Effect of Hypoxemia with or without Increased Placental Vascular Resistance on Fetal Left and Right Ventricular Myocardial Performance Index in Chronically Instrumented Sheep

Myocardial performance index (MPI) is increased in growth-restricted fetuses with placental insufficiency, but it is unknown if this is due to fetal hypoxemia or increased placental vascular resistance (Rplac). We used chronically instrumented sheep fetuses (n = 24). In 12 fetuses, placental embolization was performed 24 h before experiments. On the day of the experiment, left (LV) and right (RV) ventricular MPIs were obtained by pulsed Doppler at baseline and in the hypoxemia and recovery phases. At baseline, Rplac was greater and fetal pO2 lower in the placental embolization group, but RV and LV MPIs were comparable to those of the control group. During hypoxemia, mean LV MPI increased significantly only in fetuses with an intact placenta (0.34 vs. 0.46), returning to baseline during the recovery phase. Right ventricular MPI was unaffected. We conclude that fetal LV function is sensitive to acute hypoxemia. Exposure to chronic hypoxemia could pre-condition the fetal heart and protect its function with worsening hypoxemia.