Comparative circulatory effects of isoproterenol and dopamine in lambs with experimental cyanotic heart disease.

To determine whether the hemodynamic responses to adrenergic agonists are altered during chronic hypoxemia secondary to an intracardiac right to left shunt, we studied seven lambs with surgically created pulmonic stenosis and atrial septal defect and nine controls during infusions of isoproterenol at 0.1 and 0.5 micrograms/kg/min and dopamine at 5 and 20 micrograms/kg/min. Isoproterenol increased heart rate by 89 +/- 17% in control but only 46 +/- 6% in experimental lambs (p less than 0.05). However, because resting heart rate was higher in experimental lambs (213 +/- 7 versus 177 +/- 12 beats/min, p less than 0.05), maximal heart rates were similar (310 +/- 7 versus 326 +/- 6 beats/min; NS). Cardiac output increased during isoproterenol from 219 +/- 20 to 425 +/- 54 mL/min/kg in experimental lambs (p less than 0.05) and, similarly, from 180 +/- 20 to 425 +/- 71 in controls (p less than 0.05) (experimental versus control; NS). Dopamine also increased cardiac output similarly in both groups, at both doses, but without changing heart rate. Isoproterenol did not alter aortic oxygen saturation and increased systemic oxygen transport more than oxygen consumption. In contrast, dopamine at both doses decreased aortic oxygen saturation in experimental lambs (rest, 71 +/- 2% versus dopamine, 59 +/- 2%; p less than 0.05). With dopamine, the increase in systemic oxygen transport was equalled by an increase in oxygen consumption. Thus, circulatory responses to isoproterenol are similar in lambs with experimental cyanotic heart disease and controls, although higher resting heart rate in the experimental lambs reduces chronotropic reserve.(ABSTRACT TRUNCATED AT 250 WORDS)