Abstract

The instantaneous hemodynamic effects of i.v. nitroglycerin (25 µg/kg) and amyl nitrite inhalation were compared in seven conscious mongrel dogs two weeks or more after implantation of electromagnetic flow probes around the ascending aorta and the insertion of polyvinyl catheters into the right atrium, left atrium and ascending aorta. The hemodynamic effects of the two drugs were identical. The decrease in mean arterial pressure, stroke volume, and mean atrial pressures and the increase in heart rate and cardiac output were all statistically significant. In two conscious dogs continuous measurements of transverse internal left ventricular diameter were recorded by a sonomicrometer before and during drug administration. The end-diastolic diameter, the end-systolic diameter and the stroke excursion (end-diastolic minus end-systolic diameter) decreased from control values with both nitroglycerin and amyl nitrite (P < .05). In two dogs the heart rate was controlled by a right atrial bipolar pacemaker catheter and the experiment was repeated on four occasions with each drug. With the heart rate controlled at 210 beats/min, both nitroglycerin and amyl nitrite produced an increment rather than a decrease in stroke volume, and an increase in stroke excursion, despite a decrease in end- diastolic diameter. This study indicates that rapidly administered amyl nitrite and nitroglycerin produce identical hemodynamic changes which result from vasodilatation of resistance and capacitance vessels and the baroreceptor reflex response to a sudden decrease in mean arterial pressure.