Introduction
Poor sleep at high altitude is a well-described phenomenon and is associated with acute mountain sickness (AMS); however, large comprehensive studies characterizing sleep are lacking.
Objective
This study aims to better understand factors contributing to the observed poor-quality sleep.
Methods
We completed a descriptive analysis of the SLEEP-AID randomized controlled trial limited to the placebo arm (n=104 using resistance-free nasal strip, mean LLQ=1.86, 17% AMS incidence) and analyzed 52 participants with complete data. Minute-by-minute sleep data and oxygen saturation were acquired with WatchPAT-200 sleep monitors on the first night of trekking to 4371 to 4530 m altitude in Nepal.
Results
Participants were 70% male with an average age of 37 years (interquartile range [IQR] 27–48), and had mean 24-hour elevation gain of 448 m (IQR 380–550). Participants slept on average 477 minutes (IQR 442–517) with 11 awakening events (IQR 6–14). Their average sleep was 68% light sleep (IQR 63–78), 11% deep sleep (IQR 6–17), and 20% rapid eye movement (REM) sleep (IQR 15–24). Average sleep latency was 22 minutes (IQR 19–26) with REM latency of 104 minutes (IQR 63–119). They experienced an average of 275 desaturation events (IQR 105–399), in which oxygen saturation dropped below 80%, and spent 46% of the night below that threshold (IQR 11–84). All calculated sleep quality indices were profoundly abnormal: Respiratory Disturbance Index (mean 53, IQR 32–74), Apnea Hypopnea Index (mean 51, IQR 27–73), and Oxygen Desaturation Index (mean 37, IQR 14–54). All of these metrics (except % REM sleep) were significantly worse in participants with AMS prior to sleep than in those who did not have AMS (P<.05).
Conclusions
This study more accurately describes altitude-related sleep metrics contributing to poor sleep. There were a large number of nocturnal desaturation and awakening events likely contributing to the hypobaric hypoxic insult of sleeping at high altitude and accounting for the profoundly abnormal sleep indices.