Cognitive Deterioration in Moderate and Severe Hypobaric Hypoxia Conditions

BACKGROUND: Hypoxia continues to present risks in military aviation. Hypoxia symptoms include sensory and cognitive effects; of these, it is important to identify which components of operator performance are most vulnerable to hypoxia-induced decline in order to determine which sensory modality is most effective for alerting an impaired aviator of an imminent hypoxic episode. METHODS: A study was performed in a hypobaric chamber to characterize deterioration of cognitive performance under moderate (MH) and severe (SH) hypoxia conditions, culminating in subjects' inability to perform tasks. Subjects operated a synthetic workstation, performing multiple simultaneous tasks during hypobaric exposures equivalent to 5486 m (18,000 ft) MH and 7620 m (25,000 ft) SH ascents. Performance was compared across baseline, altitude exposure, and recovery periods within MH vs. SH altitude profiles. Ascents lasted until at least one of a list of termination criteria was met, at which point the chamber was returned to ground level pressure and the subject resumed workstation performance during recovery. RESULTS: SH conditions generated greater deficits than MH conditions, and these more severe effects hastened the termination of exposures (5 vs. 18 min mean duration, respectively). Workstation performance collapsed rapidly on SH exposure, with Mathematics and Auditory Monitoring tasks proving vulnerable to breakdown. In MH exposures, these tasks exhibited impaired accuracy (declining 11% and 9%, respectively) and speed, with declines in Auditory Monitoring lingering into recovery. DISCUSSION: The relative robustness of memory and visual monitoring vs. the vulnerability of mathematical and auditory processing suggest that care should be taken designing purely auditory cockpit hypoxia warning alerts.