BLOOD-FLOW THROUGH THE DUCTUS VENOSUS IN HUMAN FETUS - CALCULATION USING DOPPLER VELOCIMETRY AND COMPUTATIONAL FINDINGS

The present study was performed to assess a new method to calculate th e blood flow rate through the ductus venosus (DV) in normal human fetu ses using available echo-Doppler data, Color Doppler sonographic unit was used to study DV flow in 26 normal fetuses between 20 and 36 wk of gestation, Maximal velocity Bow tracings and vessel diameters were ob tained at the isthmic and the outlet portion of the DV, Time-averaged velocities in the DV were measured from the recorded tracings, The vel ocity distribution in the two investigated cross-sectional areas of th e DV was evaluated by means of computational model simulations and the velocity shape coefficients h(in) and h(out), (i.e., the ratios betwe en the maximal and mean spatial velocities) were calculated as a funct ion of vessel geometry, These values allowed us to convert maximal Dop pler velocities into mean spatial velocities for each fetus, Blood Bow rate was evaluated both at the isthmus and at the outlet of the vesse l by means of two formulae based on the ultrasonographic measures and the results of the computational model. The value of the DV blood flow rate was calculated as the average between the results provided by th e two formulae, The velocity distributions both at the isthmus (h(in) = 0.677 +/- 0.040) and the outlet (h(out) = 0.374 +/- 0.072) of the du ctus are skewed toward the inner wall. Ductus geometry, i.e., the isth mic/outlet diameter ratio, affects the shape of the velocity profiles in the vessel, particularly that at the outlet, The coefficients of va riation for repeated measurements of the ductal diameters were 9.5 +/- 7.7% and 6.7 +/- 4.9% at the isthmus and the outlet, respectively. Th e two formulae gave values statistically identical for the time-averag e blood flow rate (36.3 +/- 22.1 vs, 39.4 +/- 24.0 mL/min; R = 0.946, p = NS), The mean percent difference between the results of the two fo rmulae was 7.1%. Thus, in human fetuses, the use of the two formulae b ased on both Doppler data and computational model simulations makes it possible to calculate the ductal flow rate, When the difference betwe en the calculations of the two formulae exceeds the 30% of their avera ge value, it is convenient to adopt the flow rate value calculated at the isthmus instead of the average of the two measures, The measuremen ts at the outlet of the ductus were more difficult to obtain, and the spatial velocity profile at the outlet depends more on the DV anatomy, (C) 1998 World Federation for Ultrasound in Medicine & Biology.