Effect of excitement on coronary and systemic energetics in unanesthetized dogs

The effect of excitement on phasic aortic pressure and flow, phasic left coronary flow, and myocardial metabolism has been studied in dogs 1–8 weeks after implantation of appropriate flowmeters and other devices. The rapid increase in heart rate and mild increase in blood pressure in the first few seconds tend to maintain coronary flow per minute despite a decrease in stroke cardiac output and coronary flow throughout the cardiac cycle. The main response is a delayed rise in coronary flow per minute resulting from further elevation of heart rate and blood pressure, a moderate increase in stroke cardiac output and a sizeable increase in stroke coronary flow, the latter being divided fairly evenly between systole and diastole. From 60 to 90% of the increase in mean coronary flow arises from the increase in stroke coronary flow, and the remainder from the increased number of heartbeats per minute. Some of the possible mechanisms concerned are discussed.