Multiscale properties of instantaneous parasympathetic activity in severe congestive heart failure: A survivor vs non-survivor study.

Multifractal analysis of cardiovascular variability series is an effective tool for the characterization of pathological states associated with congestive heart failure (CHF). Consequently, variations of heartbeat scaling properties have been associated with the dynamical balancing of nonlinear sympathetic/vagal activity. Nevertheless, whether vagal dynamics has multifractal properties yet alone is currently unknown. In this study, we answer this question by conducting multifractal analysis through wavelet leader-based multiscale representations of instantaneous series of vagal activity as estimated from inhomogeneous point process models. Experimental tests were performed on data gathered from 57 CHF patients, aiming to investigate the automatic recognition accuracy in predicting survivor and non-survivor patients after a 4 years follow up. Results clearly indicate that, on both CHF groups, the instantaneous vagal activity displays power-law scaling for a large range of scales, from ≃ 0.5s to ≃ 100s. Using standard SVM algorithms, this information also allows for a prediction of mortality at a single-subject level with an accuracy of 72.72%.

Point-process high-resolution representations of heartbeat dynamics for multiscale analysis: A CHF survivor prediction study.

Multiscale analysis of human heartbeat dynamics has been proved effective in characterizeing cardiovascular control physiology in health and disease. However, estimation of multiscale properties can be affected by the interpolation procedure used to preprocess the unevenly sampled R-R intervals derived from the ECG. To this extent, in this study we propose the estimation of wavelet coefficients and wavelet leaders on the output of inhomogeneous point process models of heartbeat dynamics. The RR interval series is modeled using probability density functions (pdfs) characterizing and predicting the time until the next heartbeat event occurs, as a linear function of the past history. Multiscale analysis is then applied to the pdfs' instantaneous first order moment. The proposed approach is tested on experimental data gathered from 57 congestive heart failure (CHF) patients by evaluating the recognition accuracy in predicting survivor and non-survivor patients, and by comparing performances from the informative point-process based interpolation and non-informative spline-based interpolation. Results demonstrate that multiscale analysis of point-process high-resolution representations achieves the highest prediction accuracy of 65.45%, proving our method as a promising tool to assess risk prediction in CHF patients.

Multiscale wavelet p-leader based heart rate variability analysis for survival probability assessment in CHF patients.

A priori discrimination of high mortality risk amongst congestive heart failure patients constitutes an important clinical stake in cardiology and involves challenging analyses of the temporal dynamics of heart rate variability (HRV). The present contribution investigates the potential of a new multifractal formalism, constructed on wavelet p-leader coefficients, to help discrimination between survivor and non survivor patients. The formalism, applied to a high quality database of 108 patients collected in a Japanese hospital, enables to assess the existence of multifractal properties amongst congestive heart failure patients and to reveal significant differences in the multiscale properties of HRV between survivor and non survivor patients, for scales ranging from approximately 60 to 250 beats.

Striking effect of left ventricular high filling pressure with mitral regurgitation on mitral annular velocity during early diastole. A study using colour M-mode tissue Doppler imaging.

AIMS: To evaluate the effect of considerably high left ventricular filling pressure with mitral regurgitation on mitral annular velocity during early diastole. SUBJECTS: Two hundred and forty-three patients who underwent cardiac catheterization for evaluation of chest pain. METHODS: Mitral annular velocity during early diastole was measured by colour M-mode tissue Doppler imaging. Patients were divided into the following three groups according to the cardiac catheterization data. Group A (n=147): patients having left ventricular relaxation time constant tau<46 ms and left ventricular end-systolic volume index <38 ml m(-2); group B (n=88): patients having tau>or=46 ms and/or end-systolic volume index >or=38 ml m(-2); group C (n=8): patients having mean pulmonary capillary wedge pressure >or=16 mmHg in addition to tau>or=46 ms and end-systolic volume index >or=38 ml m(-2). RESULTS: Mitral annular velocity during early diastole was significantly less in group B (4.8+/-1.4 cm s(-1)) than in group A (7.7+/-1.9 cm s(-1)). However, there was no significant difference between groups A and C (8.3+/-0.8 cm s(-1)). A transmitral E/A >1.0 was observed in 12/147 patients of group A, 10/88 of group B, and 8/8 of group C. The incidence of >or=Sellers' grade II mitral regurgitation was higher in group C than the others. CONCLUSIONS: A paradoxically faster mitral annular velocity during early diastole is found in patients having left ventricular dysfunction with moderate to severe mitral regurgitation and considerably high left ventricular filling pressure. Attention should be paid to an interpretation of mitral annular velocity during early diastole regarding left ventricular early diastolic performance in patients having mitral regurgitation with an E/A >1.0 in their transmitral flow.

