Analysis of Heart Rate Variability Based on the Graph Method

A method of analysis of heart rate variability based on the graph theory principle was suggested. The main parameters of the heart rate graph structure were determined and analyzed using models of harmonic oscillations, white noise, and various functional tests (including controllable respiration and mental load). The efficiency of the use of parameters of the heart rate graph for diagnosing some functional states was considered. A correlation of the parameters of the heart rate graph structure with the frequency characteristics of heart rate variability was studied. A general model of changes in the heart rate graph structure parameters at different levels of mental activity was constructed in terms of entropy changes.     

An Examination of the Relationship Between Resting Heart Rate Variability and Heart Rate Reactivity to a Mental Arithmetic Stressor

Resting heart rate variability can be an index of sympathetic or parasympathetic dominance, according to the frequency of the variability studied. Sympathetic dominance of this system has been linked to increased risk of cardiovascular disease (CVD). Similarly, rapid and dramatic increases in heart rate reactivity to a stressor task have also been suggested as indicating increased risk of CVD via atherogenesis. Although both of these variables have been related to the development of cardiovascular disease, and both may be related to increased sympathetic activity or parasympathetic withdrawal, most research studies have tended to focus on either variable independently of the other. In order to investigate whether these two indices of stressor reactivity were related in relatively young and healthy subjects, resting heart rate variability data were collected from 80 volunteers for 20 minutes. In addition, heart rate reactivity data were collected during a 2-minute mental arithmetic stressor, which has been previously shown to induce significant increases in heart rate. After classifying subjects according to whether their heart rate variability data were above or below the mean for their gender, heart rate reactivity data were examined via MANOVA to detect significant differences between subject groups. Females showed significant effects, and males showed nonsignificant trends, but these two sets of data were in different directions, suggesting that gender may be a confounding factor in the relationship between heart rate reactivity and heart rate variability.     

Plastic surgeon's life: marvelous for mind, exhausting for body

Surgery is accepted as one of the most demanding professions that create both physical and mental strain on the performers. Therefore, the authors aimed to elucidate the mental burden of surgeons, which is dedicated to operative stress. They also tested the hypotheses that participating in surgery creates mental stress on surgeons that leads to cardiovascular changes, and that this stress is more pronounced for actual operators than for first assistants. The method chosen for this purpose was an analysis of heart rate variability. Twelve surgeons (five plastic surgery staff and seven plastic surgery residents) were monitored by a digital ambulatory Holter recorder on at least two occasions. Half of the recordings were carried out on operating days and the other half on office days. Heart rate variability indices (low frequency, high frequency, high frequency/low frequency ratio, and heart rate) were analyzed from those recordings using computerized research tool software. The heart rate variability indices of the operators showed statistically significant differences between operating days and office hours in favor of an increased sympathetic and decreased parasympathetic activity for the former. For first assistants, three of the parameters, with the exception of heart rate, changed in favor of a sympathetic predominance over parasympathetic activity; these changes were also statistically significant. These results showed a sympathetic hyperactivity for both operators and first assistants during the operations. When the sympathovagal balance of the actual operators was compared with that of assistants, the former group showed a more pronounced sympathetic arousal. This difference is accepted as a proof for the mental stress of the surgery being the main factor responsible for the sympathetic hyperactivity that we detected during the operations. Surgeons continuously face a unique mental strain that other professions rarely bring forth, and these psychological stressors are associated with alterations in cardiac autonomic control that may contribute to the development of cardiac disease. Prolonged sympathetic hyperactivity could anticipate cardiac discomfort in more experienced surgeons with marginal cardiac reserve. Such cardiac diseases would be reconsidered as occupation-related illnesses, which might be reimbursed to the physician. In addition, the legal responsibility of surgeons concerning their unfavorable results might be assessed with more understanding with a realization of their undue working conditions.     

