Changes in flow velocity patterns of the superior and inferior venae cavae during placental circulatory insufficiency

Placental circulatory insufficiency, expressed by the disappearance of the diastolic component of the umbilical artery Doppler velocity waveforms, causes blood flow redistribution that could disturb, to different extents, the systemic venous returns to the heart. The purpose of this study was to investigate the effect of an absence of diastolic blood flow in the umbilical artery on the relationship between the Doppler flow velocities of the venae cavae.

Fifteen normal fetuses (normal group) were matched for gestational age with 11 fetuses with absent diastolic flow in the umbilical artery (abnormal group). In the venae cavae, the following Doppler variables were measured and compared between groups: (a) during ventricular systole: maximum (S(max)) and minimum velocities (S(min)) and velocity integrals (SI); (b) during ventricular diastole: peak velocity of the E-wave and its integral (EI), the A-wave and its integral (AI). A venous velocity index (VVI) was defined as (S(max) + S(min))/S(max).

In the normal group, S(min) and VVI were significantly higher in the inferior vena cava (IVC) than in the superior vena cava (SVC). The ratio SVC-VVI/IVC-VVI was therefore always less than one. In the abnormal group, S(min), SI, E, EI and VVI were higher in the SVC compared to those of the IVC. The ratio SVC-VVI/IVC-VVI was always greater than one.

In the absence of umbilical artery diastolic flow, a reciprocal shift is observed between the IVC and SVC velocity waveforms characterized by a flow profile in the IVC which resembles that of a normal SVC profile and vice versa. These changes are another manifestation of blood flow redistribution towards the brain in the presence of placental circulatory insufficiency. They should be taken into account on Doppler assessment of ventricular diastolic function based on venous flow patterns during placental circulatory impairment.