wai-Hoi

2004-10-01

A gain-programmable, transit-time-stable, temperature-stable photomultiplier (PMT) voltage divider design is described in this paper. The signal-to-noise ratio can be increased by changing a PMT gain directly instead of adjusting the gain of the preamplifier. PMT gain can be changed only by adjusting the voltages for the dynodes instead of changing the total high voltage between the anode and the photocathode, which can cause a significant signal transit-time variation that cannot be accepted by an application with a critical timing requirement, such as positron emission tomography (PET) or time-of-flight (TOF) detection/PET. The dynode voltage can be controlled by a digital analog converter isolated with a linear optocoupler. The optocoupler consists of an infrared light emission diode (LED) optically coupled with two phototransistors, and one is used in a servo feedback circuit to control the LED drive current for compensating temperature characteristics. The results showed that a six times gain range could be achieved; the gain drift was <0.5% over a 20/spl deg/C temperature range; 250 ps transit-time variation was measured over the entire gain range. A compact print circuit board (PCB) for the voltage divider integrated with a fixed-gain preamplifier has been designed and constructed. It can save about $30 per PMT channel compared with a commercial PMT voltage divider along with a variable gain amplifier. The preamplifier can be totally disabled, therefore in a system with a large amount of PMTs, only one channel can be enabled for calibrating the PMT gain. This new PMT voltage divider design is being applied to our animal PET camera and TOF/PET research.

Nonlinear ion dynamics in Hall thruster plasma source by ion transit-time instability

NASA Astrophysics Data System (ADS)

Lim, Youbong; Choe, Wonho; Mazouffre, Stéphane; Park, Jae Sun; Kim, Holak; Seon, Jongho; Garrigues, L.

2017-03-01

High-energy tail formation in an ion energy distribution function (IEDF) is explained in a Hall thruster plasma with the stationary crossed electric and magnetic fields whose discharge current is oscillated at the ion transit-time scale with a frequency of 360 kHz. Among ions in different charge states, singly charged Xe ions (Xe+) have an IEDF that is significantly broadened and shifted toward the high-energy side, which contributes to tail formation in the entire IEDF. Analytical and numerical investigations confirm that the IEDF tail is due to nonlinear ion dynamics in the ion transit-time oscillation.

Wide sternal retraction may impede internal mammary artery graft flow and reduce myocardial function during off-pump coronary artery bypass grafting: presentation of two cases

PubMed Central

Espinoza, Andreas; Bergsland, Jacob; Lundblad, Runar; Fosse, Erik

2012-01-01

The internal mammary artery (IMA) is routinely used for grafting of the left anterior descending coronary artery (LAD), providing good flow to the anterior left ventricle (LV) wall. Impeded IMA-to-LAD flow may result in myocardial ischaemia and haemodynamic deterioration. From a study population, we describe two incidents where myocardial ischaemia was observed during off-pump coronary artery bypass surgery (CABG), with a confirmed reduction in the IMA-to-LAD flow in one patient. In patient no. 1, normal IMA flow was assessed by transit-time flow measurement after a complete IMA-to-LAD anastomosis. The anterior LV wall thickening was monitored continuously by epicardial ultrasonic transducers. Normal wall thickening was confirmed after IMA grafting. During a wide sternal opening for circumflex grafting the anterior wall motion displayed an ischaemic pattern, with reduced systolic and increased post-systolic wall thickening. IMA flow was reduced simultaneously. When easing the sternal opening, IMA flow normalized, as did the motion pattern in the anterior LV wall. In patient no. 2, similar changes in wall thickening occurred during a wide sternal opening after IMA-to-LAD grafting. When easing the retractor, the wall thickening normalized. It is important for the surgeon to be aware of this possible cause of myocardial ischaemia, with a risk of subsequent haemodynamic deterioration. This may not only be of great importance during off-pump CABG, but can also be significant for successful weaning from the cardiopulmonary bypass machine. PMID:22499803

Stent-induced flow disturbances in the ipsilateral external carotid artery following internal carotid artery stenting: a temporary cause of jaw claudication.

PubMed

Giurgea, Georgiana-Aura; Haumer, Markus; Mlekusch, Irene; Sabeti-Sandor, Schila; Dick, Petra; Schillinger, Martin; Minar, Erich; Mlekusch, Wolfgang

2017-07-01

We hypothesize that stenting of the internal carotid artery can immediately impede blood flow to the external carotid artery by either plaque shift or stent coverage of the ostium, and thereby cause ischemic symptoms like ipsilateral jaw claudication. Thirty-three patients with high-grade asymptomatic stenosis of the internal carotid artery who underwent endovascular treatment were examined by ultrasound of the external carotid artery and performed an exercise test by chewing chewing gum synchronously to an electronic metronome for 3 min. Tests were performed before, the day after, and 1 week after the stenting procedure. Claudication time was defined as the timespan until occurrence of pain of the masseter muscle and/or chewing dyssynchrony to the metronome for more than 15 s. Ten patients with an isolated, atherosclerotic stenosis of the external carotid artery served as controls. A significantly reduced claudication time (in seconds) was recorded in patients who underwent carotid artery stenting compared to baseline values; median 89 (interquartile range, IQR, 57 to 124) vs. median 180 (IQR 153 to 180; p < 0.001). By categorization of the flow velocity at the external carotid artery into faster or slower as 200 cm/sec, the effect was even accentuated. Stenting values showed improvement 1 week after but did not return to baseline levels. No respective changes were found in controls. Stenting of the internal carotid artery lead to ipsilateral flow deterioration at the external carotid artery resulting in temporary jaw claudication. This impairment attenuated over the time and was significantly reduced after 1 week.

Use of Caval Subtraction 2D Phase-Contrast MR Imaging to Measure Total Liver and Hepatic Arterial Blood Flow: Preclinical Validation and Initial Clinical Translation

PubMed Central

Walker-Samuel, Simon; Davies, Nathan; Halligan, Steve; Lythgoe, Mark F.

2016-01-01

Purpose To validate caval subtraction two-dimensional (2D) phase-contrast magnetic resonance (MR) imaging measurements of total liver blood flow (TLBF) and hepatic arterial fraction in an animal model and evaluate consistency and reproducibility in humans. Materials and Methods Approval from the institutional ethical committee for animal care and research ethics was obtained. Fifteen Sprague-Dawley rats underwent 2D phase-contrast MR imaging of the portal vein (PV) and infrahepatic and suprahepatic inferior vena cava (IVC). TLBF and hepatic arterial flow were estimated by subtracting infrahepatic from suprahepatic IVC flow and PV flow from estimated TLBF, respectively. Direct PV transit-time ultrasonography (US) and fluorescent microsphere measurements of hepatic arterial fraction were the standards of reference. Thereafter, consistency of caval subtraction phase-contrast MR imaging–derived TLBF and hepatic arterial flow was assessed in 13 volunteers (mean age, 28.3 years ± 1.4) against directly measured phase-contrast MR imaging PV and proper hepatic arterial inflow; reproducibility was measured after 7 days. Bland-Altman analysis of agreement and coefficient of variation comparisons were undertaken. Results There was good agreement between PV flow measured with phase-contrast MR imaging and that measured with transit-time US (mean difference, −3.5 mL/min/100 g; 95% limits of agreement [LOA], ±61.3 mL/min/100 g). Hepatic arterial fraction obtained with caval subtraction agreed well with those with fluorescent microspheres (mean difference, 4.2%; 95% LOA, ±20.5%). Good consistency was demonstrated between TLBF in humans measured with caval subtraction and direct inflow phase-contrast MR imaging (mean difference, −1.3 mL/min/100 g; 95% LOA, ±23.1 mL/min/100 g). TLBF reproducibility at 7 days was similar between the two methods (95% LOA, ±31.6 mL/min/100 g vs ±29.6 mL/min/100 g). Conclusion Caval subtraction phase-contrast MR imaging is a simple and

Arterial spin labeling in combination with a look-locker sampling strategy: inflow turbo-sampling EPI-FAIR (ITS-FAIR).

PubMed

Günther, M; Bock, M; Schad, L R

2001-11-01

Arterial spin labeling (ASL) permits quantification of tissue perfusion without the use of MR contrast agents. With standard ASL techniques such as flow-sensitive alternating inversion recovery (FAIR) the signal from arterial blood is measured at a fixed inversion delay after magnetic labeling. As no image information is sampled during this delay, FAIR measurements are inefficient and time-consuming. In this work the FAIR preparation was combined with a Look-Locker acquisition to sample not one but a series of images after each labeling pulse. This new method allows monitoring of the temporal dynamics of blood inflow. To quantify perfusion, a theoretical model for the signal dynamics during the Look-Locker readout was developed and applied. Also, the imaging parameters of the new ITS-FAIR technique were optimized using an expression for the variance of the calculated perfusion. For the given scanner hardware the parameters were: temporal resolution 100 ms, 23 images, flip-angle 25.4 degrees. In a normal volunteer experiment with these parameters an average perfusion value of 48.2 +/- 12.1 ml/100 g/min was measured in the brain. With the ability to obtain ITS-FAIR time series with high temporal resolution arterial transit times in the range of -138 - 1054 ms were measured, where nonphysical negative values were found in voxels containing large vessels. Copyright 2001 Wiley-Liss, Inc.

Bypass of the maxillary artery to proximal middle cerebral artery.

PubMed

Ma, Lin; Ren, He-cheng; Huang, Ying

2015-03-01

The objective of this work was to explore the feasibility of bypass between the maxillary artery (MA) and proximity of middle cerebral artery (MCA). Ten fixed and perfused adult cadaver heads were dissected bilaterally, 20 sides in total. The superficial temporal artery and its 2 branches were dissected, and outer diameters were measured. The MA and its branch were exposed as well as deep temporal artery; outer diameter of MA was measured. The lengths between the external carotid artery, internal carotid artery, maxillary artery, and proximal middle cerebral artery were measured. Ten healthy adults as targets (20 sides), inner diameter and blood flow dynamic parameters of the common carotid artery, external carotid artery, internal carotid artery, maxillary artery, superficial temporal artery, and its 2 branches were done with ultrasound examination. The mean outer diameter of MA (2.60 ± 0.20 mm) was larger than that of the temporal artery trunk (1.70 ± 0.30 mm). The mean lengths of graft vessels between the internal carotid artery, external carotid artery, and the bifurcation section of MCA (171.00 ± 2.70 and 162.40 ± 2.60 mm) were longer than the mean lengths of graft vessels between MA and MCA bifurcation section (61.70 ± 1.50 mm). In adults, the mean blood flow of the second part of MA (62.70 ± 13.30 mL/min) was more than that of the 2 branches of the superficial temporal artery (15.90 ± 3.70 mL/min and 17.70 ± 4.10 ml/min). Bypass between the maxillary artery and proximity of middle cerebral artery is feasible. It is a kind of effective high flow bypass with which the graft vessel is shorter and straighter than the bypass between internal carotid artery or external carotid artery and proximity of middle cerebral artery.

Laminar microvascular transit time distribution in the mouse somatosensory cortex revealed by Dynamic Contrast Optical Coherence Tomography.

PubMed

Merkle, Conrad W; Srinivasan, Vivek J

2016-01-15

The transit time distribution of blood through the cerebral microvasculature both constrains oxygen delivery and governs the kinetics of neuroimaging signals such as blood-oxygen-level-dependent functional Magnetic Resonance Imaging (BOLD fMRI). However, in spite of its importance, capillary transit time distribution has been challenging to quantify comprehensively and efficiently at the microscopic level. Here, we introduce a method, called Dynamic Contrast Optical Coherence Tomography (DyC-OCT), based on dynamic cross-sectional OCT imaging of an intravascular tracer as it passes through the field-of-view. Quantitative transit time metrics are derived from temporal analysis of the dynamic scattering signal, closely related to tracer concentration. Since DyC-OCT does not require calibration of the optical focus, quantitative accuracy is achieved even deep in highly scattering brain tissue where the focal spot degrades. After direct validation of DyC-OCT against dilution curves measured using a fluorescent plasma label in surface pial vessels, we used DyC-OCT to investigate the transit time distribution in microvasculature across the entire depth of the mouse somatosensory cortex. Laminar trends were identified, with earlier transit times and less heterogeneity in the middle cortical layers. The early transit times in the middle cortical layers may explain, at least in part, the early BOLD fMRI onset times observed in these layers. The layer-dependencies in heterogeneity may help explain how a single vascular supply manages to deliver oxygen to individual cortical layers with diverse metabolic needs. Copyright © 2015 Elsevier Inc. All rights reserved.

Fetal origin of the posterior cerebral artery produces left-right asymmetry on perfusion imaging.

