The Effect of Staged Decompression While Breathing 100% Oxygen on Altitude Decompression Sickness
Journal article, Feb 1990-Aug 1994
WYLE LABS LIFE SCIENCES AND SERVICES INC SAN ANTONIO TX
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Space Shuttle extravehicular activity EVA requires decompression from sea level pressure 14.7 psia to a 4.3 psia 30,300 ft pressure suit. The transition currently involves altering the shuttle atmosphere to allow shirt-sleeve denitrogenation to occur during a 12 to 36-h staged decompression SD at 10.2 psia 9,800 ft with an oxygen-enriched breathing gas 26.5 oxygen, 73.5 nitrogen. The denitrogenation provides protection from decompression sickness DCS during EVA in a 4.3 psia pressure suit. Our goal was to determine the highest altitude at which SD while breathing 100 oxygen SD100 could provide effective protection from development of DCS symptoms after further decompression to 29,500 ft 4.5 psia. There were 30 male subjects exposed to at least six of 11 conditions in random order on successive months to 29,500 ft for four hours while performing mild exercise and being monitored for venous gas emboli VGE with an echo-imaging system. The subjects received 15 min of ground-level GL preoxygenation and an additional 60 or 120 min of SD100 atone of four altitudes between 8,000 ft 10.9 psia and 18,000 ft 7.3 psia. Control exposures followed a 75-or 135-min ground-level preoxygenation. During SD100, one case of DOS occurred at 18,000 ft, but not at lower staging altitudes. Higher levels of VGE were observed during SD100 at 18,000 ft than during SD100 at any lower altitude. CONCLUSION Staged decompression at 16,000 ft and below results in decompression risk during subsequent decompression to 29,500 ft similar to that following equivalent periods of ground-level preoxygenation.
- Stress Physiology