Ductus venosus agenesis prevents transmission of central venous pulsations to the umbilical vein in fetal sheep

Velocity pulsations in the umbilical vein are widely used as a marker for congestive heart failure in the fetus. It has been suggested that the atrial pressure waves are transmitted to the umbilical vein mainly through the ductus venosus. In a case of ductus venosus agenesis in a fetal sheep of 110 days' gestation, we recorded pressures in the inferior vena cava and umbilical vein simultaneously with Doppler velocimetry in the medial hepatic vein and umbilical vein, under general anesthesia. During fetal respiratory acidosis (pH 7.01) and varying degrees of umbilical clamping, we did not observe the typical pulsations in the umbilical vein (deflections of the maximum velocity during atrial contraction) in spite of varying degrees of reversed flow in the hepatic vein (5-16%). The systolic-diastolic pressure amplitude in the inferior vena cava was 5.5-6.4 mmHg, sometimes reaching 9.19-11.03 mmHg. Varying degrees of reversed portocaval pressure gradient during atrial contraction (1.40-9.51 mmHg), periods of reversed portocaval pressure gradient throughout the entire cardiac cycle, tachycardia (240 beats/min) or bradycardia (99 beats/min) also did not produce the type of pulsation in the umbilical vein that reflects augmented atrial contractions. The results support the hypothesis that the ductus venosus is essential for the transmission of atrial pressure waves to the umbilical vein.