Karel Pardaens

Influence of demographic, anthropometric and lifestyle characteristics on heart rate and its variability in the population

OBJECTIVE The purpose of this investigation was to assess the effects of age, gender, posture and their interactions, and of body mass index and lifestyle factors, on heart rate, its total variance and its variability in the frequency domain in a population-based sample of healthy subjects. METHODS RR interval and respiration were registered in the supine and in the standing position in 302 men and 312 women, aged 25-89 years; 424 subjects were healthy and had recordings suitable for analysis. Power spectral analysis was performed by use of autoregressive modelling and by fast Fourier transform, and the low-frequency (LF) and high-frequency (HF) components were expressed in both absolute (ms2) and normalized units RESULTS In the supine position, heart rate was higher in women than in men (P<0.001) and was not affected by age. Total variance and absolute LF and HF power markedly declined with age in each gender (P<0.001). Men had higher absolute LF power than women (P<0.001), whereas HF power was similar by gender; the age-related decline of HF power tended to be steeper in women (P = 0.06). The normalized LF and HF powers also decreased with age (P<0.01), except for the LF component in women; young men had higher LF power and lower HF power than young women, but the gender difference disappeared in the sixth decade of life. The LF: HF ratio was not influenced by age in supine men; the ratio was lower in women at young age, but increased to the level of men at greater age. Heart rate increased on standing, whereas its total variance was reduced; HF power declined, irrespective of the units, normalized LF power and the LF: HF ratio increased, whereas absolute LF power decreased (P<0.001). The postural changes of heart rate and of the frequency components did not differ by gender, but were attenuated with increasing age (P<0.05). Alcohol consumption did not influence heart rate and its variability, whereas independent effects of habitual physical activity, smoking habits and body mass index explained no more than 4% of the variance of some measures of heart rate variability. CONCLUSIONS Age, gender and/or some lifestyle factors significantly affect heart rate and various components of its variability in the supine position and in response to standing. The results are similar for autoregressive modelling and fast Fourier transform, but may differ according to the units in which the spectral components are expressed.

Atrial fibrillation is associated with a lower exercise capacity in male chronic heart failure patients

Objective To study the influence of atrial fibrillation on peak oxygen uptake (peak V˙O2) in chronic heart failure. An unfavourable effect of atrial fibrillation has been shown in several patient populations, but the results have not been consistent in chronic heart failure. Methods Data were analysed from male heart transplant candidates who were able to perform graded bicycle ergometry until exhaustion with respiratory gas analysis and measurement of heart rate. Patients in atrial fibrillation (n = 18) were compared with patients in sinus rhythm (n = 93). Results Age, weight, height, and aetiology of chronic heart failure did not differ significantly between the two groups. Cardiac catheterisation at supine rest showed that heart rate was comparable, but that stroke volume and cardiac output were lower (p < 0.05) in atrial fibrillation. Systolic and diastolic left ventricular function, assessed by radionuclide angiography at rest, were not significantly different. Peak V˙O2 (mean (SD): 13.8 (3.6) v 17.1 (5.6) ml/kg/min; p < 0.01) and peak work load (78 (27) v 98 (36) W; p < 0.05) were lower in the patients with atrial fibrillation, though respiratory gas exchange ratio and Borg score were similar in the two groups. Patients with atrial fibrillation had a higher heart rate sitting at rest before exercise (93 (16) v 84 (16) beats/min) and at peak effort (156 (23) v 140 (25) beats/min) (p < 0.05). Conclusions Atrial fibrillation is associated with a 20% lower peak V˙O2 in patients with chronic heart failure, suggesting that preserved atrial contraction or a regular rhythm, or both, are critical to maintain cardiac output and exercise performance.

Peak oxygen uptake better predicts outcome than submaximal respiratory data in heart transplant candidates.

BACKGROUND Many studies have focused on the prognostic power of peak oxygen uptake VO(2) in patients with chronic heart failure, but maximal exercise testing is not without risk. The purpose of the present study was, therefore, to assess the prognostic significance of the steepness of changes in ventilation and carbon dioxide output VO(2) during submaximal exercise in comparison with VO(2). METHODS AND RESULTS The study population consisted of 284 adult heart transplant candidates who performed a graded maximal bicycle ergometer test with respiratory gas analysis. Using the respiratory data up to a gas exchange ratio of 1.0, 3 submaximal slopes were calculated in each patient. During follow-up (median, 1.33 years), 57 patients died and 149 had >/=1 cardiovascular event. When using Cox proportional hazards analysis, both peak VO(2) and submaximal respiratory slopes predicted outcome before and after accounting for age, sex, and body mass index. However, whereas the prognostic power of peak VO(2) was independent of submaximal respiratory data, the prognostic significance of the slopes was lost after controlling for peak VO(2). Stepwise regression analysis even selected peak VO(2) as an independent prognostic index among the following factors: cause of heart failure, ejection fraction, pulmonary vascular resistance, natremia, and the forced expiratory volume in 1 s. CONCLUSIONS Respiratory data during submaximal exercise are significant predictors of outcome in patients with chronic heart failure, but their prognostic power is inferior to that of peak VO(2). However, these data may be useful when maximal exercise is contraindicated or not achievable.

