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1

Basic notions of heart rate variability and its clinical applicability  

Microsoft Academic Search

Autonomic nervous system (ANS) plays an important role in the regulation of the physiological processes of the human organism during normal and pathological conditions. Among the techniques used in its evaluation, the heart rate variability (HRV) has arising as a simple and non-invasive measure of the autonomic impulses, representing one of the most promising quantitative markers of the autonomic balance.

Luiz Carlos; Marques VANDERLEI; Carlos Marcelo PASTRE; Rosângela Akemi HOSHI; Moacir Fernandes de GODOY

2009-01-01

2

Modeling soil infiltration under variables of application rate and number of irrigation  

Microsoft Academic Search

The effect of variable sprinkler water application rates on bare soil and the response of the soil infiltration after exposure to a sequence of irrigation events were investigated. A simple empirical model based on the Kostiakov equation was presented. This model will predict soil infiltration rate under variable application rates and a sequence of irrigation events. The validity of the

3

Improving flow response of a variable-rate aerial application system by interactive refinement  

Microsoft Academic Search

Experiments were conducted to evaluate response of a variable-rate aerial application controller to changing flow rates and to improve its response at correspondingly varying system pressures. System improvements have been made by refinement of the control algorithms over time in collaboration with the system manufacturer, Houma Avionics, Houma, LA, USA. The variable-rate application system consists of Differential Global Positioning System

Steven J. Thomson; Yanbo Huang; James E. Hanks; Daniel E. Martin; Lowrey A. Smith

2010-01-01

4

Integrating GIS and GPS into a spatially-variable-rate herbicide application system  

NASA Astrophysics Data System (ADS)

A spatially variable rate herbicide application system was developed and a site-specific evaluation of its field performance and accuracy was conducted. The system was capable of automatically changing on-the-go the application rate of active ingredients (AI) to meet the requirements of current sprayer field location. A 4.2 ha field was sampled on an 18.3 m grid for soil texture and percent organic matter (%OM). The soil texture ranged from sandy loam to clay, while the %OM ranged from 0.98 to 2.73 percent. For the preemergence herbicide selected, a herbicide management table was used to determine the appropriate AI application rate for each area of the field depending on spatial variation of field parameter data (soil texture and %OM). For the sampled field, the AI application rate ranged from 3510 mL/ha to 5260 mL/ha. A geographical information system (GIS) software was utilized to develop a georeferenced map (management map) of field application rates. A direct nozzle injection field sprayer was equipped with a real-time differentially corrected global positioning system (DGPS). A control program was developed to retrieve the desired application rate from the GIS map utilizing position data (latitude and longitude) supplied by the DGPS system. The retrieved application rate was sent, in a voltage format, to a 21X datalogger which was used to change on-the-go the AI flow rate to correspond with the desired application rate at a specific sprayer ground speed and field position. Results revealed that the DGPS system maintained, on the average, an accuracy of one meter. However, a distance error of location determination produced by the DGPS system reached 30.84 m with a correction message age of 98 seconds. For the four application rates used in the study, the highest average application rate error (average difference between desired and calculated application rates) and CV values were 2.0 percent and 0.07 percent, respectively for the analyzed samples. The maximum application rate error was 14 percent for 96 percent of the field data points (96 percent of the time). These results showed that the control system was accurate in producing the desired application rate. On the average, the greatest reaction time of the system was 2.2 seconds. The spatial analysis showed that most application rate errors occurred near transition zones. These analysis also revealed that the contour lines of the calculated application rate maps followed the same pattern and coincide with the management map contour lines. The developed spatially variable rate herbicide application system was found to accurately reproduce the application rate management map in a repeatable fashion.

Al-Gaadi, Khalid Ali

1998-12-01

5

Rate control for video coding over variable bit rate channels with applications to wireless transmission  

Microsoft Academic Search

Video transmission over wireless links is an emerging application which involves a time-varying channel. In this paper we propose that rate control algorithms should be used at the video encoders, along with models of the channel behavior, to improve the performance of such systems. Rather than letting information be lost as the channel conditions change, in our scheme channel state

Antonio Ortega; Masoud Khansari

1995-01-01

6

Zone mapping application for precision-farming: a decision support tool for variable rate application  

Microsoft Academic Search

A web-based decision support tool, zone mapping application for precision farming (ZoneMAP, http:\\/\\/zonemap.umac.org), has been developed to automatically determine the optimal number of management zones and delineate them using satellite\\u000a imagery and field data provided by users. Application rates, such as of fertilizer, can be prescribed for each zone and downloaded\\u000a in a variety of formats to ensure compatibility with

Xiaodong Zhang; Lijian Shi; Xinhua Jia; George Seielstad; Craig Helgason

2010-01-01

7

Clinical Applicability of Heart Rate Variability Analysis by Methods Based on Nonlinear Dynamics  

Microsoft Academic Search

Analysis of heart rate (HR) variability has become an important widely used method for assessingcardiac autonomic regulation. Conventionally, HR variability has been analyzed with time and frequency domainmethods. Analysis of HR dynamics by methods based on nonlinear systems theory has opened a novel approach forstudying the abnormalities in HR behavior. Recent studies have shown that these measures, particularly scalinganalysis methods

Timo H. Mäkikallio; Jari M. Tapanainen; Mikko P. Tulppo; Heikki V. Huikuri

2002-01-01

8

Variable rate application of nematicides on cotton fields: a promising site-specific management strategy.  

PubMed

Field tests were conducted to determine if differences in response to nematicide application (i.e., root-knot nematode (RKN) populations, cotton yield, and profitability) occurred among RKN management zones (MZ). The MZ were delineated using fuzzy clustering of five terrain (TR) and edaphic (ED) field features related to soil texture: apparent soil electrical conductivity shallow (ECa-shallow) and deep (ECa-deep), elevation (EL), slope (SL), and changes in bare soil reflectance. Zones with lowest mean values of ECa- shallow, ECa- deep, NDVI, and SL were designated as at greater risk for high RKN levels. Nematicide-treated plots (4 rows wide and 30 m long) were established in a randomized complete block design within each zone, but the number of replications in each zone varied from four to six depending on the size of the zone.The nematicides aldicarb (Temik 15 G) and 1,3-dichloropropene (1,3-D,Telone II) were applied at two rates (0.51 and 1.0 kg a.i./ha for aldicarb, and 33.1 and 66.2 kg a.i./ha for 1,3-D) to RKN MZ in commercial fields between 2007 and 2009. A consolidated analysis over the entire season showed that regardless of the zone, there were not differences between aldicarb rates and 1,3-D rates. The result across zones showed that 1,3-D provided better RKN control than did aldicarb in zones with low ECa values (high RKN risk zones exhibiting more coarse-textured sandy soils). In contrast, in low risk zones with relatively higher ECa values (heavier textured soil), the effects of 1,3-D and aldicarb were equal and application of any of the treatments provided sufficient control. In low RKN risk zones, a farmer would often have lost money if a high rate of 1,3-D was applied. This study showed that the effect of nematicide type and rate on RKN control and cotton yield varied across management zones (MZ) with the most expensive treatment likely to provide economic benefit only in zones with coarser soil texture. This study demonstrates the value of site specific application of nematicides based on management zones, although this approach might not be economically beneficial in fields with little variability in soil texture. PMID:23482903

Ortiz, Brenda V; Perry, Calvin; Sullivan, Dana; Lu, Ping; Kemerait, Robert; Davis, Richard F; Smith, Amanda; Vellidis, George; Nichols, Robert

2012-03-01

9

Validity of the ithlete™ Smart Phone Application for Determining Ultra-Short-Term Heart Rate Variability.  

PubMed

The purpose of this investigation was to cross-validate the ithlete™ heart rate variability smart phone application with an electrocardiograph for determining ultra-short-term root mean square of successive R-R intervals. The root mean square of successive R-R intervals was simultaneously determined via electrocardiograph and ithlete™ at rest in twenty five healthy participants. There were no significant differences between the electrocardiograph and ithlete™ derived root mean square of successive R-R interval values (p > 0.05) and the correlation was near perfect (r = 0.99, p < 0.001). In addition, the ithlete™ revealed a Standard Error of the Estimate of 1.47 and Bland Altman plot showed that the limits of agreement ranged from 2.57 below to 2.63 above the constant error of -0.03. In conclusion, the ithlete™ appeared to provide a suitably accurate measure of root mean square of successive R-R intervals when compared to the electrocardiograph measures obtained in the laboratory within the current sample of healthy adult participants. The current study lays groundwork for future research determining the efficacy of ithlete™ for reflecting athletic training status over a chronic conditioning period. PMID:24511344

Flatt, Andrew A; Esco, Michael R

2013-12-18

10

Autonomic dysfunction in patients with fibromyalgia: Application of power spectral analysis of heart rate variability  

Microsoft Academic Search

Objectives:To assess the interaction between the sympathetic and parasympatheticsystems in patients with fibromyalgia syndrome (FM), using power spectrum analysis (PSA) of heart rate variability (HRV). In addition, we explored the association between HRV, measures of tenderness, FM symptoms, physical function, psychological well being and quality of life.

Hagit Cohen; Lily Neumann; Margarita Shore; Marianne Amir; Yair Cassuto; Dan Buskila

2000-01-01

11

Functional assessment of heart rate variability: physiological basis and practical applications  

Microsoft Academic Search

The autonomic nervous system dynamically controls the response of the body to a range of external and internal stimuli, providing physiological stability in the individual. With the progress of information technology, it is now possible to explore the functioning of this system reliably and non-invasively using comprehensive and functional analysis of heart rate variability. This method is already an established

Jiri Pumprla; Kinga Howorka; David Groves; Michael Chester; James Nolan

2002-01-01

12

Variable rate adaptive trellis coded QAM for high bandwidth efficiency applications in Rayleigh fading channels  

Microsoft Academic Search

A high bandwidth efficiency variable rate adaptive channel coding scheme, ATCQAM, is proposed. Known pilot symbols are transmitted periodically to aid demodulation. Past channel states are fed back to the transmitter with delay. Current channel state is then predicted at the transmitter to decide on the appropriate modulation mode for the current symbol. At good channel states, high level modulation

Vincent K. N. Lau; Malcolm D. Macleod

1998-01-01

13

Application of Hilbert-Huang Transform to Heart Rate Variability Analysis  

Microsoft Academic Search

The paper introduces a new methodology of heart rate variability(HRV) in time-frequency analysis, which is based on Hilbert-Huang transform. We adopt the empirical mode decompostition(EMD) technique to decompose the R-R interval series into several mono-component signals which become analytic signal by means of Hilbert transform. So a novel algorithm based on Hilbert-Huang transform is proposed to extract the features of

Li Helong; Yang Lihua; Huang Daren

2008-01-01

14

Influence of QRS complex detection errors on entropy algorithms. Application to heart rate variability discrimination.  

PubMed

Signal entropy measures such as approximate entropy (ApEn) and sample entropy (SampEn) are widely used in heart rate variability (HRV) analysis and biomedical research. In this article, we analyze the influence of QRS detection errors on HRV results based on signal entropy measures. Specifically, we study the influence that QRS detection errors have on the discrimination power of ApEn and SampEn using the cardiac arrhythmia suppression trial (CAST) database. The experiments assessed the discrimination capability of ApEn and SampEn under different levels of QRS detection errors. The results demonstrate that these measures are sensitive to the presence of ectopic peaks: from a successful classification rate of 100%, down to a 75% when spikes are present. The discriminating capability of the metrics degraded as the number of misdetections increased. For an error rate of 2% the segmentation failed in a 12.5% of the experiments, whereas for a 5% rate, it failed in a 25%. PMID:23246085

Molina-Picó, Antonio; Cuesta-Frau, David; Miró-Martínez, Pau; Oltra-Crespo, Sandra; Aboy, Mateo

2013-04-01

15

Determinants of heart rate variability  

Microsoft Academic Search

Objectives. This study sought to examine clinical determinants of heart rate variability and to report normative reference values for eight heart rate variability measures.Background. Although the clinical implications of heart rate variability have been described, clinical determinants and normative values of heart rate variability measures have not been studied systematically in a large community-based population.Methods. The first 2 h of

Hisako Tsuji; Ferdinand J. Venditti; Emily S. Manders; Jane C. Evans; Martin G. Larson; Charles L. Feldman; Daniel Levy

1996-01-01

16

On rating curve variability in presence of movable bed and unsteady flow. Applications to Tuscan rivers.  

NASA Astrophysics Data System (ADS)

In common engineering practice, rating curves are obtained from direct stage-discharge measurements or, more often, from stage measurements coupled with flow simulations. The present work mainly focuses on the latter technique, where stage-measuring gauges are usually installed on bridges with flow conditions likely to be influenced by local geometry constraints. In such cases, backwater flow and flow transition to supercritical state may occur, influencing sediment transport capacity and triggering more intense changes in river morphology. The unsteadiness of the flow hydrograph may play an important role too, according to the velocity of its rising and falling limbs. Nevertheless, the simulations conducted to build a rating curve are often carried out with steady flow and fixed bed conditions where the afore-mentioned effects are not taken into account at all. Numerical simulations with mobile bed and different unsteady flow conditions have been conducted on some real case studies in the rivers of Tuscany (Italy), in order to assess how rating curves change with respect to the "standard" one (that is, the classical steady flow rating curve). A 1D finite volume numerical model (REMo, River Evolution Modeler) has been employed for the simulations. The model solves the 1D Shallow Water equations coupled with the sediments continuity equation in composite channels, where the overbanks are treated with fixed bed conditions while the main channel can either aggrade or be scoured. The model employs an explicit scheme with 2nd order accuracy in both space and time: this allows the correct handling of moderately stiff source terms via a local corrector step. Such capability is very important for the applications of the present work as it allows the modelling of abrupt contractions and jumps in bed bottom elevations which often occur near bridges. The outcomes of the simulations are critically analyzed in order to provide a first insight on the conditions inducing significant changes between the two types of rating curves.

Minatti, Lorenzo; Nicoletta De Cicco, Pina; Paris, Enio

2014-05-01

17

An application of fractional differintegration to heart rate variability time series.  

PubMed

Fractional differintegration is used as a new tool to characterize heart rate variability time series. This paper proposes and focuses in two indexes (?c and fnQ) derived from the fractional differintegration operator. Both indexes are applied to fractional Gaussian noise (fGn) and actual RR time series in order to test their behavior. In the analysis of monofractal time series, ?c is linearly related with the Hurst exponent and the estimation of the exponent by the proposed index has lower variance than by using Detrended Fluctuation Analysis (DFA) or the periodogram. The other index fnQ quantifies how the time series adjust to a monofractal time series. Age, postural changes and paced breathing cause significant changes on fnQ while ?c only shows significant changes due to posture. In the analyzed actual HRV time series, ?c shows good correlation with the short term scaling exponent obtained by DFA, LF/HF and RMSSD while no correlations have been found for fnQ. PMID:23510605

García-González, Miguel A; Fernández-Chimeno, Mireya; Capdevila, Lluis; Parrado, Eva; Ramos-Castro, Juan

2013-07-01

18

Application of an automatic adaptive filter for Heart Rate Variability analysis.  

PubMed

The presence of artifacts and noise effects in temporal series can seriously hinder the analysis of Heart Rate Variability (HRV). The tachograms should be carefully edited to avoid erroneous interpretations. The physician should carefully analyze the tachogram in order to detect points that might be associated with unlikely biophysical behavior and manually eliminate them from the data series. However, this is a time-consuming procedure. To facilitate the pre-analysis of the tachogram, this study uses a method of data filtering based on an adaptive filter which is quickly able to analyze a large amount of data. The method was applied to 229 time series from a database of patients with different clinical conditions: premature newborns, full-term newborns, healthy young adults, adults submitted to a very-low-calorie diet, and adults under preoperative evaluation for coronary artery bypass grafting. This proposed method is compared to the demanding conventional method, wherein the corrections of occasional ectopic beats and artifacts are usually manually executed by a specialist. To confirm the reliability of the results obtained, correlation coefficients were calculated, using both automatic and manual methods of ltering for each HRV index selected. A high correlation between the results was found, with highly significant p values, for all cases, except for some parameters analyzed in the premature newborns group, an issue that is thoroughly discussed. The authors concluded that the proposed adaptive filtering method helps to efficiently handle the task of editing temporal series for HRV analysis. PMID:23962726

Dos Santos, Laurita; Barroso, Joaquim J; Macau, Elbert E N; de Godoy, Moacir F

2013-12-01

19

Application of heart-rate variability in patients undergoing weaning from mechanical ventilation  

PubMed Central

Introduction The process of weaning may impose cardiopulmonary stress on ventilated patients. Heart-rate variability (HRV), a noninvasive tool to characterize autonomic function and cardiorespiratory interaction, may be a promising modality to assess patient capability during the weaning process. We aimed to evaluate the association between HRV change and weaning outcomes in critically ill patients. Methods This study included 101 consecutive patients recovering from acute respiratory failure. Frequency-domain analysis, including very low frequency, low frequency, high frequency, and total power of HRV was assessed during a 1-hour spontaneous breathing trial (SBT) through a T-piece and after extubation after successful SBT. Results Of 101 patients, 24 (24%) had SBT failure, and HRV analysis in these patients showed a significant decrease in total power (P = 0.003); 77 patients passed SBT and were extubated, but 13 (17%) of them required reintubation within 72 hours. In successfully extubated patients, very low frequency and total power from SBT to postextubation significantly increased (P = 0.003 and P = 0.004, respectively). Instead, patients with extubation failure were unable to increase HRV after extubation. Conclusions HRV responses differ between patients with different weaning outcomes. Measuring HRV change during the weaning process may help clinicians to predict weaning results and, in the end, to improve patient care and outcome.

2014-01-01

20

Econometric Methods for Fractional Response Variables with an Application to 401(K) Plan Participation Rates  

Microsoft Academic Search

We develop attractive functional forms and simple quasi-likelihood estimation methods for regression models with a fractional dependent variable. Compared with log-odds type procedures, there is no difficulty in recovering the regression function for the fractional variable, and there is no need to use ad hoc transformations to handle data at the extreme values of zero and one. We also offer

Leslie E. Papke; Jeffrey M. Wooldridge

1996-01-01

21

Vocalization of Heart Rate Variability.  

National Technical Information Service (NTIS)

In this paper we have proposed vocalization of heart rate variability (HRV) as a perceptual analysis tool. We adapted a phonation-production model to encode external signals and generate audible representations of them. HRV changes caused by induced pertu...

S. Saliu A. Birand G. Kudaiberdieva

2001-01-01

22

Analysis of Heart Rate Variability  

Microsoft Academic Search

Spontaneous variability of heart-rate has been related to three major physiological originating factors: quasi-oscillatory fluctuations thought to arise in blood-pressure control, variable frequency oscillations due to thermal regulation, and respiration; frequency selective analysis of cardiac interbeat interval sequences allows the separate contributions to be isolated. Using this method, a laboratory and field study of the effects of mental work load

B. Mc A. SAYKRS

1973-01-01

23

Heart rate variability: a review  

Microsoft Academic Search

Heart rate variability (HRV) is a reliable reflection of the many physiological factors modulating the normal rhythm of the\\u000a heart. In fact, they provide a powerful means of observing the interplay between the sympathetic and parasympathetic nervous\\u000a systems. It shows that the structure generating the signal is not only simply linear, but also involves nonlinear contributions.\\u000a Heart rate (HR) is

U. Rajendra Acharya; Paul K. Joseph; N. Kannathal; Choo Min Lim; Jasjit S. Suri

2006-01-01

24

Heart rate variability in weightlifters  

Microsoft Academic Search

On the basis of the literature and original data, heart rate variability (HRV) in weightlifters has been studied. The results\\u000a showed that the distribution mode (a parameter of mathematical analysis that is equal to the most frequent length of RR intervals)\\u000a indicates the intensity of physical exercise. Specific changes in the autonomic balance in athletes as dependent on their\\u000a degree

E. V. Oreshnikov; V. F. Tihonov; T. V. Agafonkina

2009-01-01

25

A brief review and clinical application of heart rate variability biofeedback in sports, exercise, and rehabilitation medicine.  

PubMed

Context:An important component of the effective management of chronic noncommunicable disease is the assessment and management of psychosocial stress. The measurement and modulation of heart rate variability (HRV) may be valuable in this regard.Objective:To describe the measurement and physiological control of HRV; to describe the impact of psychosocial stress on cardiovascular disease, metabolic syndrome, and chronic respiratory disease, and the relationship between these diseases and changes in HRV; and to describe the influence of biofeedback and exercise on HRV and the use of HRV biofeedback in the management of chronic disease.Data Sources and Study Selection:The PubMed, Medline, and Embase databases were searched (up to August 2013). Additional articles were obtained from the reference lists of relevant articles and reviews. Articles were individually selected for further review based on the quality and focus of the study, and the population studied.Results:Heart rate variability is reduced in stress and in many chronic diseases, and may even predict the development and prognosis of some diseases. Heart rate variability can be increased with both exercise and biofeedback. Although the research on the effect of exercise is conflicting, there is evidence that aerobic training may increase HRV and cardiac vagal tone both in healthy individuals and in patients with disease. Heart rate variability biofeedback is also an effective method of increasing HRV and cardiac vagal tone, and has been shown to decrease stress and reduce the morbidity and mortality of disease.Conclusion:The assessment and management of psychosocial stress is a challenging but important component of effective comprehensive lifestyle interventions for the management of noncommunicable disease. It is, therefore, important for the sports and exercise physician to have an understanding of the therapeutic use of HRV modulation, both in the reduction of stress and in the management of chronic disease. PMID:24875976

Prinsloo, Gabriell E; Rauch, H G Laurie; Derman, Wayne E

2014-05-01

26

Advanced Signal Processing Applications of the ECG: T-Wave Alternans, Heart Rate Variability, and the Signal Averaged ECG  

Microsoft Academic Search

\\u000a A variety of advanced signal processing techniques are already used in contemporary ­cardiology practice, embedded in widely\\u000a used commercial tools. This chapter focuses on three such ECG tools that have clinical trial data to support them and that\\u000a have been incorporated into practice guidelines: T-wave alternans (TWA), heart rate variability (HRV), and the signal averaged\\u000a ECG (SAECG). TWA is defined

Ashwani P. Sastry; Sanjiv M. Narayan

27

Multifractality and heart rate variability  

NASA Astrophysics Data System (ADS)

In this paper, we participate to the discussion set forth by the editor of Chaos for the controversy, ``Is the normal heart rate chaotic?'' Our objective was to debate the question, ``Is there some more appropriate term to characterize the heart rate variability (HRV) fluctuations?'' We focused on the ~24 h RR series prepared for this topic and tried to verify with two different techniques, generalized structure functions and wavelet transform modulus maxima, if they might be described as being multifractal. For normal and congestive heart failure subjects, the hq exponents showed to be decreasing for increasing q with both methods, as it should be for multifractal signals. We then built 40 surrogate series to further verify such hypothesis. For most of the series (~75%-80% of cases) multifractality stood the test of the surrogate data employed. On the other hand, series coming from patients in atrial fibrillation showed a small, if any, degree of multifractality. The population analyzed is too small for definite conclusions, but the study supports the use of multifractal series to model HRV. Also it suggests that the regulatory action of autonomous nervous system might play a role in the observed multifractality.

Sassi, Roberto; Signorini, Maria Gabriella; Cerutti, Sergio

2009-06-01

28

Method and apparatus for spatially variable rate application of agricultural chemicals based on remotely sensed vegetation data  

NASA Technical Reports Server (NTRS)

Remotely sensed spectral image data are used to develop a Vegetation Index file which represents spatial variations of actual crop vigor throughout a field that is under cultivation. The latter information is processed to place it in a format that can be used by farm personnel to correlate and calibrate it with actually observed crop conditions existing at control points within the field. Based on the results, farm personnel formulate a prescription request, which is forwarded via email or FTP to a central processing site, where the prescription is prepared. The latter is returned via email or FTP to on-side farm personnel, who can load it into a controller on a spray rig that directly applies inputs to the field at a spatially variable rate.

Hood, Kenneth Brown (Inventor); Seal, Michael R. (Inventor); Lewis, Mark David (Inventor); Johnson, James William (Inventor)

2004-01-01

29

Method and system for spatially variable rate application of agricultural chemicals based on remotely sensed vegetation data  

NASA Technical Reports Server (NTRS)

Remotely sensed spectral image data are used to develop a Vegetation Index file which represents spatial variations of actual crop vigor throughout a field that is under cultivation. The latter information is processed to place it in a format that can be used by farm personnel to correlate and calibrate it with actually observed crop conditions existing at control points within the field. Based on the results, farm personnel formulate a prescription request, which is forwarded via email or FTP to a central processing site, where the prescription is prepared. The latter is returned via email or FTP to on-side farm personnel, who can load it into a controller on a spray rig that directly applies inputs to the field at a spatially variable rate.

Hood, Kenneth Brown (Inventor); Seal, Michael R. (Inventor); Lewis, Mark David (Inventor); Johnson, James William (Inventor)

2007-01-01

30

CANONICAL CORRELATION ANALYSIS BETWEEN TIME SERIES AND STATIC OUTCOMES, WITH APPLICATION TO THE SPECTRAL ANALYSIS OF HEART RATE VARIABILITY  

PubMed Central

Although many studies collect biomedical time series signals from multiple subjects, there is a dearth of models and methods for assessing the association between frequency domain properties of time series and other study outcomes. This article introduces the random Cramér representation as a joint model for collections of time series and static outcomes where power spectra are random functions that are correlated with the outcomes. A canonical correlation analysis between cepstral coefficients and static outcomes is developed to provide a flexible yet interpretable measure of association. Estimates of the canonical correlations and weight functions are obtained from a canonical correlation analysis between the static outcomes and maximum Whittle likelihood estimates of truncated cepstral coefficients. The proposed methodology is used to analyze the association between the spectrum of heart rate variability and measures of sleep duration and fragmentation in a study of older adults who serve as the primary caregiver for their ill spouse.

Krafty, Robert T.; Hall, Martica

2014-01-01

31

Application of alpha/theta neurofeedback and heart rate variability training to young contemporary dancers: State anxiety and creativity.  

PubMed

As one in a series on the impact of EEG-neurofeedback in the performing arts, we set out to replicate a previous dance study in which alpha/theta (A/T) neurofeedback and heart rate variability (HRV) biofeedback enhanced performance in competitive ballroom dancers compared with controls. First year contemporary dance conservatoire students were randomised to the same two psychophysiological interventions or a choreology instruction comparison group or a no-training control group. While there was demonstrable neurofeedback learning, there was no impact of the three interventions on dance performance as assessed by four experts. However, HRV training reduced anxiety and the reduction correlated with improved technique and artistry in performance; the anxiety scale items focussed on autonomic functions, especially cardiovascular activity. In line with the putative impact of hypnogogic training on creativity A/T training increased cognitive creativity with the test of unusual uses, but not insight problems. Methodological and theoretical implications are considered. PMID:23684733

Gruzelier, J H; Thompson, T; Redding, E; Brandt, R; Steffert, T

2014-07-01

32

An Analysis of Heart Rate Variability  

Microsoft Academic Search

Proceeding from a formal definition of heart rate variability, some mathematical and statistical techniques from sampling statistics and time series analysis for the analytical evaluation of heart rate variability for ergonomics purposes are presented and compared. The concept of sampling statistics gives a measure of heart rate variability, arrived at by combining two measures, which were chosen according to a

H. LUCZAK; W. LAURIG

1973-01-01

33

Connecting Variability in Global Transcription Rate to Mitochondrial Variability  

PubMed Central

Populations of genetically identical eukaryotic cells show significant cell-to-cell variability in gene expression. However, we lack a good understanding of the origins of this variation. We have found marked cell-to-cell variability in average cellular rates of transcription. We also found marked cell-to-cell variability in the amount of cellular mitochondrial mass. We undertook fusion studies that suggested that variability in transcription rate depends on small diffusible factors. Following this, in vitro studies showed that transcription rate has a sensitive dependence on [ATP] but not on the concentration of other nucleotide triphosphates (NTPs). Further experiments that perturbed populations by changing nutrient levels and available [ATP] suggested this connection holds in vivo. We found evidence that cells with higher mitochondrial mass, or higher total membrane potential, have a faster rate of transcription per unit volume of nuclear material. We also found evidence that transcription rate variability is substantially modulated by the presence of anti- or prooxidants. Daughter studies showed that a cause of variability in mitochondrial content is apparently stochastic segregation of mitochondria at division. We conclude by noting that daughters that stochastically inherit a lower mitochondrial mass than their sisters have relatively longer cell cycles. Our findings reveal a link between variability in energy metabolism and variability in transcription rate.

das Neves, Ricardo Pires; Jones, Nick S.; Andreu, Lorena; Gupta, Rajeev; Enver, Tariq; Iborra, Francisco J.

2010-01-01

34

Heart Rate Variability in Athletes  

Microsoft Academic Search

athletes from training status, different types of exercise training, sex and ageing, presented from both cross-sectional and longitudinal studies. The predictability of HRV in over-training, athletic condition and athletic performance is also included. Finally, some recommendations concerning the application of HRV methods in athletes are made. The cardiovascular system is mostly controlled by autonomic regulation through the activity of sympathetic

Bert Seps; Frank Beckers

2003-01-01

35

Association between heart rate variability and manual pulse rate  

PubMed Central

Introduction: One model for neurological assessment in chiropractic pertains to autonomic variability, tested commonly with heart rate variability (HRV). Since HRV may not be convenient to use on all patient visits, more user-friendly methods may help fill-in the gaps. Accordingly, this study tests the association between manual pulse rate and heart rate variability. The manual rates were also compared to the heart rate derived from HRV. Methods: Forty-eight chiropractic students were examined with heart rate variability (SDNN and mean heart rate) and two manual radial pulse rate measurements. Inclusion criteria consisted of participants being chiropractic students. Exclusion criteria for 46 of the participants consisted of a body mass index being greater than 30, age greater than 35, and history of: a) dizziness upon standing, b) treatment of psychiatric disorders, and c) diabetes. No exclusion criteria were applied to the remaining two participants who were also convenience sample volunteers. Linear associations between the manual pulse rate methods and the two heart rate variability measures (SDNN and mean heart) were tested with Pearson’s correlation and simple linear regression. Results: Moderate strength inverse (expected) correlations were observed between both manual pulse rate methods and SDNN (r = ?0.640, 95% CI ?0.781, ?0.435; r = ?0.632, 95% CI ?0.776, ?0.425). Strong direct (expected) relationships were observed between the manual pulse rate methods and heart rate derived from HRV technology (r = 0.934, 95% CI 0.885, 0.962; r = 0.941, 95% CI 0.897, 0.966). Conclusion: Manual pulse rates may be a useful option for assessing autonomic variability. Furthermore, this study showed a strong relationship between manual pulse rates and heart rate derived from HRV technology.

Hart, John

2013-01-01

36

Human heart rate variability and sleep stages  

Microsoft Academic Search

With the aim of better understanding the dynamic changes in sympatho-vagal tone occurring during the night, human heart rate variability (HRV) during the various sleep stages was evaluated by means of autoregressive spectral analysis.

L. Toscani; P. F. Gangemi; A. Parigi; R. Silipo; P. Ragghianti; E. Sirabella; M. Morelli; L. Bagnoli; R. Vergassola; G. Zaccara

1996-01-01

37

Heart rate variability in systemic hypertension  

Microsoft Academic Search

Low heart rate (HR) variability is a risk factor for cardiac mortality in various patient populations, but it has not been well established whether patients with long-standing hypertension have abnormalities in the autonomic modulation of HR. Time and frequency domain measures of HR variability were compared in randomly selected, age-matched populations of 188 normotensive and 168 hypertensive males (mean age

Heikki V. Huikuri; Antti Ylitalo; Sirkku M. Pikkujämsä; Markku J. Ikäheimo; K. E. Juhani Airaksinen; Asko O. Rantala; Mauno Lilja; Y. Antero Kesäniemi

1996-01-01

38

Variable-rate variable-power MQAM for fading channels  

Microsoft Academic Search

We propose a variable-rate and variable-power MQAM modulation scheme for high-speed data transmission over fading channels. We first review results for the Shannon capacity of fading channels with channel side information, where capacity is achieved using adaptive transmission techniques. We then derive the spectral efficiency of our proposed modulation. We show that there is a constant power gap between the

Andrea J. Goldsmith; Soon-Ghee Chua

1997-01-01

39

Rater variables associated with ITER ratings.  

PubMed

Advocates of holistic assessment consider the ITER a more authentic way to assess performance. But this assessment format is subjective and, therefore, susceptible to rater bias. Here our objective was to study the association between rater variables and ITER ratings. In this observational study our participants were clerks at the University of Calgary and preceptors who completed online ITERs between February 2008 and July 2009. Our outcome variable was global rating on the ITER (rated 1-5), and we used a generalized estimating equation model to identify variables associated with this rating. Students were rated "above expected level" or "outstanding" on 66.4 % of 1050 online ITERs completed during the study period. Two rater variables attenuated ITER ratings: the log transformed time taken to complete the ITER [? = -0.06, 95 % confidence interval (-0.10, -0.02), p = 0.002], and the number of ITERs that a preceptor completed over the time period of the study [? = -0.008 (-0.02, -0.001), p = 0.02]. In this study we found evidence of leniency bias that resulted in two thirds of students being rated above expected level of performance. This leniency bias appeared to be attenuated by delay in ITER completion, and was also blunted in preceptors who rated more students. As all biases threaten the internal validity of the assessment process, further research is needed to confirm these and other sources of rater bias in ITER ratings, and to explore ways of limiting their impact. PMID:22777161

Paget, Michael; Wu, Caren; McIlwrick, Joann; Woloschuk, Wayne; Wright, Bruce; McLaughlin, Kevin

2013-10-01

40

Development of variable bit rate disk system  

NASA Astrophysics Data System (ADS)

CD size video disc employing the MPEGG2 system for recording moving pictures, is highly desired. However, it has been difficult to record a movie of more than 2 hours without causing a picture quality degradation. This problem has been resolved by the authors by applying a variable bit rate coding scheme. The variable bit rate coding scheme allows to allocate less codes to simple pictures and more to the portions that are needed. Therefore, a total generated code amount can be reduced with the adoption of the variable scheme, this allows to realize more flexible formats in recorded program length, which have not been possible before. This paper covers the coding, recording, and reproduction technologies of the newly developed disc system employing the variable bit rate coding scheme realized this time.

Yokouchi, Kentaro; Sugiyama, Kenji; Fujiwara, Mitsuaki; Tanaka, Kohji; Nemoto, Shigeru; Iwata, Kazumi

1995-09-01

41

Gaussian Mixture Model of Heart Rate Variability  

PubMed Central

Heart rate variability (HRV) is an important measure of sympathetic and parasympathetic functions of the autonomic nervous system and a key indicator of cardiovascular condition. This paper proposes a novel method to investigate HRV, namely by modelling it as a linear combination of Gaussians. Results show that three Gaussians are enough to describe the stationary statistics of heart variability and to provide a straightforward interpretation of the HRV power spectrum. Comparisons have been made also with synthetic data generated from different physiologically based models showing the plausibility of the Gaussian mixture parameters.

Costa, Tommaso; Boccignone, Giuseppe; Ferraro, Mario

2012-01-01

42

Study of time reversibility\\/irreversibility of cardiovascular data: theoretical results and application to laser Doppler flowmetry and heart rate variability signals  

Microsoft Academic Search

Time irreversibility can be qualitatively defined as the degree of a signal for temporal asymmetry. Recently, a time irreversibility characterization method based on entropies of positive and negative increments has been proposed for experimental signals and applied to heart rate variability (HRV) data (central cardiovascular system (CVS)). The results led to interesting information as a time asymmetry index was found

Anne Humeau-Heurtier; Guillaume Mahé; François Chapeau-Blondeau; David Rousseau; Pierre Abraham

2012-01-01

43

Abnormal heart rate variability in essential hypertension  

Microsoft Academic Search

Abnormal autonomic regulation may contribute to blood pressure elevation in arterial hypertension. This may be reflected in altered heart rate variability (HRV). During rest variations around 0.10 Hz predominantly reflect sympathetic nervous activity and to some extent parasympathetic activity. Variations around 0.30 Hz almost exclusively reflect parasympathetic activity.The aim of the present study was to compare HRV in patients with

Line B. Madsen; Dorthe S. Møller; Jens K. Rasmussen; Ole Nyvad; Erling B. Pedersen

2005-01-01

44

Modeling heart rate variability by stochastic feedback  

NASA Technical Reports Server (NTRS)

We consider the question of how the cardiac rhythm spontaneously self-regulates and propose a new mechanism as a possible answer. We model the neuroautonomic regulation of the heart rate as a stochastic feedback system and find that the model successfully accounts for key characteristics of cardiac variability, including the 1/f power spectrum, the functional form and scaling of the distribution of variations of the interbeat intervals, and the correlations in the Fourier phases which indicate nonlinear dynamics.

Amaral, L. A.; Goldberger, A. L.; Stanley, H. E.

1999-01-01

45

Quantitative analysis of heart rate variability  

Microsoft Academic Search

In the modern industrialized countries every year several hundred thousands of people diedue to the sudden cardiac death. The individual risk for this sudden cardiac death cannot bedefined precisely by common available, non-invasive diagnostic tools like Holter-monitoring,highly amplified ECG and traditional linear analysis of heart rate variability (HRV). Therefore,we apply some rather unconventional methods of nonlinear dynamics to analyse the

J. Kurths; A. Voss; P. Saparin; A. Witt; H. J. Kleiner; N. Wessel

1995-01-01

46

Variability of Recombination Rates in Higher Plants  

Microsoft Academic Search

\\u000a Recombination and chiasma frequency, like other features of meiosis, are subject to various genetic control mechanisms. Here,\\u000a we give an overview of the genetic and environmental factors as well as the genomic structures that play a role for the variability\\u000a of recombination rates in plant genomes. Suppressed or greatly reduced recombination is observed in chromosomal regions that\\u000a contain repetitive sequences

Elisabeth Esch; Renate Horn

47

Heart rate variability in familial Mediterranean fever  

Microsoft Academic Search

Familial Mediterranean fever (FMF) is a hereditary disease, characterized by recurrent episodes of fever and polyserositis.\\u000a Heart rate variability (HRV) is a powerful, simple and reliable technique to evaluate autonomic nervous system function. Previous\\u000a studies of physiologic parameters during tilt-test have suggested that patients with FMF have abnormal cardiovascular reactivity\\u000a and occult dysautonomia. Prompted by these findings, the present study

Naomi Nussinovitch; Avi Livneh; Keren Katz; Pnina Langevitz; Olga Feld; Moshe Nussinovitch; Benjamin Volovitz; Merav Lidar; Udi Nussinovitch

2011-01-01

48

A numerical model prediction for boiling multi channel flow rate distribution and application in 600MW supercritical variable-pressure once-through boiler with vertical tube coils  

NASA Astrophysics Data System (ADS)

Flow rate distribution is important in a multi channel system when the flow is heated non-uniformly. This paper describes a steady state approach for obtaining the flow distribution among various tubes of complex multi channel system. Based on the present approach, a program has been developed, which is directly applied in thermal hydraulic design and investigation of 600MW supercritical variable-pressure once through boiler.

Chen, Tingkuan; Xu, Jinliang; Wu, Lucheng

1996-04-01

49

Measurement of heart-rate variability: Part 1—Comparative study of heart-rate variability analysis methods  

Microsoft Academic Search

A definition of heart-rate variability (h.r.v.) is given. The use of h.r.v. measurement in both clinical applications and\\u000a the neural cardiovascular research is discussed. For the latter applications, four different signals describing h.r.v. are\\u000a reviewed. It is shown that these signals are based on modifications of one model, namely the integral pulse frequency modulator.\\u000a In Part 2, a hardware device

O. Rompelman; A. J. R. M. Coenen; R. I. Kitney

1977-01-01

50

Heart Rate Variability - A Historical Perspective  

PubMed Central

Heart rate variability (HRV), the beat-to-beat variation in either heart rate or the duration of the R–R interval – the heart period, has become a popular clinical and investigational tool. The temporal fluctuations in heart rate exhibit a marked synchrony with respiration (increasing during inspiration and decreasing during expiration – the so called respiratory sinus arrhythmia, RSA) and are widely believed to reflect changes in cardiac autonomic regulation. Although the exact contributions of the parasympathetic and the sympathetic divisions of the autonomic nervous system to this variability are controversial and remain the subject of active investigation and debate, a number of time and frequency domain techniques have been developed to provide insight into cardiac autonomic regulation in both health and disease. It is the purpose of this essay to provide an historical overview of the evolution in the concept of HRV. Briefly, pulse rate was first measured by ancient Greek physicians and scientists. However, it was not until the invention of the “Physician’s Pulse Watch” (a watch with a second hand that could be stopped) in 1707 that changes in pulse rate could be accurately assessed. The Rev. Stephen Hales (1733) was the first to note that pulse varied with respiration and in 1847 Carl Ludwig was the first to record RSA. With the measurement of the ECG (1895) and advent of digital signal processing techniques in the 1960s, investigation of HRV and its relationship to health and disease has exploded. This essay will conclude with a brief description of time domain, frequency domain, and non-linear dynamic analysis techniques (and their limitations) that are commonly used to measure HRV.

Billman, George E.

2011-01-01

51

Effect of hyperbaric pressure during scuba diving on autonomic modulation of the cardiac response: application of the continuous wavelet transform to the analysis of heart rate variability.  

PubMed

This study sought to determine the effects of hyperbaric pressure on heart rate modulation, by analyzing potential changes in heart rate variability (HRV). Ten divers were exposed to pressures of 1, 2, 3, and 4 atmospheres absolute (ATA). The test was performed in a hyperbaric chamber. Heart rate (HR) was recorded in supine subjects for 10 minutes per atmosphere. HRV was analyzed in the frequency mode (fast-Fourier transform and continuous wavelet transform). Results confirmed bradycardia as pressure increased. The drop in HR attained statistical significance after 2, 3, and 4 ATA. Signal energy (normalized TP values) rose progressively, becoming significant at 2 ATA. High frequency and low frequency displayed similar behavior in both cases. Although frequency band peaks did not yield clear results, continuous wave transform analysis showed that the frequency spectrum tended to shift into the high-frequency range as pressure increased. In summary, increased pressure prompted increased bradycardia, and HRV shifted into high-frequency range. PMID:20108844

Barbosa, Eduardo; García-Manso, Juan M; Martín-González, Juan M; Sarmiento, Samuel; Calderón, Francisco J; Da Silva-Grigoletto, Marzo E

2010-01-01

52

Applications of Reaction Rate  

ERIC Educational Resources Information Center

This article presents an assignment in which students are to research and report on a chemical reaction whose increased or decreased rate is of practical importance. Specifically, students are asked to represent the reaction they have chosen with an acceptable chemical equation, identify a factor that influences its rate and explain how and why it…

Cunningham, Kevin

2007-01-01

53

Soil variability in engineering applications  

NASA Astrophysics Data System (ADS)

Natural geomaterials, as soils and rocks, show spatial variability and heterogeneity of physical and mechanical properties. They can be measured by in field and laboratory testing. The heterogeneity concerns different values of litho-technical parameters pertaining similar lithological units placed close to each other. On the contrary, the variability is inherent to the formation and evolution processes experienced by each geological units (homogeneous geomaterials on average) and captured as a spatial structure of fluctuation of physical property values about their mean trend, e.g. the unit weight, the hydraulic permeability, the friction angle, the cohesion, among others. The preceding spatial variations shall be managed by engineering models to accomplish reliable designing of structures and infrastructures. Materon (1962) introduced the Geostatistics as the most comprehensive tool to manage spatial correlation of parameter measures used in a wide range of earth science applications. In the field of the engineering geology, Vanmarcke (1977) developed the first pioneering attempts to describe and manage the inherent variability in geomaterials although Terzaghi (1943) already highlighted that spatial fluctuations of physical and mechanical parameters used in geotechnical designing cannot be neglected. A few years later, Mandelbrot (1983) and Turcotte (1986) interpreted the internal arrangement of geomaterial according to Fractal Theory. In the same years, Vanmarcke (1983) proposed the Random Field Theory providing mathematical tools to deal with inherent variability of each geological units or stratigraphic succession that can be resembled as one material. In this approach, measurement fluctuations of physical parameters are interpreted through the spatial variability structure consisting in the correlation function and the scale of fluctuation. Fenton and Griffiths (1992) combined random field simulation with the finite element method to produce the Random Finite Element Method (RFEM). This method has been used to investigate the random behavior of soils in the context of a variety of classical geotechnical problems. Afterward, some following studies collected the worldwide variability values of many technical parameters of soils (Phoon and Kulhawy 1999a) and their spatial correlation functions (Phoon and Kulhawy 1999b). In Italy, Cherubini et al. (2007) calculated the spatial variability structure of sandy and clayey soils from the standard cone penetration test readings. The large extent of the worldwide measured spatial variability of soils and rocks heavily affects the reliability of geotechnical designing as well as other uncertainties introduced by testing devices and engineering models. So far, several methods have been provided to deal with the preceding sources of uncertainties in engineering designing models (e.g. First Order Reliability Method, Second Order Reliability Method, Response Surface Method, High Dimensional Model Representation, etc.). Nowadays, the efforts in this field have been focusing on (1) measuring spatial variability of different rocks and soils and (2) developing numerical models that take into account the spatial variability as additional physical variable. References Cherubini C., Vessia G. and Pula W. 2007. Statistical soil characterization of Italian sites for reliability analyses. Proc. 2nd Int. Workshop. on Characterization and Engineering Properties of Natural Soils, 3-4: 2681-2706. Griffiths D.V. and Fenton G.A. 1993. Seepage beneath water retaining structures founded on spatially random soil, Géotechnique, 43(6): 577-587. Mandelbrot B.B. 1983. The Fractal Geometry of Nature. San Francisco: W H Freeman. Matheron G. 1962. Traité de Géostatistique appliquée. Tome 1, Editions Technip, Paris, 334 p. Phoon K.K. and Kulhawy F.H. 1999a. Characterization of geotechnical variability. Can Geotech J, 36(4): 612-624. Phoon K.K. and Kulhawy F.H. 1999b. Evaluation of geotechnical property variability. Can Geotech J, 36(4): 625-639. Terzaghi K. 1943. Theoretical Soil Mechanics. New York: J

Vessia, Giovanna

2014-05-01

54

Variable Effects of Physical Training of Heart Rate Variability, Heart Rate Recovery, and Heart Rate Turbulence in Chronic Heart Failure  

Microsoft Academic Search

Background: Heart rate variability (HRV), heart rate turbulence (HRT), and heart rate recovery (HRR), indices that reflect autonomic nervous system (ANS) activity, are outcome predictors in patients with chronic heart failure (CHF). It is not clear, however, whether they reflect the same components of ANS activity. No study has examined the effects of physical training (PT) training on HRV, HRT,

EWA PIOTROWICZ; RAFA? BARANOWSKI; MA?GORZATA PIOTROWSKA; TOMASZ ZIELI?SKI; RYSZARD PIOTROWICZ

2009-01-01

55

A variable-rate filtering system for digital communications  

Microsoft Academic Search

We propose an efficient programmable transmit-receive digital filter structure consisting of a pulse shaping filter (PSF) and a cascaded integrator-comb (CIC) filter which is applicable to variable-rate digital communication systems. The CIC structure is a hardware-efficient means of constructing programmable interpolation and decimation filters, but it introduces a large amount of intersymbol interference (ISI). We solve this problem by proposing

L. Wasserman

1999-01-01

56

Fast variable selection for gas sensing applications  

Microsoft Academic Search

We introduce a new variable selection approach, which converges much faster to the optimal set of variables for a given application. The new procedure runs in two steps. First, a coarse and very fast variable selection procedure is applied: A figure of merit is defined and computed for every variable, a threshold value set and only the variables whose figure

O. Gualdron; E. Llobet; J. Brezmes; X. Vilanova; X. Correig

2004-01-01

57

Streaming updates for heart rate variability algorithms.  

PubMed

Heart rate variability (HRV) quantifies the fluctuations of the lengths of consecutive heart beat intervals, and is a reliable descriptor of many physiological factors modulating the normal rhythm of the heart. As the heart rate signal is nonstationary, indicators deduced from it may be present at all times, but may also occur episodically at nonpredetermined time instances. The potential for real-time feedback long-term ambulatory recordings is thus apparent. Numerous methods for measuring HRV have been standardized and are in active use, but are typically not designed to operate at real time. In this paper, we study the most popular HRV quantification methods and propose streaming algorithms that maximally utilize previously computed information without altering the output of the methods. We demonstrate speedups of more than two orders of magnitude for typical use-case scenarios. Using our algorithms on embedded systems that compute HRV leads to dramatic decreases in power consumption and in some cases allows for computation of metrics that were not previously possible at real time. PMID:24956611

Stergiou, Stergios; Balakrishnan, Rajalakshmi

2014-07-01

58

gHRV: Heart rate variability analysis made easy.  

