Physiology and Medicine at High Altitude: The Exposure and the Stress

Abstract

Increase in altitude causes decrease in atmospheric barometric pressure that results in decrease of inspired
partial pressure of oxygen, a source for stress and pose a challenge to climbers/trekkers or persons posted on
high altitude areas. This review discusses about the high altitude sickness, their incidence rates, pathophysiology
and the classic model of acclimatisation, which explains about how oxygen requirement in extreme environment
is achieved by complex interplay among pulmonary, hematological and cardiovascular processes. The acute
high altitude illness (AHAI) is basically composed of two syndromes: cerebral and pulmonary that can afflict
un-acclimatised climbers/trekkers. The cerebral syndrome includes acute mountain sickness (AMS) and high
altitude cerebral oedema (HACO) and pulmonary syndrome typically refers to high altitude pulmonary oedema
(HAPO). The core physiological purpose, according to the classic model is centered upon the optimisation of
increased delivery of oxygen to the cells through a coherent response involving increased ventilation, cardiac
output and hemoglobin concentration with aim to increase the oxygen flux across the oxygen cascade, which
will help in preventing the development of majority of high altitude illness.