Altered breathing pattern of lowlanders sleeping at high altitude: Novel insights from home sleep apnoea tests procedures

Lowlanders sojourning at high altitude often experience sleep disturbances, which are driven by blood gases alterations and manifest as stress-related patterns, including frequent awakenings, apnoeas, reduction in sleep duration and possibly with the occurrence of periodic breathing. This study demonstrated clinical evidence of sleep disturbances at high altitude by using portable device during a Himalayan expedition. The home sleep apnoea test was conducted on 10 participants taking part in the "Lobuche Peak - Pyramid Exploration & Physiology". The longitudinal design included five assessments, before the expedition, at pre-expedition at Kathmandu (≈1400 m), at a peak altitude of ≈ 5000 m, upon return to Kathmandu and one month after return in Italy. Total sleep time was below 7 h of duration at the highest altitude in all participants. Nocturnal SpO2 dropped below daytime measurement and was greatly reduced at high altitude; conversely, heart rate increased. All participants experienced an increase in apnea-hypopnea index at high altitude, with seven out of 10 falling in moderate-to-severe grade. Periodic breathing pattern was clearly observed in two participants, of whom one developed acute mountain sickness and one did not. All the impairments were fully reversible once back at low altitude. Translationally, our findings underscore the importance of conducting home sleep apnoea tests at living altitude. Sleep-disordered breathing arises from a complex pattern that can be due to a wide range of responses, and the overall functions revealed by home sleep apnoea testing during a field expedition have the potential to increase the safety of high altitude sojourners, while advancing our knowledge of hypoxia as the red line linking respiratory and environmental physiology.