Sleep quality in athletes under normobaric hypoxia equivalent to 1500 m altitude: A polysomnographic study

In the present study, we evaluated the duration of slow-wave sleep (Stage 3 and 4) and total delta power (<3Hz) in all-night non-rapid eye movement (NREM) sleep electroencephalograms (EEGs) of athletes during normobaric hypoxia at simulated altitudes of 1500 m. Seven male athletes slept for two nights in a normoxic condition and one night in an hypoxic condition equivalent to an altitude of 1500 m. Whole-night polysomnographic recordings, thoracic and abdominal motion, nasal and oral airflow, and blood oxygen saturation (SpO₂) were recorded. Visual sleep stage scoring and fast Fourier transformation analyses of EEG were performed using 30-s epochs. Mean and minimum SpO₂ decreased significantly during sleep in the hypoxic condition. Between groups, changes in heart rate, respiratory disturbance measures including apnoea and hypopnoea, slow-wave sleep and total delta power of the all-night NREM sleep EEG were small and non-significant for the hypoxic condition_. However, individual difference in time at an SpO₂ below 90% were large in the hypoxic condition, and both slow-wave sleep and total delta power of all-night NREM sleep EEG decreased in three participants who spent a prolonged time below 90% SpO₂. The present results suggest that monitoring time below 90% SpO₂ is recommended when studying individuals' living-high schedule even under hypoxic conditions equivalent to an altitude of 1500 m.