PubMed

Wentland, A L; Rowley, H A; Vigen, K K; Field, A S

2010-03-01

Fetal origin of the PCA is a common anatomic variation of the circle of Willis. On perfusion imaging, patients with unilateral fetal-type PCA may demonstrate left-right asymmetry that could mimic cerebrovascular disease. The aim of this study was to characterize the relationship between a fetal-type PCA and asymmetry of hemodynamic parameters derived from MR perfusion imaging. We retrospectively reviewed MR perfusion studies of 36 patients to determine the relationship between hemodynamic and vascular asymmetries in the PCA territory. Perfusion asymmetry indices for the PCA territory were computed from maps of rCBF, rCBV, MTT, T(max), and FMT. Vascular asymmetry indices were derived from calibers of the PCA-P1 segments relative to the posterior communicating arteries. Asymmetrically smaller values of FMT and T(max) were observed with unilateral fetal-type PCA, and these were strongly correlated with the degree of vascular asymmetry (Spearman's rho = 0.76 and 0.74, respectively, P < 1 x 10(-6)). Asymmetries of rCBF, MTT, and rCBV were neither significant nor related to vascular asymmetry. Faster perfusion transit times are seen for parameters sensitive to macrovascular transit effects (eg, FMT and T(max)) ipsilateral to fetal origin of the PCA in proportion to the degree of arterial asymmetry. Knowledge of this normal variation is critical in the interpretation of perfusion studies because asymmetry could mimic cerebrovascular pathology.

Efficient Transition Probability Computation for Continuous-Time Branching Processes via Compressed Sensing.

PubMed

Xu, Jason; Minin, Vladimir N

2015-07-01

Branching processes are a class of continuous-time Markov chains (CTMCs) with ubiquitous applications. A general difficulty in statistical inference under partially observed CTMC models arises in computing transition probabilities when the discrete state space is large or uncountable. Classical methods such as matrix exponentiation are infeasible for large or countably infinite state spaces, and sampling-based alternatives are computationally intensive, requiring integration over all possible hidden events. Recent work has successfully applied generating function techniques to computing transition probabilities for linear multi-type branching processes. While these techniques often require significantly fewer computations than matrix exponentiation, they also become prohibitive in applications with large populations. We propose a compressed sensing framework that significantly accelerates the generating function method, decreasing computational cost up to a logarithmic factor by only assuming the probability mass of transitions is sparse. We demonstrate accurate and efficient transition probability computations in branching process models for blood cell formation and evolution of self-replicating transposable elements in bacterial genomes.

Efficient Transition Probability Computation for Continuous-Time Branching Processes via Compressed Sensing

PubMed Central

Xu, Jason; Minin, Vladimir N.

2016-01-01

Branching processes are a class of continuous-time Markov chains (CTMCs) with ubiquitous applications. A general difficulty in statistical inference under partially observed CTMC models arises in computing transition probabilities when the discrete state space is large or uncountable. Classical methods such as matrix exponentiation are infeasible for large or countably infinite state spaces, and sampling-based alternatives are computationally intensive, requiring integration over all possible hidden events. Recent work has successfully applied generating function techniques to computing transition probabilities for linear multi-type branching processes. While these techniques often require significantly fewer computations than matrix exponentiation, they also become prohibitive in applications with large populations. We propose a compressed sensing framework that significantly accelerates the generating function method, decreasing computational cost up to a logarithmic factor by only assuming the probability mass of transitions is sparse. We demonstrate accurate and efficient transition probability computations in branching process models for blood cell formation and evolution of self-replicating transposable elements in bacterial genomes. PMID:26949377

Correlation-based perfusion mapping using time-resolved MR angiography: A feasibility study for patients with suspicions of steno-occlusive craniocervical arteries.

PubMed

Nam, Yoonho; Jang, Jinhee; Park, Sonya Youngju; Choi, Hyun Seok; Jung, So-Lyung; Ahn, Kook-Jin; Kim, Bum-Soo

2018-05-22

To explore the feasibility of using correlation-based time-delay (CTD) maps produced from time-resolved MR angiography (TRMRA) to diagnose perfusion abnormalities in patients suspected to have steno-occlusive lesions in the craniocervical arteries. Twenty-seven patients who were suspected to have steno-occlusive lesions in the craniocervical arteries underwent both TRMRA and brain single-photon emission computed tomography (SPECT). TRMRA was performed on the supra-aortic area after intravenous injection of a 0.03 mmol/kg gadolinium-based contrast agent. Time-to-peak (TTP) maps and CTD maps of the brain were automatically generated from TRMRA data, and their quality was assessed. Detection of perfusion abnormalities was compared between CTD maps and the time-series maximal intensity projection (MIP) images from TRMRA and TTP maps. Correlation coefficients between quantitative changes in SPECT and parametric maps for the abnormal perfusion areas were calculated. The CTD maps were of significantly superior quality than TTP maps (p < 0.01). For perfusion abnormality detection, CTD maps (kappa 0.84, 95% confidence interval [CI] 0.67-1.00) showed better agreement with SPECT than TTP maps (0.66, 0.46-0.85). For perfusion deficit detection, CTD maps showed higher accuracy (85.2%, 95% CI 66.3-95.8) than MIP images (66.7%, 46-83.5), with marginal significance (p = 0.07). In abnormal perfusion areas, correlation coefficients between SPECT and CTD (r = 0.74, 95% CI 0.34-0.91) were higher than those between SPECT and TTP (r = 0.66, 0.20-0.88). CTD maps generated from TRMRA were of high quality and offered good diagnostic performance for detecting perfusion abnormalities associated with steno-occlusive arterial lesions in the craniocervical area. • Generation of perfusion parametric maps from time-resolved MR angiography is clinically useful. • Correlation-based delay maps can be used to detect perfusion abnormalities associated with steno-occlusive craniocervical arteries

Factors influencing the operating time for single-port laparoscopic radical nephrectomy: focus on the anatomy and distribution of the renal artery and vein.

PubMed

Matsumoto, Kazuhiro; Miyajima, Akira; Fukumoto, Keishiro; Komatsuda, Akari; Niwa, Naoya; Hattori, Seiya; Takeda, Toshikazu; Kikuchi, Eiji; Asanuma, Hiroshi; Oya, Mototsugu

2017-10-01

It is considered that laparoscopic single-site surgery should be performed by specially trained surgeons because of the technical difficulty in using special instruments through limited access. We investigated suitable patients for single-port laparoscopic radical nephrectomy, focusing on the anatomy and distribution of the renal artery and vein. This retrospective study was conducted in 52 consecutive patients who underwent single-port radical nephrectomy by the transperitoneal approach. In patients undergoing right nephrectomy, a 2-mm port was added for liver retraction. We retrospectively re-evaluated all of the recorded surgical videos and preoperative computed tomography images. The pneumoperitoneum time (PT) was used as an objective index of surgical difficulty. The PT was significantly shorter for right nephrectomy than left nephrectomy (94 vs. 123 min, P = 0.004). With left nephrectomy, dissection of the spleno-renal ligament to mobilize the spleen medially required additional time. Also, the left renal vein could only be divided after securing the adrenal, gonadal and lumbar veins. In patients whose renal artery was located cranial to the renal vein, PT tended to be longer than in the other patients (131 vs. 108 min, P = 0.070). In patients with a superior renal artery, the inferior renal vein invariably covered the artery and made it difficult to ligate the renal artery via the umbilical approach at the first procedure. These findings indicate that patients undergoing right nephrectomy in whom the renal artery is not located cranial to the renal vein are suitable for single-port laparoscopic radical nephrectomy. © The Author 2017. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com

Tunnel injection transit-time diodes for W-band power generation

NASA Technical Reports Server (NTRS)

Kidner, C.; Eisele, H.; Haddad, G. I.

1992-01-01

GaAs p(+ +)n(+)n(-)n(+) single-drift tunnel injection transit-time (TUNNETT) diodes for W-band operation have been successfully designed and tested. An output power of 32 mW at 93.5 GHz with a dc to RF conversion efficiency of 2.6 percent was obtained. The oscillations have a clean spectrum in a conventional waveguide cavity.

Internal Carotid Artery Dissection in Brazilian Jiu-Jitsu.

PubMed

Demartini, Zeferino; Rodrigues Freire, Maxweyd; Lages, Roberto Oliver; Francisco, Alexandre Novicki; Nanni, Felipe; Maranha Gatto, Luana A; Koppe, Gelson Luis

2017-06-01

Carotid artery dissection is a significant cause of stroke in young patients. It may be asymptomatic and go undiagnosed, or minimal transient manifestations may follow, commanding a higher index of suspicion than ordinarily exists to avoid misdiagnosis. Reported herein is a 27-year-old man who suffered extracranial internal carotid artery dissection while practicing a Brazilian Jiu-Jitsu submission maneuver. The patient's condition suddenly deteriorated one week later due to distal embolization and stroke. Despite endovascular treatment, with stenting of the cervical carotid artery, neurologic deficits remained. Of note, the objective in martial arts, which is to kill or incapacitate, has yet to be fully tempered in transitioning to sport. Brazilian Jiu-jitsu, a relatively new and fast-growing form of martial art, places emphasis on submission maneuvers. Related injuries are not common knowledge and are poorly described in the literature. This account is intended to shed light on the risk of this discipline. Through education and improved supervision, vascular injuries of this nature and the potentially lethal or disabling consequences may thus be prevented in young athletes.

Internal Carotid Artery Dissection in Brazilian Jiu-Jitsu

PubMed Central

Rodrigues Freire, Maxweyd; Lages, Roberto Oliver; Francisco, Alexandre Novicki; Nanni, Felipe; Maranha Gatto, Luana A.; Koppe, Gelson Luis

2017-01-01

Carotid artery dissection is a significant cause of stroke in young patients. It may be asymptomatic and go undiagnosed, or minimal transient manifestations may follow, commanding a higher index of suspicion than ordinarily exists to avoid misdiagnosis. Reported herein is a 27-year-old man who suffered extracranial internal carotid artery dissection while practicing a Brazilian Jiu-Jitsu submission maneuver. The patient's condition suddenly deteriorated one week later due to distal embolization and stroke. Despite endovascular treatment, with stenting of the cervical carotid artery, neurologic deficits remained. Of note, the objective in martial arts, which is to kill or incapacitate, has yet to be fully tempered in transitioning to sport. Brazilian Jiu-jitsu, a relatively new and fast-growing form of martial art, places emphasis on submission maneuvers. Related injuries are not common knowledge and are poorly described in the literature. This account is intended to shed light on the risk of this discipline. Through education and improved supervision, vascular injuries of this nature and the potentially lethal or disabling consequences may thus be prevented in young athletes. PMID:29152471

Numerical and experimental analysis of the transitional flow across a real stenosis.

PubMed

Agujetas, R; Ferrera, C; Marcos, A C; Alejo, J P; Montanero, J M

2017-08-01

In this paper, we present a numerical study of the pulsatile transitional flow crossing a severe real stenosis located right in front of the bifurcation between the right subclavian and right common carotid arteries. The simulation allows one to determine relevant features of this subject-specific flow, such as the pressure waves in the right subclavian and right common carotid arteries. We explain the subclavian steal syndrome suffered by the patient in terms of the drastic pressure drop in the right subclavian artery. This pressure drop is caused by both the diverging part of the analyzed stenosis and the reverse flow in the bifurcation induced by another stenosis in the right internal carotid artery.

Investigation of powered 2-wheeler accident involvement in urban arterials by considering real-time traffic and weather data.

PubMed

Theofilatos, Athanasios; Yannis, George

2017-04-03

Understanding the various factors that affect accident risk is of particular concern to decision makers and researchers. The incorporation of real-time traffic and weather data constitutes a fruitful approach when analyzing accident risk. However, the vast majority of relevant research has no specific focus on vulnerable road users such as powered 2-wheelers (PTWs). Moreover, studies using data from urban roads and arterials are scarce. This study aims to add to the current knowledge by considering real-time traffic and weather data from 2 major urban arterials in the city of Athens, Greece, in order to estimate the effect of traffic, weather, and other characteristics on PTW accident involvement. Because of the high number of candidate variables, a random forest model was applied to reveal the most important variables. Then, the potentially significant variables were used as input to a Bayesian logistic regression model in order to reveal the magnitude of their effect on PTW accident involvement. The results of the analysis suggest that PTWs are more likely to be involved in multivehicle accidents than in single-vehicle accidents. It was also indicated that increased traffic flow and variations in speed have a significant influence on PTW accident involvement. On the other hand, weather characteristics were found to have no effect. The findings of this study can contribute to the understanding of accident mechanisms of PTWs and reduce PTW accident risk in urban arterials.