不同心理素质水平军人在厌恶情绪条件下自主神经反应特点

目的：探讨不同心理素质水平军人在厌恶情绪条件下自主神经反应特点。方法：用军人心理素质量表筛选出54名部队官兵,其中高、中、低心理素质组军人各18名。采用3份情绪视频材料,诱导被试的中性和厌恶情绪,利用八通道多参数生物反馈仪,记录自主神经反应的十个指标和相应自主神经反应指标的平均恢复时间。结果：（1）在中性情绪条件下,低心理素质组[（12．06±4．89）b／min]的心率（HR）的变化上显著大于高心理素质组[（5．75±2．80）b／min];（2）在厌恶情绪条件下,低心理素质组f（7．09±2．02）nU]的心率变异性（rmv）频谱归-化低频功率（Lfnorm）的变化显著大于中等[（3．43±1．70）nU]与高心理素质组[（2．66±1．50）nU];低心理素质组[（357．94±129．33）Hz]的总功率（TP）的变化显著大于中等[（171．1±73．02）ms。]与高心理素质组[（167．84±86．38）ms／];（3）在自主神经反应指标的恢复时间上,低心理素质组[（49．98±10．96）秒]在厌恶情绪条件下其心率（HR）的恢复时间显著大于高心理素质组[（24．65±9．38）see];低心理素质组[（37．84±21．33）sec]在厌恶情绪条件下其皮电（SC）、皮温（TEMP）、指端血容振幅（BVP）、心率（HR）四个自主神经反应指标的平均恢复时间上显著大于高心理素质组[（18．57±10．15）秒]。（4）在情绪的愉悦度、唤醒度的上,低心理素质组（0．88±1．11）在中性条件下其唤醒度的变化明显大于中等（0．50±0．70）与高心理素质组（0．12±0．33）;低心理素质组（-2．11±0．90）在厌恶条件下愉悦度的变化明显大于中等（-1．56±0．86）与高心理素质组（-1．33±0．84）。结论：在中性条件下,低心理素质军人更容易出现生理上的唤醒警觉状态。在厌恶情绪条件下,低心理素质军人是副交感神经伴有较强交感神经兴奋的自主神经反应模式;高、中等心理素质军人副交感神经伴有较弱的交感神经兴奋。     

Automatic filtering of outliers in RR intervals before analysis of heart rate variability in Holter recordings: a comparison with carefully edited data

Background  

Undetected arrhythmic beats seriously affect the power spectrum of the heart rate variability (HRV). Therefore, the series of RR intervals are normally carefully edited before HRV is analysed, but this is a time consuming procedure when 24-hours recordings are analysed. Alternatively, different methods can be used for automatic removal of arrhythmic beats and artefacts. This study compared common frequency domain indices of HRV when determined from manually edited and automatically filtered RR intervals.     

Comparison of the Effects of Septoplasty and Sinus Lifting Simulation in Rats on Changes in Heart Rate Variability

Doklady Biochemistry and Biophysics - The effects of septoplasty and sinus lifting simulation in rats on changes in the frequency domain of heart rate variability were compared. In the early...     

Inheritance of heart rate variability: the kibbutzim family study

Heart rate variability (HRV) measures are associated with coronary heart disease incidence and mortality. Therefore insight into the genetic and environmental determinants of these measures may have clinical relevance. We assessed the role of genetic and environmental factors of time domain and frequency domain HRV indices. Participants were 451 kibbutz members, aged 15 and up, belonging to 80 families. HRV indices were calculated from Holter recordings measured over 5 min. Our data indicate that for the two time- and four frequency domain indices, a mixture of two normal distributions fit the data significantly better than a single normal distribution (P<0.05). We used complex segregation analysis to infer the modes of inheritance of these HRV measures. We found evidence for possible involvement of a recessive major gene in the inheritance of the root mean square of successive differences in RR intervals (RMSSD), which is predominantly vagally mediated. A putative major gene explains 28%-34% of the adjusted inter-individual variability. The SD, determined by a mixture of mechanisms, is influenced by environmental and polygenic effects, but not by a major gene. The findings regarding the heritability of the frequency domain indices were not conclusive. However, the involvement of genetic factors was not rejected. Additional studies in extended families are needed to confirm the involvement of major genes in the determination of the autonomic activity.     

