The effects of exercise training on myocardial adrenergic and muscarinic receptors.

We investigated the effects of exercise training on heart rate variability (HRV) and myocardial adrenergic and muscarinic receptors in rats. Exercise training induced a decrease in body mass while ventricular size remained unchanged, a development we considered as a relative cardiac hypertrophy. In addition, there was a reduction in the density of myocardial beta(1)-adrenergic receptors. These structural changes were associated with functional adaptations, as illustrated by the increased response of the sinus node to sympathetic blockade.

Reliability of heart rate variability in healthy older women at rest and during orthostatic testing.

BACKGROUND AND AIMS: In the older population, the reliability of heart rate variability (HRV) has only been evaluated in a few studies, in the supine position, and covering a broad sample of age and patients of both sexes. To document the relevance of using HRV analysis in healthy older women, the aim of this study was to evaluate the reliability of HRV indexes during three classical tests. METHODS: 33 healthy women (66.9+/-0.7 years old) performed two test sessions. Each session consisted of an ECG recorded in the supine position, first with free breathing (Test 1), then with controlled breathing (Test 2), and in the upright position (Test 3). Time and frequency HRV indexes were obtained by processing the ECG signals. Reliability was assessed between sessions using Student's paired t-test, intraclass correlation coefficient (ICC) and coefficient of variation (CV). RESULTS: There were no differences between the sessions. ICC showed good reliability for all HRV indexes. CV was low for absolute HRV indexes, except in Test 3 for parasympathetic indexes with modest CV. The CV of HRV ratio indexes were modest to high in all three tests. CONCLUSIONS: Time and absolute frequency HRV indexes are reliable when testing healthy older women. Our results support the use of such indexes in gerontology research, to assess the effects of clinical or pharmacological interventions on the autonomic nervous system.

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.

Exercise heart rate variability of older women in relation to level of physical activity.

The purpose of this study was to determine the effect of the level of physical activity in older women on heart rate (HR) response to its neural control at rest and during exercise by using heart rate variability (HRV) analysis. Electrocardiogram (ECG) was recorded in 3 (low, moderately, and highly) active groups of older women at rest and during submaximal exercise. Spectral HRV indexes were obtained from the ECG signal. At rest, highly active subjects have low HR without any alteration of HRV. During incremental submaximal exercise, parasympathetic modulations of HR decreased only in the highly active subjects (p <.01) without any alteration of HR, compared with the other groups. In older women, the effects of the level of physical activity on HR and HRV are dissociated. Quite a high level of physical training induces a higher sensitivity of sinus node response to the autonomic nervous system during exercise.