Nature Of Heart Rate Variability Research Articles

Autonomic Nervous System Influences on Cardiovascular Self-Organized Criticality.

Cardiovascular self-organized criticality has recently been demonstrated. We studied a model of autonomic nervous system changes to better characterize heart rate variability self-organized criticality. The model included short and long-term autonomic changes associated with body position and physical training, respectively. Twelve professional soccer players took part in a 5-week training session divided into "Warm-up", "Intensive", and "Tapering" periods. A stand test was carried out at the beginning and end of each period. Heart rate variability was recorded beat by beat (Polar Team 2). Bradycardias, defined as successive heart rates with a decreasing value, were counted according to their length in number of heartbeat intervals. We checked whether bradycardias were distributed according to Zipf's law, a feature of self-organized criticality. Zipf's law draws a straight line when the rank of occurrence is plotted against the frequency of occurrence in a log-log graph. Bradycardias were distributed according to Zipf's law, regardless of body position or training. Bradycardias were much longer in the standing position than the supine position and Zipf's law was broken after a delay of four heartbeat intervals. Zipf's law could also be broken in some subjects with curved long bradycardia distributions by training. Zipf's law confirms the self-organized nature of heart rate variability and is strongly linked to autonomic standing adjustment. However, Zipf's law could be broken, the significance of which remains unclear.

The Inconsistent Nature of Heart Rate Variability During Sleep in Normal Children and Adolescents.

Introduction: Cardiac function is modulated by multiple factors including exogenous (circadian rhythm) and endogenous (ultradian 90–110 min sleep cycle) factors. By evaluating heart rate variability (HRV) during sleep, we will better understand their influence on cardiac activity. The aim of this study was to evaluate HRV in the dark phase of the circadian rhythm during sleep in healthy children and adolescents.Methods: One 3 min segment of pre-sleep electrocardiography (EEG) and 3, 6 min segments of electrocardiography recorded during polysomnography from 75 healthy children and adolescents were sampled during progressive cycles of slow wave sleep (SWS1, SWS2, SWS3). Three, 3 min segments of rapid eye movement sleep (REM) were also assessed, with REM1 marked at the last REM period before awakening. Studies that recorded REM3 prior to SWS3 were used for assessment. HRV variables include the following time domain values: mean NN (average RR intervals over given time), SDNN (Standard Deviation of RR intervals), and RMSSD (root Mean Square of beat-to-beat Differences). Frequency domain values include: low frequency (LF), high frequency (HF), and LF:HF.Results: Mixed linear effects model analysis revealed a significant difference in time and frequency domain values between sleep cycles and stages. Mean NN was lowest (highest heart rate) during pre—sleep then significantly increased across SWS1-3. Mean NN in SWS1 was similar to all REM periods which was significantly lower than both SWS2 and SWS3. SDNN remained at pre-sleep levels until SWS3, and then significantly increased in REM1&2. There was a large drop in LF from pre-sleep to SWS1. As cycles progressed through the night, LF remains lower than awake but increases to awake like levels by REM2. RMSSD and HF were lowest in pre-sleep and increased significantly by SWS1 and remain high and stable across stages and cycles except during the REM3 period where RMSSD decreased.Conclusion: Our results demonstrate that there are considerable changes in the spectral analysis of cardiac function occurring during different sleep stages and between sleep cycles across the night. Hence, time of night and sleep stage need to be considered when reporting any HRV differences.

