Flynn et al. showed that BNP had a weaker correlation with echocardiographic markers of PDA significance including ductal size (r = 0.62), increased pulmonary flow (r = 0.63), and increased steal (retrograde diastolic flow) in the descending aorta (DAo) and the superior mesenteric artery (SMA) (r = 0.54 and 0.41). Here, NPPB is linked to Patent ductus arteriosus.