Mild Hypoxia Reduces the Precision of Vestibular Perception

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The vestibular system – the organs in our inner ear that sense head motion and gravity – contribute to self-motion perception, balance control, and several reflexive responses. Maintaining robust vestibular sensation imposes a high metabolic load; consider that the human vestibular periphery has over 100,000 hair cells requiring energy to maintain depolarization and roughly 40,000 peripheral neurons requiring energy to support an average firing rate of nearly 100 action potentials per second for each neuron. Therefore, the aim of this study was to evaluate the impact of reduced oxygen (hypoxia) on the human vestibular system. To quantify the impacts of hypoxia, vestibular function was quantified using standard forced-choice psychophysical methods to determine the smallest earth-vertical (i.e., upward/downward) translation that a seated human could reliably sense. To manipulate blood oxygenation, we controlled the O 2 content of the air that participants breathed using a Reduced Oxygen Breathing Device 2 (Environics). To quantify blood oxygenation and pulse rate, we used a standard fingertip pulse oximeter. We hypothesized that: (1) blood oxygenation would decrease when breathing air with lower oxygen content, (2) human vestibular thresholds would worsen with reduced blood oxygenation, and (3) vestibular degradation would increase as blood oxygenation decreases. All data were collected at an elevation of ~800’. On different days, 15 participants breathed air with 20.9% or 15.4% oxygen content to simulate 0’ and 8,000’ altitudes respectively. As predicted, blood oxygenation (SpO2) reduced from an average of 96.7% when participants breathed air with 20.9% oxygen to 91.4% when breathing air with 15.4% oxygen content ( F (1,11) = 148.27, p <.001, Generalized eta squared = 0.770). Earth-vertical translation thresholds were significantly higher when breathing 15.4% oxygen than 20.9% oxygen ( F (1,14) = 22.49, p <.001, Generalized eta squared = 0.096). The largest threshold increase (median 41%; mean 33%) was observed in the 3 rd threshold test conducted 30 to 45 minutes after reducing O 2 content. Further, Type II linear regression showed that thresholds degraded as blood oxygenation decreased (R = -0.29). Despite these relatively large changes in perceptual precision, subjects reported no spatial disorientation illusions. These results show that vestibular thresholds were both significantly and substantively impacted at a simulated altitude of 8,000’. The significant correlation showing increasing thresholds with decreasing SpO2 suggests that decreases in tissue oxygenation may cause an increase in vestibular thresholds. These findings are noteworthy because the mild hypoxia condition was designed to match the cabin pressurization required in the US by the FAA for commercial flights. These results suggest that many of us who have flown in a commercial jet may have temporarily experienced degraded vestibular function. Behavioral impacts remain to be understood, but vestibular precision appears to be a harbinger of human hypoxia. Support provided by the Office of Naval Research (ONR) via a Multidisciplinary University Research Initiative grant (MURI N00014-20-1-2163). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

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