Postural response of low-frequency component of heart rate variability is an increased risk for mortality in patients with coronary artery disease.

STUDY OBJECTIVES: We examined whether autonomic functions assessed by heart rate variability (HRV) during standardized head-up tilt testing (HUTT) predict risk for death in stable patients with coronary artery disease (CAD). DESIGN AND SETTING: Retrospective cohort study in medium-sized university general hospital. MEASUREMENTS AND RESULTS: In a cohort of 250 patients with CAD who were undergoing elective coronary angiography, we analyzed HRV during standardized HUTT under paced breathing with discontinuation of treatment with all medications. During a subsequent mean follow-up period of 99 months, there were 13 cardiac deaths and 12 noncardiac deaths. Cox regression analysis adjusted for cardiovascular risks revealed that increased postural change (supine to upright) in the power of low-frequency component (LF) power predicted an increased risk for cardiac death (relative risk [per 1-ln ms(2) increment], 4.36; 95% confidence interval, 1.64 to 11.6), while neither the high-frequency component nor its response to HUTT predicted any form of death. When the patients were trichotomized by the level of postural LF change (large drop, < or = - 0.6 ln[ms(2)]; small drop and rise, > 0 ln[ms(2)]), the three groups did not differ in terms of clinical features or CAD severity at baseline or coronary interventions during the follow-up period; however, the 8-year cardiac mortality rates were 0%, 6%, and 12%, respectively (p = 0.008 [log rank test]). Additionally, the difference was enhanced when analyzed excluding 64 patients who had been treated with a beta-blocker during the follow-up period (0%, 7%, and 15%, respectively; p = 0.006 [log rank test]). CONCLUSIONS: The postural response of HRV predicts the risk for death in patients with CAD. Postural LF increase (LF rise), in particular, is an independent risk factor for cardiac death.

Striking effect of left ventricular systolic performance on propagation velocity of left ventricular early diastolic filling flow.

Propagation velocity of left ventricular (LV) early diastolic filling flow (PVE) has been acknowledged as a useful parameter for LV early diastolic performance; however, the effect of LV systolic performance on PVE is not fully understood. Thus the purpose of this study was to investigate such an effect. Propagation of LV early diastolic filling flow was visualized by M-mode color Doppler imaging, and the slopes of the peak velocity tracings were measured as PVE in 150 patients who underwent coronary angiography. In cardiac catheterization, mean pulmonary capillary wedge pressure, time constant tau of LV pressure decay, LV end-systolic volume index, and LV ejection fraction were obtained. In univariate regression analysis, PVE significantly correlated with LV end-systolic volume index (r = -0.68, P <.001), LV ejection fraction (r = 0.66, P <.001), and time constant tau (r = -0.52, P <.001). In multivariate regression analysis, PVE was regressed by the LV end-systolic volume index, tau, and mean pulmonary capillary wedge pressure. The contribution of each parameter to the variance of the PVE was 46%, 3%, and 2%, respectively. A break-point linear regression analysis showed that the relation between the LV end-systolic volume index and PVE was much better characterized by a broken line than a straight line. The broken line had a steeper slope in patients with LV end-systolic volume index < or =41 mL/m(2) than in those with >41 mL/m(2). These findings suggest that PVE is determined mainly by LV systolic performance and partly by both LV relaxation and LV filling pressure. Left ventricular systolic performance may play a key role in generating a much faster PVE, especially in patients with relatively better LV systolic performance.

