ABSTRACT
Sleep is very commonly impaired at high altitude. Typically, people complain that they wake frequently, have unpleasant dreams and do not feel refreshed in the morning. Polysomnographic studies confirm the increased frequency of arousals. Electrencephalograms show changes in the architecture of sleep, usually with a great reduction in time spent in rapid eye movement (REM) sleep. Periodic breathing is almost universal at high altitude, and is accompanied by apneic periods which may be as much as 10-15 s long. The mechanism of the periodic breathing is probably related to the strong hypoxic ventilatory drive. High altitude natives who have a blunted ventilatory response to hypoxia show less or no periodic breathing compared with lowlanders at high altitude. The severe arterial hypoxemia which follows the long apneic periods may reduce the arterial PO2 to its lowest levels of the 24-h period. Acetazolamide stimulates ventilation at high altitude, reduces the time spent in periodic breathing, and improves the arterial oxygen saturation during sleep. Benzodiazepines also reduce periodic breathing. Oxygen enrichment of room air at high altitude results in fewer apneas, less time spent in periodic breathing, and an improved subjective assessment of sleep
Everyone who has been to high altitude knows that sleeping is often impaired. This ubiquitous problem affects the skier or trekker who sleeps at altitudes of 2500-3000 m, as well as the well-acclimatized climber who spends a night as high as 8000 m. The altitude of many modern skiing resorts is over 2700 m and many people who move rapidly from sea level to that altitude have difficulties with sleep for the first two or three nights. Often they cannot get to sleep for a long period, or they wake frequently, and often they complain that they do not feel refreshed in the morning. This last comment is also frequently heard from climbers at great altitudes on expeditions (Pugh and Ward 1956). Some people trying to sleep at high altitude complain that the mind races with a kaleidoscope of thoughts tumbling through it; this is certainly the case with the writer, who recognizes this as a very characteristic feature of the first night or two at high altitude.
