Effects of Beta-Receptor Blockade on the Systemic and Coronary Hemodynamic Response to an Increasing Ventricular Rate in the Unanesthetized Dog

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Abstract
Phasic coronary and aortic blood flow and arterial pressure were measured as heart rates were increased by ventricular pacing from 120 to 270 beats/min in unanesthetized dogs before and after beta-receptor blockade with intravenous propranolol. Before beta-receptor blockade, coronary flow progressively increased and coronary vascular resistance decreased with increasing heart rates. Aortic blood flow and arterial pressure were not significantly altered at rates below 240 beats/min. After administration of propranolol, mean coronary blood flow was comparable to that before beta-receptor blockade at heart rates from 120 to 210 beats/min. However, aortic flow progressively decreased and peripheral resistance increased with increasing ventricular rates. At heart rates above 210 beats/min after propranolol coronary vascular resistance increased and coronary flow decreased. These data ascribe considerable importance to beta-receptor activity in the normal hemodynamic adjustments to rapid heart rates.