Yamazaki Fumio, Yamauchi Katsuya, Tsutsui Yuka, Endo Yutaka, Sagawa Sueko, Shiraki Keizo
Department of Clinical Pathophysiology, School of Health Sciences, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, 807-8555 Kitakyushu, Japan.
Auton Neurosci. 2003 Jan 31;103(1-2):93-9. doi: 10.1016/s1566-0702(02)00140-6.
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 degrees. 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 degrees C at thermoneutral to 37.7 +/- 0.1 degrees C during heat exposure, whereas the left atrial diameter (LAD) decreased. Both the MSNA and HR increased (P < 0.05) during hyperthermia. The baroreflex slopes of MSNA and HR in the phase II decreased 30 +/- 8% (P < 0.05) and 24 +/- 9% (P < 0.05), respectively, during hyperthermia. The HDT increased LAD, but there was no change in HR, arterial pressure and the baroreflex slopes. These results suggest that hyperthermia reduces the baroreflex responses of MSNA and HR during a transient falling period of blood pressure. These reduced baroreflex responses may not be attributable to an unloading of the cardiopulmonary baroreceptors during heat stress.
本实验旨在研究全身加热对肌肉交感神经活动（MSNA）和心率（HR）压力反射控制的可能影响。九名健康男性志愿者在使用热水灌注服暴露于热应激期间进行了瓦尔萨尔瓦动作。为排除高温期间心肺压力感受器卸载的影响，通过8度头低位倾斜（HDT）来平衡中心血容量不足。在瓦尔萨尔瓦动作的II期早期（血压下降期），通过回归分析确定MSNA和HR相对于平均动脉压的压力反射斜率。核心温度从热中性时的36.9±0.1℃在热暴露期间升至37.7±0.1℃，而左心房直径（LAD）减小。高温期间MSNA和HR均增加（P<0.05）。高温期间，II期MSNA和HR的压力反射斜率分别下降30±8%（P<0.05）和24±9%（P<0.05）。HDT增加了LAD，但HR、动脉压和压力反射斜率无变化。这些结果表明，高温在血压短暂下降期间会降低MSNA和HR的压力反射反应。这些压力反射反应降低可能并非归因于热应激期间心肺压力感受器的卸载。
