The effect of extended O2 prebreathing on altitude decompression sickness and venous gas bubbles

The purpose of this study was to determine the effect of extended O2 prebreathing on symptom and bubble incidence during decompressions simulating extravehicular activity. The 38 subjects breathed O2 for a 6-h period prior to decompression to 4.3 psi. The subjects performed upper body exercise for 6 h. Subjects were monitored with a Doppler bubble detector and were encouraged to report all symptoms. Eight subjects were exposed to the same protocol after an 8-h prebreathe. Venous bubbles were detected in 18 of 38 subjects decompressed after the 6-h prebreathe. Four of these subjects reported symptoms of altitude decompression sickness. No symptoms or bubbles were detected in the eight subjects who had prebreathed 8 h. The incidence of symptoms and bubbles when combined with prior data on 3.5- and 4.0-hour prebreathes showed an inverse correlation to pre-breathing time. The incidence of symptoms was higher than has been reported for subjects exposed to decompression of shorter duration with less activity.