Vestibular-evoked balance responses are blunted in lowlanders and Tibetan highlanders with ascent to 4,300 m.

Abstract

Hypoxia influences postural control and vestibular function. However, the vestibular control of standing balance at high altitude is poorly understood. Furthermore, Tibetan highlanders are physiologically adapted to high-altitude, but it is unclear if vestibular-driven signals for balance within this population acclimate differently than lowlanders with ascent. This study investigated vestibular-evoked balance responses in unacclimatized lowlanders and Tibetan highlanders at low altitude (1,400m) and after six- or seven-days of incremental ascent to high altitude (4,300m). Twenty-eight participants (15 lowlanders, 8F, 7M; 13 Tibetan highlanders, 7F, 6M) stood on a force plate facing forward with their eyes closed and underwent 90-second stochastic electrical vestibular stimulation trials at a peak-to-peak amplitude of ±2 or ±4 mA. Vestibular-evoked balance responses were quantified using cumulant density and coherence (0-5 Hz and 5-10 Hz) between electrical vestibular stimulation and mediolateral forces. With ±2mA stimulation, the peak-to-peak amplitude of vestibular-evoked balance responses decreased at high compared to low altitude for both groups (P=0.003). With ±4mA stimulation, only lowlanders showed a reduction in peak-to-peak amplitude at high altitude (P=0.03), and their responses were smaller than Tibetan highlanders at high altitude (P=0.046). For frequency-domain outcomes, lowlanders exhibited a smaller 0-5 Hz coherence area at high compared to low altitude with ±2mA stimulation (P=0.002), whereas Tibetan highlanders showed no change. No differences in coherence area were observed in either group with ±4mA stimulation. These findings indicate that while the vestibular control of balance is blunted at high altitude for lowlanders and highlanders, the altitude effect is greater in lowlanders.