Lower leg fluid displacement during a simulated space shuttle launch.

Reductions in leg fluid volume of about 1/per leg or 10% of total leg volume have been reported during space flight. We wanted to test the hypothesis that a significant portion of these changes occur during the prelaunch and launch periods. Fluid volume changes in the lower leg were estimated in six men during a simulated Space Shuttle launch. After 2 h in the launch position, i.e. supine with elevated legs, the subjects were exposed to 500 s of two to three times increased g force in the anterio-posterior direction in a human centrifuge. During the prelaunch period one lower leg lost a mean of (113 SD 53) ml of fluid and there was little or no additional fluid reduction during the period of increased g force. This compares with the 178-ml reduction of lower leg volume that has been reported during the 1st day of Shuttle missions. We concluded that a significant portion of the fluid reduction observed in the lower leg during the early stages of space flight had already occurred before the launch.