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-RIGHTSHUNT

Objectives. We sought to study the effects of catecholamines on myocar dial oxygen consumption ((V) over dot O-2)), regional blood flows and total body (V) over dot O-2, in lambs with circulatory congestion. Bac kground. Catecholamines are often used to support cardiovascular funct ion in children with circulatory congestion because they increase cont ractility as well as heart rate. However, these changes increase myoca rdial oxygen demand and thus can lead to a mismatch between myocardial oxygen supply and demand. Catecholamines can also change regional blo od hows and (V) over dot O-2 unfavorably. Methods. We infused isoprote renol (0.1 mu g/kg body weight per min) and dopamine (10 mu g/kg per m in) and measured myocardial and total body iio, and regional blood flo ws in chronically instrumented 7-week old lambs with and without a lef t to right shunt. Results. Isoproterenol increased myocardial (V) over dot O-2, parallel to the increase in heart rate. However, myocardial blood flow and, consequently, oxygen supply also increased. This incre ase out-weighed the increase in myocardial (V) over dot O-2 so that my ocardial oxygen extraction decreased, Isoproterenol did not change blo od flow distribution. Isoproterenol increased total body (V) over dot O-2; however, systemic oxygen supply increased even more, so that oxyg en extraction decreased and mixed venous oxygen saturation increased. In contrast, dopamine had no or little effect on myocardial (V) over d ot O-2 or blood how distribution.