The effect of maternal hypoxemia on the umbilical and femoral artery blood flow velocity waveforms and the relationship with mean arterial pressure in fetal sheep.

The relationship between the ratio femoral pulsatility index (PI)/umbilical PI and arterial oxygen content was examined in 8 fetal sheep at various stages of hypoxemia. This relationship was characterized by an inconsistent increase of the ratio femoral PI/umbilical PI at oxygen content levels beneath 1.0 mM. The correlation coefficient of the linear regression between both variables was only -0.54, indicating that prediction of fetal oxygenation on the basis of Doppler waveform measurements in peripheral fetal arteries might be invalid. The average correlation coefficient of the linear regressions between the femoral PI and fetal mean arterial pressure was 0.87 +/- 0.15 (SD), whereas the average correlation between the umbilical PI and fetal mean arterial pressure was 0.04 +/- 0.61. These data suggest that the degree of change in fetal mean arterial pressure considerably depends on the degree of change in vascular resistance in the fetal carcass.