With AMS there is increased pulmonary interstitial edema and elevated pulmonary artery pressures. Hypoxemia probably leads to increased pulmonary vascular endothelium permeability which can progress to HAPE, the most common cause of death related to high altitude. The incidence of HAPE in troops may reach 15 percent, depending upon rate of ascent, final altitude, severity of cold weather, level of exertion, and use of depressant sleeping medications. HAPE is more common in young persons, particularly males. It most commonly occurs on the second night of exposure, manifested by fatigue, dyspnea on exertion, dry cough, and need for longer rest periods.
Some peripheral edema is common.
A close examination for HAPE and HACE is absolutely necessary. As the condition worsens, tachypnea, dypsnea at rest, and audible pulmonary rales may be present. Increases in pulmonary artery pressure and pulmonary vascular resistance are present. Increasing proteinaceous interstitial exudate, sometimes resembling bronchopneumonia, develops as pulmonary edema worsens. The exudate contans vasoactive eicosanoids and complement proteins.