Time course of recovery from acute hypoxia exposure as measured by vigilance and event-related potentials.

Exposure to reduced levels of breathable oxygen is known to cause a number of deleterious effects on human performance. Previous work has demonstrated that in healthy adults, hypoxia results in decrements on a wide range of sensory, cognitive, and motor tasks. However, very little is known about the time course of recovery of cognitive functions following a hypoxic exposure. While previous studies have shown that physiological responses like heart rate and oxygen saturation rebound almost immediately, one previous study has shown a delayed recovery for response time (RT) measures following hypoxia. In the current study, we assessed the time course of neurocognitive recovery following a hypoxic exposure in healthy adults using the psychomotor vigilance task (PVT), passively elicited event-related potentials (ERPs) that assess auditory processing, and physiological measures. We also compared whether speed of recovery differed when participants were provided with 21% or 100% oxygen immediately following hypoxic exposure. Participants underwent a baseline testing session and two separate recovery sessions where they were assessed during a hypoxic exposure and at regular intervals for up to four hours post-exposure. Results demonstrated that RT, as measured by the PVT, significantly slowed during hypoxia compared to baseline and continued to be impaired until 60 min post-exposure. We assessed the mismatch negativity (MMN) and P3a ERP components in response to an auditory oddball paradigm and found a significant reduction in the amplitude of the MMN during hypoxia compared to baseline and that attenuation in amplitude persisted for up to 120 min post-exposure. Together, these results indicate that both RT and auditory processing showed a delayed recovery following hypoxia. We found no strong evidence for differential recovery speed based on recovery gas administered (21% versus 100% oxygen). These results have implications for guidance regarding return-to-duty status for military aviators following a hypoxic exposure.