Heart Rate and Heart Rate Variability in Normal Young Adults

Heart Rate and Heart Rate Variability. Introduction: The relationships between heart rate (HR) and HR variability (HRV) are not simple. Because both depend on the autonomic nervous system (ANS), they are not independent variables. Technically, the quantification of HRV is influenced by the duration of the cardiac cycles. The complexity of these relationships does not justify ignoring HK when studying HRV, as frequently occurs. Methods and Results: Using spectral and nonspectral methods, the HR and various normalized and non-normalized indices of HRV were studied in 24-hour recordings of a homogeneous cohort of seventeen 20-year-old healthy males. The HR-HRV relationships were appraised by analyzing the same data in two different ways. The 24 mean hourly values provide consistent information on the circadian behavior of the indices, while the average 24-hour individual data show a wide spectrum of normality. Combined approaches allow assessment of the direct impact of RR interval on HRV evaluation. The correlations between HR and normalized indices of HRV arc weaker in 24-hour individual data than in pooled hourly data of the same individuals. These correlations are close to 1 in the latter case, which does not mean that measuring HRV is simply another method of evaluating HR, but that normal physiology supposes a harmonious behavior of the various indices. When considered individually without normalization, the specific indices of vagal modulation (high-frequency band of the spectrum, short-term HR oscillations of the nonspectral analysis) consistently increase at night and diminish during the day. However, the low-frequency power, which supposedly reflects sympathetic influences, also increases at night, whereas more logically the longer HR oscillations would predominate during the day. Moreover, the selective analysis of HR oscillations during HR acceleration or decrease indicates that their behavior differs accordingly. Conclusion: We recommend that closer attention be paid to the complex relationships between HR and HRV. The strong correlations found in healthy subjects may reflect either the physiological harmony of ANS functions or simple redundancy. Their tendency to deteriorate in diseased hearts suggests that redundancy is not the cause and that abnormalities of ANS functions are not demonstrated by HRV analysis alone.     

Heart Rate Variability in Patients with Congenital Long QT Syndrome

Background: The congenital long QT syndrome (LQTS) affecting myocardial repolarization is caused by mutations in different cardiac potassium or sodium channel genes. Adrenergic triggers are known to initiate life‐threatening torsade de pointes ventricular tachycardias in LQTS patients, and anti‐adrenergic therapy has been shown to be effective in many cases. Despite this well‐documented adrenergic component, the data about autonomic modulation of the heart rate in LQTS, as described by heart rate variability (HRV) analysis, are very limited. Methods: Conventional time‐ and frequency‐domain and newer nonlinear measures of HRV were compared in resting conditions among 27 LQTS patients with gene mutations at the LQT1 (n = 8), LQT2 (n = 10) or LQT3 (n = 9) loci and 34 LQTS noncarrier family members. Results: None of the conventional time‐ or frequency‐domain or newer nonlinear measures of HRV differed significantly between the LQTS carriers and LQTS noncarriers or between the LQT1, LQT2, and LQT3 carriers. Conclusions: These findings suggest that baseline cardiac autonomic modulation of the heart rate measured in resting conditions by traditional or newer nonlinear measures of HRV is not altered in LQTS patients. Furthermore, no differences are observed in HRV parameters between LQTS patients with potassium (KvLQT1, HERG), and sodium (SCN5A) ion channel gene mutations. HRV analysis in resting conditions does not improve phenotypic characterization of LQTS patients. A.N.E. 2001;6(4):298–304     

Heart Rate Variability in Patients with Essential Hyperhidrosis: Dynamic Influence of Sympathetic and Parasympathetic Maneuvers

