The Pharmacologic Treatment of Pulmonary Hypertension
- Page 1: Pulmonary Arterial Pressure
- THIS PAGE: Pulmonary Arterial Hypertension - Types and Causes
- Page 3: Rationale for Pharmacologic Treatment
- Page 4: Drugs Used to Treat Pulmonary Hypertension
Pulmonary Arterial Hypertension - Types and Causes
Pulmonary arterial hypertension (PAH) is defined as a mean pulmonary arterial pressure greater than 25 mmHg at rest, or greater than 30 mmHg during exercise. One older way to classify PAH is as two broad categories: 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, chronic hypoxemia, pulmonary thrombosis (blood clots), or left ventricular failure. More recently, the World Health Organization developed a classification scheme that is based on the underlying mechanism/cause of PAH.
Hemodynamically, PAH 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.