Physiological equivalence of normobaric and hypobaric exposures of humans to 25,000 feet (7620 m).

Introduction: Skepticism exists about 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 chami ber and then in a ground-level portable reduced-oxygen training enclosure (PROTE).