Regulation of blood flow through the ductus venosus.

The ductus venosus, which is situated within the liver parenchyma, is a vascular shunt unique to the fetal and neonatal circulations. In fetal life, the ductus venosus allows variable portions of the umbilical and portal venous blood flows to bypass the liver microcirculation. After birth, when the umbilical circulation ceases, blood flow through the ductus venosus decreases substantially. The purposes of this review are to summarize the data currently available on the regulation of ductus venosus blood flow in fetal and neonatal life and to identify those factors that affect ductus venosus closure after birth. Most recent experiments indicate that mechanical factors exert the major influence on the fetal ductus venosus shunt. In the fetal sheep, for example, pressure and resistance differences across the liver are important determinants of the umbilical venous blood flow through the ductus venosus. In addition, ductus venosus blood flow can passively in response to alterations in the systemic circulation. Shortly after birth, blood flow and blood pressure in the umbilical sinus decrease abruptly. This causes the orifice of the ductus venosus to retract and narrow, resulting in functional closure of the vascular shunt. Permanent structural closure, consisting of connective tissue deposition within the entire ductus lumen, starts within days after birth and is completed by 1-3 months of age.