Cognitive and perceptual deficits of normobaric hypoxia and the time course to performance recovery.

BACKGROUND

Many in-flight hypoxia-like incidents involve exposure to normobaric hypoxia following an oxygen delivery equipment failure. Studies have documented the effect of hypoxia on specific aspects of human performance. The goal of the present study was to establish the effects of acute hypoxia on cognitive, psychomotor, and perceptual abilities and to chronicle the time required for these capabilities to fully recover to pre-exposure levels.

METHODS

Subjects were presented with a battery of tests designed to assess visual acuity, contrast sensitivity, color vision, executive control, and reaction time (simple reaction time, SRT, and choice reaction time, CRT) before, during, immediately following, 60 min, 120 min, and 24 h after hypoxic exposure. Oxygen saturation was continuously measured throughout the duration of the study using near-infrared spectroscopy measured on the forehead and finger pulse oximetry.

RESULTS

During the course of six assessment periods, contrast sensitivity, color vision, and subjective workload were affected to varying degrees during hypoxic exposure, but returned to baseline levels soon after a return to normoxia. Conversely, reaction time values and regional cerebral oxygen saturation (MrSO2), while also affected during hypoxic exposure (MSRT = 362.17 ms, MCRT = 389.55 ms, MrSO2 = 79.36%), did not return to baseline levels (MSRT = 337.35 ms, MCRT = 372.75 ms, MrSO2 = 99.75%) until the assessment period 24 h following exposure (MSRT = 324.35 ms, MCRT = 366.22 ms, MrSO2 = 99.10%).

DISCUSSION

Evidence from this study suggests an impairment of specific performance characteristics following hypoxic exposure - some for a considerable period of time. Mitigation efforts should focus more on the prevention of hypoxia exposure rather than relying exclusively on training operators to recognize and react earlier to hypoxic symptomology.