Hypoxia increases vertical translation thresholds in patients with unilateral vestibular hypofunction

Hypoxia when breathing air with the percentage of inspired oxygen (% O₂) reduced has been shown to diminish sensory, motor, and cognitive function. We recently showed that hypoxia experienced while inspiring air with 15.4% O₂ decreased sensitivity to upward and downward motions (Z-Translations). Here, we follow-up with similar Z-Translation perceptual threshold testing in 5 patients with unilateral vestibular hypofunction. All testing was completed at an altitude of 820 ft (249 m). Each patient completed Z-Translation vestibular threshold testing with inspired % O₂ set to 20.9%, 17.9%, 16.6%, and 15.4% to mimic the effects of altitudes of 820 ft, 4000 ft, 6000 ft, or 8000 ft (249 m, 1219 m, 1828 m, or 2438 m), respectively. Z-Translation thresholds significantly increased in the hypoxic conditions (F (3,88) = 8.29, p = 6.48 × 10^-5). Further, greater reductions in peripheral oxygen saturation (SpO₂) significantly predicted higher Z-Translation thresholds (estimated slope = 0.67 cm/s/%, t (73.37) = -2.83, p = 0.006). These results provide evidence that sensing whole-body motion is susceptible to hypoxia. Extra precautions and countermeasures may be warranted for people experiencing mild reductions in blood oxygenation - especially patients with vestibular hypofunction - while performing tasks that require balance and/or accurate and precise spatial orientation.