The effect of ventilation on spectral analysis of heart rate and blood pressure variability during exercise

Heart rate variability (HRV) and systolic blood pressure variability (BPV) during incremental exercise at 50, 75, and 100% of previously determined ventilatory threshold (VT) were compared to that of resting controlled breathing (CB) in 12 healthy subjects. CB was matched with exercise-associated respiratory rate, tidal volume, and end-tidal CO(2) for all stages of exercise. Power in the low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, >0.15-0.4 Hz) for HRV and BPV were calculated, using time-frequency domain analysis, from beat-to-beat ECG and non-invasive radial artery blood pressure, respectively. During CB absolute and normalized power in the LF and HF of HRV and BPV were not significantly changed from baseline to maximal breathing. Conversely, during exercise HRV, LF and HF power significantly decreased from baseline to 100% VT while BPV, LF and HF power significantly increased for the same period. These findings suggest that the increases in ventilation associated with incremental exercise do not significantly affect spectral analysis of cardiovascular autonomic modulation in healthy subjects.     

Verylow frequency variability in arterial blood pressure and blood volume pulse

Several parameters of the cardiovascular system fluctuate spontaenously owing to the activity of the autonomic nervous system. In the study, the simultaneous very low frequency (VLF) fluctuations of the arterial blood pressure, the tissue blood content and the tissue blood volume pulse are investigated. The latter two parameters are derived from the baseline BL and the amplitude AM of the photoplethysmographic (PPG) signal, measured on the fingertips of 20 healthy male subjects: the changes in the PPG parameters AM and BV, defined by BV=const.-BL, are related to the change in the tissue blood volume pulse and the total tissue blood volume, respectively. The VLF fluctuations in BV and AM are directly correlated, those of AM preceding those of BV by 4–13 heart-beats. The VLF fluctuations in the systolic (SBP) and the diastolic (DBP) blood pressure are inversely correlated to those of AM and BV, those of AM preceding those of SBP and lagging behing those of DBP by about one heart-beat. For most subjects, the period P of the PPG pulse, which is equal to the cardiac cycle period, directly correlates with AM and BV and inversely correlates with DBP and SBP. On average, the fluctuations fluctuations in tissue blood volume, systolic blood volume pulse, diastolic and systolic blood pressure, and heart period, together with their interrelationship, can provide a better understanding of the autonomic nervous control of the peripheral circulation and a potential tool for the evaluation of its function.     

Beta-adrenergic control and inter-relationships between heart rate and blood pressure in neonatal lambs

Our aim was to develop a signal analysis method for revealing interrelationships between heart rate and blood pressure and for displaying the influence of autonomic nervous control on these signals in a chronic lamb model. A chronically instrumented neonatal lamb model was made to record ECG and direct arterial blood pressure (N=15). Continuous two-minute recordings of blood pressure (BP) and ECG were digitised. The instantaneous heart rate signal (IHR) was derived from the ECG. The IHR and BP signals were bandpass filtered. Autospectra, cross-spectra, coherence spectra and phase spectra for the signals were computed to study the relative magnitudes and inter-relationships of the cardiovascular signals under normal conditions and during beta-adrenergic blockade. It was noted that both in the BP and IHR there were oscillations at the frequency of <0·1 Hz and also at the respiratory rate around 0·6 Hz. Beta-blockade reduced the oscillations of the IHR in <30-day-old lambs. It did not affect the coherence spectra or the phase lag between the signals. During quiet sleep the variability of blood pressure was decreased. In over-30-day-old-lambs the beta-blockade did not affect the variabilities of the cardiovascular parameters. These findings indicate that in neonatal lambs the sympathetic control system is a major regulator of cardiovascular interactions.     

Relationships between short-term blood-pressure fluctuations and heart-rate variability in resting subjects I: a spectral analysis approach

A method to attribute the short-term variability of blood pressure and heart rate of resting subjects to their various causes, using spectral techniques, is presented. Power spectra and cross-spectra are calculated for beat-to-beat values of R-R interval and blood pressure from subjects who were seated in a comfortable chair. Interval values as well as systolic, mean and pulse pressures show variations linked to respiration and to the so-called 10 s rhythm. The diastolic pressure values are scarcely influenced by respiration in the normal respiratory range (0·20–0·35 Hz), but do show 10 s variability. Relationships between pressure and interval variability which indicate that the 10 s variability in systolic pressure leads the interval variation by two to three beats become manifest in cross-spectra; however, no such lag is found between the respiration-linked variations in systolic pressure and intervals. It is argued that the technique presented provides a critical test for models of the fast regulation of the cardiovascular system.     

