Carotid baroreflex control of heart rate during acute exposure to simulated altitudes of 3,800 m and 4,300 m.
To examine the baroreflex response in humans during acute high-altitude exposure, the carotid baroreflex cardiac responsiveness was studied using a neck chamber in seven unacclimatized male subjects. Measurements were made in a high-altitude chamber on separate days at sea level and during 1-h exposure at two different altitudes of 3,800 m [partial pressure of oxygen in inspired air (PI(O2)) = 90 mmHg] and 4,300 m (PI(O2) = 82 mmHg). R-R intervals were plotted against neck chamber pressures, and the baroreceptor response was analyzed by applying a four-parameter sigmoidal logistic function. The baroreceptor response curve shifted downward in either altitude, reflecting a tachycardic response at high altitude, and the magnitude of the shift was greater at 4,300 m than at 3,800 m. There was no change in the sigmoidal parameters at 3,800 m compared with sea level except for a reduction (P < 0.05) of the minimum R-R interval. At 4,300 m the maximal R-R range, slope coefficient, minimum R-R interval, and maximal gain of the curve decreased significantly (P < 0.05) compared with sea level values, whereas the centering point of the curve remained unchanged. These results suggest that hypoxia (PI(O2) = 82 mmHg) reduces the sensitivity of carotid baroreflex cardiac response.
Sagawa
S
S
Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
Torii
R
R
Nagaya
K
K
Wada
F
F
Endo
Y
Y
Shiraki
K
K
D000328:Adult; D000531:Altitude; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D002339:Carotid Arteries / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D009051:Mountaineering / Q000502:physiology; D010100:Oxygen / Q000097:blood; D013997:Time Factors
D010100:Oxygen