But it positively correlated with severity of PH (PVR), right heart strain (NT-proBNP), and airflow limitation (Fig. 4, Table 2), indicating a potential pathophysiologic link between pulmonary SERT availability, NADPH oxidases, ROS production, and thus HPV in COPD patients with or without PH. Here, NPPB is linked to chronic obstructive pulmonary disease.