Background: Essential hyperhidrosis has been associated with an increased activity of the sympathetic system. In this study, we investigated cardiac autonomic function in patients with essential hyperhidrosis and healthy controls by time and frequency domain analysis of heart rate variability (HRV). Method: In this study, 12 subjects with essential hyperhidrosis and 20 healthy subjects were included. Time and frequency domain parameters of HRV were obtained from all of the participants after a 15‐minute resting period in supine position, during controlled respiration (CR) and handgrip exercise (HGE) in sitting position over 5‐minute periods in each stage. Results: Baseline values of HRV parameters including RR interval, SDNN and root mean square of successive R‐R interval differences, low frequency (LF), high frequency (HF), normalized unit of high frequency (HFnu), normalized unit of low frequency (LFnu), and LF/HF ratio were identical in two groups. During CR, no difference was detected between the two groups with respect to HRV parameters. However, the expected increase in mean heart rate (mean R‐R interval) did not occur in hyperhidrotic group, whereas it did occur in the control group (Friedman's P = 0.000). Handgrip exercise induced significant decrease in mean R‐R interval in both groups and no difference was detected between the two groups with respect to the other HRV parameters. When repeated measurements were compared with two‐way ANOVA, there was statistically significant difference only regarding mean heart rate in two groups (F = 6.5; P = 0.01). Conclusion: Our overall findings suggest that essential hyperhidrosis is a complex autonomic dysfunction rather than sympathetic overactivity, and parasympathetic system seems to be involved in pathogenesis of this disorder.     

Interaction between Heart Rate and Heart Rate Variability

Heart rate variability (HRV) is significantly associated with average heart rate (HR), therefore, HRV actually provides information on two quantities, that is, on HR and its variability. It is difficult to conclude which of these two plays a principal role in the HRV clinical value, or in other words, what is the HR contribution to the clinical significance of HRV. Moreover, the association between HRV and HR is both a physiological phenomenon and a mathematical one. The physiological HRV dependence on HR is determined by the autonomic nervous system activity, but the mathematical one is caused by the nonlinear relationship between RR interval and HR. By employing modification methods of the HRV and HR relationship, it is possible to investigate the HR contribution to the HRV clinical value. Recent studies have shown that the removal of the HR impact on HRV makes HRV more predictive for noncardiac death, however, the enhancement of this impact causes HRV to be a better predictor of cardiovascular mortality. Thus, HR seems to constitute a cardiovascular factor of the HRV predictive ability. HR also influences the reproducibility of HRV, therefore, HR changes should be considered when one compares HRV measurements in a given patient. This review summarizes methodological aspects of investigations of the HRV and HR interaction as well as latest observations concerning its clinical utility. The issues discussed in this article should also refer to any other heart rate dynamics analysis which indices are significantly associated with HR.     

Time-Frequency Analysis of Heart Rate Variability

Background: The heart rate variability (HRV) signal is mainly analyzed in frequency-domain and the signal's spectrum is estimated using either Fast Fourier Transformation (FFT) or the autoregressive (AR) model. These two methods assume that the HRV signal is stationary and additionally the AR method is based on the assumption that the model is linear and the signal is monocomponent in nature. Qualities of spectral estimates are thus closely related to the validity of the above assumptions. Evidence has accumulated indicating that HRV is a multicomponent, nonlinear and nonstationary signal. Then the spectral representations currently used would yield global, approximate, and smoothed view of HRV dynamics. Methods: We applied time-frequency (TF) analysis methods, smoothed pseudo-Wigner distribution (SPWD), and spectrogram and complemented for validation by FT spectrum to the HRV signal of fifteen apparently healthy volunteers (mean age 27.2 ± 5.6 years). Short-term electrocardiograms (ECG) were recorded during supine and upright tilting positions (baseline recording). After baseline recording we induced parasympathetic, sympathetic, and total autonomic blockade correspondingly to six, nine, and four subjects. In addition, in four patients ECGs were recorded during controlled respiration. Results: SPWD and spectrogram revealed strips in frequency, or TF components, corresponding to FT components. High frequency (HF) components appeared stationary (in wide sense), with slight mean frequency shifts during spontaneous respiration, concurrent with respiratory motions. Low frequency (LF) and very low frequency (VLF) components had a nonstationary character displaying activity burst in time and interrelation in frequency. Upright tilting caused a uniform reduction in intensity and bandwidth of the HF component and enhancement of intensity and burst activity of the LF component. There was a pronounced decline of HF and LF components’intensity and decrease of HF component's bandwidth after parasympathetic blockade and total autonomic blockade, while the VLF component did not change. Sympathetic blockade was accompanied by augmentation of the LF and HF components’intensity associated with an increase in the HF component's bandwidth and the spreading of it in the region between the LF and HF. The LF component exhibited less burst activity during tilting under sympathetic blockade, as compared to baseline recordings during tilt. The VLF component's behavior did not change after sympathetic, parasympathetic, and total autonomic blockades. Conclusion: Application of TF distributions to the HRV signal offers a new representation of HRV dynamics. SPWD unveiled features in the HRV signal not available in separate time- and frequency-domains. TF components display idiosyncratic behavior patterns in time and were effected by physiological and pharmacological interventions. A.N.E. 1996;1(4):411–418     

