A 10.2 psi staged-decompression schedule or a 4-hour preoxygenation at 14.7 psi is required prior to extravehicular activity (EVA) to reduce decompression sickness (DCS) risk. Results of recent research at the Air Force Research Laboratory (AFRL) showed that a 1-hour resting preoxygenation followed by a 4-hour, 4.3 psi exposure resulted in 77% DCS risk (N=26), while the same profile beginning with 10 min of exercise at 75% of VO2peak during preoxygenation reduced the DCS risk to 42% (P<.03; N=26). A 4-hour preoxygenation without exercise followed by the 4.3 psi exposure resulted in 47% DCS risk (N=30). The 1-hour preoxygenation with exercise and the 4-hour preoxygenation without exercise results were not significantly different. Elimination of either 3 hours of preoxygenation or 12 hours of staged-decompression are compelling reasons to consider incorporation of exercise-enhanced preoxygenation.

Aerospace Medicine↗

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Subject speech rates as a function of interviewer behaviour.

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Adolescent↗

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Preoxygenation time versus decompression sickness incidence.

Preoxygenation, breathing 100% oxygen prior to decompression, has been used for well over half of this century to reduce decompression sickness (DCS) incidence. Duration of preoxygenation has been reported to be inversely related to subsequent DCS incidence. A direct comparison of DCS incidence at 30,000 ft versus preoxygenation time is needed to allow better-informed decisions regarding the cost vs. benefit of increasing preoxygenation time to prevent DCS. To obtain such a comparison, we accomplished a retrospective study of exposures to 30,000 ft (226 mm Hg; 4.37 psia) while performing mild exercise. The 86 male exposures were preceded by preoxygenation times of one to four hours. Venous gas emboli (VGE) and DCS symptom development were monitored and recorded. Although more protection was demonstrated with increasing preoxygenation time, the cost-to-benefit ratio also increases with each additional increment of preoxygenation time. The diminishing return of increasing preoxygenation to reduce DCS would eventually impact mission planning and crew duty limitations. Alteration in the physiology of denitrogenation, such as inclusion of exercise during preoxygenation, may provide better and more cost-effective DCS protection than simply increasing preoxygenation time.

Aerospace Medicine↗