COMPUTATIONAL ANALYSIS OF THE DUCTUS VENOSUS FLUID-DYNAMICS BASED ON DOPPLER MEASUREMENTS

The simplified Bernoulli equation is currently used to evaluate pressu re gradients on the basis of Doppler velocity measurements when direct pressure data require highly invasive procedures. Recently, this meth od was applied to the ductus venosus (DV) in order to estimate the fet al central venous pressure. The complex geometry-and consequently hemo dynamics-of this fetal region suggests caution in automatically conver ting Doppler velocity measurements to pressure data. To investigate th e reliability of the Bernoulli equation for this practice, we simulate d the hemodynamics of the branching between the umbilical vein (UV) an d the DV on the basis of ultrasonographic data from a normal fetus, us ing a simplified parametric 3D numerical model of a bent tube with var ying cross section (UV) and a smaller trumpet-shaped branch (DV). A fi nite element formulation has been adopted to solve the governing Navie r-Stokes equations. The results show that the simplified Bernoulli equ ation, despite of its simplicity, provides a good estimation of the pr essure drop between the UV and the DV outlet section (with an error of about 0.25 mmHg, equal to 15%, compared with the model results). Neve rtheless, attention must be paid to the velocity measurement sites, as discussed in this paper. In turn, the error becomes notable (2.8 mmHg , i.e., 34%) for high velocity values, thus suggesting that the error in evaluating the pressure drop with the simplified Bernoulli equation during fetal inspiratory movements may be substantial. Copyright (C) 1996 World Federation for Ultrasound in Medicine & Biology