The Consequences of Subsequent Exposures of Mild and Moderate Hypoxia on the Flight Profile

Abstract : Previous studies of hypoxia have largely examined different altitudes in isolation. Pilots, however, receive two sequential exposures during in-flight hypoxic emergencies (IFHEs): the initial exposure at altitude, followed by a second mild exposure after descending and removing the breathing mask. Conventional wisdom holds that performance recovers with blood oxygen saturation and that exposure to mild hypoxia is safe, but recent studies have challenged these assumptions. This study examined the possibility that the effects of moderate hypoxia may linger to overlap with the effects of mild hypoxia to increase performance deficits during sequential exposures such as those experienced by pilots during an IFHE. Participants performed a simulated flight task and secondary task while being exposed to normobaric hypoxia via the ROBD-2. We hypothesized that performance during exposure to mild hypoxia would be worse when preceded by a moderate hypoxic exposure than when mild hypoxia was experienced in isolation. Our hypothesis was partially supported: performance during exposure to 10,000 foot-equivalent altitude was worse when preceded by exposure to 25,000 foot-equivalent altitude, but we believe that this is most likely due to a failure to recover from the original moderate exposure rather than an additive effect between the exposures. Even so, our findings suggest that pilot impairment following an IFHE may be worse than previously believed.