Effects of O₂, CO₂, and drugs on estimating coronary blood flow from Rb⁸⁶ clearance

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

The accuracy of predictions of myocardial blood flow based on Rb⁸⁶ clearance rates was determined in dogs receiving vasoactive drugs or subjected to hypoxemia or hypercapnia. In controls, the highest rate of coronary blood flow was 16.5 ml/g myocardium per 10 min. Flow could be predicted from clearance (tissue Rb⁸⁶ uptake/arterial blood Rb⁸⁶ concentration) with a mean error of 7.8% in this group. With hypoxemia estimates of flow averaged 13.8% too low when arterial blood was from 50 to 75% saturated with oxygen, and were more unreliable at lower values. Carbon dioxide tension had no effect in the range from 20 to 60 mm Hg, but at higher levels estimates of flow were frequently much too low. Reserpine slowed the pulse and resulted in predicted rates of flow which averaged 13.7% below actual rates. Angiotensin, l-norepinephrine, dipyridamole, and digitoxin had no significant effect on the prediction of flow from clearance in the range of flow observed in controls. Thus Rb⁸⁶ clearance is a valid index of coronary flow in the range of CO₂ tension, arterial oxygen saturation, and drug effects commonly observed.

Key Words: hypoxemia • hypercapnia • angiotensin • l-norepinephrine • digitoxin • reserpine • dipyridamole oxygen • carbon dioxide

Submitted on November 5, 1964