Short- and long-term effects of a single bout of exercise on heart rate variability: comparison between constant and interval training exercises

Heart rate variability (HRV) was assessed during the short- (within 1 h) and long- (within 48 h) term recovery following a single bout of either constant (CST) or interval training (SWEET) exercise performed at the same total physical work [9.4 (0.3) kJ kg^–1]. R-R intervals, systolic (SAP) and diastolic (DAP) arterial pressures were recorded in supine and upright positions before and 1, 24 and 48 h after the termination of the exercises in ten male subjects [mean (SEM), age 24.6 (0.6) years, height 177.2 (1.1) cm and body mass 68.5 (0.9) kg]. The parameters were also recorded in the supine position during the first 20 min following the end of the exercise. Spectral analysis parameters of HRV [total (TP), low- (LF), and high- (HF) frequency power, and LF/TP, HF/TP and LF/HF ratios] were determined over 5 min during each phase. Except for higher HF values in both supine and upright positions during the first hour following CST compared with SWEET, cardiovascular and HRV analysis responses were of the same magnitude after their termination. R-R intervals, TP, and HF/TP were significantly decreased while LF/TP and LF/HF were significantly increased during the early recovery, when compared with control values. This could be a response to the significant decrease in SAP and DAP at this time. Twenty-four and 48 h after the end of the exercise, HRV parameters were at the same levels as before exercises in the supine posture, but a persistent tachycardia continued to be observed in the upright posture, together with reduced TP values, showing that cardiovascular functions were still disturbed. The short-term HRV recovery seemed dependent on the type of exercise, contrary to the long-term recovery.     

Estimation of frequency shift in cardiovascular variability signals

Spectral analysis of heart rate (HR) and blood pressure (BP) oscillations has traditionally concentrated on spectral power, although a shift in spectral frequency characterises the variability better than power in some cases. Experimental data were obtained from 14 healthy males in control and pharmacological blockade conditions. When parasympathetic control was reduced, LF oscillations of HR and BP tend to shift towards lower frequencies. Three parameters were compared to estimate the spectral shift within the low frequency (LF, 0.04–0.15 Hz) band in HR and BP variability: mean (f_mean), median (f_med), and central frequency (f_c). Parameter variance (p_STD) and sensitivity to noise were also estimated using realistic HR, systolic BP (SBP) and diastolic BP (DBP) data. f_mean showed the lowest parameter variance both for an autoregressive (AR) method (SBP p_STD 3.1 vs 4.8 vs 4.7 mHz for f_mean, f_med and f_c, respectively; p<0.001) and an FFT method (SBP p_STD 4.7 vs 7.7 mHz for f_mean and f_med, respectively; p<0.001). Furthermore, f_mean was least sensitive to noise. f_c showed the poorest performance being especially sensitive to noise. To analyse the spectral shift, f_mean is preferred, since it performs better than f_c, which has been used in most previous studies. To quantify the frequency of oscillations in cardiovascular signals, the mean frequency is recommended, with analyses across different spectral bands.     

Dietary sodium effects on heart rate variability in salt sensitivity of blood pressure

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 6 days followed by a high sodium diet for 6 days. The 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.     

Acute and chronic stress influence blood pressure variability in mice

There is evidence that alterations in heart rate and blood pressure variability (BPV) are associated with cardiovascular disease. We used a mice model to investigate the effects of acute and chronic stress on blood pressure variability (BPV) and heat rate variability (HRV). Shaker stress was given acutely (5 min, 150 cycles/min) and chronically (3 days, 2 min stress, 150 cycles/min, 45 sessions/day) in male C57BLJ mice. Systolic arterial pressure (SAP) and pulse interval (PI) time series were submitted to autoregressive spectral analysis with variability measured in the low-frequency (LF, 0.1-1.0 Hz) and high-frequency (HF, 1-5 Hz) ranges. In the acute experiment, MAP was increased significantly in the first 10 min poststress period (99+/-2 vs. 113+/-2 mm Hg) and returned to control levels 30 min poststress. HR was significantly higher in the initial poststress period (537+/-12 vs. 615+/-20 bpm). These alterations were associated with a marked increase in BPV (21+/-4 vs. 55+/-11 mm Hg2) and in power of LF oscillations (18+/-3 vs. 42+/-7 mm Hg2). On the other hand, chronic stress exposure produced a reduction in BPV (16+/-4 vs. 6+/-1 mm Hg2) and LF oscillations (11+/-3 vs. 3+/-1 mm Hg2). HRV was not altered after either acute or chronic stress. Spontaneous baroreflex sensitivity (SBS), determined by cross-spectral analysis between PI and BP, was reduced significantly in acute stress (-50%), but unchanged in chronic stress. Our results show that acute stress produced changes in BPV that may be associated with increased sympathetic activity and a reduction in blood pressure buffering. Under chronic conditions, there is no alteration in baroreflex sensitivity while BPV is reduced. This is likely related to the combination of sympathetic activation in the face of vasculature alterations.     

