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To the Editor.—
I read Dr Houston's discussion on high altitude sickness (236:2193, 1976) with a great deal of interest. It has always occurred to me whenever reading articles about high altitude sickness that the clue to the origin of this condition lies in its name—altitude (that is, diminished barometric pressure).Human beings living at sea level have their bodies shaped and compressed somewhat by sea level barometric pressure. However, when one ascends, the intracellular and extracellular volume expands slightly because there is less external pressure to maintain their former volumes. The resulting diminished pulse pressure in the renal arteries associated with the relative hypovolemia causes the juxtaglomerular apparatus to activate the renin-angiotensin-aldosterone mechanism, thereby causing fluid retention. Hypoxia-induced pulmonary hypertension and other hypoxic cellular changes in combination with fluid retention may be enough to cause increased vascular permeability, which in turn causes acute mountain sickness, high altitude pulmonary edema,
Younes RP. High Altitude Illness. JAMA. 1977;237(19):2038. doi:10.1001/jama.1977.03270460024012
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