NPPB and interstitial lung disease: The prognostic index was calculated as follows: 0.6106 × modified WHO functional class – 0.0015 × 6MWD + 0.0528 × PVR – 0.0136 × EGFR + 0.3233 × thrombocytopenia + 0.4907 × mild ILD + 0.9482 × NT-proBNP/BNP + 0.6751 × Dbil (log transformed), where 6MWD is six-minute walking distance, EGFR is estimated glomerular filtration rate, ILD is interstitial lung disease, NT-proBNP/BNP is N-terminal pro-brain natriuretic peptide / brain natriuretic peptide level, and Dbil is direct bilirubin level.