Spectral Indices Of Heart Rate Variability Research Articles

Effects of antihypertensive treatment on cardiovascular autonomic control: a prospective study.

The aim of study was to propose an approach to the control of dynamics of autonomic dysfunction in cardiovascular system (CVS) under antihypertensive treatment (AT) in patients with arterial hypertension (AH), based on individual features of synchronization of 0.1-Hz rhythms in heart rate (HR) and photoplethysmogram (PPG) and spectral indices of heart rate variability (HRV). We designed prospective cohort diagnostic accuracy and studied 105 AH patients (66 females) aged 47±8 years during 8 weeks. The HRV spectral indices and the index S of synchronization between the 0.1-Hz rhythms in HR and PPG during a tilt test are compared in their ability to control the AT with angiotensin-converting enzyme inhibitors (ACE-Is) (fosinopril or enalapril) and β-blockers (atenolol or metoprolol). We apply Shapiro-Wilk, Mann-Whitney U and Wilcoxon tests. It is shown that the power of low-frequency (LF) band in HRV spectrum and index S can be used as criteria for initial assessment of the status of autonomic regulation in AH patients. The patients with S<25% in vertical body's position and LF>250 ms2 in horizontal body's position require ACE-Is treatment. The AH patients with LF<350 ms2 and S<30% in vertical body's position require β-blocker treatment. The AH patients with S>25% and LF>250 ms2 in horizontal body's position do not require any ACE-Is or β-blocker treatment. Both drug groups can be used in patients with low values of index S and low power of LF band in HRV spectrum. The control of AT can be carried out in AH patients taking into account the individual features of autonomic dysfunction in CVS. Sensitivity and specificity of our approach were 65% and 73%, respectively.

Slow yogic breathing through right and left nostril influences sympathovagal balance, heart rate variability, and cardiovascular risks in young adults.

Background:Specific nostril breathing is known to influence autonomic functions.Aim:The study was to assess the effects of right nostril breathing (RNB) and left nostril breathing (LNB) on heart rate variability (HRV) and cardiovascular functions.Material and Methods:Eighty-five student volunteers were divided into three groups: RNB group (n = 30), LNB group (n = 30), and control group (n = 25). RNB and LNB group subjects practiced right and left nostril breathing, respectively, every day 1 h for 6 weeks. The control group did not practice nostril breathing. Cardiovascular parameters and spectral indices of HRV were recorded before and after 6-week practice of nostril breathing. In RNB and LNB groups, prediction of rate-pressure product (RPP) by low-frequency to high-frequency ratio (LF-HF) of HRV was assessed by bivariate logistic regression.Results:HRV indices representing sympathetic activity were increased in the RNB group and indices representing parasympathetic activity were increased in LNB group following 6-week nostril breathing. Prediction of LF-HF to RPP, the marker of cardiovascular risks, was more significant (OR 2.65, P = 0.005) in the LNB group compared to the RNB group (OR 1.452, P = 0.016).Conclusions:Short-term practice of LNB improves vagal tone, increases HRV, and promotes cardiovascular health of medical students. Practice of RNB increases sympathetic tone and could jeopardize cardiovascular health.

Association of hypertension status and cardiovascular risks with sympathovagal imbalance in first degree relatives of type 2 diabetics.

As reports show cardiovascular (CV) risks in first-degree relatives (FDR) of type2 diabetics, and autonomic imbalance predisposing to CV risks, in the present study we have assessed the contribution of sympathovagal imbalance (SVI) to CV risks in these subjects. Body mass index (BMI), waist-to-hip ratio (WHR), basal heart rate (BHR), blood pressure (BP), rate pressure product (RPP), and spectral indices of heart rate variability (HRV) were reordered and analyzed in FDR of type2 diabetics (study group, n=293) and in subjects with no family history of diabetes (control group, n=405). The ratio of low-frequency (LF) to high-frequency (HF) power of HRV (LF-HF), a sensitive marker of SVI, was significantly increased (P<0.001) in the study group compared with the control group. The SVI in the study group was due to concomitant sympathetic activation (increased LF) and vagal inhibition (decreased HF). In the study group, the LF-HF ratio was significantly correlated with BMI, WHR, BHR, BP and RPP. Multiple regression analysis showed an independent contribution of LF-HF to hypertension status (P=0.000), and bivariate logistic regression showed significant prediction (odds ratio 2.16, confidence interval 1.130-5.115) of LF-HF to increased RPP, the marker of CV risk, in the study group. Sympathovagal imbalance in the form of increased sympathetic and decreased parasympathetic activity is present in FDR of type2 diabetics. Increased resting heart rate, elevated hypertension status, decreased HRV and increased RPP in these subjects make them vulnerable to CV risks. SVI in these subjects contributes to CV risks independent of the degree of adiposity.