PubMed

In this paper, the gHRV software tool is presented. It is a simple, free and portable tool developed in python for analysing heart rate variability. It includes a graphical user interface and it can import files in multiple formats, analyse time intervals in the signal, test statistical significance and export the results. This paper also contains, as an example of use, a clinical analysis performed with the gHRV tool, namely to determine whether the heart rate variability indexes change across different stages of sleep. Results from tests completed by researchers who have tried gHRV are also explained: in general the application was positively valued and results reflect a high level of satisfaction. gHRV is in continuous development and new versions will include suggestions made by testers. PMID:24854108

Rodríguez-Liñares, L; Lado, M J; Vila, X A; Méndez, A J; Cuesta, P

2014-08-01

59

Study of time reversibility/irreversibility of cardiovascular data: theoretical results and application to laser Doppler flowmetry and heart rate variability signals  

NASA Astrophysics Data System (ADS)

Time irreversibility can be qualitatively defined as the degree of a signal for temporal asymmetry. Recently, a time irreversibility characterization method based on entropies of positive and negative increments has been proposed for experimental signals and applied to heart rate variability (HRV) data (central cardiovascular system (CVS)). The results led to interesting information as a time asymmetry index was found different for young subjects and elderly people or heart disease patients. Nevertheless, similar analyses have not yet been conducted on laser Doppler flowmetry (LDF) signals (peripheral CVS). We first propose to further investigate the above-mentioned characterization method. Then, LDF signals, LDF signals reduced to samples acquired during ECG R peaks (LDF_RECG signals) and HRV recorded simultaneously in healthy subjects are processed. Entropies of positive and negative increments for LDF signals show a nonmonotonic pattern: oscillations—more or less pronounced, depending on subjects—are found with a period matching the one of cardiac activity. However, such oscillations are not found with LDF_RECG nor with HRV. Moreover, the asymmetry index for LDF is markedly different from the ones of LDF_RECG and HRV. The cardiac activity may therefore play a dominant role in the time irreversibility properties of LDF signals.

Humeau-Heurtier, Anne; Mahé, Guillaume; Chapeau-Blondeau, François; Rousseau, David; Abraham, Pierre

2012-07-01

60

Measurement of heart rate variability: a clinical tool or a research toy?  

Microsoft Academic Search

OBJECTIVESThe objectives of this review are to discuss the diversity of mechanisms that may explain the association between heart rate (HR) variability and mortality, to appraise the clinical applicability of traditional and new measures of HR variability and to propose future directions in this field of research. There is a large body of data demonstrating that abnormal HR variability measured

Heikki V Huikuri; Timo Mäkikallio; K. E. Juhani Airaksinen; Raul Mitrani; Agustin Castellanos; Robert J Myerburg

1999-01-01

61

Heart Rate Variability and Work-Load Measurement  

Microsoft Academic Search

Heart rate variability is a result of the superimposition of different sources of variation which are systemized. Three parameters are used to describe the phenomenon of heart rate variation. The range of variation of these parameters is discussed using examples from both laboratory and field investigations. Analyses demonstrate a correlation between heart rate and their variability. Discussion of of the

W. ROHMERT; W. LAURIG; U. PHILIPP; H. LUCZAK

1973-01-01

62

Speaking-Rate-Induced Variability in F2 Trajectories.  

ERIC Educational Resources Information Center

This study examined speaking-rate-induced spectral and temporal variability of F2 formant trajectories for target words produced in a carrier phrase at speaking rates ranging from fast to slow. Results suggest that a sliding-based model of acoustic variability associated with speaking rate change only partially accounts for the data obtained.…

Tjaden, Kris; Weismer, Gary

1998-01-01

63

Variable exhumation rates and variable displacement rates: Documenting recent slowing of Himalayan shortening in western Bhutan  

NASA Astrophysics Data System (ADS)

We link exhumational variability in space and time to the evolving geometry of the Himalayan fold-thrust belt in western Bhutan. By combining new and published geochronologic and thermochronologic data we document the burial age, peak temperatures and complete cooling history from 20 Ma to the present over an across-strike distance of ˜125 km. These integrated cooling curves highlight windows of fast exhumation that vary spatially and temporally. We propose that pulses of fast exhumation are a result of structures that facilitate the vertical motion of material, illustrated in sequentially-restored cross sections. Due to a range of permissible geometries at depth, we explore and evaluate the impact of geometry on kinematics and rates of deformation. The linked cooling history and cross sections provide estimates of both magnitude and timing of thrust sheet displacement and highlight temporal variability in potential shortening rates. Structural and chronologic data illustrate a general north to south progression of Himalayan deformation, with emplacement of the Main Central thrust (MCT), Paro thrust and Shumar thrust by 12 to no later than 9 Ma. Two different geometries and kinematic scenarios for the Lesser Himalayan duplex are proposed. A north to south propagating duplex system requires that the southern portion of that system, south of the MCT, deformed and cooled by 9 Ma, leaving only the southernmost thrust sheets, including the Main Boundary and Main Frontal thrusts, to deform between 9 and 0 Ma. This limited post 9 Ma shortening would necessitate a marked slowdown in convergence accommodated on the Main Himalayan thrust. A two-tiered duplex system, which allows for the Paro window duplex and the southern Baxa duplex to form simultaneously, permits duplex formation and accompanying exhumation until 6 Ma. Limited cooling from ˜200?°C to the surface post 6 Ma suggests either a decrease in shortening rates from 6 to 0 Ma or that duplex formation and exhumation are temporally decoupled. Our combined cooling curves highlight that the youngest cooling ages may not mark the fastest thrusting rates or the window of fastest exhumation. Instead, temporal variations in exhumation are best viewed through identifying transients in exhumation rate. We suggest that the strongest control on exhumation magnitude and variability is fold-thrust belt geometry, particularly the locations and magnitudes of footwall ramps, which can change over 10's of km distance. Balanced cross sections predict the location and magnitude of these ramps and how they vary in space and time, providing an untapped potential for testing permissible cross-section geometries and kinematics against measured cooling histories.

McQuarrie, Nadine; Tobgay, Tobgay; Long, Sean P.; Reiners, Peter W.; Cosca, Michael A.

2014-01-01

64

Normal Ranges of Heart Rate Variability During Infancy and Childhood  

Microsoft Academic Search

.   Heart rate variability is a noninvasive index of the neural activity of the heart. The present study examined heart rate\\u000a variability indices in 210 infants and children aged 3 days to 14 years to obtain normal ranges for all age classes. Heart\\u000a rate variability was measured by calculating mean RR interval over the length of the analysis, mean RR

M. Massin; G. von Bernuth

1997-01-01

65

Climate variables as predictors of basal metabolic rate: new equations.  

PubMed

Estimation of basal metabolic rate (BMR) and daily energy expenditure (DEE) in living humans and in fossil hominins can be used to understand the way populations adapt to different environmental and nutritional circumstances. One variable that should be considered in such estimates is climate, which may influence between-population variation in BMR. Overall, populations living in warmer climates tend to have lower BMR than those living in colder climates, even after controlling for body size and composition. Current methods of estimating BMR ignore climate, or deal with its effects in an insufficient manner. This may affect studies that use the factorial method to estimate DEE from BMR, when BMR is not measured but predicted using an equation. The present meta-analysis of published BMR uses stepwise regression to investigate whether the inclusion of climate variables can produce a generally applicable model for human BMR. Regression results show that mean annual temperature and high heat index temperature have a significant effect on BMR, along with body size, age and sex. Based on the regression analysis, equations predicting BMR from body size and climate variables were derived and compared with existing equations. The new equations are generally more accurate and more consistent across climates than the older ones. Estimates of DEE in living and fossil humans using the new equations are compared with estimates using previously published equations, illustrating the utility of including climate variables in estimates of BMR. The new equations derived here may prove useful for future studies of human energy expenditure. PMID:18461599

Froehle, Andrew W

2008-01-01

66

An efficient software implementation of a variable rate modem  

NASA Technical Reports Server (NTRS)

This paper describes the software implementation of the baseband portion of a variable rate modem. The modem can handle arbitrary symbol rates with a fixed input/output sample rate. This approach reduces hardware complexity related to external clock generation circuitry, offers complete flexibility in the selection of symbol rates, and conveniently accommodates symbol timing and symbol rate corrections.

Mantha, Ramesh; Hunt, Andrew; Crozier, Stewart

1995-01-01

67

Validation of pulse rate variability as a surrogate for heart rate variability in chronically instrumented rabbits.  

PubMed

Heart rate variability (HRV) is a function of cardiac autonomic tone that is widely used in both clinical and animal studies. In preclinical studies, HRV measures are frequently derived using the arterial pulse waveform from an implanted pressure telemetry device, termed pulse rate variability (PRV), instead of the electrocardiogram signal in accordance with clinical guidelines. The acceptability of PRV as a surrogate for HRV in instrumented animals is unknown. Using rabbits implanted with intracardiac leads and chronically implanted pressure transducers, we investigated the correlation and agreement of time-domain, frequency-domain, and nonlinear indexes of HRV and PRV at baseline. We also investigated the effects of ventricular pacing and autonomic blockade on both measures. At baseline, HRV and PRV time- and frequency-domain parameters showed robust correlations and moderate to high agreement, whereas nonlinear parameters showed slightly weaker correlations and varied agreement. Ventricular pacing almost completely eliminated HRV, and spectral analysis of the PRV signal revealed a HRV-independent rhythm. After cardiac autonomic blockade with atropine or metoprolol, the changes in time- and non-normalized frequency-domain measures of PRV continued to show strong correlations and moderate to high agreement with corresponding changes in HRV measures. Blockade-induced changes in nonlinear PRV indexes correlated poorly with HRV changes and showed weak agreement. These results suggest that time- and frequency-domain measures of PRV are acceptable surrogates for HRV even in the context of changing cardiac autonomic tone, but caution should be used when nonlinear measures are a primary end point or when HRV is very low as HRV-independent rhythms may predominate. PMID:24791786

Pellegrino, Peter R; Schiller, Alicia M; Zucker, Irving H

2014-07-01

68

Heart rate variability in infants, children and young adults  

Microsoft Academic Search

Heart rate variability was studied in normal subjects age 1 month-24 years while awake and in active and quiet sleep using 24 h continuous recordings of the ECG. Variability was quantified by spectral analysis for the two frequency bands: low frequency (LF) 0.03–0.15 Hz, high frequency (HF) 0.15–0.6 Hz. Heart rate variability showed an age dependence, being in general an

John P. Finley; Sherwin T. Nugent

1995-01-01

69

A fixed/variable bit-rate data compression architecture  

NASA Technical Reports Server (NTRS)

A VLSI architecture for an adaptive data compression encoder capable of sustaining fixed or variable bit-rate output has been developed. There are three modes of operation: lossless with variable bit-rate, lossy with fixed bit-rate and lossy with variable bit-rate. For lossless encoding, the implementation is identical to the USES chip designed for Landsat 7. Obtaining a fixed bit-rate is achieved with a lossy DPCM algorithm using adaptive, nonuniform scalar quantization. In lossy mode, variable bit-rate coding uses the lossless sections of the encoder for post-DPCM entropy coding. The encoder shows excellent compression performance in comparison to other current data compression techniques. No external tables or memory are required for operation.

Zweigle, Gregary C.; Venbrux, Jack; Yeh, Pen-Shu

1993-01-01

70

Analysis of heart rate variability using fuzzy measure entropy.  

PubMed

This paper proposed a new entropy measure, Fuzzy Measure Entropy (FuzzyMEn), for the analysis of heart rate variability (HRV) signals. FuzzyMEn was calculated based on the fuzzy set theory and improved the poor statistical stability in the approximate entropy (ApEn) and sample entropy (SampEn). The simulation results also demonstrated that the FuzzyMEn had better algorithm discrimination ability when compared with the recently published fuzzy entropy (FuzzyEn), The validity of FuzzyMEn was tested for clinical HRV analysis on 120 subjects (60 heart failure and 60 healthy control subjects). It is concluded that FuzzyMEn could be considered as a valid and reliable method for a clinical HRV application. PMID:23273774

Liu, Chengyu; Li, Ke; Zhao, Lina; Liu, Feng; Zheng, Dingchang; Liu, Changchun; Liu, Shutang

2013-02-01

71

Intertemporal extraction of mineral resources under variable-rate taxes  

SciTech Connect

This analysis shows that variability in tax rates, whether for output, value, or profits taxes, may create allocation incentives that are qualitatively different from those under fixed-rate taxation. The differences appear in the order in which the various grades are extracted, the rate at which they are extracted, and the total quantity extracted. 13 references.

Conrad, R.F.; Hool, R.B.

1984-11-01

72

Noncontact imaging photoplethysmography to effectively access pulse rate variability  

NASA Astrophysics Data System (ADS)

Noncontact imaging photoplethysmography (PPG) can provide physiological assessment at various anatomical locations with no discomfort to the patient. However, most previous imaging PPG (iPPG) systems have been limited by a low sample frequency, which restricts their use clinically, for instance, in the assessment of pulse rate variability (PRV). In the present study, plethysmographic signals are remotely captured via an iPPG system at a rate of 200 fps. The physiological parameters (i.e., heart and respiration rate and PRV) derived from the iPPG datasets yield statistically comparable results to those acquired using a contact PPG sensor, the gold standard. More importantly, we present evidence that the negative influence of initial low sample frequency could be compensated via interpolation to improve the time domain resolution. We thereby provide further strong support for the low-cost webcam-based iPPG technique and, importantly, open up a new avenue for effective noncontact assessment of multiple physiological parameters, with potential applications in the evaluation of cardiac autonomic activity and remote sensing of vital physiological signs.

Sun, Yu; Hu, Sijung; Azorin-Peris, Vicente; Kalawsky, Roy; Greenwald, Stephen

2013-06-01

73

Method of Discriminant Gravity Tolerance using Heart Rate Variability  

NASA Astrophysics Data System (ADS)

When returning on the earth by the space flight, the space deconditioning may be developed. As this countermeasure, the artificial gravity load device using the centrifuge is proposed in the space station. But the gravity load might cause the faint, and safe gravity load is uncertainty. We proposed that discriminate strength of gravity tolerance using heart rate variability time series. Step function was inputted to AR model estimated from heart rate variability time series during rest or under light gravity load, and strength of the gravity tolerance was discriminated by the step response function. On the result, discriminant accuracy was 87.5% by using heart rate variability time series when gravity load of 1.0 G was added to the human lying on the supine. Therefore, possibility of discriminant of gravity tolerance was obtained by using heart rate variability time series when sympathetic hyperactivity. Discriminant of the gravity tolerance is expected before countermeasure of space deconditioning is executed.

Yoshida, Yutaka; Yokoyama, Kiyoko; Takada, Hiroki; Iwase, Satoshi

74

Factors Accounting for Variability in Superintendent Ratings of Academic Preparation  

ERIC Educational Resources Information Center

This study utilized findings from the 2010 decennial study of the school superintendent to determine the extent to which four predictor variables ("courses," "professor credibility," "size" [enrollment of employing school district], and "gender") accounted for variability in superintendent overall ratings of their academic preparation. The…

Kowalski, Theodore J.; Young, I. Phillip; McCord, Robert S.

2011-01-01

75

Mental Load and the Measurement of Heart Rate Variability  

Microsoft Academic Search

A number of studies concerning heart rate variability and mental load arereviewedIt is concluded that in paced choice reaction tasks the number of reversal pointsin the cardiotachogram is the most sensitive measure of the load of the task.This measure was strongly correlated with respirationSpectral analysis of heart rate variability revealed the existence of a frequency component at about 0·10 Hz, a

G. MULDER

1973-01-01

76

Sympathetic reinnervation and heart rate variability after cardiac transplantation.  

PubMed Central

BACKGROUND: Heart rate variability is thought to measure autonomic modulation, but the relation has never been demonstrated directly in humans. AIM: To test the hypothesis that increased low frequency heart rate variability reflects sympathetic reinnervation after cardiac transplantation. PATIENTS: 24 cardiac transplant recipients at the time of routine surveillance coronary angiography two or more years after cardiac transplantation, and 10 controls with normal coronary arteries undergoing angiography for investigation of chest pain. SETTING: Regional cardiothoracic centre. METHODS: Sympathetic effector function at the sinus node was assessed by measuring the fall in cycle length for two minutes after injection of tyramine to the artery supplying the sinus node. Heart rate variability was measured from three-minute RR interval sequences at rest, during metronomic respiration, and before and after atropine. RESULTS: The logarithm of the low frequency component of heart rate variability during metronomic respiration was linearly related to the logarithm of the change in cycle length after injection of tyramine (R2 = 0.28, P = 0.007). Absolute units more accurately reflected sympathetic effector function than did normalised units or the ratio of low frequency to high frequency. Atropine did not affect high frequency heart rate variability in transplant recipients. CONCLUSIONS: The low frequency component of heart rate variability is directly related to sympathetic reinnervation to the sinus node.

Lord, S. W.; Clayton, R. H.; Mitchell, L.; Dark, J. H.; Murray, A.; McComb, J. M.

1997-01-01

77

Variable-rate coding for meteor-burst communications  

Microsoft Academic Search

The performance of variable-rate Reed-Solomon error-control coding for meteor-burst communications is considered. The code rate is allowed to vary from codeword to codeword within each packet, and the optimum number of codewords per packet and optimum rates for the codewords are determined as a function of the length of the message and the decay rate for the meteor trail. The

M. B. Pursley; S. D. Sandberg

1989-01-01

78

A North Pacific decadal variability in subduction rate  

NASA Astrophysics Data System (ADS)

Analysis of results from a global eddy-resolving general circulation model has revealed the existence of a North Pacific decadal variability in subduction rate. This decadal variability corresponds well with the Pacific Decadal Oscillation (PDO). The zero-lag correlation between the two time series reaches 0.61 for the period of integration (1950-2003), and increases to as high as 0.80 after the climate shift in the mid-1970s. Much of the North Pacific decadal variability in subduction rate is due to changes in winter mixed layer depth, which in turn are closely related to changes in surface wind and heat flux.

Qu, Tangdong; Chen, Ju

2009-11-01

79

Heart rate variability in depressive and anxiety disorders  

Microsoft Academic Search

Loss of normal autonomic nervous system control of heart rate and rhythm is an important risk factor for adverse cardiovascular events. After myocardial infarction, reduction in beat-to-beat heart rate variability, a measure of cardiac autonomic innervation by the brain, is a strong predictor of death. With loss of vagal innervation, as is noted in patients with severe neuropathy and in

Jack M. Gorman; Richard P. Sloan

2000-01-01

80

Heart rate variability associated with particulate air pollution  

Microsoft Academic Search

Background: Epidemiologic studies have linked fine particulate air pollution with cardiopulmonary mortality, yet underlying biologic mechanisms remain unknown. Changes in heart rate variability (HRV) may reflect changes in cardiac autonomic function and risk of sudden cardiac death. This study evaluated changes in mean heart rate and HRV in human beings associated with changes in exposure to particulate air pollution. Methods:

C. Arden Pope; Richard L. Verrier; Eric G. Lovett; Andrew C. Larson; Mark E. Raizenne; Richard E. Kanner; Joel Schwartz; G. Martin Villegas; Diane R. Gold; Douglas W. Dockery

1999-01-01

81

STREAMING MEDIA IN VARIABLE BIT-RATE ENVIRONMENTS  

Microsoft Academic Search

We consider streaming of video sequences over both, con- stant and variable bitrate (VBR) channels. Our goal is to enable decoding of each video unit before exceeding its displaying deadline and, hence, to guarantee successful se- quence presentation even if the media rate does not match the channel rate. In this work, we will show that the sep- aration between

Hrvoje Jenkac; Thomas Stockhammer

2003-01-01

82

Photoplethysmography pulse rate variability as a surrogate measurement of heart rate variability during non-stationary conditions  

Microsoft Academic Search

In this paper we assessed the possibility of using the pulse rate variability (PRV) extracted from the photoplethysmography signal as an alternative measurement of the HRV signal in non-stationary conditions. The study is based on analysis of the changes observed during a tilt table test in the heart rate modulation of 17 young subjects. First, the classical indices of HRV

E. Gil; M. Orini; R. Bailón; J. M. Vergara; L. Mainardi; P. Laguna

2010-01-01

83

Reproducibility of heart rate variability and blood pressure variability in individuals with spinal cord injury  

Microsoft Academic Search

Individuals with spinal cord injury (SCI) are prone to orthostatic intolerance and an increased risk of cardiovascular disease. The use of heart rate variability (HRV) and blood pressure variability (BPV) as indices of cardiovascular regulation would be valuable in this population; however, their reproducibility has yet to be tested in those with SCI. The purpose of this study was to

David S. Ditor; Mark V. Kamath; Maureen J. MacDonald; Joanne Bugaresti; Neil McCartney; Audrey L. Hicks

2005-01-01

84

Heart rate variability in risk stratification of cardiac patients.  

PubMed

Heart rate (HR) variability has been extensively studied in cardiac patients, especially in patients surviving an acute myocardial infarction (AMI) and also in patients with congestive heart failure (CHF) or left ventricular (LV) dysfunction. The majority of studies have shown that patients with reduced or abnormal HR variability have an increased risk of mortality within a few years after an AMI or after a diagnosis of CHF/LV dysfunction. Various measures of HR dynamics, such as time-domain, spectral, and non-linear measures of HR variability have been used in risk stratification. The prognostic power of various measures, except of those reflecting rapid R-R interval oscillations, has been almost identical, albeit some non-linear HR variability measures, such as short-term fractal scaling exponent have provided somewhat better prognostic information than the others. Abnormal HR variability predicts both sudden and non-sudden cardiac death. Because of remodeling of the arrhythmia substrate after AMI, early measurement of HR variability to identify those at high risk should likely be repeated later in order to assess the risk of fatal arrhythmia events. Future randomized trials using HR variability/turbulence as one of the pre-defined inclusion criteria will show whether routine measurement of HR variability/turbulence will become a routine clinical tool for risk stratification of cardiac patients. PMID:24215747

Huikuri, Heikki V; Stein, Phyllis K

2013-01-01

85

Two-Stage Variable Sample-Rate Conversion System  

NASA Technical Reports Server (NTRS)

A two-stage variable sample-rate conversion (SRC) system has been pro posed as part of a digital signal-processing system in a digital com munication radio receiver that utilizes a variety of data rates. The proposed system would be used as an interface between (1) an analog- todigital converter used in the front end of the receiver to sample an intermediatefrequency signal at a fixed input rate and (2) digita lly implemented tracking loops in subsequent stages that operate at v arious sample rates that are generally lower than the input sample r ate. This Two-Stage System would be capable of converting from an input sample rate to a desired lower output sample rate that could be var iable and not necessarily a rational fraction of the input rate.

Tkacenko, Andre

2009-01-01

86

Variability of Lekanesphaera monodi metabolic rates with habitat trophic status  

NASA Astrophysics Data System (ADS)

Regulation of metabolism is a common strategy used by individuals to respond to a changing environment. The mechanisms underlying the variability of metabolic rates in macroinvertebrates are of primary importance in studying benthic-pelagic energy transfer in transitional water ecosystems. Lekanesphaera monodi is an isopod endemic to transitional water ecosystems that can modify its metabolic rate in response to environmental changes. Therefore it is a useful model in studying the influence of environmental factors on metabolism. This study focused on the interpopulation variability of standard metabolic rates (SMR) in L. monodi populations sampled in three transitional water ecosystems differing in their trophic status. The standard metabolic rates of L. monodi individuals across the same range of body size spectra were inferred from oxygen consumption measurements in a flow-through respirometer in the three populations and a body condition index was assessed for each population. Habitat trophic status was evaluated by monthly measurement of the basic physical-chemical parameters of the water column in the ecosystems for one year. Standard metabolic rates showed high variability, ranging from 0.27 to 10.14 J d-1. Body size accounted for more than 38% of total variability. In terms of trophic status, individuals from the eutrophic ecosystem had significantly higher standard metabolic rates than individuals from the other ecosystems (SMR = 2.3 J d-1 in Spunderati Sud vs. 1.36 J d-1 in Alimini and 0.69 J d-1 in Acquatina). The body conditions index was also higher in the population from the eutrophic ecosystem. Results show that standard metabolic rates and growth rates are directly related to habitat productivity in accordance with the expectations of the food habits hypothesis. A possible extension of this hypothesis to benthic invertebrates is proposed.

Vignes, Fabio; Fedele, Marialaura; Pinna, Maurizio; Mancinelli, Giorgio; Basset, Alberto

2012-05-01

87

Heart Rate Variability as an Index of Regulated Emotional Responding  

Microsoft Academic Search

The study of individual differences in emotional responding can provide considerable insight into interpersonal dynamics and the etiology of psychopathology. Heart rate variability (HRV) analysis is emerging as an objective measure of regulated emotional responding (generating emotional responses of appropriate timing and magnitude). This review provides a theoretical and empirical rationale for the use of HRV as an index of

Bradley M. Appelhans; Linda J. Luecken

2006-01-01

88

Postprandial Changes of Sympathovagal Balance Measured by Heart Rate Variability  

Microsoft Academic Search

The aim of this study was to investigate thesympathovagal balance after meals by measuring thespectral analysis of heart rate variability (HRV). Ninehealthy volunteers were enrolled in this study. The electrocardiogram (ECG) was recorded for 30 minin a fasting state and 60 min after a 500-kcal testmeal. The HRV was derived from the ECG and was measuredby power spectral analysis using

Ching-Liang Lu; Xiaoping Zou; William C. Orr; J. D. Z. Chen

1999-01-01

89

Heart rate variability is altered following spinal cord injury  

Microsoft Academic Search

Spinal cord injury (SCI) patients are know to suffer from autonomic failure as a result of their injury. The magnitude of the dysautonomia resulting from such an injury is difficult to predict or characterize and, in varying degree, it impedes the recovery of physiological homeostasis. This study is intended to investigate the effectiveness of heart rate variability (HRV) analysis as

David C. Bunten; Alberta L. Warner; Sherry R. Brunnemann; Jack L. Segal

1998-01-01

90

Variability in Schools' Suspension Rates of Black Students  

ERIC Educational Resources Information Center

Black students are frequently suspended at much higher rates than students from other races or ethnicities. Analyses of suspension data over a three-year period were conducted to explain between-school variability in the percentages of Black students suspended in secondary schools at a large urban school district. Results of hierarchical backward…

Arcia, Emily

2007-01-01

91

Depression, Heart Rate Variability, and Acute Myocardial Infarction  

Microsoft Academic Search

Background—Clinical depression is associated with an increased risk for mortality in patients with a recent myocardial infarction (MI). Reduced heart rate variability (HRV) has been suggested as a possible explanation for this association. The purpose of this study was to determine if depression is associated with reduced HRV in patients with a recent MI. Methods and Results—Three hundred eighty acute

Robert M. Carney; James A. Blumenthal; Phyllis K. Stein; Lana Watkins; Diane Catellier; Lisa F. Berkman; Susan M. Czajkowski; Christopher O'Connor; Peter H. Stone; Kenneth E. Freedland

92

Practical Implementations of Real-Time Heart Rate Variability.  

National Technical Information Service (NTIS)

Heart rate variability (HRV) is a useful, non-invasive indicator of autonomic nervous system responsiveness that can be used to signal the need for life-saving interventions, but to date it has not been possible to use it in real-time (RT). Because HRV re...

A. Sastre

2004-01-01

93

Autonomic balance revisited: Panic anxiety and heart rate variability  

Microsoft Academic Search

The analysis of heart rate variability (HRV) is becoming widely used in clinical research to provide a window into autonomic control of HR. This technique has been valuable in elucidating the autonomic underpinnings of panic disorder (PD), a condition that is marked by reports of heart palpitations. A body of research has emerged that implicates a relative reduction in HRV

Bruce H. Friedman; JULIAN F. THAYERt

1998-01-01

94

Heart Rate Variability: Effect of Exercise Intensity on Postexercise Response  

ERIC Educational Resources Information Center

The purpose of the present study was to investigate the influence of two exercise intensities (moderate and severe) on heart rate variability (HRV) response in 16 runners 1 hr prior to (-1 hr) and at +1 hr, +24 hr, +48 hr, and +72 hr following each exercise session. Time domain indexes and a high frequency component showed a significant decrease…

James, David V. B.; Munson, Steven C.; Maldonado-Martin, Sara; De Ste Croix, Mark B. A.

2012-01-01

95

Heart Rate Variability and Drawing Impairment in Hypoxemic COPD  

ERIC Educational Resources Information Center

We studied 54 patients with hypoxemic chronic obstructive pulmonary disease (COPD). The Mini Mental State Examination and the Mental Deterioration Battery were used for neuropsychological assessment. Heart rate variability (HRV) was assessed based on 24-h Holter ECG recording. Mann-Whitney test was used to compare HRV parameters of patients…

Incalzi, Raffaele Antonelli; Corsonello, Andrea; Trojano, Luigi; Pedone, Claudio; Acanfora, Domenico; Spada, Aldo; D'Addio, Gianni; Maestri, Roberto; Rengo, Franco; Rengo, Giuseppe

2009-01-01

96

Device Variability Impact on Logic Gate Failure Rates  

Microsoft Academic Search

Well-established reliability models indicate that the failure rates of scaled CMOS will continue to increase due to manufacturing variability and wear-out caused by negativ e bias temperature instability and hot carrier injection effec ts. Thus, the reliability of future devices is a critical concern fo r circuit designers. In order to predict the feasibility and reduce the cost of these

Erin Taylor; Jose Fortes

97

A Latent-Variable Causal Model of Faculty Reputational Ratings.  

ERIC Educational Resources Information Center

A LISREL analysis demonstrates the value of regressing reputational ratings on three latent variables: size, faculty research productivity, and the quality of program graduates. The model was tested using National Research Council data for each of six disciplines: English, French, philosophy, geography, political science, and sociology.…

King, Suzanne; Wolfle, Lee M.

1987-01-01

98

Basic characteristics of variable rate video coding in ATM environment  

Microsoft Academic Search

Basic characteristics of variable-rate video coders applied to asynchronous transfer mode (ATM) transmission are described. Burstiness of video information is evaluated for conference-type scenes using various coding algorithms. Three measures (distribution, autocorrelation, and coefficient of variation) are introduced to evaluate burstiness. Video sources are modeled and characterized by the autoregressive process and coefficient of variation. Video quality improvement achieved with

M. Nomura; T. Fujii; N. Ohta

1989-01-01

99

Changes in Heart Rate Variability in Patients under Local Anesthesia  

Microsoft Academic Search

Spectral analysis of Heart Rate Variability (HRV) is widely used for the assessment of cardiovascular autonomic control. Several studies have shown the effect of anesthetic agents on HRV parameters. In this study a systematic approach of HRV analysis has been employed. The effect caused by the ectopic beats on the spectral measurements has been investigated and results are presented. A

K. Shafqat; S. K. Pal; S. Kumari; P. A. Kyriacou

2007-01-01

100

Spectral analysis of heart rate variability signal during sleep stages  

Microsoft Academic Search

The authors investigated the autonomic nervous activity during sleep stages by means of power spectrum density of heart rate variability signal. Spectral estimation was performed by autoregressive modelling of RR series. The data obtained suggest an augmented sympathetic activity during REM sleep and a progressive decrease of it when passing from awake state to stages 1,2,3-4

G. Calcagnini; G. Biancalana; F. Giubilei; S. Strano; S. Cerutti

1994-01-01

101

Heart rate variability and catecholamines during hypoglycemia and orthostasis  

Microsoft Academic Search

The low frequency component of heart rate variability (HRV) is believed to be affected by sympathetic activity, but an evidence for this suggestion remains controversial. This study analyzed association between HRV and plasma catecholamines in response to two distinct conditions activating sympathetic nervous system.Changes in HRV were analysed from ECG recording and plasma norepinephrine and epinephrine levels were measured in

Miroslav Vlcek; Zofia Radikova; Adela Penesova; Richard Kvetnansky; Richard Imrich

2008-01-01

102

Depression, heart rate variability, and exercise training in dialysis patients  

Microsoft Academic Search

Background Functional limitations, altered cardiac autonomic activity, and psychological distress are known disorders in chronic hemodialysis (HD) patients, relating to increased morbidity and mortality. The aim of this study was to examine the influence of an exercise training program on emotional parameters and heart rate variability (HRV) indices, as well as to determine whether emotional stress contributes to autonomic dysfunction

Evangelia Kouidi; Vassilis Karagiannis; Dimitrios Grekas; Apostolos Iakovides; George Kaprinis; Achilleas Tourkantonis; Asterios Deligiannis

2010-01-01

103

Downlink Power Allocation for Stored Variable-Bit-Rate Videos  

Microsoft Academic Search

In this paper, we study the problem of power allocation for streaming multiple variable-bit-rate (VBR) videos in the downlink of a cellular network. We consider a deterministic model for VBR video traffic and finite playout buffer at the mobile users. The objective is to derive the optimal downlink power allocation for the VBR video sessions, such that the video data

Yingsong Huang; Shiwen Mao; Yihan Li

2011-01-01

104

Simplified recurrence plots approach on heart rate variability data  

Microsoft Academic Search

Recurrence plot analysis has been applied to heart rate variability (HRV) data to identify hidden rhythms and complex dynamical patterns of fluctuations. Since the autonomic nervous system (ANS) is the primary regulating factor of HRV, derived measures as well as structural and qualitative aspects of these plots may be associated to different states or changes in neural control. A procedural

L. Cimponeriu; A. Bezerianos

1999-01-01

105

Water Requirements and Application Rates for Lawns.  

National Technical Information Service (NTIS)

Lawn water application rates were measured for 55 homes in Laramie and Wheatland, Wyoming, during 1975 and 1976. In addition, evapotranspiration rates were measured at both cities during 1976. Lawn water application rates in 1976 were 122 percent of the a...

L. O. Pochop J. Borrelli J. R. Barnes P. K. O'Neill

1978-01-01

106

Ordinal pattern statistics for the assessment of heart rate variability  

NASA Astrophysics Data System (ADS)

The recognition of all main features of a healthy heart rhythm (the so-called sinus rhythm) is still one of the biggest challenges in contemporary cardiology. Recently the interesting physiological phenomenon of heart rate asymmetry has been observed. This phenomenon is related to unbalanced contributions of heart rate decelerations and accelerations to heart rate variability. In this paper we apply methods based on the concept of ordinal pattern to the analysis of electrocardiograms (inter-peak intervals) of healthy subjects in the supine position. This way we observe new regularities of the heart rhythm related to the distribution of ordinal patterns of lengths 3 and 4.

Graff, G.; Graff, B.; Kaczkowska, A.; Makowiec, D.; Amigó, J. M.; Piskorski, J.; Narkiewicz, K.; Guzik, P.

2013-06-01

107

Variable-rate variable-power hybrid M-FSK M-QAM for fading channels  

Microsoft Academic Search

This paper investigates a variable-rate variable-power hybrid non-coherent M-FSK M-QAM system. The goal is to combine the spectral efficiency merit of M-QAM with the power efficiency advantage of M-FSK and as such extend the region of availability even at very low channel gain values. A basic system is first designed to maximize the average spectral efficiency while meeting average power

Fadel F. Digham; Mohamed-Slim Alouini

2003-01-01

108

Heart rate variability in normal and pathological sleep  

PubMed Central

Sleep is a physiological process involving different biological systems, from molecular to organ level; its integrity is essential for maintaining health and homeostasis in human beings. Although in the past sleep has been considered a state of quiet, experimental and clinical evidences suggest a noteworthy activation of different biological systems during sleep. A key role is played by the autonomic nervous system (ANS), whose modulation regulates cardiovascular functions during sleep onset and different sleep stages. Therefore, an interest on the evaluation of autonomic cardiovascular control in health and disease is growing by means of linear and non-linear heart rate variability (HRV) analyses. The application of classical tools for ANS analysis, such as HRV during physiological sleep, showed that the rapid eye movement (REM) stage is characterized by a likely sympathetic predominance associated with a vagal withdrawal, while the opposite trend is observed during non-REM sleep. More recently, the use of non-linear tools, such as entropy-derived indices, have provided new insight on the cardiac autonomic regulation, revealing for instance changes in the cardiovascular complexity during REM sleep, supporting the hypothesis of a reduced capability of the cardiovascular system to deal with stress challenges. Interestingly, different HRV tools have been applied to characterize autonomic cardiac control in different pathological conditions, from neurological sleep disorders to sleep disordered breathing (SDB). In summary, linear and non-linear analysis of HRV are reliable approaches to assess changes of autonomic cardiac modulation during sleep both in health and diseases. The use of these tools could provide important information of clinical and prognostic relevance.

Tobaldini, Eleonora; Nobili, Lino; Strada, Silvia; Casali, Karina R.; Braghiroli, Alberto; Montano, Nicola

2013-01-01

109

Heart Rate Conditioning in Newborn Infants: Relationships Among Conditionability, Heart Rate Variability, and Sex  

ERIC Educational Resources Information Center

Trace conditioning was evaluated in newborn infants by measurements of heart rate responses to a conditioned stimulus in anticipation of or in absence of the unconditioned stimulus. Data suggest females have higher levels of heart rate variability than males, which parallels their greater conditionability. (GO)

Stamps, Leighton E.; Porges, Stephen W.

1975-01-01

110

A Look at the MPEG Video Coding Standard for Variable Bit Rate Video Transmission  

Microsoft Academic Search

In this paper we take a close look at the MPEG video cod- ing standard for the transmission of variable bit rate video on ATM based Broadband ISDN. The MPEG standard has been defined for use in a variety of applications. Our focus in this paper is in its use for real time transmission of broadcast quality video. We were

Pramod Pancha; Magda El Zarki

1992-01-01

111

Variable rate vector quantization for medical image compression  

Microsoft Academic Search

Three techniques for variable-rate vector quantizer design are applied to medical images. The first two are extensions of an algorithm for optimal pruning in tree-structured classification and regression due to Breiman et al. The code design algorithms find subtrees of a given tree-structured vector quantizer (TSVQ), each one optimal in that it has the lowest average distortion of all subtrees

EVE A. RISKIN; TOM LOOKABAUGH; PHILIP A. CHOU; ROBERT M. GRAY

1990-01-01

112

Effects of bisoprolol on heart rate variability in heart failure  

Microsoft Academic Search

Analysis of heart rate variability (HRV) provides a noninvasive index of autonomic nervous system activity. HRV has been shown to be reduced in heart failure. Preliminary data indicate that ? blockers improve clinical status in patients with heart failure, but HRV improvement remains to be demonstrated. Fifty-four patients from the randomized double-blind, placebo-controlled Cardiac Insufficiency Bisoprolol Study were included in

Francoise Pousset; Xavier Copie; Philippe Lechat; Patrice Jaillon; Jean-Pierre Boissel; Martin Hetzel; Frédéric Fillette; Willem Remme; Louis Guize; Jean-Yves Le Heuzey

1996-01-01

113

Wavelet decomposition analysis of heart rate variability in aerobic athletes  

Microsoft Academic Search

Heart rate variability (HRV) can be quantified, among others, in the frequency domain using digital signal processing (DSP) techniques. The wavelet transform is an alternative tool for the analysis of non-stationary signals. The implementation of perfect reconstruction digital filter banks leads to multi resolution wavelet analysis. Software was developed in LabVIEW.In this study, the average power was compared at each

Dieter Verlinde; Frank Beckers; Dirk Ramaekers; André E. Aubert

2001-01-01

114

Motion-classified autoregressive modeling of variable bit rate video  

Microsoft Academic Search

A motion-adaptive variable-bit-rate (VBR) video codec is considered, and a motion-classified model is developed to represent the characteristics of various classes of motion activities, including scene changes. The codec switches between interframe, motion-compensated, and intraframe coding corresponding to low, medium, and high amounts of motion and scene changes, respectively. The model captures the motion of various video scenes by providing

Ferit Yegenoglu; Bijan Jabbari; Ya-Qin Zhang

1993-01-01

115

Heart Rate Variability and Sustained Attention in ADHD Children  

Microsoft Academic Search

The major goal of the current study was to investigate the association between continuous performance tests (CPTs) and the heart rate variability (HRV) of attention deficit hyperactivity disorder (ADHD) children. The HRV, specifically the 0.10-Hz component, may be considered to be a psychophysiological index of effort allocation (motivation): The less effort the subject allocates, the greater the 0.10-Hz component. Results

Norbert Börger; Jaap van Der Meere; Arjen Ronner; Ed Alberts; Reint Geuze; Hans Bogte

1999-01-01

116

Heart rate variability in children with neurocardiogenic syncope  

Microsoft Academic Search

In order to characterize the autonomic profile of syncopal children, we have studied heart rate variability (HRV) of 73 children, ages 11–18, with neurocardiogenic syncope and a positive outcome of head-up tilt testing (HUT).HRV was calculated over a 24-hour period for the time-domain indices (SDNN, SDANNi, SDNN, rMSSD, pNN50), and over 5-minute segments from night and day for frequency-domain indices

Agnieszka Zygmunt; Jerzy Stanczyk

2004-01-01

117

Heart rate variability in natural time and 1/f "noise"  

NASA Astrophysics Data System (ADS)

Several studies have shown that heart rate fluctuations exhibit the ubiquitous 1/f behavior which is altered in desease. Furthermore, the analysis of electrocardiograms in natural time reveals that important malfunctions in the complex system of the human heart can be identified. Here, we present a simple evolution model in natural time that exhibits the 1/fa behavior with a close to unity. The results of this model are consistent with a progressive modification of heart rate variability in healthy children and adolescents. The model results in complexity measures that separate healthy dynamics from patients as well as from sudden cardiac death individuals.

Sarlis, N. V.; Skordas, E. S.; Varotsos, P. A.

2009-07-01

118

QT intervals and heart rate variability in hypertensive patients.  

PubMed

Low heart rate variability and increased QT dispersion are risk factors for cardiac mortality in various patient populations. We studied dispersion of QT interval, i.e. an index of inhomogeneity of repolarization, and heart rate variability (HRV) i.e., a measure of cardiac autonomic modulation in 76 essential hypertension cases (45 women, 53.0 +/- 11.1 years, body mass index: 25.1 +/- 1.4 kg/m2) and 70 healthy cases (42 women, 54.0 +/- 10.2 years, body mass index: 25.5 +/- 1.6 kg/m2, p > 0.05). QT-corrected QT intervals and their dispersions were significantly higher in the hypertensive group (p < 0.0001), all showing a direct relation with the level of systolic and diastolic blood pressures, ventricular mass index and high Lown grade ventricular rhythm problems. Time domain measures like standard deviation of RR intervals, standard deviation of the means of all corrected RR intervals calculated at 5 min intervals (p < 0.0001), proportion of adjacent RR intervals differing by > 50 msec (p = 0.005), HRV triangular index (p = 0.007), the square root of the mean squared differences of successive RR intervals (p = 0.011), and the high frequency (HF, 0.16-0.40 Hz, p < 0.0001) part of the frequency domain measure of HRV were all decreased, whereas the low frequency (LF, 0.04-0.15 Hz, p = 0.013) part of the frequency domain measures and LF / HF ratio (p < 0.0001) were increased in hypertensive cases. Time domain and the HF part of frequency domain measures of heart rate variability showed an inverse relation with the increased levels of both systolic and diastolic blood pressures and Lown grading system of ventricular rhythm problems, whereas LF and LF / HF showed direct relations with high levels of systolic and diastolic blood pressures and high Lown grade ventricular rhythm problems. The measures of heart rate variability apart from LF and LF / HF were inversely related with the QT intervals and dispersions, whereas LF / HF was directly related with them. Therefore, we conclude that the levels of both systolic and diastolic blood pressures are related to the generation of ventricular rhythm problems either via increasing left ventricular mass which results in an increase in QT parameter measurements, or by altering heart rate variability measures indicating a disturbance in cardiac autonomic balance in essential hypertension. PMID:10850533

Kaftan, A H; Kaftan, O

2000-03-01

119

Heart rate variability and heart rate turbulence in mild-to-moderate aortic stenosis  

Microsoft Academic Search

Aims To study heart rate (HR) variability and HR turbulence parameters in mild-to-moderate aortic stenosis (AS) and to disclose whether any relationship exists between these parameters and echocardio- graphic findings. Methods and results Forty-three asymptomatic patients with mild-to-moderate AS (AS group) were studied. Echocardiographic parameters and HR variability and HR turbulence indices obtained over 24 Holter ECG recordings were compared

Murat Ozdemir; Sinan Altan Kocaman; Atiye Cengel

120

[Association between level of intelligence and heart rate variability].  

PubMed

Earlier we discovered that heart rate variability was associated with the level of intelligence. The purpose of this study is to confirm this association using more reliable method and to define more precisely the frequency band within which the amplitude of the heart rate modulations is related to intelligence. 13 males (aged 14 to 17) were the study subjects. The total score of the computer game Tetris was taken as a general measure of the intelligence level. Heart rate was recorded electrocardiographically both at rest and during playing Tetris. Frequency analysis of heart rate was carried out with digital Fourier transformation. Correlation analysis showed that there was positive association between the level of intelligence and the amplitude of heart rate modulation at the frequencies 0.30 and 0.15 modulations per RR interval. This association is closer for the heart rate at rest than for the heart rate during mental work and for the frequency 0.30 than for the 0.15 modulations per RR interval. PMID:21961308

Mukhin, V N; Iakovlev, N M

2011-08-01

121

Heart Rate Variability During Early Adaptation to Space  

NASA Technical Reports Server (NTRS)

A recent report hypothesized that episodes of space motion sickness (SMS) were reliably associated with low frequency oscillations (less than 0.03 to less than 0.01 Hz) in heart rate variability. This paper archives a large data set for review of investigators in this field which may facilitate the evaluation of this hypothesis. Continuous recording of Electro-cardiography (ECG) and other measures were made for 6 to 12 hours per day (waking hours) of six Shuttle crewmembers for the first 3 mission days of two separate Shuttle flights. Spectral analyses of heart rate variability during approximately 200 hours of inflight is presented. In addition, nearly 200 hours of data collected on these same individuals during ground tests prior to the mission are presented. The Purpose of this Publication is to document the incidence of low frequency oscillations of heart rate in 4 people exposed to microgravity over a period of five days. In addition, this report contains spectral analyses of heart rate data collected on these same individuals during ground-based mission simulations. By archiving these data in this manner, it is our intention to make this information available to other investigators interested in studying this phenomena.

Toscano, W. B.; Cowings, P. S.

1994-01-01

122

Circadian Variation of Heart Rate Variability Across Sleep Stages  

PubMed Central

Study Objectives: Nocturnal cardiovascular events are more frequent at the beginning and end of the night. It was proposed that this pattern reflects the nocturnal distribution of sleep and sleep stages. Using heart rate variability (HRV), we recently showed an interaction between the circadian system and vigilance states on the regulation of cardiac rhythmicity. Here, we further investigate this interaction in order to clarify the specific effects of sleep stages on the regulation of the heart. Design: Participants underwent a 72-h ultradian sleep-wake cycle procedure in time isolation consisting of alternating 60-min wake episodes in dim light and 60-min nap opportunities in total darkness. Setting: Time isolation suite. Patients or participants: Fifteen healthy young participants; two were subsequently excluded. Interventions: N/A. Measurements and Results: The current study revealed that sleep onset and progression to deeper sleep stages was associated with a shift toward greater parasympathetic modulation, whereas rapid eye movement (REM) sleep was associated with a shift toward greater sympathetic modulation. We found a circadian rhythm of heart rate (HR) and high-frequency power during wakefulness and all non-REM sleep stages. A significant circadian rhythm of HR and sympathovagal balance of the heart was also observed during REM sleep. During slow wave sleep, maximal parasympathetic modulation was observed at ?02:00, whereas during REM sleep, maximal sympathetic modulation occurred in the early morning. Conclusion: The circadian and sleep stage-specific effects on heart rate variability are clinically relevant and contribute to the understanding of the degree of cardiovascular vulnerability during sleep. Citation: Boudreau P; Yeh WH; Dumont GA; Boivin DB. Circadian variation of heart rate variability across sleep stages. SLEEP 2013;36(12):1919-1928.

Boudreau, Philippe; Yeh, Wei-Hsien; Dumont, Guy A.; Boivin, Diane B.

2013-01-01

123

Symbolic dynamics marker of heart rate variability combined with clinical variables enhance obstructive sleep apnea screening  

NASA Astrophysics Data System (ADS)

Many sleep centres try to perform a reduced portable test in order to decrease the number of overnight polysomnographies that are expensive, time-consuming, and disturbing. With some limitations, heart rate variability (HRV) has been useful in this task. The aim of this investigation was to evaluate if inclusion of symbolic dynamics variables to a logistic regression model integrating clinical and physical variables, can improve the detection of subjects for further polysomnographies. To our knowledge, this is the first contribution that innovates in that strategy. A group of 133 patients has been referred to the sleep center for suspected sleep apnea. Clinical assessment of the patients consisted of a sleep related questionnaire and a physical examination. The clinical variables related to apnea and selected in the statistical model were age (p < 10-3), neck circumference (p < 10-3), score on a questionnaire scale intended to quantify daytime sleepiness (p < 10-3), and intensity of snoring (p < 10-3). The validation of this model demonstrated an increase in classification performance when a variable based on non-linear dynamics of HRV (p < 0.01) was used additionally to the other variables. For diagnostic rule based only on clinical and physical variables, the corresponding area under the receiver operating characteristic (ROC) curve was 0.907 (95% confidence interval (CI) = 0.848, 0.967), (sensitivity 87.10% and specificity 80%). For the model including the average of a symbolic dynamic variable, the area under the ROC curve was increased to 0.941 (95% = 0.897, 0.985), (sensitivity 88.71% and specificity 82.86%). In conclusion, symbolic dynamics, coupled with significant clinical and physical variables can help to prioritize polysomnographies in patients with a high probability of apnea. In addition, the processing of the HRV is a well established low cost and robust technique.

Ravelo-García, A. G.; Saavedra-Santana, P.; Juliá-Serdá, G.; Navarro-Mesa, J. L.; Navarro-Esteva, J.; Álvarez-López, X.; Gapelyuk, A.; Penzel, T.; Wessel, N.

2014-06-01

124

General anesthesia suppresses normal heart rate variability in humans  

NASA Astrophysics Data System (ADS)

The human heart normally exhibits robust beat-to-beat heart rate variability (HRV). The loss of this variability is associated with pathology, including disease states such as congestive heart failure (CHF). The effect of general anesthesia on intrinsic HRV is unknown. In this prospective, observational study we enrolled 100 human subjects having elective major surgical procedures under general anesthesia. We recorded continuous heart rate data via continuous electrocardiogram before, during, and after anesthesia, and we assessed HRV of the R-R intervals. We assessed HRV using several common metrics including Detrended Fluctuation Analysis (DFA), Multifractal Analysis, and Multiscale Entropy Analysis. Each of these analyses was done in each of the four clinical phases for each study subject over the course of 24 h: Before anesthesia, during anesthesia, early recovery, and late recovery. On average, we observed a loss of variability on the aforementioned metrics that appeared to correspond to the state of general anesthesia. Following the conclusion of anesthesia, most study subjects appeared to regain their normal HRV, although this did not occur immediately. The resumption of normal HRV was especially delayed on DFA. Qualitatively, the reduction in HRV under anesthesia appears similar to the reduction in HRV observed in CHF. These observations will need to be validated in future studies, and the broader clinical implications of these observations, if any, are unknown.

