Effects of high-altitude exposure on the pulmonary circulation.

More than 140 million people dwell at altitudes of over 2500 m. The Andes region is home to the greatest population density at an altitude of more than 3500 m. Equally, the number of persons living at sea level (SL) is growing, and they travel to medium, high, or extreme altitudes for occupational or scientific reasons, or to enjoy tourism or recreational activities, as is the case of hikers, mountaineers, and skiers. For this reason, it is interesting to determine the effects of altitude on physiological and structural aspects of the human body. The effects of altitude are due to the low barometric pressure and, thus, to a reduction in the partial pressure of inspired oxygen. This condition of hypobaric hypoxia is what causes alveolar hypoxia and hypoxemia in humans who live at or ascend to high altitudes. There are multiple responses to the hypoxic stimulus, as well as numerous mechanisms of acclimatization. On occasions, an individual who ascends to high altitudes adapts poorly, whereas in other cases, a high-altitude native loses acclimatization. This editorial provides a brief review of the effects of altitude on the pulmonary circulation in three situations: chronic hypoxia, acute hypoxia, and subacute hypoxia.