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KMID : 0608619950050020088
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Korean Journal of Aerospace and Environmental Medicine
1995 Volume.5 No. 2 p.88 ~ p.96
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Changes in Cardiovascular and Hormonal Responses to Head-up Tilt Following 3 Hours of Sipine Bed-rest
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Jae-Hoon Bae
Won-Kyun Park
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Abstract
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Cardiovascular and hormonal responses to 20 min of 70° head-up tilt(HUT) were observed in 12 young men following 3 hrs supine bed-rest(BR protocol) and 30 min(control protocol). We measured arterial blood pressure and parameters of cardiac function before and during the HUT. Vasoactive and volume-regulating hormones and hematocrit were also measured. During HUT, 4 subjects in BR protocol developed presyncopal signs or syncope and terminated the HUT(intolerant subjects), whereas none developed in the control protocol. In intolerant subjects of BR protocol, stroke volume, end-diastolic volume, and systolic and mean arterial blood pressure decreased more than in control protocol during HUT, but heart rate, hematocrit and plasma renin activity increased more significantly. Plasma epinephrine, renin activity and actidiuretic hormone tended to increase with onset of syncopal state, but plasma norepinephrine as a marker of sympathetic nervous activity did not show a difference between control and BR protocols. In summary, the 3 hrs BR could increase the occurrence of orthostatic intolerance with the primary cause being the decrease in venous return induced by the blood pooling into lower parts of the body rather than the alteration in sympathetic nervous regulation.
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KEYWORD
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Head-up, tilt, Supine bed-rest, Orthostatic intolerance,
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