Operation Everest II: Altitude decompression sickness during repeated altitude exposure.

The incidence of altitude decompression sickness (ADS) was studied in 23 altitude scientists during repeated altitude exposure to 15,000-29,000 ft (4572-8839 m) in a decompression chamber. Prior to each altitude exposure, a 30-60-mm pre-breathing period with 100% oxygen took place. Ascent was made to an altitude at a rate of 2000 ft X min-1. The altitudes studied ranged from 15,000-29,000 ft (4572-8839 m). Symptoms reported appear consistent with previous reports. Incidence of ADS at 26,000-29,000 ft (7925-8839 m) was 29.7%, during 274 chamber flights and 1264.6 h of altitude time. Incidence appeared related to frequency of exposure, severity of altitude, and physical activity. Incidence was not related to age, duration of exposure, or body index (weight/height 2). This high incidence of ADS reported in this study is similar to that reported by NASA.