Cigarette Smoking and Heart Rate Variability: Dynamic Influence of Parasympathetic and Sympathetic Maneuvers

Background: Cigarette smoking has been associated with increased activity of the sympathetic nervous system. In this study, we investigated cardiac autonomic function in heavy smokers and nonsmoker controls by analysis of heart rate variability (HRV). Method: Twenty‐four long‐term heavy smokers (men) and twenty‐two nonsmoker subjects (hospital staff) were included to study. Time domain [mean R‐R interval (RR), the standard deviation of R‐R interval index (SDNN), and the root mean square of successive R‐R interval differences (RMSSD)] and frequency domain [high frequency (HF) low frequency (LF), and LF/HF ratio] parameters of HRV were obtained from all participants after 15 minutes resting period in supine position (S), during controlled respiration (CR), and handgrip exercise (HGE) over 5‐minute periods. Results: Baseline SDNN and RMSSD values were found to be lower in smokers than in nonsmokers. (64 ± 10 vs 78 ± 22, P < 0.05 and 35 ± 12 vs 54 ± 30 ms, P < 0.05). Baseline LF/HF ratio was also found to be higher in smokers than in nonsmokers (1.3 ± 0.6 vs 0.9 ± 0.5 ms, P < 0.05). The other HRV parameters including R‐R interval, LF, and HF were not significantly different. During CR, expected increase in RR, SDNN, and RMSSD did not occur in smokers, while it did occur in nonsmokers. Most HRV indices were significantly affected by HGE in both groups. In addition, the duration of smoking was found to be inversely correlated with RMSSD and HF and positively correlated with LF/HF ratio. Conclusion: Vagal modulation of the heart is blunted in heavy smokers, particularly during a parasympathetic maneuver. Blunted autonomic control of the heart may partly be associated with adverse event attributed to cigarette smoking.     

Circadian Variation of Heart Rate Variability in Postinfarction Patients With and Without Life-Threatening Ventricular Tachyarrhythmias

Circadian Variation of HRV. Introduction: Determination of heart rate variability (HRV) is widely used for noninvasive assessment of cardiac autonomic tone. A decreased HRV is associated with an increased mortality in patients surviving an acute myocardial infarction. There are, however, only sparse data about the circadian variation of different components of HRV that may be linked to the well-known circadian fluctuations in the occurrence of sudden death. In addition, the potential prognostic impact of circadian variations of HRV has not been examined. Methods and Results: The present study compared the circadian variation of HRV from 14 postinfarction patients who had survived at least one episode of out-of-hospital cardiac arrest (cardiac arrest group) with that of 14 age- and sex-matched patients without a history of malignant arrhythmias after their index infarct (control group). Several time- and frequency-domain measures of HRV were assessed from 24-hour Holter recordings. Circadian variations of high- (HF), low- (LF), and total-frequency (TF) components were determined by calculating for each parameter the hourly difference from the day's mean. The average of these differences was calculated for every hour as well as for predefined day and night periods. There was no significant difference between the two groups with regard to HRV indices that predominantly reflect vagal tone, such as SDNN (78 ± 25 vs 96 ± 24 msec), pNN50 (2.7%± 4.6% vs 4.9%± 4.2%), or HF (6.3 ± 3.0 vs 7.8 ± 3.2 msec; cardiac arrest vs control group). There was also no significant difference in the circadian variation of LF or TF between the two groups during daytime and nighttime. However, a significant difference in circadian variation of HF was found during daytime (0.02 ± 0.5 vs -0.6 ± 0.5 msec; P = 0.006) and nighttime (0.19 ± 0.64 vs 1.5 ± 0.75 msec; P = 0.0002). In cardiac arrest survivors, there was no difference in the mean deviation of HF between the day-and the nighttime periods. Conclusions: These results show an almost complete abolition in circadian variation of parasympathetic tone in postinfarction patients surviving an episode of out-of-hospital cardiac arrest, whereas circadian variation of sympathetic tone is comparable to that of postinfarction patients without arrhythmic episodes. These findings indicate that determination of diurnal variation of HRV may add to the prognostic value of HRV with respect to identifying patients at high risk of sudden death.     

