A radionuclide method for the simultaneous study of the effects of drugs on central and peripheral haemodynamics.

Abstract

The central and peripheral cardiovascular effects of hydralazine and glyceryl trinitrate (GTN) have been contrasted using radionuclide techniques. 2 Following intravenous injection of technetium-99m labelled human serum albumin, radionuclide ventriculography was performed by the equilibrium blood pool method using a mobile gamma camera. Simultaneous measurements of 'peripheral venous volume' were made using a collimated scintillation probe positioned above the patient's calf. 3 Ten patients with angina pectoris were studied at rest, after sublingual administration of 0.5 mg GTN and after intravenous administration of 10 mg hydralazine. 4 GTN caused a mean reduction in the end diastolic volume of the left ventricle of 14.6% + 4.5% (P < 0.005) but ejection fraction increased by 0.034 + 0.007 (P < 0.005) so that stroke volume was only reduced by 4.9% 5.0% (NS). There was a mean increase in heart rate of 10.8 2.3 beats/min (P < 0.001) but no significant change in cardiac output. The calculated systemic vascular resistance fell by 10.0% 5.4% (P < 0.05). Associated with these changes there was a mean increase of 9.6% 1.5% (P < 0.05) in the counts from the calf. 5 Hydralazine caused a significant reduction in blood pressure and increase in heart rate. End- diastolic volume was reduced by 6.0% 2.7% but there was a mean increase in ejection fraction of 0.058 0.010 (P < 0.001) so that in this instance stroke volume increased by 9.0% + 3.7% (P < 0.05) and cardiac output increased by 16.4% 4.4% (P < 0.005). The calculated systemic vascular resistance fell by 18.9% 3.8% (P < 0.001). Despite these haemodynamic changes there was no significant change in counts from the calf. 6 The results confirm that GTN has a predominant venodilator effect while hydralazine acts largely on the arterial bed. These relatively simple radionuclide methods will allow a more detailed assess- ment of the cardiovascular effects of drugs.