Determination of a pressure breathing schedule for improving +Gz tolerance.

A base of empirical data for developing optimal pressure breathing during +Gz (PBG) schedules is lacking. Relaxed +Gz-intensity tolerance with PBG was measured during gradual +Gz-onset rate centrifuge profiles using standard lightbar criteria. Constant PBG levels ranging from 18-73 mm Hg were randomly assigned. G-suit pressure followed the standard or an increased inflation schedule. Nine subjects wore a jerkin, CSU-15/P G-suit, and TLSS helmet and mask. With mean mask cavity pressures of 0, 18, 38, 60, and 73 mm Hg, corresponding +Gz-tolerances (mean +/- S.E.M.) were: 5.3 +/- 0.2, 5.8 +/- 0.1, 6.6 +/- 0.2, 7.3 +/- 0.3, and 7.5 +/- 0.3 Gz (linear correlation, r = 0.994). Increased G-suit pressure did not change the +Gz-tolerance improvement with PBG. The inverse of individual subject regression slopes ranged from 22.6 to 58.1 mm Hg/+Gz. Considering additional factors and adequate +Gz protection for all subjects while relaxed, the proposed schedule would apply 42 mm Hg PBG/+Gz beginning at +3.3 Gz with a maximum pressure of at least 73 mm Hg.