Breathing 100% oxygen compared with 50% oxygen: 50% nitrogen reduces altitude-induced venous gas emboli.

The risk of venous gas emboli (VGE) and decompression sickness (DCS) must be determined before selection of the lowest pressure for an extravehicular activity (EVA) pressure suit which eliminates the requirement for prebreathing. In earlier studies, use of a 50% oxygen:50% nitrogen breathing mixture (50:50 mix) during 139 zero-prebreathe decompressions of male subjects to 8.3-7.8 psia resulted in 51 instances of severe VGE and one case of DCS. Our current study investigated effects of 40 zero-prebreathe decompressions of male subjects to 8.3-6.8 psia for 6 h while breathing 100% oxygen and performing moderate exercise. No DCS symptoms were observed. Severe VGE were not detected at 8.3 psia, but were present during 10%, 20%, and 40% of the exposures at 7.8, 7.3, and 6.8 psia, respectively. Zero-prebreathe decompression while breathing 100% oxygen results in significantly lower VGE and DCS risk levels than while breathing a 50:50 mix. Our results show that 7.3 psia EVA pressure suits with 100% oxygen should be safer than 8.3 psia suits with a 50:50 mix.