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Altitude Decompression Sickness between 6858 and 9144 m Following a 1-h Prebreathe

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The zero prebreathe altitude threshold for developing 5 decompression sickness DCS symptoms in men has been reported to be 6248 meters 20,500 ft. However, such an altitude threshold when 1 hour of oxygen prebreathe is used has not been well-documented and was the primary purpose of this study. The 51 male subjects were exposed to 9144 meters 30,000 ft, 8382 meters 27,500 ft, 7620 meters 25,000 ft, andor 6858 meters 22,500 ft for 8 hours. They were monitored for symptoms of DCS and venous gas emboli VGE. The results showed that DCS symptom incidence after 4 hours of exposure decreased with exposure altitude from 87 at 9144 meters to 26 at 6858 meters. VGE were lower during the 4-hour, 6858-meter exposures 32 than at the higher altitudes 76-85. The symptom incidences during the first 4 hours of exposure were lower at 6858 meters and 7620 meters following a 1-hour prebreathe as compared with analogous zero-prebreathe exposures. There were no differences between incidences of VGE or DCS at any of the four altitudes after 8 vs. 4 hours of exposure. The overall results show that the altitude threshold for 5 DCS symptoms is below 6858 meters after 1 hour of prebreathe. However, during 6858-meter and 7620-meter exposures, a 1-hour prebreathe is highly beneficial in reducing DCS incidence and delaying the onset of DCS, keeping the incidence to less than 6 during the first 90 minutes of exposure. Use of 4-hour versus 8-hour exposures does not appear to underestimate DCS risk at or above 7620 meters. The data from this study also provided possible insight regarding the effects of exercise at 9144 meters on DCS incidence. The 87 DCS at 9144 meters during this study was higher than during other exposures to 9144 meters for the same duration, also with mild exercise and 1 hour of prebreathe, perhaps because the exercises used in this experiment involved more stress on the lower body than the mild exercises used in most of the authors experiments. 7

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  • Anatomy and Physiology
  • Medicine and Medical Research
  • Stress Physiology

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