Reproducibility of heart rate variability and baroreflex sensitivity measurements in children

Despite their extensive use, the reproducibility of cardiac autonomic measurements in children is not well-known. We investigated the reproducibility of short-term continuous measurements of heart rate (HR), heart rate variability (HRV, time and frequency domain), and spontaneous baroreflex sensitivity (BRS, frequency domain) in the supine and standing position in 57 children (11.2 ± 0.7 years, 52.6% boys). Reproducibility between two sessions within a two-week interval was evaluated by intraclass correlation coefficients (ICCs), standard error of measurement, coefficients of variation (CVs), limits of agreement, and Bland-Altman plots. HR and HRV were moderately-to-highly (ICC = .63-.79; CV = 5.7%-9.7%) and BRS moderately (ICC = .49-.63; CV = 11.4%-14.0%) reproducible. While the BRS measurements were slightly less reproducible than the HR and HRV measurements, all can be reliably applied in research, thus implicating sufficient capacity to detect real differences between children. Still, clinical studies focusing on individual changes in cardiac autonomic functioning need to address the considerable random variations that may occur between test-retest measurements.     

Respiratory control of heart rate

Summary Cross spectrum techniques have been used to characterise the relationships between breathing rate, sinus rhythm and peripheral blood flow. The breathing rate modulates both sinus rhythm and peripheral blood flow between certain limits, with a characteristic frequency amplitude pattern and entrains the Traube-Hering-Mayer waves within set limits. Beyond the upper limit of 0.4 Hz (24 breath min^–1) no modulation occurs. The lower limit is estimated in our subjects able to breathe at rates of 0.033 Hz (2 breath min^–1) the lower limit of modulation is approximately 0.05 Hz (3 breath min^–1) in most individuals. These observations have serious implications for heart rate measurements in sinus rhythm below 90 beat min^–1.     

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.     

Reliability and validity of heart rate variability threshold assessment during an incremental shuttle-walk test in middle-aged and older adults

Studies on the assessment of heart rate variability threshold (HRVT) duringwalking are scarce. We determined the reliability and validity of HRVTassessment during the incremental shuttle walk test (ISWT) in healthy subjects.Thirty-one participants aged 57 ± 9 years (17 females) performed 3 ISWTs. Duringthe 1st and 2nd ISWTs, instantaneous heart rate variability was calculated every30 s and HRVT was measured. Walking velocity at HRVT in these tests (WV-HRVT1and WV-HRVT2) was registered. During the 3rd ISWT, physiological responses wereassessed. The ventilatory equivalents were used to determine ventilatorythreshold (VT) and the WV at VT (WV-VT) was recorded. The difference betweenWV-HRVT1 and WV-HRVT2 was not statistically significant (median andinterquartile range = 4.8; 4.8 to 5.4 vs 4.8; 4.2 to 5.4 km/h);the correlation between WV-HRVT1 and WV-HRVT2 was significant (r = 0.84); theintraclass correlation coefficient was high (0.92; 0.82 to 0.96), and theagreement was acceptable (-0.08 km/h; -0.92 to 0.87). The difference betweenWV-VT and WV-HRVT2 was not statistically significant (4.8; 4.8 to 5.4vs 4.8; 4.2 to 5.4 km/h) and the agreement was acceptable(0.04 km/h; -1.28 to 1.36). HRVT assessment during walking is a reliable measureand permits the estimation of VT in adults. We suggest the use of the ISWT forthe assessment of exercise capacity in middle-aged and older adults.     

Controlling the emotional heart: Heart rate biofeedback improves cardiac control during emotional reactions

When regulating negative emotional reactions, one goal is to reduce physiological reactions. However, not all regulation strategies succeed in doing that. We tested whether heart rate biofeedback helped participants reduce physiological reactions in response to negative and neutral pictures. When viewing neutral pictures, participants could regulate their heart rate whether the heart rate feedback was real or not. In contrast, when viewing negative pictures, participants could regulate heart rate only when feedback was real. Ratings of task success paralleled heart rate. Participants' general level of anxiety, emotion awareness, or cognitive emotion regulation strategies did not influence the results. Our findings show that accurate online heart rate biofeedback provides an efficient way to down-regulate autonomic physiological reactions when encountering negative stimuli.     

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.     

中重度抑郁症患者心电图及心率变异性分析

目的:探讨中重度抑郁症患者心电图及心率变异性特点,为临床评估中重度抑郁症心脏自主神经功能变化提供依据.方法:选择2018年6月至2019年12月就诊于湖南省脑科医院的中重度抑郁症患者38例为研究组,32例健康志愿者为对照组,比较两组心电图异常率及心率变异性,并统计分析各指标之间的差异.结果:研究组心电图异常ST-T改变...     

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.     

