Micro-bead embolization of uterine spiral arteries and changes in uterine arterial flow velocity waveforms in the pregnant ewe.

The aim of the present study was to simulate the pathological uteroplacental circulation observed in complicated human pregnancies in the pregnant ewe and to analyze its velocimetric changes. Four pregnant ewes at 16-17 weeks of pregnancy were used in the study. Micro-beads (Gelfoam) were administered stepwise into the uterine artery and changes in the uterine circulation were assessed by Doppler velocimetry. Gelfoam administration successfully embolized the uterine spiral arteries located in the decidual segment. The Gelfoam embolization decreased the uterine blood flow dose-dependently from 550 +/- 48 ml/min (mean +/- SD) to 142 +/- 12 ml/min and reciprocally increased the uterine vascular resistance from 139 +/- 12 mmHg min l-1 to 540 +/- 46 mmHg min l-1 at 0 mg and 30 mg Gelfoam, respectively. It dose-dependently attenuated the pregnancy-related physiological elevation in diastolic flow velocity, while the systolic flow velocity was unaffected, resulting ina dose-dependent increase in the pulsatility index from 0.5 +/- 0.2 to 3.2 +/- 0.7 at 0 mg and 30 mg Gelfoam, respectively. The pulsatility index linearly correlated with the uterine vascular resistance, giving a high correlation coefficient of r = 0.947. It could be concluded that the uterine arterial pulsatility index is an indicator of uterine vascular resistance.