Pathophysiology of acute mountain sickness and high altitude pulmonary oedema: an hypothesis.

We review the evidence that acute mountain sickness (AMS) and high altitude pulmonary oedema (HAPO) occur together more often than is realized. We hypothesize that AMS and HAPO have a common pathophysiological basis: both are due to increased pressure and flow in the microcirculation, causing oedema in the brain and oedema in the lungs.