COMPARISON OF HEART RATE VARIABILITY ADJUSTED FOR AGE AND HEART RATE IN WOMEN WITH RHEUMATOID ARTHRITIS AND WOMEN WITHOUT RHEUMATIC DISEASES

Aim. To compare the 24-hour indicators of heart rate variability (HRV), adjusted for age and 24-hour average heart rate (HR24) in women with rheumatoid arthritis (RA) and women of the control group. Material and methods. Women with RA (n=291) at the age of 20-60 were examined. Women without rheumatic diseases (n=125) were included into control group. The presence of traditional cardiovascular risk factors, the results of 24-hour ECG monitoring were assessed in addition to clinical symptoms, RA activity and severity. Transformation of the initial HRV parameters in their logarithms, and the standardization of the logarithms of age and HR24, the calculation of the exponential of the standardized logarithm were performed to remove the effects of age and heart rate on HRV. Results. Time and frequency HRV indices, adjusted for age and HP24 (HRVa) in women with RA were lower than these in women of control group. HRVa decline was observed in 14–24% of women with RA. The maximum HRVa decrease was observed among the parameters that reflect an activity of parasympathetic autonomic nervous system (RMSSDn, pNN50n, HFn). Conclusion. The young and middle age women with RA differ from the women of the control group in significant decrease in the time and spectral HRV indices adjusted for age and HR24.

Short-term deceleration capacity reveals higher reproducibility than spectral heart rate variability indices during self-monitoring at home

rate variability indices during self-monitoring at home Jerzy Sacha ⁎, Jacek Sobon , Krzysztof Sacha , Alexander Muller , Georg Schmidt d a Department of Cardiology, Regional Medical Center, Opole, Poland b Faculty of Physical Education and Physiotherapy, Opole University of Technology, Opole, Poland c Uniwersytet Jagiellonski, ulica Reymonta 4, PL-30-059 Krakow, Poland d 1. Medizinische Klinik und Deutsches Herzzentrum Munchen der Technischen Universitat Munchen, Munchen, Germany

Monitoring ultradian changes in cardiorespiratory control in obstructive sleep apnea syndrome.

Spectral analysis of heart rate variability (HRV) is commonly employed to track changes in autonomic nervous system and respiratory activity during sleep. However, conventional HRV spectral indices can be seriously confounded by inter-subject differences or intra-individual changes in ventilation and ventilatory pattern, especially in subjects with obstructive sleep apnea syndrome (OSAS). We highlight the approach we have undertaken to circumvent this problem by introducing "respiration-adjusted" spectral indices of HRV. Since fluctuations in sleep state also affect HRV considerably, we describe a method for combining the information derived from sleep staging and the information derived from cardiorespiratory measurements. We also introduce a new complementary index of autonomic function, BRS(PTT), based on measurements of heart period and pulse transit time. We demonstrate that this surrogate measure of baroreflex gain correlates well with the corresponding measures of baroreflex sensitivity based on noninvasive blood pressure measurements. Our experience to date suggests that BRS(PTT), along with respiration-adjusted spectral measures of HRV, are useful as clinical tools for assessing autonomic dysfunction in OSAS.

Estimating mental fatigue based on electroencephalogram and heart rate variability