Prognostic value of invasive hemodynamic measurements at rest and during exercise in hypertensive men

In 1994, we ascertained the outcome of 143 hypertensive men in whom invasive hemodynamic measurements were performed at rest and during graded bicycle exercise during the period 1972-1982 to assess (1) which of the hemodynamic components of blood pressure is associated with the incidence of cardiovascular events and total mortality, and (2) whether the hemodynamic response to dynamic exercise adds prognostic precision to the data at rest. During 2186 patient years of follow-up, 38 patients suffered at least one fatal or nonfatal cardiovascular event and 17 patients died. Cox regression analysis showed that systolic pressure and systemic vascular resistance measured at rest, during submaximal exercise (50 W), and at peak effort were significant (P < .01) predictors of the age-adjusted incidence of cardiovascular events and total mortality. However, exercise blood pressure did not significantly predict the incidence of cardiovascular events over and above pressure at rest; by contrast, exercise systemic vascular resistance added prognostic precision to vascular resistance at rest (P < .01). As for total mortality, systolic pressure and systemic vascular resistance at peak exercise carried prognostic information that was independent of the results at rest (P < .05); this was not the case for measurements during submaximal exercise. We conclude that the prognostic importance of blood pressure is related to systemic vascular resistance. The prognostic precision of exercise pressure, on top of pressure at rest, is limited. Exercise systemic vascular resistance, however, provides prognostic information beyond that available from measurements at rest, particularly for the incidence of cardiovascular events.

The pulse pressure-to-stroke index ratio predicts cardiovascular events and death in uncomplicated hypertension.

OBJECTIVES The goal of this study was to assess the prognostic power of the pulse pressure-to-stroke index (PP-to-SVi) ratio for cardiovascular events and mortality in patients with uncomplicated hypertension. BACKGROUND The prognostic significance of pulse pressure (PP) has been studied repeatedly, but few data are available on the PP-to-SVi ratio. METHODS Invasive hemodynamic measurements, including brachial intra-arterial pressure and stroke index by the direct oxygen Fick method, were performed in the period 1972 to 1982 in 192 patients with uncomplicated hypertension; their outcome was ascertained in 1994. RESULTS Age at baseline averaged 37 +/- 12 years; brachial artery pressure was 165 mm Hg +/- 30/89 +/- 17 mm Hg; PP averaged 76 mm Hg +/- 18 mm Hg, and the PP-to-SVi ratio was 1.67 mm Hg/(ml/m2) +/- 0.73 mm Hg/(ml/m2). During 3,057 patient years of follow-up, 19 patients died, and 44 experienced at least one fatal or nonfatal cardiovascular event. Cox regression analysis revealed that the PP-to-SVi ratio was a significant predictor of fatal and nonfatal cardiovascular events and of all-cause mortality after control for age and gender (p < 0.01). Its predictive power persisted after additional adjustment for mean arterial pressure and heart rate. Each 0.75-mm Hg/(ml/m2) increase in the PP-to-SVi ratio was independently associated with a 79% increase in the risk of a cardiovascular event (p = 0.01) and a 2.05-fold greater risk of all-cause mortality (p = 0.01). CONCLUSIONS The PP-to-SVi ratio is a significant and independent predictor of cardiovascular events and mortality in selected patients with uncomplicated hypertension.

Relationships of heart rate and heart rate variability with conventional and ambulatory blood pressure in the population

Background Most studies on relationships between blood pressure and autonomic nervous function, assessed by power spectral analysis of heart rate variability, have used conventional or clinic blood pressure measurements in selected subjects, which may have influenced the results. Objective We aimed to investigate, in a population-based approach, associations of heart rate and heart rate variability, assessed in basal resting conditions and in response to standing, with conventional blood pressure measured by an investigator, and with ambulatory blood pressure monitored outside the laboratory. Methods RR interval and respiration were registered in 614 men and women, ages 25–89 years. After exclusion of subjects with myocardial infarction or diabetes and elimination of unsatisfactory recordings, 549 subjects remained for analyses at supine rest and 515 of these to assess the orthostatic responses. Hypertension was present in 39% of the subjects. The low-frequency (LF) and high-frequency (HF) components of heart rate variability were quantified by use of autoregressive modelling and expressed in absolute and normalized units. Results At supine rest, indices of heart rate variability were not independently related to 24 h systolic blood pressure, whereas some indices showed weak associations with diastolic 24 h pressure; the relationships were in general stronger for conventional blood pressure. For example, partial correlation coefficients of the relationships of the LF : HF ratio with systolic pressure were 0.12 (P ⩽ 0.01) for conventional pressure and 0.02 (NS) for 24 h pressure; these coefficients amounted to 0.20 (P ⩽ 0.001) and 0.11 (P⩽ 0.01) for the diastolic pressures. The decrease of HF power and the increase of the LF : HF ratio on standing were significantly blunted at higher blood pressure, both when measured conventionally and by ambulatory monitoring (P ⩽ 0.001 for the LF : HF ratio). Conclusions Relationships between autonomic nervous function at rest, assessed by use of power spectral analysis of heart rate variability, and conventional blood pressure, can at least partly be ascribed to the influence of the measurement conditions, whereas the orthostatic autonomic responses appear to be influenced by blood pressure per se.

