Impact of heart rate on reproducibility of heart rate variability analysis in the supine and standing positions in healthy men.

OBJECTIVE: The reliability of heart rate variability (HRV) analysis is not yet fully understood, especially considering different body positions and the mathematical influence of heart rate. The aim of this study was to evaluate the reliability of HRV in supine and standing positions, with and without mathematical adjustment of HRV by the average R-R interval (iRR). METHODS: We evaluated 37 young males (23.1±4 years; 25.1±3 kg/m2). A 5-min segment of the iRR was collected in the supine and standing positions on three occasions separated by 48-hour intervals. Absolute and relative reliability of temporal and spectral indices were assessed by the coefficient of variation (CV) and the intraclass correlation coefficient (ICC), respectively. RESULTS: We did not observe differences in HRV indices in the three occasions in the supine or standing position (p>0.05). Moderate to good reproducibility was observed for temporal and spectral indices of HRV in the supine position (ICC: 0.65-0.89; CV: 0.9-19.8). In the orthostatic position, low to good reproducibility was observed (ICC: 0.35-0.89; CV: 1.1-34.8), with higher ICCs for temporal indices. After mathematical adjustment, only a small modification in HRV reliability was observed in both positions. CONCLUSIONS: In young adult males, the mathematical adjustment of HRV by the average iRR led to a nonsignificant effect on HRV reliability. Additionally, HRV reliability is dependent on body position and the index analyzed. Promising measures in both supine and standing positions include r-MSSD and the HF band (parasympathetic indices).

Caffeine increases parasympathetic reactivation without altering resting and exercise cardiac parasympathetic modulation: A balanced placebo design.

The sympathicotonic effect of caffeine is strongly evidenced in the literature. However, the effects of caffeine or caffeine expectancy on the cardiac parasympathetic modulation remain obscure. Thus, the aim of this study was to investigate the effects of caffeine consumption and expectancy of caffeine consumption on the cardiac parasympathetic modulation under different stress conditions. Twenty-one physically active men (22.3 ± 2.9 years, 25.2 ± 2.7 kg/m2) consumed ∼3 mg/kg of caffeine received as caffeine, caffeine as placebo, placebo as placebo and placebo as caffeine. Parasympathetic modulation was assessed by heart rate variability (HRV-Poincaré SD1 index) at supine and orthostatic positions, during a submaximal exercise (HRV threshold-HRVT) and during each 60 seconds (s) within 300 s of post-exercise active recovery. A factorial ANOVA for repeated measures (p < 0.05) was used to assess the effect of caffeine, expectancy and resting time after caffeine intake on the HRV. No significant effect of caffeine or expectancy was observed on the SD1 value at supine or standing positions (p = 0.47-0.53; p = 0.57-0.31, respectively), despite an increase in this variable after resting periods in both positions (p < 0.001). During exercise, caffeine and expectancy do not alter the HRVT (p = 0.51-0.39). However, higher SD1 values were observed after caffeine administration from 60 to 300 s post-exercise recovery (p = 0.01-0.05) but not for the effects of expectancy (p = 0.19-0.94). We concluded that low doses of caffeine or expectancy do not alter the resting cardiac parasympathetic modulation or HRVT. However, caffeine, but not expectancy, increases parasympathetic reactivation after a submaximal exercise test in young men.

Impact of heart rate on reproducibility of heart rate variability analysis in the supine and standing positions in healthy men

OBJECTIVE: The reliability of heart rate variability (HRV) analysis is not yet fully understood, especially considering different body positions and the mathematical influence of heart rate. The aim of this study was to evaluate the reliability of HRV in supine and standing positions, with and without mathematical adjustment of HRV by the average R-R interval (iRR). METHODS: We evaluated 37 young males (23.1±4 years; 25.1±3 kg/m2). A 5-min segment of the iRR was collected in the supine and standing positions on three occasions separated by 48-hour intervals. Absolute and relative reliability of temporal and spectral indices were assessed by the coefficient of variation (CV) and the intraclass correlation coefficient (ICC), respectively. RESULTS: We did not observe differences in HRV indices in the three occasions in the supine or standing position (p>0.05). Moderate to good reproducibility was observed for temporal and spectral indices of HRV in the supine position (ICC: 0.65-0.89; CV: 0.9-19.8). In the orthostatic position, low to good reproducibility was observed (ICC: 0.35-0.89; CV: 1.1-34.8), with higher ICCs for temporal indices. After mathematical adjustment, only a small modification in HRV reliability was observed in both positions. CONCLUSIONS: In young adult males, the mathematical adjustment of HRV by the average iRR led to a nonsignificant effect on HRV reliability. Additionally, HRV reliability is dependent on body position and the index analyzed. Promising measures in both supine and standing positions include r-MSSD and the HF band (parasympathetic indices).