Hydroelectrolytic and hormonal modifications related to prolonged bedrest in antiorthostatic position
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Updated: Oct 4, 2026

Tilt Testing with Combined Lower Body Negative Pressure: a "Gold Standard" for Measuring Orthostatic Tolerance
Published on: March 21, 2013
Abstract:
The effects of prolonged bedrest in antiorthostatic position (-4 degrees head down) on electrolyte balance were studied in 4 young volunteers. An increase was noted in sodium excretion during the first 4 days. Plasma renin activity and plasma aldosterone varied in parallel manner during the same period. Potassium balance and creatinine clearance were not significantly modified. In light of these data we feel that prolonged bedrest in antiorthostatic position constitutes an effective way to simulate on earth metabolic and hormonal modifications occurring in man under weightlessness conditions.
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