Effects of acid-base changes, hypoxia, and catecholamines on ventricular performance

Extracellular pH changes were produced in dogs with tris (hydroxy-methyl)-aminomethane (Tris) or NaHCO3 in the presence or absence of hypoxemia and before and after beta-adrenergic blockade with propranolol. Ventricular performance (VP) was evaluated by measurement of maximum rate of rise of left ventricular pressure (dp/dt max) and left ventricular end-diastolic pressure in the canine right heart bypass preparation with aortic pressure, heart rate, and cardiac output held constant. Low pH diminished VP. Hypoxemia did not alter VP within the pH, suggesting that decreased V observed with acidosis before propranolol was due primarily to decreased myocardial response to catecholamines. Increase of pH with Tris increased VP significantly more than with NaHCO3. Beta blockade diminished the response of VP to Tris at a high pH;prior administration of reserpine abolished the inotropic effect of Tris. The data suggest that Tris can influence VP independent of its effect on pH. This effect is probably mediated by the interaction between endogenous catecholamines and myocardial beta receptors.

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