Vasodilator-Responsive Idiopathic Pulmonary Arterial Hypertension: Evidence for a NewDisease?

Idiopathic pulmonary arterial hypertension (IPAH)is a highly morbid disease characterized by progres-sive obliteration of precapillary arterioles and a con-temporary survival time after diagnosis of slightly more than 5 years (1). A small subset (5 % to 10%) of patients with IPAH displays dramatic hemodynamic im-provement in response to acute exposure to pulmo-nary vasodilators, and approximately one half of these “vasodilator-responsive ” patients improve clinically with calcium-channel blocker therapy (2). The disparity in outcomes has fueled speculation for decades that vasodilator-responsive and nonresponsive IPAH are distinct diseases. Idiopathic pulmonary arterial hypertension is be-lieved to arise from pulmonary vascular remodeling, with vasoconstriction providing a potentially small con