LOWER LEG FLUID DISPLACEMENT DURING A SIMULATED SPACE-SHUTTLE LAUNCH

Reductions in leg fluid volume of about 1 l per leg or 10% of total le g volume have been reported during space flight. We wanted to test the hypothesis that a significant portion of these changes occur during t he prelaunch and launch periods. Fluid Volume changes in the lower leg were estimated in six men during a simulated Space Shuttle launch. Af ter 2 h in the launch position, i.e. supine with elevated legs, the su bjects were exposed to 500 s of two to three times increased g force i n the anterio-posterior direction in a human centrifuge. During the pr elaunch period one lower leg lost a mean of (113 SD 53) ml of fluid an d 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 Ist day of Shuttle missi ons. We concluded that a significant portion of the fluid reduction ob served in the lower leg during the early stages of space flight had al ready occurred before the launch.