Abstract
Chronic beta adrenergic blockade was induced in eight dogs with 240 to 360 mg of oral propranolol dailty for 2 to 6 weeks. Beta blockade was confirmed by a minimal heart rate response to isoproterenol, 0.06 micrograms/kg/min, in a pentobarbital-anesthetized, open-chest preparation. Subsequent to confirmation of beta blockade, hemodynamic effects of isoproterenol and dopamine were examined individually and in combination. A desirable balance of arterial pressure and cardiac output was achieved by combining isoproterenol, 0.2 to 2.0 micrograms/kg/min, with dopamine, 5 to 20 micrograms/kg/min. This combination increased mean arterial pressure (109 +/- 9 versus 81 +/- 7), cardiac output (4.3 +/- .5 versus 2.8 +/- .3 L/min) and heart rate 156 +/- 4 versus 120 +/- 7) (p less than 0.05). The hemodynamic effects of combined isoproterenol-dopamine were superior to the effects of either drug alone and suggest a method for effective circulatory support of man during chronic beta adrenergic blockade.
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