[Exacerbation of obstructive sleep apnea syndrome at altitude 3,850 m]

Recently more people visit extremely high-altitude places for sightseeing or business. As a result, patients with obstructive sleep apnea (OSAS) also are likely to stay at such places. However the changes of severity of OSAS at extremely high-altitude are not certain. A 44-year-old man was given a diagnosis of OSAS in 2004 and had been using continuous positive airway pressure CPAP at night. On a visit to Nepal the severity of his OSAS was evaluated at Kyanjing Gompa (3,850 m) and at other places. At Kyanjing Gompa, his apnea-hypopnea index (AHI) was 41.8/hr on one night and 52.2/hr on another night, and the periods of SpO2 less than 85% were 51.4% of total sleeping duration and 83.2% respectively. When he returned to Hachioji (altitude 150 m), his AHIs were 10.5/hr and 9.5/hr on two consecutive nights. These results suggested that OSAS worsened by persistent hypobaric hypocapnia and by developing periodic breathing.