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A mechanism for the reduction in risk of decompression sickness in microgravity environmentThere is an apparent reduction in the incidence of decompression sickness reported by astronauts (from both the USA and the USSR) during extravehicular activity (EVA). The expected incidence, based on studies conducted under unit gravity conditions in Earth-based laboratories, is greater than that encountered during EVA. A biophysical explanation has been proposed for this difference based upon the mechanism of stress-assisted nucleation. Since the partial pressure ratio at which this gas phase forms is considerably smaller in living systems that in quiescent in vitro models, it was proposed that mechanical forces are involved. In that the lower extremities of astronautics are not gravitationally loaded in microgravity, it is possible that tissue gas micronuclei are but minimally regenerated. Most likely, gas micronuclei formed on Earth (by ambulation under 1 g conditions) would be eventually depleted. In a crossover study, 20 individuals were decompressed--from 1 ATA to 0.43 ATA for 3 hours--following either being fully ambulatory at unit gravity or following being hypokinetic and adynamic (simulated microgravity of 3-day bed rest). The subjects were monitored for gas phase formation by means of precordial Doppler monitoring. The results indicate a reduction in whole body gas phase formation in individuals who were bed rested as compared with themselves when fully ambulatory (p = 0.02). In hypokinetic individuals, the protection conferred was equivalent to an extra 175 minutes of oxygen prebreathe. These results are compatible with a hypothesis relating stress-assisted nucleation to the continual formation of tissue gas micronuclei and their gradual depletion with hypokinesia.
Document ID
Document Type
Conference Paper
Powell, Michael R. (Space Biomedical Research Inst. Houston, TX, United States)
Date Acquired
September 6, 2013
Publication Date
February 1, 1993
Publication Information
Publication: NASA. Johnson Space Center, Sixth Annual Workshop on Space Operations Applications and Research (SOAR 1992), Volume 2
Subject Category
Distribution Limits
Work of the US Gov. Public Use Permitted.

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IDRelationTitle19940007055Analytic PrimarySixth Annual Workshop on Space Operations Applications and Research (SOAR 1992), volume 2