Genetic Algorithm for Multiple Bus Line Coordination on Urban Arterial

PubMed Central

Yang, Zhen; Wang, Wei; Chen, Shuyan; Ding, Haoyang; Li, Xiaowei

2015-01-01

Bus travel time on road section is defined and analyzed with the effect of multiple bus lines. An analytical model is formulated to calculate the total red time a bus encounters when travelling along the arterial. Genetic algorithm is used to optimize the offset scheme of traffic signals to minimize the total red time that all bus lines encounter in two directions of the arterial. The model and algorithm are applied to the major part of Zhongshan North Street in the city of Nanjing. The results show that the methods in this paper can reduce total red time of all the bus lines by 31.9% on the object arterial and thus improve the traffic efficiency of the whole arterial and promote public transport priority. PMID:25663837

Rheological approaches of arteries.

PubMed

Bauer, R D

1984-01-01

A fundamental problem of haemodynamics lies in the description of the rheological properties of arteries. The time and history dependency of stress and strain, the nonlinearity of the stress-radius relationship, and the activity of vascular smooth muscle complicate or even prevent a complete mathematical characterization of the arterial wall mechanics. Due to this nonlinearity, dynamic investigations were hitherto performed in excised arteries in vitro by means of small sinusoidal changes of stress and radius at different stress levels in a wide frequency range. To allow an analysis of the dynamic rheological properties of arteries in vivo, we have developed a procedure which permits the separate determination of the elastic, the viscous, and the inertial forces acting on the arterial wall. The stress can be subdivided into an elastic stress which is a function of radius (r), a viscous stress which is a function of dr/dt, and an inertial stress which is a function of d2r/dt2. These stresses are formulated as polynomials. Under cyclic loading and unloading, hysteresis loops appear in the stress-radius diagrams of arteries. Since the elastic stress-radius diagram must be free from any loop, the coefficients of the viscous and the inertial stress can be found by a fitting procedure, using the criterion of loop elimination. Investigations were performed on exposed canine arteries in vivo. The main result was that the elastic stress-radius curve was markedly nonlinear at greater pulse pressures. The viscous wall behaviour, too, was nonlinear and depended mainly on the square of the vessel radius.

Test of synthetic DNA tracers in a periodic hydrodynamic system for time-variable transit time distribution assessment

NASA Astrophysics Data System (ADS)

Dahlke, H. E.; Wang, C.; McNew, C.; McLaughlin, S.; Lyon, S. W.

2016-12-01

Recent research on time-varying transport through hydrologic systems proposed using decomposed over-printed tracer breakthrough curves to directly observe transport through complex flow systems. This method, also known as the PERTH (Periodic Tracer Hierarchy) method requires periodic flow and multiple tracer injections to reveal changes in flow pathways and transport behavior. Time-variable transit time distributions (TTD) estimated from tracer breakthrough curves often vary with the storage state of the system, which in turn is influenced by internal and external variabilities, such as the arrangement of flow pathways and fluctuations in system inputs. Deciphering internal from external variabilities in TTDs might help to advance the use of TTDs for estimating the physical state of a system; however, thus far the finite number of unique conservative tracers available for tracing has limited deeper insights. Synthetic DNA tracers consisting of short strands of synthetic DNA encapsulated by polylactic acid (PLA) microspheres could potentially provide multiple unique tracers with identical transport properties needed to explore time varying transport through hydrologic systems in more detail. An experiment was conducted on the miniLeo hillslope, a 1 m3 sloping lysimeter, within the Biosphere 2 Landscape Evolution Observatory near Tucson, AZ to investigate transit time variability. The goal of the experiment was to 1) test the suitability of using synthetic DNA tracers for estimating TTDs in a hydrologic system and 2) to determine the TTDs of individual tracer pulses under periodic steady-state conditions. Five DNA tracers, consisting of four unique, encapsulated DNA sequences and one free/non-encapsulated DNA sequence, were applied as reference and probe tracers together with deuterium, using the PERTH method. The lysimeter received three 2-hour pulses of rainfall at a rate of 30 mm/hr for 10 days. Initial results show that both the encapsulated and free DNA tracers

Two-Year Institution Part-Time Nurse Faculty Experiences During Role Transition and Identity Development: A Phenomenological Study.

PubMed

Owens, Rhoda A

This study explored two-year institution part-time nurse faculty's perceptions of their experiences during their role transitions from nurses in clinical practice to part-time clinical instructors. Part-time nurse faculty enter academia as expert clinicians, but most have little or no training in the pedagogy of effective student learning. A phenomenological study was used to explore the faculty role transition experiences. Findings support the proposition that six participants transitioned from their expert clinician to instructor identities; however, two continue in the process. Critical to this process are relationships with individuals in their environments, past and present experiences, the incentive to learn to be better instructors, and the importance of support and training. A model emerged, Process of Role Transition and Professional Identity Formation for Part-Time Clinical Instructors at Two-Year Institutions, that is potentially useful for administrators in developing individualized orientation and professional development programs.

Coronary Artery Bypass

MedlinePlus

... 000 procedures performed each year in the United States. Arteries can become clogged over time by the buildup of fatty plaque. Bypass surgery improves the blood flow to the heart with a new route or “ ...

Central retinal vein occlusion with cilioretinal infarction from branch flow exclusion and choroidal arterial steal.

PubMed

McLeod, David

2009-01-01

The first definitive study of retinal vein occlusion complicated by infarction within the territory of one or more cilioretinal arteries was published in 1976. Many individual cases and further case series have been reported in the interim, but the nature of the interrelationship is still under debate. A review was undertaken of the relevant clinical and fundus fluorescein angiographic characteristics of this combined retinal vascular disorder together with the pathophysiological mechanisms currently presented in the literature to explain their association. Scientific publications up to 2008 were evaluated by one of the authors of the original report. There are broad similarities between publications in their descriptions of the clinical features, but significant differences of detail and interpretation are also evident. Most of the mechanisms so far proposed to account for cilioretinal infarction after central or hemisphere retinal vein occlusion do not withstand critical scrutiny. Two related hypotheses are expounded that appear to satisfactorily elucidate this interrelationship -- branch flow exclusion and branch flow diversion (otherwise termed "choroidal arterial steal"). In eyes with a cilioretinal supply, the probability that cilioretinal infarction will complicate retinal vein occlusion increases with increasing severity of venous obstruction and the more distally the cilioretinal artery arises from the posterior ciliary arterial tree. A distal branch point also facilitates observation of dye front reciprocation within the artery. Indicators of the degree of venous obstruction that may be necessary to instigate cilioretinal infarction include very prolonged dye transit times in the central retinal circulation, exaggerated venous cyanosis and tortuosity, perivenous cotton-wool sentinels, and macular perivenular whitening.

Realization of a multipath ultrasonic gas flowmeter based on transit-time technique.

PubMed

Chen, Qiang; Li, Weihua; Wu, Jiangtao

2014-01-01

A microcomputer-based ultrasonic gas flowmeter with transit-time method is presented. Modules of the flowmeter are designed systematically, including the acoustic path arrangement, ultrasound emission and reception module, transit-time measurement module, the software and so on. Four 200 kHz transducers forming two acoustic paths are used to send and receive ultrasound simultaneously. The synchronization of the transducers can eliminate the influence caused by the inherent switch time in simple chord flowmeter. The distribution of the acoustic paths on the mechanical apparatus follows the Tailored integration, which could reduce the inherent error by 2-3% compared with the Gaussian integration commonly used in the ultrasonic flowmeter now. This work also develops timing modules to determine the flight time of the acoustic signal. The timing mechanism is different from the traditional method. The timing circuit here adopts high capability chip TDC-GP2, with the typical resolution of 50 ps. The software of Labview is used to receive data from the circuit and calculate the gas flow value. Finally, the two paths flowmeter has been calibrated and validated on the test facilities for air flow in Shaanxi Institute of Measurement & Testing. Copyright © 2013 Elsevier B.V. All rights reserved.

Channel noise-induced temporal coherence transitions and synchronization transitions in adaptive neuronal networks with time delay

NASA Astrophysics Data System (ADS)

Gong, Yubing; Xie, Huijuan

2017-09-01

Using spike-timing-dependent plasticity (STDP), we study the effect of channel noise on temporal coherence and synchronization of adaptive scale-free Hodgkin-Huxley neuronal networks with time delay. It is found that the spiking regularity and spatial synchronization of the neurons intermittently increase and decrease as channel noise intensity is varied, exhibiting transitions of temporal coherence and synchronization. Moreover, this phenomenon depends on time delay, STDP, and network average degree. As time delay increases, the phenomenon is weakened, however, there are optimal STDP and network average degree by which the phenomenon becomes strongest. These results show that channel noise can intermittently enhance the temporal coherence and synchronization of the delayed adaptive neuronal networks. These findings provide a new insight into channel noise for the information processing and transmission in neural systems.

Does timing and sequencing of transitions to adulthood make a difference? Stress, smoking, and physical activity among young Australian women.

PubMed

Bell, Sandra; Lee, Christina

2006-01-01

The major changes of the transition to adulthood are argued to be stressful, and health-related behaviors such as smoking and physical activity may be adopted, consolidated, or abandoned at this time. On the other hand, research has suggested that the normative transitions of emerging adulthood, although involving considerable change, may be associated with low stress because they are perceived as both positive and normal at this life stage. This article examines relations between the timing and sequencing of life transitions and stress and health-related behaviors, focusing on the transition to young adulthood among Australian women. A total of 853 women aged 22 to 27 provided information about the timing and sequencing of 6 life transitions: moving out of home, stopping full-time education, starting full-time work, having the first live-in relationship, marriage, and motherhood-and stress, smoking, and physical activity. Most had moved out of home, stopped full-time education, and started full-time work, but only 14% had undertaken all 6 transitions. Overall, 70% of participants had made transitions "in order." Overall, the findings suggest that the relations between timing and sequencing of transitions, and indicators of health, are moderate for smoking, but small for stress and for physical activity. These effects remained after controlling for socioeconomic status of the participants' families of origin. Matching current social norms for the timing and sequencing of life changes may be of less importance for women's well-being than is commonly believed. Although the significant relations between early or "out of order" transitions and smoking are of concern, the smaller relations with stress and with sedentariness suggest that such transitions may have limited negative consequences, and support the view that individuals are active in choosing the life path that is appropriate for them and their circumstances.

Intervention time until discharge for newborns on transition from gavage to exclusive oral feeding.

PubMed

Medeiros, Andréa Monteiro Correia; Ramos, Blenda Karen Batista; Bomfim, Déborah Letticia Santana Santos; Alvelos, Conceição Lima; Silva, Talita Cardoso da; Barreto, Ikaro Daniel de Carvalho; Santos, Felipe Batista; Gurgel, Ricardo Queiroz

2018-01-01

Purpose Measure the intervention time required for transition from gavage to exclusive oral feeding, comparing newborns exposed exclusively to the mother's breast with those who, in addition to breastfeeding, received supplementation using a cup or baby bottle. Methods Analytical, longitudinal, cohort study conducted with 165 newborns (NB) divided into groups according to severity of medical complications (G1-with no complications; G2-with significant complications), and into subgroups according to feeding mechanism (A and B). All NBs were low birth weight, on Kangaroo Mother Care, and breast stimulated according to medical prescription and hospital routine. Regarding feeding pattern, subgroup A comprised NBs exclusively breastfed at hospital discharge, whereas subgroup B was composed of NBs fed through cup/bottle at some time during hospitalization. The number of days spent in each stage of transition was recorded for each NB. Results History of clinical complications significantly influenced total intervention time. Study participants in subgroups G1-A (10 days), G1-B (9 days), and G2-A (12 days) displayed greater chances of early discharge compared with those in subgroup G2-B (16 days). Conclusion NBs with no important history of clinical complications displayed greater chances of early hospital discharge. NBs with significant history of clinical complications that underwent gavage to exclusive breastfeeding transition presented smaller intervention time than those that required supplementation using cup/bottle. Feeding transition using the gavage-to-exclusive oral feeding technique is recommended for Speech-language Pathology practice in Neonatology.

Coronary Arteries

MedlinePlus

... its own vascular system, called coronary circulation. The aorta (the main blood supplier to the body) branches ... blood to the rest of the body. Tags: aorta , arteries , blood , coronary arteries , coronary artery , coronary artery ...

Increased postflight carotid artery stiffness and inflight insulin resistance resulting from 6-mo spaceflight in male and female astronauts.

