Tolerance of females to +GZ centrifugation before and after bedrest.

Because women may be included as passengers in the proposed Space Shuttle System, this study was designed to investigate the +GZ tolerance of women and the possible degradation of this tolerance after a period of weightlessness as simulated by bedrest. Twelve healthy Air Force Flight Nurses served as test subjects. Over a 1-week period, each subject was exposed to +GZ levels starting at +2 GZ and increasing by 0.5 GZ increments to a gray-out point. This point was determined by peripheral vision loss with a standard lightbar and by reverse blood flow in the temporal artery. Ultimately, each woman was subjected to three runs at the +3 GZ level; each run was approximately 55 min long, separated by 5-min rest periods. Eight subjects with the best tolerance times were selected for 14 d of bedrest in a horizontal position; the other four were ambulatory controls. Tests before bedrest, immediately following, and 5 d later showed that average +GZ tolerance decreased by 67% after bedrest.