On- and off-responses of heart rate to exercise - relations to heart rate variability

During physical exercise, heart rate (HR) increases by parasympathetic withdrawal and increase of sympathetic activity to the heart. HR variability (HRV) in time and frequency domains provides information about autonomic control of the cardiovascular system. Non-linear analysis using the Poincaré plot method is able to reveal supplementary information about cardiac autonomic control. The aim of this study was to determine the association between HRV parameters, the initial increase of HR at the onset of exercise (on-response) and HR decrease in the recovery phase after acute exercise (off-response). HR was continuously monitored in 17 healthy male subjects (mean age: 20.3 +/- 0.2 (SEM) years) at rest (25 min supine; 5 min standing), during exercise (8 min of step test at 70% of maximal power output) and in the recovery phase (30 min supine). HRV analysis in time and frequency domains and evaluation of the Poincaré plot measures (length, widths) were performed on selected segments of HR time series. HR on- and off-responses were quantified using an exponential curve fitting technique. The time constants T(on) and T(off), representing the rate of on- and off-responses to exercise, were computed. Postexercise HRV indices and time constant of on-response - T(on) - to exercise were negatively correlated. From preexercise HRV indices, only Poincaré plot parameters were correlated with T(on). No correlation between HRV indices and parameters of off-response was found. In conclusion, preexercise HRV parameters are not closely correlated with the rate of cardioacceleration at the onset of exercise and cannot predict the rate of HR recovery. On the other hand, postexercise HRV parameters are related to the rate of initial adjustment of HR to exercise referring to the importance of rapid HR on-response for a faster recovery after exercise.     

Respiratory sinus arrhythmia and carotid baroreflex control of heart rate in endurance athletes and untrained controls

Summary. The purpose of this study was to compare the magnitude of the respiratory sinus arrhythmia, an index of cardiac vagal tone, and carotid baroreflex control of heart rate in endurance-trained athletes (n= 12, aged 20 ± 1 years, X?±SE) and untrained control subjects (n= 12, aged 22 ± 1 year). Average R-R interval (ECG) and its variability were determined at rest under controlled breathing conditions, and the changes in R-R interval in response to brief applications of suction (-10, -25, -40 mmHg) and pressure (10 and 30 mmHg) to the carotid sinus region of the neck were also measured. The average R-R interval at rest was greater in the athletes vs. controls (1150 ± 45 vs. 854 ±44 ms, P<0·001), but the standard deviation of the R-R intervals was similar in the two groups (72 ± 15 vs. 70 ± 9 ms). The magnitude of the tachycardia in response to neck pressure was also similar in the athletes and controls. Although the heart rate responses to neck suction were not significantly different between the two groups, there was a strong trend for attenuated bradycardic responses in the athletes at the two highest stimulus levels (70 ± 14 vs. 97 ± 25 ms and 86 ± 14 vs. 145 ± 38 ms for the -25 and -40 mmHg levels, respectively, P>0·1). The results of this study do not support the postulate that cardiac vagal tone is enhanced in the endurance-trained state. Furthermore, our findings indicate that arterial baroreflex control of heart rate during modest decreases in carotid sinus transmural pressure is not altered in endurance athletes; however, the magnitude of the reflex bradycardia in response to increases in carotid sinus pressure might be attenuated in these highly trained men.     

Taichiquan acutely increases heart rate variability

A group of 15 elderly men and 14 young male students of physical education made twice a series of Taichiquan (TCQ) practices. Their electrocardiograms were recorded on tape-recorder and heart rates and heart rate variability (HRV) were calculated from digitized data. Here we report the results of recordings in supine positions before and after the first and second series of TCQ. Intervals between heart beats (RRIs) and their standard deviation (SDNN) increased in older men from recordings before the exercise to postexercise. In young subjects the SDNN and total variance (TV) of RRIs increased. HRV increases immediately after TCQ-exercise in young and old male healthy subjects. Whether these practices have permanent effects and effects in patients need controlled and prospective studies.     