Differential effects of hypoxia and hypercapnia on respiratory sinus arrhythmia in conscious dogs.

To test the hypothesis that hypoxia and hypercapnia have different effects on the genesis of respiratory sinus arrhythmia (RSA), the magnitude of RSA to these stimuli was compared in 3 unanesthetized dogs. Respiration was continuously monitored through a permanent tracheostomy, and the electrocardiogram and blood pressure were also monitored. The magnitude of RSA was assessed as an instantaneous amplitude of the R-R interval oscillation in the high-frequency band of 0.15-0.80Hz by means of complex demodulation. In a total of 47 runs with hypoxia, heart rate, mean arterial pressure, respiratory rate and tidal volume increased, but RSA magnitude decreased even after adjusting for the effects of respiratory rate and tidal volume. In a total of 39 runs with hypercapnia, heart rate and mean arterial pressure did not change, despite the increased respiratory rate and tidal volume. In contrast to hypoxia, RSA magnitude increased even after adjusting for the effects of respiratory rate and tidal volume. The different effects of the two respiratory stimuli on RSA magnitude were noted at any level of ventilation and support the original hypothesis.

Augmentation of respiratory sinus arrhythmia in response to progressive hypercapnia in conscious dogs.

Respiratory sinus arrhythmia (RSA) may serve to enhance pulmonary gas exchange efficiency by matching pulmonary blood flow with lung volume within each respiratory cycle. We examined the hypothesis that RSA is augmented as an active physiological response to hypercapnia. We measured electrocardiograms and arterial blood pressure during progressive hypercapnia in conscious dogs that were prepared with a permanent tracheostomy and an implanted blood pressure telemetry unit. The intensity of RSA was assessed continuously as the amplitude of respiratory fluctuation of heart rate using complex demodulation. In a total of 39 runs of hypercapnia in 3 dogs, RSA increased by 38 and 43% of the control level when minute ventilation reached 10 and 15 l/min, respectively (P < 0.0001 for both), and heart rate and mean arterial pressure showed no significant change. The increases in RSA were significant even after adjustment for the effects of increased tidal volume, respiratory rate, and respiratory fluctuation of arterial blood pressure (P < 0.001). These observations indicate that increased RSA during hypercapnia is not the consequence of altered autonomic balance or respiratory patterns and support the hypothesis that RSA is augmented as an active physiological response to hypercapnia.

Effects of shift work on 24-hour ambulatory blood pressure and its variability among Japanese workers.

OBJECTIVES: This study examined the effects of rotating shift work on blood pressure in a comparison of ambulatory blood pressure and long-term changes in blood pressure between shift and day workers. METHODS: Ambulatory blood pressure was measured for 24-hour periods at an interval of 30 minutes for 27 shift workers and 26 day workers when they worked during the day. Blood pressure was compared between these 2 groups of workers for 4 time categories (awake, sleep, nonwork awake, and work periods). Their long-term blood pressures, recorded in annual surveys, were reviewed for long-term changes. These comparisons were adjusted for the effects of body mass index, alcohol intake, anger expression, and physical activity. RESULTS: On the average, sleep time was shorter and the anger-in (ie, anger suppressed) score was higher for the shift workers than for the day workers, but body mass index and alcohol intake did not differ between the 2 groups. Even after adjustment for these co-variables, the mean systolic blood pressure during the 24-hour, awake, and work periods were higher among the shift workers than among the day workers. The 24-hour standard deviations of the systolic blood pressures were also higher for the shift workers than for the day workers. Among the shift workers, but not among the day workers, a significant long-term increase was observed in systolic blood pressure measured in the annual surveys. CONCLUSIONS: These results suggest that shift work may increase systolic blood pressure levels among Japanese men.

