Submitted on January 2, 2008
Revised on June 17, 2008
Accepted on July 2, 2008
Effect of heavy exercise on spectral baroreflex sensitivity, heart rate and blood pressure variability in well-trained humans
François Cottin1*, Claire Médigue2, and Yves PAPELIER3
1 Laboratory of Exercise Physiology (LEPHE), University of Evry, E.A. 3872, Genopole, Boulevard F Mitterrand, F-91025 Evry cedex, France.
2 INRIA
3 Laboratory of Physiology
* To whom correspondence should be addressed. E-mail: francois.cottin{at}univ-evry.fr.
The aim of the study was to assess the instantaneous spectral components of heart rate variability (HRV), systolic blood pressure variability (SBPV) and determine the low frequency (LF) and high frequency-baroreflex sensitivity (HF-BRS) during a graded maximal exercise test. The first hypothesis was that the hyperpnea elicited by heavy exercise could entail a significant increase in HF-SBPV by mechanical effect once the first and second ventilatory thresholds (VTs) were exceeded. It was secondly hypothesized that, vagal tone progressively withdrawing with increasing load, HF-BRS could decrease during the exercise test. Fifteen well-trained subjects participated in this study. ECG, blood pressure and gas exchanges were recorded during a cycloergometer test. Ventilatory equivalents were computed from gas exchange parameters to assess VTs. Spectral analysis was applied on cardiovascular series to compute RR and SBP power spectral densities, cross spectral coherence, gain and alpha-index of BRS. Three exercise intensity stages were compared: below (A1), between (A2) and above (A3) VTs. From A1 to A3: both HF-SBPV (A1: 45±6; A2: 65±10; A3:120±23 mm2Hg, p<0.001) and HF-HRV increased (A1: 20±5; A2: 23±8; A3:40±11 ms2, p<0.02) maintaining HF-BRS (gain, A1: 0.68±0.12; A2: 0.63±0.08; A3: 0.57±0.09; alpha-index, A1: 0.58±0.08; A2: 0.48±0.06; A3: 0.50±0.09 ms.mmHg-1, NS). However, LF-BRS decreased (gain, A1: 0.39±0.06; A2: 0.17±0.02; A3: 0.11±0.01, p<0.001; alpha-index, A1: 0.46±0.07; A2: 0.20±0.02; A3: 0.14±0.01 ms.mmHg-1, p<0.001). As expected, once VTs were exceeded hyperpnea induced a marked increase in both HF-HRV and HF-SBPV. However, this concomitant increase allowed the maintenance of HF-BRS, presumably by mechano-electric feedback mechanism.
