NEWS: 18th May 2007
 
Sleep at High Altitude

Ascending to high altitude forces climbers and trekkers to deal with many physiological challenges. One of the most common of these ?challenges? is obtaining a good night?s sleep.

When people climb to altitudes of ~ 2500 m and above, ?periodic breathing? can disrupt normal sleep. Periodic breathing takes the form of repeated ?apnoeas?, or episodes when breathing stops for ~30 seconds at a time throughout the night. This phenomenon causes sleep to be very fragmented, with the individual waking up repeatedly during the night with a feeling of suffocation. This phenomenon at high altitude has been referred to as Chyene-Stokes breathing, first described in the nineteenth century in people with impaired circulation due to problems such as heart failure or stroke. However, the periodic breathing seen at high altitude is a physiologically distinct event separate from the true Chyene-Stokes breathing found in seriously ill patients.

When ascent to altitude is rapid, periodic breathing can be extremely annoying. The trouble arises because we breathe more rapidly and deeply at high altitude in order to increase the oxygen content of our blood and tissue. As a result, we exhale excessive amounts of carbon dioxide (CO2) ? a chemical that is highly influential in control of breathing. Under normal circumstances, it is the ?build-up? of CO2 in our bodies that provides the stimulus to breathe rather than low oxygen levels. The low levels of CO2 that result from rapid breathing during sleep at high altitude means that the brain may register little need to breathe. When breathing ceases, this gives CO2 a chance to increase, which will typically restart an individual?s respiratory efforts after 15 or 30 seconds.

It is interesting to note that this high altitude sleep trouble rarely manifests itself during consciousness. This relative lack of apnoeas while awake at high altitude is thought to be because the ?apnoea threshold? of chemical control of breathing is different during sleep. Nonetheless, one will occasionally find that while awake (and at rest) at altitude one must breathe quickly and deeply for several seconds for no apparent reason ? this is the conscious equivalent to nocturnal periodic breathing.

With increasing time spent at high altitude during any given ascent, periodic breathing becomes less problematic in most individuals. Altered chemical concentrations in the body with acclimatization to altitude are largely responsible for this adaptation. Nevertheless, for those unwilling to wait for this natural process to occur, and for those who still have difficulties with nocturnal periodic apnoeas even after an adequate acclimatization phase, there are reliable therapies available to treat the problem.