PubMed

Hughson, Richard L; Robertson, Andrew D; Arbeille, Philippe; Shoemaker, J Kevin; Rush, James W E; Fraser, Katelyn S; Greaves, Danielle K

2016-03-01

Removal of the normal head-to-foot gravity vector and chronic weightlessness during spaceflight might induce cardiovascular and metabolic adaptations related to changes in arterial pressure and reduction in physical activity. We tested hypotheses that stiffness of arteries located above the heart would be increased postflight, and that blood biomarkers inflight would be consistent with changes in vascular function. Possible sex differences in responses were explored in four male and four female astronauts who lived on the International Space Station for 6 mo. Carotid artery distensibility coefficient (P = 0.005) and β-stiffness index (P = 0.006) reflected 17-30% increases in arterial stiffness when measured within 38 h of return to Earth compared with preflight. Spaceflight-by-sex interaction effects were found with greater changes in β-stiffness index in women (P = 0.017), but greater changes in pulse wave transit time in men (P = 0.006). Several blood biomarkers were changed from preflight to inflight, including an increase in an index of insulin resistance (P < 0.001) with a spaceflight-by-sex term suggesting greater change in men (P = 0.034). Spaceflight-by-sex interactions for renin (P = 0.016) and aldosterone (P = 0.010) indicated greater increases in women than men. Six-month spaceflight caused increased arterial stiffness. Altered hydrostatic arterial pressure gradients as well as changes in insulin resistance and other biomarkers might have contributed to alterations in arterial properties, including sex differences between male and female astronauts. Copyright © 2016 the American Physiological Society.

Objective Measurement of Arterial Flow Before and After Transcatheter Arterial Chemoembolization: A Feasibility Study Using Quantitative Color-Coding Analysis.

PubMed

Lin, Yi-Yang; Lee, Rheun-Chuan; Tseng, Hsiuo-Shan; Liu, Chien-An; Guo, Wan-Yuo; Chang, Cheng-Yen

2015-12-01

To quantitatively measure the hemodynamic change of hepatic artery before and after transcatheter arterial chemoembolization (TACE) of hepatocellular carcinoma (HCC) by quantitative color-coding analysis (QCA). This prospective study registered 64 consecutive HCC patients who underwent segmental or subsegmental TACE with epirubicin and lipiodol at level 2 or 3 of the subjective angiographic chemoembolization endpoint. QCA was used to determine the maximal density time (T(max)) of selected intravascular region of interest (ROI). Relative T(max) (rT(max)) was defined as the T(max) at the selected ROI minus the time of contrast medium spurting from the catheter tip. The rT(max) of hepatic arteries was analyzed before and after embolization. The pre- and post-treatment rT(max) of the landmarks at the treated segmental artery were 1.96 ± 0.48 and 3.14 ± 1.77 s, p < 0.001. According to the treated lobe, 30 patients were treated for the right lobe alone, and 8 patients were treated for the left lobe alone. The pre- and post-rT(max) of treated segmental artery were 2.06 ± 0.54, 3.34 ± 1.63 s, p < 0.001 and 1.89 ± 0.45, 2.68 ± 1.46 s, p = 0.12, respectively. The rT(max) of the proximal lobar hepatic arteries or proper hepatic artery had no significant change before and after TACE. The QCA is feasible to quantify embolization endpoints by comparing the rT(max) in selected hepatic arteries before and after TACE. The rT(max) of treated segmental artery was significant prolonged after optimized procedures.

Evaluation of the applicability of territorial arterial spin labeling in meningiomas for presurgical assessments compared with 3-dimensional time-of-flight magnetic resonance angiography.

PubMed

Lu, Yiping; Luan, Shihai; Liu, Li; Xiong, Ji; Wen, Jianbo; Qu, Jianxun; Geng, Daoying; Yin, Bo

2017-10-01

To prospectively evaluate the application of territorial arterial spin labelling (t-ASL) in comparison with unenhanced three-dimensional time-of-flight magnetic resonance angiography (3D-TOF-MRA) in the identification of the feeding vasculature of meningiomas. Thirty consecutive patients with suspected meningiomas underwent conventional MR imaging, unenhanced 3D-TOF-MRA and t-ASL scanning. Four experienced neuro-radiologists assessed the feeding vessels with different techniques separately. For the identification of the origin of the feeding arteries on t-ASL, the inter-observer agreement was excellent (к = 0.913), while the inter-observer agreement of 3D-TOF-MRA was good (к = 0.653). The inter-modality agreement between t-ASL and 3D-TOF-MRA for the feeding arteries was moderate (к = 0.514). All 8 patients with motor or sensory disorders proved to have meningiomas supplied completely or partially by the internal carotid arteries, while all 14 patients with meningiomas supplied by the external carotid arteries or basilar arteries didn't show any symptoms concerning motor or sensory disorders (p = 0.003). T-ASL could complement unenhanced 3D-TOF-MRA and increase accuracy in the identification of the supplying arteries of meningiomas in a safe, intuitive, non-radioactive manner. The information about feeding arteries was potentially related to patients' symptoms and pathology, making it more crucial for neurosurgeons in planning surgery as well as evaluating prognosis. • A comprehensive understanding of feeding vasculature is helpful for optimized treatment decisions. • T-ASL could identify main supplying arteries of meningiomas with excellent inter-observer agreement. • The inter-modality agreement for identification of the main feeding arteries was moderate. • Blood supply from ICAs was related to motor or sensory disorders. • High-level meningiomas were found to have double main supplying arteries.

Bronchial-arterial interdependence in isolated dog lung.

PubMed

Lai-Fook, S J; Kallok, M J

1982-04-01

The bronchus and artery, embedded in the lung parenchyma, were modeled as adjoining cylindrical tubes in an elastic continuum. Solutions using finite-element analysis of nonuniform stress and strain occurring from an initial uniform state were computed for a reduction in arterial pressure. Maximal nonuniform principal and shear stresses in the parenchyma, equal to 2.5 times the mean periarterial stresses, occurred in the region adjacent to the bronchial-arterial joint. Bronchial cross section became oval and elongated along the line passing through the centers of the tubes, whereas arterial cross section elongated at right angles to this line. These predicted changes in shape of bronchus and artery were verified by radiographic measurements in isolated lobes, held at constant transpulmonary pressures of 4 and 25 cmH2O while arterial pressure was varied. Results suggest that peribronchovascular interstitial fluid pressure may be nonuniform and that the bronchial-arterial joint may be the preferential site for emphysematous perivascular lesions, which may occur on lung hyperinflation.

Time-varying coupling functions: Dynamical inference and cause of synchronization transitions

NASA Astrophysics Data System (ADS)

Stankovski, Tomislav

2017-02-01

Interactions in nature can be described by their coupling strength, direction of coupling, and coupling function. The coupling strength and directionality are relatively well understood and studied, at least for two interacting systems; however, there can be a complexity in the interactions uniquely dependent on the coupling functions. Such a special case is studied here: synchronization transition occurs only due to the time variability of the coupling functions, while the net coupling strength is constant throughout the observation time. To motivate the investigation, an example is used to present an analysis of cross-frequency coupling functions between delta and alpha brain waves extracted from the electroencephalography recording of a healthy human subject in a free-running resting state. The results indicate that time-varying coupling functions are a reality for biological interactions. A model of phase oscillators is used to demonstrate and detect the synchronization transition caused by the varying coupling functions during an invariant coupling strength. The ability to detect this phenomenon is discussed with the method of dynamical Bayesian inference, which was able to infer the time-varying coupling functions. The form of the coupling function acts as an additional dimension for the interactions, and it should be taken into account when detecting biological or other interactions from data.

Mycotic pulmonary artery aneurysm following pulmonary artery banding.

PubMed

Kumar, R V; Roughneen, P T; de Leval, M R

1994-01-01

A neonate with situs inversus, transposition of the great arteries, ventricular septal defect, criss-cross ventricles and hypoplastic right ventricle underwent pulmonary artery banding at the age of 7 days. The course was complicated by septicaemia and subsequently the development of an aneurysm of the pulmonary artery. Serratia marcessans was grown from the band site. The pulmonary artery aneurysm was resected and the pulmonary artery was repaired. The literature is reviewed with the emphasis on diagnosis, natural history and surgical management.

Parity-time symmetry-breaking mechanism of dynamic Mott transitions in dissipative systems

DOE PAGES

Tripathi, Vikram; Galda, Alexey; Barman, Himadri; ...

2016-07-05

Here, we describe the critical behavior of the electric field-driven (dynamic) Mott insulator-to-metal transitions in dissipative Fermi and Bose systems in terms of non-Hermitian Hamiltonians invariant under simultaneous parity (P) and time-reversal (T) operations. The dynamic Mott transition is identified as a PT symmetry-breaking phase transition, with the Mott insulating state corresponding to the regime of unbroken PT symmetry with a real energy spectrum. We also established that the imaginary part of the Hamiltonian arises from the combined effects of the driving field and inherent dissipation. We derive the renormalization and collapse of the Mott gap at the dielectric breakdownmore » and describe the resulting critical behavior of transport characteristics. The critical exponent we obtained is in an excellent agreement with experimental findings.« less

Noninvasive measurement of beat-to-beat arterial blood pressure by the Korotkoff sound delay time.

PubMed

Xiang, Haiyan; Liu, Yanyong; Li, Yinhua; Qin, Yufei; Yu, Mengsun

2012-02-01

To propose a novel noninvasive beat-to-beat arterial blood pressure measurement method based on the Korotkoff sound delay time (KDT) and evaluate its accuracy in preliminary experiments. KDT decreases as the cuff pressure P deflates, which can be described by a function KDT=f (P). Actually, KDT is a function of arterial transmural pressure. Therefore, the variation in blood pressure can be obtained by the transmural pressure, which is estimated by the KDT. Holding the cuff pressure at an approximate constant pressure between systolic pressure and diastolic pressure, the variation in blood pressure ΔEBP between successive heartbeats can be estimated according to KDT and f'(p), which represents the variation of KDT corresponding to unit pressure. Then the blood pressure for each heartbeat can be obtained by accumulating the ΔEBP. Invasive and noninvasive blood pressure values of six participants were measured simultaneously to evaluate the method. The average of the correlation coefficients between the invasive mean arterial pressure (MAP) and the KDT for six participants was -0.91. The average of the correlation coefficients between the invasive MAP and the estimated mean blood pressure (EBP) was 0.92. The mean difference between EBP and MAP was 0.51 mmHg, and the SD was 2.65 mmHg. The mean blood pressure estimated by the KDT is consistent with the invasive MAP. The beat-to-beat blood pressure estimated by KDT provides an accurate estimate of MAP in the preliminary experiments and represents a potential acceptable alternative to invasive blood pressure monitoring during laboratory studies.

Quantitative myocardial perfusion from static cardiac and dynamic arterial CT

NASA Astrophysics Data System (ADS)

Bindschadler, Michael; Branch, Kelley R.; Alessio, Adam M.

2018-05-01

Quantitative myocardial blood flow (MBF) estimation by dynamic contrast enhanced cardiac computed tomography (CT) requires multi-frame acquisition of contrast transit through the blood pool and myocardium to inform the arterial input and tissue response functions. Both the input and the tissue response functions for the entire myocardium are sampled with each acquisition. However, the long breath holds and frequent sampling can result in significant motion artifacts and relatively high radiation dose. To address these limitations, we propose and evaluate a new static cardiac and dynamic arterial (SCDA) quantitative MBF approach where (1) the input function is well sampled using either prediction from pre-scan timing bolus data or measured from dynamic thin slice ‘bolus tracking’ acquisitions, and (2) the whole-heart tissue response data is limited to one contrast enhanced CT acquisition. A perfusion model uses the dynamic arterial input function to generate a family of possible myocardial contrast enhancement curves corresponding to a range of MBF values. Combined with the timing of the single whole-heart acquisition, these curves generate a lookup table relating myocardial contrast enhancement to quantitative MBF. We tested the SCDA approach in 28 patients that underwent a full dynamic CT protocol both at rest and vasodilator stress conditions. Using measured input function plus single (enhanced CT only) or plus double (enhanced and contrast free baseline CT’s) myocardial acquisitions yielded MBF estimates with root mean square (RMS) error of 1.2 ml/min/g and 0.35 ml/min/g, and radiation dose reductions of 90% and 83%, respectively. The prediction of the input function based on timing bolus data and the static acquisition had an RMS error compared to the measured input function of 26.0% which led to MBF estimation errors greater than threefold higher than using the measured input function. SCDA presents a new, simplified approach for quantitative

Cerebral perfusion characteristics show differences in younger versus older children with sickle cell anaemia: Results from a multiple-inflow-time arterial spin labelling study.