Matchett, Gerald; Wood, Philip

2014-06-01

125

Investigation of noise exposure effect on heart rate variability parameters.  

PubMed

This paper deals with the study of the effect of 135 min exposure to noise with intensity Leq 95 dB(A) in experimental conditions. Three experimental sessions: before, at the onset, and at the end of the noise exposure were conducted. The comparison of heart rate variability (HRV) parameters before and on the onset of the experiment showed tendency for significant decrease of the cardiointervals variability parameters: standard deviation (SD), sum of positive differences between successive cardiointervals (S), total wave energy in the cardiotachogram (S*Ns), mean difference between successive cardiointervals (V). Statistically significant increase of the mean value was found at HRV parameters related to the distribution of the cardiointervals: control adequacy parameter (IARP), equilibrium autonomic parameter (IVE), autonomous balance (IVB), homeostasis parameter (HI). At the end of the third experimental session HRV parameters were almost restored, but they did not achieve the initial values. An elevation of the sympathetic activity under noise exposure effect was found. In this aspect, the heart rate variability parameters were interpreted as a sensitive indicator for the quality of cardiac rhythm and they can be used for assessment of the functional status and the level of preserving of the adaptive reserves of the investigated persons. PMID:11505734

Tzaneva, L; Danev, S; Nikolova, R

2001-08-01

126

Rates of profit as correlated sums of random variables  

NASA Astrophysics Data System (ADS)

Profit realization is the dominant feature of market-based economic systems, determining their dynamics to a large extent. Rather than attaining an equilibrium, profit rates vary widely across firms, and the variation persists over time. Differing definitions of profit result in differing empirical distributions. To study the statistical properties of profit rates, I used data from a publicly available database for the US Economy for 2009-2010 (Risk Management Association). For each of three profit rate measures, the sample space consists of 771 points. Each point represents aggregate data from a small number of US manufacturing firms of similar size and type (NAICS code of principal product). When comparing the empirical distributions of profit rates, significant ‘heavy tails’ were observed, corresponding principally to a number of firms with larger profit rates than would be expected from simple models. An apparently novel correlated sum of random variables statistical model was used to model the data. In the case of operating and net profit rates, a number of firms show negative profits (losses), ruling out simple gamma or lognormal distributions as complete models for these data.

Greenblatt, R. E.

2013-10-01

127

Heart rate variability in patients with Sjögren's syndrome.  

PubMed

Heart rate variability (HRV) gives information about sympathetic parasympathetic autonomic balance. Our purpose was to determine whether HRV is abnormal in patients with Sjögren's syndrome. In 16 patients with Sjögren's syndrome and 30 matched controls, a short time analysis of HRV was performed for both the frequency and the time domain. In the time domain, patients tended to display a slower heart rate, greater R-R variability and higher standard deviation of the mean (SDNN) than did healthy subjects, but the differences were not statistically significant. In the frequency domain the spectral measures of HRV showed a slight reduction of LF and an increase of HF; as a result, the ratio between high and low frequencies, representative of sympathovagal modulation, was significantly reduced. Our data suggest an increase in the parasympathetic control of heart rate in patients with Sjögren's syndrome. This predominance in vagal tone could exert a protective and antiarrhythmic role in patients with primary Sjögren's syndrome, and may be relevant with reference to the lower incidence of sudden death in this disorder compared to other major autoimmune diseases. PMID:11147760

Tumiati, B; Perazzoli, F; Negro, A; Pantaleoni, M; Regolisti, G

2000-01-01

128

Heart rate variability and its relation to ventricular arrhythmias in congestive heart failure  

Microsoft Academic Search

BACKGROUND--It has been shown that heart rate variability is decreased in patients with congestive heart failure and that depressed heart rate variability is associated with a propensity to ventricular arrhythmias. Little is known, however, about heart rate variability in patients with both congestive heart failure and ventricular arrhythmias. METHODS--Spectral heart rate variability was analysed from 24 hour ambulatory electrocardiograms in

L. Fei; P. J. Keeling; J. S. Gill; Y. Bashir; D. J. Statters; J. Poloniecki; W. J. McKenna; A. J. Camm

1994-01-01

129

Heart rate variability during cycloergometric exercise or judo wrestling eliciting the same heart rate level  

Microsoft Academic Search

This study compared heart rate variability (HRV) in ten male judokas between two types of exercise eliciting the same near-maximal average heart rate (HR): judo wrestling vs. cycloergometric bout. Beat-to-beat RR intervals were recorded during (1) a 4-min judo randori (wrestling); (2) a 4-min cycloergometric exercise eliciting maximal oxygen consumption ( V?O 2MAX). Time series were analyzed both by short

François Cottin; François Durbin; Yves Papelier

2004-01-01

130

Variable-rate colour image quantization based on quadtree segmentation  

NASA Astrophysics Data System (ADS)

A novel variable-sized block encoding with threshold control for colour image quantization (CIQ) is presented in this paper. In CIQ, the colour palette used has a great influence on the reconstructed image quality. Typically, a higher image quality and a larger storage cost are obtained when a larger-sized palette is used in CIQ. To cut down the storage cost while preserving quality of the reconstructed images, the threshold control policy for quadtree segmentation is used in this paper. Experimental results show that the proposed method adaptively provides desired bit rates while having better image qualities comparing to CIQ with the usage of multiple palettes of different sizes.

Hu, Y. C.; Li, C. Y.; Chuang, J. C.; Lo, C. C.

2011-09-01

131

Metaiodobenzylguanidine and heart rate variability in heart failure.  

PubMed

It is assumed that the low-frequency power (LF) of heart rate variability (HRV) increases with progress of congestive heart failure (CHF), therefore positively correlating with cardiac 123I-metaiodobenzylguanidine (MIBG) washout. It is demonstrated here that HRV, including normalized LF, correlated inversely with MIBG washout and positively with the ratio of heart-to-mediastinum MIBG activity in controls and CHF patients, whereas these correlations were not observed within CHF patients. Thus MIBG washout may increase and HRV including normalized LF may decrease with CHF, although the HRV and MIBG measures may not similarly change in proportion to the severity of the cardiac autonomic dysfunction in CHF. PMID:9805260

Kurata, C; Shouda, S; Mikami, T; Uehara, A; Ishikawa, K; Tawarahara, K; Nakano, T; Matoh, F; Takeuchi, K

1998-10-01

132

Drug Effects on Heart Rate and Heart Rate Variability During a Prolonged Reaction Task.  

National Technical Information Service (NTIS)

The effects of an amphetamine and a barbiturate on heart rate were investigated during long term performance (three hours in a serial reaction task). Besides the interbeat interval (IBI) derived from the successive R-tops of the ECG, the variability of IB...

A. W. K. Gaillard D. A. Trumbo A. J. Krul

1975-01-01

133

Study of Heart Rate and Heart Rate Variability during Rapid Decompression to 50,000 FT.  

National Technical Information Service (NTIS)

A previous study of the heart rate (HR) response to positive pressure breathing (PPB), anxiety and hypoxia during rapid decompression (RD) revealed a consistent pattern in the beat-to-beat or interbeat interval variability of HR, known in the literature a...

C. S. Chopp J. B. Bomar J. A. Dellinger

1994-01-01

134

Development and Evaluation of a High School Rating Conversion Table for NROTC Applicants.  

National Technical Information Service (NTIS)

Naval Reserve Office Training Corps (NROTC) scholarship applicants are evaluated, in part, on their high school rating (HSR). HSR is a selection variable that reflects individuals' percentile rank in their high school class. For those applicants who are m...

J. E. Edwards N. M. Abrahams R. L. Burch

1990-01-01

135

Explicit and Implicit Ratings for Mobile Applications  

Microsoft Academic Search

Today most mobile operating systems provide an application portal (e.g. Android Market, AppStore) where users can search by keywords and explicitly rate applications published by third-party developers. In this paper we go beyond this approach and introduce an implicit rating mechanism for Android programs. Our approach, captures installation, update, and removal events, and allows to show them among users. Based

Andrea Girardello; Florian Michahelles

2010-01-01

136

Heart rate variability analysis during central hypovolemia using wavelet transformation.  

PubMed

Detection of hypovolemia prior to overt hemodynamic decompensation remains an elusive goal in the treatment of critically injured patients in both civilian and combat settings. Monitoring of heart rate variability has been advocated as a potential means to monitor the rapid changes in the physiological state of hemorrhaging patients, with the most popular methods involving calculation of the R-R interval signal's power spectral density (PSD) or use of fractal dimensions (FD). However, the latter method poses technical challenges, while the former is best suited to stationary signals rather than the non-stationary R-R interval. Both approaches are also limited by high inter- and intra-individual variability, a serious issue when applying these indices to the clinical setting. We propose an approach which applies the discrete wavelet transform (DWT) to the R-R interval signal to extract information at both 500 and 125 Hz sampling rates. The utility of machine learning models based on these features were tested in assessing electrocardiogram signals from volunteers subjected to lower body negative pressure induced central hypovolemia as a surrogate of hemorrhage. These machine learning models based on DWT features were compared against those based on the traditional PSD and FD, at both sampling rates and their performance was evaluated based on leave-one-subject-out fold cross-validation. Results demonstrate that the proposed DWT-based model outperforms individual PSD and FD methods as well as the combination of these two traditional methods at both sample rates of 500 Hz (p value <0.0001) and 125 Hz (p value <0.0001) in detecting the degree of hypovolemia. These findings indicate the potential of the proposed DWT approach in monitoring the physiological changes caused by hemorrhage. The speed and relatively low computational costs in deriving these features may make it particularly suited for implementation in portable devices for remote monitoring. PMID:23371800

Ji, Soo-Yeon; Belle, Ashwin; Ward, Kevin R; Ryan, Kathy L; Rickards, Caroline A; Convertino, Victor A; Najarian, Kayvan

2013-06-01

137

Can Photoplethysmography Variability Serve as an Alternative Approach to Obtain Heart Rate Variability Information?  

Microsoft Academic Search

Heart rate variability (HRV), extracted from an electrocardiogram, is known to be a noninvasive indicator reflecting the dynamic\\u000a interplay between perturbations to cardiovascular function and the dynamic response of the cardiovascular regulatory system.\\u000a Photoplethysmography (PPG) is a noninvasive method to monitor arterial oxygen saturation on a continuous basis. Given the\\u000a rich cardiovascular information in the PPG signal, and the ubiquity

Sheng Lu; He Zhao; Kihwan Ju; Kunson Shin; Myoungho Lee; Kirk Shelley; Ki H. Chon

2008-01-01

138

Kramers-Moyal Expansion of Heart Rate Variability  

NASA Astrophysics Data System (ADS)

The first six Kramers-Moyal coefficients were extracted from human heart rate variability recordings. The method requires the determination of the Markov time and of the proper conditional probability densities. We analyzed heart rate data recorded in a group of ten young, healthy subjects. We obtained non-negligible higher order Kramers-Moyal (K-M) terms in 6 h nighttime parts of the 24 h recordings. This indicates that the data is a non-Gaussian process and probably a correlated signal. The analysis yielded important new insights into the character and distribution of the stochastic processes measured in healthy group. In the night hours, the dominant oscillation in the heart rate is the so called respiratory sinus arrhythmia (RSA) -- a physiological phenomenon in which respiration acts as a drive for the heart rate. Certain kinds of pathology may disrupt RSA. We compared nighttime recordings of the healthy group with those recorded in six patients with hypertrophic cardiomyopathy (HCM). HCM is generally a pathology of heart cells but abnormalities in autonomic regulation are also observed. Using the higher order Kramers-Moyal coefficients, we analyzed the skewness and kurtosis in the nighttime recordings for the normal subjects.

Petelczyc, M.; ?ebrowski, J. J.; Baranowski, R.

2009-05-01

139

Decreased heart rate variability is associated with poststroke depression  

PubMed Central

Objective Although decreased heart rate variability (HRV) has been well documented in association with depression following myocardial infarction, this phenomenon has not been studied in patients with stroke. The present study was designed to prospectively assess HR in relationship to depression among patients with acute stroke. Design Using 24 hour Holter monitoring, assess HRV. Setting A large university rehabilitation hospital. Participants patients, with first ever stroke and no other severe physical illness, cigarette smoking or drug therapy that could affect HRV, were evaluated over 24 hours for heart rate variability. Measurements Patients were evaluated using the Structured Clinical Interview for depression diagnosis. Severity was assessed by Hamilton Depression Rating Scale. Stroke severity was assessed by the NIH Stroke Scale, the Barthel Index and the Mini Mental State Exam. The standard deviation of time in msec between normal heart beats (SDNN) was the primary measure of HRV. Results Among patients with poststroke major or minor depression (N=33), the SDNN was 109±32.6 SD compared with nondepressed patients (N=16) whose SDNN was 133.9±40.1 SD(Wilcoxon rank test S=492, p=0.048). The SDNN was significantly and independently related to the existence of depression, but no other intergroup differences. Conclusions These findings, for the first time, have provided some evidence that both major and minor poststroke depression may lead to decreased HRV. Future research in larger groups of patients should determine whether other measures of HRV more specific to sympathetic-parasympathetic tone are decreased in patients with poststroke depression.

Spalletta, Gianfranco; Jorge, Ricardo E.; Bassi, Andrea; Colivicchi, Furio; Ripa, Alessandra; Caltagirone, Carlo

2008-01-01

140

Heart rate and heart rate variability responses to Tai Chi and jogging in Beijing and Graz  

PubMed Central

Background: Tai Chi is a famous training method in China, and jogging is a popular kind of exercise both in Austria and China. Nevertheless, there is little information concerning online monitoring of biosignals during both training activities in parallel. Within the last years innovative scientific monitoring tools for evaluating features of neurocardial fitness have been developed. Aims: The goal of this study was to demonstrate heart rate and heart rate variability analysis for the first time during Tai Chi and jogging. Volunteers and Methods: Continuous electrocardiographic monitoring over a period of 75 minutes was performed simultaneously in two healthy volunteers using the same type of equipment (medilog AR12 systems). Two healthy persons (both male, 49 years and 52 years, respectively), both hobby sportsmen, were monitored continuously during two resting periods before and after active sport and also during Tai Chi and jogging, respectively. Results: Data acquisition was performed without any technical problems in both subjects. Poincaré plots of sequential R-R intervals (beat to beat variability) show two ellipses of different shape and magnitude. During resting periods blood pressure effects can be clearly seen in one subject (jogging). The same effects, however reduced, are obvious in the other volunteer during Tai Chi. Conclusions: The present investigations during Tai Chi and jogging highlight the potential value of heart rate and heart rate variability monitoring even under difficult conditions. The innovative kind of analysis helps to show how well the human body reacts to sport, stress and recovery.

Litscher, Gerhard; Zhang, Weibo; Huang, Tao; Wang, Lu

2011-01-01

141

Heart rate variability and sympathovagal balance: pharmacological validation  

PubMed Central

Rationale We validated heart rate (HR) and six time and six frequency domain measures of heart rate variability (HRV) as estimators of autonomic outflow in 44 young healthy male subjects. Gold standards for autonomic outflow were the Rosenblueth-Simeone factors m (sympathetic tone) and n (vagal tone), and the sympathovagal balance m·n, determined by two-stage complete autonomic blockade. Methods Rank correlations were computed between HR and the HRV measures obtained before autonomic blockade, and m, n and m·n. Also, the maximal mean performances (averaged sensitivity and specificity) for HR and HRV as discriminators between low and high values of m, n or m·n were computed. Results The spectral HRV measures showed less good correlations and performances than the time domain HRV measures. Correlations with sympathetic tone were all below 0.31. Respiratory sinus arrhythmia during 15 cycles/min metronome breathing was superior in estimating vagal tone and sympathovagal balance (correlations -0.71/-0.73; both performances 0.82), heart rate scored similarly for assessing the sympathovagal balance (correlation 0.71; performance 0.82). Conclusions It does not appear justified to evaluate HR or HRV in terms of sympathetic tone, vagal tone, or sympathovagal balance. HR and HRV are specifically weak in assessing sympathetic tone. Respiratory sinus arrhythmia during 15 cycles/min metronome breathing is superior in assessing vagal tone. Current HRV analysis techniques offer no advantages compared with HR in assessing the sympathovagal balance.

Bootsma, M.; Swenne, C.A.; Janssen, M.J.A.; Cats, V. Manger; Schalij, M.J.

2003-01-01

142

Music structure determines heart rate variability of singers.  

PubMed

Choir singing is known to promote wellbeing. One reason for this may be that singing demands a slower than normal respiration, which may in turn affect heart activity. Coupling of heart rate variability (HRV) to respiration is called Respiratory sinus arrhythmia (RSA). This coupling has a subjective as well as a biologically soothing effect, and it is beneficial for cardiovascular function. RSA is seen to be more marked during slow-paced breathing and at lower respiration rates (0.1 Hz and below). In this study, we investigate how singing, which is a form of guided breathing, affects HRV and RSA. The study comprises a group of healthy 18 year olds of mixed gender. The subjects are asked to; (1) hum a single tone and breathe whenever they need to; (2) sing a hymn with free, unguided breathing; and (3) sing a slow mantra and breathe solely between phrases. Heart rate (HR) is measured continuously during the study. The study design makes it possible to compare above three levels of song structure. In a separate case study, we examine five individuals performing singing tasks (1-3). We collect data with more advanced equipment, simultaneously recording HR, respiration, skin conductance and finger temperature. We show how song structure, respiration and HR are connected. Unison singing of regular song structures makes the hearts of the singers accelerate and decelerate simultaneously. Implications concerning the effect on wellbeing and health are discussed as well as the question how this inner entrainment may affect perception and behavior. PMID:23847555

Vickhoff, Björn; Malmgren, Helge; Aström, Rickard; Nyberg, Gunnar; Ekström, Seth-Reino; Engwall, Mathias; Snygg, Johan; Nilsson, Michael; Jörnsten, Rebecka

2013-01-01

143

Music structure determines heart rate variability of singers  

PubMed Central

Choir singing is known to promote wellbeing. One reason for this may be that singing demands a slower than normal respiration, which may in turn affect heart activity. Coupling of heart rate variability (HRV) to respiration is called Respiratory sinus arrhythmia (RSA). This coupling has a subjective as well as a biologically soothing effect, and it is beneficial for cardiovascular function. RSA is seen to be more marked during slow-paced breathing and at lower respiration rates (0.1 Hz and below). In this study, we investigate how singing, which is a form of guided breathing, affects HRV and RSA. The study comprises a group of healthy 18 year olds of mixed gender. The subjects are asked to; (1) hum a single tone and breathe whenever they need to; (2) sing a hymn with free, unguided breathing; and (3) sing a slow mantra and breathe solely between phrases. Heart rate (HR) is measured continuously during the study. The study design makes it possible to compare above three levels of song structure. In a separate case study, we examine five individuals performing singing tasks (1–3). We collect data with more advanced equipment, simultaneously recording HR, respiration, skin conductance and finger temperature. We show how song structure, respiration and HR are connected. Unison singing of regular song structures makes the hearts of the singers accelerate and decelerate simultaneously. Implications concerning the effect on wellbeing and health are discussed as well as the question how this inner entrainment may affect perception and behavior.

Vickhoff, Bjorn; Malmgren, Helge; Astrom, Rickard; Nyberg, Gunnar; Ekstrom, Seth-Reino; Engwall, Mathias; Snygg, Johan; Nilsson, Michael; Jornsten, Rebecka

2013-01-01

144

Heart rate variability and disease characteristics in patients with COPD.  

PubMed

Heart rate variability (HRV) is reduced in patients with chronic obstructive pulmonary disease (COPD). However, the relationships among HRV and characteristics of COPD are unknown. The aim of this study was to characterize HRV in patients with COPD and to verify the correlation of HRV measured during rest with disease severity and pulmonary, muscular, and functional impairment. Thirty-one patients with COPD (16 male; 66 +/- 8 years; BMI = 24 +/- 6 kg/m(2); FEV(1) = 46 +/- 16% predicted) without severe cardiac dysfunction were included. HRV assessment was performed by the head-up tilt test (HUTT), and the main variables used for analysis were SDNN index, LF/HF ratio, and R-R intervals. Other tests included spirometry, bioelectrical impedance, cardiopulmonary exercise test, 6-minute walk test, respiratory and peripheral muscle force, health-related quality of life and functional status questionnaires, and objective quantification of physical activity level in daily life with the DynaPort and SenseWear armband activity monitors, besides calculation of the BODE index. There was a statistical difference in all variables of HRV between the HUTT positions (lying and standing). There was no correlation of HRV with BODE index or FEV(1). Out of the BODE index, just the BMI was correlated with SDNN and R-R intervals (r = 0.44; p < 0.05 and r = 0.37; p < 0.05, respectively). There was correlation between HRV reduction and a lower level of physical activity in daily life, besides worse health-related quality of life, functional status, and respiratory and peripheral muscle force. Cardiac autonomic function of patients with COPD is not related to disease severity but mainly to the level of physical activity in daily life. PMID:18815834

Camillo, Carlos A; Pitta, Fabio; Possani, Heloíse V; Barbosa, Marcus V R A; Marques, Divina S O; Cavalheri, Vinícius; Probst, Vanessa S; Brunetto, Antonio F

2008-01-01

145

Heart rate variability predicts control over memory retrieval.  

PubMed

Stopping retrieval of unwanted memories has been characterized as a process that requires inhibition. However, little research has examined the relationship between control over memory retrieval and individual differences in inhibitory control. Higher levels of resting heart rate variability (HRV) are associated with greater inhibitory control, as indicated by better performance on a number of cognitive, affective, and motor tasks. Therefore, we tested the hypothesis that higher levels of resting HRV predict enhanced memory inhibition as indexed by performance on the think/no-think task. Efforts to suppress no-think word pairs resulted in impaired recall for those items, as in past studies. Moreover, higher levels of resting HRV were associated with more successful suppression, as indicated by lower recall of the to-be-avoided stimuli relative to baseline stimuli. These findings are among the first to suggest that physiological markers of inhibitory control can be used to index a person's capacity to control unwanted memories. PMID:24335601

Gillie, Brandon L; Vasey, Michael W; Thayer, Julian F

2014-02-01

146

Characterizing heart rate variability by scale-dependent Lyapunov exponent  

NASA Astrophysics Data System (ADS)

Previous studies on heart rate variability (HRV) using chaos theory, fractal scaling analysis, and many other methods, while fruitful in many aspects, have produced much confusion in the literature. Especially the issue of whether normal HRV is chaotic or stochastic remains highly controversial. Here, we employ a new multiscale complexity measure, the scale-dependent Lyapunov exponent (SDLE), to characterize HRV. SDLE has been shown to readily characterize major models of complex time series including deterministic chaos, noisy chaos, stochastic oscillations, random 1/f processes, random Levy processes, and complex time series with multiple scaling behaviors. Here we use SDLE to characterize the relative importance of nonlinear, chaotic, and stochastic dynamics in HRV of healthy, congestive heart failure, and atrial fibrillation subjects. We show that while HRV data of all these three types are mostly stochastic, the stochasticity is different among the three groups.

Hu, Jing; Gao, Jianbo; Tung, Wen-Wen

2009-06-01

147

Heart rate variability at different thermal comfort levels.  

PubMed

The mechanism of human thermal comfort is important for building a comfortable and healthy indoor environment. This paper analyzes human heart rate variability (HRV) at different thermal comfort levels and discusses the mechanism of human thermal comfort. A total of 33 subjects were divided in 3 groups. Under air temperatures of 21, 24, 26, 28, 29, and 30 degrees C, the subjects' electrocardiogram was recorded for 5 min. HRV (the ratio of absolute powers in low- and high-frequency bands, LF/HF ratio) was analyzed. LF/HF at discomfort level were significantly higher than that at comfort level (P < 0.05), despite the same thermal sensation. The results indicate that sympathetic activity plays an important role in subjects' thermal discomfort and the LF/HF ratio may be used as an indicator for human thermal comfort. PMID:18351379

Liu, Weiwei; Lian, Zhiwei; Liu, Yuanmou

2008-06-01

148

Sign series entropy analysis of short-term heart rate variability  

Microsoft Academic Search

Complexity and nonlinearity approaches can be used to study the temporal and structural order in heart rate variability (HRV)\\u000a signal, which is helpful for understanding the underlying rule and physiological essence of cardiovascular regulation. For\\u000a clinical applications, methods suitable for short-term HRV analysis are more valuable. In this paper, sign series entropy\\u000a analysis (SSEA) is proposed to characterize the feature

ChunHua Bian; QianLi Ma; JunFeng Si; XuHui Wu; Jun Shao; XinBao Ning; DongJin Wang

2009-01-01

149

Packet error rate-constrained optimized variable rate scheme for convolutionally coded M-QAM system  

Microsoft Academic Search

Link adaptation using adaptive modulation and coding (AMC) is a popular physical layer technique for efficient use of time-varying fading channel. In this paper, using a cross-layer approach, we analyze the spectral efficiency of a variable rate transmission scheme in a convolutionally-coded M-ary quadrature amplitude modulation (M-QAM) system under block fading situation. For imperfect channel state information (CSI), a closed

J. W. Hwang; K. Nehra; M. Shikh-Bahaei

2012-01-01

150

Heart rate variability related to effort at work.  

PubMed

Changes in autonomic nervous system function have been related to work stress induced increases in cardiovascular morbidity and mortality. Our purpose was to examine whether various heart rate variability (HRV) measures and new HRV-based relaxation measures are related to self-reported chronic work stress and daily emotions. The relaxation measures are based on neural network modelling of individual baseline heart rate and HRV information. Nineteen healthy hospital workers were studied during two work days during the same work period. Daytime, work time and night time heart rate, as well as physical activity were recorded. An effort-reward imbalance (ERI) questionnaire was used to assess chronic work stress. The emotions of stress, irritation and satisfaction were assessed six times during both days. Seventeen subjects had an ERI ratio over 1, indicating imbalance between effort and reward, that is, chronic work stress. Of the daily emotions, satisfaction was the predominant emotion. The daytime relaxation percentage was higher on Day 2 than on Day 1 (4 ± 6% vs. 2 ± 3%, p < 0.05) and the night time relaxation (43 ± 30%) was significantly higher than daytime or work time relaxation on the both Days. Chronic work stress correlated with the vagal activity index of HRV. However, effort at work had many HRV correlates: the higher the work effort the lower daytime HRV and relaxation time. Emotions at work were also correlated with work time (stress and satisfaction) and night time (irritation) HRV. These results indicate that daily emotions at work and chronic work stress, especially effort, is associated with cardiac autonomic function. Neural network modelling of individual heart rate and HRV information may provide additional information in stress research in field conditions. PMID:21356531

Uusitalo, Arja; Mets, Terhi; Martinmäki, Kaisu; Mauno, Saija; Kinnunen, Ulla; Rusko, Heikki

2011-11-01

151

The relationship between resting heart rate variability and heart rate recovery  

Microsoft Academic Search

Objective  There is limited research available regarding a possible relationship between resting heart rate variability (HRV) and post-exercise\\u000a heart rate recovery (HRR). The aim of this study was to examine the relationship between resting HRV and HRR after maximal\\u000a exercise.\\u000a \\u000a \\u000a \\u000a Methods  Sixty-six college age men participated in this study. HRV was measured in a supine position before and for 30 min after a

Michael R. Esco; Michele S. Olson; Henry N. Williford; Daniel L. Blessing; David Shannon; Peter Grandjean

2010-01-01

152

26 CFR 1.1275-5 - Variable rate debt instruments.  

Code of Federal Regulations, 2013 CFR

...atâ (A) One or more qualified floating rates; (B) A single fixed rate and one or more qualified floating rates; (C) A single objective rate...objective rate that is a qualified inverse floating rate. (ii) Certain debt...

2013-04-01

153

Electrochemical Corrosion Rate Sensors for Waste Incineration Applications  

SciTech Connect

Electrochemical corrosion rate sensors work in high temperature waste incineration applications where ash is deposited. The ash serves as the electrolyte for electrochemical measurements, such as liner polarization resistance, electrochemical noise, and harmonic distortion analyses. Results to date have shown that these types of sensors respond qualitatively to changes in temperature, gas composition, alloy composition, and type of ash. Several years of research have shown that high temperature corrosion rate probes need to be better understood before corrosion rate can be used as a process variable by power plant operators. More recent research has shown that electrochemical corrosion probes typically measure lower corrosion rates than those measured by standard mass loss techniques. While still useful for monitoring changes in corrosion rates, absolute probe corrosion rates will need a calibration factor to be useful. Ideas for research that may help resolve these issues are presented.

Covino, B.S., Jr.; Bullard, S.J.; Matthes, S.A.; Holcomb, G.R.; Ziomek-Moroz, M.; Eden, D.A. (Honeywell Intercorr)

2007-03-01

154

Variable beam dose rate and DMLC IMRT to moving body anatomy  

SciTech Connect

Derivation of formulas relating leaf speeds and beam dose rates for delivering planned intensity profiles to static and moving targets in dynamic multileaf collimator (DMLC) intensity modulated radiation therapy (IMRT) is presented. The analysis of equations determining algorithms for DMLC IMRT delivery under a variable beam dose rate reveals a multitude of possible delivery strategies for a given intensity map and for any given target motion patterns. From among all equivalent delivery strategies for DMLC IMRT treatments specific subclasses of strategies can be selected to provide deliveries that are particularly suitable for clinical applications providing existing delivery devices are used. Special attention is devoted to the subclass of beam dose rate variable DMLC delivery strategies to moving body anatomy that generalize existing techniques of such deliveries in Varian DMLC irradiation methodology to static body anatomy. Few examples of deliveries from this subclass of DMLC IMRT irradiations are investigated to illustrate the principle and show practical benefits of proposed techniques.

Papiez, Lech; Abolfath, Ramin M. [Department of Radiation Oncology, UTSouthwestern Medical Center, Dallas, Texas 75390 (United States)

2008-11-15

155

Determinants for Heart Rate Variability in a Normal Korean Population  

PubMed Central

This study examined the normal ranges and the determinants for various parameters of the short-term heart rate variability (HRV) measurements in a large Korean sample of healthy people. HRV measurements were obtained in 2,748 healthy men and 735 healthy women 18-65 yr of age. The mean total power (TP), low frequency (LF), high frequency (HF), and LF/HF ratio were 1,358.9 ± 1,840.8 ms2, 417.3 ± 807.6 ms2, 254.1 ± 414.1 ms2, and 2.4 ± 20.9 ms2 in the frequency-domain spectral analysis. The mean standard deviation of the normal-to-normal (NN) interval (SDNN) and the square root of the mean squared differences of successive NN intervals (RMSSD) were 39.6 ± 22.1 ms and 29.7 ± 18.1 ms in the time-domain analysis. The female subjects had significantly higher SDNN, RMSSD, and HF values than the male subjects. After controlling for age, there was no statistically significant difference in the SDNN. Quantile regression analysis showed that age and mean heart rate had a significant impact on short-term HRV measurement. Given that both clinicians and researchers are increasingly relying on short-term HRV assessment in measuring stress, our work suggests that age and gender should be considered as independent determinants for HRV.

Kim, Gyung-Mee

2011-01-01

156

Determinants for heart rate variability in a normal Korean population.  

PubMed

This study examined the normal ranges and the determinants for various parameters of the short-term heart rate variability (HRV) measurements in a large Korean sample of healthy people. HRV measurements were obtained in 2,748 healthy men and 735 healthy women 18-65 yr of age. The mean total power (TP), low frequency (LF), high frequency (HF), and LF/HF ratio were 1,358.9 ± 1,840.8 ms(2), 417.3 ± 807.6 ms(2), 254.1 ± 414.1 ms(2), and 2.4 ± 20.9 ms(2) in the frequency-domain spectral analysis. The mean standard deviation of the normal-to-normal (NN) interval (SDNN) and the square root of the mean squared differences of successive NN intervals (RMSSD) were 39.6 ± 22.1 ms and 29.7 ± 18.1 ms in the time-domain analysis. The female subjects had significantly higher SDNN, RMSSD, and HF values than the male subjects. After controlling for age, there was no statistically significant difference in the SDNN. Quantile regression analysis showed that age and mean heart rate had a significant impact on short-term HRV measurement. Given that both clinicians and researchers are increasingly relying on short-term HRV assessment in measuring stress, our work suggests that age and gender should be considered as independent determinants for HRV. PMID:22022180

Kim, Gyung-Mee; Woo, Jong-Min

2011-10-01

157

Acute exposure to environmental tobacco smoke and heart rate variability.  

PubMed Central

Environmental tobacco smoke (ETS) has been associated with cardiovascular mortality. Pathophysiologic pathways leading from ETS exposure to cardiopulmonary disease are still being explored. Reduced cardiac autonomic function, as measured by heart rate variability (HRV), has been associated with cardiac vulnerability and may represent an important pathophysiologic mechanism linking ETS and risk of cardiac mortality. In this study we evaluated acute ETS exposure in a commercial airport with changes in HRV in 16 adult nonsmokers. We conducted ambulatory electrocardiographic (ECG) monitoring for 8-hr periods while participants alternated 2 hr in nonsmoking and smoking areas. Nicotine and respirable suspended particle concentrations and participants' blood oxygen saturation were also monitored. We calculated time and frequency domain measures of HRV for periods in and out of the smoking area, and we evaluated associations with ETS using comparative statistics and regression modeling. ETS exposure was negatively associated with all measures of HRV. During exposure periods, we observed an average decrement of approximately 12% in the standard deviation of all normal-to-normal heart beat intervals (an estimate of overall HRV). ETS exposures were not associated with mean heart rate or blood oxygen saturation. Altered cardiac autonomic function, assessed by decrements in HRV, is associated with acute exposure to ETS and may be part of the pathophysiologic mechanisms linking ETS exposure and increased cardiac vulnerability.

Pope, C A; Eatough, D J; Gold, D R; Pang, Y; Nielsen, K R; Nath, P; Verrier, R L; Kanner, R E

2001-01-01

158

Variable dose rate single-arc IMAT delivered with a constant dose rate and variable angular spacing  

NASA Astrophysics Data System (ADS)

Single-arc intensity-modulated arc therapy (IMAT) has gained worldwide interest in both research and clinical implementation due to its superior plan quality and delivery efficiency. Single-arc IMAT techniques such as the Varian RapidArc™ deliver conformal dose distributions to the target in one single gantry rotation, resulting in a delivery time in the order of 2 min. The segments in these techniques are evenly distributed within an arc and are allowed to have different monitor unit (MU) weightings. Therefore, a variable dose-rate (VDR) is required for delivery. Because the VDR requirement complicates the control hardware and software of the linear accelerators (linacs) and prevents most existing linacs from delivering IMAT, we propose an alternative planning approach for IMAT using constant dose-rate (CDR) delivery with variable angular spacing. We prove the equivalence by converting VDR-optimized RapidArc plans to CDR plans, where the evenly spaced beams in the VDR plan are redistributed to uneven spacing such that the segments with larger MU weighting occupy a greater angular interval. To minimize perturbation in the optimized dose distribution, the angular deviation of the segments was restricted to <=± 5°. This restriction requires the treatment arc to be broken into multiple sectors such that the local MU fluctuation within each sector is reduced, thereby lowering the angular deviation of the segments during redistribution. The converted CDR plans were delivered with a single gantry sweep as in the VDR plans but each sector was delivered with a different value of CDR. For four patient cases, including two head-and-neck, one brain and one prostate, all CDR plans developed with the variable spacing scheme produced similar dose distributions to the original VDR plans. For plans with complex angular MU distributions, the number of sectors increased up to four in the CDR plans in order to maintain the original plan quality. Since each sector was delivered with a different dose rate, extra mode-up time (xMOT) was needed between the transitions of the successive sectors during delivery. On average, the delivery times of the CDR plans were approximately less than 1 min longer than the treatment times of the VDR plans, with an average of about 0.33 min of xMOT per sector transition. The results have shown that VDR may not be necessary for single-arc IMAT. Using variable angular spacing, VDR RapidArc plans can be implemented into the clinics that are not equipped with the new VDR-enabled machines without compromising the plan quality or treatment efficiency. With a prospective optimization approach using variable angular spacing, CDR delivery times can be further minimized while maintaining the high delivery efficiency of single-arc IMAT treatment.

Tang, Grace; Earl, Matthew A.; Yu, Cedric X.

2009-11-01

159

Heart rate recovery after exercise is related to the insulin resistance syndrome and heart rate variability in elderly men  

Microsoft Academic Search

Objective We investigated the associations between heart rate recovery after exercise (as a suggested measure of vagal activity), heart rate variability, and measurements of the insulin resistance syndrome. Material and Methods Seventy men aged 70 years were examined with a symptom-limited bicycle exercise test, a 24-hour heart rate variability test, and different measurements of different components of the insulin resistance

Lars Lind; Bertil Andrén

2002-01-01

160

Variable Impacts of Imazapic Rate on Downy Brome (Bromus tectorum) and Seeded Species in Two Rangeland Communities  

Microsoft Academic Search

The herbicide imazapic is registered for use on rangelands and provides effective short-term control of certain invasive annual grasses. However, details about optimal application rates for downy brome and susceptibility of simultaneously seeded species are lacking. Thus, we investigated downy brome and seeded species responses to variable rates of imazapic (0, 35, 70, 105, and 140 g ai\\/ha) in two

Christo Morris; Thomas A. Monaco; Craig W. Rigby

2009-01-01

161

Heart rate variability and target organ damage in hypertensive patients  

PubMed Central

Background We evaluated the association between linear standard Heart Rate Variability (HRV) measures and vascular, renal and cardiac target organ damage (TOD). Methods A retrospective analysis was performed including 200 patients registered in the Regione Campania network (aged 62.4?±?12, male 64%). HRV analysis was performed by 24-h holter ECG. Renal damage was assessed by estimated glomerular filtration rate (eGFR), vascular damage by carotid intima-media thickness (IMT), and cardiac damage by left ventricular mass index. Results Significantly lower values of the ratio of low to high frequency power (LF/HF) were found in the patients with moderate or severe eGFR (p-value?

2012-01-01

162

Ear Acupressure, Heart Rate, and Heart Rate Variability in Patients with Insomnia  

PubMed Central

This high-tech “teleacupuncture study” describes a neurovegetative ear acupressure effect in patients with chronic insomnia by using heart rate variability analysis. Heart rate (HR) and heart rate variability (HRV) measurements in 31 patients (mean age?±?SD: 54.3?±?10.6 years) were performed under standardized conditions in Harbin, China, and the data analysis was performed in Graz, Austria. Similar to our previous clinical and basic teleacupuncture research works, the electrocardiograms (ECGs) were recorded by an HRV Medilog AR12 system during ear acupressure of the Shenmen point on the left ear. HR decreased significantly (P < 0.05) during and after acupressure stimulation. The effect was not visible after the first stimulation, rather it appeared in the phase following the second acupressure stimulation (10 min after the first stimulation). Total HRV showed significant stimulation-dependent increases (P < 0.05), immediately after each acupressure stimulation with a maximum after the third stimulation (20 min after the first stimulation), but there was no long-lasting effect. The present results can serve as a solid basis for the further investigations of auricular point stimulation for noninvasive complementary use in treating insomnia.

Wang, Lu; Cheng, Weiping; Sun, Zhongren; Xu, Yangyang; Cheng, Guangyu; Kuang, Haixue

2013-01-01

163

Heart rate variability and cognitive function: effects of physical effort.  

PubMed

This study investigated alterations in heart rate variability (HRV) and cognitive performance before and after physical effort, for 30 high-level track and field athletes (23 males and 7 females). Interbeat intervals were assessed at the baseline and during each task of a CogState cognitive battery (simple reaction time, choice reaction time, working memory, short-term memory and sustained attention). Time and frequency domain measures of HRV were compared between conditions and between tasks. The results indicated differences in HRV between executive and non-executive tasks. There was a significant increase in sympathetic-modulation-related indices after physical effort. The differences between executive and non-executive tasks were the same in post-test. Correlations were found between HRV and cognitive performance, which differed by speed and accuracy. We conclude that HRV is related to cognitive demand and that the correlation between HRV and cognitive performance seems to be stronger after physical exercise. The results raise questions about the psychophysiological meaning of different HRV signals and this has implications for future research about the relationship between HRV and cognition. PMID:19632295

Luft, Caroline Di Bernardi; Takase, Emílio; Darby, David

2009-10-01

164

Heart rate variability in type 2 diabetes mellitus.  

PubMed

Heart rate variability (HRV) is a noninvasive measure of cardiac autonomic modulation. Time and frequency domain measures have primarily been examined in patients with type 2 diabetes mellitus (T2D). Not only do frequency domain HRV parameters tend to be reduced in T2D, but healthy individuals with low HRV are also more likely to develop T2D. Furthermore, patients with T2D with low HRV have an increased prevalence of complications and risk of mortality compared with those with normal autonomic function. These findings provide support for the use of HRV as a risk indicator in T2D. Exercise is considered an important component to T2D prevention and treatment strategies. To date, few studies have examined the changes in HRV with exercise in T2D. One study showed changes in resting HRV, two studies showed changes in HRV during or following acute stressors, and one study showed no changes in HRV but improvements in baroreflex sensitivity. The most pronounced changes in HRV were realized following the exercise intervention with the greatest frequency of supervised exercise sessions and with the greatest intensity and duration of exercise bouts. These findings suggest that exercise following current American College of Sports Medicine/American Diabetes Association guidelines may be important in the prevention and treatment of T2D to improve autonomic function and reduce the risk of complications and mortality. PMID:24580567

Stuckey, Melanie I; Petrella, Robert J

2013-01-01

165

Heart rate variability in patients with untreated Parkinson's disease.  

PubMed

The aim of this study was to evaluate cardiovascular responses as a marker of autonomic nervous system (ANS) disturbances in patients with untreated Parkinson's disease (PD) and to assess the relationship between them and the clinical characteristics of PD. The ANS functions were investigated in 50 patients with PD and 55 healthy subjects by measuring standard cardiovascular autonomic reflexes and heart rate variability (HRV) at rest using spectral analysis (the autoregressive model and the fast Fourier transformation), the percentage of the counts of beat-to-beat variation greater than 50 ms and the fractal dimension. Significantly attenuated HRV and deficient blood pressure reaction to tilting were found in the PD patient group. The patients with hypokinesia/rigidity as the initial symptom of PD had a more pronounced HRV deficit than those with tremor onset. Untreated PD patients suffer significant failure in cardiovascular nervous system regulation, and in patients with hypokinesia/rigidity as their initial disease manifestation the risk of this ANS dysfunction is high. However, in the early stages of PD these changes did not reach significance at individual level. PMID:11136353

Kallio, M; Haapaniemi, T; Turkka, J; Suominen, K; Tolonen, U; Sotaniemi, K; Heikkilä, V P; Myllylä, V

2000-11-01

166

Nonlinear Control of Heart Rate Variability in Human Infants  

NASA Astrophysics Data System (ADS)

Nonlinear analyses of infant heart rhythms reveal a marked rise in the complexity of the electrocardiogram with maturation. We find that normal mature infants (gestation >= 35 weeks) have complex and distinctly nonlinear heart rhythms (consistent with recent reports for healthy adults) but that such nonlinearity is lacking in preterm infants (gestation <= 27 weeks) where parasympathetic-sympathetic interaction and function are presumed to be less well developed. Our study further shows that infants with clinical brain death and those treated with atropine exhibit a similar lack of nonlinear feedback control. These three lines of evidence support the hypothesis championed by Goldberger et al. [Goldberger, A. L., Rigney, D. R. & West, B. J. (1990) Sci. Am. 262, 43-49] that autonomic nervous system control underlies the nonlinearity and possible chaos of normal heart rhythms. This report demonstrates the acquisition of nonlinear heart rate dynamics and possible chaos in developing human infants and its loss in brain death and with the administration of atropine. It parallels earlier work documenting changes in the variability of heart rhythms in each of these cases and suggests that nonlinearity may provide additional power in characterizing physiological states.

Sugihara, George; Allan, Walter; Sobel, Daniel; Allan, Kenneth D.

1996-03-01

167

Kubios HRV--heart rate variability analysis software.  

PubMed

Kubios HRV is an advanced and easy to use software for heart rate variability (HRV) analysis. The software supports several input data formats for electrocardiogram (ECG) data and beat-to-beat RR interval data. It includes an adaptive QRS detection algorithm and tools for artifact correction, trend removal and analysis sample selection. The software computes all the commonly used time-domain and frequency-domain HRV parameters and several nonlinear parameters. There are several adjustable analysis settings through which the analysis methods can be optimized for different data. The ECG derived respiratory frequency is also computed, which is important for reliable interpretation of the analysis results. The analysis results can be saved as an ASCII text file (easy to import into MS Excel or SPSS), Matlab MAT-file, or as a PDF report. The software is easy to use through its compact graphical user interface. The software is available free of charge for Windows and Linux operating systems at http://kubios.uef.fi. PMID:24054542

Tarvainen, Mika P; Niskanen, Juha-Pekka; Lipponen, Jukka A; Ranta-Aho, Perttu O; Karjalainen, Pasi A

2014-01-01

168

Classification of heart rate variability in patients with mild hypertension.  

PubMed

The diagnostic performance of two pattern classification methods to detect hypertension was evaluated in a population of 29 mildly hypertensive and 20 normal subjects. The heart rate variability (HRV) signal of each subject was recorded during rest and isometric handgrip exercise. Feature vectors composed of up to 6 features from both the time and frequency domain representation of the HRV signal were constructed and applied to a Bayes' likelihood classifier and a voting k-nearest neighbours classifier. Each subject was classified as hypertensive or normal, and the classification compared to the clinical diagnosis for each subject. The diagnostic performance of each classifier/feature vector combination was evaluated using the leave-one-out method. The best performance of 90% correct classifications was achieved using a nearest neighbour classifier, a Euclidean distance metric and 3 features. The Bayes' classifier achieved a best performance of 84% correct classification. The work shows promise for the detection of the autonomic disturbance which precedes and accompanies the hypertensive state. PMID:9503692

Raymond, B; Taverner, D; Nandagopal, D; Mazumdar, J

1997-12-01

169

Population growth rates: issues and an application.  

PubMed Central

Current issues in population dynamics are discussed in the context of The Royal Society Discussion Meeting 'Population growth rate: determining factors and role in population regulation'. In particular, different views on the centrality of population growth rates to the study of population dynamics and the role of experiments and theory are explored. Major themes emerging include the role of modern statistical techniques in bringing together experimental and theoretical studies, the importance of long-term experimentation and the need for ecology to have model systems, and the value of population growth rate as a means of understanding and predicting population change. The last point is illustrated by the application of a recently introduced technique, integral projection modelling, to study the population growth rate of a monocarpic perennial plant, its elasticities to different life-history components and the evolution of an evolutionarily stable strategy size at flowering.

Godfray, H Charles J; Rees, Mark

2002-01-01

170

Testing the effect of metabolic rate on DNA variability at the intra-specific level.  

PubMed

We tested the metabolic rate hypothesis (whereby rates of mtDNA evolution are postulated to be mediated primarily by mutagenic by-products of respiration) by examining whether mass-specific metabolic rate was correlated with root-to-tip distance on a set of mtDNA trees for the springtail Cryptopygus antarcticus travei from sub-Antarctic Marion Island.Using Bayesian analyses and a novel application of the comparative phylogenetic method, we did not find significant evidence that contemporary metabolic rates directly correlate with mutation rate (i.e., root-to-tip distance) once the underlying phylogeny is taken into account. However, we did find significant evidence that metabolic rate is dependent on the underlying mtDNA tree, or in other words, lineages with related mtDNA also have similar metabolic rates.We anticipate that future analyses which apply this methodology to datasets with longer sequences, more taxa, or greater variability will have more power to detect a significant direct correlation between metabolic rate and mutation rate. We conclude with suggestions for future analyses that would extend the preliminary approach applied here, in particular highlighting ways to tease apart oxidative stress effects from the effects of population size and/or selection coefficients operating on the molecular evolutionary rate. PMID:20300626

McGaughran, Angela; Holland, Barbara R

2010-01-01

171

44 CFR 61.8 - Applicability of risk premium rates.  

Code of Federal Regulations, 2013 CFR

...Applicability of risk premium rates...8 Emergency Management and Assistance FEDERAL EMERGENCY MANAGEMENT AGENCY, DEPARTMENT...Applicability of risk premium rates...structure, the construction or...

2013-10-01

172

LF/(LF+HF) index in ventricular repolarization variability correlated and uncorrelated with heart rate variability.  

