Sleep at high altitude.

The sensation of disrupted sleep following ascent to high altitude is associated with frequent awakenings, which may reflect sleep disruption due to respiratory dysrhythmia consisting typically of monotonously repetitive periodic breathing. This seems to arise from the combined effects of hypocapnia, which leads to suppression of respiratory effort in NREM sleep, and hypoxia, which stimulates termination of apnea and hyperpnea with consequent hypocapnia, leading to perpetuation of periodicity. Sleep disruption and periodic breathing decrease with time at altitude but may also be considerably reduced by pretreatment with acetazolamide, which may act by correction of alkalosis or through some other mechanism. In long-term residents of high altitude less distinctive, undulating respiratory dysrhythmias are described with unstable and decreased arterial oxygenation.