EXERCISE-ENHANCED PREOXYGENATION INCREASES PROTECTION FROM DECOMPRESSION-SICKNESS

Introduction: Prevention of decompression sickness (DCS) during exposu re to altitude equivalents of 30,000 ft (9144 m) requires extensive de nitrogenation. In preparation for extravehicular activity (EVA), prese nt NASA policy is to denitrogenate using a 10.2 psia staged decompress ion of the entire shuttle for at least 12 h, including 100 min of preo xygenation (breathing 100% oxygen at 14.7 psia prior to decompression) , before decompression to the 4.3 psia (30,000 ft; 9144 m) suit pressu re. This staged decompression provides the same or better protection f rom DCS as a 3.5- or 4-h preoxygenation used on earlier Shuttle EVA's. For high altitude reconnaissance Rights at similar cockpit altitudes, a I-h preoxygenation is currently required. Methods: We have investig ated the use of a l-h and a 15-min preoxygenation period, each beginni ng with 10 min of dual-cycle ergometry performed at 75% of each subjec t's peak oxygen consumption (VO(2)peak) to enhance preoxygenation effi ciency by increasing perfusion and ventilation. Male subjects accompli shed a l-h preoxygenation with exercise, a 15-min preoxygenation with exercise, or a l-h resting preoxygenation before exposure to 4.3 psia for 4 h while performing light to moderate exercise. Results: Incidenc e of DCS following the l-h preoxygenation with exercise (42%; n = 26) was significantly less than that following the l-h resting preoxygenat ion (77%; n = 26). Incidence and onset of DCS following the 15-min pre oxygenation with exercise (64%; n = 22) was not significantly differen t from the incidence following the l-h resting control. Conclusion: Pr eoxygenation with exercise has been shown to provide significantly imp roved DCS protection when compared with resting preoxygenation.