PubMed

The purpose of this study, was to asses whether LF/(LF+HF) obtained from ventricular repolarization variability (VRV) reflects the state of sympathovagal balance. The VRV time series and heart rate variability (HRV) time series from seventy two electrocardiogram (ECG) records in four different autonomic nervous system (ANS) profiles (athletes, cardiac transplant patient, heart failure patients and normal subjects) were extracted. A dynamic linear parametric model was applied to separate the VRV in two parts, VRV correlated with HRV (VRV(r)) and VRV uncorrelated with HRV (VRV(u)). Spectral indices were obtained from HRV, VRV, VRV(u) and VRV(u) time series. Changes of these indicators from rest to tilt position were analyzed. Results showed that: i) only LF/(LF+HF) from HRV time series increases significantly from rest to tilt in all ANS profiles, this information could not be retrieved in the other three series (VRV, VRV (u) and VRV(u)) ii) LF/(LF+HF) index in HRV series are significantly different between normal subjects and heart failure patients, while cardiac transplant patients show a low coherence between HRV and VRV power spectra and iii) HF rhythm in VRV series seem to be related to the mechanical effect of respiration. PMID:17946042

Altuve, M; Wong, S; Passariello, G; Carrault, G; Hernandez, A

2006-01-01

173

LF/(LF+HF) index in ventricular repolarization variability correlated and uncorrelated with heart rate variability  

PubMed Central

The purpose of this study, was to asses whether LF/(LF+HF) obtained from ventricular repolarization variability (VRV) reflects the state of sympathovagal balance. The VRV time series and Heart Rate Variability (HRV) time series from seventy two electrocardiogram (ECG) records in four different Autonomic Nervous System (ANS) profiles (athletes, cardiac transplant patient, heart failure patients and normal subjects) were extracted. A dynamic linear parametric model was applied to separate the VRV in two parts, VRV correlated with HRV (VRVr) and VRV uncorrelated with HRV (VRVu). Spectral indices were obtained from HRV, VRV, VRVu and VRVu time series. Changes of these indicators from rest to tilt position were analyzed. Results showed that: i) only LF/(LF+HF) from HRV time series increases significantly from rest to tilt in all ANS profiles, this information could not be retrieved in the other three series (VRV, VRVu and VRVu), ii) LF/(LF+HF) index in HRV series are significantly different between normal subjects and heart failure patients, while cardiac transplant patients show a low coherence between HRV and VRV power spectra and iii) HF rhythm in VRV series seem to be related to the mechanical effect of respiration.

Altuve, Miguel; Wong, Sara; Passariello, Gianfranco; Carrault, Guy; Hernandez, Alfredo I.

2006-01-01

174

Heart Rate Variability and Blood Pressure during Dynamic and Static Exercise at Similar Heart Rate Levels  

PubMed Central

Aim was to elucidate autonomic responses to dynamic and static (isometric) exercise of the lower limbs eliciting the same moderate heart rate (HR) response. Method: 23 males performed two kinds of voluntary exercise in a supine position at similar heart rates: static exercise (SE) of the lower limbs (static leg press) and dynamic exercise (DE) of the lower limbs (cycling). Subjective effort, systolic (SBP) and diastolic blood pressure (DBP), mean arterial pressure (MAP), rate pressure product (RPP) and the time between consecutive heart beats (RR-intervals) were measured. Time-domain (SDNN, RMSSD), frequency-domain (power in the low and high frequency band (LFP, HFP)) and geometric measures (SD1, SD2) as well as non-linear measures of regularity (approximate entropy (ApEn), sample entropy (SampEn) and correlation dimension D2) were calculated. Results: Although HR was similar during both exercise conditions (88±10 bpm), subjective effort, SBP, DBP, MAP and RPP were significantly enhanced during SE. HRV indicators representing overall variability (SDNN, SD 2) and vagal modulated variability (RMSSD, HFP, SD 1) were increased. LFP, thought to be modulated by both autonomic branches, tended to be higher during SE. ApEn and SampEn were decreased whereas D2 was enhanced during SE. It can be concluded that autonomic control processes during SE and DE were qualitatively different despite similar heart rate levels. The differences were reflected by blood pressure and HRV indices. HRV-measures indicated a stronger vagal cardiac activity during SE, while blood pressure response indicated a stronger sympathetic efferent activity to the vessels. The elevated vagal cardiac activity during SE might be a response mechanism, compensating a possible co-activation of sympathetic cardiac efferents, as HR and LF/HF was similar and LFP tended to be higher. However, this conclusion must be drawn cautiously as there is no HRV-marker reflecting “pure” sympathetic cardiac activity.

Weippert, Matthias; Behrens, Kristin; Rieger, Annika; Stoll, Regina; Kreuzfeld, Steffi

2013-01-01

175

Heart rate variability in overactive bladder experimental model  

PubMed Central

Introduction Two main pathophysiological concepts of overactive bladder (OAB) are postulated: the neurogenic and myogenic theories. Autonomic nervous system (ANS) dysfunction is also involved in OAB pathophysiology. The purpose of our study was to estimate ANS activity by heart rate variability (HRV) assessment in two OAB experimental models evoked by cyclophosphamide administration: acute (AOAB) and chronic (COAB) overactive ones. Material and methods In the AOAB model, an i.p. dose of cyclophosphamide was administered (200 mg/kg body weight) while the COAB model received 4 times the i.p. administration of cyclophosphamide (75 mg/kg body weight). In each subject, after urethane anaesthesia (1.2 g/kg body weight), 20-minute ECG recordings (PowerLab) were performed with subsequent HRV analysis. Results Most of the differences in time domain analysis parameters were insignificant, except those concerning SDNN and rMSSD (p < 0.05). In frequency analysis, a power decrease of all standard spectral components was revealed in both OAB groups. In AOAB, TP (1.43 ±1.21 vs. 7.92 ±6.22 in control; p < 0.05) and VLF (0.95 ±1.08 vs. 6.97 ±5.99 in control; p < 0.05) showed significant power decrease, whereas the COAB group was mostly characterized by LF (0.09 ±0.15 vs. 0.34 ±0.33 in control; p < 0.05) and HF (0.25 ±0.29 vs. 0.60 ±0.41 in control; p < 0.05) decrease. Conclusions The ANS disturbances, found as standard spectral parameter abnormalities, were demonstrated in both AOAB and COAB. When this finding is analysed, together with the lack of statistically significant differences in normalized nLF and nHF powers, the VLF changes seem to play an essential role, probably reflecting the progression in bladder inflammatory changes.

Thor, Piotr

2012-01-01

176

Reappraisal of heart rate variability in acute ischemic stroke.  

PubMed

Cardiac autonomic dysfunction is a common complication after acute ischemic stroke (IS). Prior investigators have emphasized that infarction of brain stem or hemispheres with insular involvement is related to this dysfunction and may predict poor clinical outcome. From the viewpoint of stroke physicians, however, all stroke patients, particularly large-artery atherosclerosis (LAA) should be monitored for possible cardiac complications after acute IS. This study aimed to investigate cardiac autonomic impaction in patients with acute IS and to make the comparison between LAA and small-vessel occlusion (SVO) subtypes. Of the 126 acute IS patients prospectively enrolled in this study, 32 had LAA, 56 had SVO, and 38 had undetermined etiology according to the Trial of Org 10172 in Acute Stroke Treatment criteria. Cardiac autonomic function of all patients was assessed by measuring heart rate variability (HRV). The low- and high-frequency components of HRV in all stroke patients were significantly lower than those of control subjects after comparing multivariable models, including additional adjustments for age, gender, and all risk factors. There were no significant differences on HRV between LAA and SVO although post hoc comparisons showed that stroke patients of SVO had increased sympathetic modulation and reduced vagal activity. In conclusion, in acute IS patients, both LAA and SVO are predisposed to have cardiac autonomic dysfunction, manifesting as abnormalities in HRV, whether in hemispheric or brain stem lesions. Stroke patients of SVO are at higher risks of cardiac abnormalities, which might suggest an early cardiac dysfunction because of long-term hypertension. The HF component of HRV thought to be for vagal control might be a cardinal marker for predicting cardiac autonomic dysfunction after acute IS. Short-term HRV spectral analysis is a convenient approach for stroke clinicians to assess autonomic function in acute stroke. Long-term follow-up for HRV and clinical outcome relative to LAA and SVO stroke subtypes is warranted, particularly when an abnormal HRV is found at admission. PMID:21601166

Chen, Chien-Fu; Lai, Chiou-Lian; Lin, Hsiu-Fen; Liou, Li-Min; Lin, Ruey-Tay

2011-06-01

177

Estimating mental fatigue based on electroencephalogram and heart rate variability  

NASA Astrophysics Data System (ADS)

The effects of long term mental arithmetic task on psychology are investigated by subjective self-reporting measures and action performance test. Based on electroencephalogram (EEG) and heart rate variability (HRV), the impacts of prolonged cognitive activity on central nervous system and autonomic nervous system are observed and analyzed. Wavelet packet parameters of EEG and power spectral indices of HRV are combined to estimate the change of mental fatigue. Then wavelet packet parameters of EEG which change significantly are extracted as the features of brain activity in different mental fatigue state, support vector machine (SVM) algorithm is applied to differentiate two mental fatigue states. The experimental results show that long term mental arithmetic task induces the mental fatigue. The wavelet packet parameters of EEG and power spectral indices of HRV are strongly correlated with mental fatigue. The predominant activity of autonomic nervous system of subjects turns to the sympathetic activity from parasympathetic activity after the task. Moreover, the slow waves of EEG increase, the fast waves of EEG and the degree of disorder of brain decrease compared with the pre-task. The SVM algorithm can effectively differentiate two mental fatigue states, which achieves the maximum classification accuracy (91%). The SVM algorithm could be a promising tool for the evaluation of mental fatigue. Fatigue, especially mental fatigue, is a common phenomenon in modern life, is a persistent occupational hazard for professional. Mental fatigue is usually accompanied with a sense of weariness, reduced alertness, and reduced mental performance, which would lead the accidents in life, decrease productivity in workplace and harm the health. Therefore, the evaluation of mental fatigue is important for the occupational risk protection, productivity, and occupational health.

Zhang, Chong; Yu, Xiaolin

2010-01-01

178

Wavelet transform analysis of heart rate variability during myocardial ischaemia.  

PubMed

Analysis of heart rate variability (HRV) is a valuable, non-invasive method for quantifying autonomic cardiac control in humans. Frequency-domain analysis of HRV involving myocardial ischaemic episodes should take into account its non-stationary behaviour. The wavelet transform is an alternative tool for the analysis of non-stationary signals. Fourteen patients have been analysed, ranging from 40 to 64 years old and selected from the European Electrocardiographic ST-T Database (ESDB). These records contain 33 ST episodes, according to the notation of the ESDB, with durations of between 40s and 12 min. A method for analysing HRV signals using the wavelet transform was applied to obtain a time-scale representation for very low-frequency (VLF), low-frequency (LF) and high-frequency (HF) bands using the orthogonal multiresolution pyramidal algorithm. The design and implementation using fast algorithms included a specially adapted decomposition quadrature mirror filter bank for the frequency bands of interest. Comparing a normality zone against the ischaemic episode in the same record, increases in LF (0.0112 +/- 0.0101 against 0.0175 +/- 0.0208 s2 Hz(-1); p<0.1) and HF (0.0011 +/- 0.0008 against 0.00 17 +/- 0.0020 s2 Hz(-1); p<0.05) were obtained. The possibility of using these indexes to develop an ischaemic-episode classifier was also tested. Results suggest that wavelet analysis provides useful information for the assessment of dynamic changes and patterns of HRV during myocardial ischaemia. PMID:11954711

Gamero, L G; Vila, J; Palacios, F

2002-01-01

179

Heart Rate Variability in Men with Erectile dysfunction  

PubMed Central

Purpose The objective of this study is to investigate alteration of autonomic nervous system (ANS) activity in patients suffering from erectile dysfunction (ED) by comparing parameters of heart rate variability (HRV) between men with ED and healthy subjects. Methods A retrospective review was performed on 40 ED patients (mean age, 46.0±8.49 years) without any disease and 180 healthy control people (mean age, 44.4±7.83 years) without ED in our institution from June 2008 to July 2010. And electrocardiographic signals were obtained to measure HRV parameters for both patients and controls in a resting state. Results For the time domain analysis, square root of the mean differences between successive RR intervals (RMSSD) representing parasympathetic activity was lower in patients than controls although P-value was not statistically significant (P=0.060). For the frequency domain analysis, high frequency (HF) representing parasympathetic activity was lower in patients than controls (P=0.232) and low frequency (LF) representing mainly sympathetic activity was higher in patients than controls (P=0.416). Lastly, LF/HF ratio reflecting sympathetic/parasympathetic activity ratio was statistically higher in patients than controls (P=0.027). Conclusions Patients with ED exhibited different HRV parameters compared with normal controls. This suggests that the patients with ED may have some kind of imbalance in the ANS and it may be possible that general imbalance of the ANS is one of the causes of ED. Thus, HRV analysis may give valuable diagnostic information and serve as a rapid screening tool to evaluate altered ANS activity in patients with ED.

Lee, Ji Yong; Joo, Kwan-Joong; Kim, Jin Tae; Cho, Sung Tae; Cho, Dae Sung; Won, Yong-Yeun

2011-01-01

180

Analysis of heart rate variability after a ranger training course.  

PubMed

We studied the effects of prolonged physical activities on resting heart rate variability (HRV) during a training session attended by 23 cadets of the French military academy. This course lasts 1 month and is concluded by a 5-day field exercise simulation with physical and psychological stress. Data collection took place before (B) and immediately at the end (E) of the course. It included HRV recordings during a stand test (5 minutes lying down and 5 minutes standing), with a Polar R-R monitor, followed by blood sampling to assay plasma testosterone. The results (B and E) showed that the testosterone level fell by approximately 28.6 +/- 7%, indicating a high level of fatigue. During the stand test, the total power (TP) of the HRV spectrum increased in a supine position. The TP of B was 5,515.7 ms2 (SE, 718.4) and of E was 13018.9 ms2 (SE, 2,539.2; p < 0.001). High-frequency (HF) normalized values increased and low-frequency (LF) normalized values fell, regardless of position (HF normalized values and LF normalized values: supine, p < 0.01, p < 0.05; standing, p < 0.05, p < 0.01, respectively). LF:HF ratio fell 66.2 (SE, 12.9%; p < 0.01) in a lying position. During the time-domain analysis of HRV, differences between adjacent normal R-R intervals more than 50 milliseconds, expressed as a percentage, and differences between the coupling intervals of adjacent normal RR intervals increased in the lying position (p < 0.001). These results as a whole suggest that parasympathetic nervous system activity increases with fatigue. PMID:15379067

Jouanin, Jean-Claude; Dussault, Caroline; Pérès, Michel; Satabin, Pascale; Piérard, Christophe; Guézennec, Charles Yannick

2004-08-01

181

Effect of early bereavement on heart rate and heart rate variability.  

PubMed

Early bereavement is associated with increased cardiovascular events. The mechanism, however, has not been well studied. We assessed whether bereavement is associated with an increased heart rate (HR) and decreased heart rate variability that might contribute to increased cardiovascular risk. A total of 78 bereaved spouses and parents (55 women and 23 men; aged 34 to 87 years, mean 65) were studied with 24-hour Holter monitoring within 2 weeks of bereavement (acute) and at 6 months. Their findings were compared to those from a nonbereaved reference group (52 women and 27 men) aged 33 to 91 years (mean 63.6). All participants were in sinus rhythm. We assessed the mean HR, atrial and ventricular arrhythmias, and both time and frequency domain heart rate variability measures. Acute bereavement was associated with increased 24-hour HR (mean ± SE, 75.1 ± 1.1 vs 70.7 ± 1.0; p = 0.004) and reduced heart rate variability, as indicated by lower standard deviation of the NN intervals index (median 45.4 vs 49.9, p = 0.017), total power (7.78 ± 0.10 vs 8.02 ± 0.09, p = 0.03), very low frequency (7.23 ± 0.09 vs 7.44, p = 0.046) and low frequency (5.76 ± 0.12 vs 6.16 ± 0.09, p = 0.01). At 6 months, the bereaved had a significantly lower HR (p = 0.001) and increased standard deviation of the NN intervals index (p = 0.02), square root of the mean square of differences of successive intervals (p = 0.045), number of interval differences of successive NN intervals >50 ms divided by the number of NN intervals (p = 0.039), low-frequency power (p = 0.02), and high frequency (p = 0.002) compared to the initial acute levels. In conclusion, the present study, the first to report 24-hour HR monitoring in the early weeks of bereavement, has demonstrated increased HR and altered autonomic function that might contribute to the increased cardiovascular events in early bereavement. PMID:22853984

Buckley, Thomas; Stannard, Angela; Bartrop, Roger; McKinley, Sharon; Ward, Christopher; Mihailidou, Anastasia Susie; Morel-Kopp, Marie-Christie; Spinaze, Monica; Tofler, Geoffrey

2012-11-01

182

Who Uses Physician-Rating Websites? Differences in Sociodemographic Variables, Psychographic Variables, and Health Status of Users and Nonusers of Physician-Rating Websites  

PubMed Central

Background The number of physician-rating websites (PRWs) is rising rapidly, but usage is still poor. So far, there has been little discussion about what kind of variables influence usage of PRWs. Objective We focused on sociodemographic variables, psychographic variables, and health status of PRW users and nonusers. Methods An online survey of 1006 randomly selected German patients was conducted in September 2012. We analyzed the patients’ knowledge and use of online PRWs. We also analyzed the impact of sociodemographic variables (gender, age, and education), psychographic variables (eg, feelings toward the Internet, digital literacy), and health status on use or nonuse as well as the judgment of and behavior intentions toward PRWs. The survey instrument was based on existing literature and was guided by several research questions. Results A total of 29.3% (289/986) of the sample knew of a PRW and 26.1% (257/986) had already used a PRW. Younger people were more prone than older ones to use PRWs (t 967=2.27, P=.02). Women used them more than men (?2 1=9.4, P=.002), the more highly educated more than less educated people (?2 4=19.7, P=.001), and people with chronic diseases more than people without (?2 1=5.6, P=.02). No differences were found between users and nonusers in their daily private Internet use and in their use of the Internet for health-related information. Users had more positive feelings about the Internet and other Web-based applications in general (t 489=3.07, P=.002) than nonusers, and they had higher digital literacy (t 520=4.20, P<.001). Users ascribed higher usefulness to PRWs than nonusers (t 612=11.61, P<.001) and users trusted information on PRWs to a greater degree than nonusers (t 559=11.48, P<.001). Users were also more likely to rate a physician on a PRW in the future (t 367=7.63, P<.001) and to use a PRW in the future (t 619=15.01, P<.001). The results of 2 binary logistic regression analyses demonstrated that sociodemographic variables (gender, age, education) and health status alone did not predict whether persons were prone to use PRWs or not. Adding psychographic variables and information-seeking behavior variables to the binary logistic regression analyses led to a satisfying fit of the model and revealed that higher education, poorer health status, higher digital literacy (at the 10% level of significance), lower importance of family and pharmacist for health-related information, higher trust in information on PRWs, and higher appraisal of usefulness of PRWs served as significant predictors for usage of PRWs. Conclusions Sociodemographic variables alone do not sufficiently predict use or nonuse of PRWs; specific psychographic variables and health status need to be taken into account. The results can help designers of PRWs to better tailor their product to specific target groups, which may increase use of PRWs in the future.

Bidmon, Sonja; Rottl, Johanna

2014-01-01

183

Variable neighborhood search: Principles and applications  

Microsoft Academic Search

Systematic change of neighborhood within a possibly randomized local search algorithm yields a simple and effective metaheuristic for combinatorial and global optimization, called variable neighborhood search (VNS). We present a basic scheme for this purpose, which can easily be implemented using any local search algorithm as a subroutine. Its effectiveness is illustrated by solving several classical combinatorial or global optimization

Pierre Hansen; Nenad Mladenovic

2001-01-01

184

Heart Rate Variability Analysis in the Assessment of Autonomic Function in Heart Failure.  

National Technical Information Service (NTIS)

Heart rate is not static but rather changes continuously in response to physical and mental demands. In fact, an invariant heart rate is associated with disease processes such as heart failure. Heart rate variability analysis is a noninvasive technique us...

M. J. De Jong D. C. Randall

2004-01-01

185

Endurance training guided individually by daily heart rate variability measurements.  

PubMed

Purpose of this study was to test utility of heart rate variability (HRV) in daily endurance exercise prescriptions. Twenty-six healthy, moderately fit males were randomized into predefined training group (TRA, n = 8), HRV-guided training group (HRV, n = 9), and control group (n = 9). Four-week training period consisted of running sessions lasting 40 min each at either low- or high-intensity level. TRA group trained on 6 days a week, with two sessions at low and four at high intensity. Individual training program for HRV group was based on individual changes in high-frequency R-R interval oscillations measured every morning. Increase or no change in HRV resulted in high-intensity training on that day. If there was significant decrease in HRV (below reference value [10-day mean-SD] or decreasing trend for 2 days), low-intensity training or rest was prescribed. Peak oxygen consumption (VO(2peak)) and maximal running velocity (Load(max)) were measured in maximal treadmill test before and after the training. In TRA group, Load(max) increased from 15.1 +/- 1.3 to 15.7 +/- 1.2 km h(-1) (P = 0.004), whereas VO(2peak) did not change significantly (54 +/- 4 pre and 55 +/- 3 ml kg(-1) min(-1) post, P = 0.224). In HRV group, significant increases were observed in both Load(max) (from 15.5 +/- 1.0 to 16.4 +/- 1.0 km h(-1), P < 0.001) and VO(2peak) (from 56 +/- 4 to 60 +/- 5 ml kg(-1) min(-1), P = 0.002). The change in Load(max) was significantly greater in HRV group compared to TRA group (0.5 +/- 0.4 vs. 0.9 +/- 0.2 km h(-1), P = 0.048, adjusted for baseline values). No significant differences were observed in the changes of VO(2peak) between the groups. We concluded that cardiorespiratory fitness can be improved effectively by using HRV for daily training prescription. PMID:17849143

Kiviniemi, Antti M; Hautala, Arto J; Kinnunen, Hannu; Tulppo, Mikko P

2007-12-01

186

Genus-Specific Substitution Rate Variability among Picornaviruses ?†  

PubMed Central

Picornaviruses have some of the highest nucleotide substitution rates among viruses, but there have been no comparisons of evolutionary rates within this broad family. We combined our own Bayesian coalescent analyses of VP1 regions from four picornaviruses with 22 published VP1 rates to produce the first within-family meta-analysis of viral evolutionary rates. Similarly, we compared our rate estimates for the RNA polymerase 3Dpol gene from five viruses to four published 3Dpol rates. Both a structural and a nonstructural gene show that enteroviruses are evolving, on average, a half order of magnitude faster than members of other genera within the Picornaviridae family.

Hicks, Allison L.; Duffy, Siobain

2011-01-01

187

A comparison of subjective and mathematical estimations of fetal heart rate variability  

Microsoft Academic Search

Objectives. To develop a computerized algorithm to quantify fetal heart rate (FHR) variability and compare it to perinatologists' interpretation of FHR variability. Methods. FHR variability was calculated using data from 30 women who had a fetal scalp electrode placed for a clinical indication, and compared to the assessment of FHR variability from four perinatologists who interpreted paper tracings of the

Adam J. Wolfberg; David J. Derosier; Trevor Roberts; Zeeshan Syed; Gari D. Clifford; David Acker; Adre Du Plessis

2008-01-01

188

The effect of heart rate on the heart rate variability response to autonomic interventions.  

PubMed

Heart rate variability (HRV), the beat-to-beat variation in either heart rate (HR) or heart period (R-R interval), has become a popular clinical and investigational tool to quantify cardiac autonomic regulation. However, it is not widely appreciated that, due to the inverse curvilinear relationship between HR and R-R interval, HR per se can profoundly influence HRV. It is, therefore, critical to correct HRV for the prevailing HR particularly, as HR changes in response to autonomic neural activation or inhibition. The present study evaluated the effects of HR on the HRV response to autonomic interventions that either increased (submaximal exercise, n = 25 or baroreceptor reflex activation, n = 20) or reduced (pharmacological blockade: ?-adrenergic receptor, muscarinic receptor antagonists alone and in combination, n = 25, or bilateral cervical vagotomy, n = 9) autonomic neural activity in a canine model. Both total (RR interval standard deviation, RRSD) and the high frequency (HF) variability (HF, 0.24-1.04 Hz) were determined before and in response to an autonomic intervention. All interventions that reduced or abolished cardiac parasympathetic regulation provoked large reductions in HRV even after HR correction [division by mean RRsec or (mean RRsec)(2) for RRSD and HF, respectively] while interventions that reduced HR yielded mixed results. ?-adrenergic receptor blockade reduced HRV (RRSD but not HF) while both RRSD and HF increased in response to increases in arterial blood (baroreceptor reflex activation) even after HR correction. These data suggest that the physiological basis for HRV is revealed after correction for prevailing HR and, further, that cardiac parasympathetic activity is responsible for a major portion of the HRV in the dog. PMID:23986716

Billman, George E

2013-01-01

189

Spectral analysis of heart rate variability in the sepsis syndrome  

Microsoft Academic Search

Sympathetic and parasympathetic activity was evaluated on 39 occasions in 17 patients with the sepsis syndrome, by measurement of the variation in resting heart rate using frequency spectrum analysis. Heart rate was recorded by electrocardiography and respiratory rate by impedance plethysmography. The sepsis syndrome was established on the basis of established clinical and physiological criteria. Subjects were studied, whenever possible,

Christopher S. Garrard; Dimitrios A. Kontoyannis; Massimo Piepoli

1993-01-01

190

Low and Variable Visitor Compliance Rates at Voluntary Trail Registers.  

National Technical Information Service (NTIS)

Only 20 percent of the visitors to the Bob Marshall Wilderness, Mont., during 1981 complied at voluntary trail registers. Rates varied from 0 for day-use horseback riders to 47 percent for backpackers. Summer rates were seven times as high as fall rates. ...

R. C. Lucas

1983-01-01

191

Heart rate variability is related to training load variables in interval running exercises.  

PubMed

Overload principle of training states that training load (TL) must be sufficient to threaten the homeostasis of cells, tissues, organs and/or body. However, there is no "golden standard" for TL measurement. The aim of the present study was to investigate if post-exercise heart rate variability (HRV) could be used to evaluate TL of interval running exercises with different intensities and durations. Thirteen endurance-trained men (35 ± 5 years) performed MO(250) [moderate intensity, 2 × 6 × 250 m/rec 30 s/5 min at 85% of the maximal velocity of the graded maximal test (V (max))], MO(500) (2 × 3 × 500 m/rec 1 min/5 min at 85% V (max)) and HI(250) (high intensity, 2 × 6 × 250 m/rec 30 s/5 min at 105% V (max)) interval exercises on a treadmill. HRV was analyzed during rest, exercise and immediate 15 min recovery. Fast recovery of LFP (P < 0.001), HFP (P < 0.01) and TP (P < 0.01) occurred during the first two recovery minutes after each exercise. Strong negative correlations (P < 0.01) were found between post-exercise HRV and perceived exertion as well as excess post-exercise oxygen consumption. Post-exercise HRV differentiated interval exercises of equal work, but varying intensity or distance of running bout. The results of the present study suggest that immediate post-exercise HRV may offer objective information on TL of interval exercises with different bout durations and intensities. PMID:21678140

Kaikkonen, Piia; Hynynen, Esa; Mann, Theresa; Rusko, Heikki; Nummela, Ari

2012-03-01

192

Heart rate and heart rate variability modification in chronic insomnia patients.  

PubMed

Chronic insomnia is highly prevalent in the general population, provoking personal distress and increased risk for psychiatric and medical disorders. Autonomic hyper-arousal could be a pathogenic mechanism of chronic primary insomnia. The aim of this study was to investigate autonomic activity in patients with chronic primary insomnia by means of heart rate variability (HRV) analysis. Eighty-five consecutive patients affected by chronic primary insomnia were enrolled (38 men and 47 women; mean age: 53.2 ± 13.6). Patients were compared with a control group composed of 55 healthy participants matched for age and gender (23 men and 32 women; mean age: 54.2 ± 13.9). Patients underwent an insomnia study protocol that included subjective sleep evaluation, psychometric measures, and home-based polysomnography with evaluation of HRV in wake before sleep, in all sleep stages, and in wake after final awakening. Patients showed modifications of heart rate and HRV parameters, consistent with increased sympathetic activity, while awake before sleep and during Stage-2 non-REM sleep. No significant differences between insomniacs and controls could be detected during slow-wave sleep, REM sleep, and post-sleep wake. These results are consistent with the hypothesis that autonomic hyper-arousal is a major pathogenic mechanism in primary insomnia, and confirm that this condition is associated with an increased cardiovascular risk. PMID:24128278

Farina, Benedetto; Dittoni, Serena; Colicchio, Salvatore; Testani, Elisa; Losurdo, Anna; Gnoni, Valentina; Di Blasi, Chiara; Brunetti, Riccardo; Contardi, Anna; Mazza, Salvatore; Della Marca, Giacomo

2014-07-01

193

Continuously Variable Transmission: Assessment of Applicability to Advance Electric Vehicles.  

National Technical Information Service (NTIS)

A brief historical account of the evolution of continuously variable transmissions (CVT) for automotive use is given. The CVT concepts which are potentially suitable for application with electric and hybrid vehicles are discussed. The arrangement and func...

R. J. Parker S. H. Loewenthal

1981-01-01

194

Continuously Variable Transmission: Assessment of Applicability to Advanced Electric Vehicles.  

National Technical Information Service (NTIS)

A brief historical account of the evolution of continuously variable transmissions (CVT) for automotive use is given. CVT concepts which are potentially suitable for application with electric and hybrid vehicles are discussed. The arrangement and function...

S. H. Loewenthal R. J. Parker

1981-01-01

195

On the nature of heart rate variability in a breathing normal subject: A stochastic process analysis  

NASA Astrophysics Data System (ADS)

Human heart rate is moderated by the autonomous nervous system acting predominantly through the sinus node (the main cardiac physiological pacemaker). One of the dominant factors that determine the heart rate in physiological conditions is its coupling with the respiratory rhythm. Using the language of stochastic processes, we analyzed both rhythms simultaneously taking the data from polysomnographic recordings of two healthy individuals. Each rhythm was treated as a sum of a deterministic drift term and a diffusion term (Kramers-Moyal expansion). We found that normal heart rate variability may be considered as the result of a bidirectional coupling of two nonlinear oscillators: the heart itself and the respiratory system. On average, the diffusion (noise) component measured is comparable in magnitude to the oscillatory (deterministic) term for both signals investigated. The application of the Kramers-Moyal expansion may be useful for medical diagnostics providing information on the relation between respiration and heart rate variability. This interaction is mediated by the autonomous nervous system, including the baroreflex, and results in a commonly observed phenomenon-respiratory sinus arrhythmia which is typical for normal subjects and often impaired by pathology.

Buchner, Teodor; Petelczyc, Monika; ?ebrowski, Jan J.; Prejbisz, Aleksander; Kabat, Marek; Januszewicz, Andrzej; Piotrowska, Anna Justyna; Szelenberger, Waldemar

2009-06-01

196

Heart rate variability, trait anxiety, and perceived stress among physically fit men and women  

Microsoft Academic Search

Background: It is unclear from prior reports whether the relationships between self-ratings of anxiety or emotional stress and parasympathetic nervous system components of heart rate variability are independent of personality and cardiorespiratory fitness. We examined those relationships in a clinical setting prior to a standardized exercise test. Methods and results: Heart rate variability (HRV) was measured during 5 min of

Rod K. Dishman; Yoshio Nakamura; Melissa E. Garcia; Ray W. Thompson; Andrea L. Dunn; Steven N. Blair

2000-01-01

197

An oversimplified inquiry into the sources of exchange rate variability  

Microsoft Academic Search

Real exchange rates as well as relative price level and output movements are decomposed into components associated with nominal shocks as well as shocks to aggregate supply and aggregate demand. In contrast to previous analyses of such decompositions based on statistical vector autoregression (VAR) analysis, this study takes as a starting point a simple textbook model of exchange rate determination,

Bernd Kempa

2005-01-01

198

Understanding garnet variability: Application of geometallurgy to diamonds and exploration  

NASA Astrophysics Data System (ADS)

Peridotitic and eclogitic garnets are a fundamental component in understanding mantle petrology, diamond petrogenesis, and the ascent of mantle materials in kimberlites. They are also critical in exploration programs, as the presence of mantle garnets at the earth's surface provides an indication of dispersion from a deeply derived magmatic carrier. The composition of these garnets further is used as an indicator of diamond prospectivity, on the basis of comparison with garnet compositions known to be in some degree of equilibrium with diamonds. For mantle xenoliths and kimberlites, optical microscopy, electron microprobe analysis (EPMA), and scanning electron microscopy (SEM) are the main tools used for understanding key mineralogical and textural variability relationships. Mineralogy and texture reflect diamond genesis, metasomatic alteration, fluid migration and manifestation, volcanological processes, peridotite disaggregation, and other manifestations of mantle processes that are observable, describable, and applicable in exploration and mining. Mineralogy and texture studies lead to further questions that are better addressed by higher resolution chemical analysis of isotopes and rare earth elements, or luminescence. Understanding mineralogical and textural variability is the primary geological input for geometallurgy (geomet), the field integrating the earth sciences with the extractive industries. The framework for geomet encompasses geology, mineralogy, deposit modeling and extraction methods for the optimum value return of resources, and it relies on the fact that the mineralogy and texture of rocks influence subsequent interpretation and downstream applications. Developments in this area have been made possible by the new generation of high-speed SEM-based quantitative mineralogical instruments, enabling the statistical assessment of thousands of grains or particles, or samples, and their application to models for exploration, ore deposits, or geomet. For diamonds, this means identification and quantification of large mineralogical and textural data sets, and gives the geologist more involvement in model development. In this study, peridotitic and eclogitic garnets were examined in situ and as xenocrysts to gain understanding of the mineralogical and textural variability of the grains using SEM-based quantitative mineralogy. For concentrate garnets, the new technology presented here is the development of mineral definitions that reflect SEM counts and correlate with EPMA data. Internal compositional variability is mapped across individual grains as compared to EPMA spot analysis; designations of G10-G9 compositions, for example, are more complex when viewed in terms of individual internal grain compositional variability. The new mineral lists based on percentages of Ca-Cr count rates are compared to unknown garnets from exploration samples, and digitally categorized into bins reflecting potential diamond prospectivity or secondary alteration, as desired. The high analysis rate (approx. 150 determinations/second) means the SEM-based technique can be faster and produce more statistical information for the geologist who is making the model assessment in the field. Combined with new nontoxic mineral separation methodology in the field and software on the geologist's laptop, a great deal of interpretation can be accommodated in the field, at a reduced cost for shipping large volumes of samples to a central laboratory. Geomet for diamonds provides the mechanism for thinking of the entirety of a project, and using the geological and mineralogical information to predict process implications.

Hoal, K. O.; Appleby, S. K.; Stammer, J. G.

2009-05-01

199

Dimensional Analysis of Heart Rate Variability in Heart Transplant Recipients.  

National Technical Information Service (NTIS)

The authors discuss periodicities in the heart rate in normal and transplanted hearts. The authors then consider the possibility of dimensional analysis of these periodicities in transplanted hearts and problems associated with the record. (ERA citation 1...

J. P. Zbilut G. Mayer-Kress K. Geist

1987-01-01

200

Dimensional analysis of heart rate variability in heart transplant recipients  

SciTech Connect

We discuss periodicities in the heart rate in normal and transplanted hearts. We then consider the possibility of dimensional analysis of these periodicities in transplanted hearts and problems associated with the record.

Zbilut, J.P.; Mayer-Kress, G.; Geist, K.

1987-01-01

201

Transfer of Online Learning to Performance in Variable Application Environments  

ERIC Educational Resources Information Center

The use of online learning (OL) has increased dramatically in the last decade; however, many instructional methods used in OL training design have not been appropriately applied or developed. Complicating this phenomenon, learners of different organizations often find the application of training content problematic in variable application

Merkley, Rodney J.; Nichols, Susan

2007-01-01

202

Improved Variable Index constant false alarm rate radar processors  

Microsoft Academic Search

In the cases when the statistical distribution of range return samples are not known, constant false alarm rate (CFAR) processors can be used. Cell Averaging (CA) CFAR radar processors which have the best performance in Gaussian homogeneous environments, exhibits performance degradation in the presence of an interfering target or in regions of abrupt change in the backround clutter power. The

Y. C. U?n; K. M. U?ner

2010-01-01

203

A Jet Viscometer with Variable Rate of Shear  

Microsoft Academic Search

A viscometer consisting of a glass jet which is inserted in a closed system is described. With this instrument high rates of shear of the order of magnitude of 100,000 sec.?1 can be reached for hydraulic oils. Observations on straight mineral oils of sufficiently high viscosity to exclude turbulence, on refined rape oil, and on castor oil, showed that Poiseuille's

William John Morris; Robert Schnurmann

1946-01-01

204

Variable-clock-rate A/D converter  

NASA Technical Reports Server (NTRS)

Analog-to-digital (A/D) converter operates at two different rates (slow and fast) so that low amplitude noise is reduced without loss of transient response. During tracking, when sensitivity is important, slow clock reduces noise. In search mode, when signal may change rapidly, fast clock ensures rapid response.

Lipoma, P. C.

1980-01-01

205

Variable Rates of Evolution Among Drosophila Opsin Genes  

Microsoft Academic Search

DNA sequences and chromosomal locations of four Drosophila pseudoobscura opsin genes were compared with those from Drosophila melanogaster, to determine factors that influence the evolution of multigene families. Although the opsin proteins perform the same primary functions, the compar- isons reveal a wide range of evolutionary rates. Amino acid identities for the opsins range from 90% for Rh2 to more

John P. Carulli; Daniel L. Hart

1992-01-01

206

Perceptual mapping of multiple variable batteries by plotting supplementary variables in correspondence analysis of rating data  

Microsoft Academic Search

In this paper we consider the use of correspondence analysis (CA) of rating data. CA of rating data allows a joint representation of the rated items (e.g. attributes or products) and individuals. However, as the number of individuals increases, the interpretation of the CA map becomes difficult. To overcome this problem, we propose a method that allows the depiction of

Anna Torres; Michel van de Velden

2007-01-01

207

Effects of impaired glucose metabolism on heart rate variability and blood pessure variability in essential hpertensive patients  

Microsoft Academic Search

Summary  To investigate the effects of impaired glucose metabolism (IGM) on cardiovascular autonomic nervous systems in essential hypertensive\\u000a (EH) patients by comparing heart rate variability (HRV) and blood pressure variability (BPV) in EH patients with or without\\u000a type 2 diabetes mellitus (T2DM). Simultaneous 24-h recordings of ambulatory ECG and blood pressure monitoring were performed\\u000a in 36 male old patients with simple

Gang Wang

2006-01-01

208

The influence of ventilatory control on heart rate variability in children  

Microsoft Academic Search

The aim of this study was to determine the influence of breathing frequency and tidal volume on resting heart rate variability in children aged 9 years ( n = 29) and 16 years ( n = 19). Heart rate variability was measured in four conditions: (1) without the control of ventilation followed at random by (2) a fixed breathing frequency

Craig A. Williams; Philippe Lopes

2002-01-01

209

Heart rate variability: sleep stage, time of night, and arousal influences  

Microsoft Academic Search

Spectral analysis was used to assess heart rate variability in consecutive 5-min epochs during the night in 12 normal adults. Simultaneous time coding of EEG and digitized EKG allowed examination of heart rate variability as a function of sleep stage, time of night and presence of EEG arousal. The results replicated previous studies in showing increases in high frequency components

M. H. Bonnet; D. L. Arand

1997-01-01

210

Decreased heart rate variability in survivors of sudden cardiac death not associated with coronary artery disease  

Microsoft Academic Search

BACKGROUND--Although heart rate variability has already been studied in survivors of sudden cardiac death secondary to coronary artery disease, an assessment of heart rate variability in survivors of sudden cardiac death not associated with coronary artery disease has not been made. METHODS--10 patients with aborted sudden cardiac death not associated with coronary artery disease (seven patients with primary ventricular fibrillation

J Singh; M. H. Anderson; D. Katritsis; J. Sneddon; D. J. Statters; M. Malik; A. J. Camm

1994-01-01

211

Effect of exercise training on heart rate variability in healthy older adults  

Microsoft Academic Search

Objective To determine the effect of exercise training on cardiac autonomic modulation in normal older adults by using analysis of heart rate variability. Subjects The exercise group consisted of 7 men and 9 women aged 66 ± 4 years. The comparison group consisted of 7 men and 9 women also aged 66 ± 4 years. Method Heart rate variability was

Phyllis K. Stein; Ali A. Ehsani; Peter P. Domitrovich; Robert E. Kleiger; Jeffrey N. Rottman

1999-01-01

212

Variable temperature effects on release rates of readily soluble nuclides  

SciTech Connect

In this paper we study the effect of temperature on the release rate of readily soluble nuclides, as affected by a time-temperature dependent diffusion coefficient. In this analysis ground water fills the voids in the waste package at t = 0 and one percent of the inventories of cesium and iodine are immediately dissolved into the void water. Mass transfer resistance of partly failed container and cladding is conservatively neglected. The nuclides move through the void space into the surrounding rock under a concentration gradient. We use an analytic solution to compute the nuclide concentration in the gap or void, and the mass flux rate into the porous rock. 8 refs., 4 figs.

Kim, C.-L.; Light, W.B.; Lee, W.W.-L.; Chambre, P.L.; Pigford, T.H. (Korea Advanced Energy Research Inst., Daeduk (Republic of Korea); Lawrence Berkeley Lab., CA (USA))

1988-09-01

213

Scheduling variable rate links via a spectrum server  

Microsoft Academic Search

We consider a centralized spectrum server that coordinates the transmissions of a group of links sharing a common spectrum. Links employ on-off modulation with fixed transmit power when active. In the on state, a link obtains a data rate determined by the signal-to-interference ratio on the link. By knowing the link gains in the network, the spectrum server finds an

Chandrasekharan Raman; Roy D. Yates; Narayan B. Mandayam

2005-01-01

214

Approximate minimum bias multichannel spectral estimation for heart rate variability  

Microsoft Academic Search

Spectral decomposition of variations in heart rate permits noninvasive measurement of autonomic nervous activity in humans\\u000a and animals. Autonomic metrics based on spectral analysis are useful in monitoring clinical conditions such as diabetic neuropathy\\u000a and reinnervation in heart transplant patients. A persistent problem in deriving such autonomic measures is the prerequisite\\u000a of an accurate and unbiased power spectrum of heart

Eric G. Lovett; Joel B. Myklebust

1997-01-01

215

Heart rate and heart rate variability during a novel object test and a handling test in young horses  

Microsoft Academic Search

Forty-one Dutch Warmblood immature horses were used in a study to quantify temperamental traits on the basis of heart rate (HR) and heart rate variability (HRV) measures. Half of the horses received additional training from the age of 5 months onwards; the other half did not. Horses were tested at 9, 10, 21 and 22 months of age in a

E. K. Visser; C. G. van Reenen; M. B. H. Schilder; J. H. Knaap; A. Barneveld; H. J. Blokhuis

2002-01-01

216

Human heart rate variability relation is unchanged during motion sickness  

NASA Technical Reports Server (NTRS)

In a study of 18 human subjects, we applied a new technique, estimation of the transfer function between instantaneous lung volume (ILV) and instantaneous heart rate (HR), to assess autonomic activity during motion sickness. Two control recordings of ILV and electrocardiogram (ECG) were made prior to the development of motion sickness. During the first, subjects were seated motionless, and during the second they were seated rotating sinusoidally about an earth vertical axis. Subjects then wore prism goggles that reverse the left-right visual field and performed manual tasks until they developed moderate motion sickness. Finally, ILV and ECG were recorded while subjects maintained a relatively constant level of sickness by intermittent eye closure during rotation with the goggles. Based on analyses of ILV to HR transfer functions from the three conditions, we were unable to demonstrate a change in autonomic control of heart rate due to rotation alone or due to motion sickness. These findings do not support the notion that moderate motion sickness is manifested as a generalized autonomic response.

Mullen, T. J.; Berger, R. D.; Oman, C. M.; Cohen, R. J.

1998-01-01

217

ARTIFICIAL NEURAL NETWORK APPLICATION OF MODELLING FAILURE RATE FOR BOEING 737 TIRES  

Microsoft Academic Search

This paper presents an application of artificial neural network technique for predicting the failure rate of Boeing 737 tires. For this purpose, an artificial neural network model utilizing the feed-forward back- propagation algorithm as a learning rule is developed. The inputs to the neural network are the independent variables and the output is the failure rate of the tires. Two

Ahmed Z. Al-Garn; Ahmad Jamal

218

Conventional heart rate variability analysis of ambulatory electrocardiographic recordings fails to predict imminent ventricular fibrillation  

NASA Technical Reports Server (NTRS)

OBJECTIVES. The purpose of this report was to study heart rate variability in Holter recordings of patients who experienced ventricular fibrillation during the recording. BACKGROUND. Decreased heart rate variability is recognized as a long-term predictor of overall and arrhythmic death after myocardial infarction. It was therefore postulated that heart rate variability would be lowest when measured immediately before ventricular fibrillation. METHODS. Conventional indexes of heart rate variability were calculated from Holter recordings of 24 patients with structural heart disease who had ventricular fibrillation during monitoring. The control group consisted of 19 patients with coronary artery disease, of comparable age and left ventricular ejection fraction, who had nonsustained ventricular tachycardia but no ventricular fibrillation. RESULTS. Heart rate variability did not differ between the two groups, and no consistent trends in heart rate variability were observed before ventricular fibrillation occurred. CONCLUSIONS. Although conventional heart rate variability is an independent long-term predictor of adverse outcome after myocardial infarction, its clinical utility as a short-term predictor of life-threatening arrhythmias remains to be elucidated.

Vybiral, T.; Glaeser, D. H.; Goldberger, A. L.; Rigney, D. R.; Hess, K. R.; Mietus, J.; Skinner, J. E.; Francis, M.; Pratt, C. M.

1993-01-01

219

Scaling-up crop models for climate variability applications  

Microsoft Academic Search

Although most dynamic crop models have been developed and tested for the scale of a homogeneous plot, applications related to climate variability are often at broader spatial scales that can incorporate considerable heterogeneity. This study reviews issues and approaches related to applying crop models at scales larger than the plot. Perfect aggregate prediction at larger scales requires perfect integration of

J. W. Hansen; J. W. Jones

2000-01-01

220

Cooled variable nozzle radial turbine for rotor craft applications  

NASA Technical Reports Server (NTRS)

An advanced, small 2.27 kb/sec (5 lbs/sec), high temperature, variable area radial turbine was studied for a rotor craft application. Variable capacity cycles including single-shaft and free-turbine engine configurations were analyzed to define an optimum engine design configuration. Parametric optimizations were made on cooled and uncooled rotor configurations. A detailed structural and heat transfer analysis was conducted to provide a 4000-hour life HP turbine with material properties of the 1988 time frame. A pivoted vane and a moveable sidewall geometry were analyzed. Cooling and variable geometry penalties were included in the cycle analysis. A variable geometry free-turbine engine configuration with a design 1477K (2200 F) inlet temperature and a compressor pressure ratio of 16:1 was selected. An uncooled HP radial turbine rotor with a moveable sidewall nozzle showed the highest performance potential for a time weighted duty cycle.

Rogo, C.

1981-01-01

221

Bayesian variable selection for high dimensional generalized linear models: convergence rates of the fitted densities  

Microsoft Academic Search

Bayesian variable selection has gained much empirical success recently in a variety of applications when the number $K$ of explanatory variables $(x_1,...,x_K)$ is possibly much larger than the sample size $n$. For generalized linear models, if most of the $x_j$'s have very small effects on the response $y$, we show that it is possible to use Bayesian variable selection to

Wenxin Jiang

2007-01-01

222

[Heart rate variability is significantly reduced in non-diabetic patients with hypertension].  

PubMed

Introductions: Heart rate variability is reduced among patients with hypertension or those with diabetes mellitus. Hypertension and diabetes show frequent co-morbidity, but it is still not entirely clear whether heart arte variability is reduced in non-diabetic patients with hypertension. Aim: The aim of the authors was to evaluate the heart rate variability in hypertensive patients with and without diabetes and in control subjects. Method: 130 patients with hypertension, 48 patients with hypertension and type 2 diabetes mellitus, and 87 control subjects were involved in the study. Minimum, mean and maximum heart rate, and parameters of heart rate variability were measured. Results: The mean of minimum heart rate did not differ significantly between the three groups. However, all other parameters were significantly reduced in patients with hypertension with and without diabetes as compared to the control group. No significant differences were observed between hypertensive patients with and without diabetes mellitus. Conclusions: Heart rate variability is significantly reduced in non-diabetic patients with hypertension. It seems that type 2 diabetes results in no further significant reduction of heart rate variability in patients with hypertension. Orv. Hetil., 2014, 155(22), 865-870. PMID:24860051

Nagy, Krisztina; Sipos, Evelin; El Hadj Othmane, Taha

2014-06-01

223

Sympatho-vagal activity described by the complex and deterministic behavior of heart rate variability  

Microsoft Academic Search

Presents new variables to improve the characterization of autonomic nervous system function by analyzing heart rate variability. These new variables are the effective energies (Efe), defined from the Hartley-Shannon theorem, in the three frequency bands EfeVLF (0-0.04 Hz), EfeLF (0.04-0.15 Hz) and EfeHF (0.15-0.45 Hz). The effective energy is obtained using a complexity measure of the R-R signal (the Shannon

F. Claria; M. Vallverdu; A. Martinez; X Vifiolas; W. Zareba; A Bayes de Luna; P. Caminal

2001-01-01

224

PARTICULATE MATTER AND HEART RATE VARIABILITY AMONG ELDERLY RETIREES: THE BALTIMORE 1998 PM STUDY  

EPA Science Inventory

This study investigates the reported relationship between ambient fine particle pollution and impaired cardiac autonomic control in the elderly. Heart rate variability (HRV) among 56 elderly (mean age 82) nonsmoking residents of a retirement center in Baltimore County, Maryland,...

225

Variability in Constant-Load-Amplitude Fatigue Crack Growth Rates in Marine Environments.  

National Technical Information Service (NTIS)

This report describes the results of an interlaboratory test program conducted to (1) assess the variability in corrosion fatigue crack growth rate data obtained while using a proposed Navy standard test method, (2) identify and resolve problems with the ...

S. J. Gill T. W. Crooker

1985-01-01

226

Short-term heart rate variability--age dependence in healthy subjects.  