心率变异性的研究及应用进展

心率变异性是评价自主神经功能最常用的无创方法,随着计算技术的发展越来越多测量心率变异性的新方法进入到实践之中。自主神经系统在不同系统疾病中的影响和作用,正由于这种无创评估方法的实用化而被逐渐认识。现仅就心率变异性方法学和应用领域方面的进展进行简要概述。     

Effect of Ramipril on Heart Rate Variability in Digitalis-Treated Patients with Chronic Heart Failure

The aim of this study was to evaluate the effect of an angiotensin-converting enzyme (ACE) inhibitor, ramipril, on heart rate variability in patients with heart failure simultaneously treated with digitalis. This study was a multicentric, randomized, double-blind, placebo-controlled study including 50 patients with chronic heart failure (CHF). All patients were in NYHA functional class II and III. The etiology of CHF was mainly idiopathic dilated cardiomyopathy and ischemic heart disease. After a 4-week placebo run-in period with digoxin and diuretics, patients were randomized to receive additional ramipril or placebo. To assess heart rate variability (HRV) and arrhythmias, 24-hour ECGs were recorded at the end of the placebo run-in period, 8 and 24 weeks after randomization. Spectral analysis of HRV was performed during one diurnal and one nocturnal 5-minute time period. No statistically significant differences in HRV within low-, high-, and total-frequency bands were induced by ramipril in either the diurnal or nocturnal periods, both at 8 and 24 weeks after randomization. Ramipril produced a significant decrease in nonsustained ventricular tachycardia at 24 weeks of treatment (p = 0.01). These results run against previous observations showing an increase in parasympathetic tone with ACE inhibitors in heart failure. The present study thus suggests that the effects of ACE inhibitors in CHF are variable and depend on the patient and concomitant treatment that might influence HRV such as digoxin treatment. This revised version was published online in July 2006 with corrections to the Cover Date.     

阻塞性睡眠呼吸暂停综合征患者的心率变异性分析

目的:分析阻塞性睡眠呼吸暂停综合征(OSAS)患者的心率变异性(HRV),探讨阻塞性睡眠呼吸暂停对HRV的影响。 方法:对118例鼾症患者行多导睡眠图监测,根据呼吸紊乱指数(AHI)分为OSAS组(AHI≥5,n=56)与非OSAS组(AHI<5,n=62),分别观察两组患者觉醒期及睡眠期的心率变异性指标,包括:正常RR间期平均值及其标准差值(SDNN)、正常RR间期差值均方根(rMSSD)、低频峰(LF,0.04-0.10 Hz)、高频峰(HF,>0.15 Hz)、总频谱(TP,0-0.4 Hz)。 结果:OSAS组觉醒期与睡眠期各项指标均低于同期非OSAS组,均有显著差异(P<0.05-0.01),非OSAS组组内比较觉醒期与睡眠期的各指标差异有显著性(P<0.05-0.01)。 结论:OSAS对心率变异性有较大影响,且在睡眠的不同阶段有着不均衡的影响,这可能是OSAS患者发生恶性心律失常等严重心脏事件甚至猝死的重要原因,应予以积极防治及进一步研究。     

Heart Rate Variability in Heart Failure

The autonomic nervous system has an important role in the development and progression of the heart failure syndrome. Increased sympathetic, reduced parasympathetic, and impaired baroreceptor activity are well-documented features of heart failure. The analysis of heart rate variability can give insight into these autonomic abnormalities. A number of techniques now exist for assessing heart rate variability, and in general they reflect the known autonomic abnormalities. Power spectral analysis of RR variability has been claimed to reflect sympathovagal balance, but the reduced or absent low-frequency component in heart failure is paradoxical. It is likely that the absent low-frequency component in heart failure reflects impaired baroreceptor function. Although these various techniques of heart rate variability may be useful, reliability and reproducibility are problematic in this area. Better, more refined techniques for the noninvasive assessment of autonomic and baroreceptor function are still needed.     

