Pulmonary hypertension is a diffuse disorder of the pulmonary vasculature that is characterized by an elevated pulmonary artery pressure (a resting pulmonary artery pressure of 25 mm Hg or more). There is an increase in the pulmonary vascular resistance (PVR) in the pulmonary vessels.
The most recent classification of pulmonary hypertension includes five categories (Simonneau G, Robbins IM, Begetti M, et al. Updated clinical classification of pulmonary hypertension. J Am Coll Cardiol 2009; 54:S43):
Pulmonary arterial hypertension (PAH)
PAH is characterized by an increase in the pulmonary vascular resistance in the small pulmonary arterioles.
It may be idiopathic, familial, related to drug toxicity, or associated with pulmonary veno-occlusive disease.
Pulmonary hypertension owing to left heart disease
In this category pulmonary hypertension is secondary to pulmonary venous congestion (e.g. left ventricular failure).
Pulmonary hypertension owing to lung diseases and/or hypoxia
In this category pulmonary hypertension is due to hypoxia as seen in a multitude of pulmonary diseases or bodily oxygenation problems (COPD).