PubMed

Heart rate variability (HRV) analysis is an established method to characterize the autonomic regulation and is based mostly on 24h Holter recordings. The importance of short-term HRV (less than 30 min) for various applications is growing consistently. Major reasons for this are the suitability for ambulatory care and patient monitoring and the ability to provide an almost immediate test result. So far, there have been only a few studies that provided statistically relevant reference values for short-term HRV. In our study, 5 min short-term HRV indices were determined from 1906 healthy subjects. From these records, linear and nonlinear indices were extracted. To determine general age-related influences, HRV indices were compared from subjects aged 25-49 years with subjects aged 50-74 years. In a second approach, we examined the development of HRV indices by age in terms of age decades (25-34, 35-44, 45-54, 55-64 and 65-74 years). Our results showed significant variations of HRV indices by age in almost all domains. While marked dynamics in terms of parameter change (variability reduction) were observed in the first age decades, in particular the last two age decades showed certain constancy with respect to the HRV indices examined. PMID:22813869

Voss, A; Heitmann, A; Schroeder, R; Peters, A; Perz, S

2012-08-01

227

Heart Rate Variability in Idiopathic Dilated Cardiomyopathy: Characteristics and Prognostic Value  

Microsoft Academic Search

Objectives. This study was designed to evaluate heart rate variability (HRV) in patients with idiopathic dilated cardiomyopathy (IDC), to determine its correlation with hemodynamic variables and ventricular arrhythmias and to evaluate its prognostic value in IDC.Background. Previous studies have shown that HRV could predict arrhythmic events in patients after infarction, but the characteristics of HRV in IDC have not been

Laurent Fauchier; Dominique Babuty; Pierre Cosnay; Marie Laurence Autret; Jean Paul Fauchier

1997-01-01

228

Association of depression witk reduced heart rate variability in coronary artery disease  

Microsoft Academic Search

Decreased heart rate (HR) variability is an independent risk factor for mortality in cardiac populations. Clinical depression has also been associated with adverse outcomes in patients with coronary artery disease (CAD). This study tests the hypothesis that depressed patients with CAD have decreased HR variability compared with nondepressed CAD patients. Nineteen patients with angiographically documented CAD and either major or

Robert M. Carney; Roger D. Saunders; Kenneth E. Freedland; Phyllis Stein; Michael W. Rich; Allan S. Jaffe

1995-01-01

229

Bandwidth Requirements of Variable Bit Rate MPEG Sources in ATM Networks  

Microsoft Academic Search

The performance of variable bandwidth allocation schemes that estimate the required bandwidth for a variable-bit-rate (VBR) MPEG video source using a simple prediction algorithm is studied. The advantages of using a layered MPEG coder over the standard MPEG coder are discussed. A method for controlling a layered MPEG coder in order to reduce the effect of cell losses when compared

Pramod Pancha; Magda El Zarki

1993-01-01

230

Variable dual-frequency electrostatic wave launcher for plasma applications  

NASA Astrophysics Data System (ADS)

A variable tuning system is presented for launching two electrostatic waves concurrently in a magnetized plasma. The purpose of this system is to satisfy the wave launching requirements for plasma applications where maximal power must be coupled into two carefully tuned electrostatic waves while minimizing erosion to the launching antenna. Two parallel LC traps with fixed inductors and variable capacitors are used to provide an impedance match between a two-wave source and a loop antenna placed outside the plasma. Equivalent circuit analysis is then employed to derive an analytical expression for the normalized, average magnetic flux density produced by the antenna in this system as a function of capacitance and frequency. It is found with this metric that the wave launcher can couple to electrostatic modes at two variable frequencies concurrently while attenuating noise from the source signal at undesired frequencies. An example based on an experiment for plasma heating with two electrostatic waves is used to demonstrate a procedure for tailoring the wave launcher to accommodate the frequency range and flux densities of a specific two-wave application. This example is also used to illustrate a method based on averaging over wave frequencies for evaluating the overall efficacy of the system. The wave launcher is shown to be particularly effective for the illustrative example--generating magnetic flux densities in excess of 50% of the ideal case at two variable frequencies concurrently--with a high adaptability to a number of plasma dynamics and heating applications.

Jorns, Benjamin; Sorenson, Robert; Choueiri, Edgar

2011-12-01

231

Rats' performance on variable-interval schedules with a linear feedback loop between response rate and reinforcement rate.  

PubMed Central

Three experiments investigated whether rats are sensitive to the molar properties of a variable-interval (VI) schedule with a positive relation between response rate and reinforcement rate (i.e., a VI+ schedule). In Experiment 1, rats responded faster on a variable ratio (VR) schedule than on a VI+ schedule with an equivalent feedback function. Reinforced interresponse times (IRTs) were shorter on the VR as compared to the VI+ schedule. In Experiments 2 and 3, there was no systematic difference in response rates maintained by a VI+ schedule and a VI schedule yoked in terms of reinforcement rate. This was found both when the yoking procedure was between-subject (Experiment 2) and within-subject (Experiment 3). Mean reinforced IRTs were similar on both the VI+ and yoked VI schedules, but these values were more variable on the VI+ schedule. These results provided no evidence that rats are sensitive to the feedback function relating response rate to reinforcement rate on a VI+ schedule.

Reed, Phil; Hildebrandt, Tom; DeJongh, Julie; Soh, Mariane

2003-01-01

232

Heart Rate Variability during Exercise Performed below and above Ventilatory Threshold  

Microsoft Academic Search

COTTIN, F., C. MEDIGUE, P.-M. LEPRETRE, Y. PAPELIER, J.-P. KORALSZTEIN, and V. BILLAT. Heart Rate Variability during Exercise Performed below and above Ventilatory Threshold. Med. Sci. Sports Exerc., Vol. 36, No. 4, pp. 594 - 600, 2004. Purpose: To examine whether differences in heart rate variability (HRV) can distinguish sub- from supra-ventilatory-threshold exercise and whether the exercise duration at supra-threshold

FRANCOIS COTTIN; CLAIRE MEDIGUE; PIERRE-MARIE LEPRETRE; YVES PAPELIER; JEAN-PIERRE KORALSZTEIN; VERONIQUE BILLAT

2004-01-01

233

Inverse coupling between ultradian oscillations in delta wave activity and heart rate variability during sleep  

Microsoft Academic Search

Objective: We investigate the relationship between changes in heart rate variability and electroencephalographic (EEG) activity during sleep.Method: Nine male subjects with regular non-rapid-eye movement-rapid-eye movement (NREM-REM) sleep cycles were included in the study. They underwent EEG and cardiac recordings during one experimental night. Heart rate variability was determined over 5-min periods by the ratio of low frequency to low frequency

Gabrielle Brandenberger; Jean Ehrhart; François Piquard; Chantal Simon

2001-01-01

234

[Design of hand-held heart rate variability acquisition and analysis system].  

PubMed

A design of handheld heart rate variability acquisition and analysis system is proposed. The system collects and stores the patient's ECG every five minutes through both hands touching on the electrodes, and then -uploads data to a PC through USB port. The system uses software written in LabVIEW to analyze heart rate variability parameters, The parameters calculated function is programmed and generated to components in Matlab. PMID:23189641

Li, Kaiyuan; Wang, Buqing; Wang, Weidong

2012-07-01

235

Effects of head-down bed rest on complex heart rate variability: Response to LBNP testing  

NASA Technical Reports Server (NTRS)

Head-down bed rest is used to model physiological changes during spaceflight. We postulated that bed rest would decrease the degree of complex physiological heart rate variability. We analyzed continuous heart rate data from digitized Holter recordings in eight healthy female volunteers (age 28-34 yr) who underwent a 13-day 6 deg head-down bed rest study with serial lower body negative pressure (LBNP) trials. Heart rate variability was measured on a 4-min data sets using conventional time and frequency domain measures as well as with a new measure of signal 'complexity' (approximate entropy). Data were obtained pre-bed rest (control), during bed rest (day 4 and day 9 or 11), and 2 days post-bed rest (recovery). Tolerance to LBNP was significantly reduced on both bed rest days vs. pre-bed rest. Heart rate variability was assessed at peak LBNP. Heart rate approximate entropy was significantly decreased at day 4 and day 9 or 11, returning toward normal during recovery. Heart rate standard deviation and the ratio of high- to low-power frequency did not change significantly. We conclude that short-term bed rest is associated with a decrease in the complex variability of heart rate during LBNP testing in healthy young adult women. Measurement of heart rate complexity, using a method derived from nonlinear dynamics ('chaos theory'), may provide a sensitive marker of this loss of physiological variability, complementing conventional time and frequency domain statistical measures.

Goldberger, Ary L.; Mietus, Joseph E.; Rigney, David R.; Wood, Margie L.; Fortney, Suzanne M.

1994-01-01

236

Twenty-Four Hour Time Domain Heart Rate Variability and Heart Rate: Relations to Age and Gender Over Nine Decades  

Microsoft Academic Search

Objectives. This study sought to define the effects of age and gender effects on the normal range of time domain heart rate variability (HRV) over nine decades in healthy subjects.Background. Low HRV is considered an independent marker of mortality risk. However, the age-related decline in HRV may limit its predictive value, particularly in the elderly. Delineation of the range of

Ken Umetani; Donald H Singer; Rollin McCraty; Mike Atkinson

1998-01-01

237

Assessment of mental stress in warmblood horses: heart rate variability in comparison to heart rate and selected behavioural parameters  

Microsoft Academic Search

The aim of the study was to investigate whether heart rate variability (HRV) could assess alterations of the autonomic nervous system (ANS) at different levels of excitement. The behavioural and physiological responses of 20 warmblood horses to a challenging ground exercise task were studied. Prior to the experiment, the horses were evaluated at rest and during forward walking (FW). The

T. R. Rietmann; A. E. A. Stuart; P. Bernasconi; M. Stauffacher; J. A. Auer; M. A. Weishaupt

2004-01-01

238

Impacts of Variable-Rate Phosphorus Fertilization Based on Dense Grid Soil Sampling on Soil-Test Phosphorus and Grain Yield of Corn and Soybean  

Microsoft Academic Search

Most agricultural fields have high soil-test phosphorus (STP) vari- ability. Variable-rate (VR) technology facilitates application of differ- ent P rates over a field and could improve nutrient application and crop yield. Replicated strip trials (6-12 ha) were established at six Iowa fields and were evaluated during 4 yr to compare VR and fixed- rate (FR) P fertilization for corn (Zea

Manuel Bermudez; Antonio P. Mallarino

2007-01-01

239

MEMS variable optical attenuator (VOA) for DWDM applications  

NASA Astrophysics Data System (ADS)

Variable optical attenuators (VOAs) have wide applications in DWDM optical communication systems, for example, equalizing the power levers of different wavelength channels, flattening the gain of optical amplifiers, etc. A MEMS variable optical attenuator with fibers connectorized has been developed using proprietary drawbridge structure, which has achieved 1.5 dB insertion loss, 45 dB dynamic range and 37 ms response time, and requires only 8 V driving voltage. Finite element model and analytical model have also been studied and compared with the experimental data, showing that the two models predict the mechanical characteristics of MEMS VOA with reasonable accuracy.

Zhang, Xu M.; Liu, Ai Q.; Lu, Chao; Tang, Ding Y.; Wang, Fang; Liu, Zishun; Lu, C.

2002-04-01

240

Investigation of Rate-Controlled Speech for Training Applications.  

National Technical Information Service (NTIS)

Two experimental evaluations were conducted to obtain empirical data on the effects of rate-controlled speech variables upon the listening comprehension of Navy trainees using representative Navy training materials. The results of the first experiment ind...

J. H. Steinemann O. A. Larson

1973-01-01

241

Physical activity is a major contributor to the ultra low frequency components of heart rate variability  

PubMed Central

OBJECTIVE—To investigate the link between changes in level of physical activity and the pattern of heart rate variability during long term ambulatory monitoring.?DESIGN—Heart rate variability was measured simultaneously with a quantitative indicator of muscle activity by electromyography (EMG) in five men and five women while they did activities typical of daily life or while they rested for 2-3 hours. Spectral and cross spectral analyses were performed on both variables with standard fast Fourier transform.?RESULTS—There was a marked reduction in spectral power in the ultra low frequency band (< 0.003 Hz) on going from active to rest conditions for both heart rate variability (men 6187 (1801) v 410 (89) ms2/Hz; women 4056 (1161) v 2094 (801), mean (SEM); p < 0.01) and EMG (p < 0.001). Cross spectral analysis showed a strong positive gain between the EMG and heart rate variability signal that was virtually eliminated in the resting condition (p < 0.01). A sex-by-condition effect (p = 0.06) was noted with a reduction in total spectral power for heart rate variability during rest in men, while it increased slightly in women.?CONCLUSIONS—There is a quantitative link between muscle activation and heart rate variability in the lowest frequency band. Voluntary restriction of physical activity in healthy young subjects caused marked reduction in spectral power in the lowest frequency band which is often used to assess patient prognosis. The findings strongly suggest that studies of ambulatory heart rate variability should always include an indication of physical activity patterns.???Keywords: spectral analysis; electromyography; Holter monitoring; sex effect

Serrador, J; Finlayson, H; Hughson, R

1999-01-01

242

Correlation of heart rate variability with cardiac functional and metabolic variables in cyclists with training induced left ventricular hypertrophy  

Microsoft Academic Search

OBJECTIVETo examine the correlation between heart rate variability and left ventricular mass in cyclists with an athlete’s heart.METHODSLeft ventricular mass and diastolic function were determined at rest and myocardial high energy phosphates were quantified at rest and during atropine–dobutamine stress in 12 male cyclists and 10 control subjects, using magnetic resonance techniques. Ambulatory 24 hour ECG recordings were obtained, and

B M Pluim; C A Swenne; A H Zwinderman; A C Maan; A van der Laarse; J Doornbos; E E Van der Wall

1999-01-01

243

Holocene activity of an alpine debris-flow catchment: does climate control erosion rate variability?  

NASA Astrophysics Data System (ADS)

The Zielbach catchment is located in the central-eastern Italian Alps. It covers an area of ca. 40 km2 and is characterized by fluvial sediment transport along the main drainage basin, and by the supply of sediment through debris flows, derived from a ca. 10 km2 tributary catchment. A debris-flow database demonstrates that nowadays this latter tributary dominates the sediment budget of the entire Zielbach. In this study, we analyze modern and paleo-erosion rates of the catchment through the application of the cosmogenic nuclides technique. For modern erosion rate, samples of river-born sand were taken from the main river and tributaries along the entire drainage system, while paleo-erosion rates are calculated thanks to cores' samples, which were collected on the alluvial fan and which were likewise dated based on 14C measurements of organic matter. Results obtained from the modern drainage system reveal the spatial erosion rate variability that characterizes the catchment nowadays (values ranging from 2.6 to 0.15 mm/yr). This spatial pattern is characterized by a generally increasing trend of 10Be values where hillslope contributions predominate and by a decreasing concentration trend where sediment has been supplied by debris flows. Results obtained from the cores allow the reconstruction of the Zielbach Holocene evolution and the assignment of the climate role on the temporal erosion rate variability (values ranging between 21 and 0.43 mm/yr). 14C concentrations of organic material collected from the core material indicate a lowermost age of 10'000 yr at ca. 35 m depth. The sedimentary fabric of the deposits indicates that the fan is built up by alternation of alluvial and debris-flow deposits, where the latter ones dominate in volumes. The stratigraphic architecture also infers that alluvial deposits correspond to periods of low activity of the debris-flow catchment. Most important, however, paleo-erosion rates indicate a decreasing trend for the debris-flow activity from ca. 10'000 yr to the present, with values decreasing from ca. 21 to 0.8 mm/yr. During the same time span, the alluvial sediment supplied by the main catchment appears to have been steady, as indicated by a constant basin-averaged denudation rate of 0.45 mm/yr. The comparison of these results with the climatic history of the valley reveals that periods of high activity of the debris flow catchment (associated with higher 10Be-based erosion rates) correspond to periods of a wetter and cooler climate. In particular, the highest value (21 mm/yr) seems to be related to the late glacial phase, which presumably started after the LGM and terminated around 10'000 yr, while a reactivation of the debris-flow activity, with erosion rates around 1.0 mm/yr, corresponds to the Holocene climatic deterioration at ca. 3'500 yr B.P. The alluvial phase of the Zielbach catchment (erosion rate of ca. 0.43 mm/yr), marked by absent or lower debris-flow activity, seems to be related to the Holocene climatic optimum between 8'000 and 4'000 years ago.

Savi, S.; Norton, K. P.; Brardinoni, F.; Akçar, N.; Kubik, P.; Picotti, V.; Schlunegger, F.

2012-12-01

244

Aerobic exercise during pregnancy influences fetal cardiac autonomic control of heart rate and heart rate variability  

Microsoft Academic Search

BackgroundPrevious studies using ultrasound technology showed that fetal heart rate (HR) may be responsive to maternal aerobic exercise. Although it is recognized that cardiac autonomic control may be influenced by the intrauterine environment, little is known about how maternal exercise affects fetal heart development.

Linda E. May; Alan Glaros; Hung-Wen Yeh; James F. Clapp III; Kathleen M. Gustafson

2010-01-01

245

An Integrated Account of the Effects of Acoustic Variability in First Language and Second Language: Evidence from Amplitude, Fundamental Frequency, and Speaking Rate Variability  

ERIC Educational Resources Information Center

This study examined how three different sources of stimulus variability--overall amplitude, fundamental frequency, and speaking rate--affect second language (L2) vocabulary learning. Native English speakers learned Spanish words in presentation formats with no variability, moderate variability, and high variability. Dependent measures were…

Sommers, Mitchell S.; Barcroft, Joe

2007-01-01

246

Continuously variable transmission: Assessment of applicability to advance electric vehicles  

NASA Technical Reports Server (NTRS)

A brief historical account of the evolution of continuously variable transmissions (CVT) for automotive use is given. The CVT concepts which are potentially suitable for application with electric and hybrid vehicles are discussed. The arrangement and function of several CVT concepts are cited along with their current developmental status. The results of preliminary design studies conducted on four CVT concepts for use in advanced electric vehicles are discussed.

Loewenthal, S. H.; Parker, R. J.

1981-01-01

247

Maximum likelihood phylogenetic estimation from DNA sequences with variable rates over sites: Approximate methods  

Microsoft Academic Search

Two approximate methods are proposed for maximum likelihood phylogenetic estimation, which allow variable rates of substitution across nucleotide sites. Three data sets with quite different characteristics were analyzed to examine empirically the performance of these methods. The first, called the “discrete gamma model,” uses several categories of rates to approximate the gamma distribution, with equal probability for each category. The

Ziheng Yang

1994-01-01

248

HEART RATE VARIABILITY DURING RECOVERY IN TWO GROUPS WITH DIFFERENT TRAINING LEVEL  

Microsoft Academic Search

Heart Rate Variability (HRV) study, beside having a clini- cal interest, it has also worried researchers in exercise re- sponse and training adaptation. Although heart rate recov- ery (HRR) has been used as a cardiovascular index in mul- tiple tests, there is little information about the physiological mechanisms that explain the process of heart recovery af- ter exercise (1). Objective.

Lorenzo Irma; Calderón Francisco Javier; Benito Pedro

249

Power spectrum of heart rate variability in exercising humans: The effect of exercise intensity  

Microsoft Academic Search

Power spectral analysis of heart rate variability (HRV) has been estimated by means of a Fourier transform method at rest in seven healthy men and three women, during a 30?minutes steady state cycle exercise test at 40%, 50%, 60%, 70% and 80% respectively, of maximal heart rate reserve (MHRR) defined as (HRmax ? HRrest). Total power (PT) of HRV was

Pavel Stejskal; Jana Rechbergová; Jirí Salinger; Radim Šlachta; Milan Elfmark; Martn Kalina; Radim Jur?a; Iva Rehová

2001-01-01

250

Telemetric measuring system for the diagnostics of heart rate variability-VariaPulse TF  

Microsoft Academic Search

Summary form only given. Heart rate variability (HRV) is an important marker in the diagnostics of some diseases associated with autonomic nervous system (ANS) dysfunctions. One of the advanced methods is the spectral analysis of heart rate variations (SAHRV). Early diagnosis of ANS disfunction is very important from the point of view of prevention and subsequent therapy. This fact served

R. Vychodil; J. Sabinger; J. Novotny

1997-01-01

251

Dynamic and Stochastic Instability and the Unbiased Forward Rate Hypothesis: A Variable Mean Response Approach  

Microsoft Academic Search

Since the mid-1970's, the unbiased forward rate hypothesis (UFRH) of forward and spot exchange rates has been intensively studied and tested with inconclusive and contradictory results. On the basis of the hypothesis, this paper provides variable mean response (VMR) random coefficients models to capture the time-varying and stochastic behavior of the slope coefficient to be referred to as the currency

Winston T. Lin

252

Effects of slow repetitive transcranial magnetic stimulation on heart rate variability according to power spectrum analysis  

Microsoft Academic Search

We examined whether repetitive transcranial magnetic stimulation (rTMS) at a low rate could influence autonomic function, specially heart rate variability (HRV) by power spectrum analysis. We studied 16 healthy male volunteers as a stimulation group and 16 others as a sham group. The stimulation group received magnetic stimulations from a circular coil over Cz at a frequency of 0.2 Hz

Takeshi Yoshida; Aihide Yoshino; Yuji Kobayashi; Masayuki Inoue; Keiko Kamakura; Soichiro Nomura

2001-01-01

253

Short-term analysis of heart-rate variability of adapted wavelet transforms  

Microsoft Academic Search

The purpose of this study is to characterize the heart rate variability (HRV) signal in the frequency domain by using wavelet and cosine packets. Here, the authors introduce the adapted wavelet transform methods to analyze heart-rate fluctuations. These methods were chosen because the components in the signals can be analyzed and quantified at different scales, e.g., long windows can be

U. Wiklund; M. Akay; U. Niklasson

1997-01-01

254

Cardiac Autonomic Regulation under Hypnosis Assessed by Heart Rate Variability: Spectral Analysis and Fractal Complexity  

Microsoft Academic Search

Objective: This study examined the effects of hypnosis on autonomic cardiac control. We hypothesized a modification of autonomic modulation of the heart rate with an enhanced vagal tone during hypnosis compared to baseline. Methods: In 12 healthy subjects (6 men and 6 women, 22.2 ± 1.0 years of age) ECG was recorded at baseline and during hypnosis. Heart rate variability

André E. Aubert; Bart Verheyden; Frank Beckers; Jan Tack; Joris Vandenberghe

2009-01-01

255

Assessment of autonomic regulation to heart rate variability by the method of complex demodulation  

Microsoft Academic Search

Complex demodulation of heart-rate variability was used to analyze changes in the autonomic regulation of dog heart rate during differential classical conditioning before and after autonomic blockade. This method tracked the rapid withdrawal of parasympathetic tone following the onset of the warning signal and detected a later rise in low-frequency power that was tentatively identified as a sympathetic increase. Results

S. Shin; S. S. Reisman; W. N. Tapp; B. H. Natelson

1988-01-01

256

The Successful E-Rate Application  

ERIC Educational Resources Information Center

The E-rate regulations are complex, and the guidance and rules seem to change each year. There are many deadlines stakeholders need to know about and compliance issues that are important to understand. In this article, the author presents a few quick tips that should help with this process.

Kaplan, Peter

2007-01-01

257

Variability in heart rate recovery measurements over 1 year in healthy, middle-aged adults.  

PubMed

This study assessed the longer-term (12-month) variability in post-exercise heart rate recovery following a submaximal exercise test. Longitudinal data was analysed for 97 healthy middle-aged adults (74 male, 23 female) from 2 occasions, 12 months apart. Participants were retrospectively selected if they had stable physical activity habits, submaximal treadmill fitness and anthropometric measurements between the 2 assessment visits. A submaximal Bruce treadmill test was performed to at least 85% age-predicted maximum heart rate. Absolute heart rate and ? heart rate recovery (change from peak exercise heart rate) were recorded for 1 and 2 min post-exercise in an immediate supine position. Heart rate recovery at both time-points was shown to be reliable with intra-class correlation coefficient values ? 0.714. Absolute heart rate 1-min post-exercise showed the strongest agreement between repeat tests (r = 0.867, P < 0.001). Lower coefficient of variation (??10.2%) and narrower limits of agreement were found for actual heart rate values rather than ? heart rate recovery, and for 1-min rather than 2-min post-exercise recovery time points. Log-transformed values generated better variability with acceptable coefficient of variation for all measures (2.2-10%). Overall, 1 min post-exercise heart rate recovery data had least variability over the 12-month period in apparently healthy middle-aged adults. PMID:23868686

Mellis, M G; Ingle, L; Carroll, S

2014-02-01

258

40-Gb/s FSK modulated WDM-PON with variable-rate multicast overlay.  

PubMed

This paper proposes a novel conjugate-driven frequency shift keying (FSK) modulated wavelength division multiplexing passive network (WDM-PON) with variable-rate multicast services. Optical orthogonal frequency division multiplexing (OFDM) is adopted for multicast overlay services with different rate requirements. A differential detection is used for the demodulation of FSK signal, which can eliminate the crosstalk from the OFDM signal. A total 40-Gb/s FSK point to point (P2P) signal and 6.3-Gb/s OFDM overlay with three kinds of variable-rate multicast services are experimentally demonstrated. A physical-layer adaptive identification is proposed for the variable-rate multicast services. After 25 km single mode fiber (SMF) transmission, the power penalties of FSK P2P signal and OFDM multicast overlay are 1.3 dB and 1.7 dB respectively. PMID:21716492

Xin, Xiangjun; Liu, Bo; Zhang, Lijia; Yu, Jianjun

2011-06-20

259

Multi-Rate and Variable-Rate Modeling of Speech At Phone and Syllable Time Scales  

Microsoft Academic Search

This paper introduces a multi-rate extension of hidden Markov models (HMMs), for joint acoustic modeling of speech at multi- ple time scales. The approach complements the usual short-term, phone-based representation of speech with wide-context modeling units and long-term temporal features. We consider two alterna- tives for coarse scale modeling units and features, representing ei- ther phones, or syllable structure and

O. Cetin; M. Ostendorf

2005-01-01

260

Variable-Rate Ring Convolutional Coded Continuous Phase Modulation Using Puncturing  

NASA Astrophysics Data System (ADS)

In this paper, puncturing technique is used to establish variable-rate ring convolutional coded continuous phase modulation (CPM) systems. Maximum likelihood sequence detectors over both AWGN channels and Rayleigh flat-fading channels are considered. The suggested system provides us with different rates and performance when simple adjustment is taken to the puncturing matrix. Since the performance of the first error event of this system is represented by normalized minimum squared Euclidean distance (NMSED), some typical codes with maximum NMSED are searched and given. The performance of symbol error rate for the suggested system is simulated using computer software, and the results show that this system provides good performance of symbol error rate with variable-rate capabilities in time varying channels. Furthermore, simulation results also prove that the transmission efficiency increases when code rate is decreasing.

Zhang, Lei; Wu, Jun; Zhu, Aiming

2013-01-01

261

Rate of Mutual Information Between Coarse-Grained Non-Markovian Variables  

NASA Astrophysics Data System (ADS)

The problem of calculating the rate of mutual information between two coarse-grained variables that together specify a continuous time Markov process is addressed. As a main obstacle, the coarse-grained variables are in general non-Markovian, therefore, an expression for their Shannon entropy rates in terms of the stationary probability distribution is not known. A numerical method to estimate the Shannon entropy rate of continuous time hidden-Markov processes from a single time series is developed. With this method the rate of mutual information can be determined numerically. Moreover, an analytical upper bound on the rate of mutual information is calculated for a class of Markov processes for which the transition rates have a bipartite character. Our general results are illustrated with explicit calculations for four-state networks.

Barato, Andre C.; Hartich, David; Seifert, Udo

2013-11-01

262

Heart rate variability and circulating catecholamine concentrations during steady state exercise in healthy volunteers.  

PubMed Central

OBJECTIVES--To assess whether exercise induced suppression of heart rate variability in the low frequency domain (0.06-0.15 Hz) is related to the increase in circulating catecholamine concentrations. DESIGN--Randomised crossover trial of three exercise tests characterised by different workloads. Pharmacological simulation of exercise-induced changes in vagal and sympathetic activity. PARTICIPANTS--Six healthy men with a mean age of 31.2 (SD 3.0) years. INTERVENTIONS--Three different workloads of steady state cycling ergometry: control state without cycling, cycling at a target heart rate of 100 beats/min, and cycling at a target heart rate of 150 beats/min. Intravenous infusion of atropine (target heart rate 100 beats/min) followed by the additional infusion of adrenaline and noradrenaline. MAIN OUTCOME MEASURES--Fast Fourier analysis of heart rate variability; blood pressure; and venous plasma concentrations of lactate, adrenaline, and noradrenaline. RESULTS--During the control exercise period there were no changes in the assessed variables compared with the preceding resting period. During exercise at a heart rate of 100 beats/min systolic blood pressure increased and heart rate variability decreased. During exercise at a heart rate of 150 beats/min systolic blood pressure and lactate, adrenaline, and noradrenaline concentrations increased. In addition, low frequency (LF) was lower than during exercise at 100 beats/min, high frequency (HF 0.15-0.80 Hz) resembled that during exercise at 100 beats/min, and diastolic blood pressure was reduced. Infusion of atropine caused no changes in blood pressure or plasma concentrations of lactate, adrenaline, and noradrenaline and decreased heart rate variability. The additional infusion of adrenaline and noradrenaline completely suppressed heart rate variability and increased blood pressure. CONCLUSIONS--The reduction in LF and HF during exercise at a heart rate of 100 beats/min, which is not characterised by increased plasma catecholamine concentrations, and during atropine infusion suggests that heart rate variability in the supine state is largely influenced by vagal activity. The additional reduction in LF during exercise at 150 beats/min and during catecholamine infusion may reflect a negative feedback of circulating catecholamines on the sympathetic control of heart rate.

Breuer, H W; Skyschally, A; Schulz, R; Martin, C; Wehr, M; Heusch, G

1993-01-01

263

Carotid artery stenting and endarterectomy have different effects on heart rate variability  

Microsoft Academic Search

ObjectiveDue to their close proximity to the carotid sinus baroreceptor region, carotid endarterectomy (CEA) and carotid angioplasty\\/stenting (CAS) carry an inherent risk of affecting baroreflex-mediated regulation of the heart rate. Variations in the heart rate can be studied by measuring heart rate variability (HRV), in which distinct frequency bands in the power spectrum represent sympathetic and parasympathetic modulations on sinus

Mehmet Demirci; Okay Sar?ba?; Kay?han Uluç; Saruhan Çekirge; Erkmen Böke; Hakan Ay

2006-01-01

264

Relation of heart rate recovery to heart rate variability in persons with paraplegia  

Microsoft Academic Search

Purpose  Heart rate recovery (HRR) after treadmill exercise testing is an index of cardiac autonomic activity in non-disabled persons,\\u000a but it is unknown if this is also the case in individuals with spinal cord injury (SCI). We investigated the relationship\\u000a between HRR after maximal arm exercise testing and resting autonomic activity in persons with paraplegia.\\u000a \\u000a \\u000a \\u000a \\u000a Methods  A total of 17 (male n = 9,

Sae Young Jae; Kevin S. Heffernan; Miyoung Lee; Bo Fernhall

2011-01-01

265

Response Time Variability is Related to Parent Ratings of Inattention, Hyperactivity and Executive Function  

PubMed Central

Objective: Individuals with Attention-Deficit/Hyperactivity Disorder (ADHD) are often characterized as inconsistent across many contexts. ADHD is also associated with deficits in executive function. We examined the relationships between response time variability on five brief computer tasks to parents’ ratings of ADHD-related features and executive function in a group of children with a broad range of ADHD symptoms from none to full diagnosis. Methods: We tested 98 children (mean age 9.9±1.4 yrs; 66 boys) from community clinics on short Tasks of Executive Control (TEC) and the Eriksen Flanker Task, while a parent completed the Conners Parent Rating Scale and Behavior Rating Inventory of Executive Function. Results: Variability for two of the TEC tasks explained significant proportions of the variance of all five ADHD-related Conners subscales and several executive function subscales. By contrast, variability on the flanker task or mean response times for any task were not associated with any rating scale. Conclusions: The significant dimensional relationships observed between variability measures and parent ratings support the utility of response time variability as an objective measure in ADHD and aspects of executive functioning that is superior to response time means or accuracy measures.

Gomez-Guerrero, Lorena; Dominguez-Martin, Cristina; Mairena, Maria Angeles; Martino, Adriana Di; Wang, Jing; Mendelsohn, Alan; Dreyer, Benard; Isquith, Peter; Gioia, Gerard; Petkova, Eva; Castellanos, F. Xavier

2013-01-01

266

Inhalation of ultrafine carbon particles alters heart rate and heart rate variability in people with type 2 diabetes  

PubMed Central

Background Diabetes may confer an increased risk for the cardiovascular health effects of particulate air pollution, but few human clinical studies of air pollution have included people with diabetes. Ultrafine particles (UFP, ?100 nm in diameter) have been hypothesized to be an important component of particulate air pollution with regard to cardiovascular health effects. Methods 17 never-smoker subjects 30–60 years of age, with stable type 2 diabetes but otherwise healthy, inhaled either filtered air (0–10 particles/cm3) or elemental carbon UFP (~107 particles/cm3, ~50 ug/m3, count median diameter 32 nm) by mouthpiece, for 2 hours at rest, in a double-blind, randomized, crossover study design. A digital 12-lead electrocardiogram (ECG) was recorded continuously for 48 hours, beginning 1 hour prior to exposure. Results Analysis of 5-minute segments of the ECG during quiet rest showed reduced high-frequency heart rate variability with UFP relative to air exposure (p?=?0.014), paralleled by non-significant reductions in time-domain heart rate variability parameters. In the analysis of longer durations of the ECG, we found that UFP exposure increased the heart rate relative to air exposure. During the 21- to 45-hour interval after exposure, the average heart rate increased approximately 8 beats per minute with UFP, compared to 5 beats per minute with air (p?=?0.045). There were no UFP effects on cardiac rhythm or repolarization. Conclusions Inhalation of elemental carbon ultrafine particles alters heart rate and heart rate variability in people with type 2 diabetes. Our findings suggest that effects may occur and persist hours after a single 2-hour exposure.

2014-01-01

267

School Counselors as Social Capital: The Effects of High School College Counseling on College Application Rates  

ERIC Educational Resources Information Center

Using social capital theory as a framework, the authors examined data from the Educational Longitudinal Study of 2002 (Ingels, Pratt, Rogers, Siegel, & Stutts, 2004) to investigate how student contact with high school counselors about college information and other college-related variables influence students' college application rates. In addition…

Bryan, Julia; Moore-Thomas, Cheryl; Day-Vines, Norma L.; Holcomb-McCoy, Cheryl

2011-01-01

268

Prognostic value of heart rate variability for sudden death and major arrhythmic events in patients with idiopathic dilated cardiomyopathy  

Microsoft Academic Search

OBJECTIVEThis study was designed to evaluate the prognostic value of heart rate variability for sudden death, resuscitated ventricular fibrillation or sustained ventricular tachycardia in patients with idiopathic dilated cardiomyopathy.BACKGROUNDPrevious studies have shown that heart rate variability could predict arrhythmic events and sudden death in postinfarction patients, but the prognostic value of heart rate variability for arrhythmic events or sudden death

Laurent Fauchier; Dominique Babuty; Pierre Cosnay; Jean Paul Fauchier

1999-01-01

269

Effect of cold or thermoneutral water immersion on post-exercise heart rate recovery and heart rate variability indices  

Microsoft Academic Search

This study aimed to investigate the effect of cold and thermoneutral water immersion on post-exercise parasympathetic reactivation, inferred from heart rate (HR) recovery (HRR) and HR variability (HRV) indices. Twelve men performed, on three separate occasions, an intermittent exercise bout (all-out 30-s Wingate test, 5min seated recovery, followed by 5min of submaximal running exercise), randomly followed by 5min of passive

Hani Al Haddad; Paul B. Laursen; Didier Chollet; Frédéric Lemaitre; Saïd Ahmaidi; Martin Buchheit

2010-01-01

270

Evaluation of cardiac autonomic functions in patients with ankylosing spondylitis via heart rate recovery and heart rate variability  

Microsoft Academic Search

Objective  The aim of this study was to evaluate heart rate variability (HRV) and heart rate recovery (HRR) in otherwise healthy ankylosing\\u000a spondlitis (AS) patients and control subjects.\\u000a \\u000a \\u000a \\u000a \\u000a Methods  A total of 28 patients with AS and 30 volunteers matched for age and sex were enrolled. All subjects underwent HRV analysis,\\u000a exercise testing (ET), and transthoracic echocardiography. HRR indices were calculated by

Ergun Baris Kaya; Sercan Okutucu; Hakan Aksoy; Ugur Nadir Karakulak; Erol Tulumen; Oya Ozdemir; Fatma Inanici; Kudret Aytemir; Giray Kabakci; Lale Tokgozoglu; Hilmi Ozkutlu; Ali Oto

2010-01-01

271

Determining the causes of fault slip rate variability for Northern Apennine thrusts on intermediate timescales  

NASA Astrophysics Data System (ADS)

Documenting fault slip rate variability on intermediate (10^4-10^5 yr) timescales is crucial for understanding the process-linkages of short-term (10^1-10^3 yr) and long-term (10^6 yr) patterns of deformation; however, the lack of long records of fault slip with 10^4-10^5 yr resolution presents a major barrier to understanding the underlying process responsible for slip rate variability at those timescales. Taking advantage of spectacular, continuous exposure of growth strata, we document 10^4-10^5 yr resolution records of unsteady fault slip for the past 3.0 myr for three unconnected, shallow blind thrust anticlines growing along the Northern Apennine mountain front, Italy. Fault slip rates for these thrusts were determined from progressive restorations of marine and continental growth strata deposited on the anticlinal limbs. These restorations were supported by subsurface corre-lations of the measured growth sections in order to constrain the fold geometries and kin-ematics. Magnetostratigraphy, cyclostratigraphy, cosmogenic radionuclide (CRN) burial dating, and optically stimulated luminescence (OSL) burial dating provided the high-resolution age models for the growth sections. Slip histories determined from our pro-gressive restorations indicate that all three of the thrust faults exhibited high-frequency slip rate variability. This variability is typically manifest by longer periods of decelerated fault slip punctuated by shorter periods of accelerated fault slip, typically lasting between 80-200 kyr. During times when slip rates were slow, growth strata geometries show ac-celerated slip was accommodated by more foreland structures, suggesting slip partitioning at 10^4-10^5 yr timescales. This high frequency variability is superimposed on a low frequency slip rate variability manifest by an overall deceleration in slip on the shallow thrusts since 3.0 myr. Major decelerations in slip rates were coincident with the activation of thick-skinned thrusting in the Apennines, representing a dynamic reorganization of the Apennine wedge. This suggests two separate causes for slip rate variability on Apennines thrusts: a high-frequency variability that is likely due to processes internal to the wedge, such as slip partitioning, and a low frequency variability that is probably caused by exter-nal forces affecting the entire Apennine wedge.

Gunderson, K. L.; Anastasio, D. J.; Pazzaglia, F. J.

2012-12-01

272

Heart Rate Variability and Intensity of Habitual Physical Activity in Middle-Aged Persons  

Microsoft Academic Search

BUCHHEIT, M., C. SIMON, A. CHARLOUX, S. DOUTRELEAU, F. PIQUARD, and G. BRANDENBERGER. Heart Rate Variability and Intensity of Habitual Physical Activity in Middle-Aged Persons. Med. Sci. Sports Exerc., Vol. 37, No. 9, pp. 1530-1534, 2005. Purpose: In the middle-aged, it has been shown that moderate physical activity is associated with increased global HR variability (HRV) and vagal-related HRV indexes.

MARTIN BUCHHEIT; CHANTAL SIMON; ANNE CHARLOUX; GABRIELLE BRANDENBERGER

2005-01-01

273

Bandwidth-allocation schemes for variable-bit-rate MPEG sources in ATM networks  

Microsoft Academic Search

The complex traffic characteristics of variable-bit-rate (VBR) video sources makes them difficult to accommodate in asynchronous-transfer-mode (ATM) networks. To efficiently transport these services will require both an understanding of the source traffic and novel network control schemes. The performance of variable-bandwidth-allocation schemes that estimate the required bandwidth for a VBR Motion Picture Experts Group (MPEG) video source is studied using

Pramod Pancha; M. El Zarki

1993-01-01

274

Applications of Autocorrelation Analysis to the Study of Variable Stars  

NASA Astrophysics Data System (ADS)

Autocorrelation analysis is a simple method for looking for cyclic behavior in variable star data. We have found it to be a useful adjunct to light curves and Fourier analysis, especially for stars which are only semi-regular. Its aliasing properties are different from those of Fourier analysis, and it does not require the star to be strictly periodic. The method was described by Burki et al. (A&A 65, 363 (1978)) and implemented independently by Percy & Sen (IAU IBVS #3670 (1991)). Because it is conceptually simple, it is quite suitable for student research. We describe two general applications: (i) period analysis of yellow and red semi-regular variables, and luminous blue variables such as P Cyg; in these stars, the seasonal gaps in the data are often similar to the periods of the stars; and (ii) period analysis of short-period variables of A and B type using Hipparcos epoch photometry, which has many measurements over several hours, then gaps of several weeks. We show specific examples of each kind. We also discuss the limitations of the method. Thanks to NSERC Canada, the AAVSO visual and photoelectric programs, and a score of student collaborators for supporting this research.

Percy, J. R.

2001-05-01

275

Variable rate phosphorus fertilization experiment based on on-line visible and near infrared soil sensing  

NASA Astrophysics Data System (ADS)

Soil phosphorus is an important nutrient particularly for root and seed development, and deficiency of soil P could result in poor crop yield. However, over-application of Phosphorous causes waste of fertilizer and contamination to the environment. Variable rate (VR) fertilization may allow for a better phosphorous management in the soil, if within field variability in soil available P (P_av) can be characterized at a desirable fine scale. Visible and near infrared (vis-NIR) spectroscopy has been proven to be fast, cheap and non-destructive tool for the measurement of P_av. On-line vis-NIR sensors enable the collection of high resolution data on P_av with acceptable accuracy. The aim of this paper was to compare the economic and environmental benefits of VR phosphorous fertilization based on on-line vis-NIR soil sensing (OVR) against uniform rate (UR) and traditional precision farming variable rate (TVR). A trial plot experiment consisting of 9 plots was designed and implemented in a field with spring barely in 2013. Triplication plots (24 m width) for each of the three fertilization methods (OVR, UR and TVR) were randomly laid out in the field. Prior to the fertilization experiment, an on-line vis-NIR measurement was carried out to measure within field variation in P_av. Fertilizer input (P2O5 in kg ha-1) and yield output of each plot was measured to run a basic cost-benefit analysis. The validation of the on-line measurement with an independent validation set showed moderate measurement accuracy of P_av (R2= 0.72, RMSEP = 0.55 mg/100g and RPD = 1.99). The lowest amount of P2O5 was recommended and applied in OVR plots, which indicated a reduction of fertilizer use by 40 and 54 kg ha-1, as compared to UR and TPF method, respectively. Small yield difference was observed between the three treatments, although UR plots showed a slightly higher yield (6.990 kg ha-1). However, ANOVA analysis resulted in a smaller F value of 0.22 than F critical (3.22), which allows the conclusion that the differences of yield between the three treatments are insignificant at 5% confidence (p < 0.05) level. The cost-benefit analysis showed the OVR method to provide comparable margin to TVR method, as only extra £2 per ha was calculated with OVR. A much larger margin of about £31 per ha was obtained with the innovative the OVR method, as compared to the TVR. A longer term experiment is still underway in the same to understand and confirm the mechanism and agronomic link if any between fertilizer input and crop growth and yield, as practical experience indicated that more than one cropping season is needed to record actual crop response to phosphorous application. It can be concluded that a clear environmental benefit can be achieved by using the innovative OVR concept. However, a longer term study is needed to prove the economic benefit, as compared particularly to TVR. .

Kuang, Boyan; Mouazen, Abdul

2014-05-01

276

Effects of transcatheter closure of atrial septal defects on heart rate variability.  

PubMed

This study evaluated heart rate variability and its changes in 30 patients before and after transcatheter closure of secundum atrial septal defects. Heart rate variability data from 30 healthy volunteers with normal echocardiographic parameters and no history of atrial septal defects were included as controls. Values for the SD of all the normal RR intervals (SDNN), the SD of the means of all the 5-min segment normal RR intervals (SDANN), and the mean of all the 5-min SDs of normal RR intervals during the 24-h period (SDNN index) in patients with atrial septal defects before transcatheter closure were statistically significantly different from controls. At 6 months after closure of the defects these values were not statistically different from controls. It is concluded that transcatheter closure of secundum atrial septal defects had positive effects on heart rate variability and, consequently, may contribute to less mortality and morbidity. PMID:21672371

Cansel, M; Yagmur, J; Ermis, N; Acikgoz, N; Ta?olar, H; Atas, H; Muezzinoglu, K; Pekdemir, H; Ozdemir, R

2011-01-01

277

Development of multiscale complexity and multifractality of fetal heart rate variability.  

PubMed

During fetal development a complex system grows and coordination over multiple time scales is formed towards an integrated behavior of the organism. Since essential cardiovascular and associated coordination is mediated by the autonomic nervous system (ANS) and the ANS activity is reflected in recordable heart rate patterns, multiscale heart rate analysis is a tool predestined for the diagnosis of prenatal maturation. The analyses over multiple time scales requires sufficiently long data sets while the recordings of fetal heart rate as well as the behavioral states studied are themselves short. Care must be taken that the analysis methods used are appropriate for short data lengths. We investigated multiscale entropy and multifractal scaling exponents from 30 minute recordings of 27 normal fetuses, aged between 23 and 38 weeks of gestational age (WGA) during the quiet state. In multiscale entropy, we found complexity lower than that of non-correlated white noise over all 20 coarse graining time scales investigated. Significant maturation age related complexity increase was strongest expressed at scale 2, both using sample entropy and generalized mutual information as complexity estimates. Multiscale multifractal analysis (MMA) in which the Hurst surface h(q,s) is calculated, where q is the multifractal parameter and s is the scale, was applied to the fetal heart rate data. MMA is a method derived from detrended fluctuation analysis (DFA). We modified the base algorithm of MMA to be applicable for short time series analysis using overlapping data windows and a reduction of the scale range. We looked for such q and s for which the Hurst exponent h(q,s) is most correlated with gestational age. We used this value of the Hurst exponent to predict the gestational age based only on fetal heart rate variability properties. Comparison with the true age of the fetus gave satisfying results (error 2.17±3.29 weeks; p<0.001; R(2)=0.52). In addition, we found that the normally used DFA scale range is non-optimal for fetal age evaluation. We conclude that 30 min recordings are appropriate and sufficient for assessing fetal age by multiscale entropy and multiscale multifractal analysis. The predominant prognostic role of scale 2 heart beats for MSE and scale 39 heart beats (at q=-0.7) for MMA cannot be explored neither by single scale complexity measures nor by standard detrended fluctuation analysis. PMID:23466040

Giera?towski, Jan; Hoyer, Dirk; Tetschke, Florian; Nowack, Samuel; Schneider, Uwe; Zebrowski, Jan

2013-11-01

278

REDUCED HEART RATE VARIABILITY IS ASSOCIATED WITH WORSE COGNITIVE PERFORMANCE IN ELDERLY MEXICAN AMERICANS  

PubMed Central

Reduced Heart Rate Variability is a strong predictor of cardiovascular risk factors, cardiovascular events and mortality; and thus may be associated with cognitive neurodegeneration. Yet this has been relatively unexplored, particularly in minority populations with high cardiovascular burden. We used data from the Sacramento Area Latino Study on Aging to examine the cross-sectional association of reduced heart rate variability with cognitive function among elderly Mexican Americans. A total of 869 participants (mean age of 75 years; 59% females) had their 6-minute heart rate variability measured using an ECG monitor and respiration pacer in response to deep breathing. We used the Mean Circular Resultant, known as R bar, as a measure of heart rate variability and categorized it into quartiles (Q1 to Q4 of R bar: reduced to high heart rate variability). Cognitive function was assessed using the Modified Mini Mental State Exam, a 100-point test of global cognitive function and the Spanish and English Verbal Learning Test, a 15-point test of verbal memory recall. In fully-adjusted linear regression models, participants in quartile 1 had a 4-point lower Modified Mini Mental State Exam score (p<0.01), those in quartile 2 had 2-point lower score (p=0.04), and those in quartile 3 had 1-point lower score (p=0.35), as compared to those in the highest quartile of R bar. Reduced R bar was not associated with verbal memory. Our results suggest that reduced heart rate variability is associated with worse performance on the test of global cognitive function, above and beyond traditional cardiovascular risk factors.

Al Hazzouri, Adina Zeki; Haan, Mary N.; Deng, Yingzi; Neuhaus, John; Yaffe, Kristine

2014-01-01

279

Automatic detection and quantification of sleep apnea using heart rate variability.  

PubMed

Detection of sleep apnea using electrocardiographic (ECG) parameters is noninvasive and inexpensive. Our approach is based on the hypothesis that the patient's sleep-wake cycle during episodes of sleep apnea modulates heart rate (HR) oscillations. These HR oscillations appear as low-frequency fluctuations of instantaneous HR (IHR) and can be detected using HR variability analysis in the frequency domain. The purpose of this study was to evaluate the efficacy of our ECG-based algorithm for sleep apnea detection and quantification. The algorithm first detects normal QRS complexes and R-R intervals used to derive IHR and to estimate its spectral power in several frequency ranges. A quadratic classifier, trained on the learning set, uses 2 parameters to classify the 1-minute epoch in the middle of each 6-minute window as either apneic or normal. The windows are advanced by 1-minute steps, and the classification process is repeated. As a measure of quantification, the algorithm correctly classified 84.7% of all the 1-minute epochs in the evaluation database; and as a measure of the accuracy of apnea classification, the algorithm correctly classified all 30 test recordings in the evaluation database either as apneic or normal. Our sleep apnea detection algorithm based on analysis of a single-lead ECG provides accurate apnea detection and quantification. Because of its noninvasive and low-cost nature, this algorithm has the potential for numerous applications in sleep medicine. PMID:20719334

Babaeizadeh, Saeed; White, David P; Pittman, Stephen D; Zhou, Sophia H

2010-01-01

280

Low-frequency heart rate variability is related to the breath-to-breath variability in the respiratory pattern.  

