Jt. Webb et al., EXERCISE-ENHANCED PREOXYGENATION INCREASES PROTECTION FROM DECOMPRESSION-SICKNESS, Aviation, space, and environmental medicine, 67(7), 1996, pp. 618-624
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.