Fetal oxygenation and Doppler ultrasonography of cardiovascular hemodynamics in a chronic near-term sheep model

Objective: We hypothesized that a decrease in fetal oxygenation without acidemia in a near-term fetal sheep leads to cardiovascular hemodynamic changes that are detectable by Doppler ultrasonography. Study design: Twelve ewes and fetuses were instrumented at 112 to 127 days of gestation. After a 5-day recovery period, experiments were performed with general anesthesia. Uterine and placental volume blood flows and fetal arterial and venous blood pressures were measured. Fetal cardiovascular hemodynamics was assessed by Doppler ultrasonography. All the measurements were performed at baseline, during fetal hypo-oxygenation, and at recovery phase. Results: A drop in fetal Po₂ was related to increased (P < .05) weight-indexed right ventricular and combined cardiac outputs and proximal branch pulmonary artery pulsatility index values. The increase in proximal branch pulmonary artery pulsatility index values correlated (R = .59; P < .05) with the decrease in fetal oxygen saturation. In the aortic isthmus, the time-velocity integral ratio between antegrade and retrograde blood flow components decreased (P < .05) when fetal Po₂ dropped. Conclusion: During decreased fetal oxygenation Doppler ultrasonography demonstrated increased fetal cardiac output and pulmonary arterial vascular impedance and a relative increase in the retrograde blood flow component in the aortic isthmus.