ABSTRACT
During fetal development, gas exchange is accomplished at the placenta. Fetal pulmonary blood flow is less than 10% of biventricular output, and pulmonary arterial blood pressure exceeds systemic blood pressure. Closely regulated pulmonary blood flow is necessary for optimal lung development (1). Recent evidence suggests that branching morphogenesis and alveolarization is contingent, to a significant degree, on carefully regulated blood flow in the fetal lung (2-4).
