...in idiopathic PAH patients who are "nonresponders" to the acute vasoreactivity test (such as those enrolled in this study), the main mechanism for the increase of the PAP and the PVR is related to the fixed proliferative and obstructive lesions of the distal pulmonary arteries and not to functional and potentially reversible vasoconstriction (1). ...13 of 21 patients (62%) were men (men are not more than 30% to 35% of the population in most idiopathic PAH series), all patients were on long-term oxygen therapy (utilized by no more than 30% of patients in most idiopathic PAH series), and the interval between initial symptoms and PADN was on average about 6.8 years (long-term survivors?) It is also highly unusual that a patient population of idiopathic PAH defined in the methods as "not responding optimally to current medical therapy" have normal right atrial pressures at rest.