Spectral analysis of heart rate variability in the beluga (<Emphasis Type="Italic">Delphinapterus leucas</Emphasis>) during exposure to acoustic noise

The spectral parameters of heart rate variability are a measure of activation of the sympathetic and parasympathetic branches of the mammalian autonomic nervous system. In this study, spectral analysis was used for the first time to evaluate the impact of acoustic noise (one of the major anthropogenic factors) on a cetacean. We analyzed cardiac intervals in a captive beluga (a member of the Odontoceti whales) in response to a 10-min band-pass acoustic noise at an intensity of 150–165 dB and frequency of 19–38 kHz. The beluga’s response to acoustic noise, when examined shortly after the animal’s capture, was characterized by a sharp tachycardia (the first phase) followed by a decrease in the heart rate (the second phase). Based on spectral analysis, the frequency range of heart rate oscillations in the beluga decreased during the period of tachycardia while shifting to a lower frequency range (below 0.01 Hz) as compared with the control conditions. Accordingly, the spectral power of low-frequency components was reduced. During the second phase, the range of heart rate variability oscillations expanded and fully recovered only after the noise had been turned off. After one year in captivity, no significant changes in the heart rate parameters (both in time and frequency domain) were recorded in response to a similar noise exposure. Therefore, the changes in the heart rate spectral components in the studied beluga exposed to acoustic noise were comparable to those recorded in terrestrial mammals and in humans in stressful and emotionally negative situations. The spectral characteristics of heart rate oscillations can be used as a quantitative measure of beluga whales’ response to acoustic noise as a stress factor.     

Are Complexity Metrics Reliable in Assessing HRV Control in Obese Patients During Sleep?

Obesity is associated with cardiovascular mortality. Linear methods, including time domain and frequency domain analysis, are normally applied on the heart rate variability (HRV) signal to investigate autonomic cardiovascular control, whose imbalance might promote cardiovascular disease in these patients. However, given the cardiac activity non-linearities, non-linear methods might provide better insight. HRV complexity was hereby analyzed during wakefulness and different sleep stages in healthy and obese subjects. Given the short duration of each sleep stage, complexity measures, normally extracted from long-period signals, needed be calculated on short-term signals. Sample entropy, Lempel-Ziv complexity and detrended fluctuation analysis were evaluated and results showed no significant differences among the values calculated over ten-minute signals and longer durations, confirming the reliability of such analysis when performed on short-term signals. Complexity parameters were extracted from ten-minute signal portions selected during wakefulness and different sleep stages on HRV signals obtained from eighteen obese patients and twenty controls. The obese group presented significantly reduced complexity during light and deep sleep, suggesting a deficiency in the control mechanisms integration during these sleep stages. To our knowledge, this study reports for the first time on how the HRV complexity changes in obesity during wakefulness and sleep. Further investigation is needed to quantify altered HRV impact on cardiovascular mortality in obesity.     

Long-term spectral analysis of heart rate variability — An algorithm based on segmental frequency distributions of beat-to-beat intervals

Reduced heart rate variability has been reported as a predictor of long-term mortality in recent myocardial infarction patients. However, it has not been systematically investigated whether the reduction in heart rate variability in those post myocardial infarction patients who later suffer death or severe arrhythmias is caused by a reduction of short-term variability of heart rate (such as respiratory arrhythmia) or whether the differences in long term variability (such as diurnal rhythm) are involved. In order to perform such an evaluation, a new algorithm has been developed which permits different wavelength components (including the long-term components due to diurnal rhythm) of heart rate variability to be approximated. In general, the method uses segmental frequency distributions of durations of intervals between successive normal cardiac beats. To assess the spectral components of heart rate variability, a scale of wavelength limits is used and for each limit of this scale, the algorithm excludes the rate changes of wavelength longer than the given bound. The method was applied to the analysis of electrocardiograms recorded in 14 post myocardial infarction patients who later suffered death or ventricular tachycardia, and in 14 other randomly selected patients with an uncomplicated course following acute myocardial infarction. The rate variability spectra obtained for both groups of patients were compared statistically and the results showed that the groups of positive and negative cases were most significantly distinguished when including both short- and long-term components of heart rate variability. Separate evaluation of different wavelength components showed that the very long-term components of heart rate variability were more powerful in distinguishing between positive and negative cases than the short term components.     