PubMed

Kawadler, Jamie M; Hales, Patrick W; Barker, Simon; Cox, Timothy C S; Kirkham, Fenella J; Clark, Chris A

2018-03-30

Sickle cell anaemia (SCA) is associated with chronic anaemia and oxygen desaturation, which elevate cerebral blood flow (CBF) and increase the risk of neurocognitive complications. Arterial spin labelling (ASL) provides a methodology for measuring CBF non-invasively; however, ASL techniques using only a single inflow time are not sufficient to fully characterize abnormal haemodynamic behaviour in SCA. This study investigated haemodynamic parameters from a multi-inflow-time ASL acquisition in younger (8-12 years) and older (13-18 years) children with SCA with and without silent cerebral infarction (SCI+/-) (n = 20 and 19 respectively, 6 and 4 SCI+ respectively) and healthy controls (n = 9 and 7 respectively). Compared with controls, CBF was elevated globally in both groups of patients. In the younger SCA patients, blood oxygen content was negatively correlated with CBF in the middle and posterior cerebral artery territories and significantly positively correlated with bolus arrival time (BAT) in the anterior and middle cerebral artery territories. In older children, SCA patients had significantly shorter BAT than healthy controls and there was a significant negative correlation between CBF and oxygen content only in the territory of the posterior cerebral artery, with a trend for a correlation in the anterior cerebral artery but no relationship for the middle cerebral artery territory. In the younger group, SCI+ patients had significantly higher CBF in the posterior cerebral artery territory (SCI+ mean = 92.78 ml/100 g/min; SCI- mean = 72.71 ml/100 g/min; F = 4.28, p = 0.04), but this no longer reached significance when two children with abnormal transcranial Doppler and one with haemoglobin SC disease were excluded, and there were no significant differences between patients with and without SCI in the older children. With age, there appears to be increasing disparity between patients and controls in terms of the relationship between CBF and oxygen

Transit timing analysis of the exoplanets TrES-1 and TrES-2

NASA Astrophysics Data System (ADS)

Rabus, M.; Deeg, H. J.; Alonso, R.; Belmonte, J. A.; Almenara, J. M.

2009-12-01

Aims. The aim of this work is a detailed analysis of transit light curves from TrES-1 and TrES-2, obtained over a period of three to four years, in order to search for variabilities in observed mid-transit times and to set constraints on the presence of additional third bodies. Methods: Using the IAC 80 cm telescope, we observed transits of TrES-1 and TrES-2 over several years. Based on these new data and previously published work, we studied the observed light curves and searched for variations in the difference between observed and calculated (based on a fixed ephemeris) transit times. To model possible transit timing variations, we used polynomials of different orders, simulated O-C diagrams corresponding to a perturbing third mass, and we used sinusoidal fits. For each model we calculated the χ2 residuals and the false alarm probability (FAP). Results: For TrES-1, we can exclude planetary companions (>1 M⊕) in the 3:2 and 2:1 MMRs having high FAPs based on our transit observations from the ground. Likewise, a light time effect caused, e.g., by a 0.09 M_⊙ mass star at a distance of 7.8 AU is possible. As for TrES-2, we find a better ephemeris of Tc = 2 453 957.63512(28) + 2.4706101(18) × Epoch and a good fit for a sine function with a period of 0.2 days, compatible with a moon around TrES-2 and an amplitude of 57 s, but it is not a uniquely low χ2 value that would indicate a clear signal. In both cases, TrES-1 and TrES-2, we are able to put upper constraints on the presence of additional perturbers masses. We also conclude that any sinusoidal variations that might be indicative of exomoons need to be confirmed with higher statistical significance by further observations, noting that TrES-2 is in the field-of-view of the Kepler Space Telescope. Photometric data for TrES-1 and TrES-2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/508/1011

Bilateral Internal Carotid Artery Occlusion, External Carotid Artery Stenosis, and Vertebral Artery Kinking: May It Be Asymptomatic?

PubMed

Fatic, Nikola; Jaffer, Usman; Ivana, Saicic; Gordana, Globarevic-Vukcevic; Markovic, Dragan; Kostic, Dusan; Davidovic, Lazar

2017-10-01

The clinical spectrum of internal carotid artery occlusion ranges from being a completely asymptomatic occlusion to a devastating stroke or death. The prevalence of asymptomatic internal carotid artery occlusion is unknown, particularly for bilateral occlusion. The distal branches of the external carotid artery anastomose with distal branches of the internal carotid artery provide important sources of collateral circulation to the brain. Stenosis of the external carotid artery with ipsilateral/bilateral internal occlusion may result in ischemic sequelae. Coiling or kinking of the vertebral artery is a rare morphological entity that is infrequently reported because it remains asymptomatic and has no clinical relevance. Currently, there is little evidence to support management strategies for this disease entity and no official recommendations for asymptomatic bilateral carotid artery occlusion. We present a case of a 62-year-old female with asymptomatic bilateral internal carotid artery occlusion, bilateral external carotid artery stenoses, and bilateral kinking of the vertebral artery at the V2 segment, who has been successfully managed conservatively for over 5 years. An individualized approach to management of patients with bilateral internal carotid artery occlusion, especially in combination with external carotid artery stenosis and elongation malformations of the vertebral artery is key to a successful strategy. Copyright © 2017 Elsevier Inc. All rights reserved.

Effect of arterial baroreceptor denervation on sodium balance.

PubMed

DiBona, Gerald F; Sawin, Linda L

2002-10-01

During chronic increased dietary sodium intake, arterial baroreceptors buffer against sustained increases in arterial pressure, and renal sympathoinhibition contributes importantly to the maintenance of sodium balance by decreasing renal tubular sodium reabsorption and increasing urinary sodium excretion. The present study examined the effect of arterial baroreceptor denervation on sodium balance in conscious rats during low, normal, and high dietary sodium intake. Compared with measurements made before arterial baroreceptor denervation, arterial baroreceptor-denervated rats had similar sodium balance during normal dietary sodium intake but significantly more negative sodium balance during low dietary sodium intake and significantly more positive sodium balance during high dietary sodium intake. At the end of the high dietary sodium intake period, arterial pressure (under anesthesia) was 159+/-5 mm Hg after arterial baroreceptor denervation and 115+/-1 mm Hg before arterial baroreceptor denervation. Sham arterial baroreceptor denervation in time control rats had no effect on sodium balance or arterial pressure during the different dietary sodium intakes. These studies indicate that (1) arterial baroreceptor denervation impairs the ability to establish sodium balance during both low and high dietary sodium intake, and (2) arterial baroreceptor denervation leads to the development of increased arterial pressure during high dietary sodium intake in association with increased renal sodium retention.

[Anatomy character of renal artery and treatment of living-donor renal transplantation].

PubMed

Zhang, Lei; Fei, Ji-guang; Chen, Li-zhong; Wang, Chang-xi; Deng, Su-xiong; Qiu, Jiang; Li, Jun; Chen, Guo-dong; Huang, Gang

2009-12-15

To study the anatomy characters of renal artery and the treatment of multiple arteries in living donor renal grafts. Records of 142 living donors were analyzed in our center. We analyzed the anatomic structure of renal arteries by DSA and CTA pre-transplantation. Thirty-one kidneys with multiple arteries were transplanted after reconstruction. Then clinical effects were compared between multiple-renal-arteries group (n=31) and single-renal-artery group (n=111). The incidence of multiple renal artery was 30.99%, and there was no difference between both sides (left kidney 22.54%, right kidney 22.13%). If the multiple artery occurred in left or right kidney, the incidence of the multiple artery occurred in the other side was 56.25% and 60.00%, respectively. The diameter of left main renal artery was more magnanimous (P=0.001) and the first branch was more closed to abdominal aorta (P=0.004). Operation time and warm/cool ischemia time were longer in the multiple-renal-arteries group. However, estimated blood loss, delayed graft function, acute rejection and flow rate of arcuate artery were similar in both groups, the same as serum creatinine and serum creatinine clearance rate on day 7, 1 month and 3 month post-operation. It was shown by repeated measures ANOVA that graft with multiple arteries didn't affect the tendency of renal function at early time post-operation. Comprehending the character of renal artery and accurate treatment of multiple artery anastomosis are critical for the effect of the living kidney transplantation.

Supporting Students in Military Families during Times of Transition: A Call for Awareness and Action

ERIC Educational Resources Information Center

Cole, Rebekah F.

2017-01-01

Throughout their time in school, students in military families face many challenging periods of transition, which include deployments, relocations, and the family's separation from the military. During these transitions, students in military families may be especially susceptible to social, emotional, and academic challenges both in their home…

Influence of blood flow velocity on arterial distensibility of carotid artery in healthy men.

PubMed

Tomoto, Tsubasa; Maeda, Seiji; Sugawara, Jun

2017-01-01

Decreased distensibility of carotid artery is independently associated with the incidence of cardiovascular and cerebrovascular events. Arterial distensibility is determined by vascular tone. Since shear stress is an important driving force of vasodilatory substances production form endothelial cells, we hypothesized that local basal (i.e., resting) arterial blood flow velocity is associated with regional arterial distensibility. To test this hypothesis, we determined the influence of local blood flow velocity on carotid arterial distensibility in cross-sectional study design. In a total of 73 apparent healthy men (18-64 years), carotid arterial properties, including measures of carotid arterial distensibility and BFV at rest, were evaluated via B-mode and Doppler ultrasound imaging and applanation tonometry system. Carotid arterial peak BFV and the absolute and normalized pulsatile BFV significantly correlated with age (r = -0.453 to -0.600, p < 0.0001), whereas mean and minimum BFV were not influenced by age. Distensibility coefficient of carotid artery correlated with peak BFV (r = 0.305, p < 0.01) and more strongly with pulsatile (i.e., systolic minus end-diastolic) BFV (r = 0.406, p < 0.0001) and the normalized pulsatile BFV by time-averaged velocity (r = 0.591, p < 0.0001). Multi-regression analysis revealed that age (β = -0.57, p < 0.0001) was the primary independent determinant for distensibility coefficient. In addition with this, carotid lumen diameter (β = -0.202, p < 0.01) and the normalized pulsatile BFV (β = 0.237, p < 0.05) were significant independent determinants of distensibility coefficient. Qualitatively similar results (although inverse in direction) were obtained by use of β-stiffness index. These results suggest that greater gradient of blood flow velocity during a cardiac cycle are favorably associated with distensibility of carotid artery.

Exploring the Dynamics of Transit Times and Subsurface Mixing in a Small Agricultural Catchment

NASA Astrophysics Data System (ADS)

Yang, Jie; Heidbüchel, Ingo; Musolff, Andreas; Reinstorf, Frido; Fleckenstein, Jan H.

2018-03-01

The analysis of transit/residence time distributions (TTDs and RTDs) provides important insights into the dynamics of stream-water ages and subsurface mixing. These insights have significant implications for water quality. For a small agricultural catchment in central Germany, we use a 3D fully coupled surface-subsurface hydrological model to simulate water flow and perform particle tracking to determine flow paths and transit times. The TTDs of discharge, RTDs of storage and fractional StorAge Selection (fSAS) functions are computed and analyzed on daily basis for a period of 10 years. Results show strong seasonal fluctuations of the median transit time of discharge and the median residence time, with the former being strongly related to the catchment wetness. Computed fSAS functions suggest systematic shifts of the discharge selection preference over four main periods: In the wet period, the youngest water in storage is preferentially selected, and this preference shifts gradually toward older ages of stored water when the catchment transitions into the drying, dry and wetting periods. These changes are driven by distinct shifts in the dominance of deeper flow paths and fast shallow flow paths. Changes in the shape of the fSAS functions can be captured by changes in the two parameters of the approximating Beta distributions, allowing the generation of continuous fSAS functions representing the general catchment behavior. These results improve our understanding of the seasonal dynamics of TTDs and fSAS functions for a complex real-world catchment and are important for interpreting solute export to the stream in a spatially implicit manner.

Estimation of cardiac output and pulmonary vascular resistance by contrast echocardiography transit time measurement: a prospective pilot study.

PubMed

Choi, Brian G; Sanai, Reza; Yang, Benjamin; Young, Heather A; Mazhari, Ramesh; Reiner, Jonathan S; Lewis, Jannet F

2014-10-31

Studies with other imaging modalities have demonstrated a relationship between contrast transit and cardiac output (CO) and pulmonary vascular resistance (PVR). We tested the hypothesis that the transit time during contrast echocardiography could accurately estimate both CO and PVR compared to right heart catheterization (RHC). 27 patients scheduled for RHC had 2D-echocardiogram immediately prior to RHC. 3 ml of DEFINITY contrast followed by a 10 ml saline flush was injected, and a multi-cycle echo clip was acquired from the beginning of injection to opacification of the left ventricle. 2D-echo based calculations of CO and PVR along with the DEFINITY-based transit time calculations were subsequently correlated with the RHC-determined CO and PVR. The transit time from full opacification of the right ventricle to full opacification of the left ventricle inversely correlated with CO (r=-0.61, p<0.001). The transit time from peak opacification of the right ventricle to first appearance in the left ventricle moderately correlated with PVR (r=0.46, p<0.01). Previously described echocardiographic methods for the determination of CO (Huntsman method) and PVR (Abbas and Haddad methods) did not correlate with RHC-determined values (p = 0.20 for CO, p = 0.18 and p = 0.22 for PVR, respectively). The contrast transit time method demonstrated reliable intra- (p<0.0001) and inter-observer correlation (p<0.001). We describe a novel method for the quantification of CO and estimation of PVR using contrast echocardiography transit time. This technique adds to the methodologies used for noninvasive hemodynamic assessment, but requires further validation to determine overall applicability.

