The cerebral hemodynamic response to administration of hydralazine.

PRECEDING INVESTIGATIONS have shown that administration of hydralazine (1-hydrazinophthalazine) is accompanied by an inerease in cardiac output,1-5 particularly if the decrease in blood pressure subsequent to its administration is not excessive,5 and by increased renal,6 hepatic,4 and coronary7 blood flow. Cerebral blood flow has been reported to be unchanged by hydralazine, even though cerebral vascular resistance decreased significantly after its administration.8 Material and Methods This study was performed on five hypertensive subjects (three Smithwick grade IV, one grade III, and one grade II), and one subject who had labile blood pressure but was not hypertensive at the time of the study. All subjects were fasting. The drug was administered intravenously as a single dose to all subjects except the one with labile blood pressure in whom a supplemental intravenous dose was given. The dose of hydralazine ranged from 0.2 mg./Kg. to 0.3 mg./Kg., and the average dose was 0.25 mg./Kg. The interval between administration of the drug and the second determination of cerebral blood flow varied from 32 to 42 minutes, with ani average of 37 minutes for five of the subjects. In the other subject, 0.24 mg./Kg. of hydralazine was given 52 minutes before the second study and 0.08 mg./Kg. 33 minutes before the second study because the change in blood pressure was not significant subsequent to the first dose.