Derangement of heart rate variability during a catastrophic earthquake: a possible mechanism for increased heart attacks

At 1:47 AM on September 21, 1999, the middle part of Taiwan was struck by a major earthquake measuring 7.3 on the Richter scale. It has been shown that the mental stress caused by an earthquake could lead to a short- or long-term increase in frequency of cardiac death probably through activation of the sympathetic nervous system. The aim of this study was to investigate the effects of emotional stress on the autonomic system during an actual earthquake. Fifteen patients receiving a 24-hour Holter ECG study starting from 10+/-4 hours before the onset of the earthquake were included for the analysis of time- and frequency-domains of heart rate variability (HRV) at several time periods. A 24-hour Holter study recorded 2-6 months before the earthquake in 30 age- and sex-matched subjects served as the control group. Heart rate and the low frequency (LF) to high frequency (HF) ratio increased significantly after the earthquake and were attributed mainly to the withdrawal of the high frequency component (parasympathetic activity) of HRV. Sympathetic activation was blunted in elderly subjects > 60 years old. The concomitant ST-T depression observed in the Holter study correlated with a higher increment of LF as compared to HF components. The changes observed in HRV recovered completely 40 minutes following the earthquake. The derangement of HRV results from the withdrawal of the parasympathetic component and the arousal of sympathetic activity by the stressful earthquake. However, this autonomic derangement returned towards normal 40 minutes following the earthquake.     

Absence of parasympathetic reactivation after maximal exercise

The ability of the human organism to recover its autonomic balance soon after physical exercise cessation has an important impact on the individual's health status. Although the dynamics of heart rate recovery after maximal exercise has been studied, little is known about heart rate variability after this type of exercise. The aim of this study is to analyse the dynamics of heart rate and heart rate variability recovery after maximal exercise in healthy young men. Fifteen healthy male subjects (21·7 ± 3·4 years; 24·0 ± 2·1 kg m^?2) participated in the study. The experimental protocol consisted of an incremental maximal exercise test on a cycle ergometer, until maximal voluntary exhaustion. After the test, recovery R‐R intervals were recorded for 5 min. From the absolute differences between peak heart rate values and the heart rate values at 1 and 5 min of the recovery, the heart rate recovery was calculated. Postexercise heart rate variability was analysed from calculations of the SDNN and RMSSD indexes, in 30‐s windows (SDNN_30s and RMSSD_30s) throughout recovery. One and 5 min after maximal exercise cessation, the heart rate recovered 34·7 (±6·6) and 75·5 (±6·1) bpm, respectively. With regard to HRV recovery, while the SDNN_30s index had a slight increase, RMSSD_30s index remained totally suppressed throughout the recovery, suggesting an absence of vagal modulation reactivation and, possibly, a discrete sympathetic withdrawal. Therefore, it is possible that the main mechanism associated with the fall of HR after maximal exercise is sympathetic withdrawal or a vagal tone restoration without vagal modulation recovery.     

Heart rate recovery: autonomic determinants,methods of assessment and association with mortality and cardiovascular diseases

Cardiovascular disease (CVD) is the primary cause of mortality worldwide. Cardiac autonomic dysfunction seems to be related to the genesis of several CVDs and is also linked to the increased risk of mortality in CVD patients. The quantification of heart rate decrement after exercise – known as heart rate recovery (HRR) – is a simple tool for assessing cardiac autonomic activity in healthy and CVD patients. Furthermore, since The Cleveland Clinic studies, HRR has also been used as a powerful index for predicting mortality. For these reasons, in recent years, the scientific community has been interested in proposing methods and protocols to investigate HRR and understand its underlying mechanisms. The aim of this review is to discuss current knowledge about HRR, including its potential primary and secondary physiological determinants, as well as its role in predicting mortality. Published data show that HRR can be modelled by an exponential curve, with a fast and a slow decay component. HRR may be influenced by population and exercise characteristics. The fast component mainly seems to be dictated by the cardiac parasympathetic reactivation, probably promoted by the deactivation of central command and mechanoreflex inputs immediately after exercise cessation. On the other hand, the slow phase of HRR may be determined by cardiac sympathetic withdrawal, possibly via the deactivation of metaboreflex and thermoregulatory mechanisms. All these pathways seem to be impaired in CVD, helping to explain the slower HRR in such patients and the increased rate of mortality in individuals who present a slower HRR.     

