ROLE OF PHARMACOLOGICAL TESTS IN THE TREATMENT OF PRIMARY PULMONARY-HYPERTENSION

Primary pulmonary hypertension (PPH) is a rare disease of unknown etio logy characterized by a constant progression toward right ventricular failure and death. Vasoconstriction is 1 of the pathophysiologic facto rs responsible for the increase of pulmonary vascular resistance (PVR) and pulmonary artery pressure (PAP) in patients with PPH. Thus vasodi lator treatment is considered 1 of the logical approaches to medical t herapy of such a condition. Acute drug challenge with a short-acting, titratable vasodilator during heart catheterization is recommended to select patients who are most likely to respond to longterm treatment. Accurate methodologic guidelines need to be followed to minimize the s pontaneous variability of PAP and pulmonary arteriolar resistance. Pat hophysiologic interpretation of pharmacologic trials requires analysis of the 2 components of the right ventricular hydraulic toad, i.e., re sistance and compliance of the pulmonary vascular bed. Reduction of th e calculated PVR may be considered as a demonstration of pulmonary vas odilation only if PVR is assessed using the critical opening pressure or if it is associated with a simultaneous reduction of PAP. Only thos e patients in whom a reduction of PVR of greater than or equal to 20% is associated with a decrease in PAP of greater than or equal to 20% s hould be considered as ''responders'' to the acute tests. In clinical studies only 20-30% of the patients are short-term responders. The mos t intensively studied short-acting drug for shortterm challenge is pro stacyclin, but other agents such as acetylcholine, adenosine, and nitr ic oxide have been utilized. Prostacyclin has been shown to predict pu lmonary vasodilator response