Analysis of pulse rate variability derived from photoplethysmography with the combination of lagged Poincaré plots and spectral characteristics

A combination of lagged Poincaré plots and spectral characteristics were used to investigate the effect of cigarette smoking on the autonomic nervous system (ANS). Heart rate variability (HRV) was determined from pulse-to-pulse intervals (PPI) of ear photoplethysmography (PPG) waveforms. Spectral power analysis of the pulse rate variability (PRV) was performed to determine low frequency (LF) and high frequency (HF) components, and a lagged Poincaré plot was introduced to evaluate the nonlinear characteristics of PRV. The correlations between lagged Poincaré plot and spectral power indices were studied in a group of apparently healthy habitual cigarette smokers and compared to non-smokers. The width (SD1_m) and the length (SD2_m) of lagged Poincaré plots significantly shrunk in the smokers for all lags (p < 0.05) except SD1₄ and SD1₅. The results of this pilot study indicated that habitual smoking is associated with parasympathetic withdrawal and augments sympathetic nerve activity. The results also demonstrated that the combination of lagged Poincaré plots and spectral characteristics could show promise as a method for distinguishing between different cardiovascular disease groups.     

低体温与心率变异性和血压变异性的关系

目的: 研究低体温与自主神经功能变化的关系。方法: 采用体表物理降温法逐步降低直肠温度,直肠温度变化范围为19-37 ℃。分别记录不同直肠温度下大鼠动态心电和血压信号。应用心率变异性和血压变异性分析系统评价低体温对心率变异性和收缩压变异性的影响。结果: 心率变异分析表明，直肠温度下降到29 ℃以下,R-R间期均延长（P<0.01）,提示心率明显降低;当直肠温度下降到19-21 ℃时,心率变异归一化低频功率降低（P<0.05）和归一化高频功率增加（P<0.05），而且自主神经的平衡向心迷走神经张力增强的方向发生了转移（P<0.05）。血压变异性分析表明，体温下降到31℃时与呼吸有关的归一化高频功率开始增加（P<0.01）；直肠温度下降到29 ℃以下(除27 ℃外),与呼吸有关的归一化高频功率增加（P<0.05或P<0.01），同时自主神经的平衡也发生了改变（P<0.05）。结论： 随着体温的降低，心血管迷走神经活性增加，自主神经的平衡向迷走神经张力增强的方向转移。低体温对血压变异性的影响敏感于心率变异性。     

Very high frequency oscillations in the heart rate and blood pressure of heart transplant patients

The authors studied the recently reported very high frequency (VHF) peaks in the heart rate (HR) and blood pressure (BP) power spectra of heart transplant (HT) patients. These VHF peaks appear at frequencies much higher than the respiratory frequency, in addition to the typical low-frequency and high-frequency peaks. Twenty-five recordings obtained from 13 male HT patients (0.5–65 months following surgery) were compared with recordings from 14 normal male subjects. The ECG, continuous BP and respiration were recorded during 45 min of supine rest. Eight recordings from HT patients were excluded owing to arrhythmias. Spectral analysis was performed on all other recordings. VHF peaks were found in the spectra of both BP and HR in nine recordings obtained from six HT patients. In some cases, the power in the VHF peaks was markedly higher than that of the high-frequency peak. No VHF peaks were observed in eight recordings obtained from four HT patients or in recording from any of the normal subjects. No correlation was found between the incidence of VHF peaks and time after transplant. It was proved that the VHF peaks were not artifactual, and their significance within the framework of the theory of communication systems is discussed. The presence of those peaks was attributed to vagal denervation.     

