Body volume changes during simulated microgravity I: Technique and comparison of men and women during horizontal bed rest.

It has been hypothesized that many of the adaptive processes that occur in man during exposure to microgravity involve the rapid headward shift of fluids during the first few hours of spaceflight. Impedance plethysmography was used to measure lower body volume changes in men and women during horizontal bed rest simulated microgravity. Segmental volumes calculated from the leg impedance values are compared to similar volumes determined from detailed anthropometric measurements. The results of this experiment indicate that men and women respond differently to bed rest and that impedance plethysmography can be used to quantify the extent of fluid redistribution in the body during actual or simulated microgravity in a manner that corresponds well with anthropometric determinations.