DILATATION OF THE DUCTUS VENOSUS IN HUMAN FETUSES - ULTRASONOGRAPHIC EVIDENCE AND MATHEMATICAL-MODELING

Autonomic regulation of blood flow through the fetal ductus venosus ha s been suggested, but the existence of a sphincter at the ductal entra nce in human fetuses has yet to be established. In this paper two case s of apparent ductus venosus dilatation in two growth-restricted human fetuses are reported. Prolonged ultrasonographic analysis (45 min) sh owed rapid and substantial changes (>80%) of ductal diameters. Pulsed Doppler analysis was used to investigate flow velocity in the ductus v enosus and umbilical vein for both normal and dilated conditions. Dila ted conditions caused manifest modifications of velocity tracings. Sys tolic peak velocity in the ductus did not change visibly, whereas velo city at the atrial contraction showed evident reduction; consequently, pulsatility indexes increased. Furthermore, the umbilical vein presen ted flow velocity pulsations. The mean blood flow rate through the duc tus seemed to increase substantially (>70%) for high dilatation. To in vestigate these findings further, we performed simulations of ductal d ilatation by means of a lumped-parameter mathematical model of the hum an fetal circulation. Model results agreed with clinical evidence and confirmed the relationship between ductal dilatation and the observed velocity alterations. Simulated systolic peak velocity slightly increa sed for small dilatation (<30%), whereas atrial velocity was reduced w hen the ductus dilated. Furthermore, the model indicated that umbilica l venous pressure decreases for increasing dilatation, whereas no chan ge occurs in the central venous pressure. The present results seem to indicate the presence of active dilatation of the ductus venosus in hu man fetuses.