The Correlation Dimension of Heart Rate Variability Reflects Cardiac Autonomic Activity

Background: Linear methods of time series analysis such as summary statistics and frequency-domain parameters have been used to measure heart rate variability (HRV). More recently, nonlinear methods including the correlation dimension (CDim) have been used to evaluate HRV. The aim of this study was to examine the effect of autonomic perturbations on the CDim. Methods: The CDim was calculated from 2000 data points (RR intervals) collected over a relatively short period of time (20–40 min) in 12 healthy subjects aged between 20 and 40 years (mean 30 ± 2 years) during: (a) supine rest; (b) head up tilt (sympathetic activation, parasympathetic nervous system activity withdrawal); (c) intravenous infusion of atropine (parasympathetic nervous system activity withdrawal); and (d) following overnight administration of low dose transdermal scopolamine (parasympathetic nervous system augmentation. Results: The CDim was determined at rest (7.8 ± 0.3) and found to be significantly reduced during tilt (5.9 ± 0.4, P < 0.01) and atropine administration (4.2 ± 0.4, P < 0.01) and possibly increased by scopolamine (8.3 ± 0.5, NS). Conclusions: The changes following these interventions suggest that CDim can accurately measure cardiac autonomic nervous system activity.     

缺血性心脏病患者心率变异性研究

应用Ｈｏｌｔｅｒ，测定４０～４９，５０～５９，６０～６９以及７０岁以上４个年龄段的缺血性心脏病患者的心率变异性（ＨＲＶ）并与相应年龄的对照组进行比较，指标为时域法的２４ｈ平均正常Ｒ－Ｒ间期标准差（ＳＤＮＮ）。结果：缺血组与对照组各年龄段比较有显著性差异，分别为：１４１．５２±２８．９２ｍｓＶＳ９３．７２±２７．５４ｍｓ；１３２．４２±２７．６３ｍｓＶＳ９３．１９±３３．１８ｍｓ；１２１．８４±２７．８７ｍｓＶＳ７４．５０±２４．０１ｍｓ；１１０．３１±２３．９６ｍｓＶＳ６３．９３±２３．７３ｍｓ，Ｐ均＜０．０１；对照组及缺血组的ＨＲＶ均随年龄增长呈下降趋势（组内比较，Ｐ均＜０．０１），呈完全负相关（ｒ（对照组）＝－０．９５，ｒ（缺血组）＝－０．９８）。随访发现缺血组中ＨＲＶ≤５０ｍｓ患者发生心源性猝死（ＳＣＤ）９例和室性心动过速１例；＞５０ｍｓ者发生ＳＣＤ２例。     

肠易激综合征患者心血管自主神经功能变化与心率变异性的关系

目的 :探讨肠易激综合征 (1BS)患者心血管自主神经功能变化与心率变异性 (HRV)的关系。方法 :对IBS患者 50例进行标准心血管自主神经功能测试 ,将其结果分成阳性组 (DNA+ )及阴性组 (DNA- ) ,健康人 30名为对照组。 2 4h动态心电图进行HRV分析。结果 :IBS患者自主神经功能异常的发生率为 58% ,主要表现为迷走神经功能异常 ;HRV时域分析中DNA+ 组SDNN、SDANN、SDNNindex明显减少 ;DNA+ 及DNA- 组中反映副交感神经张力的RMSSD、PNN50 、HF等指标明显增高 ,LF/HF比值明显减低 ,与对照组比较有显著性差异 (P <0 .0 5)。结论 :IBS患者存在副交感神经张力增加。HRV分析是发现IBS患者自主神经功能异常的较好方法