Impact of acute hypoxia on heart rate and blood pressure variability in conscious dogs.

To examine whether the impacts of hypoxia on autonomic regulations involve the phasic modulations as well as tonic controls of cardiovascular variables, heart rate, blood pressure, and their variability during isocapnic progressive hypoxia were analyzed in trained conscious dogs prepared with a permanent tracheostomy and an implanted blood pressure telemetry unit. Data were obtained at baseline and when minute ventilation (VI) first reached 10 (VI10), 15 (VI15), and 20 (VI20) l/min during hypoxia. Time-dependent changes in the amplitudes of the high-frequency component of the R-R interval (RRIHF) and the low-frequency component of mean arterial pressure (MAPLF) were analyzed by complex demodulation. In a total of 47 progressive hypoxic runs in three dogs, RRIHF decreased at VI15 and VI20 and MAPLF increased at VI10 and VI15 but not at VI20, whereas heart rate and arterial pressure increased progressively with advancing hypoxia. We conclude that the autonomic responses to isocapnic progressive hypoxia involve tonic controls and phasic modulations of cardiovascular variables; the latter may be characterized by a progressive reduction in respiratory vagal modulation of heart rate and a transient augmentation in low-frequency sympathetic modulation of blood pressure.

Reduced ventricular response irregularity is associated with increased mortality in patients with chronic atrial fibrillation.

BACKGROUND-Variations in the ventricular response interval (VRI) during atrial fibrillation (AF) may be reduced in patients with adverse clinical outcomes. The properties of VRI dynamics associated with prognosis remain undetermined. METHODS AND RESULTS-In 107 patients with chronic AF (age, 64+/-9 years), we analyzed a 24-hour ambulatory ECG for VRI variability (SD, SD of successive differences, and SD of 5-minute averages) and VRI irregularity (Shannon entropy of histogram, symbolic dynamics, and approximate entropy of beat-to-beat and minute-to-minute fluctuations [ApEn(b-b) and ApEn(m-m)]). During a follow-up period of 33+/-16 months, 18 patients died (17%), 9 from cardiac causes, 7 from fatal strokes, and 2 from malignancies. Reductions in all VRI variability and irregularity measures were associated with an increased risk for cardiac death but not for fatal stroke. A significant association with cardiac death was also found for ejection fraction (relative risk, 1.10; 95% confidence interval [CI], 1.04 to 1.17, per 1% decrement) and ischemic AF (relative risk, 6.52; 95% CI, 1.62 to 26. 3). After adjustment for these clinical variables, all irregularity measures except symbolic dynamics had predictive value (relative risks [95% CIs] per 1SD decrement: Shannon entropy of histogram, 2. 03 [1.14 to 3.61]; ApEn(b-b), 1.72 [1.14 to 2.60]; and ApEn(m-m), 1. 90 [1.03 to 3.52]); however, the predictive power of variability measures was no longer significant. When the patients were stratified with the 33rd and 67th percentile values of ApEn(b-b) (1. 83 and 1.94, respectively), the 5-year cardiac mortality rates for the upper, middle, and lower tertiles were 0%, 13%, and 43%, respectively (log-rank test, P=0.04). CONCLUSIONS-Reduced VRI irregularity in a 24-hour ambulatory ECG has an independent prognostic value for cardiac mortality during long-term follow-up in patients with chronic AF.

Exercise and weight loss reduce blood pressure in men and women with mild hypertension: effects on cardiovascular, metabolic, and hemodynamic functioning.