Estimating mental fatigue based on electroencephalogram and heart rate variability The effects of long term mental arithmetic task on psychology are investigated by subjective self-reporting measures and action performance test. Based on electroencephalogram (EEG) and heart rate variability (HRV), the impacts of prolonged cognitive activity on central nervous system and autonomic nervous system are observed and analyzed. Wavelet packet parameters of EEG and power spectral indices of HRV are combined to estimate the change of mental fatigue. Then wavelet packet parameters of EEG which change significantly are extracted as the features of brain activity in different mental fatigue state, support vector machine (SVM) algorithm is applied to differentiate two mental fatigue states. The experimental results show that long term mental arithmetic task induces the mental fatigue. The wavelet packet parameters of EEG and power spectral indices of HRV are strongly correlated with mental fatigue. The predominant activity of autonomic nervous system of subjects turns to the sympathetic activity from parasympathetic activity after the task. Moreover, the slow waves of EEG increase, the fast waves of EEG and the degree of disorder of brain decrease compared with the pre-task. The SVM algorithm can effectively differentiate two mental fatigue states, which achieves the maximum classification accuracy (91%). The SVM algorithm could be a promising tool for the evaluation of mental fatigue. Fatigue, especially mental fatigue, is a common phenomenon in modern life, is a persistent occupational hazard for professional. Mental fatigue is usually accompanied with a sense of weariness, reduced alertness, and reduced mental performance, which would lead the accidents in life, decrease productivity in workplace and harm the health. Therefore, the evaluation of mental fatigue is important for the occupational risk protection, productivity, and occupational health.

Reproducibility and Gender‐Related Differences of Heart Rate Variability during All‐Day Activity in Young Men and Women

Only few data are available on reproducibility over time in healthy young men and women and the corresponding gender-related changes of heart rate variability (HRV) measurements. We studied temporal and spectral HRV indices obtained from 24-hour Holter recordings in 32 healthy volunteers (14 men and 18 women, mean age 29 +/- 3 years) during 2 days of their usual all-day activity. Time-domain measures and the spectral low-frequency (LF) and high-frequency (HF) components as well as the LF/HF ratio were comparable on both test days. Significantly higher values on test day 2 were observed only for the spectral very-low-frequency (VLF) component and for the resulting total power. Compared to men, women had higher day- and nighttime vagus-associated HRV indices, including root mean square of successive differences (RMSSD), pNN50 (NN50 count divided by the total number of all NN intervals), and HF power, and lower day- and nighttime VLF and LF power with lower LF/HF ratio and total power. Temporal indices and the LF and HF spectral HRV measures are reproducible over usual all-day activity in young healthy subjects. Young women have higher day-and nighttime vagal tone than men with similar age range.

Abnormal autonomic cardiac response to transient hypoxia in sickle cell anemia

The objective of this study was to non-invasively assess cardiac autonomic control in subjects with sickle cell anemia (SCA) by tracking the changes in heart rate variability (HRV) that occur following brief exposure to a hypoxic stimulus. Five African–American SCA patients and seven healthy control subjects were recruited to participate in this study. Each subject was exposed to a controlled hypoxic stimulus consisting of five breaths of nitrogen. Time-varying spectral analysis of HRV was applied to estimate the cardiac autonomic response to the transient episode of hypoxia. The confounding effects of changes in respiration on the HRV spectral indices were reduced by using a computational model. A significant decrease in the parameters related to parasympathetic control was detected in the post-hypoxic responses of the SCA subjects relative to normal controls. The spectral index related to sympathetic activity, on the other hand, showed a tendency to increase the following hypoxic stimulation, but the change was not significant. This study suggests that there is some degree of cardiovascular autonomic dysfunction in SCA that is revealed by the response to transient hypoxia.

Estimating VDT Mental Fatigue Using Multichannel Linear Descriptors and KPCA-HMM

The impacts of prolonged visual display terminal (VDT) work on central nervous system and autonomic nervous system are observed and analyzed based on electroencephalogram (EEG) and heart rate variability (HRV). Power spectral indices of HRV, the P300 components based on visual oddball task, and multichannel linear descriptors of EEG are combined to estimate the change of mental fatigue. The results show that long-term VDT work induces the mental fatigue. The power spectral of HRV, the P300 components, and multichannel linear descriptors of EEG are correlated with mental fatigue level. The cognitive information processing would come down after long-term VDT work. Moreover, the multichannel linear descriptors of EEG can effectively reflect the changes of θ, α, and β waves and may be used as the indices of the mental fatigue level. The kernel principal component analysis (KPCA) and hidden Markov model (HMM) are combined to differentiate two mental fatigue states. The investigation suggests that the joint KPCA-HMM method can effectively reduce the dimensions of the feature vectors, accelerate the classification speed, and improve the accuracy of mental fatigue to achieve themaximum 88%. Hence KPCA-HMM could be a promising model for the estimation of mental fatigue.