Preoperative evaluation of hepatic arterial and portal venous anatomy using the time resolved echo-shared MR angiographic technique in living liver donors.

PubMed

Lee, Min Woo; Lee, Jeong Min; Lee, Jae Young; Kim, Se Hyung; Park, Eun-Ah; Han, Joon Koo; Choi, Jin-Young; Kim, Young Jun; Suh, Kyung-Suk; Choi, Byung Ihn

2007-04-01

The purpose of this study was to determine whether MR angiography utilizing the time resolved echo-shared angiographic technique (TREAT) can provide an effective assessment of the hepatic artery (HA) and portal vein (PV) in living donor candidates. MR angiography (MRA)was performed in 27 patients (23 men and 4 women; mean age, 31 years) by using TREAT. Two blinded radiologists evaluated HA anatomy, origin of segment IV feeding artery and PV anatomy in consensus. Qualitative evaluations of MRA images were performed using the following criteria: (a) overall image quality, (b) presence of artifacts, and (c) degree of venous contamination of the arterial phase. Using intraoperative findings as a standard of reference, the accuracy for the HA anatomy, origin of segment IV feeding artery and PV anatomy on TREAT-MRA were 93% (25/27), 85% (23/27), and 96% (26/27), respectively. Overall image qualities were as follows: excellent (n=22, 81%), good (n=4, 15%), and fair (n=1, 4%). Significant artifacts or venous contamination of the arterial phase images was not noted in any patient. TREAT-MRA can provide a complete evaluation of HA and PV anatomy during preoperative evaluation of living liver donors. Furthermore, it provides a more detailed anatomy of the HA without venous contamination.

Robust estimation of pulse wave transit time using group delay.

PubMed

Meloni, Antonella; Zymeski, Heather; Pepe, Alessia; Lombardi, Massimo; Wood, John C

2014-03-01

To evaluate the efficiency of a novel transit time (Δt) estimation method from cardiovascular magnetic resonance flow curves. Flow curves were estimated from phase contrast images of 30 patients. Our method (TT-GD: transit time group delay) operates in the frequency domain and models the ascending aortic waveform as an input passing through a discrete-component "filter," producing the observed descending aortic waveform. The GD of the filter represents the average time delay (Δt) across individual frequency bands of the input. This method was compared with two previously described time-domain methods: TT-point using the half-maximum of the curves and TT-wave using cross-correlation. High temporal resolution flow images were studied at multiple downsampling rates to study the impact of differences in temporal resolution. Mean Δts obtained with the three methods were comparable. The TT-GD method was the most robust to reduced temporal resolution. While the TT-GD and the TT-wave produced comparable results for velocity and flow waveforms, the TT-point resulted in significant shorter Δts when calculated from velocity waveforms (difference: 1.8±2.7 msec; coefficient of variability: 8.7%). The TT-GD method was the most reproducible, with an intraobserver variability of 3.4% and an interobserver variability of 3.7%. Compared to the traditional TT-point and TT-wave methods, the TT-GD approach was more robust to the choice of temporal resolution, waveform type, and observer. Copyright © 2013 Wiley Periodicals, Inc.

The 9 May 2016 Mercury transit – a timely opportunity for outreach

NASA Astrophysics Data System (ADS)

Rothery, David; Benkhoff, Johannes; Zender, Joe; Gill, Ranpal

2015-04-01

People across most of the globe will have a chance to witness Mercury's next solar transit, 11:12-18:42 UT, Monday 9 May 2016. Occurring a year after the end of the MESSENGER mission and a few months before the launch of BepiColombo, this transit (the first since 2006) will be an ideal occasion to draw the public's attention to the science goals of those missions, to showcase what we have recently learned about Mercury, and to draw attention to the conundrums that make Mercury such a fascinating object to study. The 2004 and 2012 transits of Venus were accompanied by major outreach events, and stimulated day-long media interest. The 2016 Mercury transit offers a similar opportunity, which the Mercury science community should seize upon. It is especially timely as an occasion to showcase the science achieved by MESSENGER and planned for BepiColombo. As a bonus, outreach infrastructure and momentum should still be fresh enough to re-use for the next transit, on 11 Nov 2019 (after that there will be a 13-year gap until 2032). Inexpensive solar projectors adequate to show the transit are readily available, and a recent upsurge of amateurs posting H-alpha and Ca-K solar images via social media shows that the amateur astronomy community is well-equipped to observe the Sun. Provisional plans for Mercury transit day 2016 are to webstream images for the benefit of those in darkness or afflicted by cloud, taking images from satellites such as PROBA-2 and SOHO as well as ground-based observatories. We will also webstream interviews and features about Mercury itself, to show what a fascinating world BepiColombo will be visiting. We would like to encourage observatories and astronomical societies to invite the public to view the transit using their facilities, and hope to be able to provide an on-line searchable list of transit events so members of the public can find one nearby.

Liver graft vascular variant with 3 extra-hepatic arteries.

PubMed

Martins, Paulo N

2010-06-01

Vascular anatomy of the liver is varied, and the "standard" anatomy is seen in 55%-80% of cases. It is very important that extrahepatic arteries are identified precisely at the time of graft procurement to avoid injuries that might compromise the liver function. In the present case the liver donor had the vascular anatomy of Michels type VII, e.g. a hepatic artery originating from the celiac trunk and going to the left lobe, an accessory left hepatic artery coming from the left gastric artery, and a replaced right hepatic artery coming from the superior mesenteric artery. This pattern of vascular supply is uncommon, representing less than 5% of cases. The replaced hepatic artery was reconstructed in the back-table with polypropylene suture 7.0 by connecting it to the stump of the splenic artery, and the celiac trunk of the graft was anastomosed to the recipient common hepatic artery.

Using isotopes to quantify evaporation and non-stationary transit times distributions in lake water budgets

NASA Astrophysics Data System (ADS)

Smith, A. A.; Tetzlaff, D.; Soulsby, C.

2017-12-01

Evaporative fluxes from northern lakes are essential components of catchment water balances, providing large supplies of water to the atmosphere, and affecting downstream water availability. However, measurement of lake evaporation is difficult in many catchments due to remoteness and inaccessibility. Evaporative flux may also influence mean transit times of lakes and catchments, identified through water- and tracer mass-balance. We combined stable water isotopes (δ2H and δ18O), transit, and residence time distributions in a non-stationary transit time model to estimate the evaporative flux from two lakes in the Scottish Highlands. The lakes were in close proximity to each other ( 2km), shallow (mean depth, 1.5 m) with one large (0.88km2) and one small (0.4km2). Model calibration used measurements of precipitation, air temperature, water level, and isotopic stream compositions of lake inflow and outflows. Evaporation flux was identified using lake fractionation of δ2H and δ18O. Mixing patterns of the lakes and their respective outlet isotopic compositions were accounted for by comparing three probability distributions for discharge and evaporation. We found that the evaporation flux was strongly influenced by these discharge and evaporation distributions. Decreased mixing within the lake resulted in greater evaporation fluxes. One of the three distributions yielded similar mean daily evaporation and uncertainty for both lakes (max 5mm/day), while evaporation using the other two distributions was inconsistent between the lakes. Importantly, our approach also estimated distributions of evaporation age, which were significantly different between the lakes, reflecting a combination of inflow stream magnitude and the mixing regimes. The mean evaporation flux age of the large lake was 160 days, and 14 days for the small lake. Our integrated approach of stable isotopes, time variant transit time distributions has shown to be a useful tool for quantifying evaporative

[The gastroduodenal artery and its variations. Study of 100 arteriographies].

PubMed

Milon, J; Milon, D; Boullier, G; Le Guerrier, A; Lanchou, G

1978-12-01

The gastro-duodenal artery, whose study has been based on a series of one hundred digestive arteriographies, is visualized in all cases. Its variations of origine are directly connected to the different possible dispositions of the hepatic arterial supply. The analysis of the results confirms the literary data: each time there is a middle hepatic artery, it gives the gastro-duodenal artery.

Efficacy and indications of transradial and transfemoral approaches for peripheral artery stent implantation.

PubMed

Chen, Peng; Li, Huijie; Zeng, Chunyu; Fang, Yuqiang; Shi, Weibin; Zhang, Xiaoqun; Yang, Chengming

2017-06-01

The transradial approach (TRA) has become an attractive alternative to the transfemoral approach (TFA) in percutaneous coronary intervention. To date, however, these two approaches have not been systematically compared in various percutaneous peripheral artery interventions (PPAIs). In the present study 258 patients with peripheral artery disease that underwent PPAI via the TRA (n=75) or the TFA (n=183) were analyzed. Clinical factors and outcomes in these two groups were compared. The puncture time was significantly longer (P<0.05) and the prevalence of artery vasospasm significantly higher (P<0.05) in patients who underwent PPAI via the TRA rather than via the TFA. However, the complication rate was significantly lower (P<0.05) and the artery compression time (P<0.05) and time bedridden (P<0.05) were significantly shorter via the TRA than via the TFA. These results suggest that PPAI via the TRA was associated with a lower complication rate, and shorter artery compression time and bedridden time than PPAI via the TFA. The TRA may be preferable for bilateral vertebral artery stenosis, whereas the TFA may be preferable for interventional treatment of carotid and subclavian artery stenosis. Therefore, the catheter length, artery support and push force should be comprehensively considered before choosing the TRA or TFA in the interventional treatment of renal artery stenosis.

Efficacy and indications of transradial and transfemoral approaches for peripheral artery stent implantation

PubMed Central

Chen, Peng; Li, Huijie; Zeng, Chunyu; Fang, Yuqiang; Shi, Weibin; Zhang, Xiaoqun; Yang, Chengming

2017-01-01

The transradial approach (TRA) has become an attractive alternative to the transfemoral approach (TFA) in percutaneous coronary intervention. To date, however, these two approaches have not been systematically compared in various percutaneous peripheral artery interventions (PPAIs). In the present study 258 patients with peripheral artery disease that underwent PPAI via the TRA (n=75) or the TFA (n=183) were analyzed. Clinical factors and outcomes in these two groups were compared. The puncture time was significantly longer (P<0.05) and the prevalence of artery vasospasm significantly higher (P<0.05) in patients who underwent PPAI via the TRA rather than via the TFA. However, the complication rate was significantly lower (P<0.05) and the artery compression time (P<0.05) and time bedridden (P<0.05) were significantly shorter via the TRA than via the TFA. These results suggest that PPAI via the TRA was associated with a lower complication rate, and shorter artery compression time and bedridden time than PPAI via the TFA. The TRA may be preferable for bilateral vertebral artery stenosis, whereas the TFA may be preferable for interventional treatment of carotid and subclavian artery stenosis. Therefore, the catheter length, artery support and push force should be comprehensively considered before choosing the TRA or TFA in the interventional treatment of renal artery stenosis. PMID:28587369

Late time cosmological phase transitions 1: Particle physics models and cosmic evolution

NASA Technical Reports Server (NTRS)

Frieman, Joshua A.; Hill, Christopher T.; Watkins, Richard

1991-01-01

We described a natural particle physics basis for late-time phase transitions in the universe. Such a transition can seed the formation of large-scale structure while leaving a minimal imprint upon the microwave background anisotropy. The key ingredient is an ultra-light pseudo-Nambu-Goldstone boson with an astronomically large (O(kpc-Mpc)) Compton wavelength. We analyze the cosmological signatures of and constraints upon a wide class of scenarios which do not involve domain walls. In addition to seeding structure, coherent ultra-light bosons may also provide unclustered dark matter in a spatially flat universe, omega sub phi approx. = 1.

Applying the payoff time framework to carotid artery disease management.

PubMed

Yuo, Theodore H; Roberts, Mark S; Braithwaite, R Scott; Chang, Chung-Chou H; Kraemer, Kevin L

2013-11-01

and Asymptomatic stenosis of the carotid arteries is associated with stroke. Carotid revascularization can reduce the future risk of stroke but can also trigger an immediate stroke. The objective was to model the generic relationship between immediate risk, long-term benefit, and life expectancy for any one-time prophylactic treatment and then apply the model to the use of revascularization in the management of asymptomatic carotid disease. In the "payoff time" framework, the possibility of losing quality-adjusted life-years (QALYs) because of revascularization failure is conceptualized as an "investment" that is eventually recouped over time, on average. Using this framework, we developed simple mathematical forms that define relationships between the following: perioperative probability of stroke (P); annual stroke rate without revascularization (r0); annual stroke rate after revascularization, conditional on not having suffered perioperative stroke (r1); utility levels assigned to the asymptomatic state (ua) and stroke state (us); and mortality rates (λ). In patients whose life expectancy is below a critical life expectancy (CLE = P/(1-P)r0-r1, the "investment" will never pay off, and revascularization will lead to loss of QALYs, on average. CLE is independent of utilities assigned to the health states if a rank ordering exists in which ua > us. For clinically relevant values (P = 3%, r0 = 1%, r1 = 0.5%), the CLE is approximately 6.4 years, which is longer than published guidelines regarding patient selection for revascularization. In managing asymptomatic carotid disease, the payoff time framework specifies a CLE beneath which patients, on average, will not benefit from revascularization. This formula is suitable for clinical use at the patient's bedside and can account for patient variability, the ability of clinicians who perform revascularization, and the particular revascularization technology that is chosen.

