Variation of the maximum velocity along the umbilical vein supports the Reynolds pulsometer model

To challenge, with a modern sonographic approach and a numerical model, the Reynolds's concept which suggests that the vascular structure of the umbilical cord could act as a pulsometer facilitating the venous return to the foetus.

Forty-five patients between 20 and 28 weeks of gestation were included in the study. The blood maximum velocity in the umbilical vein, measured at both foetal and placental ends, was assessed. Several sonographic parameters of the cord, including the diameter of the umbilical vein at both extremities, cord cross-sectional area and Wharton's jelly section surface were measured. We compare our data with those of a numerical model.

A difference in maximum velocity between the two extremities of the umbilical vein (Δ^UVV_max) was noted. The maximum velocity was significantly higher at the foetal umbilical end (14.12 +/-3.18 cm/s) than at the placental end (11.93 +/-2.55 cm/s; p < 0.0001). The mean difference is 2.2 +/- 2.3 cm/s. No difference in the umbilical vein diameter was measured at both cord ends (umbilical 4.85 +/-0.9 mm, placental 4.86 +/-0.87 mm, p < 0.0001). There is no significant relationship between Δ^UVV_max and the cord cross-sectional area or Wharton's jelly index.

Modifications of the spatial velocity profile together with the pulsometer model could explain the maximum velocity changes that is measured in the umbilical vein along the cord. This numerical model consolidates the sonographic observations.