Effects of oxygen pressure on baroreflex in humans

Research Project

Project/Area Number	04670103
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	環境生理学(含体力医学･栄養生理学)
Research Institution	Universtity of Occupational and Environmental Health, Japan
Principal Investigator	SAGAWA Sueko Department of Physiology, School of medicine, University of Occupational and Environmental Hearlth, Associate professor, 医学部, 助教授 (20035489)
Project Period (FY)	1992 – 1993
Project Status	Completed (Fiscal Year 1993)
Budget Amount *help	¥2,200,000 (Direct Cost: ¥2,200,000) Fiscal Year 1993: ¥1,000,000 (Direct Cost: ¥1,000,000) Fiscal Year 1992: ¥1,200,000 (Direct Cost: ¥1,200,000)
Keywords	Baroreceptors / Baroreflex / Neck chamber / R-R interval / 頚動脈圧受容器 / 筋交感神経活動
Research Abstract	The first studies were carried out to examine the effects of high altitude on cardiovascular responses to orthostasis. Eleven healthy males were tested at a 10 min passive 70ﾟ head-up tilt at sea level and at a simulated altitude of 3,700 m. Mean arterial pressure remained unchanged during head-up tilt at sea level(SL) but it reduced by 10 mmHg (P<0.05) at high altitude. Three subjects showed syncopal sign at altitude of 3,700 m and none of the subjects was able to tolerate a 70ﾟ head-up tilt for 15 min at altitude of 4,300 m. The second studies were conducted. therefore, to investigate further the effects of low oxygen pressure on carotid sinus baroreflex control of the cardiac interval in 8 healthy males. R-R interval response was measured during a sequence of neck pressure changes during held expiration at SL, altitudes of 3,800 m and 4,300 m, and was plotted as a funcion of the neck chamber pressure. Baroreflex response curve shifted to lower only at altitude of 4,300 m and maximal gain significantly reduced (P<0.05). Moreover, a shifted baroreflex response curve at altitude of 4300m returned to normal range during inhalation of oxygen (hypobaric normoxia). Above results suggest that an attenuated baroreflex control of cardiac interval at high altitude is related with the orthostatic hypotension.