Does intravenous propranolol alter the systemic and coronary hemodynamic response to increasing ventricular rates in unanesthetized dogs?
Beta-receptor activity plays a crucial role in normal hemodynamic adjustments, specifically maintaining coronary flow, during rapid heart rates.
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.
Cobb et al. (Mon,) studied this question.
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