Application of time series spectral analysis theory: analysis of cardiovascular variability signals

The paper focuses on the most important application problems commonly encountered in spectral analysis of short-term (less than 10 min) recordings of cardiovascular variability signals (CVSs), critically analysing the different approaches to these problems presented in the literature and suggesting practical solutions based on sound theoretical and empirical considerations. The Blackman-Tukey (BT) and Burg methods have been selected as the most representative of classical and AR spectral estimators, respectively. For realistic simulations, ‘synthetic’ CVSs are generated as AR processes whose parameters are estimated on corresponding time series of normal, post-myocardial infarction and congestive heart failure subjects. The problem of resolution of spectral estimates is addressed, and an empirical method is proposed for model order selection in AR estimation. The issue of the understandability and interpretability of spectral shapes is discussed. The problem of non-stationarity and removing trends is dealt with. The important issue of identification and estimation of spectral components is discussed, and the main advantages and drawbacks of spectral decomposition algorithms are critically evaluated.     

The effect of mental stress on heart rate variability and blood pressure during computer work

The aim was to evaluate the cardiovascular and subjective stress response to a combined physical and mental workload, and the effect of rest. Twelve females who had no prior experience of laboratory experiments participated in the study. Computer-work-related mental stressors were either added to or removed from a standardized computer work session in the laboratory. Beat-to-beat blood pressure and electrocardiogram (ECG) were recorded continuously during the experiment. The participants reported subjective experiences of stress in six categories using an 11-point scale before and at the end of the work. Heart rate variability (HRV) variables were calculated from the ECG recordings, and a reduction in the high-frequency component of HRV and an increase in the low- to high-frequency ratio were observed in the stress situation compared to the control session. No changes were seen in the low-frequency component of HRV. The stressors induced an increase in blood pressure compared to baseline that persisted, and for the diastolic pressure it even increased in the subsequent control session. No differences were observed for subjective experience of stress with the exception of a time trend in the exhaustion scale, i.e. a progression in reported exhaustion with time. The results—and the dissociation between HRV and blood pressure variables—indicate that HRV is a more sensitive and selective measure of mental stress. It could be speculated that heart rate-derived variables reflect a central pathway in cardiovascular control mechanisms (central command), while the blood pressure response is more influenced by local conditions in the working muscles that partly mask the effect of changes in mental workloads. In the rest period after each work session, HRV and blood pressure variables were partly normalized as expected. However, an 8-min period of rest was insufficient to restore blood pressure to resting values.     

Baroreflex sensitivity assessment and heart rate variability: relation to maneuver and technique

In the present study, we examined two baroreflex sensitivity (BRS) issues that remain uncertain: the differences among diverse BRS assessment techniques and the association between BRS and vagal outflow. Accordingly, the electrocardiogram and non-invasive arterial pressure were recorded in 27 healthy subjects, during supine with and without controlled breathing, standing, exercise, and recovery conditions. Vagal outflow was estimated by heart rate variability indexes, whereas BRS was computed by alpha-coefficient, transfer function, complex demodulation in low- and high-frequency bands, and by sequence technique. Our results indicated that only supine maneuvers showed significantly greater BRS values over the high frequency than in the low-frequency band. For maneuvers at the same frequency region, supine conditions presented a larger number of significant differences among techniques. The plots between BRS and vagal measures depicted a funnel-shaped relationship with significant log–log correlations (r=0.880–0.958). Very short latencies between systolic pressure and RR interval series in high-frequency band and strong log–log correlations between frequency bands were found. Higher variability among different baroreflex measurements was associated with higher level of vagal outflow. Methodological assumptions for each technique seem affected by non-baroreflex variation sources, and a modified responsiveness of vagal motoneurons due to distinct stimulation levels for each maneuver was suggested. Thus, highest vagal outflows corresponded to greatest BRS values, with maximum respiratory effect for the high-frequency band values. In conclusion, BRS values and differences across the tested techniques were strongly related to the vagal outflow induced by the maneuvers.     

Post-exercise recovery of autonomic cardiovascular control: a study by spectrum and cross-spectrum analysis in humans