Assessment of heart rate variability derived from finger-tip photoplethysmography as compared to electrocardiography

Heart rate variability (HRV) is traditionally derived from RR interval time series of electrocardiography (ECG). Photoplethysmography (PPG) also reflects the cardiac rhythm since the mechanical activity of the heart is coupled to its electrical activity. Thus, theoretically, PPG can be used for determining the interval between successive heartbeats and heart rate variability. However, the PPG wave lags behind the ECG signal by the time required for transmission of pulse wave. In this study, finger-tip PPG and standard lead II ECG were recorded for five minutes from 10 healthy subjects at rest. The results showed a high correlation (median = 0.97) between the ECG-derived RR intervals and PPG-derived peak-to-peak (PP) intervals. PP variability was accurate (0.1 ms) as compared to RR variability. The time domain, frequency domain and Poincaré plot HRV parameters computed using RR interval method and PP interval method showed no significant differences (p < 0.05). The error analysis also showed insignificant differences between the HRV indices obtained by the two methods. Bland-Altman analysis showed high degree of agreement between the two methods for all the parameters of HRV. Thus, HRV can also be reliably estimated from the PPG based PP interval method.     

Effects of high altitude acclimatization on heart rate variability in resting humans

The sympatho-vagal nerve interaction at the heart was studied by means of power spectrum analysis of heart rate variability in seven Caucasians (aged 27–35 years) in resting supine and sitting positions before and during 35 days of a sojourn at 5050 m above sea level (asl) and in six Sherpas (aged 22–30 years) at high altitude only. A high frequency peak (HF)-central frequency between 0.20 and 0.33 Hz, a low frequency peak (LF)-central frequency between 0.08 and 0.14 Hz, and a very low frequency component ( < 0.05 Hz), no peak observed, were found in the power spectrum in both positions and independent of altitude. The peak powers, as a percentage of the total power, were affected by both body position and altitude. At sea level the change from a supine to a sitting position yielded a decrease in percentage HF from 25 (SEM 1.9)% to 6.2 (SEM 1.5) % (P < 0.05) and a significant increase in the ratio between LF and HF powers (LF : HF) from 1.7 (SEM 0.4) to 6.9 (SEM 1.6). At altitude compared to sea level in the supine position, percentage HF decreased from 25% to 10.9 (SEM 1.0)% (P < 0.05) and the LF:HF ratio increased from 1.7 to 4.8 (SEM 0.7) (P < 0.05). No changes occurred at altitude in the sitting position either in the peak powers or in the LF:HF ratio, but the central frequency of HF peak increased significantly from 0.25 (SEM 0.02) Hz to 0.32 (SEM 0.01) Hz. In the Sherpas comparable results to the Caucasians were found in both body positions. The high LF:HF ratios observed at altitude in both body positions and groups would suggest that hypoxia caused a shift of sympatho-vagal nerve interaction at rest toward a dominance of the sympathetic system, which was found at sea level only in the sitting position. An acclimatization period of 10 days higher than 2850 m asl and 1 month at 5050 m asl did not modify the interactions of the autonomic systems.     

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

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.     

Microcomputer control of canine heart rate through chronotropic drug infusion

Cardiovascular changes principally take two forms: (a) inotropic or pressure-related changes, and (b) chronotropic or rate-related changes. Although the two are not mutually exclusive in the biofeedback of a normally functioning animal, this work was concerned principally with affecting the heart rate of a dog by infusing a rate-altering drug. The purpose of this project was to design an external heart-rate control system which consisted of a dog, an infusion pump containing a chronotropic drug and an infusion-pump/heart-rate controller. Input to the system was a target heart rate. The feedback element and the system output was the dog's actual heart rate, ideally being driven to that target heart rate by the controller. A microcomputer-based system was used with proportional derivative control to accommodate the inherent plant delay. Through the use of an inline solid-state relay, on/off control was chosen because of (i) the capability to use any type of infusion pump, and (ii) the simplicity of design due to slow animal response. The experimental results have demonstrated success at overriding the dog's own biological feedback network and driving its heart rate to some artificially chosen target.     

正常家兔心率变异特点

目的:记录测定正常家兔在体和离体短程心率变异情况,探讨心脏自主神经功能的变化情况,为进一步研究家兔冠状动脉粥样硬化、冠脉痉挛时自主神经变化反映在心率变异性上的特点提供基础数据.方法:在体组用正交法记录胸前心电;离体组,采用兰氏(Langendorff)心脏灌流系统基础上,用正交悬浮电极法记录心电.采用Powerlab/8sp多道生理仪采集心电波.利用Chart模块对电信号进行短程心率变异分析.结果:正常家兔在体和离体组,短程心率变异分析结果值有明显不同.结论:正常家兔短程HRV特征较人体有明显区别,其频段取值范围有明显差异;在体与离体组HRV差异与神经体液调节因素有关.     