Sensitivity of Catchment Transit Times to Rainfall Variability Under Present and Future Climates

NASA Astrophysics Data System (ADS)

Wilusz, Daniel C.; Harman, Ciaran J.; Ball, William P.

2017-12-01

Hydrologists have a relatively good understanding of how rainfall variability shapes the catchment hydrograph, a reflection of the celerity of hydraulic head propagation. Much less is known about the influence of rainfall variability on catchment transit times, a reflection of water velocities that control solute transport. This work uses catchment-scale lumped parameter models to decompose the relationship between rainfall variability and an important metric of transit times, the time-varying fraction of young water (<90 days old) in streams (FYW). A coupled rainfall-runoff model and rank StorAge Selection (rSAS) transit time model were calibrated to extensive hydrometric and environmental tracer data from neighboring headwater catchments in Plynlimon, Wales from 1999 to 2008. At both sites, the mean annual FYW increased more than 13 percentage points from the driest to the wettest year. Yearly mean rainfall explained most between-year variation, but certain signatures of rainfall pattern were also associated with higher FYW including: more clustered storms, more negatively skewed storms, and higher covariance between daily rainfall and discharge. We show that these signatures are symptomatic of an "inverse storage effect" that may be common among watersheds. Looking to the future, changes in rainfall due to projected climate change caused an up to 19 percentage point increase in simulated mean winter FYW and similarly large decreases in the mean summer FYW. Thus, climate change could seasonally alter the ages of water in streams at these sites, with concomitant impacts on water quality.

Predictors of early graft failure after coronary artery bypass grafting for chronic total occlusion.

PubMed

Oshima, Hideki; Tokuda, Yoshiyuki; Araki, Yoshimori; Ishii, Hideki; Murohara, Toyoaki; Ozaki, Yukio; Usui, Akihiko

2016-07-01

Little is known regarding the transit-time flow measurement (TTFM) variables in grafts anastomosed to chronically totally occluded vessels (CTOs). We aimed to establish the TTFM cut-off values for detecting graft failure in bypass grafts anastomosed to chronically totally occluded arteries and clarify the relationship between early graft failure and the grade of collateral circulation/regional wall motion of the CTO territory. Among 491 patients who underwent isolated coronary artery bypass grafting (CABG) from 2009 to 2015, 196 cases with CTOs underwent postoperative coronary angiography within 1 month after CABG. Two hundred and forty-one CTOs in all patients were examined. Thirty-two CTOs (13%) were not bypassed and 214 conduits were anastomosed to CTOs and underwent intraoperative TTFM. Arterial conduits and saphenous vein grafts (SVGs) were used in 102 and 112 cases, respectively. Among the arterial conduit procedures that were performed, 78 involved the left internal thoracic artery (LITA), 10 involved the right internal thoracic artery (RITA) and 14 involved the right gastroepiploic artery (rGEA). Any graft showing Fitzgibbon type B or O lesions on angiography was considered to be a failing graft. The insufficiency rates for LITA, RITA, rGEA and SVG procedures were 5.1, 10, 14.3 and 7.1%, respectively. The TTFM variables recorded in failing grafts had a significantly lower mean flow (Qmean) and higher pulsatility index (PI) compared with patent grafts. Furthermore, akinetic or dyskinetic wall motion in the territory of bypassed CTOs was observed at a significantly higher rate in failing grafts. A multivariable regression analysis and receiver operating characteristic analysis revealed good predictors of early graft failure as follows: a Qmean value of < 11.5 ml/min for arterial conduits, a PI value of >5.85 and akinetic/dyskinetic wall motion in the CTO territory for SVGs. The Rentrop collateral grade was not associated with early graft failure. The Qmean

Effect of puberty on coronary arteries from female pigs.

PubMed

Chatrath, Ritu; Ronningen, Karen L; LaBreche, Peter; Severson, Sandra R; Jayachandran, Muthuvel; Bracamonte, Margarita P; Miller, Virginia M

2003-10-01

Vascular function changes following loss of ovarian hormones in women at menopause and in experimental animals following surgical ovariectomy. Little is known about changes in vascular function during hormonal transition from sexual immaturity (juvenile) to sexual maturity. Therefore, experiments were designed to determine effects of natural puberty on vascular function in female pigs. Tissue was studied from eight juvenile (2-3 mo) and eight adult (5-6 mo) female pigs. Plasma nitric oxide (NO) was measured, and mRNA for endothelium-derived NO synthase (eNOS) and eNOS protein were determined in aortic endothelial cells. Rings of coronary arteries were suspended for measurement of isometric force in organ chambers. Serum 17beta-estradiol levels were comparable in the two groups, whereas the arithmetic mean of progesterone levels was about two-thirds lower in adults compared with juvenile pigs. Plasma NO was significantly higher in juveniles compared with adults, but mRNA and protein for eNOS were comparable. In coronary arteries, an alpha2-adrenergic agonist caused greater endothelium-dependent relaxations in rings from juvenile compared with adult pigs. Relaxations to bradykinin were similar in arteries from both groups, but inhibition of NO reduced relaxations only in arteries from juvenile pigs. Relaxations from NO were greater in arteries from adult compared with juvenile female pigs. In conclusion, coronary arterial endothelial and smooth muscle responses are selectively modulated at puberty in female pigs. At maturity, plasma NO is reduced and sensitivity of the smooth muscle to exogenous NO is increased. Posttranscriptional regulation of eNOS protein may explain differences in NO bioavailability in juvenile pigs.

Evaluation of changes in left ventricular structure and function in hypertensive patients with coronary artery disease after PCI using real-time three-dimensional echocardiography.

PubMed

Meng, Yanhong; Zong, Ling; Zhang, Ziteng; Han, Youdong; Wang, Yanhui

2018-02-01

We aimed to evaluate the changes in left ventricular structure and function in hypertensive patients with coronary artery disease before and after percutaneous coronary intervention (PCI) using real-time three-dimensional echocardiography. Two hundred and eighty hypertensive patients with coronary artery disease undergoing PCI and 120 cases who did not receive PCI in our hospital were selected as the subjects of our study. All patients were administered with routine antiplatelet, anticoagulant, lipid-lowering, antihypertensive, dilating coronary artery and other medications. The left ventricular systolic function and systolic synchrony index changes before and after subjects were treated by PCI were analyzed using three-dimensional echocardiography. At 2 days before surgery, there were no significant differences in the left ventricular end-diastolic volume, left ventricular end-systolic volume (LVESV) and ejection fraction (EF) between the two patient groups (P>0.05). At 3 months and 9 months, the two key time points after PCI, the LVESV level in the PCI group was distinctly decreased, while EF was significantly increased (P<0.05). In addition, before treatment, there were no significant differences in the parameters of time from the corresponding segment of the myocardium to the minimal systolic volume in two patient groups, such as Tmsv-16SD, Tmsv-16Dif, Tmsv-12SD, Tmsv-12Dif, Tmsv-6SD and Tmsv-6Dif (P>0.05); however, the parameters of time from the corresponding segment of the myocardium to the minimal systolic volume in patients in the PCI group were significantly reduced at 3 and 9 months after surgery (P<0.05). Three-dimensional echocardiography can evaluate the critical parameters in the prognosis of hypertensive patients with coronary artery disease after PCI accurately and in real-time, which may play a significant role.

Traumatic common hepatic artery injury causing isolated right hepatic ischemia due to a left accessory artery. A case report.

PubMed

Fernandes, Eduardo; Pedrazzani, Corrado; Gerena, Marielia; Omi, Ellen

2017-01-01

Hepatic arterial liver flow is renowned for its redundancy. Previous studies have demonstrated that the common hepatic artery is not essential for liver survival. We present a case of a 31year-old involved in a high-speed motor vehicle accident whose liver survived thanks to the presence of an accessory hepatic artery. We present the case of a 31year-old male who sustained a traumatic injury of the proper hepatic artery following a motor vehicle accident. The patient suffered temporary right liver lobe ischemia due to the presence of an accessory left hepatic artery. This resulted in the selective formation of 'biliary lakes' distinctively within the territory of the right hepatic artery supply. Simultaneously the patient developed a pseudo-aneurysm of the proper hepatic artery which required radiology intervention. At the time of pseudo-aneurysm embolisation, a rich network of arterial collaterals had formed between the accessory left hepatic and the inferior phrenic artery. On follow up the biliary lakes to the right lobe had resolved, but a small area at the periphery of the right lobe had encountered atrophy. This case report is an 'in vivo' demonstration of liver resilience to arterial flow re-distribution and demonstrates the ability of the biliary epithelium to recover from and ischemic injury. Parenchymal liver survival is mostly independent from flow within the common hepatic artery. Acute and chronic liver parenchyma changes following interruption of hepatic artery flow can still occur. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Increased pulmonary transit times in asymptomatic dogs with mitral regurgitation.

PubMed

Lord, Peter; Eriksson, Anders; Häggström, Jens; Järvinen, Anna-Kaisa; Kvart, Clarence; Hansson, Kerstin; Maripuu, Enn; Mäkelä, Olli

2003-01-01

Pulmonary transit time (PTT) normalized to heart rate (nPTT) is a measure of the pulmonary blood volume (PBV) to stroke volume ratio (PBV/SV). It is an index of cardiac performance. To determine the effect of compensated mitral regurgitation (CMR) and decompensated mitral regurgitation (DMR) caused by valvular endocardiosis on the index nPTT, we measured nPTT by first-pass radionuclide angiocardiography and ECG in 13 normal dogs, 18 dogs with CMR, and 13 dogs with DMR. PTT was measured as time between onset of appearance of activity at the pulmonary trunk and the left atrium. In the normal dogs, the relationship between PTT and mean R-R interval (mRR) was PTT = 4.08 x mRR + 0.15 (R2 = 0.71). Normal nPTT was 4.4 +/- 0.6 (SD) (range. 3.6-5.3). in CMR, 6.3 +/- 1.6 (SD) (range, 4.0-9.7). and in DMR, 11.9 +/- 3.4 (SD) (range, 8.0-18.8). The differences among all groups were significant. Heart rates were 110 +/- 22 bpm in normal dogs, 111 +/- 20 in dogs with CMR, and 144 +/- 18 in dogs with DMR (P < .001 for difference between DMR group and normal and CMR groups). Increased nPTT in CMR indicates preclinical heart pump dysfunction. Heart rate-normalized pulmonary transit times may be a useful index of heart function in mitral regurgitation.

Agreement of arterial sodium and arterial potassium levels with venous sodium and venous potassium in patients admitted to intensive care unit.

PubMed

Nanda, Sunil Kumar; Ray, Lopamudra; Dinakaran, Asha

2015-02-01

Electrolyte abnormalities are one of the common causes of morbidity and mortality in critically ill patients. The turnaround time for electrolyte reporting should be as low as possible. Electrolytes are measured conventionally in serum obtained from venous blood by electrolyte analyser which takes 20 to 30 min. Point of care analysers are now available where in electrolytes can be measured in arterial blood within 5 min. This study was done to study the agreement of arterial sodium and arterial potassium with venous sodium and venous potassium levels. Venous sodium and venous potassium levels and arterial sodium and arterial potassium levels were analysed on 206 patient samples admitted to Intensive Care Unit (ICU). The venous values were compared with the arterial values for correlation. Venous sodium was compared with arterial sodium by spearman correlation. Venous potassium was compared with arterial potassium by pearson correlation. The mean value of arterial sodium was 134 and venous sodium was 137. The mean value of arterial potassium was 3.6 and venous potassium was 4.1. The correlation coefficient obtained for sodium was 0.787 and correlation coefficient obtained for potassium was 0.701. There was positive correlation of arterial sodium and arterial potassium with venous sodium and venous potassium indicating agreement between the parameters. Arterial sodium and arterial potassium can be used instead of venous sodium and venous potassium levels in management of critically ill patients.

Temperature-Controlled High-Speed AFM: Real-Time Observation of Ripple Phase Transitions.

