NPPB and chronic kidney disease: In univariable Cox analysis, WHO-FC, 6MWD, SvO2, RAP, cardiac index, mPAP, PVR, NT-proBNP, total bilirubin (TBIL), creatinine, uric acid, blood urea nitrogen, coronary heart disease and CKD were significant predictors for survival (Additional file 1: Table S1).