PubMed

Changes in heart rate variability (HRV) at "respiratory" frequencies (0.15-0.5?Hz) may result from changes in respiration rather than autonomic control. We now investigate if the differences in HRV power in the low-frequency (LF) band (0.05-0.15?Hz, HRV(LF)) can also be predicted by respiration variability, quantified by the fraction of tidal volume power in the LF (V(LF,n)). Three experimental protocols were considered: paced breathing, mental effort tasks, and a repeated attentional task. Significant intra- and interindividual correlations were found between changes in HRV(LF) and V(LF,n) despite all subjects having a respiratory frequency above the LF band. Respiratory parameters (respiratory period, tidal volume, and V(LF,n)) could predict up to 79% of HRV(LF) differences in some cases. This suggests that respiratory variability is another mechanism of HRV(LF) generation, which should be always monitored, assessed, and considered in the interpretation of HRV changes. PMID:24423137

Beda, Alessandro; Simpson, David M; Carvalho, Nadja C; Carvalho, Alysson Roncally S

2014-02-01

281

The predictive value of low heart rate and heart rate variability during stress for reoffending in delinquent male adolescents.  

PubMed

Low autonomic (re)activity is a consistent correlate of antisocial behavior in juveniles. However, longitudinal research relating autonomic measures to persistent antisocial behavior has remained scarce. Therefore, in the present study we examined the predictive value of heart rate (HR) and heart rate variability (HRV, often studied as respiratory sinus arrhythmia) for reoffending in delinquent male adolescents. At initial assessment, HR and HRV were measured at rest and in response to a public speaking task. Registered reoffending was assessed after 5-year follow-up. Attenuated HR response and stronger HRV response to stress predicted higher reoffending rates. Results provide evidence that HR/HRV reactivity are neurobiological markers for persistent juvenile antisocial behavior. Although effect sizes were small to moderate, our findings underscore the consistency of the relationship between autonomic markers and antisocial behavior. PMID:21824152

De Vries-Bouw, Marjan; Popma, Arne; Vermeiren, Robert; Doreleijers, Theo A H; Van De Ven, Peter M; Jansen, Lucres M C

2011-11-01

282

Design of test method and detailed ratings of variable air volume fan-coil units  

Microsoft Academic Search

The purpose of this paper is to proceed with a series of performance tests for variable air volume (VAV) fan-coil units to establish complete testing and rating procedures. Based on the guidelines described in ASHRAE standard 79-1984 (ANSI\\/ASHRAE 79-1984. Methods in testing for rating room fan-coil air conditioners) for constant air-volume (CAV) fan-coil units, we have proposed a unique testing

M. T. Ke

2002-01-01

283

Stretching increases heart rate variability in healthy athletes complaining about limited muscular flexibility  

Microsoft Academic Search

An increase in muscular flexibility, as well as a significant beneficial effect on heart rate and heart rate variability (HRV), was observed in healthy male athletes after performing a standardized 15-minute stretching-program over a period of 28 days. We believe the HRV increase to be due, at least in part, to the improved vagal and\\/or diminished sympathetic control. Therefore, we

Michael Mueck-Weymann; G. Janshoff; H. Mueck

2004-01-01

284

A real time generic variable pattern selection algorithm for very low bit-rate video coding  

Microsoft Academic Search

The selection of an optimal regular-shaped pattern set for very low bit-rate video coding, focusing on moving regions has been the objective of much recent research in order to try and improve bit-rate efficiency. Selecting the optimal pattern set however, is an NP hard problem. This paper presents a Generic Variable Pattern Selection (GVPS) algorithm, which introduces a pattern selection

Manoranjan Paul; M. Manzur Murshed; Laurence Dooley

2003-01-01

285

Intracoronary autologous bone marrow cell transplantation beneficially modulates heart rate variability.  

PubMed

The effect of intracoronary administration of autologous bone marrow cells on autonomic modulation of heart rate has not yet been demonstrated. Therefore, we investigated different parameters of heart rate variability (HRV) in 46 patients without (n=23) or with (n=23) intracoronary stem cell therapy after transmural myocardial infarction. After three to twelve months of follow up, patients receiving stem cells showed a significant increase of HRV parameters that have been linked to cardiovascular prognosis. PMID:17050010

Schueller, Per Otto; Meyer, Christian; Brehm, Michael; Wernet, P; Schannwell, Christiana Mira; Strauer, Bodo Eckehard

2007-07-31

286

Heat accumulation effects in femtosecond laser-written waveguides with variable repetition rate  

Microsoft Academic Search

High-repetition rate femtosecond lasers are shown to drive heat accumulation processes that are attractive for rapid writing of low-loss optical waveguides in transparent glasses. A novel femtosecond fiber laser system (IMRA America, FCPA muJewel) providing variable repetition rate between 0.1 and 5 MHz was used to study the relationship between heat accumulation and resulting waveguide properties in fused silica and

Shane M. Eaton; Haibin Zhang; Peter R. Herman; Fumiyo Yoshino; Lawrence Shah; James Bovatsek; Alan Y. Arai

2005-01-01

287

Does fractality in heart rate variability indicate the development of fetal neural processes?  

NASA Astrophysics Data System (ADS)

By using an improved detrended fluctuation analysis we studied the scaling behaviour of 53 long-term series of fetal heart rate fluctuations. Our results suggest that fractality begins to arise around 24 weeks of normal human gestation and that this condition, showing some additional developments, seems to be preserved during gestation. This may provide new evidence of a role played by cortical-to-subcortical pathways in the long-term fractal nature of heart rate variability data.

Echeverría, J. C.; Woolfson, M. S.; Crowe, J. A.; Hayes-Gill, B. R.; Piéri, Jean F.; Spencer, C. J.; James, D. K.

2004-10-01

288

Comparison of heart and respiratory rate variability measures using an intermittent incremental submaximal exercise model.  

PubMed

To better understand the alterations in cardiorespiratory variability during exercise, the present study characterized the patterns of change in heart rate variability (HRV), respiratory rate variability (RRV), and combined cardiorespiratory variability (HRV-RRV) during an intermittent incremental submaximal exercise model. Six males and six females completed a submaximal exercise protocol consisting of an initial baseline resting period followed by three 10-min bouts of exercise at 20%, 40%, and 60% of maximal aerobic capacity (V?O2max). The R-R interval and interbreath interval variability were measured at baseline rest and throughout the submaximal exercise. A group of 93 HRV, 83 RRV, and 28 HRV-RRV measures of variability were tracked over time through a windowed analysis using a 5-min window size and 30-s window step. A total of 91 HRV measures were able to detect the presence of exercise, whereas only 46 RRV and 3 HRV-RRV measures were able to detect the same stimulus. Moreover, there was a loss of overall HRV and RRV, loss of complexity of HRV and RRV, and loss of parasympathetic modulation of HRV (up to 40% V?O2max) with exercise. Conflicting changes in scale-invariant structure of HRV and RRV with increases in exercise intensity were also observed. In summary, in this simultaneous evaluation of HRV and RRV, we found more consistent changes across HRV metrics compared with RRV and HRV-RRV. PMID:24053520

Barrera-Ramirez, Juliana; Bravi, Andrea; Green, Geoffrey; Seely, Andrew J; Kenny, Glen P

2013-11-01

289

Effects of ?-blockade with bisoprolol on heart rate variability in advanced heart failure: Analysis of scatterplots of RR intervals at selected heart rates  

Microsoft Academic Search

The effect of ?-blockade on heart-rate variability was assessed at different heart rates in 52 patients with heart failure included in the randomized, placebo-controlled, Cardiac Insufficiency Bisoprolol Study (CIBIS). Scatterplots of R-R intervals display beat-to-beat variability by plotting each R-R interval against the preceding interval. Scatterplot dispersion at different R-R intervals provides a measure of beat-to-beat heart-rate variability at different

Xavier Copie; Françoise Pousset; Philippe Lechat; Patrice Jaillon; Louis Guize; Jean-Yves Le Heuzey

1996-01-01

290

Intra-task variability of trunk coordination during a rate-controlled bipedal dance jump.  

PubMed

In this study, we investigated trunk coordination during rate-controlled bipedal vertical dance jumps. The aims of the study were to investigate the pattern of coordination and the magnitude of coordination variability within jump phases and relative to phase-defining events during the jump. Lumbar and thoracic kinematics were collected from seven dancers during a series of jumps at 95 beats per minute. The vector coding technique was used to quantify the pattern and variability of trunk coordination. Coordination was predominantly anti-phase during propulsion and landing. Mean coordination variability peaked just before the landing phase and at the transition from landing to propulsion phases, and was lowest during the propulsion phase just before toe-off. The results indicate that peaks in variability could be explained by task and phase-specific biomechanical demands. PMID:22117102

Smith, Jo Armour; Siemienski, Adam; Popovich, John M; Kulig, Kornelia

2012-01-01

291

Heart rate variability and cardiac arrhythmias in patients with chronic renal failure  

Microsoft Academic Search

Heart rate variability was measured from 24-h electrocardiograms in 61 patients with end stage chronic renal failure. The method used counts the number of times successive RR intervals differ by more than 50 ms over the 24-h period, and is a reliable indicator of cardiac parasympathetic activity. Also analysed were the frequency and type of ectopic beats and other arrhythmias.

B. J. Thomson; D. McAreavey; J. M. M. Neilson; R. J. Winney; D. J. Ewing

1991-01-01

292

Association of health behaviour with heart rate variability: a population-based study  

Microsoft Academic Search

BACKGROUND: Reduced heart rate variability (HRV), a non-invasive marker of autonomic dysfunction, and an unhealthy lifestyle are associated with an increased morbidity and mortality of cardiovascular diseases (CVD). The autonomic dysfunction is a potential mediator of the association of behavioural risk factors with adverse health outcomes. We studied the association of HRV with behavioural risk factors in an elderly population.

Alexander Kluttig; Barbara Schumann; Cees A Swenne; Jan A Kors; Oliver Kuss; Hendrik Schmidt; Karl Werdan; Johannes Haerting; Karin H Greiser

2010-01-01

293

Change in heart rate variability in bedridden patients with severe physical disability  

Microsoft Academic Search

The change in power spectral density of heart rate variability (HRV) during sitting and to an exposure to lower body negative pressure of ?20 mmHg was estimated in 21 bedridden patients with severe physical disability and in 18 normal persons in order to investigate the change in their autonomic activity and its subsequent effect upon cardiovascular regulation. From the power

Katsumi Mita; Yumi Takahashi; Kumi Akataki; Makoto Watakabe; Nobuharu Suzuki

1998-01-01

294

Heart rate variability in soccer players with mitral valve prolapse or benign arrhythmia  

Microsoft Academic Search

Numerous studies have reported increased cardiac vagal activity in well endurance-trained athletes. However, no clear data exist regarding the cardiac autonomic activity in athletes with common cardiovascular findings, such as mild mitral valve prolapse (MVP) and transient benign arrhythmias. Therefore, the purpose of this study was to investigate and compare the cardiac autonomic outflow by heart rate variability (HRV) analysis

N. Koutlianos; E. Kouidi; A. Deligiannis

2004-01-01

295

Ventilatory threshold prediction by spectral analysis of heart rate variability in incremental maximal tests  

Microsoft Academic Search

Ventilatory thresholds (VT1 and VT2) are useful in many fields of medicine and sports. Nevertheless, their measurement is cumbersome and needs trained personnel. This work proposes an alternative method to predict VT1, VT2 and maximum loads in incremental maximal tests based on heart rate variability (HRV) analysis. Twelve competitive male cyclists executed an incremental exhaustive test. During the test, RR

A. Beni?tez; M. A. Garci?a-Gonza?lez; R. Angulo; F. Rodri?guez; X. Iglesias; R. Besco?s; M. Marina; J. M. Padulle?s

2010-01-01

296

Continuous positive airway pressure increases heart rate variability in heart failure patients with obstructive sleep apnoea  

Microsoft Academic Search

Patients with heart failure or OSA (obstructive sleep apnoea) have reduced HF-HRV (high- frequency heart rate variability), indicating reduced cardiac vagal modulation, a marker of poor prognosis. CPAP (continuous positive airway pressure) abolishes OSA in patients with heart failure, but effects on daytime HF-HRV have not been determined. We hypothesized that, in patients with heart failure, treatment of coexisting OSA

Kengo Usui; Yasuyuki Kaneko

2008-01-01

297

Measurement of heart rate variability and stress evaluation by using microwave reflectometric vital signal sensing  

Microsoft Academic Search

In this paper, we present two robust signal processing techniques for stress evaluation using a microwave reflectometric cardiopulmonary sensing instrument. These techniques enable the heart rate variability (HRV) to be recovered from measurements of body-surface dynamic motion, which is subsequently used for the stress evaluation. Specifically, two novel elements are introduced: one is a reconfiguration of the HRV from the

Daisuke Nagae; Atsushi Mase

2010-01-01

298

The Relationship of Heart Rate Variability with Severity and Prognosis of Cirrhosis  

Microsoft Academic Search

Many studies have demonstrated that cirrhosis is frequently associated with autonomic dysfunction. The aim of this study was to test autonomic dysfunction in cirrhotic patients by analyzing heart rate variability (HRV), to determine whether or not the degree of autonomic dysfunction is correlated with the severity of disease, and, also, to compare the changes of HRV between survivor and nonsurvivor

Fehmi Ates; Ergun Topal; Feridun Kosar; Melih Karincaoglu; Bulent Yildirim; Yuksel Aksoy; Murat Aladag; Murat M. M. Harputluoglu; Ulvi Demirel; Hakan Alan; Fatih Hilmioglu

2006-01-01

299

Acute effect of ambient ozone on heart rate variability in healthy elderly subjects  

Microsoft Academic Search

Acute ambient ozone (O3) exposure is associated with the increased mortality and morbidity of cardiovascular diseases. The dysfunction of cardiac autonomic nervous system (ANS), indicated by the disturbed heart rate variability (HRV), may be the most important underlying mechanism. Previous studies reported the heterogeneous associations between O3 within several hours’ exposure and HRV on general elderly subjects, in which poor

Xiaofeng Jia; Xiaoming Song; Masayuki Shima; Kenji Tamura; Furong Deng; Xinbiao Guo

2011-01-01

300

Heart rate variability and saliva cortisol assessment in shelter dog: Human–animal interaction effects  

Microsoft Academic Search

The aim of this study is to investigate the effects of a human interaction program on shelter dogs and to determine the effect on canine heart rate variability, behaviour, and salivary cortisol levels. Twenty dogs were behaviourally (temperament tests) and clinically (full cardiologic examination) pre-tested and then matched in two homogenous groups. Ten dogs (group A) were submitted to a

Luciana Bergamasco; Maria Cristina Osella; Paolo Savarino; Giuseppe Larosa; Laura Ozella; Monica Manassero; Paola Badino; Rosangela Odore; Raffaella Barbero; Giovanni Re

2010-01-01

301

Ambient fine particles modify heart rate variability in young healthy adults  

Microsoft Academic Search

Particulate air pollution has been related with cardiopulmonary morbidity and mortality. Recent studies have shown that an increase in particulate matter (PM)2.5 ambient concentrations was associated with a decrease in heart rate variability (HRV) in the elderly with cardiovascular conditions, which could increase the risk of death. In order to assess if this association could also be observed in young

Maite Vallejo; Silvia Ruiz; Antonio G Hermosillo; Víctor H Borja-Aburto; Manuel Cárdenas

2006-01-01

302

Evaluation of Association Between Demographic Variables with Smoking Rate in Rural Cultures  

Microsoft Academic Search

Objective-Smoking remains the single most important modifiable risk factor for cardiovascular disease and also the leading preventable cause of death. There have been a good many studes on the association between demographic variables and smoking rate in urban areas; however, very little has been done in rural areas. Methods- This cross-sectional study was conducted on 1375 individuals randomly selected from

H. Farshidi; M. Nikparvar; S. Abedini; D. Saed

303

Fetal Heart Rate and Variability: Stability and Prediction to Developmental Outcomes in Early Childhood  

ERIC Educational Resources Information Center

Stability in cardiac indicators before birth and their utility in predicting variation in postnatal development were examined. Fetal heart rate and variability were measured longitudinally from 20 through 38 weeks gestation (n = 137) and again at age 2 (n = 79). Significant within-individual stability during the prenatal period and into childhood…

DiPietro, Janet A.; Bornstein, Marc H.; Hahn, Chun-Shin; Costigan, Kathleen; Achy-Brou, Aristide

2007-01-01

304

EXPOSURE TO CONCENTRATED AMBIENT PARTICLES IN DETROIT ALTERS HEART RATE VARIABILITY IN SPONTANEOUSLY HYPERTENSIVE RATS  

EPA Science Inventory

Elevations in airborne particulate matter (PM) are linked to increased mortality and morbidity in humans with cardiopulmonary disease. Clinical studies show that PM is associated with altered heart rate variability (HRV) and suggests that loss of autonomic control may underlie ca...

305

Independent and incremental prognostic value of heart rate variability in patients with chronic heart failure  

Microsoft Academic Search

Background Decreased heart rate variability (HRV), indicating derangement in cardiac autonomic control, has been reported in patients with chronic heart failure. However, the independent and incremental prognostic value of HRV over clinical data and measures of left ventricular dysfunction has been less thoroughly investigated. This study was designed to evaluate the predictive value of HRV and Poincaré plots as assessed

Domenico Bonaduce; Mario Petretta; Fortunato Marciano; Maria L. E. Vicario; Claudio Apicella; Maria A. E. Rao; Emanuele Nicolai; Massimo Volpe

1999-01-01

306

Multiscale multifractal analysis of heart rate variability recordings with a large number of occurrences of arrhythmia  

NASA Astrophysics Data System (ADS)

Human heart rate variability, in the form of time series of intervals between heart beats, shows complex, fractal properties. Recently, it was demonstrated many times that the fractal properties vary from point to point along the series, leading to multifractality. In this paper, we concentrate not only on the fact that the human heart rate has multifractal properties but also that these properties depend on the time scale in which the multifractality is measured. This time scale is related to the frequency band of the signal. We find that human heart rate variability appears to be far more complex than hitherto reported in the studies using a fixed time scale. We introduce a method called multiscale multifractal analysis (MMA), which allows us to extend the description of heart rate variability to include the dependence on the magnitude of the variability and time scale (or frequency band). MMA is relatively immune to additive noise and nonstationarity, including the nonstationarity due to inclusions into the time series of events of a different dynamics (e.g., arrhythmic events in sinus rhythm). The MMA method may provide new ways of measuring the nonlinearity of a signal, and it may help to develop new methods of medical diagnostics.

Giera?towski, J.; ?ebrowski, J. J.; Baranowski, R.

2012-02-01

307

Metabolic Syndrome and Short-Term Heart Rate Variability in Adults with Intellectual Disabilities  

ERIC Educational Resources Information Center

Metabolic syndrome (MetS) increases the risk of cardiovascular events. Heart rate variability (HRV) represents autonomic functioning, and reduced HRV significantly increases cardiovascular mortality. The aims of the present paper are to assess the prevalence of MetS in adults with intellectual disabilities (ID), the difference in short-term HRV…

Chang, Yaw-Wen; Lin, Jin-Ding; Chen, Wei-Liang; Yen, Chia-Feng; Loh, Ching-Hui; Fang, Wen-Hui; Wu, Li-Wei

2012-01-01

308

Fractal Analysis of Heart Rate Variability and Mortality After an Acute Myocardial Infarction  

Microsoft Academic Search

The recently developed fractal analysis of heart rate (HR) variability has been suggested to provide prognostic information about patients with heart failure. This pro- spective multicenter study was designed to assess the prognostic significance of fractal and traditional HR vari- ability parameters in a large, consecutive series of sur- vivors of an acute myocardial infarction (AMI). A con- secutive series

Jari M. Tapanainen; Poul Erik; Bloch Thomsen; Lars Køber; Christian Torp-Pedersen; Timo H. Makikallio; Kai S. Lindgren; Heikki V. Huikuri

2002-01-01

309

Field Validity of Heart Rate Variability Metrics Produced by QRSTool and CMetX  

ERIC Educational Resources Information Center

Interest in heart rate variability (HRV) metrics as markers of physiological and psychological health continues to grow beyond those with psychophysiological expertise, increasing the importance of developing suitable tools for researchers new to the field. Allen, Chambers, and Towers (2007) developed QRSTool and CMetX software as simple,…

Hibbert, Anita S.; Weinberg, Anna; Klonsky, E. David

2012-01-01

310

Association of hyperglycemia with reduced heart rate variability (The Framingham Heart Study)  

Microsoft Academic Search

This study was designed to examine the association of heart rate variability (HRV) with blood glucose levels in a large community-based population. Previous reports have shown HRV to be reduced in diabetics, suggesting the presence of abnormalities in neural regulatory mechanisms. There is scant information about HRV across the spectrum of blood glucose levels in a population-based cohort. One thousand

Jagmeet P Singh; Martin G Larson; Christopher J O’Donnell; Peter F Wilson; Hisako Tsuji; Donald M Lloyd-Jones; Daniel Levy

2000-01-01

311

HEART RATE VARIABILITY IN RODENTS ? USES AND CAVEATS IN TOXICOLOGICAL STUDIES  

EPA Science Inventory

Heart rate variability (HRV) is a measure of cardiac pacing dynamics that has recently garnered a great deal of interest in environmental health studies. While the use of these measures has become popular, much uncertainty remains in the interpretation of results, both in terms ...

312

The Effect of Listening to Specific Musical Genre Selections on Measures of Heart Rate Variability  

ERIC Educational Resources Information Center

University students (N = 30) individually listened to the Billboard 100 top-ranked musical selection for their most and least liked musical genre. Two minutes of silence preceded each musical listening condition, and heart rate variability (HRV) was recorded throughout. All HRV measures decreased during music listening as compared with silence.…

Orman, Evelyn K.

2011-01-01

313

Childhood Psychopathology and Autonomic Dysregulation: Exploring the Links Using Heart Rate Variability  

ERIC Educational Resources Information Center

Changes in cardiovascular reactivity have been used as a psychophysiological marker of various emotional states in both children and adults. Recent decades have seen increasing use of heart rate variability as a non-invasive marker of cardiac autonomic function and of central processes involved in autonomic function regulation. Developmental…

Srinivasan, Krishnamachari

2007-01-01

314

Improved Heart Rate Variability Signal Analysis from the Beat Occurrence Times According to the IPFM Model  

Microsoft Academic Search

The heart rate variability (HRV) is an extended tool to analyze the mechanisms controlling the cardiovascular system. In this paper, the integral pulse frequency modulation model (IPFM) is assumed. It generates the beat occurrence times from a modulating signal. This signal is thought to represent the autonomic nervous system action, mostly studied in its frequency components. Different spectral estimation methods

Javier Mateo; Pablo Laguna

2000-01-01

315

Particulate matter and heart rate variability among elderly retirees: the Baltimore 1998 PM study  

Microsoft Academic Search

This study investigates the relationship between ambient fine particle pollution and impaired cardiac autonomic control in the elderly. Heart rate variability (HRV) among 56 elderly (mean age 82) nonsmoking residents of a retirement center in Baltimore County, Maryland, was monitored for 4 weeks, from July 27 through August 22, 1998. The weather was seasonally mild (63–84°F mean daily temperature) with

JOHN CREASON; LUCAS NEAS; DEBRA WALSH; RON WILLIAMS; LINDA SHELDON; DUANPING LIAO; CARL SHY

2001-01-01

316

Complex demodulation of heart rate variability during parabolic flight: an exploratory study  

Microsoft Academic Search

The aim of this study was to evaluate the usefulness of complex demodulation (CDM) in assessing frequency components of heart rate variability (HRV) in the setting of dynamic amplitude variations. First, analysis of simulated data showed that the upper limit of rapid amplitude variations corresponded to a period of less than 16 s in order to allow a 95% reliable

B. Verheyden; K. Cockuyt; F. Beckers; A. E. Aubert

2005-01-01

317

Statistical analysis of nuclear power plant pump failure rate variability: some preliminary results  

Microsoft Academic Search

In-Plant Reliability Data System (IPRDS) pump failure data on over 60 selected pumps in four nuclear power plants are statistically analyzed using the Failure Rate Analysis Code (FRAC). A major purpose of the analysis is to determine which environmental, system, and operating factors adequately explain the variability in the failure data. Catastrophic, degraded, and incipient failure severity categories are considered

H. F. Martz; D. E. Whiteman

1984-01-01

318

Variable bit-rate coding of video signals for ATM networks  

Microsoft Academic Search

Statistical characteristics of video signals for video packet coding, are clarified and a variable-bit-rate coding method for asynchronous transfer mode (ATM) networks is described that is capable of compensating for packet loss. ATM capabilities are shown to be greatly affected by delay, delay jitter, and packet loss probability. Packet loss has the greatest influence on picture quality. Packets may be

FUMIO KISHINO; KATSUTOSHI MANABE; YASUHITO HAYASHI; HIROSHI YASUDA

1989-01-01

319

An energy search approach to variable frame rate front-end processing for robust ASR  

Microsoft Academic Search

Extensive research has been devoted to robustness in the presence of various types and degrees of environmental noise over the past several years, however this remains one of the main problems facing automatic speech recognition systems. This paper describes a new variable frame rate analysis technique, based upon searching a predefined lookahead interval for the next frame position that maximizes

Julien Epps; Eric H. C. Choi

2005-01-01

320

Rates of Convergence in the CLT for Some Weakly Dependent Random Variables  

Microsoft Academic Search

We provide rates in the central limit theorem (CLT) for some weakly dependent sequences under a power decay of their covariance. Those sequences are assumed to be associated with or to satisfy a common property of Gaussian processes and positively (or negatively) dependent random variables. For this, we extend the Lindeberg method in our framework, following a method due to

S. Louhichi

2002-01-01

321

Evaluation of Heart Rate Variability by Using Wavelet Transform and a Recurrent Neural Network.  

National Technical Information Service (NTIS)

The purpose of this paper is to evaluate the physical and mental stress based on the physiological index, and a new evaluation method of heart rate variability is proposed. This method combines the wavelet transform with a recurrent neural network. The fe...

O. Fukuda Y. Nagata K. Homma T. Tsuji

2001-01-01

322

New Model-Based Ectopic Beat Correction Algorithm for Heart Rate Variability.  

National Technical Information Service (NTIS)

We propose a new ectopic beat correction algorithm for Heart Rate Variability (HRV) that is based on the Integral Pulse Frequency Modulation (IPFM) model The model is used to infer the modulation signal that has generated the beats surrounding the ectopic...

M. Brennan M. Palaniswami P. Kamen

2001-01-01

323

Bilateral Hegu Acupoints Have the Same Effect on the Heart Rate Variability of the Healthy Subjects  

PubMed Central

Background. The specificity of acupuncture points (acupoints) is one of the key concepts in traditional acupuncture theory, but the question of whether there is adequate scientific evidence to prove or disprove specificity has been vigorously debated in recent years. Acupoint laterality is an important aspect of acupoint specificity. Data is particularly scarce regarding the laterality of the same channel, namesake acupoint located on opposite sides of the body. Our previous study results suggest that Neiguan acupoint (PC6) has the laterality. The aim of this study was to investigate whether Hegu (LI4) also has laterality from the perspective of heart rate variability. Methods. A total of twenty-eight healthy female volunteers were recruited for this study and were randomly separated into the group I (n = 14) and the group II (n = 14) according to the register order. In the group I, left LI4 was stimulated in the first epoch and the right LI4 was stimulated in the second epoch. In the group II, right LI4 was stimulated in the first epoch and left LI4 was stimulated in the second epoch. Electrocardiogram was recorded and heart rate variability was analyzed. Results. The results show that there were no significant differences of heart rate variablity between the group I and the group II in the time domain and in the frequency domain. Conclusions. Bilateral Hegu acupoints have the same effect on the heart rate variability of the healthy subjects.

Yuying, Tian; Shuyong, Jia; Wenting, Zhou; Weibo, Zhang

2014-01-01

324

Comparison of heart rate variability in patients with chronic fatigue syndrome and controls  

Microsoft Academic Search

Recent studies have reported a close association between chronic fatigue syndrome and neurally mediated hypotension. We hypothesized that this association may result from an abnormality in autonomic function among patients with chronic fatigue syndrome, which may be detectable using an analysis of heart rate variability. We prospectively studied 19 patients who fulfilled the Centers for Disease Control criteria for chronic

A. Yataco; H. Talo; P. Rowe; D. A. Kass; R. D. Berger; H. Calkins

1997-01-01

325

Central hemodynamic and heart rate variability parameters in athletes during different training programs  

Microsoft Academic Search

Central hemodynamic and heart rate variability (HRV) parameters were assessed in highly qualified athletes differing in the\\u000a types of their training programs at relative rest. During endurance (the endurance group, n = 27) and strength (the strength group, n = 17) trainings, the total peripheral resistance (TPR) was decreased by 15% (p = 0.003) in the endurance group and by

A. Yu. Mal’tsev; A. A. Mel’nikov; A. D. Vikulov; K. S. Gromova

2010-01-01

326

Relation between heart rate variability and training load in middle-distance runners  

Microsoft Academic Search

V. PICHOT, F. ROCHE, J. M. GASPOZ, F. ENJOLRAS, A. ANTONIADIS, P. MININI, F. COSTES, T. BUSSO, J. R. LACOUR, and J. C. BARTHELEMY. Relation between heart rate variability and training load in middle-distance runners. Med. Sci. Sports Exerc., Vol. 32, No. 10, pp. 1729-1736, 2000. Purpose: Monitoring physical performance is of major importance in competitive sports. Indices commonly used,

Vincent PICHOT; Jean-Michel GASPOZ; Franck ENJOLRAS; Anestis ANTONIADIS; Pascal MININI; Thierry BUSSO

2000-01-01

327

Cardiac denervation occurs independent of orthostatic hypotension and impaired heart rate variability in Parkinson's disease  

Microsoft Academic Search

Patients with idiopathic Parkinson's disease (PD) have impaired sympathetically mediated neurocirculatory innervation. Here we analyzed the correlation between cardiac 123I-metaiodobenzylguanidine (MIBG) uptake, orthostatic hypotension and heart rate variability in treated patients with PD. Orthostatic hypotension (OH) as a hallmark of sympathetic neurocirculatory failure was found with a high prevalence in PD. PD is known to affect cardiac innervation, resulting in

C.-A. Haensch; H. Lerch; J. Jörg; S. Isenmann

2009-01-01

328

Blood pressure and heart rate variability in patients with essential hyperhidrosis  

Microsoft Academic Search

Introduction Essential hyperhidrosis (EH) is often considered to be related to an increased activity of sympathetic nervous system (SNS). However, there is a lack of studies comparing autonomic nervous system (ANS) activity in controls and in EH patients. The aim of the present study was to simultaneously investigate in patients with severe EH, blood pressure, heart rate variability and plasma

Jean-Michel Senard; Marion Simonetta-Moreau; Marie-Antoinette Tran

2003-01-01

329

Original Research Article Climate Variables as Predictors of Basal Metabolic Rate: New Equations  

Microsoft Academic Search

Estimation of basal metabolic rate (BMR) and daily energy expenditure (DEE) in living humans and in fossil hominins can be used to understand the way populations adapt to different environmental and nutritional cir- cumstances. One variable that should be considered in such estimates is climate, which may influence between-popula- tion variation in BMR. Overall, populations living in warmer climates tend

ANDREW W. FROEHLE

330

Simple and Efficient Models for Variable Bit Rate MPEG Video Traffic  

Microsoft Academic Search

For the performance analysis of ATM networks carrying Variable Bit Rate (VBR) MPEG video sequences there is a need for appropriate video traffic models. In this paper, we discuss Markov chain models for this specific type of traffic with respect to several statistical properties and their ability to predict cell losses at buffers of ATM multiplexers. We intentionally selected a

Oliver Rose

1997-01-01

331

Exposure to wood smoke increases arterial stiffness and decreases heart rate variability in humans  

PubMed Central

Background Emissions from biomass combustion are a major source of indoor and outdoor air pollution, and are estimated to cause millions of premature deaths worldwide annually. Whilst adverse respiratory health effects of biomass exposure are well established, less is known about its effects on the cardiovascular system. In this study we assessed the effect of exposure to wood smoke on heart rate, blood pressure, central arterial stiffness and heart rate variability in otherwise healthy persons. Methods Fourteen healthy non-smoking subjects participated in a randomized, double-blind crossover study. Subjects were exposed to dilute wood smoke (mean particle concentration of 314±38 ?g/m3) or filtered air for three hours during intermittent exercise. Heart rate, blood pressure, central arterial stiffness and heart rate variability were measured at baseline and for one hour post-exposure. Results Central arterial stiffness, measured as augmentation index, augmentation pressure and pulse wave velocity, was higher after wood smoke exposure as compared to filtered air (p < 0.01 for all), and heart rate was increased (p < 0.01) although there was no effect on blood pressure. Heart rate variability (SDNN, RMSSD and pNN50; p = 0.003, p < 0.001 and p < 0.001 respectively) was decreased one hour following exposure to wood smoke compared to filtered air. Conclusions Acute exposure to wood smoke as a model of exposure to biomass combustion is associated with an immediate increase in central arterial stiffness and a simultaneous reduction in heart rate variability. As biomass is used for cooking and heating by a large fraction of the global population and is currently advocated as a sustainable alternative energy source, further studies are required to establish its likely impact on cardiovascular disease. Trial registration ClinicalTrials.gov, NCT01488500

2013-01-01

332

Exposure to wood smoke increases arterial stiffness and decreases heart rate variability in humans.  

PubMed

BACKGROUND: Emissions from biomass combustion are a major source of indoor and outdoor air pollution, and are estimated to cause millions of premature deaths worldwide annually. Whilst adverse respiratory health effects of biomass exposure are well established, less is known about its effects on the cardiovascular system. In this study we assessed the effect of exposure to wood smoke on heart rate, blood pressure, central arterial stiffness and heart rate variability in otherwise healthy persons. METHODS: Fourteen healthy non-smoking subjects participated in a randomized, double-blind crossover study. Subjects were exposed to dilute wood smoke (mean particle concentration of 314+/-38 mug/m3) or filtered air for three hours during intermittent exercise. Heart rate, blood pressure, central arterial stiffness and heart rate variability were measured at baseline and for one hour post-exposure. RESULTS: Central arterial stiffness, measured as augmentation index, augmentation pressure and pulse wave velocity, was higher after wood smoke exposure as compared to filtered air (p < 0.01 for all), and heart rate was increased (p < 0.01) although there was no effect on blood pressure. Heart rate variability (SDNN, RMSSD and pNN50; p = 0.003, p < 0.001 and p < 0.001 respectively) was decreased one hour following exposure to wood smoke compared to filtered air. CONCLUSIONS: Acute exposure to wood smoke as a model of exposure to biomass combustion is associated with an immediate increase in central arterial stiffness and a simultaneous reduction in heart rate variability. As biomass is used for cooking and heating by a large fraction of the global population and is currently advocated as a sustainable alternative energy source, further studies are required to establish its likely impact on cardiovascular disease.Trial registration: ClinicalTrials.gov, NCT01488500. PMID:23742058

Unosson, Jon; Blomberg, Anders; Sandström, Thomas; Muala, Ala; Boman, Christoffer; Nyström, Robin; Westerholm, Roger; Mills, Nicholas L; Newby, David E; Langrish, Jeremy P; Bosson, Jenny A

2013-06-01

333

Effects of variability and rate on battery charge storage and lifespan  

NASA Astrophysics Data System (ADS)

The growing prevalence of hybrid and electric vehicles, intermittent renewable energy sources, and other complex power systems has triggered a rapid increase in demand for energy storage. Unlike portable electronic devices, whose batteries can be recharged according to a pre-determined protocol simply by plugging them into the wall, many of these applications are characterized by highly variable charge and demand profiles. The central objective of this work is to assess the impact of power distribution and frequency on battery behavior in order to improve overall system efficiency and lifespan in these variable power applications. We first develop and experimentally verify a model to describe the trade-off between battery charging power and energy stored to assess how varying power input affects battery efficiency. This relationship is influenced both by efficiency losses at high powers and by premature voltage cutoffs, which contribute to incomplete battery charging and discharging. We experimentally study the impact of variable power on battery aging in lead-acid, nickel metal hydride, lithium-ion and lithium iron phosphate batteries. As a case study we focus on off-grid wind systems, and analyze the impact of both power distribution and frequency on charge acceptance and degradation in each of these chemistries. We suggest that lithium iron phosphate batteries may be more suitable for off-grid electrification projects than standard lead-acid batteries. We experimentally assess the impact of additional variable charging parameters on battery performance, including the interplay between efficiency, frequency of power oscillations, state-of-charge, incomplete charging and path dependence. We develop a frequency-domain model for hybrid energy storage systems that couples non-stationary frequency analysis of variable power signals to a frequency-based metric for energy storage device performance. The experimental and modeling work developed herein can be utilized to optimize energy storage system design and control algorithms for variable power applications.

Krieger, Elena Marie

334

Do physiological and pathological stresses produce different changes in heart rate variability?  

PubMed Central

Although physiological (e.g., exercise) and pathological (e.g., infection) stress affecting the cardiovascular system have both been documented to be associated with a reduction in overall heart rate variability (HRV), it remains unclear if loss of HRV is ubiquitously similar across different domains of variability analysis or if distinct patterns of altered HRV exist depending on the stressor. Using Continuous Individualized Multiorgan Variability Analysis (CIMVA™) software, heart rate (HR) and four selected measures of variability were measured over time (windowed analysis) from two datasets, a set (n = 13) of patients who developed systemic infection (i.e., sepsis) after bone marrow transplant (BMT), and a matched set of healthy subjects undergoing physical exercise under controlled conditions. HR and the four HRV measures showed similar trends in both sepsis and exercise. The comparison through Wilcoxon sign-rank test of the levels of variability at baseline and during the stress (i.e., exercise or after days of sepsis development) showed similar changes, except for LF/HF, ratio of power at low (LF) and high (HF) frequencies (associated with sympathovagal modulation), which was affected by exercise but did not show any change during sepsis. Furthermore, HRV measures during sepsis showed a lower level of correlation with each other, as compared to HRV during exercise. In conclusion, this exploratory study highlights similar responses during both exercise and infection, with differences in terms of correlation and inter-subject fluctuations, whose physiologic significance merits further investigation.

Bravi, Andrea; Green, Geoffrey; Herry, Christophe; Wright, Heather E.; Longtin, Andre; Kenny, Glen P.; Seely, Andrew J. E.

2013-01-01

335

Skinfold thickness is related to cardiovascular autonomic control as assessed by heart rate variability and heart rate recovery.  

PubMed

The purpose of this study was to determine if heart rate recovery (HRR) and heart rate variability (HRV) are related to maximal aerobic fitness and selected body composition measurements. Fifty men (age = 21.9 ± 3.0 years, height = 180.8 ± 7.2 cm, weight = 80.4 ± 9.1 kg, volunteered to participate in this study. For each subject, body mass index (BMI), waist circumference (WC), and the sum of skinfolds across the chest, abdomen, and thigh regions (SUMSF) were recorded. Heart rate variability (HRV) was assessed during a 5-minute period while the subjects rested in a supine position. The following frequency domain parameters of HRV were recorded: normalized high-frequency power (HFnu), and low-frequency to high-frequency power ratio (LF:HF). To determine maximal aerobic fitness (i.e., VO2max), each subject performed a maximal graded exercise test on a treadmill. Heart rate recovery was recorded 1 (HRR1) and 2 (HRR2) minutes during a cool-down period. Mean VO2max and BMI for all the subjects were 49.5 ± 7.5 ml·kg(-1)·min(-1) and 24.7 ± 2.2 kg·m(-2), respectively. Although VO2max, WC, and SUMSF was each significantly correlated to HRR and HRV, only SUMSF had a significant independent correlation to HRR1, HRR2, HFnu, LF:HF (p < 0.01). The results of the regression procedure showed that SUMSF accounted for the greatest variance in HRR1, HRR2, HFnu, and LF:HF (p < 0.01). The results of this study suggest that cardiovascular autonomic modulation is significantly related to maximal aerobic fitness and body composition. However, SUMSF appears to have the strongest independent relationship with HRR and HRV, compared to other body composition parameters and VO2max. PMID:21691230

Esco, Michael R; Williford, Henry N; Olson, Michele S

2011-08-01

336

A conceptual evaluation of sustainable variable-rate agricultural residue removal.  

PubMed

Agricultural residues have near-term potential as a feedstock for bioenergy production, but their removal must be managed carefully to maintain soil health and productivity. Recent studies have shown that subfield scale variability in soil properties (e.g., slope, texture, and organic matter content) that affect grain yield significantly affect the amount of residue that can be sustainably removed from different areas within a single field. This modeling study examines the concept of variable-rate residue removal equipment that would be capable of on-the-fly residue removal rate adjustments ranging from 0 to 80%. Thirteen residue removal rates (0% and 25-80% in 5% increments) were simulated using a subfield scale integrated modeling framework that evaluates residue removal sustainability considering wind erosion, water erosion, and soil carbon constraints. Three Iowa fields with diverse soil, slope, and grain yield characteristics were examined and showed sustainable, variable-rate agricultural residue removal that averaged 2.35, 7.69, and 5.62 Mg ha, respectively. In contrast, the projected sustainable removal rates using rake and bale removal for the entire field averaged 0.0, 6.40, and 5.06 Mg ha, respectively. The modeling procedure also projected that variable-rate residue harvest would result in 100% of the land area in all three fields being managed in a sustainable manner, whereas Field 1 could not be sustainably managed using rake and bale removal, and only 83 and 62% of the land area in Fields 2 and 3 would be managed sustainably using a rake and bale operation for the entire field. In addition, it was found that residue removal adjustments of 40 to 65% are sufficient to collect 90% of the sustainably available agricultural residue. PMID:23128737

Muth, D; Bryden, K M

2012-01-01

337

A Conceptual Evaluation of Sustainable Variable-Rate Agricultural Residue Removal  

SciTech Connect

Agricultural residues have near-term potential as a feedstock for bioenergy production, but their removal must be managed carefully to maintain soil health and productivity. Recent studies have shown that subfield scale variability in soil properties (e.g., slope, texture, and organic matter content) that affect grain yield significantly affect the amount of residue that can be sustainably removed from different areas within a single field. This modeling study examines the concept of variable-rate residue removal equipment that would be capable of on-the-fly residue removal rate adjustments ranging from 0 to 80%. Thirteen residue removal rates (0% and 25–80% in 5% increments) were simulated using a subfield scale integrated modeling framework that evaluates residue removal sustainability considering wind erosion, water erosion, and soil carbon constraints. Three Iowa fields with diverse soil, slope, and grain yield characteristics were examined and showed sustainable, variable-rate agricultural residue removal that averaged 2.35, 7.69, and 5.62 Mg ha-1, respectively. In contrast, the projected sustainable removal rates using rake and bale removal for the entire field averaged 0.0, 6.40, and 5.06 Mg ha-1, respectively. The modeling procedure also projected that variable-rate residue harvest would result in 100% of the land area in all three fields being managed in a sustainable manner, whereas Field 1 could not be sustainably managed using rake and bale removal, and only 83 and 62% of the land area in Fields 2 and 3 would be managed sustainably using a rake and bale operation for the entire field. In addition, it was found that residue removal adjustments of 40 to 65% are sufficient to collect 90% of the sustainably available agricultural residue.

David J. Muth, Jr.; K. M. Bryden

2012-10-01

338

Highly accurate moving object detection in variable bit rate video-based traffic monitoring systems.  

PubMed

Automated motion detection, which segments moving objects from video streams, is the key technology of intelligent transportation systems for traffic management. Traffic surveillance systems use video communication over real-world networks with limited bandwidth, which frequently suffers because of either network congestion or unstable bandwidth. Evidence supporting these problems abounds in publications about wireless video communication. Thus, to effectively perform the arduous task of motion detection over a network with unstable bandwidth, a process by which bit-rate is allocated to match the available network bandwidth is necessitated. This process is accomplished by the rate control scheme. This paper presents a new motion detection approach that is based on the cerebellar-model-articulation-controller (CMAC) through artificial neural networks to completely and accurately detect moving objects in both high and low bit-rate video streams. The proposed approach is consisted of a probabilistic background generation (PBG) module and a moving object detection (MOD) module. To ensure that the properties of variable bit-rate video streams are accommodated, the proposed PBG module effectively produces a probabilistic background model through an unsupervised learning process over variable bit-rate video streams. Next, the MOD module, which is based on the CMAC network, completely and accurately detects moving objects in both low and high bit-rate video streams by implementing two procedures: 1) a block selection procedure and 2) an object detection procedure. The detection results show that our proposed approach is capable of performing with higher efficacy when compared with the results produced by other state-of-the-art approaches in variable bit-rate video streams over real-world limited bandwidth networks. Both qualitative and quantitative evaluations support this claim; for instance, the proposed approach achieves Similarity and F1 accuracy rates that are 76.40% and 84.37% higher than those of existing approaches, respectively. PMID:24805212

Shih-Chia Huang; Bo-Hao Chen

2013-12-01

339

Design of rate control for wireless video telephony applications  

NASA Astrophysics Data System (ADS)

We propose a design of a rate control algorithm for low-delay video transmission over wireless channels. Our objective is to meet delay constraints and to make sure that the decoder buffer does not overflow or underflow. We approach this problem analytically, by studying the leaky bucket model in the variable rate transmission scenario, and deriving sufficient conditions for meeting our objective. We then employ these conditions in the design of the rate control algorithm. We report results obtained by using this algorithm with an MPEG-4 AVC/H.264 encoder and LTE channel simulator as a test platform.

Chen, Zhifeng; Reznik, Yuriy A.

2012-10-01

340

Can anatomical morphomic variables help predict abdominal injury rates in frontal vehicle crashes?  

PubMed

Objective: Abdominal injuries resulting from vehicle crashes can be significant, in particular when undetected. In this study, abdominal injuries for occupants involved in frontal impacts were assessed using crash and medical data. Methods: Injury rates and patterns were first assessed with respect to thoracic injuries. A statistical analysis was then conducted to predict abdominal injury outcome using 18 covariate variables, including 4 vehicle, 4 demographic, and 10 morphomic, derived from computed tomography (CT) scans. More than 260,000 logistic regression models were fitted using all possible variable combinations. The models were ranked using the Akaike information criterion (AIC) and combined through the model-averaging approach to produce the optimal predictive model. The performance of the models was then assessed using the area under the curve (AUC). Results: The rate of serious thoracic injury was 2.49 times higher than the rate of abdominal injury. The associated odds ratio was 2.31 (P <.01). These results suggest a strong association between serious abdominal and thoracic injuries. The optimal model AUC was 0.646 when using solely vehicle data, 0.696 when combining vehicle and demographic data, 0.866 when combining vehicle and morphomic data, and 0.879 when combining vehicle, demographic, and morphomic data. These results suggest that morphomic variables better predict abdominal injury outcomes than demographic variables. The most important morphomics variables included visceral fat area, trabecular bone density, and spine angulation. Conclusion: This study is the first to combine vehicle, demographic, and anatomical data to predict abdominal injury rates in frontal crashes. PMID:24867572

Parenteau, Chantal S; Zhang, Peng; Holcombe, Sven; Kohoyda-Inglis, Carla; Wang, Stewart C

2014-08-18

341

The effects of auditory stimulation with music on heart rate variability in healthy women  

PubMed Central

OBJECTIVES: There are no data in the literature with regard to the acute effects of different styles of music on the geometric indices of heart rate variability. In this study, we evaluated the acute effects of relaxant baroque and excitatory heavy metal music on the geometric indices of heart rate variability in women. METHODS: We conducted this study in 21 healthy women ranging in age from 18 to 35 years. We excluded persons with previous experience with musical instruments and persons who had an affinity for the song styles. We evaluated two groups: Group 1 (n?=?21), who were exposed to relaxant classical baroque musical and excitatory heavy metal auditory stimulation; and Group 2 (n?=?19), who were exposed to both styles of music and white noise auditory stimulation. Using earphones, the volunteers were exposed to baroque or heavy metal music for five minutes. After the first music exposure to baroque or heavy metal music, they remained at rest for five minutes; subsequently, they were re-exposed to the opposite music (70-80 dB). A different group of women were exposed to the same music styles plus white noise auditory stimulation (90 dB). The sequence of the songs was randomized for each individual. We analyzed the following indices: triangular index, triangular interpolation of RR intervals and Poincaré plot (standard deviation of instantaneous beat-by-beat variability, standard deviation of the long-term RR interval, standard deviation of instantaneous beat-by-beat variability and standard deviation of the long-term RR interval ratio), low frequency, high frequency, low frequency/high frequency ratio, standard deviation of all the normal RR intervals, root-mean square of differences between the adjacent normal RR intervals and the percentage of adjacent RR intervals with a difference of duration greater than 50 ms. Heart rate variability was recorded at rest for 10 minutes. RESULTS: The triangular index and the standard deviation of the long-term RR interval indices were reduced during exposure to both music styles in the first group and tended to decrease in the second group whereas the white noise exposure decreased the high frequency index. We observed no changes regarding the triangular interpolation of RR intervals, standard deviation of instantaneous beat-by-beat variability and standard deviation of instantaneous beat-by-beat variability/standard deviation in the long-term RR interval ratio. CONCLUSION: We suggest that relaxant baroque and excitatory heavy metal music slightly decrease global heart rate variability because of the equivalent sound level.

