The use of lower body negative pressure as a means of -Gz protection

The use of lower body negative pressure (LBNP) as a means of increasing negative (-Gz) tolerance was investigated. Ten subjects were seated at a zero-degree seatback angle with their heads outward away from the center of rotation in a human centrifuge. The subjects were exposed to -50 and -100 mm Hg gauge pressure, as well as to ambient pressure, while experiencing -1.0, -1.5, and -2.0 Gz plateaus for 30-s duration. The tests were conducted on the dynamic environment simulator, a three-axis man-rated centrifuge. Electrocardiographic data showed that significant decreases in heart rates occurred at -2.0 G_z with ambient suit pressure. Comparing the same -G_z level with -100 mm Hg, heart rates increased by 56%, indicating that blood was being pooled in the lower body during the -G_z exposure. In addition, subjective data indicated that subjects experienced a decrease in cephalad pressures with the aid of LBNP for all -G_z exposures. LBNP at pressures between -50 to -100 mm Hg appears to be a viable means of counteracting the adverse physiologic effects of -G_z acceleration