Factors affecting human tolerance to sustained acceleration.

Linear increases in G tolerance with increases in anti-G suit (AGS) bladder inflation pressure occurred when relaxed subjects were exposed to acceleration plateaus while riding a centrifuge and were either seated upright, (15 degrees seat back angle or SBA) or supine (60 degrees SBA). Supine G tolerance with AGS bladder inflation decreased as G onset time was increased by factors of two and four. Changing the mode of operation of a new servo-controlled anti-G valve regulating AGS bladder pressure had no effect on G tolerance nor on AGS comfort scores. Comfort was unaffected by G onset time and reduced with high AGS bladder pressures. Results support the hypotheses that G protection provided by simultaneously applied anti-G techniques is additive and that the simple hydrostatic model of the circulatory system can adequately account for AGS bladder pressure changes required for G protection when body position is changed.