The cardiac response to a small i.v. dose of dihydralazine, a safe drug for diagnostic tests?

. Dihydralazine, given in small i.v. doses, has been of great value in diagnostic tests for unilateral renovascular hypertension, where it enhances renin release on the affected side. The acute hemodynamic effects of an i.v. dose of 0.1 mg/kg b.wt. were studied in 14 patients with essential hypertension, using a quantitative renographic technique for determination of effective renal plasma flow and radiocardiographic technique for determination of the parameters in systemic circulation. Cardiac index increased from 4.040 to 6.423 1/min-m2 (p <0.01), stroke index from 59 to 66 ml/beat.m2 (p <0.05), heart rate from 70.4 to 96.6 beats/min (p <0.01) and left ventricular work index from 1.04 to 1.49 W/m2 (p <0.01), while mean arterial BP decreased from 125 to 110 mmHg (p <0.01) and total peripheral resistance index from 2927 to 1534 105.N.s.m-3 (p <0.01). Effective renal plasma flow and pulmonary plasma volume were unchanged. Peripheral renin activity increased from 0.5 to 1.6 nmol A1/l-h (p <0.02). It is concluded that even a small test dose of 0.1 mg/kg of dihydralazine elicits a considerable additional work load on the heart, a circumstance that must be taken into consideration in studies of patients with coronary heart disease.