NPPB and idiopathic pulmonary arterial hypertension: NT-proBNP (Figure 2(b)) was significantly higher in IPAH and COPD-PH than normal group (933.59 ± 210.09 and 1806.38 ± 474.07 versus 83.436 ± 22.33 pg/mL, both p < 0.05), but there is no difference between IPAH and COPD-PH groups.