Roque, Adriano L.; Valenti, Vitor E.; Guida, Heraldo L.; Campos, Monica F.; Knap, Andre; Vanderlei, Luiz Carlos M.; Ferreira, Lucas L.; Ferreira, Celso; de Abreu, Luiz Carlos

2013-01-01

342

Heat accumulation effects in femtosecond laser-written waveguides with variable repetition rate.  

PubMed

High-repetition rate femtosecond lasers are shown to drive heat accumulation processes that are attractive for rapid writing of low-loss optical waveguides in transparent glasses. A novel femtosecond fiber laser system (IMRA America, FCPA muJewel) providing variable repetition rate between 0.1 and 5 MHz was used to study the relationship between heat accumulation and resulting waveguide properties in fused silica and various borosilicate glasses. Increasing repetition rate was seen to increase the waveguide diameter and decrease the waveguide loss, with waveguides written with 1-MHz repetition rate yielding ~0.2-dB/cm propagation loss in Schott AF45 glass. A finite-difference thermal diffusion model accurately tracks the waveguide diameter as cumulative heating expands the modification zone above 200-kHz repetition rate. PMID:19495387

Eaton, Shane; Zhang, Haibin; Herman, Peter; Yoshino, Fumiyo; Shah, Lawrence; Bovatsek, James; Arai, Alan

2005-06-13

343

Variability of the isotopic lapse rate across the mountain ranges in Wyoming  

NASA Astrophysics Data System (ADS)

Stable isotope based paleoaltimetry studies require knowledge of the isotope-elevation gradient during the time of interest, but this information is rarely available. As a result, many studies often apply the modern local lapse rate or a global average lapse rate and assume these values are valid for the area of interest and that they hold through time. However, natural variability in local-scale climate and mountain geometry and morphology can influence the isotope-elevation (and temperature-elevation) gradient. We evaluate the inter- and intra-mountain range variability of modern climate and isotope values of stream water for three Laramide ranges in Wyoming (Wind River Range, Bighorn and Laramie Mountains), as well as for a regional elevation transect across the central Rocky mountain front. Samples of steam water were taken from major catchments across Wyoming in 2007, 2011, and 2012. We find that the modern lapse rate for these ranges is -1.7‰/km, -2.2‰/km and -1.8‰/km respectively. Although these values are very similar to one another and to the global isotopic lapse rate (-2.1‰/km), large variation (up to 6‰/km) exists among individual small river catchments of the Bighorn Mountains. The variability in catchment-scale lapse rate does not appear to be systematically related to annual, or seasonal surface air temperature, precipitation amount, or catchment area. However, the range-scale lapse rates may yet reflect the regional climate, which is generally coolest and driest in the Wind River Range (lowest lapse rate) and warmest and wettest in the Bighorn Mountains (highest lapse rate). Similar d-excess values exist across individual mountain ranges, but inter-mountain range differences indicate that the Laramie Mountains (and regions of western Nebraska) receive evaporatively enriched rainwater compared to those in the Wind River Range and Bighorn Mountains. These differences do not necessarily require separate vapor sources as the lower d-excess values in the Laramie Range and western Nebraska may result from increased subcloud evaporation of rain drops. Year-to-year climate variability is not significantly different, but 2011 had a cold, wet spring compared to the 30-year normal and 2012 had a remarkably warm, dry spring. Streams recharged with snowmelt having low oxygen isotope values in the late spring, 2011 generally yielded lower lapse rates than samples from 2007. This data suggests that the influence of changes in climate on modern stream water isotopic lapse rate can provide insights into the reconstruction of paleoelevation.

Brian, H.; Fan, M.

2012-12-01

344

Variable reluctance harvester for applications in railroad monitoring  

NASA Astrophysics Data System (ADS)

We present the design, realization, and testing of a variable reluctance energy harvester for the detection of moving ferromagnetic parts, e.g. the wheels of a train while passing over a train passage detector. Measurements were done to determine the output voltage, the energy output per event and the power output with the frequency of the moving ferromagnetic body. Results are compared with finite element analysis (FEA) to estimate the change in magnetic flux and the output voltages. A maximum energy output of 131 ?J per pulse was measured for a simulated condition of a train wheel passing with a speed of 81.5 km/h, which results in a mean output power of 5.9 mW, with a spacing of 10 mm between wheel and the reluctance circuit. This shows that the variable reluctance principle, a well-known method used for numerous sensor applications, is also a comfortable, energy-autonomous and reliable method to detect passing train wheels or other moving ferromagnetic parts, with a simple setup and fairly high useable output power.

Kroener, M.; Ravindran, S. K. T.; Woias, P.

2013-12-01

345

Cepheid variables and their application to the cosmological distance scale  

NASA Astrophysics Data System (ADS)

In the current era of "precision cosmology", measuring the expansion rate of the Universe (Hubble constant, or H 0) more accurately and precisely helps to better constrain the properties of dark energy. Cepheid-based distances are a critical step in the Extragalactic Distance Scale and have been recently used to measure H 0 with a total uncertainty of only 3.4%. I will present my work on Cepheid variables in three different galaxies as part of this effort. NGC 4258 is a galaxy with a very precise and accurate distance (3% uncertainty) based on radio interferometric observations of water masers orbiting its central massive black hole. Therefore, it can be used to obtain a robust absolute calibration of the Cepheid Period-Luminosity relation. I analyzed observations of NGC 4258 obtained at Gemini North over four years and increased the number of long-period Cepheids (P>45 days) known in this galaxy. NGC 5584 was the host of type Ia SN 2007af. I applied a difference imaging technique to Hubble Space Telescope (HST) observations of this galaxy and discovered several hundred Cepheids. I compared my results with previous work based on traditional PSF photometry. The distance estimates of the two samples matched within the errors of the measurements, and so the difference imaging technique was a success. Additionally, I validated the first "white-light" variability search with the HST F350LP filter for discovering Cepheids. NGC 4921 is located in the heart of the Coma cluster at a distance of about 100Mpc. I conducted a search for Cepheid variables using HST, extending the reach of Hubble by a factor of 3 relative to previous Cepheid work. Since Coma is in the Hubble flow, this approach eliminates the need for a secondary distance indicator and enables a direct determination of H0 based exclusively on a Cepheid distance. I present preliminary results from this challenging project.

Hoffman, Samantha Leigh

346

Fetal Heart Rate and Variability: Stability and Prediction to Developmental Outcomes in Early Childhood  

PubMed Central

Stability in cardiac indicators before birth and their utility in predicting variation in postnatal development were examined. Fetal heart rate and variability were measured longitudinally from 20 through 38 weeks gestation (n = 137) and again at age 2 (n = 79). Significant within-individual stability during the prenatal period and into childhood was demonstrated. Fetal heart rate variability at or after 28 weeks gestation and steeper developmental trajectories were significantly associated with mental and psychomotor development at 2 years (n = 82) and language ability at 2.5 years (n = 61). These data suggest that the foundations of individual differences in autonomic control originate during gestation and the developmental momentum of the fetal period continues after birth.

DiPietro, Janet A.; Bornstein, Marc H.; Hahn, Chun-Shin; Costigan, Kathleen; Achy-Brou, Aristide

2008-01-01

347

[Anti-arrhythmic therapy: diagnostic possibilities of signal-averaged electrocardiography and heart rate variability].  

PubMed

Effects of monotherapy with class IC, II and III antiarrhythmic drugs on parameters of signal averaged (SA) ECG and heart rate variability were studied in 88 patients (mean age 45.6+/-7.8 years). Class IC drugs (ethacizine, disopyramide) caused worsening of qualitative parameters of SA ECG and appearance of ventricular late potentials. Therapy with beta-adrenoblockers, amiodarone and sotalol in patients with ventricular arrhythmias was associated with improvement of parameters of SA ECG, lowering of sympathetic and augmentation of parasympathetic activity without sings of arrhrythmogenic and negative inotropic effects. Combination of noninvasive diagnostic methods including SA ECG, temporal and spectral analysis of heart rate variability, Holter ECG monitoring can facilitate selection of appropriate antiarrhythmic therapy and control of its efficacy. PMID:12891276

Tatarchenko, I P; Pozdniakova, N V; Shevyrev, V A; Morozova, O I

2003-01-01

348

Controlling Variable Emittance (MEMS) Coatings for Space Applications  

NASA Technical Reports Server (NTRS)

Small spacecraft, including micro and nanosats, as they are envisioned for future missions, will require an alternative means to achieve thermal control due to their small power and mass budgets. One of the proposed alternatives is Variable Emittance (Vari-E) Coatings for spacecraft radiators. Space Technology-5 (ST-5) is a technology demonstration mission through NASA Goddard Space Flight Center (GSFC) that will utilize Vari-E Coatings. This mission involves a constellation of three (3) satellites in a highly elliptical orbit with a perigee altitude of approximately 200 kilometers and an apogee of approximately 38,000 kilometers. Such an environment will expose the spacecraft to a wide swing in the thermal and radiation environment of the earth's atmosphere. There are three (3) different technologies associated with this mission. The three technologies are electrophoretic, electrochromic, and Micro ElectroMechanical Systems (MEMS). The ultimate goal is to make use of Van-E coatings, in order to achieve various levels of thermal control. The focus of this paper is to highlight the Vari-E Coating MEMS instrument, with an emphasis on the Electronic Control Unit responsible for operating the MEMS device. The Test & Evaluation approach, along with the results, is specific for application on ST-5, yet the information provides a guideline for future experiments and/or thermal applications on the exterior structure of a spacecraft.

Farrar, D.; Schneider, W.; Osiander, R.; Champion, J. L.; Darrin, A. G.; Douglas, Donya; Swanson, Ted D.

2003-01-01

349

Reliability of heart rate variability measures at rest and during light exercise in children  

Microsoft Academic Search

Objectives: To investigate the reliability of heart rate variability (HRV) measures at rest and during light exercise in children.Methods: Short term (five minute) HRV was assessed in 12 children (11–12 years of age). HRV measures were collected at rest with the children supine, breathing at 12 breaths\\/min, and during exercise on a cycle ergometer while exercising at 25% of peak

R J Winsley; N Armstrong; K Bywater; S G Fawkner

2003-01-01

350

Moderate physical exercise increases cardiac autonomic nervous system activity in children with low heart rate variability  

Microsoft Academic Search

Object Our objective was to investigate the effect of a long-term moderate exercise program on cardiac autonomic nervous system (ANS) activity in healthy children. Methods Three hundred and five children aged 6–11 years participated in a 12-month school-based exercise training program (130–140 bpm, 20 min\\/day, 5 days\\/week). Cardiac ANS activities were measured using heart rate variability (HRV) power spectral analysis in resting conditions. Following

Narumi Nagai; Taku Hamada; Tetsuya Kimura; Toshio Moritani

2004-01-01

351

Overall increase in heart rate variability after the Square-Wave Endurance Exercise Test training  

Microsoft Academic Search

Objectives. – We studied the influence of the “Square-Wave Endurance Exercise Test” (SWEET) training program on heart rate (HR) variability during supine rest, 60° upright position and submaximal constant exercise.Methods. – Beat-by-beat HR was recorded during 10 min in the three conditions in 14 healthy women. Before and after 6 weeks of training (45 min, three times a week; n = 7) or

L. Mourot; N. Tordi; S. Perrey; M. Bouhaddi; J.-D. Rouillon; J. Regnard

2005-01-01

352

Increased heart rate variability and executive performance after aerobic training in the elderly  

Microsoft Academic Search

This study examined the effects of two short physical training programs on various parameters of heart rate variability (HRV)\\u000a and on executive performance in older people. Twenty-four sedentary men and women aged 65–78 years were randomly assigned\\u000a to an aerobic exercise program or a stretching program three times a week for 12 weeks. Resting HRV was measured in time and\\u000a frequency domains

Cédric T. Albinet; Geoffroy Boucard; Cédric A. Bouquet; Michel Audiffren

2010-01-01

353

THE ACUTE EFFECTS OF INHALING DIFFERENT CONCENTRATIONS OF OXYGEN ON HEART RATE VARIABILITY AFTER EXHAUSTIVE EXERCISE  

Microsoft Academic Search

The purpose of this study was to investigate the effects of inhaling different percentages of oxygen (O2) after maximal exercise on heart rate variability (HRV). Eight active college males (age, 19.9 ± 1.5 years; height, 177.8 ± 6.3 cm; weight, 76.2 ± 12.7 kg) volunteered to participate in this study. Each subject inhaled normo- baric 21%O2 (NO), 12%O2 (LO), and

Chia-Lun Lee; Ching-Feng Cheng; Wen-Chih Lee; Jung-Charng Lin

2007-01-01

354

Five minute recordings of heart rate variability for population studies: repeatability and age–sex characteristics  

Microsoft Academic Search

ObjectiveTo evaluate the stability of short recordings of heart rate variability (HRV) with time, and the association of HRV with age and sex.DesignFive minute Holter recordings were made twice over a two month interval (tracking study). In addition, HRV was measured in a cross sectional study.SettingResidents of 11 Israeli kibbutzim were examined in their settlements.Subjects32 men and 38 women (aged

R Sinnreich; J D Kark; Y Friedlander; D Sapoznikov; M H Luria

1998-01-01

355

Heart Rate Variability Reflects Self-Regulatory Strength, Effort, and Fatigue  

Microsoft Academic Search

Experimental research reliably demonstrates thatself-regulatorydeficitsareaconsequenceofpriorself- regulatory effort. However, in naturalistic settings, al- though people know that they are sometimes vulnerable to saying, eating, or doing the wrong thing, they cannot ac- curately gauge their capacity to self-regulate at any given time. Because self-regulation and autonomic regulation colocalize in the brain, an autonomic measure, heart rate variability (HRV), could provide an

Suzanne C. Segerstrom; Lise Solberg Nes

2007-01-01

356

The base-scale entropy analysis of short-term heart rate variability signal  

Microsoft Academic Search

The complexity of heart rate variability (HRV) signal can reflect physiological functions and healthy status of heart system.\\u000a Detecting complexity of the short-term HRV signal has an important practical meaning. We introduce the base-scale entropy\\u000a method to analyze the complexity of time series. The advantages of our method are its simplicity, extremely fast calculation\\u000a for very short data and anti-noise

Jin Li; Xinbao Ning

2005-01-01

357

Spectral Analysis of Heart Rate Variability in the ICU: A Measure of Autonomic Function  

Microsoft Academic Search

Beat-to-beat heart rate variability (HRV) is a measure of autonomic nervous system activity, which can be quantified using frequency domain analysis. Despite its potential utility, routine serial analysis of HRV in an ICU setting has rarely been attempted. We have developed an automated system for real-time spectral analysis of HRV and have utilized this system to study the effect of

Robert J. Winchell; David B. Hoyt

1996-01-01

358

Power-Law Relationship of Heart Rate Variability as a Predictor of Mortality in the Elderly  

Microsoft Academic Search

Background—The prognostic role of heart rate (HR) variability analyzed from 24-hour ECG recordings in the general population is not well known. We studied whether analysis of 24-hour HR behavior is able to predict mortality in a random population of elderly subjects. Methods and Results—A random sample of 347 subjects of $65 years of age (mean, 7366 years) underwent a comprehensive

Heikki V. Huikuri; Timo H. Makikallio; K. E. Juhani Airaksinen; Tapio Seppanen; Pauli Puukka; Ismo J. Raiha; Leif B. Sourander

359

Pilot study employing heart rate variability biofeedback training to decrease anxiety in patients with eating disorders  

PubMed Central

Heart rate variability (HRV) biofeedback, a technique which encourages slow meditative breathing, was offered to 25 in-patients with various eating disorder diagnoses-anorexia nervosa, bulimia nervosa and binge eating disorder. We found that this modality had no serious side effects, and was subjectively useful to most participants. An enhanced ability to generate highly coherent HRV patterns in patients with recent onset anorexia nervosa was observed.

2014-01-01

360

Screening of Obstructive Sleep Apnea Syndrome by Heart Rate Variability Analysis  

Microsoft Academic Search

Background—Enhanced nocturnal heart rate variability (HRV) has been evoked in sleep-related breathing disorders. However, its capacity to detect obstructive sleep apnea syndrome (OSAS) has not been systematically determined. Thus, we evaluated the discriminant power of HRV parameters in a first group of patients (G1) and validated their discriminant capacity in a second group (G2). Methods and Results—In G1, 39 of

Frederic Roche; Jean-Michel Gaspoz; Isabelle Court-Fortune; Pascal Minini; Vincent Pichot; David Duverney; Frederic Costes; Jean-Claude Barthelemy

2010-01-01

361

Short-Term Heart Rate Variability Strongly Predicts Sudden Cardiac Death in Chronic Heart Failure Patients  

Microsoft Academic Search

Background—The predictive value of heart rate variability (HRV) in chronic heart failure (CHF) has never been tested in a comprehensive multivariate model using short-term laboratory recordings designed to avoid the confounding effects of respiration and behavioral factors. Methods and Results—A multivariate survival model for the identification of sudden (presumably arrhythmic) death was developed with data from 202 consecutive patients referred

Maria Teresa La Rovere; Gian Domenico Pinna; Roberto Maestri; Andrea Mortara; Soccorso Capomolla; Oreste Febo; Roberto Ferrari; Mariella Franchini; Marco Gnemmi; Cristina Opasich; Pier Giorgio Riccardi; Egidio Traversi; Franco Cobelli

362

Effect of lecturing to 200 students on heart rate variability and alpha-amylase activity  

Microsoft Academic Search

The aim of this study was to examine cardiovascular [heart rate variability (HRV)] and autonomic nervous system activation\\u000a (by evaluating salivary alpha-amylase activity) that occur in professors both to, and after, the delivery of a lecture to\\u000a 200 students and to determine whether gender is an influencing factor upon response. Fifty-two participants (26 women and\\u000a 26 men) collected eight unstimulated

Edith Filaire; Hugues Portier; Alain Massart; Luis Ramat; Anna Teixeira

2010-01-01

363

On-line prediction of nonstationary variable-bit-rate video traffic  

Microsoft Academic Search

In this paper, we propose a model-based bandwidth prediction scheme for variable-bit-rate (VBR) video traffic with regular group of pictures (GOP) pattern. Multiplicative ARIMA (autoregressive integrated moving-average) process called GOP ARIMA (ARIMA for GOP) is used as a base stochastic model, which consists of two key ingredients: prediction and model validity check. For traffic prediction, we deploy a Kalman filter

Sungjoo Kang; Seongjin Lee; Youjip Won; Byeongchan Seong

2010-01-01

364

Ethnicity and Type D personality as predictors of heart rate variability.  

PubMed

This study examined the relationship between Type D personality and heart rate variability (HRV) during three guided imagery experiences (baseline, stressful, and uplifting) in a non-medical sample. The interaction between African-American ethnicity and Type D personality was predictive of both low and high frequency HRV during stressful imagery experiences. The importance of identifying group influences when assessing psychological and cardiovascular health was discussed. PMID:20211208

Martin, Luci A; Doster, Joseph A; Critelli, Joseph W; Lambert, Paul L; Purdum, Michael; Powers, Catherine; Prazak, Michael

2010-05-01

365

The Superposition of Variable Bit Rate Sources in an ATM Multiplexer  

Microsoft Academic Search

When variable-bit-rate sources are multiplexed in an asynchronous transfer mode (ATM) network, there arise queues with a particular form of correlated arrival process. Such queues are analyzed by exploiting a result expressing the distribution of work in system of the G\\/G\\/1 queue originally derived by V.E. Benes (1963). A simple alternative demonstration of this result is analyzed and extended to

Ilkka Norros; James W. Roberts; Alain Simonian; Jorma T. Virtamo

1991-01-01

366

A new approach to variable frame rate front-end processing for robust speech recognition  

Microsoft Academic Search

Robustness in the presence of various types and severities of environmental noise has been researched extensively over the past several years, however this remains one of the main problems facing automatic speech recognition systems. This paper describes a noise-robust ASR front-end that employs a new variable frame rate analysis, based upon the first-order difference of the log energy for each

Julien Epps

2005-01-01

367

Heart rate variability analysis in postural orthostatic tachycardia syndrome: a case report  

PubMed Central

The authors present a case of 36 year old male patient with idiopathic postural orthostatic tachycardia syndrome (POTS) diagnosed during head-up tilt testing. Power spectral analysis of heart rate variability (HRV) during the tilt test revealed that the ratio of low and high frequency powers (LF/HF) increased with the onset of orthostatic intolerance. This analysis confirmed in our patient a strong activation in sympathetic tone.

RUSSO, VINCENZO; DE CRESCENZO, ILARIA; AMMENDOLA, ERNESTO; PAGANO, CAROLINA; SAVARESE, CRISTINA; SANTANGELO, LUCIO; CALABRO, RAFFAELE

2006-01-01

368

Effects of Air Pollution on Heart Rate Variability: The VA Normative Aging Study  

Microsoft Academic Search

Reduced heart rate variability (HRV), a marker of poor cardiac autonomic function, has been associated with air pollution, especially fine particulate matter (< 2.5 µm in aerodynamic diameter (PM2.5)). We examined the relationship between HRV (standard deviation of normal-to-normal intervals (SDNN), power in high frequency (HF) and low frequency (LF), and LF:HF ratio) and ambient air pollutants in 497 men

Sung Kyun Park; Marie S. O’Neill; Pantel S. Vokonas; David Sparrow; Joel Schwartz

2004-01-01

369

Modified autonomic balance in offsprings of diabetics detected by spectral analysis of heart rate variability  

Microsoft Academic Search

This study was performed to evaluate the influence of family history for non[ndash ]insulin-dependent diabetes mellitus (NIDDM) on autonomic balance. The latter was assessed by spectral analysis of heart rate variability (SA-HRV) and by analyzing the relative contribution of low-frequency (LF) and high-frequency (HF) components. Twenty glucose normotolerant offsprings of NIDDM parents and 20 controls underwent a 1-hour continuous electrocardiogram

Claudio De Angelis; Pietro Perelli; Roberto Trezza; Maria Casagrande; Roberto Biselli; Gaetano Pannitteri; Benedetto Marino; Stefano Farrace

2001-01-01

370

Discrimination power of long-term heart rate variability measures for chronic heart failure detection  

Microsoft Academic Search

The aim of this study was to investigate the discrimination power of standard long-term heart rate variability (HRV) measures\\u000a for the diagnosis of chronic heart failure (CHF). The authors performed a retrospective analysis on four public Holter databases,\\u000a analyzing the data of 72 normal subjects and 44 patients suffering from CHF. To assess the discrimination power of HRV measures,\\u000a an

Paolo Melillo; Roberta Fusco; Mario Sansone; Marcello Bracale; Leandro Pecchia

2011-01-01

371

Prediction Algorithms for Real-Time Variable-Bit-Rate Video  

Microsoft Academic Search

Accurate prediction of variable bit rate (VBR) video traffic can be used to improve the network utilization efficiency while supporting guaranteed QoS requirements of VBR video. On-line prediction algorithms have been proposed in the literature to forecast real-time VBR video traffic for dynamic bandwidth allocation. In this paper, we survey a number of algorithms both in time domain and wavelet

Huabing Liu; Guoqiang Mao

2005-01-01

372

A point process adaptive filter for time-variant analysis of heart rate variability  

Microsoft Academic Search

Estimating time-variant heart variability indices from R-R interval beat series has been widely investigated by current research involving cardiovascular control. Most of the currently accepted approaches in time-variant heart rate analysis ignore the underlying discrete structure of human heart beats, and usually require minutes of data. We derive an adaptive point process Bayes' filter based on a statistical model which

R. Barbieri; E. N. Brown

2004-01-01

373

Can extremely low frequency alternating magnetic fields modulate heart rate or its variability in humans?  

Microsoft Academic Search

This study is a reexamination of the possibility that exposure to extremely low frequency alternating magnetic field (ELF-MF) may influence heart rate (HR) or its variability (HRV) in humans. In a wooden room (cube with 2.7-m sides) surrounded with wire, three series of experiments were performed on 50 healthy volunteers, who were exposed to MFs at frequencies ranging from 50

Yoshika Kurokawa; Hiroshi Nitta; Hideki Imai; Michinori Kabuto

2003-01-01

374

Common multifractality in the heart rate variability and brain activity of healthy humans  

NASA Astrophysics Data System (ADS)

The influence from the central nervous system on the human multifractal heart rate variability (HRV) is examined under the autonomic nervous system perturbation induced by the head-up-tilt body maneuver. We conducted the multifractal factorization analysis to factor out the common multifractal factor in the joint fluctuation of the beat-to-beat heart rate and electroencephalography data. Evidence of a central link in the multifractal HRV was found, where the transition towards increased (decreased) HRV multifractal complexity is associated with a stronger (weaker) multifractal correlation between the central and autonomic nervous systems.

Lin, D. C.; Sharif, A.

2010-06-01

375

[Extraction of sleep structure information from heart rate variability based on spectrum analysis].  

PubMed

In this study we made full use of the heart rate spectrum analysis to obtain the character parameters of heart rate variability related to EEG sleep phase information, and then we discarded the correlation between characteristics by employing Principal Component Analysis. Finally, by means of the decision tree based on Fisher rules, we established two full automatic models for identifying healthy people and sleep apnea hypopnea syndroma (SAHS) patients respectively. The result of experiments indicates that the model is accurate and robust. PMID:15143542

Wu, Feng; Yu, Mengsun; Cheng, Qiming; Jin, Zhangrui; Zhang, Hongjin

2004-04-01

376

Effects of caffeine on linear and nonlinear measures of heart rate variability before and after exercise.  

PubMed

Caffeine intake is associated with an increase in heart rate (HR) variability. This study sought to examine the effects of caffeine on HR variability measures before and during progressive exercise in 11 healthy volunteers in a double-blind randomized and counterbalanced placebo-controlled paradigm. As expected, there were significant increases in HR and decreases in HR variability after exercise during both placebo and caffeine conditions; however, pre-exercise caffeine condition was associated with a significant increase of HR variability, especially in the high-frequency range (0.15-0.5 Hz), and also approximate entropy (APEN), which is usually attributed to cardiac vagal function. But during progressive exercise, caffeine intake resulted in a greater decrease of HF power as well as HR APEN. Caffeine also was associated with significantly higher LF power during exercise compared to the placebo condition. These results suggest that caffeine may have different effects on HR variability at rest, compared to exercise. These findings may have implications for patients with cardiac illness and anxiety, depression, and psychotic disorders who use beverages containing excessive caffeine. PMID:15965989

Yeragani, Vikram K; Krishnan, Siddartha; Engels, Hermann J; Gretebeck, Randall

2005-01-01

377

Analysis of long term heart rate variability: methods, 1/f scaling and implications  

NASA Technical Reports Server (NTRS)

The use of spectral techniques to quantify short term heart rate fluctuations on the order of seconds to minutes has helped define the autonomic contributions to beat-to-beat control of heart rate. We used similar techniques to quantify the entire spectrum (0.00003-1.0 Hz) of heart rate variability during 24 hour ambulatory ECG monitoring. The ECG from standard Holter monitor recordings from normal subjects was sampled with the use of a phase locked loop, and a heart rate time series was constructed at 3 Hz. Frequency analysis of the heart rate signal was performed after a nonlinear filtering algorithm was used to eliminate artifacts. A power spectrum of the entire 24 hour record revealed power that was inversely proportional to frequency, 1/f, over 4 decades from 0.00003 to 0.1 Hz (period approximately 10 hours to 10 seconds). Displaying consecutive spectra calculated at 5 minute intervals revealed marked variability in the peaks at all frequencies throughout the 24 hours, probably accounting for the lack of distinct peaks in the spectra of the entire records.

Saul, J. P.; Albrecht, P.; Berger, R. D.; Cohen, R. J.

1988-01-01

378

Association between Heart Rate Variability, Blood Pressure and Autonomic Activity in Cyclic Alternating Pattern during Sleep  

PubMed Central

Study Objectives: Cyclic alternating pattern (CAP) is frequently followed by changes in heart rate (HR) and blood pressure (BP), but the sequential associations between CAP and autonomic nerve activity have not been studied. The study aimed to reveal the precise changes in heart rate variability (HRV) during phase A of the CAP cycle. Design: Polysomnography was recorded according to the CAP Atlas (Terzano, 2002), and BP and electrocardiogram were simultaneously recorded. The complex demodulation method was used for analysis of HRV and evaluation of autonomic nerve activity. Setting: Academic sleep laboratory. Participants: Ten healthy males. Measurements and Results: The increase in HR (median [first quartile – third quartile]) for each subtype was as follows: A1, 0.64 (-0.30 to 1.69), A2, 1.44 (0.02 to 3.79), and A3, 6.24 (2.53 to 10.76) bpm (A1 vs. A2 P < 0.001, A1 vs. A3 P < 0.001, A2 vs. A3 P < 0.001). The increase in BP for each subtype was as follows: A1, 1.23 (-2.04 to 5.75), A2, 1.76 (-1.46 to 9.32), and A3, 12.51 (4.75 to 19.94) mm Hg (A1 vs. A2 P = 0.249, A1 vs. A3 P < 0.001, A2 vs. A3 P < 0.001). In all of phase A, the peak values for HR and BP appeared at 4.2 (3.5 to 5.4) and 8.4 (7.0 to 10.3) seconds, respectively, after the onset of phase A. The area under the curve for low-frequency and high-frequency amplitude significantly increased after the onset of CAP phase A (P < 0.001) and was higher in the order of subtype A3, A2, and A1 (P < 0.001). Conclusions: All phase A subtypes were accompanied with increased heart rate variability, and the largest heart rate variability was seen in subtype A3, while a tendency for less heart rate variability was seen in subtype A1. Citation: Kondo H; Ozone M; Ohki N; Sagawa Y; Yamamichi K; Fukuju M; Yoshida T; Nishi C; Kawasaki; Mori; Kanbayashi T; Izumi M; Hishikawa Y; Nishino S; Shimizu T. Association between heart rate variability, blood pressure and autonomic activity in cyclic alternating pattern during sleep. SLEEP 2014;37(1):187-194.

Kondo, Hideaki; Ozone, Motohiro; Ohki, Noboru; Sagawa, Yohei; Yamamichi, Keiichirou; Fukuju, Mitsuki; Yoshida, Takeshi; Nishi, Chikako; Kawasaki, Akiko; Mori, Kaori; Kanbayashi, Takashi; Izumi, Motomori; Hishikawa, Yasuo; Nishino, Seiji; Shimizu, Tetsuo

2014-01-01

379

Nonlinear relationships between vital rates and state variables in demographic models.  

PubMed

To accurately estimate population dynamics and viability, structured population models account for among-individual differences in demographic parameters that are related to individual state. In the widely used matrix models, such differences are incorporated in terms of discrete state categories, whereas integral projection models (IPMs) use continuous state variables to avoid artificial classes. In IPMs, and sometimes also in matrix models, parameterization is based on regressions that do not always model nonlinear relationships between demographic parameters and state variables. We stress the importance of testing for nonlinearity and propose using restricted cubic splines in order to allow for a wide variety of relationships in regressions and demographic models. For the plant Borderea pyrenaica, we found that vital rate relationships with size and age were nonlinear and that the parameterization method had large effects on predicted population growth rates, X (linear IPM, 0.95; nonlinear IPMs, 1.00; matrix model, 0.96). Our results suggest that restricted cubic spline models are more reliable than linear or polynomial models. Because even weak nonlinearity in relationships between vital rates and state variables can have large effects on model predictions, we suggest that restricted cubic regression splines should be considered for parameterizing models of population dynamics whenever linearity cannot be assumed. PMID:21661579

Dahlgren, Johan P; García, María B; Ehrlén, Johan

2011-05-01

380

Applications of Precision Doppler Velocity Measurements in Variable Star Studies  

NASA Astrophysics Data System (ADS)

Techniques developed over the last 10 years have improved the precision of Doppler velocity measurements by more than two orders of magnitude. While most of this work has centered on the discovery of extrasolar planets, a number of applications have been developed for the study of variable stars. Work carried out with the Lick Observatory Iodine absorption cell has resulted in the direct detection of velocity gradients in Cepheid photospheres, the first precision comparison of Doppler velocities in the visible and near IR, and a 6 year survey of photometrically non-variable supergiants in and about the Cepheid instability strip. Most of the photometric non-variables show Doppler velocity variations of 50 to 1,000 m/s and periods of 40 to 250 days. In addition, the Lick Planet Survey has shown that slowly rotating solar-type stars are intrinsically stable to at least 3 m/s. The Keck Iodine absorption cell has been used for search for solar-type oscillations in the bright K1 dwarf star 107 Psc. A precision of 2 m/s was obtained on a six hour data string of 200 observations. The detection threshold was 55 cm/s over the expected oscillation frequency window. We did not detect any oscillations at this level. In comparison, the solar 5 minute oscillation has an amplitude of 0.23 m/s, thus this technique is already within a factor of two of achieving the necessary detection threshold. The Lick Observatory precision Doppler technique makes use of a fast echelle spectrograph at resolution of R=62,000 and a large format CCD which acquires the entire visible and near IR spectrum in each exposure. Starlight is sent through an iodine absorption cell placed at the spectrometer entrance slit. The resulting superimposed iodine lines provide a fiducial wavelength scale against which to measure radial velocity shifts. The shapes of iodine lines convey the PSF of the spectrometer to account for changes in spectrometer optics and illumination on all time scales.

Butler, R. P.

381

Applicability and efficacy of variable light in schools.  

PubMed

There is a range of reliable, empirical data on the effects of special lighting techniques on the performance of adults in the work environment in the literature. However, these studies have not adequately addressed the effects of lighting on school children in the classroom environment. In the present study, the effect of variable lighting (VL) i.e., lighting that is variable in illuminance and color temperature, was studied in the classroom using a variety of student performance and attitude measures. Two classrooms each in two separate schools were studied over a period of nine months; one class in each school served as an intervention group, and a parallel class in each school served as a control group. The effects of the individual VL programs were assessed using standardized test modules. The overall effect was measured using standardized surveys of students and teachers given at the beginning and the end of the project. The results showed that the students made fewer errors, particularly fewer errors of omission, on a standardized test of attention under the VL "Concentrate" program. Reading speed, as measured using standardized reading tests, rose significantly. Reading comprehension also improved, but this improvement was not statistically significant. In contrast, the achievement motivation of the students and the classroom atmosphere did not change over the nine-month period. Overall, the students and teachers rated VL positively and found it useful during lessons. These results are in line with previous research findings. Thus, VL represents an environmental factor that can be useful to optimize general learning conditions in schools in the future. PMID:22001491

Barkmann, Claus; Wessolowski, Nino; Schulte-Markwort, Michael

2012-02-01

382

The effect of gender on heart rate variability in asthmatic and normal healthy adults  

PubMed Central

Objective Low heart rate variability (HRV) has been identified as a strong predictor of a large number of diseases, reflecting the vital role of autonomic nervous system in maintaining health. It has been hypothesized that the gender differences in autonomic modulation may explain the gender differences in morbidity and/or mortality rate. This study aims to compare the autonomic balance of males with that of females based on short-term HRV analysis. Materials and Methods This cross sectional case-control study involved eighty males matched with seventy-six females. The age M±SD is 28.5±5.4 years in males and 27.3±5.6 years in females. Biocom 3000 ECG recorder was used for studying HRV. Data was analyzed using SPSS Software (v.17), screening studied variables for significant differences in the means between the groups was performed using unpaired t test. Mean heart rate (MHR) was introduced as a covariate in the statistical analysis of HRV using general linear model. Results All short-term HRV (5-min) time domain indices, total power (TP), very low frequency (VLF), low frequency (LF) and high frequency (HF) components of frequency domains were significantly higher in males except MHR, which was significantly higher in females (P<0.05 for all). Conclusion Global autonomic activity was higher in males. In contrast, females have higher heart rate compared with males.

Lutfi, Mohamed Faisal; Sukkar, Mohamed Yosif

2011-01-01

383

Usefulness of the heart-rate variability complex for predicting cardiac mortality after acute myocardial infarction  

PubMed Central

Background Previous studies indicate that decreased heart-rate variability (HRV) is related to the risk of death in patients after acute myocardial infarction (AMI). However, the conventional indices of HRV have poor predictive value for mortality. Our aim was to develop novel predictive models based on support vector machine (SVM) to study the integrated features of HRV for improving risk stratification after AMI. Methods A series of heart-rate dynamic parameters from 208 patients were analyzed after a mean follow-up time of 28 months. Patient electrocardiographic data were classified as either survivals or cardiac deaths. SVM models were established based on different combinations of heart-rate dynamic variables and compared to left ventricular ejection fraction (LVEF), standard deviation of normal-to-normal intervals (SDNN) and deceleration capacity (DC) of heart rate. We tested the accuracy of predictors by assessing the area under the receiver-operator characteristics curve (AUC). Results We evaluated a SVM algorithm that integrated various electrocardiographic features based on three models: (A) HRV complex; (B) 6 dimension vector; and (C) 8 dimension vector. Mean AUC of HRV complex was 0.8902, 0.8880 for 6 dimension vector and 0.8579 for 8 dimension vector, compared with 0.7424 for LVEF, 0.7932 for SDNN and 0.7399 for DC. Conclusions HRV complex yielded the largest AUC and is the best classifier for predicting cardiac death after AMI.

2014-01-01

384

The interpretation of very high frequency band of instantaneous pulse rate variability during paced respiration  

PubMed Central

Background Pulse rate (PR) indicates heart beat rhythm and contains various intrinsic characteristics of peripheral regulation. Pulse rate variability (PRV) is a reliable method to assess autonomic nervous system function quantitatively as an effective alternative to heart rate variability. However, the frequency range of PRV is limited by the temporal resolution of PR based on heart rate and it is further restricted the exploration of optimal autoregulation frequency based on spectral analysis. Methods Recently, a new novel method, called instantaneous PRV (iPRV), was proposed. iPRV breaks the limitation of temporal resolution and extends the frequency band. Moreover, iPRV provides a new frequency band, called very high frequency band (VHF; 0.4-0.9 Hz). Results The results showed that the VHF indicated the influences of respiratory maneuvers (paced respiration at 6-cycle and 30-cycle) and the nonstationary condition (head-up tilt; HUT). Conclusions VHF is as a potential indication of autoregulation in higher frequency range and with peripheral regulation. It helps for the frequency exploration of cardiovascular autoregulation.

2014-01-01

385

Heart rate and heart rate variability in pregnant warmblood and Shetland mares as well as their fetuses.  

PubMed

Heart rate (HR) is an important parameter of fetal well-being. In horses, HR and heart rate variability (HRV) can be determined by fetomaternal electrocardiography (ECG) from mid-pregnancy to foaling. Normal values for physiological parameters in larger breeds are often used as reference values in ponies. However, HR increases with decreasing size of the animal and in ponies is higher than in warmblood horses. It is not known if fetal HR is affected by breed and if values obtained in larger breeds can be used to assess Shetland fetuses. We have determined fetomaternal beat-to-beat (RR) interval (inversely correlated to HR) and HRV in warmblood (n=6) and Shetland pregnancies (n=7) at days 280 and 300 of gestation by ECG. Maternal RR interval was lower in pony than in warmblood mares (day 280: Shetland: 958±110, warmblood: 1489±126ms, p<0.01) The SDRR (standard deviation of RR interval) and the RMSSD (root mean square of successive RR differences) did not differ between breeds at any time. Also RR interval as well as HRV did not differ between warmblood and pony fetuses (RR interval day 280: Shetland: 606±39, warmblood: 589±38ms). In conclusion, although maternal RR interval is clearly higher in Shetland than in warmblood mares, fetal RR interval in the two breeds is on the same level. PMID:21907506

Nagel, Christina; Aurich, Jörg; Palm, Franziska; Aurich, Christine

2011-09-01

386

Variable structure strategy to avoid amplitude and rate saturation in pitch control of a wind turbine  

Microsoft Academic Search

This work proposes the application of a recent compensation technique for input constraints avoidance to the pitch control of a wind turbine. The pitch angle actuators commonly present a hard limit on their rate of change together with the natural amplitude saturation, and a dynamics during their unconstrained operation that can be modeled as a first-order linear system. This dynamic

Fabricio Garelli; Pablo Camocardi; Ricardo J. Mantz

2010-01-01

387

Analysis of heart rate variability in individuals subjected to different positive end expiratory pressure levels using expiratory positive airway pressure  

PubMed Central

Introduction The increase in the number of studies has led to greater security in the application of this method and the determination of its effectiveness in adults.. The purpose of the present study was to evaluate heart rate variability in healthy individuals submitted to different levels of positive expiratory pressure using an expiratory positive airway pressure (EPAP) device. Material and methods The study involved 27 healthy male individuals ranging in age from 20 to 35 years. Patient histories were taken and the subjects were submitted to a physical examination. The volunteers were monitored using the Polar 810s® and submitted to the EPAP experiment. Analyses were performed on variables of the frequency domain. Sympathetic and parasympathetic bands and their relationship with sympathovagal response were also analyzed. Results The mean value of this variable was 526.89 (55.50) ms2 in the first period, 2811.0 (721.10) ms2 in the fourth period and 726.52 (123.41) ms2 in the fifth period. Regarding the parasympathetic area, significant differences were detected when Periods 1 and 5 (no load) were compared with periods in which the individuals were subjected to the use of the therapy. Sympathetic and parasympathetic areas together, a significant difference was detected regarding the sympathetic/parasympathetic ratio in the comparison between Periods 1 and 4 (p < 0.01) as well as Periods 2 and 4 (p < 0.05). Conclusions The findings of the present study suggest that the therapeutic use of EPAP significantly alters the parameters of heart rate variability in the frequency domain, highlighting the importance of monitoring and care during the practice of EPAP.

Pinto, Thiago Lorentz; Costa, Ivan Peres; Kawaguchi, Leandro Yukio Alves; de Carvalho, Flavio Aimbire Soares; de Carvalho, Regiane Albertini

2013-01-01

388

Real-time Continuous Assessment Method for Mental and Physiological Condition using Heart Rate Variability  

NASA Astrophysics Data System (ADS)

It is necessary to monitor the daily health condition for preventing stress syndrome. In this study, it was proposed the method assessing the mental and physiological condition, such as the work stress or the relaxation, using heart rate variability at real time and continuously. The instantanuous heart rate (HR), and the ratio of the number of extreme points (NEP) and the number of heart beats were calculated for assessing mental and physiological condition. In this method, 20 beats heart rate were used to calculate these indexes. These were calculated in one beat interval. Three conditions, which are sitting rest, performing mental arithmetic and watching relaxation movie, were assessed using our proposed algorithm. The assessment accuracies were 71.9% and 55.8%, when performing mental arithmetic and watching relaxation movie respectively. In this method, the mental and physiological condition was assessed using only 20 regressive heart beats, so this method is considered as the real time assessment method.

Yoshida, Yutaka; Yokoyama, Kiyoko; Ishii, Naohiro

389

DIETARY SODIUM EFFECTS ON HEART RATE VARIABILITY IN SALT-SENSITIVITY OF BLOOD PRESSURE  

PubMed Central

High dietary sodium intake is a risk factor for hypertension, and heart rate variability (HRV) is decreased in hypertension. Effects of dietary sodium intake on HRV of normotensive persons have not, however, been investigated to date. The present study examined effects of low and high sodium diets on blood pressure, heart rate, and HRV in 36 healthy, normotensive women, ages 40–70. Each was placed on a low sodium diet for six days followed by a high sodium diet for six days. High salt diet increased mean systolic blood pressure, decreased heart rate, and increased high frequency HRV (HF). Cardiac vagal tone, estimated at baseline from heart period and a time domain estimate of respiratory sinus arrhythmia, was higher in salt-sensitive than salt-insensitive subjects. The finding of increased vagal tone in normotensive persons on high salt intake indicates that dietary sodium status should be considered in behavioral studies of HRV.

JD, McNeely; BG, Windham; DE, Anderson

2008-01-01

390

Assessment of variable camber for application to transport aircraft  

NASA Technical Reports Server (NTRS)

The potential benefits were determined for the variable camber of commercial transport airplanes designed for intercontinental and domestic missions. A variable camber concept was developed and incorporated into airplanes designed for the two missions. Benefits were evaluated by comparing the mission performance and direct operating costs for the variable camber airplanes with those for reference airplanes designed for the same missions but having fixed geometry high speed wings. Several technical uncertainties associated with implementing variable camber were also examined.

1980-01-01

391

Microgravity alters respiratory sinus arrhythmia and short-term heart rate variability in humans  

NASA Technical Reports Server (NTRS)

We studied heart rate (HR), heart rate variability (HRV), and respiratory sinus arrhythmia (RSA) in four male subjects before, during, and after 16 days of spaceflight. The electrocardiogram and respiration were recorded during two periods of 4 min controlled breathing at 7.5 and 15 breaths/min in standing and supine postures on the ground and in microgravity. Low (LF)- and high (HF)-frequency components of the short-term HRV (< or =3 min) were computed through Fourier spectral analysis of the R-R intervals. Early in microgravity, HR was decreased compared with both standing and supine positions and had returned to the supine value by the end of the flight. In microgravity, overall variability, the LF-to-HF ratio, and RSA amplitude and phase were similar to preflight supine values. Immediately postflight, HR increased by approximately 15% and remained elevated 15 days after landing. LF/HF was increased, suggesting an increased sympathetic control of HR standing. The overall variability and RSA amplitude in supine decreased postflight, suggesting that vagal tone decreased, which coupled with the decrease in RSA phase shift suggests that this was the result of an adaptation of autonomic control of HR to microgravity. In addition, these alterations persisted for at least 15 days after return to normal gravity (1G).

Migeotte, P-F; Prisk, G. Kim; Paiva, M.; West, J. B. (Principal Investigator)

2003-01-01

392

Monitoring and Identification of Sepsis Development through a Composite Measure of Heart Rate Variability  

PubMed Central

Tracking the physiological conditions of a patient developing infection is of utmost importance to provide optimal care at an early stage. This work presents a procedure to integrate multiple measures of heart rate variability into a unique measure for the tracking of sepsis development. An early warning system is used to illustrate its potential clinical value. The study involved 17 adults (age median 51 (interquartile range 46–62)) who experienced a period of neutropenia following chemoradiotherapy and bone marrow transplant; 14 developed sepsis, and 3 did not. A comprehensive panel (N?=?92) of variability measures was calculated for 5 min-windows throughout the period of monitoring (12±4 days). Variability measures underwent filtering and two steps of data reduction with the objective of enhancing the information related to the greatest degree of change. The proposed composite measure was capable of tracking the development of sepsis in 12 out of 14 patients. Simulating a real-time monitoring setting, the sum of the energy over the very low frequency range of the composite measure was used to classify the probability of developing sepsis. The composite revealed information about the onset of sepsis about 60 hours (median value) before of sepsis diagnosis. In a real monitoring setting this quicker detection time would be associated to increased efficacy in the treatment of sepsis, therefore highlighting the potential clinical utility of a composite measure of variability.

Bravi, Andrea; Green, Geoffrey; Longtin, Andre; Seely, Andrew J. E.

2012-01-01

393

SVM Variable selection with application to pedestrian detection  

Microsoft Academic Search

Nowadays, to solve a learning from examples problem, a large amount of data can be available due to the prolife- ration of acquisition systems. Besides, more and more fea- tures characterize each example. Variable selection algo- rithms adress the problem of selecting the input variables that are most predictive for a given task. In this paper, we present a variable

Alain Rakotomamonjy; Frédéric Suard

394

Prognostic value of reduced heart rate variability after myocardial infarction: clinical evaluation of a new analysis method  

Microsoft Academic Search

The relation between heart rate variability, measured from standard 24 hour electrocardiogram recordings in patients convalescent after a myocardial infarction, and the occurrence of sudden death and spontaneous, symptomatic, sustained ventricular tachycardia were assessed in a consecutive series of 177 patients admitted with acute myocardial infarction and surviving to 7 days. In addition to the analysis of heart rate variability,

T R Cripps; M Malik; T G Farrell; A J Camm

1991-01-01

395

Severe depression is associated with markedly reduced heart rate variability in patients with stable coronary heart disease  

Microsoft Academic Search

Objective: The purpose of this study was to investigate the relationship between depression and heart rate variability in cardiac patients. Methods: Heart rate variability was measured during 24-hour ambulatory electrocardiographic (ECG) monitoring in 40 medically stable out-patients with documented coronary heart disease meeting current diagnostic criteria for major depression, and 32 nondepressed, but otherwise comparable, patients. Patients discontinued ?-blockers and

Phyllis K Stein; Robert M Carney; Kenneth E Freedland; Judith A Skala; Allan S Jaffe; Robert E Kleiger; Jeffrey N Rottman

2000-01-01

396

Effects of controlled breathing, mental activity and mental stress with or without verbalization on heart rate variability  

Microsoft Academic Search

OBJECTIVESTo assess whether talking or reading (silently or aloud) could affect heart rate variability (HRV) and to what extent these changes require a simultaneous recording of respiratory activity to be correctly interpreted.BACKGROUNDSympathetic predominance in the power spectrum obtained from short- and long-term HRV recordings predicts a poor prognosis in a number of cardiac diseases. Heart rate variability is often recorded

Luciano Bernardi; Joanna Wdowczyk-Szulc; Cinzia Valenti; Stefano Castoldi; Claudio Passino; Giammario Spadacini; Peter Sleight

2000-01-01

397

Heart rate variability from short electrocardiographic recordings predicts mortality from all causes in middle-aged and elderly men  

Microsoft Academic Search

Low heart rate variability is associated with high risk of sudden death in myocardial infarction patients. This has been attributed to unfavorable autonomic cardiac control. In the present study, the predictive value of heart rate variability for sudden death, mortality from coronary heart disease, and from all causes was investigated in the general population, using brief electrocardiographic recordings. From 1960

Jacqueline M. Dekker; Evert G. Schouten; Peter Klootwijk; Jan Pool; Cees A. Swenne; Daan Kromhout

1997-01-01

398

Distribution and variability of the 24-h average air exchange rates and interzonal flow rates in 26 Japanese residences in 5 seasons  

NASA Astrophysics Data System (ADS)

In this study, to evaluate the distribution of air exchange rates in Japan, daily, seasonal, and inter-residence variabilities were determined as well as the air exchange rate itself. In addition, airflows among multiple zones were also evaluated. For this purpose, the 24 h average air exchange rates and interzonal air flow rates were measured using a passive perfluorocarbon tracer (PFT) method with three kinds of tracer gases for 1 week in three rooms of 26 Japanese residences over five seasons: summer and autumn of 2005, and winter, spring, and summer of 2006. During these seasons, the weekly average air exchange rates were found to be 1.6 ± 1.7, 0.58 ± 0.94, 0.61 ± 0.93, 1.2 ± 2.5, and 1.7 ± 1.8 h -1, respectively. Two-way repeated measure analysis of variance (ANOVA) revealed that the air exchange rates differed significantly with respect to the seasons, residences, and interaction of seasons and residences ( p < 0.01). In addition, the air exchange rates in both summers and spring were statistically higher than those in autumn and winter (Sheffe test, p < 0.01). According to the ANOVA, the percentage contribution of inter-residence variability, seasonal variability, interaction of seasonal and inter-residence variabilities, and daily variability to the total variability of the 24 h average air exchange rates in the present survey was 51%, 44%, 3.7%, and 1.0%, respectively.

