The Pharmacologic Treatment of Pulmonary Hypertension

Pulmonary Artery Hypertension - Types and Causes

Pulmonary artery hypertension (PAH) is defined as a mean pulmonary artery pressure greater than 25 mmHg at rest, or greater than 30 mmHg during exercise. PAH is classified as either primary PAH or secondary PAH. Primary PAH has no known precipitating cause (i.e., it is idiopathic) and appears to be hereditary in some individuals. This is a progressive disease that has a poor prognosis and no known cure. Secondary PAH results from an identifiable cause or condition. The most common cause of secondary PAH is chronic obstructive pulmonary disease. Chronic hypoxia associated with this condition results in pulmonary vasoconstriction (hypoxic vasoconstriction). Other causes include obstructive sleep apnea, congenital heart disease, pulmonary thrombosis (blood clots), or left ventricular failure.

Hemodynamically, pulmonary hypertension can be caused by increased right ventricular output, increased pulmonary systemic vascular resistance, or increased pulmonary venous pressure. Because the pulmonary vasculature is normally very compliant, large increases in right ventricular output do not normally cause PAH. However, if the pulmonary vasculature loses its compliance due to disease, then increased right ventricular output can lead to PAH during exercise, for example. Most individuals with primary or secondary PAH have increased pulmonary vascular resistance, which can be caused by structural changes in the vasculature or by increased smooth contraction. Patients who have left ventricular systolic or diastolic failure, or who have severe mitral valve stenosis or regurgitation, can also have secondary pulmonary hypertension because of an increase in pulmonary venous pressure.

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Rationale for Pharmacologic Treatment

Revised 03/14/07