Interpretation of Normalized Spectral Heart Rate Variability Indices In Sleep Research: A Critical Review

The normalized spectral heart rate variability (HRV) measures low-frequency (LF)nu and high-frequency (HF)nu are frequently used in contemporary sleep research studies to quantify modulation of the sympathetic and parasympathetic branches of the autonomic nervous system. The purpose of this tutorial and methodologic critique is to concisely demonstrate the structural algebraic redundancy inherent in the normalized spectral HRV measures with respect to each other, and also with respect to the well-known HRV index of sympathovagal balance, LF:HF ratio. The statistical problems and interpretational paradoxes related to the mathematical definitions of LFnu and HFnu are briefly outlined. Examples of use of normalized spectral HRV measures in recent articles from the sleep-relevant research literature are critically reviewed. LFnu, HFnu, and LF:HF ratio should be considered equivalent carriers of information about sympathovagal balance.

Sleep stage dependent patterns of nonlinear heart rate dynamics in postmenopausal women

Objective To study the effects of sleep stage changes on nocturnal nonlinear heart rate variability (HRV) in postmenopausal women. Design A prospective study. Population Seventy-one healthy postmenopausal women. Methods The women underwent two separate sleep studies four months apart. One steady state epoch per night of the awake state, stage 2 (light) non-REM sleep, stage 3–4 (deep) non-REM sleep and REM sleep were extracted. From the ECG, the fractal scaling exponents α 1 and α 2, approximate entropy (ApEn), the Poincaré plot variability coefficients SD1 and SD2, along with the low (LF) and high frequency (HF) bands of linear HRV as well as the LF/HF ratio were calculated. Results None of the spectral measures of HRV changed significantly during the non-REM sleep compared to awake state. However, in non-REM sleep, α 2 ( p < 0.001) decreased significantly compared to the awake state, while α 1 and ApEn remained unchanged. SD1 was slightly increased in stage 2 sleep ( p < 0.05), while SD2 decreased in slow wave sleep ( p < 0.001). In REM sleep, α 2 values returned to the awake values, while ApEn and α 1 increased above the awake levels ( p < 0.01 for all variables), and SD1 decreased ( p < 0.01). HF spectral component decreased slightly ( p < 0.05 compared to stage 2 sleep) and LF/HF ratio increased during REM sleep ( p < 0.001). ApEn and α 2 had no correlations with any of the spectral measures of HRV, and α 1 had a modest correlation with the LF/HF ratio only during sleep. Conclusions We found that nonlinear indices of HRV describe specific features in HR dynamics during various sleep stages that are not detected by traditional spectral HRV indices.

Novel spectral indexes of heart rate variability as predictors of sudden and non‐sudden cardiac death after an acute myocardial infarction

Background. Various indexes of 24‐hour heart rate variability (HRV) have been able to predict all‐cause mortality after an acute myocardial infarction (AMI), but their value in predicting specific modes of cardiac death has been limited.Aim. The aim of this study was to assess the role of two novel spectral indexes of HRV as predictors of either sudden (SCD) or non‐sudden cardiac death after an AMI.Method. We used two novel methods of spectral analysis of HRV: 1) the high‐frequency (HF) spectral component, Vindex, calculated as an average HF power from the most linear portion of HF power versus the R‐R interval regression curve, and 2) the prevalent low‐frequency oscillation of heart rate (PLF). Vindex, conventional HRV measures, and PLF were analyzed from 24‐hour Holter recordings of 590 patients with a recent AMI.Results. During the mean follow‐up of 39±14 months, SCD occurred in 3% (n = 17) and non‐sudden cardiac death in 5% (n = 28) of the patients. In univariate analysis, Vindex was the most potent predictor of SCD (RR: 6.0, 95% CI: 1.7–20.7, P<0.01), also remaining the most powerful predictor of SCD after adjustment for clinical variables and ejection fraction (RR: 4.2, 95% CI: 1.2–15.2, P<0.05). PLF was a potent predictor of non‐sudden cardiac death (RR: 13.9, 95% CI: 5.9–32.5, P<0.001), but it did not predict SCD.Conclusions. Novel spectral HRV analysis methods, Vindex and PLF, provide significant information of the risk of the specific mode of death after an AMI.

