Whole body heating reduces the baroreflex response of sympathetic nerve activity during Valsalva straining

Abstract The present experiment was carried out to examine the possible effects of whole body heating on the baroreflex control of muscle sympathetic nerve activity (MSNA) and heart rate (HR). Nine healthy male volunteers underwent the Valsalva maneuver during exposure to heat stress using a hot water-perfused suit. To exclude an effect from the unloading of the cardiopulmonary baroreceptors during hyperthermia, the central hypovolemia was counterbalanced by head-down tilt (HDT) at 8°. The baroreflex slopes of MSNA and HR against mean arterial pressure were determined by regression analysis during the early phase II (falling blood pressure period) of the Valsalva maneuver. The core temperature increased from 36.9±0.1 °C at thermoneutral to 37.7±0.1 °C during heat exposure, whereas the left atrial diameter (LAD) decreased. Both the MSNA and HR increased ( P P P