High altitude pulmonary hypertension: overlap with other types of pulmonary hypertension and implications for treatment.

High altitude pulmonary hypertension occurs in a subset of the 80-140 million people who live at altitudes ≥2500 m. This type of pulmonary hypertension is generally defined by a mean pulmonary artery pressure >30 mm Hg and is associated with symptoms of exercise intolerance, with possible progression to right heart failure. High altitude pulmonary hypertension can be difficult to distinguish from other forms of pulmonary hypertension, including pulmonary arterial hypertension and pulmonary hypertension caused by lung disease. In theory, removal from high altitude effectively treats high altitude pulmonary hypertension but not pulmonary arterial hypertension and pulmonary hypertension caused by lung disease. In reality, mechanistic overlap between the diseases exists, and the clinical phenotypes may likewise overlap. Limited evidence exists for other treatments for high altitude pulmonary hypertension, with the greatest rationale currently for pulmonary vasodilators. Future research should revisit the diagnostic threshold for high altitude pulmonary hypertension and for other forms of pulmonary hypertension at high altitude. Also, more research is needed to better differentiate between patients living at high altitude with high altitude pulmonary hypertension and those with other forms of pulmonary hypertension, and to define which treatments can be extrapolated from other types of pulmonary hypertension to high altitude pulmonary hypertension.