Physiologic validation of a short-arm centrifuge for space application

A short-arm centrifuge (SAC) of 5-6 ft (1.5-1.8 m) radius may be useful in space to measure tolerances to acceleration (G) and to stimulate the cardiovascular system, thereby reducing cardiovascular decompensation that occurs in weightlessness. Relaxed rapid (1G/s onset rate, ROR) and gradual (0.1 G/s onset rate, GOR) G tolerances were measured on seven men using a 5-ft (1.5 m) radius centrifuge and compared with their G tolerances obtained on the 20-ft (6.1 m) radius human-use centrifuge at the Armstrong Laboratory, Brooks AFB, TX. Since the subjects were required to flex their legs to assume a squatting position on the SAC, a similar position was used on the 20 ft (6.1 m) centrifuge called feet up (FU), and compared with normal-seated +Gz tolerances (controls). The subjects tolerated the SAC exposures without any problems. ROR and GOR tolerances were as follows: control, 3.6 G and 4.2 G; FU, 4.5 G and 5.6 G; and SAC, 4.6 G and 6.4 G. We concluded that a 5-ft radius centrifuge can be used to measure G tolerances. The increases in the SAC GOR tolerances over ROR tolerances indicate that the baroreceptors were stimulated by the G, and the SAC exposure would be useful in preventing cardiovascular decompensation in microgravity.