Shinohara, Naohide; Kataoka, Toshiyuki; Takamine, Koichi; Gamo, Masashi

2011-07-01

399

Seismologic applications of GRACE time-variable gravity measurements  

NASA Astrophysics Data System (ADS)

The Gravity Recovery and Climate Experiment (GRACE) has been measuring temporal and spatial variations of mass redistribution within the Earth system since 2002. As large earthquakes cause significant mass changes on and under the Earth's surface, GRACE provides a new means from space to observe mass redistribution due to earthquake deformations. GRACE serves as a good complement to other earthquake measurements because of its extensive spatial coverage and being free from terrestrial restriction. During its over 10 years mission, GRACE has successfully detected seismic gravitational changes of several giant earthquakes, which include the 2004 Sumatra-Andaman earthquake, 2010 Maule (Chile) earthquake, and 2011 Tohoku-Oki (Japan) earthquake. In this review, we describe by examples how to process GRACE time-variable gravity data to retrieve seismic signals, and summarize the results of recent studies that apply GRACE observations to detect co- and post-seismic signals and constrain fault slip models and viscous lithospheric structures. We also discuss major problems and give an outlook in this field of GRACE application.

Li, Jin; Chen, Jianli; Zhang, Zizhan

2014-04-01

400

Seismologic applications of GRACE time-variable gravity measurements  

NASA Astrophysics Data System (ADS)

The Gravity Recovery and Climate Experiment (GRACE) has been measuring temporal and spatial variations of mass redistribution within the Earth system since 2002. As large earthquakes cause significant mass changes on and under the Earth's surface, GRACE provides a new means from space to observe mass redistribution due to earthquake deformations. GRACE serves as a good complement to other earthquake measurements because of its extensive spatial coverage and being free from terrestrial restriction. During its over 10 years mission, GRACE has successfully detected seismic gravitational changes of several giant earthquakes, which include the 2004 Sumatra-Andaman earthquake, 2010 Maule (Chile) earthquake, and 2011 Tohoku-Oki (Japan) earthquake. In this review, we describe by examples how to process GRACE time-variable gravity data to retrieve seismic signals, and summarize the results of recent studies that apply GRACE observations to detect co- and post-seismic signals and constrain fault slip models and viscous lithospheric structures. We also discuss major problems and give an outlook in this field of GRACE application.

Li, Jin; Chen, Jianli; Zhang, Zizhan

2014-03-01

401

Theory and applications of ignition with variable activation energy  

NASA Astrophysics Data System (ADS)

The determination of critical conditions for thermal ignition of combustible materials has been traditionally studied by the use of one overall reaction with bounded parameter values for the activation energy and other chemical constants. Significant errors can occur in the values of the threshold parameters for ignition when there are two (or more) simultaneous reactions present with distinct values of the chemical constants. Recent work with simultaneous parallel reactions showed the thresholds for ignition could be lowered in this case. In this paper, motivated by experimental results for forest litter and coal, it is shown that for sequential reactions (different values of parameters in different temperature ranges) that the threshold conditions are changed (safer for lower ambient temperatures and less safe for higher ambient temperatures). The mathematical analysis is summarised and a detailed analysis is given for the forest litter and crushed coal applications. The experimental results show that variable activation energy does occur and that this extension of the classical Frank-Kamenetskii theory is needed. Here the analysis is confined to the slab geometry only but the ideas developed can easily be extended to more general systems, including those involving mass transport, consumption, and phase changes.

Wake, G. C.; Sleeman, M.; Chen, X. D.; Jones, J. C.

1992-09-01

402

Scheduling and Application Rates of Irrigation in Humid Climate.  

National Technical Information Service (NTIS)

A four-year study of two irrigation scheduling methods and application rates was conducted to determine more efficient uses of supplemental water in a humid climate. One model based the decision to irrigate on weather forecast and soil moisture conditions...

C. D. Busch E. W. Rochester

1975-01-01

403

?-MYN: a new algorithm for estimating Ka and Ks with consideration of variable substitution rates  

PubMed Central

Background Over the past two decades, there have been several approximate methods that adopt different mutation models and used for estimating nonsynonymous and synonymous substitution rates (Ka and Ks) based on protein-coding sequences across species or even different evolutionary lineages. Among them, MYN method (a Modified version of Yang-Nielsen method) considers three major dynamic features of evolving DNA sequences–bias in transition/transversion rate, nucleotide frequency, and unequal transitional substitution but leaves out another important feature: unequal substitution rates among different sites or nucleotide positions. Results We incorporated a new feature for analyzing evolving DNA sequences–unequal substitution rates among different sites–into MYN method, and proposed a modified version, namely ? (gamma)-MYN, based on an assumption that the evolutionary rate at each site follows a mode of ?-distribution. We applied ?-MYN to analyze the key estimator of selective pressure ? (Ka/Ks) and other relevant parameters in comparison to two other related methods, YN and MYN, and found that neglecting the variation of substitution rates among different sites may lead to biased estimations of ?. Our new method appears to have minimal deviations when relevant parameters vary within normal ranges defined by empirical data. Conclusion Our results indicate that unequal substitution rates among different sites have variable influences on ? under different evolutionary rates while both transition/transversion rate ratio and unequal nucleotide frequencies affect Ka and Ks thus selective pressure ?. Reviewers This paper was reviewed by Kateryna Makova, David A. Liberles (nominated by David H Ardell), Zhaolei Zhang (nominated by Mark Gerstein), and Shamil Sunyaev.

Wang, Da-Peng; Wan, Hao-Lei; Zhang, Song; Yu, Jun

2009-01-01

404

Rates, variability, and associated factors of polypharmacy in nursing home patients  

PubMed Central

Objectives To determine the rate and variability of polypharmacy in nursing home (NH) residents and investigate its relationship to age, sex, functional status, length of stay, and comorbidities. Methods We conducted a cross sectional, multicenter study that included six nursing homes. Demographic, clinical characteristics, Charlson comorbidity index (CCI), the number and classes of chronic medications, rate of polypharmacy >5 drugs (per day) and polypharmacy >7 drugs (per day) were recorded. Results Nine hundred and ninety-three residents were included; 750 (75.5%) fully dependent residents and 243 (24.5%) mobile demented residents requiring institutional care. The mean age was 85.04±7.55 (65–108) years. The mean rates of polypharmacy >5 drugs and polypharmacy >7 drugs were 42.6% and 18.6%, respectively. Differences in polypharmacy >5 drugs and polypharmacy >7 drugs were observed in NHs 24.7%–56% and 4.9%–30.4%, respectively (P<0.001). Mean number of chronic drugs per resident was 5.14±2.60 from 3.81±2.24 to 5.95±2.73 (P<0.001). No differences in polypharmacy were found between sex and fully dependent versus mobile demented residents. The most common medications taken were for gastrointestinal, neurological, and cardiovascular disorders. Regression analysis revealed four independent variables for polypharmacy >5 drugs: groups aged 75–84 and >85 relative to 65–74, odds ratio (OR) 0.46 (95% confidence interval [CI] 0.27–0.78) P=0.004, OR 0.35 (95% confidence interval 0.19–0.53), respectively, P<0.001; length of stay >2 years, OR 0.51 (95% CI 0.36–0.73) P<0.001; CCI, OR 1.58 (95% CI 1.42–1.75) P<0.001; and feeding tube versus normal feeding, OR 0.27 (95% CI 0.12–0.60) P=0.001. Conclusion Rates of polypharmacy in NHs are high with significant variability. Variability rates of polypharmacy, distinct residents’ characteristics, and excessive use of certain drug groups may indicate that a decrease in medication is potentially feasible.

Beloosesky, Yichayaou; Nenaydenko, Olga; Gross Nevo, Revital Feige; Adunsky, Abraham; Weiss, Avraham

2013-01-01

405

The relation of aerobic fitness to cognitive control and heart rate variability: A neurovisceral integration study.  

PubMed

This aim of the present study was to investigate relationships between aerobic fitness, sympathetic and parasympathetic cardiac control using pre-ejection period (PEP) and high frequency heart rate variability (HF HRV), and performance on a task requiring variable amounts of cognitive control. Fifty-six participants completed a modified-version of the Eriksen flanker task while PEP and HF HRV were collected. A graded maximal exercise test was subsequently used to measure aerobic fitness by assessing maximal oxygen uptake. Results indicated a significant relation of fitness to reaction time performance. Although no fitness differences were observed in resting state PEP or HF HRV, higher fit adults exhibited greater task-induced parasympathetic cardiac control. However, no significant mediation was found for HF HRV on the fitness-cognitive control relationship, suggesting other mediators may be important. These findings highlight the role of aerobic fitness in enhancing integrated autonomic and neurocognitive health. PMID:24560874

Alderman, Brandon L; Olson, Ryan L

2014-05-01

406

A Multivariate Study of Variables Effecting Student Ratings of Teaching and Course Outcomes Within a Multiple Instructor Mode.  

ERIC Educational Resources Information Center

The study investigated the interrelationships of student ratings of teaching, course outcome and self ratings within a multiple instructor course mode, and the appropriateness of these variables for predicting overall instructor and course evaluations. Student rating of teaching and course related items and student self ratings were gleaned from a…

McCook, William M.

407

Tunnel restorations in general practice. Influence of some clinical variables on the success rate.  

PubMed

Using bitewing radiographs and clinical inspection, the success rate for tunnel restorations was assessed in a population with low caries activity. The material consisted of 242 tunnel restorations in permanent premolars and molars in 142 individuals (mean age = 18.8 years). The median DFSappr value (decayed and filled approximal surfaces) at the time of restoration was 4.0. The mean follow-up time was 25 months. Bivariate associations between the outcome variable (success/failure of the tunnel restoration) and conceivable explanatory variables were investigated. In a multivariate logistic regression analysis, the independent variables tooth type (premolars vs molars), surface site (mesial vs distal), radiographic stage of approximal carious progression and age of patient at the time of restoration (9-15 years vs > 15 years) were used to estimate the effect on the dependent variable success/failure. Using the life table method, the estimated cumulative proportion of successful restorations was 81% after 2 years and 64% after 3.5 years. The success rate was not related to caries activity and did not differ between the two types of tunnel preparation techniques nor between different follow-up periods. In the multivariate regression analysis, tooth type (molars vs premolars) was the only factor significantly associated with failure. Thus, a failure occurred about 5 times as often in molars as in premolars. Of the failures, half were due to caries; either radiographically observed adjacent to the restoration or progressing enamel caries on the outer proximal surface. Marginal ridge fractures constituted 26% of the failures. From the present results it can be concluded that in a population with low caries activity, the tunnel restoration technique can be recommended for premolars. PMID:10540929

Pyk, N; Mejàre, I

1999-08-01

408

Escape rates and variability constraints for high energy sodium sources at Mercury  

NASA Astrophysics Data System (ADS)

We present 3D time-dependent modeling of Mercury's extended sodium exosphere to address new data sets describing the distant neutral tail. These sodium atoms are liberated from the planet's surface by photon-stimulated desorption, ion sputtering and micrometeoroid impact vaporization, ejected at energies capable of escaping Mercury's gravity via substantial aid from solar radiation pressure. Escape rates of these source processes in Mercury's exosphere are determined, and the effects of orbital motion, surface-gas interactions, variable source rates, and spatially heterogeneous sources are explored. More substantial losses of the exosphere than previously considered are needed to match the observed sodium D line brightness in wide-field measurements of Baumgardner et al. (2008) and Schmidt et al. (2010). A simulation of a short-term pulse in high energy sources leads to constraints on the potential detection of variable ejection rates at the surface. Wide-field observations of high energy sodium at Mercury, combined with time-dependent numerical modeling using Monte Carlo techniques, form a powerful tool in our understanding of tenuous surface-bound exospheres.

Schmidt, C.; Baumgardner, J.; Mendillo, M.; Wilson, J.

2011-10-01

409

C-fuzzy variable-branch decision tree with storage and classification error rate constraints  

NASA Astrophysics Data System (ADS)

The C-fuzzy decision tree (CFDT), which is based on the fuzzy C-means algorithm, has recently been proposed. The CFDT is grown by selecting the nodes to be split according to its classification error rate. However, the CFDT design does not consider the classification time taken to classify the input vector. Thus, the CFDT can be improved. We propose a new C-fuzzy variable-branch decision tree (CFVBDT) with storage and classification error rate constraints. The design of the CFVBDT consists of two phases-growing and pruning. The CFVBDT is grown by selecting the nodes to be split according to the classification error rate and the classification time in the decision tree. Additionally, the pruning method selects the nodes to prune based on the storage requirement and the classification time of the CFVBDT. Furthermore, the number of branches of each internal node is variable in the CFVBDT. Experimental results indicate that the proposed CFVBDT outperforms the CFDT and other methods.

Yang, Shiueng-Bien

2009-10-01

410

Spatial scaling of avian population dynamics: population abundance, growth rate, and variability.  

PubMed

Synchrony in population fluctuations has been identified as an important component of population dynamics. In a previous study, we determined that local-scale (<15-km) spatial synchrony of bird populations in New England was correlated with synchronous fluctuations in lepidopteran larvae abundance and with the North Atlantic Oscillation. Here we address five questions that extend the scope of our earlier study using North American Breeding Bird Survey data. First, do bird populations in eastern North America exhibit spatial synchrony in abundances at scales beyond those we have documented previously? Second, does spatial synchrony depend on what population metric is analyzed (e.g., abundance, growth rate, or variability)? Third, is there geographic concordance in where species exhibit synchrony? Fourth, for those species that exhibit significant geographic concordance, are there landscape and habitat variables that contribute to the observed patterns? Fifth, is spatial synchrony affected by a species' life history traits? Significant spatial synchrony was common and its magnitude was dependent on the population metric analyzed. Twenty-four of 29 species examined exhibited significant synchrony in population abundance: mean local autocorrelation (rho)= 0.15; mean spatial extent (mean distance where rho=0) = 420.7 km. Five of the 29 species exhibited significant synchrony in annual population growth rate (mean local autocorrelation = 0.06, mean distance = 457.8 km). Ten of the 29 species exhibited significant synchrony in population abundance variability (mean local autocorrelation = 0.49, mean distance = 413.8 km). Analyses of landscape structure indicated that habitat variables were infrequent contributors to spatial synchrony. Likewise, we detected no effects of life history traits on synchrony in population abundance or growth rate. However, short-distance migrants exhibited more spatially extensive synchrony in population variability than either year-round residents or long-distance migrants. The dissimilarity of the spatial extent of synchrony across species suggests that most populations are not regulated at similar spatial scales. The spatial scale of the population synchrony patterns we describe is likely larger than the actual scale of population regulation, and in turn, the scale of population regulation is undoubtedly larger than the scale of individual ecological requirements. PMID:18027754

Jones, Jason; Doran, Patrick J; Holmes, Richard T

2007-10-01

411

Role of genetic and environmental influences on heart rate variability in middle-aged men.  

PubMed

Our aim was to estimate causal relationships of genetic factors and different specific environmental factors in determination of the level of cardiac autonomic modulation, i.e., heart rate variability (HRV), in healthy male twins and male twins with chronic diseases. The subjects were 208 monozygotic (MZ, 104 healthy) and 296 dizygotic (DZ, 173 healthy) male twins. A structured interview was used to obtain data on lifetime exposures of occupational loading, regularly performed leisure-time sport activities, coffee consumption, smoking history, and chronic diseases from 12 yr of age through the present. A 5-min ECG at supine rest was recorded for the HRV analyses. In univariate statistical analyses based on genetic models with additive genetic, dominance genetic, and unique environmental effects, genetic effects accounted for 31-57% of HRV variance. In multivariate statistical analysis, body mass index, percent body fat, coffee consumption, smoking, medication, and chronic diseases were associated with different HRV variables, accounting for 1-11% of their variance. Occupational physical loading and leisure-time sport activities did not account for variation in any HRV variable. However, in the subgroup analysis of healthy and diseased twins, occupational loading explained 4% of the variability in heart periods. Otherwise, the interaction between health status and genetic effects was significant for only two HRV variables. In conclusion, genetic factors accounted for a major portion of the interindividual differences in HRV, with no remarkable effect of health status. No single behavioral determinant appeared to have a major influence on HRV. The effects of medication and diseases may mask the minimal effect of occupational loading on HRV. PMID:17400723

Uusitalo, A L T; Vanninen, E; Levälahti, E; Battié, M C; Videman, T; Kaprio, J

2007-08-01

412

Heart rate variability on antihypertensive drugs in black patients living in sub-Saharan Africa.  

PubMed

Abstract Background. Compared with Caucasians, African Americans have lower heart rate variability (HRV) in the high-frequency domain, but there are no studies in blacks born and living in Africa. Methods. In the Newer versus Older Antihypertensive agents in African Hypertensive patients trial (NCT01030458), patients (30-69 years) with uncomplicated hypertension (140-179/90-109 mmHg) were randomized to single-pill combinations of bisoprolol/hydrochlorothiazide (R) or amlodipine/valsartan (E). 72 R and 84 E patients underwent 5-min ECG recordings at randomization and 8, 16 and 24 weeks. HRV was determined by fast Fourier transform and autoregressive modelling. Results. Heart rate decreased by 9.5 beats/min in R patients with no change in E patients (- 2.2 beats/min). R patients had reduced total (- 0.13 ms²; p = 0.0038) and low-frequency power (- 3.6 nu; p = 0.057), higher high-frequency (+ 3.3 nu; p = 0.050) and a reduced low- to high-frequency ratio (- 0.08; p = 0.040). With adjustment for heart rate, these differences disappeared, except for the reduced low-frequency power in the R group (- 4.67 nu; p = 0.02). Analyses confined to 39 R and 47 E patients with HRV measurements at all visits or based on autoregressive modelling were confirmatory. Conclusion. In native black African patients, antihypertensive drugs modulate HRV, an index of autonomous nervous tone. However, these effects were mediated by changes in heart rate except for low-frequency variability, which was reduced on beta blockade independent of heart rate. PMID:24066715

Osakwe, Chukwunomso E; Jacobs, Lotte; Anisiuba, Benedict C; Ndiaye, Mouhamado B; Lemogoum, Daniel; Ijoma, Chinwuba K; Kamdem, Marius M; Thijs, Lutgarde; Boombhi, Hilaire J; Kaptue, Joseph; Kolo, Philip M; Mipinda, Jean B; Odili, Augustine N; Ezeala-Adikaibe, Birinus; Kingue, Samuel; Omotoso, Babatunde A; Ba, Serigne A; Ulasi, Ifeoma I; M'buyamba-Kabangu, Jean-Rene; Staessen, Jan A

2014-06-01

413

Heart rate variability on antihypertensive drugs in black patients living in sub-Saharan Africa  

PubMed Central

Background Compared with Caucasians, African Americans have lower heart rate variability (HRV) in the high-frequency domain, but there are no studies in blacks born and living in Africa. Methods In the Newer versus Older Antihypertensive agents in African Hypertensive patients trial (NCT01030458), patients (30–69 years) with uncomplicated hypertension (140–179/90–109 mmHg) were randomized to single-pill combinations of bisoprolol/hydrochlorothiazide (R) or amlodipine/valsartan (E). 72 R and 84 E patients underwent 5-min ECG recordings at randomization and 8, 16 and 24 weeks. HRV was determined by fast Fourier transform and autoregressive modelling. Results Heart rate decreased by 9.5 beats/min in R patients with no change in E patients (? 2.2 beats/min). R patients had reduced total (? 0.13 ms²; p = 0.0038) and low-frequency power (? 3.6 nu; p = 0.057), higher high-frequency (+ 3.3 nu; p = 0.050) and a reduced low- to high-frequency ratio (? 0.08; p = 0.040). With adjustment for heart rate, these differences disappeared, except for the reduced low-frequency power in the R group (? 4.67 nu; p = 0.02). Analyses confined to 39 R and 47 E patients with HRV measurements at all visits or based on autoregressive modelling were confirmatory. Conclusion In native black African patients, antihypertensive drugs modulate HRV, an index of autonomous nervous tone. However, these effects were mediated by changes in heart rate except for low-frequency variability, which was reduced on beta blockade independent of heart rate.

Osakwe, Chukwunomso E.; Jacobs, Lotte; Anisiuba, Benedict C.; Ndiaye, Mouhamado B.; Lemogoum, Daniel; Ijoma, Chinwuba K.; Kamdem, Marius M.; Thijs, Lutgarde; Boombhi, Hilaire J.; Kaptue, Joseph; Kolo, Philip M.; Mipinda, Jean B.; Odili, Augustine N.; Ezeala-Adikaibe, Birinus; Kingue, Samuel; Omotoso, Babatunde A.; Ba, Serigne A.; Ulasi, Ifeoma I.; M'buyamba-Kabangu, Jean-Rene

2014-01-01

414

Effect of immersion, submersion, and scuba diving on heart rate variability  

PubMed Central

Background—Heart rate variability (HRV) describes the cyclic variations in heart rate and offers a non-invasive tool for investigating the modulatory effects of neural mechanisms elicited by the autonomic nervous system on intrinsic heart rate. Objective—To introduce the HRV concept to healthy volunteers under control conditions and during scuba diving. In contrast with more established manoeuvres, diving probably activates both the sympathetic and parasympathetic nervous system through various stimuli—for example, through cardiac stretch receptors, respiration pattern, psychological stress, and diving reflex. A further aim of the study was to introduce a measure for determining a candidate's ability to scuba dive by providing (a) standard values for HRV measures (three from the time domain and three from the frequency domain) and (b) physiological responses to a strenuous manoeuvre such as scuba diving. Methods—Twenty five trained scuba divers were investigated while diving under pool conditions (27°C) after the effects of head out immersion and submersion on HRV had been studied. Results and conclusions—(a) Immersion under pool conditions is a powerful stimulus for both the sympathetic and parasympathetic nervous system. (b) As neither the heart rate nor the HRV changed on going from immersion to submersion, the parasympathetic activation was probably due to haemodynamic alterations. (c) All HRV measures showed an increase in the parasympathetic activity. (d) If a physiological HRV is a mechanism for providing adaptability and flexibility, diving should not provoke circulatory problems in healthy subjects. (e) Either a lower than normal HRV under control conditions or a reduction in HRV induced by diving would be unphysiological, and a scuba diving candidate showing such characteristics should be further investigated. Key Words: immersion; submersion; scuba diving; autonomous nervous system; heart rate variability

Schipke, J; Pelzer, M

2001-01-01

415

Sampling Rate of Heart Rate Variability Impacts the Ability to Detect Acidemia in Ovine Fetuses Near-Term  

PubMed Central

Background: To evaluate the impact of sampling rate on the predictive capability of continuous fetal heart rate (FHR) variability (fHRV) monitoring for detecting fetal acidemia during labor, we tested the performance of the root mean square of successive differences (RMSSD) in R–R intervals from the ECG when acquired with the sampling rate of 4?Hz currently available in FHR monitors, in comparison to the gold standard of 1000?Hz. Methods: Near-term ovine fetuses (N?=?9) were chronically prepared with precordial electrodes for recording ECG, vascular catheters for blood sampling, and an umbilical cord occluder. For 1?min every 2.5?min, animals underwent mild partial umbilical cord occlusions (UCO)?×?1?h, moderate partial UCO?×?1?h, then complete UCO?×?2?h, or until arterial pH reached <7.00. Arterial blood samples were drawn at baseline and every 20?min during the UCO series. RMSSD was calculated continuously in 5?min windows using an automated, standardized system (CIMVA.com). Results are presented as mean?±?SEM with significance assumed for p?rate of 4?Hz used clinically, RMSSD remained unchanged until terminally when the nadir pH was reached. For early detection of fetal acidemia during labor, more sensitive means of acquiring FHR are therefore recommended than currently deployed, e.g., trans-abdominal fetal ECG.

Durosier, L. Daniel; Green, Geoffrey; Batkin, Izmail; Seely, Andrew J.; Ross, Michael G.; Richardson, Bryan S.; Frasch, Martin G.

2014-01-01

416

Bivalve growth rate and isotopic variability across the Barents Sea Polar Front  

NASA Astrophysics Data System (ADS)

Analysis of bivalve shell increments provides a means to reconstruct long-term patterns in growth histories and assess factors that regulate marine ecosystems, while tissue stable isotopes are indicators of food sources and trophic dynamics. We examined shell growth patterns and tissue stable isotopic composition (?13C and ?15N) of the hairy cockle (Ciliatocardium ciliatum) in the northwest Barents Sea to evaluate the influence of different water masses and the Polar Front on growth rates and food sources and to assess the influence of climatic variability on ecological processes over seasonal to decadal scales. Shell growth rates were highest in Atlantic water, intermediate in Arctic water, and lowest at the Polar Front. Temporal patterns of ontogenetically-adjusted growth (SGI) were negatively correlated with the Atlantic Multidecadal Oscillation (AMO), local precipitation and ice-free days. The highest growth occurred during colder periods with more sea ice, while lower growth was associated with warmer periods and less sea ice. Stable isotope values of lipid-extracted tissues from Atlantic water cockles were enriched in ?13C by up to 2.1‰ and ?15N by 1.5‰ compared to animals from Arctic waters. Distinct seasonal and water mass variations in stable isotopic values reflect spatial and temporal variability in food supplies to the bivalves in this region on small spatial scales. Overall, Atlantic waters supported the highest growth rates, the most complex trophic webs, and the greatest sensitivity to interannual variability in environmental conditions. Bivalves from Arctic waters were the most distinct of the three groups in their response to regional climate forcing and local environmental manifestations of those conditions. The Polar Front exhibits growth and isotopic characteristics predominantly of the Atlantic domain.

Carroll, Michael L.; Ambrose, William G.; Locke V, William L.; Ryan, Stuart K.; Johnson, Beverly J.

2014-02-01

417

Children's Sleep and Autonomic Function: Low Sleep Quality Has an Impact on Heart Rate Variability  

PubMed Central

Objectives: Short sleep duration and poor sleep quality in children have been associated with concentration, problem behavior, and emotional instability, but recently also with disrupted autonomic nervous function, which predicts cardiovascular health. Heart rate variability (HRV) was used as noninvasive indicator of autonomic function to examine the influence of sleep. Design: Cross-sectional and longitudinal observational study on the effect of sleep on HRV Participants: Belgian children (5-11 years) of the ChiBS study in 2010 (N = 334) and 2011 (N = 293). Interventions: N/A. Methods: Sleep duration was reported and in a subgroup sleep quality (efficiency, latency, awakenings) was measured with accelerometry. High-frequency (HF) power and autonomic balance (LF/HF) were calculated on supine 5-minute HRV measurements. Stress was measured by emotion and problem behavior questionnaires. Sleep duration and quality were used as HRV predictors in corrected cross-sectional and longitudinal regressions. Stress was tested as mediator (intermediate pathway) or moderator (interaction) in sleep-HRV associations. Results: In both cross-sectional and longitudinal analyses, long sleep latency could predict lower HF (parasympathetic activity), while nocturnal awakenings, sleep latency, low sleep efficiency, and low corrected sleep duration were related to higher LF/HF (sympathetic/parasympathetic balance). Parental reported sleep duration was not associated with HRV. The significances remained after correction for stress. Stress was not a mediator, but a moderator (enhancer) in the relationship between sleep quality and HRV. Conclusions: Low sleep quality but not parent-reported low sleep duration leads to an unhealthier heart rate variability pattern (sympathetic over parasympathetic dominance). This stresses the importance of good sleep quality for cardiovascular health in children. Citation: Michels N; Clays E; De Buyzere M; Vanaelst B; De Henauw S; Sioen I. Children's sleep and autonomic function: low sleep quality has an impact on heart rate variability. SLEEP 2013;36(12):1939-1946.

Michels, Nathalie; Clays, Els; De Buyzere, Marc; Vanaelst, Barbara; De Henauw, Stefaan; Sioen, Isabelle

2013-01-01

418

Spectral analysis of heart rate variability with the autoregressive method: what model order to choose?  

PubMed

This work assessed the influence of the autoregressive model order (ARMO) on the spectral analysis of the heart rate variability (HRV). A sample of 68 R-R series obtained from digital ECG records of young healthy adults in the supine position was used. Normalized spectral indexes for each ARMO were compared by Friedman test followed by the Dunn's procedure and statistical significance was set at P<0.05. The results showed that the AR method using orders from 9 to 25 produces normalized spectral parameters statistically similar and, hence, the algorithms commonly employed to estimate optimum order are not mandatory in this case. PMID:22136799

Dantas, Eduardo Miranda; Sant'Anna, Marcela Lima; Andreão, Rodrigo Varejão; Gonçalves, Christine Pereira; Morra, Elis Aguiar; Baldo, Marcelo Perim; Rodrigues, Sérgio Lamêgo; Mill, José Geraldo

2012-02-01

419

Heart rate variability dynamics during early recovery after different endurance exercises  

Microsoft Academic Search

Since heart rate variability (HRV) during the first minutes of the recovery after exercise has barely been studied, we wanted\\u000a to find out HRV dynamics immediately after five different constant-speed exercises. Thirteen sedentary women performed two\\u000a low-intensity (3,500 m [3,500LI] and 7,000 m [7,000LI] at 50% of the velocity of VO2max [vVO2max]), two moderate-intensity (3,500 m [3,500MI] and 7,000 m [7,000MI] at ?63% vVO2max)

Piia Kaikkonen; Ari Nummela; Heikki Rusko

2007-01-01

420

[The analysis of heart rate variability as non-invasive method of cardiovascular system assessment].  

PubMed

Heart rate variability (HRV) is estimated using time and frequency method. This analysis allows a non-invasive assessment of both the heart and autonomic nervous system. The usefulness of HRV estimation has been confirmed in patients not only with diabetic neuropathy, tetraplegia, various heart diseases (after heart transplantation, with heart failure, after myocardial infarction, with hypertrophic and dilated cardiomyopathy, with cardiological syndrome X and with arrhythmia), but also with thyroid gland diseases and in physiological states of human being. The described information indicate a wide range and increasing usefulness of HRV analysis in medical studies. PMID:11816300

Jagodzi?ski, L; Siela?czyk, A; Ciesió?ka, A; Gmyrek, J; Niepsuj, K

2001-01-01

421

Association between heart rate variability and training response in sedentary middle-aged men  

Microsoft Academic Search

The effect of exercise training on heart rate variability (HRV) and improvements in peak oxygen consumption (\\u000a$$\\\\dot V{\\\\text{O}}_{\\\\text{2}} $$\\u000a\\u000apeak) was examined in sedentary middle-aged men. The HRV and absolute and relative\\u000a$$\\\\dot V{\\\\text{O}}_{\\\\text{2}} $$\\u000a\\u000apeak of training (n = 19) and control (n = 15) subjects were assessed before and after a 24-session moderate intensity exercise training programme.

Stephen H. Boutcher; Phyllis Stein

1995-01-01

422

Do heart and respiratory rate variability improve prediction of extubation outcomes in critically ill patients?  

PubMed Central

Introduction Prolonged ventilation and failed extubation are associated with increased harm and cost. The added value of heart and respiratory rate variability (HRV and RRV) during spontaneous breathing trials (SBTs) to predict extubation failure remains unknown. Methods We enrolled 721 patients in a multicenter (12 sites), prospective, observational study, evaluating clinical estimates of risk of extubation failure, physiologic measures recorded during SBTs, HRV and RRV recorded before and during the last SBT prior to extubation, and extubation outcomes. We excluded 287 patients because of protocol or technical violations, or poor data quality. Measures of variability (97 HRV, 82 RRV) were calculated from electrocardiogram and capnography waveforms followed by automated cleaning and variability analysis using Continuous Individualized Multiorgan Variability Analysis (CIMVA™) software. Repeated randomized subsampling with training, validation, and testing were used to derive and compare predictive models. Results Of 434 patients with high-quality data, 51 (12%) failed extubation. Two HRV and eight RRV measures showed statistically significant association with extubation failure (P <0.0041, 5% false discovery rate). An ensemble average of five univariate logistic regression models using RRV during SBT, yielding a probability of extubation failure (called WAVE score), demonstrated optimal predictive capacity. With repeated random subsampling and testing, the model showed mean receiver operating characteristic area under the curve (ROC AUC) of 0.69, higher than heart rate (0.51), rapid shallow breathing index (RBSI; 0.61) and respiratory rate (0.63). After deriving a WAVE model based on all data, training-set performance demonstrated that the model increased its predictive power when applied to patients conventionally considered high risk: a WAVE score >0.5 in patients with RSBI >105 and perceived high risk of failure yielded a fold increase in risk of extubation failure of 3.0 (95% confidence interval (CI) 1.2 to 5.2) and 3.5 (95% CI 1.9 to 5.4), respectively. Conclusions Altered HRV and RRV (during the SBT prior to extubation) are significantly associated with extubation failure. A predictive model using RRV during the last SBT provided optimal accuracy of prediction in all patients, with improved accuracy when combined with clinical impression or RSBI. This model requires a validation cohort to evaluate accuracy and generalizability. Trial registration ClinicalTrials.gov NCT01237886. Registered 13 October 2010.

2014-01-01

423

Heart rate variability during constant work rate exercise at and above the critical power in patients with severe chronic obstructive pulmonary disease  

Microsoft Academic Search

ObjectiveHeart rate variability is useful in evaluating cardiac autonomic balance. We investigated cardiac autonomic modulation in patients with severe chronic obstructive pulmonary disease (COPD) during heavy and very heavy exercise at and above the critical power (CP).

En-Ting Chang; David Silberstein; Mehdi Rambod; Janos Porszasz; Richard Casaburi

2011-01-01

424

Capacity region of a multi-code DS-UWB system supporting variable bit rate multiclass services  

Microsoft Academic Search

An analytical formulation of the outage probability in terms of bit error rate specification for variable bit rate (VBR) multiclass services in a multi-code direct-sequence ultra-wideband (DS-UWB) system is presented. The analytical framework is formulated for the general case in which different traffic classes have different varying bit rates. Multiple spreading codes are used by each user to achieve variable

T. C. Wong; J. W. Mark; K. C. Chua

2005-01-01

425

Method of variable bias and its application to estimating subsurface temperature  

SciTech Connect

A method of obtaining variable-bias estimates of physical quantities from noisy and incomplete data is introduced, and its application to estimating subsurface temperature is illustrated by application to temperature data from the Iberia salt dome in south Louisiana.

Deming, D.; Hanor, J.S.; Nunn, J.A. (Louisiana State Univ., Baton Rouge (USA))

1990-10-01

426

Cardiac autonomic function measured by heart rate variability and turbulence in pre-hypertensive subjects.  

PubMed

Non-dipping blood pressure pattern was shown to be associated with increased cardiovascular events. In addition, cardiac autonomic dysfunction was found to be associated with non-dipper phenomenon. In this study, we aimed to evaluate the cardiac autonomic functions in dipper and non-dipper pre-hypertensive subjects. A total of 65 pre-hypertensive subjects were enrolled in this study. They were divided into two groups as non-dippers (40 subjects, 52% female) and dippers (25 subjects, 52.5% female). Cardiac autonomic functions of the two groups were compared with the aid of heart rate variability, heart rate turbulence (HRT), atrial premature contractions (APCs), ventricular premature contractions (VPCs), and mean heart rate (MHR). There was no significant difference between non-dippers and dippers in basal characteristics. The two parameters of HRT, turbulence onset and turbulence slope, were found to be significantly abnormal in non-dippers than in dippers (P < .011 and P < .002, respectively). Heart rate variability parameters, including SDNN, SDANN, RMSSD, and pNN50, were found to be similar in dipper and non-dipper pre-hypertensive subjects (P < .998, P < .453, P < .205, and P < .788, respectively). APCs, VPCs, and MHR were compared, and there were statistical differences between the groups (APCs 5.80 ± 4.55, 9.14 ± 7.33, P < .024; VPCs 8.48 ± 8.83, 13.23 ± 9.68, P < .044; and MHR 70.16 ± 11.08, 76.26 ± 11.31, P < .035; respectively). This study demonstrated a possible cardiac autonomic dysfunction in pre-hypertensive subjects with non-dipper pattern. This may be a basis for future studies related to pre-hypertension and non-dipping BP pattern. PMID:22676318

Erdem, Alim; Uenishi, Masahiro; Küçükdurmaz, Zekeriya; Matsumoto, Kazuo; Kato, Ritsushi; Hara, Motoki; Yaz?c?, Mehmet

2013-01-01

427

Application of semiclassical methods to reaction rate theory  

SciTech Connect

This work is concerned with the development of approximate methods to describe relatively large chemical systems. This effort has been divided into two primary directions: First, we have extended and applied a semiclassical transition state theory (SCTST) originally proposed by Miller to obtain microcanonical and canonical (thermal) rates for chemical reactions described by a nonseparable Hamiltonian, i.e. most reactions. Second, we have developed a method to describe the fluctuations of decay rates of individual energy states from the average RRKM rate in systems where the direct calculation of individual rates would be impossible. Combined with the semiclassical theory this latter effort has provided a direct comparison to the experimental results of Moore and coworkers. In SCTST, the Hamiltonian is expanded about the barrier and the ``good`` action-angle variables are obtained perturbatively; a WKB analysis of the effectively one-dimensional reactive direction then provides the transmission probabilities. The advantages of this local approximate treatment are that it includes tunneling effects and anharmonicity, and it systematically provides a multi-dimensional dividing surface in phase space. The SCTST thermal rate expression has been reformulated providing increased numerical efficiency (as compared to a naive Boltzmann average), an appealing link to conventional transition state theory (involving a ``prereactive`` partition function depending on the action of the reactive mode), and the ability to go beyond the perturbative approximation.

Hernandez, R.

1993-11-01

428

320-detector row CT coronary angiography: effects of heart rate and heart rate variability on image quality, diagnostic accuracy and radiation exposure  

PubMed Central

Objectives To evaluate the effects of heart rate and heart rate variability on image quality, patient dose and diagnostic accuracy of 320-detector row CT. Methods 94 patients were prospectively enrolled. Heart rate was defined as the mean value of different intervals elapsing between two consecutive R waves in an electrocardiogram (R–R intervals) and the heart rate variability was calculated as the standard deviation from the average heart rate. The image quality was evaluated by four grades, according to motion artefacts (“step artefacts” and “blurring artefacts”). The diagnostic accuracy was analysed in 43 patients who were scheduled for invasive coronary angiography (ICA). The coeffects of heart rate and heart rate variability on image quality, radiation dose and diagnostic accuracy were evaluated by multivariate regression. Results The mean image quality score was 1.2±0.5 and the mean effective dose was 14.8±9.8 mSv. The results showed that heart rate (74.0±11.2 beats per minute) was the single factor influencing image quality (p<0.001) and radiation dose (p<0.001), while heart rate variability (3.7±4.6) had no significant effect on them (p=0.16 and p=0.47, respectively). For 43 patients who underwent ICA, heart rate and heart rate variability showed no influence on the accuracy (p=0.17 and p=0.12, respectively). Overall sensitivity was 97.4% (37/38), specificity was 99.4% (351/353), positive predictive value was 94.9% (37/39) and negative predictive value was 99.7% (351/352). Conclusion 320-detector row CT, with improved longitudinal coverage of detector, resolves step artefact and high patient dose caused by irregular heart rate. However, it is still recommended to control heart rate to a lower level to eliminate blurring artefact and radiation dose.

Sun, G; Li, M; Jiang, X-S; Li, L; Peng, Z-H; Li, G-Y; Xu, L

2012-01-01

429

Time-domain heart rate variability in coronary artery disease patients affected by thyroid dysfunction.  

PubMed

Subclinical hypothyroidism and hyperthyroidism have been recognized as clinical entities with negative effects on the cardiovascular system. Moreover, the effect of treated thyroid dysfunction on parameters associated with the cardiovascular control system has been poorly investigated. In the present study we analyzed time-domain heart rate variability in coronary artery disease (CAD) patients with known thyroid diseases. Twenty-four hour ECG monitoring was performed in 344 patients with coronary artery disease (174 with thyroid dysfunction and 170 without thyroid dysfunction used as a control group), using a 3-channel tape recorder. Time domain parameters of heart rate variability (HRV) were definitely lower both in patients with subclinical hypothyroidism and subclinical hyperthyroidism than in the control group, with statistically significant differences in SDNN, RMSSD, TINN, and mean RR for both subgroups. Furthermore, patients on L-thyroxine treatment and restored euthyroidism had generally higher HRV values than patients with subclinical hypothyroidism, nevertheless SDNN, RMSSD, SDNN index, TINN, and mean RR were significantly lower when compared to those of the control group. Significant differences in HRV were also found between hyperthyroid patients under treatment and control group subjects with respect to RMSSD, TINN, and mean RR values. In conclusion, patients with cardiac disease and known thyroid disease, even when the disease is in the subclinical range or despite treatment, should be regarded as patients at additional risk conveyed by thyroid hormone disturbances. PMID:24463923

Falcone, Colomba; Matrone, Benedetta; Bozzini, Sara; Guasti, Luigina; Falcone, Rossana; Benzi, Alberto; Colonna, Anna; Savulescu, Ioana; Vailati, Alberto; Pelissero, Gabriele

2014-01-01

430

Short communication: Changes in heart rate variability of dairy cows during conventional milking with nonvoluntary exit.  

PubMed

Heart rate variability (HRV), as a physiological measure of animal welfare, was investigated in 36 cows milked in a parallel milking parlor with nonvoluntary exit. Heart rate variability parameters measured during the morning resting (baseline period) were compared with those measured during different stages of the entire milking process. No differences were found in HRV parameters between the baseline period, preparation, and main milking. A considerable reduction in vagal activity was detected during the movement of the cows to the milking parlor (driving) and while cows were in the holding area. The parasympathetic measures of HRV decreased whereas the sympatho-vagal balance increased compared with baseline. The same pattern was observed regarding the stage between removing the teat cups and leaving the milking parlor (waiting). No differences in any sympathetic measures were observed between the baseline period and any of the milking stages. These findings indicate that the milking process itself (preparation and main milking) is not stressful for cows. Decreased parasympathetic activity during driving might be the result of the physical activity of the cows, whereas waiting in the holding area and in the milking stall after milking caused stress for animals. PMID:24140325

Kovács, L; T?zsér, J; Bakony, M; Jurkovich, V

2013-12-01

431

Analysis of heart rate variability signal in meditation using second-order difference plot  

NASA Astrophysics Data System (ADS)

In this article, the heart rate variability signal taken from subjects practising different types of meditations have been investigated to find the underlying similarity among them and how they differ from the non-meditative condition. Four different groups of subjects having different meditation techniques are involved. The data have been obtained from the Physionet and also collected with our own ECG machine. For data analysis, the second order difference plot is applied. Each of the plots obtained from the second order differences form a single cluster which is nearly elliptical in shape except for some outliers. In meditation, the axis of the elliptical cluster rotates anticlockwise from the cluster formed from the premeditation data, although the amount of rotation is not of the same extent in every case. This form study reveals definite and specific changes in the heart rate variability of the subjects during meditation. All the four groups of subjects followed different procedures but surprisingly the resulting physiological effect is the same to some extent. It indicates that there is some commonness among all the meditative techniques in spite of their apparent dissimilarity and it may be hoped that each of them leads to the same result as preached by the masters of meditation. The study shows that meditative state has a completely different physiology and that it can be achieved by any meditation technique we have observed. Possible use of this tool in clinical setting such as in stress management and in the treatment of hypertension is also mentioned.

Goswami, Damodar Prasad; Tibarewala, Dewaki Nandan; Bhattacharya, Dilip Kumar

2011-06-01

432

Second ventilatory threshold from heart-rate variability: valid when the upper body is involved?  

PubMed

To determine the most accurate method based on spectral analysis of heart-rate variability (SA-HRV) during an incremental and continuous maximal test involving the upper body, the authors tested 4 different methods to obtain the heart rate (HR) at the second ventilatory threshold (VT2). Sixteen ski mountaineers (mean ± SD; age 25 ± 3 y, height 177 ± 8 cm, mass 69 ± 10 kg) performed a roller-ski test on a treadmill. Respiratory variables and HR were continuously recorded, and the 4 SA-HRV methods were compared with the gas-exchange method through Bland and Altman analyses. The best method was the one based on a time-varying spectral analysis with high frequency ranging from 0.15 Hz to a cutoff point relative to the individual's respiratory sinus arrhythmia. The HR values were significantly correlated (r2 = .903), with a mean HR difference with the respiratory method of 0.1 ± 3.0 beats/min and low limits of agreements (around -6 /+6 beats/min). The 3 other methods led to larger errors and lower agreements (up to 5 beats/min and around -23/+20 beats/min). It is possible to accurately determine VT2 with an HR monitor during an incremental test involving the upper body if the appropriate HRV method is used. PMID:24231307

Mourot, Laurent; Fabre, Nicolas; Savoldelli, Aldo; Schena, Federico

2014-07-01

433

Heart Rate Variability in Sleeping Preterm Neonates Exposed to Cool and Warm Thermal Conditions  

PubMed Central

Sudden infant death syndrome (SIDS) remains the main cause of postneonatal infant death. Thermal stress is a major risk factor and makes infants more vulnerable to SIDS. Although it has been suggested that thermal stress could lead to SIDS by disrupting autonomic functions, clinical and physiopathological data on this hypothesis are scarce. We evaluated the influence of ambient temperature on autonomic nervous activity during sleep in thirty-four preterm neonates (mean ± SD gestational age: 31.4±1.5 weeks, postmenstrual age: 36.2±0.9 weeks). Heart rate variability was assessed as a function of the sleep stage at three different ambient temperatures (thermoneutrality and warm and cool thermal conditions). An elevated ambient temperature was associated with a higher basal heart rate and lower short- and long-term variability in all sleep stages, together with higher sympathetic activity and lower parasympathetic activity. Our study results showed that modification of the ambient temperature led to significant changes in autonomic nervous system control in sleeping preterm neonates. The latter changes are very similar to those observed in infants at risk of SIDS. Our findings may provide greater insight into the thermally-induced disease mechanisms related to SIDS and may help improve prevention strategies.

Stephan-Blanchard, Erwan; Chardon, Karen; Leke, Andre; Delanaud, Stephane; Bach, Veronique; Telliez, Frederic

2013-01-01

434

Heart rate variability in sleeping preterm neonates exposed to cool and warm thermal conditions.  

PubMed

Sudden infant death syndrome (SIDS) remains the main cause of postneonatal infant death. Thermal stress is a major risk factor and makes infants more vulnerable to SIDS. Although it has been suggested that thermal stress could lead to SIDS by disrupting autonomic functions, clinical and physiopathological data on this hypothesis are scarce. We evaluated the influence of ambient temperature on autonomic nervous activity during sleep in thirty-four preterm neonates (mean ± SD gestational age: 31.4±1.5 weeks, postmenstrual age: 36.2±0.9 weeks). Heart rate variability was assessed as a function of the sleep stage at three different ambient temperatures (thermoneutrality and warm and cool thermal conditions). An elevated ambient temperature was associated with a higher basal heart rate and lower short- and long-term variability in all sleep stages, together with higher sympathetic activity and lower parasympathetic activity. Our study results showed that modification of the ambient temperature led to significant changes in autonomic nervous system control in sleeping preterm neonates. The latter changes are very similar to those observed in infants at risk of SIDS. Our findings may provide greater insight into the thermally-induced disease mechanisms related to SIDS and may help improve prevention strategies. PMID:23840888

Stéphan-Blanchard, Erwan; Chardon, Karen; Léké, André; Delanaud, Stéphane; Bach, Véronique; Telliez, Frédéric

2013-01-01

435

Study of Heart Rate Variability in Bipolar Disorder: Linear and Non-Linear Parameters during Sleep  

PubMed Central

The aim of the study is to define physiological parameters and vital signs that may be related to the mood and mental status in patients affected by bipolar disorder. In particular we explored the autonomic nervous system through the analysis of the heart rate variability. Many different parameters, in the time and in the frequency domain, linear and non-linear were evaluated during the sleep in a group of normal subject and in one patient in four different conditions. The recording of the signals was performed through a wearable sensorized T-shirt. Heart rate variability (HRV) signal and movement analysis allowed also obtaining sleep staging and the estimation of REM sleep percentage over the total sleep time. A group of eight normal females constituted the control group, on which normality ranges were estimated. The pathologic subject was recorded during four different nights, at time intervals of at least 1?week, and during different phases of the disturbance. Some of the examined parameters (MEANNN, SDNN, RMSSD) confirmed reduced HRV in depression and bipolar disorder. REM sleep percentage was found to be increased. Lempel–Ziv complexity and sample entropy, on the other hand, seem to correlate with the depression level. Even if the number of examined subjects is still small, and the results need further validation, the proposed methodology and the calculated parameters seem promising tools for the monitoring of mood changes in psychiatric disorders.

Migliorini, Matteo; Mendez, Martin O.; Bianchi, Anna M.

2012-01-01

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