The effect of voluntary hypocapnic hyperventilation on thermoregulatory responses in exercising humans

Abstract

We tested the hypothesis that voluntary hypocapnic hyperventilation (VHH) attenuates thermoregulatory responses in exercising humans. 10 healthy active males performed cycling exercise at 120W (30°C, 50%RH) during 1) spontaneous breathing, 2) eucapnic voluntary hyperventilation, and 3) VHH. Cutaneous vascular conductance was evaluated as cutaneous red blood cell flux measured by laser‐Doppler flowmeter/mean arterial blood pressure at forearm (CVCforearm) and forehead (CVCforehead). Forearm sweat rate was measured by ventilated capsule method. Our results indicated that esophageal temperature (Tes) threshold for increases in CVCforearm and CVCforehead was significantly or tended to be higher, while slope relating Tes with CVCforearm was significantly or tended to be lower in VHH than in the other two conditions. Neither Tes threshold nor slope for sweat rate was different among conditions. These results suggest that in exercising humans, although VHH does not affect sweat response, it attenuates cutaneous vasodilation response, and this attenuation is greater for forearm than forehead skin.This study was supported by grants from the Ministry of Education, Science, and Culture of Japan. N. Fujii is the recipient of a research fellowship for young scientists from Japan Society of the Promotion of Science.