Correlation of heart rate recovery and heart rate variability with atrial fibrillation progression

ObjectiveTo examine the combination of heart rate recovery (HRR) and heart rate variability (HRV) in predicting atrial fibrillation (AF) progression.MethodsData from patients with a first detected episode of AF who underwent treadmill exercise testing and 24-h Holter electrocardiography were retrospectively analysed. Autonomic dysfunction was verified using HRR values. Sympathetic and parasympathetic modulation was analysed by HRV. AF progression was defined as transition from the first detected paroxysmal episode to persistent/permanent AF.ResultsOf 306 patients, mean LF/HF ratio and HRR did not differ significantly by AF progression regardless of age (< or ≥65 years). However, when the LF/HF ratio was divided into tertiles, in patients aged <65 years, the mid LF/HF (1.60–2.40) ratio was significantly associated with lower AF progression rates and longer maintenance of normal sinus rhythm. For patients aged <65 years, less metabolic equivalents were related to higher AF progression rates. For patients aged ≥65 years, a low HRR was associated with high AF progression rates.ConclusionIn relatively younger age, high physical capacity and balanced autonomic nervous system regulation are important predictors of AF progression. Evaluation of autonomic function assessed by age could predict AF progression.     

Heart rate recovery: a practical clinical indicator of abnormal cardiac autonomic function

The autonomic nervous system (ANS) and cardiovascular function are intricately and closely related. One of the most frequently used diagnostic and prognostic tools for evaluating cardiovascular function is the exercise stress test. Exercise is associated with increased sympathetic and decreased parasympathetic activity and the period of recovery after maximum exercise is characterized by a combination of sympathetic withdrawal and parasympathetic reactivation, which are the two main arms of the ANS. Heart rate recovery after graded exercise is one of the commonly used techniques that reflects autonomic activity and predicts cardiovascular events and mortality, not only in cardiovascular system disorders, but also in various systemic disorders. In this article, the definition, applications and protocols of heart rate recovery and its value in various diseases, in addition to exercise physiology, the ANS and their relationship, will be discussed.     

Effect of diabetes mellitus on heart rate variability in patients with congestive heart failure

This study sought to determine if the severity of autonomic perturbations in patients with heart failure are affected by the presence of diabetes. Decreased HRV is frequent in diabetic patients free of clinically apparent heart disease and has been invoked as a risk factor for sudden cardiac death. However, reduced HRV is also commonly present in patients with left ventricular dysfunction. The effect of diabetes on autonomic dysfunction in this setting is not known. Holter ECGs from 69 diabetic patients and 85 nondiabetic control subjects with heart failure were analyzed. The severity of autonomic dysfunction was assessed using 24-hour time- and frequency-domain HRV analysis. Prognostically important time- and frequency-domain HRV measures (SDNN, SDANN5, total power, and ultra-low frequency power) were not different between the two groups. Time- and frequency-domain parameters modulated by parasympathetic tone (pNN50, RMSSD, and HF power) were depressed to a similar degree in the diabetic and the nondiabetic groups. The low frequency power was significantly lower in diabetic patients (5.8 +/- 0.7 vs 5.3 +/- 1.0, P = 0.02). The ratio of low to high frequency power was substantially lower in the diabetic group (2.2 +/- 0.2 vs 1.4 +/- 0.2, P < 0.0001). These differences were more apparent in insulin-treated diabetics. In the presence of heart failure, HRV parameters that are most predictive of adverse outcome are similar in diabetic and nondiabetic patients. Furthermore, during increased sympathetic stimulation in the setting of heart failure, diabetes does not worsen parasympathetic withdrawal but may mitigate sympathetic activation.     

Comparison of Polar® RS800G3™ heart rate monitor with Polar® S810i™ and electrocardiogram to obtain the series of RR intervals and analysis of heart rate variability at rest

The Polar^® RS800G3^? rate monitor was released in the market to replace the Polar^® S810i^?, and few studies have assessed that the RR series obtained by this equipment is reliable for analysis of heart rate variability (HRV). We compared HRV indexes among the devices Polar^® RS800G3^?, Polar^® S810i^? and eletrocardiogram (ECG) to know whether the series of Polar^® RS800G3^? are as reliable as those devices already validated. We analysed data from 30 healthy young adults, male, with an average age of 20·66 ± 1·40 years, which had captured the heart rate beat to beat in the three devices simultaneously with spontaneously breathing, first in the supine position and subsequently sit both for 30 min. The obtained series of RR intervals was used to calculate the indexes of HRV in the time domain (SDNN and RMSSD) and in the frequency domain (LF, HF and LF/HF). There were no significant differences in HRV indexes calculated from series obtained by the three devices, regardless of the position analysed, and a high correlation coefficient was observed. The results suggest that the Polar^® RS800G3^? is able to capture series of RR intervals for analysis of HRV indexes as reliable as those obtained by ECG and Polar^® S810i^?.     

