EFFECTS OF ACUTE HYPOXEMIA ON UMBILICAL ARTERIAL DOPPLER INDEXES IN A FETAL OVINE MODEL

Changes in umbilical arterial Doppler waveform in response to acute maternal hypoxemia were assessed in a chronic ovine model. Maternal heart rate, blood gases, fetal heart rate and umbilical arterial Doppler indices measured at baseline conditions and during periods of maternal hypoxemia were compared. The indices measured were systolic-diastolic ratio (S/D), pulsatility index (PI) and resistance index (RI). Fetal heart rate decreased (< 80 beats/min) and umbilical arterial Doppler indices increased (P < 0.001) during the periods of hypoxemia. Furthermore, the Doppler indices were highly but negatively correlated with alterations in the fetal heart rate (FHR) (P < 0.001). Analysis of the Doppler waveform phase intervals revealed nearly constant systolic intervals while diastolic intervals varied inversely with the heart rate alterations. Moreover, the umbilical arterial Doppler indices, when corrected for FHR changes, were relatively unchanged from baseline measurements. This study indicates that maternal hypoxemia induced changes in the umbilical arterial Doppler indices may be primarily attributable to the changes in FHR.