Diagnosis

In a patient suspected of having PAH, a right-sided heart catheterization is performed to measure pulmonary arterial pressures, allowing the calculation of the PVR, which is equal to the decrease in pressure across the pulmonary vascular system (mean pulmonary arterial pressure [mPAP] minus the pulmonary arterial occlusion pressure [PAOP]—an indirect measure of left atrial pressure) divided by the cardiac output (CO):

< ?xml:namespace prefix = "mml" />PVR=(mPAP–PAOP)CO

The normal resting mPAP value is 14 ± 3.3 mm Hg; the World Health Organization defines PAH as a sustained elevation of mPAP to more than 25 mm Hg at rest or to more than 30 mm Hg with exercise, with a mean PAOP or left ventricular end-diastolic pressure of less than 15 mm Hg. The World Health Organization classifies PAH as primary or secondary, with recognition that considerable overlap exists between groups, and further divides secondary PAH into left-sided heart disease, PAH from hypoxemia, PAH from pulmonary thrombotic disease, and PAH from miscellaneous causes (Box 228-1). The distinguishing feature between PAH caused by left-sided heart disease and other causes of PAH is that the latter diagnoses require a PVR greater than 3 Wood units (1 Wood unit = 80 dyn·sec⁻¹·cm⁻⁵). If left atrial (PAOP) pressure is high (e.g., in patients with mitral valve insufficiency), then PVR is unlikely to be greater than 3 Wood units, and the PAH is secondary to left-sided heart disease.

Treatment

Once a diagnosis of PAH is made, treatment first focuses on correcting any secondary causes of the disease; these treatments include, for example, supplemental O₂