BACKGROUND: Lifestyle modifications have been recommended as the initial treatment strategy for lowering high blood pressure (BP). However, evidence for the efficacy of exercise and weight loss in the management of high BP remains controversial. METHODS: One hundred thirty-three sedentary, overweight men and women with unmedicated high normal BP or stage 1 to 2 hypertension were randomly assigned to aerobic exercise only; a behavioral weight management program, including exercise; or a waiting list control group. Before and following treatment, systolic and diastolic BPs were measured in the clinic, during daily life, and during exercise and mental stress testing. Hemodynamic measures and metabolic functioning also were assessed. RESULTS: Although participants in both active treatment groups exhibited significant reductions in BP relative to controls, those in the weight management group generally had larger reductions. Weight management was associated with a 7-mm Hg systolic and a 5-mm Hg diastolic clinic BP reduction, compared with a 4-mm Hg systolic and diastolic BP reduction associated with aerobic exercise; the BP for controls did not change. Participants in both treatment groups also displayed reduced peripheral resistance and increased cardiac output compared with controls, with the greatest reductions in peripheral resistance in those in the weight management group. Weight management participants also exhibited significantly lower fasting and postprandial glucose and insulin levels than participants in the other groups. CONCLUSIONS: Although exercise alone was effective in reducing BP, the addition of a behavioral weight loss program enhanced this effect. Aerobic exercise combined with weight loss is recommended for the management of elevated BP in sedentary, overweight individuals.

Difference in human cardiovascular response between upright and supine recovery from upright cycle exercise.

Cardiovascular responses were examined in seven healthy male subjects during 10 min of recovery in the upright or supine position following 5 min of upright cycle exercise at 80% peak oxygen uptake. An initial rapid decrease in heart rate (fc) during the early phase of recovery followed by much slower decrease was observed for both the upright and supine positions. The average fc at the 10th min of recovery was significantly lower (P < 0.05) in the supine position than in the upright position, while they were both significantly greater than the corresponding pre-exercise levels (each P < 0.05). Accordingly, the amplitude of the high frequency (HF) component of R-R interval variability (by spectrum analysis) in both positions was reduced with a decrease in mean R-R interval, the relationship being expressed by a regression line--mean R-R interval = 0.006 x HF amplitude + 0.570 (r = 0.905, n = 28, P < 0.001). These results would suggest that the slower reduction in fc following the initial rapid reduction in both positions is partly attributable to a retardation in the restoration of the activity of the cardiac parasympathetic nervous system. Post-exercise upright stroke volume (SV, by impedance cardiography) decreased gradually to just below the pre-exercise level, whereas post-exercise supine SV increased markedly to a level similar to that at rest before exercise. The resultant cardiac output (Qc) and the total peripheral vascular resistance (TPR) in the upright and supine positions returned gradually to their respective pre-exercise levels in the corresponding positions. At the 10th min of recovery, both average SV and Qc were significantly greater (each P < 0.005) in the supine than in the upright position, while average TPR was significantly lower (P < 0.05) in the supine than in the upright position. In contrast, immediately after exercise, mean blood pressure dropped markedly in both the supine and upright positions, and their levels at the 10th min of recovery were similar. Therefore we concluded that arterial blood pressure is maintained relatively constant through various compensatory mechanisms associated with fc, SV, Qc, and TPR during rest and recovery in different body positions.

Is the blood flow in the left ventricle during the isovolumic relaxation period a useful parameter of left ventricular systolic and early diastolic performance?

Left ventricular (LV) early diastolic performance is determined by LV behavior in the late systole to early diastole and may relate to the physical potential of patients. Isovolumic relaxation flow (IRF) velocity was obtained by continuous Doppler echocardiography in the left ventricle from the apex in 26 patients with atypical chest pain and 63 patients with coronary artery disease (CAD) with or without prior myocardial infarction (MI) who underwent cardiac catheterization. In each patient, a time constant of LV relaxation (tau) was calculated from the LV pressure waves obtained by a catheter-tipped micromanometer. The LV end-systolic volume index was measured using contrast left ventriculography. IRF velocity in patients having CAD with prior MI (24.8 +/- 5.4 cm/s) was significantly less than in those with atypical chest pain (41.2 +/- 9.6 cm/s). It was also significantly less than in patients having CAD without prior MI (37.3 +/- 6.8 cm/s). IRF velocity significantly correlated with the time constant tau (r = -0.42, p < 0.001) and LV end-systolic volume index (r = -0.84, p < 0.001). This study indicates that IRF velocity obtained by continuous Doppler echocardiography in the left ventricle provides important information regarding LV systolic performance and early diastolic performance.

