ESTIMATION OF THE PRESSURE-GRADIENT ACROSS THE FETAL DUCTUS VENOSUS BASED ON DOPPLER VELOCIMETRY

In the fetus, the umbilical vein is directly linked to the inferior ve na cava by the narrow ductus venosus. Thus, the ductus venosus blood v elocity probably reflects the pressure gradient between the umbilical vein and the central venous system. In a longitudinal study that inclu ded 29 normal fetuses, pulsed Doppler velocimetry was carried out in t he umbilical vein and the ductus venosus during the last half of the p regnancy. By applying the Bernoulli equation, we estimated the pressur e gradient across the ductus venosus to vary between 0-3 mm Hg during the heart cycle; it remained within those ranges during gestational we eks 18-40. During fetal inspiratory movement, pressure gradients up to 22 mm Hg were estimated. The estimated ductus venosus pressure gradie nt seems to be within ranges compatible with known umbilical venous pr essures, and may provide a new opportunity to understand central venou s hemodynamics and respiratory force in the fetus once methodological limitations are controlled.