Influence of Respiratory Acidosis on Circulatory Effect of Epinephrine in Dogs

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Abstract
The circulatory depressant effects of respiratory acidosis and the relation between acidosis and the circulatory effects of epinephrine were studied in anesthetized intact dogs after sympathetic and parasympathetic block. Respiratory acidosis invariably depressed myocardial contractile force, cardiac rate, and mean arterial pressure, but only the fall, in contractile force showed a relation with the degree of acidosis. The effect of epinephrine on myocardial contractile force decreased with decreasing arterial pH, but no correlation was found between pH and the effect of epinephrine on arterial blood pressure and on cardiac rate. During continuous infusion of epinephrine, arterial pressure continued to rise after the contractile force had reached its maximum. With repeated periods of epinephrine infusion in the same animal, the response of the myocardial contractile force declined, while the response of the arterial blood pressure was unchanged. Such "differential tachyphylaxis" may occur under clinical conditions with prolonged infusions of vasopressor agents.