NPPB and idiopathic pulmonary arterial hypertension: We found the PetO2 at unloaded, PetCO2 at unloaded, PetO2 at AT, PetCO2 at AT, peak load, peak load%pred, peakVO2, peakVO2%pred, peak PetO2, peak PetCO2 and NT-proBNP, were progressively more abnormal as the physiologic severity increased not only in IPAH (Table 2) but also in CTEPH patients (Table 3).