The ductus venosus.

Until recently, our information on the ductus venosus was based on postmortem and experimental studies. The present review relates to the modern concept of this vein predominantly founded on clinical studies. Recent publications show that the blood distribution through the ductus venosus is particularly sensitive to changes in umbilical venous pressure, blood viscosity, and an active regulation of diameter of the entire ductus venosus. The mean fraction of umbilical blood shunted through the ductus is reduced from 30% to 20% during the second half of the human pregnancy, indicating that, during this period, the fetal liver has a higher priority than the shunting through the ductus venosus, apart from the compensatory redistribution needed during extreme challenges of placental compromize and hypoxemia. Additionally, the ductus venosus acts as a transmission line to the umbilical vein for pulse waves generated in the heart. These waves, reflecting cardiac function, are substantially influenced by the local variation of impedance and compliance.