PubMed

Takahashi, Hirohide; Miyagi, Atsushi; Redondo-Morata, Lorena; Scheuring, Simon

2016-11-01

With nanometer lateral and Angstrom vertical resolution, atomic force microscopy (AFM) has contributed unique data improving the understanding of lipid bilayers. Lipid bilayers are found in several different temperature-dependent states, termed phases; the main phases are solid and fluid phases. The transition temperature between solid and fluid phases is lipid composition specific. Under certain conditions some lipid bilayers adopt a so-called ripple phase, a structure where solid and fluid phase domains alternate with constant periodicity. Because of its narrow regime of existence and heterogeneity ripple phase and its transition dynamics remain poorly understood. Here, a temperature control device to high-speed atomic force microscopy (HS-AFM) to observe dynamics of phase transition from ripple phase to fluid phase reversibly in real time is developed and integrated. Based on HS-AFM imaging, the phase transition processes from ripple phase to fluid phase and from ripple phase to metastable ripple phase to fluid phase could be reversibly, phenomenologically, and quantitatively studied. The results here show phase transition hysteresis in fast cooling and heating processes, while both melting and condensation occur at 24.15 °C in quasi-steady state situation. A second metastable ripple phase with larger periodicity is formed at the ripple phase to fluid phase transition when the buffer contains Ca 2+ . The presented temperature-controlled HS-AFM is a new unique experimental system to observe dynamics of temperature-sensitive processes at the nanoscopic level. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A general stochastic model for studying time evolution of transition networks

NASA Astrophysics Data System (ADS)

Zhan, Choujun; Tse, Chi K.; Small, Michael

2016-12-01

We consider a class of complex networks whose nodes assume one of several possible states at any time and may change their states from time to time. Such networks represent practical networks of rumor spreading, disease spreading, language evolution, and so on. Here, we derive a model describing the dynamics of this kind of network and a simulation algorithm for studying the network evolutionary behavior. This model, derived at a microscopic level, can reveal the transition dynamics of every node. A numerical simulation is taken as an ;experiment; or ;realization; of the model. We use this model to study the disease propagation dynamics in four different prototypical networks, namely, the regular nearest-neighbor (RN) network, the classical Erdös-Renyí (ER) random graph, the Watts-Strogátz small-world (SW) network, and the Barabási-Albert (BA) scalefree network. We find that the disease propagation dynamics in these four networks generally have different properties but they do share some common features. Furthermore, we utilize the transition network model to predict user growth in the Facebook network. Simulation shows that our model agrees with the historical data. The study can provide a useful tool for a more thorough understanding of the dynamics networks.

Vascular mechanics of the coronary artery

NASA Technical Reports Server (NTRS)

Veress, A. I.; Vince, D. G.; Anderson, P. M.; Cornhill, J. F.; Herderick, E. E.; Klingensmith, J. D.; Kuban, B. D.; Greenberg, N. L.; Thomas, J. D.

2000-01-01

This paper describes our research into the vascular mechanics of the coronary artery and plaque. The three sections describe the determination of arterial mechanical properties using intravascular ultrasound (IVUS), a constitutive relation for the arterial wall, and finite element method (FEM) models of the arterial wall and atheroma. METHODS: Inflation testing of porcine left anterior descending coronary arteries was conducted. The changes in the vessel geometry were monitored using IVUS, and intracoronary pressure was recorded using a pressure transducer. The creep and quasistatic stress/strain responses were determined. A Standard Linear Solid (SLS) was modified to reproduce the non-linear elastic behavior of the arterial wall. This Standard Non-linear Solid (SNS) was implemented into an axisymetric thick-walled cylinder numerical model. Finite element analysis models were created for five age groups and four levels of stenosis using the Pathobiological Determinants of Atherosclerosis Youth (PDAY) database. RESULTS: The arteries exhibited non-linear elastic behavior. The total tissue creep strain was epsilon creep = 0.082 +/- 0.018 mm/mm. The numerical model could reproduce both the non-linearity of the porcine data and time dependent behavior of the arterial wall found in the literature with a correlation coefficient of 0.985. Increasing age had a strong positive correlation with the shoulder stress level, (r = 0.95). The 30% stenosis had the highest shoulder stress due to the combination of a fully formed lipid pool and a thin cap. CONCLUSIONS: Studying the solid mechanics of the arterial wall and the atheroma provide important insights into the mechanisms involved in plaque rupture.

Fine tuning the color-transition temperature of thermoreversible polydiacetylene/zinc oxide nanocomposites: The effect of photopolymerization time.

PubMed

Traiphol, Nisanart; Faisadcha, Kunruethai; Potai, Ruttayapon; Traiphol, Rakchart

2015-02-01

An ability to control the thermochromic behaviors of polydiacetylene (PDA)-based materials is very important for their utilization. Recently, our group has developed the PDA/zinc oxide (ZnO) nanocomposites, which exhibit reversible thermochromism (Traiphol et al., 2011). In this study, we present our continuation work demonstrating a rather simple method for fine tuning their color-transition temperature. The PDA/ZnO nanocomposites are prepared by varying photopolymerization time, which in turn affects the length of PDA conjugated backbone. We have found that the increase of photopolymerization time from 1 to 120min results in systematically decrease of the color-transition temperature from about 85 to 40°C. These PDA/ZnO nanocomposites still exhibit reversible thermochromism. The PDA/ZnO nanocomposites embedded in polyvinyl alcohol films show two-step color-transition processes, the reversible blue to purple and then irreversible purple to orange. Interestingly, the increase of photopolymerization time causes an increase of the irreversible color-transition temperature. Our method is quite simple and cheap, which can provide a library of PDA-based materials with controllable color-transition temperature. Copyright © 2014 Elsevier Inc. All rights reserved.

Sharp Dissection versus Electrocautery for Radial Artery Harvesting

PubMed Central

Marzban, Mehrab; Arya, Reza; Mandegar, Mohammad Hossein; Karimi, Abbas Ali; Abbasi, Kiomars; Movahed, Namvar; Abbasi, Seyed Hesameddin

2006-01-01

Radial arteries have been increasingly used during the last decade as conduits for coronary artery revascularization. Although various harvesting techniques have been described, there has been little comparative study of arterial damage and patency. A radial artery graft was used in 44 consecutive patients, who were randomly divided into 2 groups. In the 1st group, the radial artery was harvested by sharp dissection and in the 2nd, by electrocautery. These groups were compared with regard to radial artery free flow, harvest time, number of clips used, complications, and endothelial damage. Radial artery free flow before and after intraluminal administration of papaverine was significantly greater in the electrocautery group (84.3 ± 50.7 mL/min and 109.7 ± 68.5 mL/min) than in the sharp-dissection group (52.9 ± 18.3 mL/min and 69.6 ± 28.2 mL/ min) (P =0.003). Harvesting time by electrocautery was significantly shorter (25.4 ± 4.3 min vs 34.4 ± 5.9 min) (P =0.0001). Electrocautery consumed an average of 9.76 clips, versus 22.45 clips consumed by sharp dissection. The 2 groups were not different regarding postoperative complications, except for 3 cases of temporary paresthesia of the thumb in the electrocautery group; histopathologic examination found no endothelial damage. We conclude that radial artery harvesting by electrocautery is faster and more economical than harvesting by sharp dissection and is associated with better intraoperative flow and good preservation of endothelial integrity. PMID:16572861

The Life Course in the Making: Gender and the Development of Adolescents' Expected Timing of Adult Role Transitions

ERIC Educational Resources Information Center

Crockett, Lisa J.; Beal, Sarah J.

2012-01-01

Adolescents' expectations about the timing of adult role transitions have the potential to shape their actual transitions, setting the stage for their adult lives. Although expectations about timing emerge by early adolescence, little is known about how these expectations develop across adolescence. This longitudinal study examined developmental…

Glycosaminoglycans contribute to extracellular matrix fiber recruitment and arterial wall mechanics.

PubMed

Mattson, Jeffrey M; Turcotte, Raphaël; Zhang, Yanhang

2017-02-01

Elastic and collagen fibers are well known to be the major load-bearing extracellular matrix (ECM) components of the arterial wall. Studies of the structural components and mechanics of arterial ECM generally focus on elastin and collagen fibers, and glycosaminoglycans (GAGs) are often neglected. Although GAGs represent only a small component of the vessel wall ECM, they are considerably important because of their diverse functionality and their role in pathological processes. The goal of this study was to study the mechanical and structural contributions of GAGs to the arterial wall. Biaxial tensile testing was paired with multiphoton microscopic imaging of elastic and collagen fibers in order to establish the structure-function relationships of porcine thoracic aorta before and after enzymatic GAG removal. Removal of GAGs results in an earlier transition point of the nonlinear stress-strain curves [Formula: see text]. However, stiffness was not significantly different after GAG removal treatment, indicating earlier but not absolute stiffening. Multiphoton microscopy showed that when GAGs are removed, the adventitial collagen fibers are straighter, and both elastin and collagen fibers are recruited at lower levels of strain, in agreement with the mechanical change. The amount of stress relaxation also decreased in GAG-depleted arteries [Formula: see text]. These findings suggest that the interaction between GAGs and other ECM constituents plays an important role in the mechanics of the arterial wall, and GAGs should be considered in addition to elastic and collagen fibers when studying arterial function.

Asynchronous arterial systolic expansion as a marker of vascular aging: assessment of the carotid artery with velocity vector imaging.

PubMed

Yang, Woo-In; Shim, Chi Y; Bang, Woo D; Oh, Chang M; Chang, Hyuk J; Chung, Namsik; Ha, Jong-Won

2011-12-01

Arterial elastic properties change with aging. Measurements of pulse wave velocity and augmentation index are useful for the evaluation of arterial stiffness. However, they likely represent only global characteristics of the arterial tree rather than local vascular alterations. The aim of this study was to evaluate whether local vascular properties assessed by velocity vector imaging differed with aging. Vascular properties of carotid arteries with ages were assessed in 100 healthy volunteers (52 men) ranging from 20 to 68 years using velocity vector imaging. The peak circumferential strain and strain rate of the six segments in left common carotid arteries were analyzed and the standard deviation of the time to peak circumferential strain and strain rate of the six segments, representing the synchronicity of the arterial expansion, were calculated. Central blood pressure, augmentation index and pulse wave velocity were assessed by commercially available radial artery tonometry, the SphygmoCor system (AtCor Medical, West Ryde, Australia). A validated generalized transfer function was used to acquire the central aortic pressures and pressure waveforms. Pulse wave velocity, augmentation index and velocity vector imaging parameters showed significant changes with age. However, the age-related changes in pulse wave velocity, augmentation index and velocity vector imaging parameters were different. The increase in pulse wave velocity was more prominent in older individuals, whereas the changes in augmentation index and carotid strain and strain rate were evident earlier, at the age of 30 years. Unlike augmentation index, which showed little change in older individuals, the standard deviation of time to peak strain and strain rate showed a steady increase from younger to older individuals. Asynchronous arterial expansion could be a useful discriminative marker of vascular aging independent of individual's age.

Association of rumination time with subclinical ketosis in transition dairy cows.

PubMed

Kaufman, E I; LeBlanc, S J; McBride, B W; Duffield, T F; DeVries, T J

2016-07-01

The objective of this study was to characterize the relationship between rumination and subclinical ketosis (SCK) in transition dairy cows. A study was conducted on 4 commercial dairy farms in eastern Ontario, Canada. A total of 339 Holstein dairy cows (107 primiparous and 232 multiparous) were monitored for rumination activity and SCK from 14 d before calving until 28 d after calving. Rumination was recorded daily using an automated monitoring system. A blood sample was taken from the coccygeal vein of each cow for measurement of β-hydroxybutyrate (BHB) once weekly throughout the 6-wk observation period. Cows with BHB ≥1.2mmol/L in any of the 4 postpartum samples were considered to have SCK. Cases of retained placenta, metritis, milk fever, or mastitis during the study period were also recorded. Cows were categorized into 1 of 4 groups: healthy cows (HLT) that had no SCK or any other recorded health problem (n=139); cows treated for at least one health issue other than SCK (HLT+; n=50); cows with SCK (hyperketonemia; HYK) with no other health problems during transition (n=97); or cows (HYK+) that had SCK and one or more other health problems (n=53). Daily rumination time was summarized by week and comparisons were made between HLT and HYK and HYK+. From 2 wk before calving (wk -2) to 4 wk after calving (wk +4), there was no difference in rumination time (409±9.8min/d) among HLT, HYK, and HYK+ cows in their first lactation. Multiparous cows in HLT spent an average of 459±11.3min/d ruminating from wk -2 to wk +4. Multiparous HYK cows ruminated 25±12.8min/d less than HLT cows, whereas HYK+ cows ruminated 44±15.6min/d less than HLT cows. The largest differences in rumination time between HLT and HYK+ cows were seen during wk -1, +1, and +2, when HYK+ cows ruminated 48±17.2, 73±16.0, and 65±19.4min/d less than HLT cows, respectively. In multiparous cows, increased odds of HYK were associated with greater milk yield in the previous lactation, greater loss of