Correlations between frequency-domain HRV indices and lagged Poincaré plot width in healthy and diabetic subjects

The conventional Poincaré plot for heart rate variability (HRV) analysis is a scatterplot of successive (lag 1) pairs of RR intervals (intervals between heartbeats), and its width (SD1) is considered a measure of short-term variability. It has been shown that SD1 correlates better with HF than with LF (high- and low-frequency bands of the spectrum, respectively). Our aim was to assess how these correlations were affected when SD1 was obtained for longer lags. 10 min ECGs were used to construct Poincaré plots with lags of 1–10 heartbeats in two groups of subjects, one with normal HRV and the other with impaired HRV (control and diabetic groups respectively, N = 15 each). SD1 was quantified for these subjects and HRV spectral indices were estimated. The diabetic group had lower LF, HF and SD1 than the control group (p < 0.05). In both groups, SD1 tended to increase as the lag increased. In the control group, SD1 for lags 1 and 2 was highly correlated with HF (rs > 0.9), while SD1 for lags ⩾ 4 correlated better with LF (rs ⩾ 0.9) than with HF (0.65 ⩽ rs ⩽ 0.73). However, in the diabetic group, the correlation results did not change in that way for different lags (correlation results between HF and SD1: rs ⩾ 0.95 for lags 1–10). In conclusion, the comparative strength of the correlations between lagged Poincaré widths and spectral indices might be useful to distinguish normal from pathological HRV.

Heart Rate Variability Following Neonatal Heart Surgery for Complex Congenital Heart Disease

Altered cardiac autonomic control may play a role in the morbidity and mortality suffered by neonates who undergo surgery for complex congenital heart disease (CHD). The purpose of this study was to evaluate cardiac autonomic activity, as measured by spectral indices of heart rate variability (HRV), prior to and early after infant surgery for CHD and attempt to correlate HRV indices with clinical outcome. In addition, we assessed the hypothesis that single-ventricle physiology and surgical interruption of the great arteries negatively affects HRV. Sixty neonates prospectively wore 24-hour Holter monitors at three time points: before and early after CHD surgery, and at 3- to 6-month follow-up. Standard spectral indices of HRV were measured. In the early postoperative time point, patients with single-ventricle physiology had lower low-frequency power (LF) compared to patients with two ventricles (P=0.040). Surgical interruption of the great arteries did not affect HRV in this cohort. For the entire cohort, LF (P=0.004) and high-frequency power (HF) (P<0.001) increased over the three time points, while LF/HF (P=0.119) did not significantly change. In the multivariable linear regression model, significant predictors of longer postoperative hospital stay included longer total support time (P=or<0.001), longer duration of inotrope support (P=0.012), elevated mean heart rate at postoperative time point (P=0.002), and lower LF/HF ratio at the postoperative time point (P=0.014). Patients with single-ventricle physiology have a significant physiologic reduction in LF in the early postoperative period compared to patients with two ventricles. Diminished cardiac autonomic control is associated with longer hospitalization following neonatal cardiac surgery.

Circadian rhythm of spectral indices of heart rate variability in healthy subjects

Circadian pattern of heart rate variability spectral indices, including hourly, 24-hour, night, day, morning, and sex-adjusted measures of low frequency (LF), high frequency (HF), and LF/HF, was evaluated in healthy persons in 24-hour 3-lead electrocardiogram. HF showed circadian pattern with the greatest night values and LF/HF with the smallest night values. Peaks of hourly LF were found between 5 and 9 am and between 4 and 6 pm. The smallest LF was between 11 pm and 3 am. Hourly HF peaked between 11 pm and 5 am. The smallest HF was observed between midday and 2 pm. LF/HF peaked between 6 and 9 am as well as between 4 and 6 pm with the smallest values between midnight and 5 am. Sex adjustment was of no significance. In healthy subjects, HF and LF/HF have circadian pattern. Evaluation of all 5-minute intervals of 24-hour period seems to be a precise method of heart rate variability analysis.

Circadian rhythm of the QT interval dispersion in healthy subjects. Correlation with heart rate variability circadian pattern

Circadian variation of QT interval dispersion (QTd) and heart rate variability spectral indices was evaluated in healthy persons in 24-hour 3-lead electrocardiogram. Mean values, SD, and SD/mean were evaluated for 24 hours, each hour separately and in night, day, and morning periods. Table Curve2D and multiple regression were applied to find correlations between parameters. In 50% of subjects, a significant negative correlation was revealed between QTd and HF. Also, in 50% of persons, a significant positive correlation was found between QTd and low frequency/high frequency. After adjustment for periods, correlations were only observed during morning hours. With TableCurve 2D, 2 models of correlations between QTd and HF were found. Multiple regression analysis revealed relations between mean QTd and R-R as well as mean QTd and HF. It is possible that it is sympathovagal balance, as reflected in heart rate variability, and not the tone of both autonomic components that affects QTd variability.

