Hemodynamic changes across the human ductus venosus : A comparison between clinical findings and mathematical calculations

We investigated the hemodynamics of the ductus venosus in the human fetus by means of a combined approach based on Doppler and computational techniques. The aim of our study was to assess the blood velocity changes across the ductus venosus. Color Doppler equipment was used to investigate 29 normal fetuses between 20 and 39 weeks of gestation. Velocities at the systolic peak (S), diastolic peak (D) and atrial contraction (A) were measured at the isthmus and at the outlet of the ductus venosus, and the corresponding angle-independent indices (S/A, (S-A)/S, (S-A)/D) were calculated. A parametric computational model was developed in order to investigate the influence of anatomical features of the ductus venosus on the hemodynamics of the vessel. In all the fetuses the S, D and A velocities at the outlet portion were significantly lower than those at the isthmic part of the ductus venosus (p < 0.0001). The mean percentages of velocity reduction were 23.1%, 26.5% and 33.6%, respectively. Computational simulations also showed a relevant decrease of the velocity along the ductus venosus during the whole cardiac cycle. Velocity reduction along the ductus was mainly due to its conicity and this reduction generally caused velocity values at the outlet to be below the normal range. Conversely, angle-independent indices measured both at the isthmus and at the outlet lay within the same range of the reported reference values and therefore were not influenced by sampling site.