Spontaneous arterial baroreflex control of the heart rate during head-down tilt in heat-stressed humans.
The purpose of this study was to elucidate the effect of raised body temperature per se during acute heat stress on the spontaneous arterial baroreflex control of heart rate (fc) in humans. To investigate whether unloading of cardiopulmonary baroreceptors during whole-body heating would alter the arterial baroreflex control of fc, we controlled loading of the cardiopulmonary baroreceptors by head-down tilt (HDT) at angles of 5 degrees, 10 degrees, 15 degrees, and 30 degrees during heat stress produced by hot-water-perfused suits. The sensitivity of the arterial baroreceptor-cardiac reflex was calculated from the spontaneous changes in beat-to-beat arterial pressure and fc. As an index of cardiopulmonary baroreceptor loading, the left atrial diameter (LAD) was measured by echocardiography. During whole-body heating, the LAD decreased with the rising body core temperature and increased with the HDT. The decreased LAD during heating almost recovered to the normothermic control level by 10 degrees HDT. In the supine position, cardiac baroreflex sensitivity remained unchanged during heating. Arterial pressure, fc and cardiac baroreflex sensitivity were not changed by HDT ranging from 5 degrees to 30 degrees during heating. These results suggest that cardiac baroreflex sensitivity remain unchanged during graded loading of the cardiopulmonary baroreceptors in heat-stressed humans. Also, we conclude that the sensitivity of the spontaneous arterial baroreflex controlling the fc is not influenced by raised body temperature per se during acute heat stress.
Yamazaki
F
F
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
Matsumura
F
F
Nagata
J
J
Ando
A
A
Imura
T
T
D000328:Adult; D016275:Atrial Function; D017704:Baroreflex / Q000502:physiology*; D004947:Esophagus; D005260:Female; D018475:Head-Down Tilt / Q000502:physiology; D006321:Heart / Q000294:innervation / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D018882:Heat Stress Disorders / Q000503:physiopathology*; D006801:Humans; D008297:Male; D012039:Regional Blood Flow / Q000502:physiology; D012867:Skin / Q000098:blood supply