Does the level of chronic physical activity alter heart rate variability in healthy older women?

In the present study, we investigated the effects of three levels of chronic physical activity on HRV (heart rate variability) in healthy older women. ECG recordings were taken in three (low-, moderate- and high-) activity groups in supine position with free and with controlled breathing, and during orthostatic stress. Temporal and spectral HRV indices were obtained from the ECG signal processing. The main results showed that, in supine position with free and controlled breathing, the HF (high-frequency) spectral component (P<0.01) and the rMSSD (square root of the mean squared differences) between two adjacent RR intervals (P<0.05 and P<0.01 respectively) were elevated in the high-activity group compared with the low-activity group. No significant difference was observed between groups during the orthostatic test. Within groups, in the supine position, the change from free to controlled breathing produced a decrease in the LF (low-frequency) spectral component in all three groups (P<0.01). The change from supine to standing position produced a decrease in RR in all three groups (P<0.05 in low- and moderate-activity groups, and P<0.01 in high-activity group); the rMSSD and the HF spectral component decreased only in the high-activity group (P<0.01). In conclusion, this study performed on older women showed that parasympathetic indices of resting HRV were significantly elevated in a high physical activity group compared with in a low physical activity group. Furthermore, parasympathetic indices of HRV decreased during an orthostatic test only in the high-activity group. The influence of chronic moderate physical activity on HRV in older women was small in the present study.

Bias and uncertainty in heart rate variability spectral indices due to the finite ECG sampling frequency

Spectral analysis of the heart rate variability is becoming a usual tool as a marker of the autonomic nervous system. The final output of the spectral analysis is a set of indices that are always estimators due to technical limitations. In this work, the bias and the uncertainty in the VLF, LF, HF and LF/HF indices due to the finite sampling frequency of the ECG are analysed. The results indicate that for low sampling frequency (125 Hz), the bias and uncertainty in the HF and LF/HF indices can blur the results of the analysis, especially if the RR time series has low variability. The HF index is overestimated and, accordingly, the LF/HF index is underestimated. Then, results from RR time series with low sampling frequency must be used with care. The uncertainty of the spectral indices is proportional to the inverse of the sampling frequency and the bias is proportional to the inverse of the square sampling frequency.

Heart rate variability is related to leucocyte count in men and to blood lipoproteins in women in a healthy population of 35‐year‐old subjects

To investigate if, in a healthy randomly-selected population of 35-year-old men and women, there already is a relation between decreased heart rate variability and conventional risk factors for cardiovascular disease. Analysis of heart rate variability (HRV) has been used for estimating tonic autonomic activity. HRV is reduced in patients with various cardiovascular diseases. If a decreased HRV is a late phenomenon in the progression of cardiovascular disease, or if it parallels or even precedes manifest disease is unknown. Spectral analysis of HRV was made from 24-hour ambulatory electrocardiograms in a randomised population of healthy 35-year-old men (n = 63) and women (n = 70). The different spectral indices of HRV were analysed against gender, leucocyte count (previously described as an independent risk factor for cardiovascular disease), blood lipoproteins, smoking, heredity, body mass index (BMI) and systolic blood pressure. A research centre of general medicine and a university hospital. Mean heart rate was lower, total power (TP), very low frequency power (VLF) and low frequency power (LF) were higher in men than in women. In women TP, VLF and LF were negatively correlated to BMI, smoking, triglycerides and positively correlated to HDL cholesterol. TP and VLF were also negatively correlated to risk factor score. High frequency power (HF), a marker of parasympathetic activity, was positively related to HDL cholesterol. In men, at daytime, TP, VLF, LF and HF were negatively correlated to leucocyte count. TP, VLF and LF were also negatively correlated to triglycerides and VLF also to risk factor score. There are correlations between HRV and known risk factors for cardiovascular disease already in a healthy 35-year-old population. A novel observation is the relationship in men between leucocyte count and heart rate variability.