Pulmonary arterial hypertension - PAH
Pulmonary arterial hypertension (PAH): One of five categories of pulmonary hypertension; this category includes PH of unknown origin. Most kinds of pulmonary hypertension are PAH. PAH constricts or contracts the arterioles of the lungs, which are small, muscular branches of arteries within the lungs. When they are constricted, they increase resistance to blood flow, and blood pressure in the pulmonary artery increases.