个体化有氧运动对冠心病患者心率恢复及运动能力的影响

目的:探讨个体化有氧运动对心率恢复异常冠心病患者心率恢复情况及运动能力的影响,并分析两者间的相关性。方法:招募经冠状动脉造影确诊的冠心病患者行心肺运动试验(CPET),将75例心率恢复异常(试验终止1min时的心率恢复值(HRR1)≤12次/min)的患者纳入研究,并随机分为康复组(38例)和对照组(37例)。对照组进行常规药物治疗;康复组在对照组基础上加以强度为60%—85%目标心率的个体化有氧运动训练,每次40min,每周3次,共12周。所有患者研究结束后再次进行CPET评估心率恢复及运动能力情况。结果:训练前,两组患者HRR1、峰值功率(PP)、峰值摄氧量(VO2peak)、无氧阈(AT)均无显著差异(P>0.05);训练后,康复组的PP、VO2peak、AT与训练前相比,差异具有显著性(P<0.01,P<0.01,P<0.05),且优于对照组(P<0.05);在HRR1方面,康复组与训练前比较,差异具有显著性(P<0.05);但与对照组相比,差异并不显著(P>0.05),训练后,康复组有16例患者HRR1>12次/min,且PP、VO2peak与HRR1≤12次/min的患者相比,差异具有显著性(P<0.05);康复组HRR1的提高值(△HRR1)与运动能力提高水平(△VO2peak、△PP)呈显著相关性(r=0.347,P<0.05;r=0.419,P<0.01)。结论:虽然有氧运动在改善心率恢复方面并不像提高运动能力那样显著,但是有氧运动可以改善心率恢复并与运动能力的提高密切相关。     

Response of sympathetic nervous system activity to exercise in patients with congestive heart failure

To investigate the serial sympathetic nervous system response to exercise, plasma norepinephrine (NE) and epinephrine (E) concentrations were measured at rest, during each stage of treadmill exercise, and immediately and 5 minutes after exercise in 68 congestive heart failure (CHF) patients (NYHA functional class I 24, II 25, III 19) and 30 normal subjects. Circulatory responses of NYHA class II patients increased at early stages of exercise. Systolic blood pressure and double product at peak exercise were significantly lower in NYHA class III patients. Plasma NE response of NYHA class I patients was similar to that of normal subjects. However, plasma NE at rest, and during and after exercise were significantly higher in NYHA classes II and III patients than in normal subjects and NYHA class I patients (peak NE (pg ml-1); Normals: 547 +/- 37, I: 535 +/- 53, II: 867 +/- 87, III: 1033 +/- 157). There was no significant difference in plasma E levels among the four groups. NE response to exercise was augmented according to the severity of heart failure, which suggested compensatory activation of sympathetic nervous system activity. Circulatory responses were reduced in NYHA class III patients despite the exaggerated compensatory activation of the sympathetic nervous system. Blunted circulatory responses to increased NE concentration in NYHA class III patients might relate to a decreased cardiac responsiveness to sympathetic activity in severe CHF patients.     

Cosinor analysis of heart rate variability in ambulatory migraineurs

OBJECTIVE: To clarify whether the circadian rhythm of heart rate variability parameters can be identified in patients with migraine during a headache-free period and to identify any specific pattern of the circadian rhythm of heart rate variability, using time-domain and spectral analysis and cosinor rhythm analysis of heart rate variability during normal daily activity. METHODS: Forty-eight-hour Holter electrocardiograms were recorded for 27 patients with migraine during headache-free periods and 24 healthy controls during free activity. The circadian rhythms of heart rate fluctuation parameters, that is, mean interval, standard deviation, root-mean-square successive differences (RMSSD), %RR50, and low (0. 020 to 0.150 Hz) and high frequency (0.150 to 0.400 Hz) heart rate fluctuations were analyzed with the group mean cosinor method. RESULTS: The group mean cosinor analysis and the acrophase-amplitude analysis demonstrated significant differences in circadian rhythm in SD, RMSSD, %RR50, and high frequency between the group with migraine and controls. The amplitudes of SD, RMSSD, %RR50, and high frequency in the group with migraine were smaller than those in controls, which implied parasympathetic hypofunction in migraineurs. There were no significant differences in the MESOR (midline estimating statistic of rhythms) of the analyzed heart rate parameters except for low frequency. The MESOR of low frequency in the migraineurs was significantly smaller than that in the controls. CONCLUSIONS: Patients with migraine have hypofunction in the parasympathetic nervous system during normal daily activity in the headache-free period.     

