Hemodynamic model for analysis of Doppler ultrasound indexes of umbilical blood flow

A hemodynamic model for pulsatile fluid flow in a pressurized thin-walled e lastic tube was applied for the computation of volumetric blood flow and ve locity profiles for a given set of system parameters at any selected locati on along the umbilical artery. The velocity profiles over one heart cycle p rovide the fetal blood flow velocity waveforms (FVW) from which the usual D oppler indexes (DI) can be derived. The model was used for a comprehensive investigation of the correlation between DI and system parameters that refl ect the anatomy and physiology of umbilical blood flow. The simulations sho wed that the radial location of the Doppler measurement is insignificant fo r the calculated DI, whereas the axial site is important. The analysis show ed that decreasing the diameter or increasing the length of the umbilical a rtery reduces fetal mean blood flow rate and increases the DI. Increasing b lood viscosity tends to induce similar patterns, whereas decreasing arteria l compliance or increasing blood density decreases the DI with little effec t on blood flow rate. Fetal heart rate has a minor effect on both DI and fe tal blood flow rate. This study provides insight into the dependence of DI on the anatomic and physiological characteristics of umbilical blood flow.