Effect of hypoxemia and hypercapnia on regional distribution of myocardial blood flow

¹ Department of Medicine, University of Mississippi School of Medicine, Jackson, Mississippi

The effect of hypoxia and hypercapnia on regional coronary blood flow and vascular resistance (CVR) was studied in dogs without thoracotomy. Gas tensions were varied by ventilation at controlled rates with gas mixtures containing 4–100% O₂ and 0–24% CO₂. After 10 min intravenous infusion of Rb⁸⁶, the animals were killed and the heart isotope content determined. Blood flow to the left ventricle was calculated by the Fick principle from the isotope uptake and the mean difference in radioactivity of arterial and coronary sinus blood. Patterns of flow elsewhere were estimated from the rates of regional Rb⁸⁶ clearance. Myocardial Rb⁸⁶ clearance in the right and left ventricles has been previously shown to be closely related to the rate of coronary blood flow. Hypoxemia and severe hypercapnia (pCO₂ above 100 mm Hg) both produced a profound fall in CVR. With hypoxemia this decrease was more marked in the right ventricle. Elevation of pCO₂ exaggerated the normal difference in Rb⁸⁶ uptake between inner and outer thirds of the wall of the left ventricle, while hypoxemia reversed the normal gradients. Hypercapnia did not affect these gradients in the right ventricle, but hypoxemia significantly reduced them.

Key Words: O₂ • CO₂ • coronary blood flow • coronary vascular resistance • Rb⁸⁶

Submitted on November 19, 1964