The contributions of nocturnal hypoxaemia and sleep disturbances to acute mountain sickness

Abstract

Acute mountain sickness (AMS) is common after ascent to altitude, yet individual susceptibility remains difficult to predict and diagnosis relies on subjective report. Sleep disturbances and nocturnal hypoxaemia at altitude may provide insight, but their relationship to AMS is incompletely understood. In a sub‐study of a randomized, placebo‐controlled trial, 112 healthy, lowland‐dwelling volunteers rapidly ascended to 3810 m. AMS was assessed using the 2018 Lake Louise Scoring System (LLSS); sleep scores were recorded separately. Overnight monitoring used the WatchPAT300 device to measure oxygen saturation, oxygen desaturation index, respiratory disturbance index, apnoea–hypopnoea index and inferred sleep stage. Thirty‐eight participants (34%) developed AMS by the 2018 LLSS criteria. Compared with unaffected individuals, those with AMS had lower mean nocturnal , greater cumulative time with  < 70%, and higher oxygen desaturation index and respiratory disturbance index on nights 2 and 3. Respiratory disturbance indices improved only in participants without AMS, while AMS‐positive subjects demonstrated persistent reductions in estimated deep sleep, and higher self‐reported sleep disturbance scores. A sensitivity analysis applying 1993 LLSS criteria identified 64 subjects (58%) with AMS, and strengthened between‐group differences in nocturnal , but not respiratory indices. In exploratory multivariable analysis, cumulative time with   < 70% and first‐night sleep disturbance score at altitude remained independently associated with AMS. In summary, nocturnal hypoxaemia was associated with AMS status under both 2018 and 1993 criteria, while failure of respiratory index normalization and impaired sleep architecture are associated with AMS persistence, suggesting a longitudinal signal of failed acclimatization. These findings support further examination of sleep‐related metrics in relation to AMS assessment.