Local vasoactivity of oxygen and carbon dioxide in the right coronary circulation of the dog and pig.

Abstract

Mongrel dogs (8) were anesthetized with sodium thiamylal and chloralose urethane, ventilated, vagotomized and heparinized. Five Poland-China pigs were anesthetized with sodium thiamylal and nitrous oxide, ventilated, vagotomized and heparinized. Extracorporeal perfusion of the right coronary artery at constant pressure (100 mm Hg) was instituted. A lung from a donor animal was interposed in the coronary perfusion circuit to effect changes in CO2 and O2 tensions in the coronary arterial blood while systemic blood gases were maintained at normal levels. Local hypoxia (PO2 [partial pressure of O2] range 17-22 mm Hg) produced a 25-75% decrease in coronary vascular resistance (P < 0.05) and a 0-24% (not significant) decrease in right ventricular dP/dt [change in pressure with time]. Local changes in PCO2 over the range 8-105 mm Hg were associated with a 17-58% decrease in coronary vascular resistance (P < 0.05), a 19-24% decrease in right ventricular dP/dt (P < 0.05) with no change in right ventricular end-diastolic pressure, and a 1-18% (not significant) decrease in heart rate. Local decreases in O2 or increases in CO2 tensions produce decreases in right coronary vascular resistance that are in the opposite direction to those that would be expected from the observed changes in heart rate and contractility (2 primary determinants of myocardial O2 consumption). Apparently, CO2 and O2 are locally vasoactive in the coronary circulation.