Left ventricular diastolic function predicts outcome in uncomplicated hypertension.

Whereas left ventricular systolic function has been shown to predict outcome in hypertensive patients without clinical evidence of heart failure, the prognostic power of diastolic function has not been examined. We assessed the relation of mean pulmonary capillary wedge pressure as an index of left ventricular diastolic function to mortality and the incidence of cardiovascular events in patients with uncomplicated hypertension at baseline. Invasive hemodynamic measurements were performed in the period 1972 to 1982 in 172 hypertensive patients without evidence of cardiovascular disease, cardiomegaly or heart failure, and their outcome was ascertained in 1994. Age at baseline averaged 37 +/- 12 years, brachial artery pressure was 162 +/- 30/88 +/- 18 mm Hg, and mean pulmonary wedge pressure 6.3 +/- 3.0 mm Hg. During 2675 patient-years of follow-up, 15 patients died and 34 suffered at least one fatal or nonfatal cardiovascular event. Cox regression analysis showed that pulmonary wedge pressure was a significant predictor of total mortality and of cardiovascular events, after control for age and gender (P < .05). Each 1 mm Hg increase in wedge pressure was associated with a 23% increase in the risk of all-cause mortality and a 13% increase in the risk of a cardiovascular event. The prognostic power was independent of mean brachial artery pressure, body mass index, serum cholesterol, electrocardiographic left ventricular hypertrophy, and smoking at baseline. We conclude that mean pulmonary wedge pressure, which is likely to reflect left ventricular diastolic function in the selected patients of the current study, is a significant and independent predictor of mortality and of cardiovascular events in uncomplicated hypertension.

Effects of Post-absorptive and Postprandial Exercise on Glucoregulation in Metabolic Syndrome

Objective: The aim of this study was to investigate the effects of an acute exercise bout in the morning in the post‐absorptive or postprandial state on the glycemic and insulinemic response to three standardized meals throughout the day. It is hypothesized that post‐absorptive exercise enhances fat oxidation rate during exercise and thereafter attenuates the glucose and insulin response to subsequent meals.

Prognostic significance of peak oxygen uptake in hypertension

The aim of this study was to investigate the prognostic value of cardiopulmonary fitness in hypertension. From 1972 to 1982 oxygen uptake and heart rate were recorded during an exercise test to exhaustion in 216 patients (143 men). Their outcome was ascertained in 1994. During 3,411 patient years of follow-up, 53 patients suffered at least one fatal or nonfatal cardiovascular event and 25 patients died. After adjustment for age, gender, and weight, the relative hazard rates (RHR; Cox regression) of peak oxygen uptake (l.min-1) amounted to 0.44 (P = 0.01) for the first occurring cardiovascular events and 0.35 (P = 0.05) for all-cause mortality. These RHR remained significant after additional adjustment for traditional cardiovascular risk factors (RHR = 0.45 and 0.28, respectively; P < 0.05). Heart rate at 50 W did not predict outcome after adjustment for age and gender (P = 0.94 and 0.14, respectively), nor after additional adjustment for heart rate at rest (P = 0.86 and 0.61, respectively). In conclusion, a lower peak oxygen uptake, but not a higher submaximal heart rate, is significantly and independently associated with a higher incidence of cardiovascular events and a higher total mortality in hypertensive patients.

Prognostic significance of exercise versus resting blood pressure in patients with chronic heart failure

BACKGROUND Results on the prognostic value of exercise blood pressure differ among studies; this may be related to the characteristics of the studied population. OBJECTIVE To assess the prognostic significance of blood pressure measured during exercise in patients with chronic heart failure being considered for heart transplantation. DESIGN AND METHODS Symptom-limited bicycle exercise testing with measurement of blood pressure and respiratory gas analysis was performed in 274 potential candidates for heart transplantation. They were then followed up for mortality and cardiovascular events. RESULTS Results are given as the mean +/- SD. The age of the patients was 51.5+/-11.0 years, the resting blood pressure was 114+/-20/75+/-12 mmHg, the peak work load was 91+/-33 W and the peak oxygen uptake was 15.1+/-5.0 ml/min per kg. The systolic blood pressure increased to 128+/-21 mmHg at 30 W and to 133+/-23 mmHg at 50% of the peak work load. During the total follow-up time of 513 years, 55 patients died and 145 suffered at least one cardiovascular event. After controlling for age, gender and body mass index, mortality and incidence of events were inversely related to the systolic pressure at 30 W or at 50% of the peak work load, or to both (P < 0.05). The inverse associations of outcome with the systolic pressure at 50% of the peak work load persisted after additional adjustment for resting pressure and for peak oxygen uptake. CONCLUSION The data indicate that a lower exercise systolic pressure, particularly at 50% of the peak work load, is associated with a higher mortality and a greater incidence of cardiovascular events.