Thermal stress modulates arterial pressure variability and arterial baroreflex response of heart rate during head-up tilt in humans.
To examine the effects of thermal stress on the blood pressure variability and the arterial baroreceptor-cardiac reflex during orthostatic stress, 11 male volunteers underwent whole body thermal stress using a cool or hot water-perfused suit during 5 min of 70 degrees head-up tilt (HUT). The spontaneous variability in arterial pressure was quantified by power spectrum analysis. The sensitivity of the arterial baroreceptor-cardiac reflex was calculated from the spontaneous changes in beat-to-beat arterial pressure and heart rate (fc). During supine rest the variability of arterial pressure decreased during cooling, while it remained unchanged during heating. The variability increased with HUT; it was greater (P < 0.05) with heating than with cooling. In the supine condition, the arterial baroreflex sensitivity of fc increased during cooling, while it did not change during heating. The sensitivities decreased (P < 0.05) with HUT during both thermal stresses; the decreased rate of sensitivity from the pre-tilt value was greater during heating [mean 63 (SEM 4)%] and smaller during cooling [mean 11 (SEM 24)%] than during normothermia [mean 47 (SEM 4)%] (both, P < 0.05). There were significant negative correlations between the sensitivities and the amplitude of the arterial pressure variability during normothermia and heating (P < 0.0001). The results suggest that the spontaneous baroreflex response of fc is a modulatory factor for the changes of arterial pressure variability brought about by thermal stress during orthostatic stress.
Yamazaki
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Department of Clinical Pathophysiology, School of Health Sciences, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, 807-8555 Kitakyushu, Japan. yamazaki@health.uoeh-u.ac.jp
Sone
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R
D000328:Adult; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology*; D005334:Fever / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D013312:Stress, Physiological / Q000503:physiopathology*; D018667:Tilt-Table Test