Effects of sympathetic nerve blockades on low-frequency oscillations of human earlobe skin blood flow.

Earlobe skin blood flow measured by laser Doppler flowmetry often shows low-frequency oscillations with a frequency around 0.1 Hz. We evaluated the effects of different sympathetic blocking techniques on the oscillations. Power spectrum of 5-min time series of beat-to-beat peak earlobe skin blood flow showed a distinct spectral peak at a frequency around 0.1 Hz (mean +/- SD, 0.107+/-0.016 Hz). The power of the spectral peak measured as coefficient of component variance (CCV) was diminished with total spinal anesthesia (TSA, n = 4) and cervicothoracic epidural anesthesia (CTEA, n = 4; P<0.05 for both). The CCV was unchanged significantly with bilateral thoracic sympathetic ganglionic excision (TSGE, n = 5). Right stellate ganglion block (RSGB, n = 6) caused a trend towards an increase in the CCV on the right (blocked)-side (P = 0.072) but no change on the left (intact)-side. Cross-spectrum analysis revealed that the low-frequency oscillations were not coherent between the right- and left-side earlobes or with low-frequency oscillations in systolic blood pressure either before or after RSGB. TSA and CTEA are known to cause extensive sympathetic nerve blockade in a broad area, while TSGE and RSGB are known to cause local and partial sympathetic blockade. Our results suggest that although the low-frequency oscillations in earlobe skin blood flow may be mediated non-neurally, magnitude of the oscillations may be modified by sympathetic vasomotor tone.

Influence of body composition on electrocardiographic identification of left ventricular hypertrophy in adolescents.

We investigated the influence of body composition on electrocardiographic (ECG) detection of left ventricular (LV) hypertrophy in 894 high-school students. The percent body fat and LV mass were estimated by bioelectrical impedance and echocardiography, respectively. There was no significant difference in LV mass among subjects classified according to the percent body fat. The cutoff ECG amplitudes (RV5 and SV1+RV5) for detection of LV hypertrophy (LV mass >/=90th percentile in both boys and girls) with 90% specificity were highest in the low-fat group and lowest in the high-fat group. When the effects of the percent body fat on ECG amplitudes were taken into account, the sensitivity of the ECG for detection of LV hypertrophy improved from 32.7 to 38.2% in boys; however, no improvement was observed in girls (from 33.3 to 30.6%). Evaluation of the percent body fat may improve the efficacy of ECG detection of LV hypertrophy in adolescent boys, but the usefulness of this method may be limited in girls.

Differentiation of abnormal relaxation pattern with aging from abnormal relaxation pattern with coronary artery disease in transmitral flow with the use of tissue Doppler imaging of the mitral annulus.

An abnormal relaxation pattern in transmitral flow velocity waveforms has been observed in older healthy subjects as well as in patients with heart disease. Accordingly, we investigated whether the hemodynamic differences between patients with coronary artery disease (CAD) with an abnormal relaxation pattern in transmitral flow (ratio of E-wave to A-wave velocities < 1.0) and healthy older subjects with an abnormal relaxation pattern can be distinguished with the use of mitral annular velocity (MAV) during early diastole. We measured MAV in the longitudinal direction of the heart during early diastole by M-mode color tissue Doppler imaging in 24 patients with atypical chest pain (defined as healthy subjects in this study) and 70 patients with CAD who underwent cardiac catheterization. In all patients a time constant of left ventricular pressure decay (tau) and the left ventricular (LV) end-systolic volume index were also measured. Twenty-one healthy subjects and 59 patients with CAD had an abnormal relaxation pattern in their transmitral flow. The age, heart rate, mean blood pressure, and ratio of E-wave to A-wave velocities were not different between the two groups. However, the tau was longer and the LV end-systolic volume index was greater in patients who had an abnormal relaxation pattern with CAD than in healthy subjects with an abnormal relaxation pattern. The MAV during early diastole was lower in the former than in the latter (5.8 +/- 1. 9 vs 9.8 +/- 1.9 cm/s, P <.001). Mitral annular velocity during early diastole by M-mode color tissue Doppler imaging can detect the differences in LV relaxation and LV systolic performance between the abnormal relaxation pattern with CAD and the physiologically abnormal relaxation pattern with aging, providing further information regarding the meaning of an LV abnormal relaxation pattern.