Comparison of finger plethysmograph to ECG in the measurement of heart rate variability

Two experiments compared finger plethysmograph (FP) to electrocardiogram (ECG) in providing accurate heart periods for use in heart rate variability (HRV) calculations. In Experiment 1, simultaneous ECG and FP recordings were taken from 16 healthy subjects at rest. In Experiment 2, 10 additional healthy subjects were recorded at rest and during the Stroop Color-Word Test. In both studies, high correlations were found between FP-derived and ECG-derived band variance for high and low frequency HRV at rest. But, during the Stroop task, correlations were strongly diminished. In addition, under both conditions, HRV measures were significantly higher using the FP signal. Thus, FP may be adequate for determining HRV at rest, but, for experimental use, ECG may still be recommended. Nonetheless, further studies that include test-retest reliability assessment of both data collection techniques are warranted before a more certain determination can be made.     

Resting high‐frequency heart rate variability is related to resting brain perfusion

We examined the neural correlates of resting cardiac vagal activity in a sample of 432 participants (206 male; 61 African American; mean age 42 years). Pulsed arterial spin labeling was used to quantify whole brain and regional cerebral blood flow at rest. High‐frequency heart rate variability (HF‐HRV) was used to measure cardiac vagal activity at rest. The primary aim was to determine whether brain regions implicated in regulating cardiac vagal reactions were also related to cardiac vagal activity at rest, and whether these associations varied by sex or race. Brain areas previously related to vagal reactivity were related to resting HF‐HRV. Directionality of relationships differed between overall and regional flows. Some relationships were only observed in women and African Americans. There appears to be communality between brain regions associated with task‐induced vagal reactivity and those associated with resting cardiac vagal activity.     

Hemodynamic responses and linear and non-linear dynamics of cardiovascular autonomic regulation following supramaximal exercise

The purpose of this study was to examine hemodynamic responses and cardiovascular autonomic regulation following supramaximal exercise. Electrocardiographic R–R intervals and beat-to-beat hemodynamics were recorded before and for 10 min after a 30-s Wingate test in 11 males. Spectral analysis of heart rate (HR) and arterial pressure variability, analysis of HR complexity, the sequence technique and the cross-spectral transfer function were used to quantify autonomic regulation and baroreflex sensitivity. After exercise, the high frequency component of HR variability (vagal-related index) was lower than pre-exercise values, whereas the ratio low frequency to high frequency (index of sympathovagal balance) and the low frequency component of blood pressure variability (index of sympathetic vasomotor tone) were greater than baseline (p < 0.05). Post-exercise HR complexity and baroreflex sensitivity were reduced compared to baseline, p < 0.05. Cardiovascular autonomic control requires more than 10 min to fully recover after intense physical exertion of only 30-s in young healthy males.     

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.     

Facial EMG and heart rate responses to emotion-inducing film clips in boys with disruptive behavior disorders

We examined aspects of emotional empathy across different physiological response systems in boys with disruptive behavior disorders (DBD) and normal controls. Heart rate (HR) and electromyographic (EMG) reactivity in zygomaticus major and corrugator supercilii muscles were monitored during sadness-, anger-, or happiness-inducing film clips. Relative to controls, DBD boys showed significantly less HR reduction during sadness, and a smaller increase in corrugator EMG activity both during sadness and anger. No significant group differences emerged in HR and zygomaticus EMG responsivity during happiness. We also examined cardiac activity at rest and found higher resting HR and lower respiratory sinus arrhythmia in DBD boys compared to controls. Findings give evidence for a selective impairment in empathy with sadness and anger (not happiness) among DBD boys who exhibit relatively high levels of anxiety and poor emotional control.     

Breathing at a rate of 5.5 breaths per minute with equal inhalation-to-exhalation ratio increases heart rate variability

Objectives

Prior studies have found that a breathing pattern of 6 or 5.5 breaths per minute (bpm) was associated with greater heart rate variability (HRV) than that of spontaneous breathing rate. However, the effects of combining the breathing rate with the inhalation-to-exhalation ratio (I:E ratio) on HRV indices are inconsistent. This study aimed to examine the differences in HRV indices and subjective feelings of anxiety and relaxation among four different breathing patterns.

Methods

Forty-seven healthy college students were recruited for the study, and a Latin square experimental design with a counterbalance in random sequences was applied. Participants were instructed to breathe at two different breathing rates (6 and 5.5 breaths) and two different I:E ratios (5:5 and 4:6). The HRV indices as well as anxiety and relaxation levels were measured at baseline (spontaneous breathing) and for the four different breathing patterns.

Results

The results revealed that a pattern of 5.5 bpm with an I:E ratio of 5:5 produced a higher NN interval standard deviation and higher low frequency power than the other breathing patterns. Moreover, the four different breathing patterns were associated with significantly increased feeling of relaxation compared with baseline.

Conclusion

The study confirmed that a breathing pattern of 5.5 bpm with an I:E ratio of 5:5 achieved greater HRV than the other breathing patterns. This finding can be applied to HRV biofeedback or breathing training in the future.