Oxygen consumption at altitude as a risk factor for altitude decompression sickness

The existence of a general influence of exercise on the incidence of decompression sickness (DCS) has been known for more than a half-century. However, quantification of the effect has not been done for several reasons, including isolation of exercise as the only variable. The DCS database at Brooks City-Base, TX, contains detailed physiologic information on over 3000 altitude exposures. The purpose of this study was to measure Vo2 during the activities performed during those exposures to retrospectively determine if Vo2, a quantifiable index of exercise intensity, was related to the level of reported DCS.

Ground-level activity was designed to duplicate the standardized activity during the altitude exposures. Breath-by-breath Vo2 was determined for each activity using a COSMED metabolic measurement system. Comparison of the Vo2 during four levels of activity performed under otherwise comparable conditions allowed a determination of correlation between Vo2 and DCS risk observed during the altitude exposures.

Four previous altitude exposure profiles at 8992 m to 9144 m (29,500 to 30,000 ft; 231 to 226 mmHg) for 4 h following a 1-h prebreathe resulted in 38-86% DCS. This study provided the Vo2 of activities during those studies. The correlation between DCS incidence and the highest 1-min Vo2 of activity was 0.89.

The highest 1-min Vo2 showed a high correlation with level of DCS risk. Future exposures involving lower levels of activity could provide data that would allow improvement in modeling of DCS risk.