Mechanical properties of the fetal ductus venosus and umbilical vein

During fetal circulatory compromise, velocity pulsations in the precordial veins increase and are commonly transmitted through the ductus venosus into the umbilical vein, indicating a serious prognosis. The nature of the puls ations and their transmission into the periphery, specifically the umbilica l vein, is poorly understood. We present information on the mechanical prop erties of fetal veins as a basis for describing the pulse wave propagation. Five fetal sheep livers with connecting veins (gestational age 0.8-0.9) we re studied in vitro. The transmural pressure, obtained with a fluid-filled catheter, was reduced stepwise from 10.3 to 0mmHg, and the diameter determi ned by ultrasonography. Each data set was fitted to an exponential function to determine the stiffness parameter and the area at a standard pressure, which we proposed to be 5 mmHg for the fetal venous circulation. The stiffn ess parameter was 6.2 +/- 1.8 at the ductus venosus outlet, 3.4 +/- 1.3 at the ductus venosus inlet, and 4.0 +/- 1.0 in the umbilical vein. Correspond ingly, values for compliance and pulse wave velocity for the three venous s ections were established for a physiological pressure range. The estimated pulse wave velocity of 1-3 m/s is comparable with Values estimated for vein s in adults. The mechanical properties of fetal veins are comparable with t hose described for veins later in life. The stiffness parameter represents the elastic properties at all pressure levels and conveniently permits infe rence of compliance and pulse wave velocity.