EFFECTS OF PROLONGED BED REST ON PHYSIOLOGICAL FUNCTIONS AND COUNTER-MEASUREMENT AGAINST THE EFFECTS IN HUMAN SUBJECTS

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To investigate the effects of prolonged bed rest on human physiological conditioning, total 29 young subjects (18 males, 11 females) had been studied before and after 20 days of horizontal bed rest (BR) for 3 years period since 1992. The results of measured variables after BR as compared before BR were as following : (1) Despite unchanged body weight body fat mass increased, and muscle mass of lower body, specially antigravity muscle mass, was decreased as well as the muscle strength. (2) Maximal oxygen uptake, and cardiac output (CO) and stroke volume (SV) during both supine exercise and upright exercise with mild-moderate intensities were decreased, but maximal heart rate (HR) was unchanged and mechanical efficiency was increased. (3) supine resting left ventricular end diastolic diameter (LVDd) was decreased as well as the SV in order to the increased HR,while the oxygen uptake was slightly decrease and CO and arterial blood pressure were unchanged. (4) LVDd during -40 mmHg lower bo … More dy negative pressure (LBNP) and orthostatic intolerance were decreased and the HR increased. However, despite the decreased HR the orthostatic tolerance time reduced against LBNP was not improved by intravenous propranolol. The tachycardia exaggerated during LBNP after the BR could not be explained by changes in carotid, aortic, and cardiopulmonary reflexes or autonomous reactivity. (5) Neither arm nor venous compliance was changed by the BR.(6) Bone mineral density (BMD) of the lumber bone decreased after BR, and also urinary daily excretion of deoxtptridinoline increased at day 10 and declined at day 20. However, neither alkaline phosphataes nor tartarated-resistant acid phosphatase changed. The interrelation between resorption makers for bone matrix and peripheral monocyte of the cytokines interlocking 1 alpha and tumor necrosis factor alpha was unchanged. (7) plasma concentrations of total cholesterol, high density lipoprotein cholesterol, triglyceride, free fatty acid and apolipoprotein B were unchanged in fasting blood after BR,while apolipoprotain AI decreased from day 3 and remained the decrease until day 20. In the very low density lipoprotein fraction, triglyceride and cholesterol increased. In the lipolytic enzyme activity, lectin cholesterol acyltrasferase activity increased, lipoprotein lipase activity decreased, but hepatic triglyceride lipase activity was unchanged. (8) total glucose concentration summed during 75 g oral glucose tolerance test was unchanged, but the total insulin concentration increased after BR,and thus blood glucose/insulin ratio decreased. (9) The General Health Questionnaire increased, Zung' self-rating depression scale elevated after BR, and urinary excretion of 17-hydroxycorticosteroid increased at day 9. (10) Fluctuation of body action center of gravitational weight was increased and thus functions of maintaining standing position was reduced after BR.(11) An adjustment of deep sensation to knee angle might be lowered by the re Less