Hemodynamic action of verapamil in dogs with controlled aortic pressure--influence of sympathetic activation.

Verapamil was given to 18 anesthetized dogs (alpha-chloralose 100 mg/kg) as a bolus injection (200 micrograms/kg) followed by constant rate infusion (10 micrograms/kg per min). Hemodynamic parameters were evaluated before and during verapamil administration. After a suitable period of time for complete reversal of hemodynamic effects, verapamil administration as well as hemodynamic measurements were repeated during graded aortic occlusion. This technique stabilized central aortic pressure so that the level of reflex baroreceptor stimulation could be kept constant. Atrio-ventricular conduction disturbances observed in 5 dogs during balloon occlusion are attributed to lack of sympathetic stimulation. Without balloon occlusion, verapamil produced significant decreases in peripheral systemic vascular resistance and pressure and marked increases in cardiac output. Heart rate, pulmonary arterial and pulmonary wedge pressures did not change significantly. During graded aortic occlusion, systemic resistance and cardiac output were less markedly affected but there was an increase in both pulmonary arterial and wedge pressures.