Sudden Cardiac Death from the Perspective of Nonlinear Dynamics

There are some reports that sympathetic nerve activity (SNA) shows a characteristic pattern a few hours before the onset of lethal ventricular arrhythmias. If so, it could be possible to predict sudden cardiac death a few hours in advance of its occurrence. Recently, we reported that a previously unidentified V-trough of SNA is a potential precursor of lethal cardiac events by examining 24-hour ambulatory electrocardiograms in which such an event was recorded by chance. In contrast, the chaotic nature of heart rate variability has been noted recently from the viewpoint of nonlinear dynamics. This study models the hemodynamics, consisting of heart rate, SNA, and blood pressure (BP), by modifying a known chaotic electrical circuit, the Chua circuit. A V-trough of the SNA appears when the resistive element between the SNA and BP in the circuit is increased, which corresponds to the impaired regulation of BP by the SNA. This finding is consistent with an acknowledged finding that a depressed baroreflex (a reflex of the BP by SNA) may trigger a lethal arrhythmia. This study indicates that a V-trough of the SNA is a possible precursor of sudden cardiac death on the basis of experimental and clinical findings as well as mathematical modeling.

The Effect of Chi Meditation on the Multifractal Nature of Heart Rate Variability

The Effect of Chi Meditation on the Multifractal Nature of Heart Rate Variability

Short-term stability of resting heart rate variability: influence of position and gender

Heart rate variability (HRV) is utilized within laboratory and clinical settings as a noninvasive indicator of cardiac autonomic modulation. Past research has utilized a wide variety of resting methodologies and, as such, it is difficult to draw conclusions on the nature of HRV from different studies. Therefore, the current study aimed to assess the short-term stability of resting HRV during a 40-min resting trial and the impact of body position and gender on this short-term stability. Resting HRV was determined from 40-min trials in 3standard positions (supine, seated, and standing) for healthy males (n = 14) and females (n = 16). Time-domain, geometric, and frequency-domain measures of resting HRV were examined during consecutive 10-min segments using a 3-way ANOVA (time× position× gender) and Tukeys' post-hoc tests with reproducibility assessed by intraclass correlation coefficients (ICC) and coefficients of variation. During rest, most HRV measures fluctuated over time, were greater in the supine compared to the standing position, and were greater for males compared with females. Variables that reflected primarily vagal modulations of heart rate remained stable, whereas other HRV measures varied over time. The majority of HRV variables exhibited substantial to excellent short-term reproducibility (ICC> 0.6) with time-domain and geometric measures of HRV demonstrating greater values compared with frequency-domain parameters. Based on the current results, the recording and analysis of HRV at 0-10min of rest was recommended as a standardized protocol for the assessment of resting HRV in any standard position for either gender during laboratory and (or) clinical settings.

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

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.

液体荷役の自動化のための機能配分と過誤防止効果について

The thinking faculty and operating ability of cargo operators tend to be affected by their mental task loads under the pressure from liquid cargo loading/unloading environment. The suitable cargo handling support system has to be taken to cope with the relation between tensional stress degrees and human errors of operators during cargo handling.This paper, on the subject of mental stress and task loads of a liquid cargo control operator, consists of the quantitative analysis of the tensional stresses by measuring the fractal nature of heart rate variability under mental work-load during cargo handling on two domestic oil tankers that are respectively equipped with/without the automatic cargo control system. And the way of supporting cargo handling in order to reduce the work-load and human errors is predicted for the task with high-tension under complicated condition of cargo handling.Furthermore, the specific method to search for almost all of the human error factors, that could be taken measures by the automatic handling system, is proposed. And the evaluation method of the quantitative degree of the improved safety on the basis of probability of human error in the functional system is carried out using apprehensive degree that is defined as similar to the sense scale based on the experience of skilled ship cargo operators. The quantitative evaluation for the improvement of safety is predicted respectively to the conventional site operation, the simple remote operation with monitoring and the operation by full automatic system for comparison.

A Stochastic State-transition and Safety Assessment for Marine Accidents Based on Human Factors

The thinking faculty and operating ability of ship operators tend to be affected by their mental workload under the pressure from navigation environment. The suitable safety measures have to be taken to cope with the relation between stress degrees of operators and human errors based on the state-transition during operating man-machine systems such as a ship maneuvering system.This paper, on the subject of the state-transition and stress degrees of operators, consists of (1) the estimation of accident incident probability based on the fault tree analysis and (2) the quantitative analysis of the tensional stresses by measuring the fractal nature of heart rate variability under mental work-load during maneuvering several kinds of ships. Then these results are compared with the environmental stress model proposed by K. Inoue et al., and the specific property of tensional stress generated under severe environment may be clarified with a view of to prevent marine accidents.

