The Effect of Dihydralazine on Blood Velocity in Branches of the Uterine Artery in Pregnancy Induced Hypertension

Abstract

Dihydralazine is frequently used in severe pregnancy induced hypertension (PIH). Little is known about its effect on the human uteroplacental circulation. In this study, Doppler ultrasound recordings were made from branches of the uterine artery in 5 women with PIH and blood pressure (BP) greater than or equal to 150/100 who received either 7.5 or 10 mg dihydralazine, as repeated intravenous doses of 2.5 mg, before obtaining near-normal/normal BP values. The measurements started 5-10 min prior to the injections and continued as undisrupted as possible during injections and the subsequent 30 min. When the reduction in BP was obtained, the median blood velocity was reduced by 23% (range 10-29%). A/B ratio was calculated at the same time as an indicator of peripheral vascular resistance. The ratio increased, compared with pre-experiment values, in 3 subjects (5, 26 and 31%) but decreased in 2 (4 and 6%). Maternal tachycardia was noted in all but one woman. Continuous fetal heart rate (FHR) recording showed no signs of fetal distress. The uteroplacental circulation does not seem to benefit from the vasodilatory effects of dihydralazine, the response to the decreased perfusion pressure being a reduction in blood velocity and unchanged peripheral resistance.