An assessment of ductus venosus tapering and wave transmission from the fetal heart

Pressure and flow pulsations in the fetal heart propagate through the precordial vein and the ductus venosus (DV) but are normally not transmitted into the umbilical vein (UV). Pulsations in the umbilical vein do occur, however, in early pregnancy and in pathological conditions. Such transmission into the umbilical vein is not well understood. In particular, the effect of the impedance changes in the DV due to its tapered geometry is not known. This paper presents a mathematical model that we developed to study the transmission of pulsations, originating in the fetal heart, through the DV to the umbilical vein. In our model, the tapered geometry of the DV was found to be of minor importance and the only effective reflection site in the DV appears to be at the DV inlet. Differences between the DV inlet and outlet flow were also found to be minor for medium to large umbilical vein-DV diameter ratios. Finally, the results of a previously proposed lumped model were found to agree well with the present model of the DV-umbilical vein bifurcation.