研究 心拍の揺らぎのフラクタル的性格と自律神経活動の関連:起立負荷試験を用いた検討

研究 心拍の揺らぎのフラクタル的性格と自律神経活動の関連:起立負荷試験を用いた検討

On the fractal nature of heart rate variability in humans: effects of vagal blockade.

The purpose of the present study was to investigate the effects of the vagal blocker atropine on the fractal nature of human heart rate variability (HRV) at rest. Approximately 10-min segments of beat-to-beat heartbeat intervals, i.e., HRV, of 10 normal subjects and 11 cardiac disease patients were measured before and after intravenous injection of 0.5-0.75 mg atropine sulfate. HRV data were analyzed by coarse graining spectral analysis (Y. Yamamoto and R. L. Hughson, Physica 68D: 250-264, 1993) to break down their total power into harmonic and nonharmonic (fractal) components. The harmonic component was used to calculate the contribution of high (> 0.15 Hz)-frequency components to total HRV power (%HF). From the fractal component, the contribution of the fractal component to total HRV power (%fractal), the spectral exponent beta, and Hurst scaling exponent (H) were calculated. For both normal subjects and cardiac patients, atropine resulted in significantly (P < 0.05) less mean HRV and significantly (P < 0.05) greater beta compared with control, whereas mean values for %fractal were as high as 70% and were not significantly (P > 0.05) different between atropine and control. The mean value of H with atropine was significantly (P < 0.05) greater than that for control. Directional changes in %HF and beta were consistent with only one exception for a patient who had the smallest change in log %HF by atropine. The normally irregular fractal pattern of resting HRV was decreased by atropine as shown by the decrease in %HF and the increase in beta.(ABSTRACT TRUNCATED AT 250 WORDS)

On the fractal nature of heart rate variability in humans: effects of data length and beta-adrenergic blockade

In the present study, we reinvestigated the question of whether human heart rate variability (HRV) is fractal in nature. Ten healthy volunteers participated in either of two studies conducted while beat-by-beat long-term HRV (8,500 heartbeats) was recorded for 2-3 h in the quiet, awake state in the supine position. In the first study, five subjects were tested four times each to evaluate the basic fractal nature of human HRV. The other five subjects were examined for the effects of oral propranolol (2 x 80 mg/day) on the fractal property of HRV in the second study. HRV data were analyzed by coarse-graining spectral analysis to break down their total power into harmonic and nonharmonic (fractal) components. The harmonic component was further divided into low (0.0-0.15 Hz; LF)- and high (> 0.15 Hz; HF)-frequency components. From these spectral components, %Fractal, %LF, and %HF as functions of total power were calculated. The fractal component was used to calculate the spectral exponent, beta. The %Fractal of human resting HRV was 85.5 +/- 4.4% (mean +/- SD, n = 20). The beta for the fractal HRV was 1.08 +/- 0.18 (n = 20). With propranolol, these basic properties of fractal HRV dynamics remained unchanged despite an increase in the mean RR interval (placebo, 912 +/- 111 ms; propranolol, 1,134 +/- 133 ms, P < 0.05) and a change in the harmonic spectral shape evaluated by LF/HF (placebo, 2.76 +/- 1.57; propranolol, 1.82 +/- 0.81, P < 0.05). For short-term data, less power was extracted as fractal because of the absence of the very low frequency component, yet the beta and LF/HF were unchanged from long-term data. These findings indicate that 1) the observed inversely proportional frequency (1/f) spectrum in human resting HRV is due to underlying random fractal dynamics and 2) the sympathetic nervous system seemed to play a minor role in modulating the fractal HRV dynamics.