Space shuttle inflight and postflight fluid shifts measured by leg volume changes.

This is a study of the inflight and postflight leg volume changes associated with spaceflight on Space Shuttle missions. The results of this study show an inflight volume loss of 2 L from lower extremities, 1 L from each leg, representing an 11.6% volume change. The vast majority of this change appears to be a shift in body fluids, both intravascular and extravascular. The fluid shift occurs rapidly on Mission Day 1 (MD-1), with it being essentially complete by 6 to 10 h. The regional origin of shift and leg volume change shows a far greater absolute volume (708 ml vs. 318 ml) and percentage (69% vs. 31%) of the total change coming from the thigh as compared to the lower leg. Postflight, the return of fluid to the lower extremities occurs rapidly with the majority of volume return complete within 1.5 h postlanding. At 1 week postflight there is a residual leg volume decrement of 283 ml or 3.2% that is probably due to tissue loss secondary to atrophic deconditioning and weight loss.