Prognostic value of heart rate variability during long-term follow-up in chronic haemodialysis patients with end-stage renal disease.

BACKGROUND: Mortality is high in chronic haemodialysis patients with cardiovascular disease, and many of them die suddenly. Reduced heart rate variability (HRV) is an increased risk for death in various populations, but its prognostic value in haemodialysis patients remains uninvestigated. METHODS: We analysed the associations between 24-h HRV measures and long-term mortality through a prospective follow-up of 31 chronic haemodialysis patients who underwent diagnostic coronary angiography. RESULTS: Of the 31 patients, at baseline, seven had a previous myocardial infarction, five had a history of congestive heart failure and 14 had significant (> or =75%) coronary stenosis (four had multi-vessel stenosis). During follow-up for 60+/-5 months, 14 patients died, 11 of them suddenly. A left ventricular ejection fraction of <0.45, multi-vessel coronary stenosis, ventricular tachycardia on 24-h ECG and decreased/abnormal 24-h HRV (triangular index <22 and abnormal Poincaré plot) carried a univariate risk of all-cause death, while the risk of sudden death was only correlated with decreased HRV (standard deviation of normal-normal R-R interval <50 ms, triangular index <22 and ultra-low frequency power <8.7 ln(ms2)). Multivariate analysis revealed that a triangular index <22 was the best predictor of increased risk for both all-cause and sudden death (hazards ratio (95% CI); 8.1 (1.3-48.6) and 12.6 (1.3-126.4), respectively) and that the association was independent of cardiac function, macrovascular diseases, ventricular arrhythmias and cardiovascular risk factors. The 5-year mortality when the triangular index was > or =22 or <22 was 33 or 88% for patients with coronary artery disease and 0 or 50% for those without. CONCLUSIONS: These results indicate that HRV has an independent prognostic value in chronic haemodialysis patients and identifies an increased risk for all-cause and sudden death.

Aging and spectral characteristics of the nonharmonic component of 24-h heart rate variability.

To examine whether heart rate variability (HRV) during daily life shows power law behavior independently of age and interindividual difference in the total power, log-log scaled coarse-graining spectra of the nonharmonic component of 24-h HRV were studied in 62 healthy men (age 21-79 yr). The spectra declined with increasing frequency in all subjects, but they appeared as broken lines slightly bending downward, particularly in young subjects with a large total power. Regression of the spectrum by a broken line with a single break point revealed that the spectral exponent (beta) was greater in the region below than above the break point (1.63 +/- 0. 23 vs. 0.96 +/- 0.21, P < 0.001). The break point frequency increased with age (r = 0.51, P < 0.001) and beta correlated with age negatively below the break point (r = 0.39) and positively above the break point (r = 0.70). The contribution to interindividual difference in total power was greater from the differences in the power spectral density at frequencies closer to both ends of the frequency axis and minimal from that at -3.25 log(Hz), suggesting hingelike movement of the spectral shape at this frequency with the difference in total power. These characteristics of the 24-h HRV spectrum were simulated by an artificial signal generated by adding two noises with different beta values. Given that the power law assumption is fundamental to the analysis of dynamics through the log-log scaled spectrum, our observations are substantial for physiological and clinical studies of the heartbeat dynamic during daily life and suggest that the nonharmonic component of HRV in normal subjects during daily life may include at least two 1/fbeta fluctuations that differ in dynamics and age dependency.