[Sleep and respiration at an altitude of 6,400 m (Aconcagua, Argentina]

Persons at extreme altitudes are known to experience disturbances in the regulation of ventilation and sleep structure. However, except for simulated studies using the decompression chamber, only single events of sleep or ventilation were measured so far in field studies up to an altitude of 5800 m. Modifying a portable sleep lab (Vitalog HMS 5000), we were able to conduct 7 channel polygraphy on our ascent to the Aconcagua up to an altitude of 6400 m.

In 6 climbers (age 38-62 y, 1 f, 6 m), ECG, EOG, SaO2, chest and abdominal movements, breathing and snoring sounds, body position, nasal and oral airflow were measured 4 weeks prior to the expedition at an altitude of 500 m, at base camp (4200 m) and in 3 climbers at 6400 m (2nd base camp) at the Aconcagua mountain. All participants had a repeat study at 500 m altitude 4 weeks after the expedition.

The total number of obstructive apnoeas and hypopnoeas (OA/H) at night increased at an altitude of 4200 m in the mean of all 6 climbers from 36 to 67.7 compared to 500 m altitude, Central Apneas and Cheyne stokes (CA/CS) increased from 6.7 to 45.2. At 6400 m altitude the OA/H fell to 3 and 4 respectively in 2 climbers and CA to 1 and 2 respectively. In one climber, suffering from recurrent snoring with oxygen desaturation at 500 m altitude level, the number of OA/H and CA/CS increased further to 201 and 322, respectively, at 6400 m. Total sleep time including the REM position increased in all 6 climbers by 10% at base camp in comparison to an altitude of 500 m. Whereas the total sleep time remained constant in the 3 climbers at 6400 m altitude, the REM position declined by 10% in comparison to base camp (4200 m). However, significant fluctuations between individuals were noticed.

Although significant alterations in sleep and breathing are noticeable at altitudes above 300 m, the respiratory drive in healthy subjects provides for a regular ventilation at high frequency at the extreme altitude above 6000 m. Sleep-related breathing disturbances at low altitude appear to be amplified at high altitudes.