Blood pressure and heart rate variability response to noninvasive ventilation in patients with exacerbations of chronic obstructive pulmonary disease

Sympathetic activation and parasympathetic withdrawal are commonly observed during acute exacerbations of chronic obstructive pulmonary disease (COPD). We have demonstrated previously that noninvasive positive-pressure ventilation (NPPV) improves parasympathetic neural control of heart rate in patients with obstructive sleep apnea. We hypothesized that NPPV may exert such beneficial effects in COPD as well. Therefore, we assessed the acute effects of NPPV on systemic blood pressure and indexes of heart rate variability (HRV) in 23 patients with acute exacerbations of COPD. The measurements of HRV in the frequency domain were computed by an autoregressive spectral technique. The use of NPPV resulted in significant increases of oxygen saturation (from 89.2+/-1.0 to 92.4+/-0.9 %, p<0.001) in association with reductions in systolic and diastolic blood pressures and heart rate (from 147+/-3 to 138+/-3 mm Hg, from 86+/-2 to 81+/-2 mm Hg, from 85+/-3 to 75+/-2 bpm, p<0.001 for all variables), and increases in ln-transformed high frequency band of HRV (from 6.4+/-0.5 to 7.4+/-0.6 ms(2)/Hz, p<0.01). Reductions in heart rate and increases in ln-transformed HF band persisted after NPPV withdrawal. In conclusion, these findings suggest that NPPV may cause improvements in the neural control of heart rate in patients with acute exacerbations of COPD.     

The effect of sinus node depression on heart rate variability in humans using zatebradine, a selective bradycardic agent

Zatebradine is a bradycardic agent with a selective effect on the pacemaker current in the sinus node. The effect of such drugs on heart rate variability is not known. Thirty-six patients without structural heart disease were randomly assigned to receive 10 mg of zatebradine i.v. (n = 24) or isotonic saline (n = 12). Heart rate variability (HRV) was recorded as power in the very low frequency (VLF, 0.003-0.040 Hz), low frequency (LF, 0.040-0.150 Hz), and high frequency (HF, 0.150-0.400 Hz) spectral bands as well as total power (TP, 0.003-0.400 Hz) during 5-min ECG acquisitions at baseline, 30, and 60 min following the start of the infusion. No change in heart rate variability was detected in the control group. Zatebradine significantly reduced heart rate variability at 60 min in all frequency bands: VLF (-12+/-4%, p<0.001), LF (-19+/-4%, p<0.001), and HF (-26+/-5%, p<0.001). The reduction in HRV following zatebradine is due to depression of sinus node response to all external stimuli and underscores the need for documentation of normal sinus node function in HRV research.     

Heart Rate Dynamics after Combined Strength and Endurance Training in Middle-Aged Women: Heterogeneity of Responses

The loss of complexity in physiological systems may be a dynamical biomarker of aging and disease. In this study the effects of combined strength and endurance training compared with those of endurance training or strength training alone on heart rate (HR) complexity and traditional HR variability indices were examined in middle-aged women. 90 previously untrained female volunteers between the age of 40 and 65 years completed a 21 week progressive training period of either strength training, endurance training or their combination, or served as controls. Continuous HR time series were obtained during supine rest and submaximal steady state exercise. The complexity of HR dynamics was assessed using multiscale entropy analysis. In addition, standard time and frequency domain measures were also computed. Endurance training led to increases in HR complexity and selected time and frequency domain measures of HR variability (P<0.01) when measured during exercise. Combined strength and endurance training or strength training alone did not produce significant changes in HR dynamics. Inter-subject heterogeneity of responses was particularly noticeable in the combined training group. At supine rest, no training-induced changes in HR parameters were observed in any of the groups. The present findings emphasize the potential utility of endurance training in increasing the complex variability of HR in middle-aged women. Further studies are needed to explore the combined endurance and strength training adaptations and possible gender and age related factors, as well as other mechanisms, that may mediate the effects of different training regimens on HR dynamics.     

Causal interactions between the cerebral cortex and the autonomic nervous system

Mental states such as stress and anxiety can cause heart disease.On the other hand,meditation can improve cardiac performance.In this study,the heart rate variability,directed transfer function and corrected conditional entropy were used to investigate the effects of mental tasks on cardiac performance,and the functional coupling between the cerebral cortex and the heart.When subjects tried to decrease their heart rate by volition,the sympathetic nervous system was inhibited and the heart rate decreased.When subjects tried to increase their heart rate by volition,the parasympathetic nervous system was inhibited and the sympathetic nervous system was stimulated,and the heart rate increased.When autonomic nervous system activity was regulated by mental tasks,the information flow from the post-central areas to the pre-central areas of the cerebral cortex increased,and there was greater coupling between the brain and the heart.Use of directed transfer function and corrected conditional entropy techniques enabled analysis of electroencephalographic recordings,and of the information flow causing functional coupling between the brain and the heart.     

