- Any elevation greater than 1,500 meters (4,921 feet) is considered to be high altitude; ‘‘very high altitude’’ is defined as 3,500 to 5,500 meters (11,483 to 18,045 feet), and ‘‘extreme altitude’’ is 5,500 to 8,850 meters (18,045 to 29,035 feet).
- New arrivals to altitude commonly experience poor-quality sleep. These complaints are associated with frequent brief arousals, which are, in turn, linked to periodic breathing.
- Changes in sleep architecture include a shift toward lighter sleep stages, with a significant decrease in slow-wave sleep and with variable decreases in rapid eye movement (REM) sleep.
- Periodic breathing at altitude reflects alternating respiratory stimulation by hypoxia and subsequent inhibition by hyperventilation-induced hypocapnia. Increased hypoxic ventilatory responsiveness and loss of regularization of breathing during sleep contribute to the occurrence of periodicity.
- The problem of periodic breathing, poor quality sleep and its associated consequences is of particular concern to competitive and recreational athletes (skiers, snow boarders, and mountain climbers) and military personnel, who are often deployed to areas at high altitude.
