Comparative Effects of Isoproterenol and Dopamine on Myocardial Oxygen Consumption, Blood Flow Distribution and Total Body Oxygen Consumption in Conscious Lambs With and Without an Aortopulmonary Left to Right Shunt

Abstract

Objectives. We sought to study the effects of catecholamines on myocardial oxygen consumption (V̇o2), regional blood flows and total body V̇o2in lambs with circulatory congestion.Background. Catecholamines are often used to support cardiovascular function in children with circulatory congestion because they increase contractility as well as heart rate. However, these changes increase myocardial oxygen demand and thus can lead to a mismatch between myocardial oxygen supply and demand. Catecholamines can also change regional blood flows and V̇o2unfavorably.Methods. We infused isoproterenol (0.1 μg/kg body weight per min) and dopamine (10 μg/kg per min) and measured myocardial and total body V̇o2and regional blood flows in chronically instrumented 7-week old lambs with and without a left to right shunt.Results. Isoproterenol increased myocardial V̇o2, parallel to the increase in heart rate. However, myocardial blood flow and, consequently, oxygen supply also increased. This increase outweighed the increase in myocardial V̇o2, so that myocardial oxygen extraction decreased. Isoproterenol did not change blood flow distribution. Isoproterenol increased total body V̇o2; however, systemic oxygen supply increased even more, so that oxygen extraction decreased and mixed venous oxygen saturation increased. In contrast, dopamine had no or little effect on myocardial V̇o2or blood flow distribution.Conclusions. We conclude that the catecholamines isoproterenol and dopamine do not lead to a mismatch between myocardial oxygen supply and demand, nor do they change blood flow distribution unfavorably in 7-week old lambs with a left to right shunt. We demonstrated that isoproterenol is superior to dopamine, because it shifts the balance between oxygen supply and consumption toward supply so that systemic oxygen extraction reserve increases.