Mutual information detects a decreased interdependence between RR and SAP in orthostatic intolerance after microgravity condition

Orthostatic intolerance is the most serious symptom of cardiovascular deconditioning induced by microgravity. However, the exact mechanisms underlying these alterations have not been completely clarified. Several methods for studying the time series of systolic arterial pressure and RR interval have been proposed both in the time and in the frequency domain. However, these methods did not produce definitive results. In fact heart rate and arterial pressure show a complex pattern of global variability which is likely due to non linear feedback which involves the autonomic nervous system and to "stochastic" influences. Aim of this study was to evaluate the degree of interdependence between the mechanisms responsible for the variability of SAP and RR signals in subjects exposed to head down (HD). This quantification was achieved by using Mutual Information (MI).     

Association between level of intelligence and heart rate variability

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.     

New approach to the statistical analysis of cardiovascular data.

Fourier-based approaches to analysis of variability of R-R intervals or blood pressure typically compute power in a given frequency band (e.g., 0.01-0.07 Hz) by aggregating the power at each constituent frequency within that band. This paper describes a new approach to the analysis of these data. We propose to partition the blood pressure variability spectrum into more narrow components by computing power in 0.01-Hz-wide bands. Therefore, instead of a single measure of variability in a specific frequency interval, we obtain several measurements. The approach generates a more complex data structure that requires a careful account of the nested repeated measures. We briefly describe a statistical methodology based on generalized estimating equations that suitably handles this more complex data structure. To illustrate the methods, we consider systolic blood pressure data collected during psychological and orthostatic challenge. We compare the results with those obtained using the conventional methods to compute blood pressure variability, and we show that our approach yields more efficient results and more powerful statistical tests. We conclude that this approach may allow a more thorough analysis of cardiovascular parameters that are measured under different experimental conditions, such as blood pressure or heart rate variability.     

Dependency of characteristics of heart rate variability on the average value of the R--R-intervals

By the means of spectral analysis, dependency of heart rate variability (HRV) on average R--R-intervals (R--Rav, sec) is explored at controlled (forced) breathing. According to our findings, the dependency of the peak frequency at a spectral density graph for source series of R--R-intervals upon the RRav may be presented by the following formula: fp 1.0 = fr: RRav, where fp 1.0--peak frequency when R--Rav = 1.0 sec, fp--peak frequency at current R--Rav. For correcting (standardization) the frequency domain borders of spectral power (fd) of sources series of the R--Rav-intervals it is possible to use the formula: fd = fd 1.0 R--Rav, where fd 1.0--frequency domain border at R--Rav = 1.0 sec. The correction (standardization) of frequency domain borders of spectral power (fd), frequency peaks (fp 1.0) of sources series of the R--Rav-intervals as compared to current R--Rav allows to compare different series of the R--Rav-intervals without using the transformation to the discrete event series (DES).     

精神疲劳评价方法研究进展

长时间飞行活动所致的精神疲劳一直是航空航天医学中一个重要的课题。尤其随着我军航空技术的发展,精神疲劳已经成为影响飞行安全的重要原因之一。研究发现,精神疲劳发生时,机体的生理、心理、生化和工作绩效等功能会发生变化。例如,精神疲劳时,脑电图的theta波、delta波和alpha波发生变化、瞳孔直径增大、心率变异性的低频谱功率升高和高频谱功率降低、姿势控制能力下降、反应时延长、临界融合频率降低、血浆中氨基酸等功能性分子水平改变和认知能力的下降等。精神疲劳的客观评定方法就是研究者借助于某些设备来监测到这些变化,并根据这些变化对疲劳状态进行判断。本文将从生理、心理、生化和作业绩效等方面阐述了精神疲劳客观的评定方法,并指出了这些方法的优缺点。最后,本文对精神疲劳评价方法发展趋势做出了初步的判断,即我们应对精神疲劳进行综合量化评定,这样才能更全面准确地评估精神疲劳。