The recovery of the baseline autonomic control of cardiovascular activity after exercise has not been extensively studied. In 12 healthy subjects, we assessed the time-course of recovery by autoregressive spectrum and cross-spectrum analysis of heart period and systolic blood pressure during the 3 h after the end of 20 min of steady-state exercise at 50% (light workload, LW) and 80% (moderate workload, MW) of the individual's anaerobic threshold. The electrocardiogram and non-invasive blood pressure were simultaneously recorded during 10 min periods in the sitting position, at rest before exercise, and at 15, 60 and 180 min of recovery after exercise. At 15 min we observed a persistent tachycardia and relative hypotension; after MW, at 60 min heart rate was still slightly higher. Spectrum and cross-spectrum analysis showed, at 15 min, an increase in the low frequency component of systolic blood pressure, a reduction in the high frequency component of heart rate (larger in MW), and a decrease in baroreceptor sensitivity. After 60 and 180 min none of these parameters was significantly different from those at rest, although, in MW, some subjects still displayed signs of sympathetic activation after 1 h. We concluded that, after 15 min of recovery, the cardiovascular reflexes were blunted, that sympathetic nerve activity was still enhanced, and that the tone in the vagus had not fully recovered. Only the persistent vagal restraint seemed to be exercise intensity-dependent. For complete restoration of autonomic control after LW 1 h of rest was sufficient, and just enough after MW. Accepted: 2 November 2000     

基于脉搏波信号和血管弹性腔模型的动脉血压连续测量方法

目的为满足健康监护中的连续测量血压的要求,研究并实现一种基于脉搏波信号和血管弹性腔模型的动脉血压拟合计算方法。方法利用自制的穿戴式人体生理参数监测系统收集测试对象的脉搏波信号、心电信号以及血压数据。根据心电信号与脉搏波信号的时间关系,推导出收缩压和脉搏波传导时间的回归分析方程,而舒张压的测量,则是通过脉搏波的波形系数分析以及血管单弹性腔模型的参数计算完成。结果试验结果表明,该方法血压测量结果的平均偏差和标准偏差为(0.51±0.74)kPa([384±5.54)mmHg],达到了美国医疗仪器促进协会建议的(0.665±1.064)kPa([5±8)mmHg]标准。结论结合脉搏波信号和弹性腔模型可以估算人体血压值,为连续血压测量提供了新的实现方法。     

Striking a chord: moods, blood pressure, and heart rate in everyday life

The objective of this study was to assess the relation between the intensity of single moods and of mood combinations on blood pressure (BP) and heart rate (HR). The subjects were 203 healthy registered nurses, all women, who were studied on two work and two off days. Ambulatory BP and HR were recorded every 20 min. On each occasion subjects rated their moods on a 5-point scale. Graded increases in BP and HR were shown with higher ratings of negative moods and decreases for a mood related to energy level. Little change was observed for a positive mood. These effects depended on concurrent changes in other moods. A positive mood countered the effects of a negative mood, whereas two negative moods resulted in unique patterns of BP and HR. The energy level mood moderated the cardiovascular effects of positive and negative moods. Ambulatory methods provide a way of probing into the nature and consequences of everyday emotional experiences.     

Effects of nicotine and its major metabolites on blood pressure in anaesthetized rats

Summary Blood pressure and heart rate in anaesthetized rats has been determined after i.v. injection of increasing doses of nicotine (NI) and its major metabolites, i.e. continine (CO), nornicotine (NOR), metanicotine (MN) and dihydrometanicotine (DMN). NI and MN elicited similar dose response curves, increasing blood pressure according to the dose injected. However, the dose response curve of MN was shifted to the right. Furthermore DMN caused similar pressor effects than MN and the pressor effects of NOR was even weaker. Only after injection of CO was a dose-dependent depressor effect observed and this was reversed after very high doses. CO also reduced heart rate in a dose-dependent manner, whereas NI and its other metabolites did not significantly change heart rate.Abbreviations CO cotinine - DMN dihydrometanicotine - MN metanicotine - NI nicotine - NOR nornicotine - SEM standard error of the mean Supported by the German council of smoking and health     

Effect of exercise on systemic blood pressure and heart rate in horses

Summary Carotid loops were prepared in 3 horses several months prior to the experiments. Systemic blood pressure was recorded at rest and during exercise by insertion of a plastic cannula into the carotid artery. The pressure transducer was fixed at the neck of the animal. The blood pressure signal was transmitted by telemetry.When the horses were standing under the rider, the following results were obtained: heart rate 38±5 beats · min^–1, systolic pressure 115±15, disstolic pressure 83±10, mean pressure 97±12, and pulse pressure 32±9 mm Hg. During steady gallop at a mean speed of 548±90 m · min^–1, heart rate rose to 184±23 beats · min^–1, systolic pressure to 205±23, diastolic pressure to 116±12, mean pressure to 160±20 and pulse pressure to 89±19 mm Hg. These values remained stable throughout the exercise period of 5–6 min.When the horses were exercised at stepwise increasing speed from walk through trot to gallop, both the mean arterial blood pressure and the pulse pressure rose in proportion to the running speed.