EFFECT OF HYPOXIA AND HYPEROXIA ON HUMAN +G(Z) DURATION TOLERANCE

To determine the effects of varying inspired O-2 on positive radial ac celeration (+G(z); i.e., head-to-foot inertial load) duration toleranc e, seven men were exposed to the +4.5- to +7.0-G(z) simulated aerial c ombat maneuver (SACM) by use of the Armstrong Laboratory (Brooks Air F orce Base) centrifuge. Exposures were repeated on different days while subjects breathed gas mixtures of fractional concentration of O-2 in inspired air (FIO2) between 0.12 and 0.6. SACM duration tolerance was positively related to inspired O-2 of FIO2 between 0.12 and 0.2 but wa s unchanged at FIO2 between 0.2 and 0.6. SACM exposure decreased arter ial O-2 saturation and increased heart rates; SACM-induced changes wer e additive to FIO2 effects. The positive relationship between blood la ctate and SACM duration tolerance at all FIO2 indicated an anaerobic c omponent. It is concluded that SACM duration tolerance is limited by r educed FIO2 but not enhanced by hyperoxia. Thus the aerobic component of +4.5- to +7.0-Gz SACM duration tolerance is much greater than previ ously believed.