The Influence of Hydration Status on Heat Rate Variability After Exercise Heat Stress
ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA THERMAL AND MOUNTAIN MEDICINE DIVISION
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While exercise heat stress and hydration status are known to independently influence heart rate variability HRV, the combined effect of these physiological stressors is unknown. Thus, heat-acclimated subjects t 5 performed exercise heat trials 40 deg C, 20 relative humidity in the euhydrated and hypohydrated state 3.9 or - O.7 body weight loss. During each trial, cardiac cycle R-R interval data were collected for 45 min at rest pre- and after post- completing 90 min of cycle ergometer exercise. Pre- and post-exercise RRI data were analyzed by Fast Fourier Power Spectral analysis to determine the high-frequency HF, low-frequency LF, very low-frequency VLF, and total power TP components of HRV. Overall HRV was decreased by both hypohydration and exercise heat stress. Hypohydration reduced TP, LF, VLF, and LFHF ratio Po.05 while HF was significantly higher. The change in both LF and HF power pre- vs. post-exercise were blunted during hypohydration compared to euhydration. These data suggest that dehydration alone positively influences the parasympathetic HF control of HRV, but the reduction in overall HRV and the blunted oscillations in LF and HF power following exercise heat stress support an overall deleterious effect of dehydration on autonomic cardiac stability. Published by Elsevier Ltd.
- Stress Physiology