Epidemiology of decompression sickness under simulated space extravehicular activities

Several ground-based trials were conducted by NASA at the Lyndon B. Johnson Space Center, Houston, TX, during 1982-90 to examine the risk of altitude decompression sickness (DCS) during space extravehicular activities. There were 22 different pressure profiles involving single and staged decompression procedures, each lasting from 180 to 360 min at the final altitude. A total of 164 healthy subjects participated in 426 exposures to altitude. Symptoms of DCS occurred in 17% (74/426) and circulating microbubbles by precordial Doppler ultrasound were detected in 42% (179/426) of all exposures. About 27% (20/74) of exposures with symptoms resulted in test abort, and one-third of all test aborts required treatment in the hyperbaric chamber. There was about 3.20 times (95% Confidence Interval [95% CI] = 1.56-6.66) higher risk of symptoms in the presence of Doppler-detectable microbubbles. Examination of individual risk factors showed that there was about 4.3 times (95% CI = 1.62-11.50) higher risk of symptoms with increasing number of exposures. These findings emphasize the importance of evaluating risk factors from ground-based trials for application in operational decision-making and treatment strategies.