Uterine and umbilical flow velocity waveforms in normotensive and hypertensive subjects during the angiotensin II sensitivity test

The systemic and uterine circulatory effects of angiotensin II infusion in five normotensive and 10 hypertensive subjects at the end of the third trimester of gestation were studied. Color Doppler ultrasonography was used for investigating the systolic/diastolic ratios on flow velocity waveforms in the uterine and umbilical arteries. A significant increase was observed in the systolic/diastolic ratio in the uterine artery in both groups. In normotensive subjects a differential effect of angiotensin II on the systemic diastolic blood pressure and on the systolic/diastolic ratio was observed; the uterine circulation had a slower response and a faster recovery than the maternal diastolic blood pressure. In hypertensive subjects this relative refractoriness to angiotensin II was less marked; the increase in uterine vascular resistance was faster and the recovery slower than in the normotensive group. No changes in the systolic/diastolic ratio in the umbilical artery were observed in either group. These results indicate that the uterine circulation of normotensive subjects is remarkably more refractory to angiotensin II than the circulation of hypertensive subjects.