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Physiological equivalence of normobaric and hypobaric exposures of humans to 25,000 feet
- ""Introduction : Skepticism exists whether normobaric and hypobaric hypoxic exposures are equivalent. We have evaluated if physiological differences between the two environments would translate into actual differences in hypoxia symptoms. Methods : We exposed 20 subjects to 5-min 25,000 ft (7620 m) equivalent environments in an altitude chamber and then in a ground-level portable reduced-oxygen training enclosure (PROTE). Heart rate and hemoglobin oxygen saturation (SAO₂) were continuously monitored. Alveolar gas samples were collected at 1-, 3-, and 4-min elapsed time. Subjects completed hypoxia symptom questionnaires at the same time points. Results : Mean 4th min alveolar oxygen tension (P [subscript] AO₂), alveolar carbon dioxide tension (P [subscript] AO₂), and respiratory quotient (RQ) differed significantly between the chamber and PROTE. Declines in SAO₂ appeared biphasic, with steepest declines seen in the first minute. Rates of SAO₂ decline over the 5-min exposure were significantly different. Heart rate was not different, even when indexed to body surface area. Mean number of hypoxia symptoms between hypobaric and normobaric environments after 1 min were significant. However, the temporal pattern of symptom frequencies across subjects between the chamber and PROTE were similar. Conclusions : Alveolar gas composition, as well as arterial hemoglobin oxygen desaturation patterns, differed between a ground-level and hypobaric exposure. Differences in mean number of hypoxia symptoms between hypobaric and normobaric environments after 1 min, but not at 3 and 4 min, coupled with similar patterns in symptom frequencies, suggest that ground-level hypoxia training may be a sufficiently faithful surrogate for altitude chamber training."--Report documentation page."
- "Physiological equivalence of normobaric and hypobaric exposures of humans to 25,000 feet"
- "Physiological equivalence of normobaric and hypobaric exposures of humans to 25,000 feet"@en