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.

Intensity and daily reliability of the six-minute walk test in moderate chronic heart failure patients.

OBJECTIVE: To assess the intensity and daily reliability of the six-minute walk test (6MWT) in patients with moderate chronic heart failure (CHF). DESIGN: Evaluation of testing protocol. SETTING: Hospitalized care. PARTICIPANTS: CHF patients under optimal drug treatment (CHF-D, n=12) or optimal drug treatment plus multisite cardiac pacing (CHF-P, n=12). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Peak values of oxygen uptake (VO2) and heart rate during a symptom-limited, treadmill exercise test and VO2, heart rate, and distance during 2 6MWT sessions (morning and afternoon). The 6MWT intensity was estimated by the ratio (%) of VO2 and heart rate values measured at the end of this test in relation to the respective peak values obtained during the treadmill exercise test. RESULTS: Subjects' VO2 and heart rate during the 6MWT were lower (P<.001) and were about 90% of the peak values (VO2: CHF-D, 90.5%+/-11.1%; CHF-P, 93.0%+/-13.2%; heart rate: CHF-D, 90.6%+/-6.6%; CHF-P, 91.4%+/-9.6%). The distance walked during both 6MWT sessions did not differ significantly, with low coefficients of variation (< or =2.0%) and high intraclass correlation coefficients (> or =.98). In CHF-D only, the patients' VO2 and heart rate were significantly (P<.01, P<.05, respectively) higher during the afternoon session. CONCLUSIONS: Despite an intensity significantly lower but close to that of the symptom-limited exercise test, the 6MWT was well tolerated in both CHF groups. In these populations, the 6MWT is reliable on a daily basis, for the distance walked. However, for assessing VO2 and heart rate values in CHF-D patients, the 6MWT must always be performed at the same time of day.

Cardiorespiratory adaptations during the six-minute walk test in chronic heart failure patients.

BACKGROUND: The six-minute walk test (6-MWT) is widely used to assess exercise tolerance in chronic heart failure patients (CHF). The aim of this study was to analyse cardiorespiratory parameters kinetics during the 6-MWT in CHF and in healthy subjects. METHODS: A treadmill, symptom-limited exercise test and a 6-MWT were performed by 14 CHF under optimal drug treatment (CHFD), 17 CHF with cardiac resynchronization (CHFP), and 12 healthy subjects. Cardiorespiratory responses were assessed by a validated portable system. RESULTS: All subjects exceeded their ventilatory threshold during the 6-MWT. Healthy subjects and CHF performed the 6-MWT around 75 and 90% of peak oxygen uptake (V'O2) respectively (P<0.001). In CHF, a steady state was observed only for walking speed and V'O2, with a slight delay in comparison with healthy subjects, for whom a steady state was also observed for carbon dioxide production and ventilation (V'E). During the 6-MWT, the V'E adaptation was due mainly to an increase in tidal volume (VT) in CHFD, whereas in CHFP, it was due to a similar increase in VT and breathing frequency (f). In these patients, the 6-MWT VT/f slope was lower than in CHFD (P<0.01). CONCLUSIONS: During the 6-MWT, the V'O2 steady state is slightly delayed in CHF, which could be related partly to their higher exercise intensity. Moreover, each CHF group is characterized by a specific ventilation components response during the 6-MWT.

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.

Reliability and intensity of the six-minute walk test in healthy elderly subjects.

PURPOSE: The 6-min walk test (6-MWT) is an easy and validated field test, generally used in patients to assess their physical capacity. We think that the 6-MWT could also be conducted in the same perspective in healthy subjects, aged 60-70 yr. However, little is known about the effect of the familiarization on the 6-MWT performance and the relative intensity of this test. The aims of this study were therefore to bring precision to the 6-MWT reliability and intensity in this population. METHODS; Over 3 d, 12 subjects performed two maximal exercise tests on treadmill and five 6-MWT (two in the morning and three in the afternoon) with a portable metabolic measurement system (Cosmed K4, Rome, Italy). The distance, walking speed, oxygen uptake (VO2 (max)), and heart rate (HR) values were measured during the 6-MWT. RESULTS: Distance, walking speed, and VO2(max) were only lower during the first two 6-MWT (respectively, P< 0.001, P< 0.001, and P< 0.05). HR was reliable from the first 6-MWT and was higher during the tests performed in the afternoon (P< 0.001). The intensity of the 6-MWT corresponded to 79.6 +/- 4.5% of the VO2(max), 85.8 +/- 2.5% of the HR (max), and 78.0 +/- 6.3% of the HR (reserve). Moreover, it was higher than the ventilatory threshold in each subject (P< 0.01). CONCLUSION: In healthy elderly subjects, the 6-MWT represents a submaximal exercise, but at almost 80% of the VO2(max). To be exploitable, two familiarization attempts are required to limit the learning effect. Finally, the 6-MWT time of day must be taken into account when assessing HR.

Effects of an enhanced heart rate reserve on aerobic performance in patients with a heart transplant.

OBJECTIVE: The aim of this study was to investigate whether a high-intensity warm-up at the start of a graded, symptom-limited exercise test would enhance heart rate reserve and thus improve the aerobic performance of orthotopic heart transplant patients. DESIGN: Adrenal and cardiorespiratory responses were compared in 10 orthotopic heart transplant patients who performed two graded, symptom-limited exercise tests on an ergocycle. RESULTS: At the start of the graded, symptom-limited exercise test, high intensity increased the norepinephrine level more than usual intensity between rest and the third minute of exercise. This higher norepinephrine level was followed by a higher heart rate response from the fourth minute of exercise. Heart rate reserve was enhanced during high-intensity exercise, without any significant change in peak oxygen uptake. CONCLUSIONS: This specific warm-up enhanced heart rate reserve during a graded, symptom-limited exercise test on an ergocycle. Mechanisms more important than limited heart rate reserve are involved in the limitation of exercise tolerance in orthotopic heart transplant patients.