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Integrative and Comparative Biology Advance Access first published online on January 6, 2006
This version published online on February 21, 2006
Integrative and Comparative Biology, doi:10.1093/icb/icj005
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© The Society for Integrative and Comparative Biology 2006. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org.

Adaptations to Life at High Elevation

Human responses to extreme altitudes

John B. West 1 *
1 Department of Medicine, University of California San Diego, La Jolla California CA 92093-0623

* To whom correspondence should be addressed.
John B. West, E-mail: jwest{at}ucsd.edu


  Abstract

Synopsis It is a strange coincidence that the highest point on Earth is very close to the limit of human tolerance to hypoxia. The physiological changes that allow humans to reach these extreme altitudes involve enormous alterations of their normal state. It is useful to contrast this response with two others to high altitude. One is acclimatization that allows lowlanders to ascend to altitudes of up to 5000 m and remain there for an indefinite period. The other is evolutionary adaptation which allows highlanders to live continuously over generations at altitudes up to 5000 m. These two responses enable humans to survive for an indefinite period at high altitude. By contrast, the changes that allow ascent to extreme altitudes are not compatible with an extended stay because of a poorly-understood process called high-altitude deterioration. The most important physiological response to extreme altitude is extreme hyperventilation which, on the summit of Mt. Everest, drives the alveolar PCOCO2 down to 7-8 mmHg. This is associated with a marked respiratory alkalosis with an arterial pH exceeding 7.7. Interestingly this alkalosis increases the oxygen affinity of hemoglobin, a response which the successful climber shares with many other animals in oxygen-deprived environments. The arterial POO2 on the Everest summit is only about 30 mmHg and falls on exercise because of diffusion limitation of oxygen across the blood-gas barrier. Maximal oxygen consumption on the summit is just over 1 liter.min-1. Anaerobic metabolism as measured by blood lactate levels is paradoxically reduced at extreme altitudes.

From the symposium "Adaptations to Life at High Elevation" presented at the annual meeting of the Society for Integrative and Comparative Biology, January 4-8, 2005, at San Diego, California.
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