Effects of isometric handgrip training on cardiac autonomic profile: A systematic review and meta‐analysis study

Meta‐analyses have shown that isometric handgrip training reduces blood pressure in normotensive and hypertensive subjects. However, the effects on cardiac autonomic modulation are still controversial. Thus, the aim of this systematic review and meta‐analysis was to analyse the effects of isometric handgrip training on cardiac autonomic modulation in normotensive and hypertensive subjects. For this, Medline, Cinhal, Embase, Spordiscus and PEdro were searched for relevant studies published until December 2018. Randomized controlled trials investigating the effect of isometric handgrip training on heart rate variability parameters were considered eligible. Parameters were obtained in time (standard deviation of all the RR intervals‐SDNN, root mean square of successive differences between the normal adjacent RR intervals‐RMSSD and the percentage of adjacent intervals with more than 50 ms‐PNN50) and frequency domain (low frequency‐LF, high frequency‐HF and sympathovagal balance‐LF/HF). Mean difference (MD) and 95% confidence interval (95% CI) were calculated using an inverse variance method with a random effects model. Seven trials were included in the systematic review and meta‐analysis, totalling 86 participants. No significant effect was observed in heart rate variability parameters after isometric handgrip training (4 trials to SDNN: MD = ?1.44 ms and 95% CI = ?8.02, 5.14 ms; RMSSD: MD = ?1.48 ms and 95% CI = ?9.41, 6.45 ms; PNN50: MD = 0.85% and 95% CI = ?1.10, 2.81%; 7 trials to LF: ?0.17 n.u. and 95% CI = ?6.32, 5.98 n.u.; HF: MD = 0.17 n.u. and 95% CI = ?5.97, 6.30 n.u.; and LF/HF: MD = 0.13 and 95% CI = ?0.34, 0.59). In conclusion, current literature indicates that isometric handgrip training does not improve heart rate variability.     

Chronotropic incompetence response to exercise in congestive heart failure,relationship with the cardiac autonomic status

In chronic congestive heart failure (CHF), attenuated heart rate response to exercise, a manifestation of chronotropic incompetence (CI), contributes to limiting exercise capacity. The present study was thus conducted to evaluate the respective role of chronic attenuation of cardiac vagal tone associated with depressed baroreflex sensitivity or affected cardiac sympathetic responsiveness in CHF patients with CI. Spontaneous cardiac baroreflex sensitivity (BRS) assessed by sequence method and spectral‐ and time‐domain analysis of heart rate variability (HRV) were analysed in 21 chronic CHF patients. All patients performed a symptom‐limited exercise test with measurement of gas exchange. Chronic incompetence which was defined as failure to achieve ≥80% of the heart rate reserve (%HRR) given by (HR_peak – HR_rest)/(predictive maximal heart rate – HR_rest) was observed in 14 (66%) patients. There was no significant difference in age, heart rate, peak oxygen uptake or left ventricular ejection fraction between the patients with and without CI. Although there was no significant difference in BRS, low frequency power of HRV in normalized units (LFnu) and SDNN were significantly lower in CI patients. Percentage of HRR correlated significantly with LFnu on 15 min (r=0·64, P<0·005) and, with LFnu on 24 h (r=0·52, P<0·01), SDNN (r=0·48, P=0·03) and SDANN (r=0·48, P=0·03), but not BRS (r=0·04, P=NS). Autonomic nervous system derangement is a complex process in CHF. The role of basal depressed cardiac sympathetic tone seems to contribute more closely than depressed baroreflex sensitivity to the impaired heart rate response to exercise frequently observed in CHF patients.     

冠心病患者心率变异性分析

目的了解冠心病（CHD）患者的心率变异性（HRV）特点,探讨CHD患者自主神经变化的临床意义。方法测定93例CHD患者和49例健康对照者24h心率变异性的时域指标,并进行比较分析。结果CHD组24hHRV指标水平明显低于健康对照组（P〈0．01）,差异有统计学意义。结论CHD患者HRV降低提示心血管自主神经系统功能受损害。