NPPB and chronic thromboembolic pulmonary hypertension: In a study that observed whether prostacyclin therapy improves PH in patients with CTEPH prior to undergoing PAH, receiving intravenous prostacyclin reduced pulmonary vascular resistance by 28%, from 1510 ± 53 wood units to 1088 ± 58 wood units (p < 0.001), and plasma BNP levels significantly decreased from 547 ± 112 pg/mL to 188 ± 30 pg/mL (p < 0.01) [94].