NPPB and pulmonary arterial hypertension: Treatment with PAH-specific therapy, underlying lung disease, functional vital capacity (FVC), severely reduced DLCO, hypoxemia, and elevated BNP (defined as >100 pg/mL) were included in the regression model; pulmonary hemodynamic parameters were not, as all patients in this analysis had severe PH and similar pulmonary hemodynamics across the treated and untreated groups.