Dynamic responses to intravenous urapidil and dihydralazine in normal subjects*

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Abstract
Hemodynamic responses after urapidil [an antihypertensive vasodilator] were compared with those after dihydralazine in placebo-controlled, double-blind studies afte cumulative i.v. doses. Heart rate, blood pressure, systolic time intervals corrected for heart rate (electromechanical systole and preejection period), electrical impedance cardiography [(dZ/dt)/RZ index [cardiac performance index] and mean electrical thorax impedance], and M-mode echocardiogram (end-systolic and -diastolic diameters, end-systolic wall stress, fractional shortening, and cardiac output) were recorded. Both drugs induced dose-dependent reductions in total peripheral resistance, which resulted in reduction in left ventricular end-systolic wall stress and increases in heart rate (limited at + 10 bpm [beats per min] with urapidil), fractional shortening, cardiac output, and the (dZ/dt)/RZ index. With each drug, diastolic blood pressure fell by 5 mm Hg, the corrected preejection period shortened (dihydralazine > urapidil), the corrected electromechanical systole did not change, and mean electrical thorax impedance rose with urapidil. The spectrum of effects indicates that both drugs reduce left ventricular afterload, thereby increasing left ventricular pump performance. Urapidil also exerts some preload reduction.