Mild hypoxia adversely impacts human vestibular function

Hypoxia has been found to adversely affect sensory function at altitudes above 3000 m, but sensory decrements have not been reported in peer-reviewed literature at or below 2400 m nor has research focused on the impact of hypoxia on human vestibular thresholds. These knowledge gaps are problematic, because the vestibular system has high metabolic needs and makes fundamental behavioral contributions. We hypothesized that mild hypoxia would impact vestibular function, which we tested by having participants breathe air with 15.4% O₂ to simulate an altitude of 2400 m (8000 ft)-mimicking the oxygen available on commercial aircraft. We measured earth-vertical translation thresholds and arterial oxygen saturation (SpO₂) and found that the average threshold increased by over 20% relative to thresholds measured while breathing air with 20.9% O₂, and that these threshold changes negatively correlated with changes in SpO₂. These findings suggest that vestibular changes provide a harbinger of hypoxia.