Fig. 6

The pressure–flow relationship of the pulmonary artery. In normal subjects, increase in trans-pulmonary pressure (PAP-PAOP) is suppressed in the high flow range. The angles of θ1 and θ2 indicate pulmonary artery resistance (PVR) at cardiac output of 2 and 10 l/min, respectively. PVR varies with change in cardiac output even in the same subject [33]. In patients with pulmonary hypertension (PH), this regression curve becomes steeper, reflecting impaired pulmonary vascular autoregulation against increased flow. PAP mean pulmonary artery pressure, PAOP pulmonary artery occlusion pressure