Myocardial and total body extractions of radiorubidium in anesthetized dogs

Myocardium (EM) and average total body (ETB) extractions of 86-Rb were determined in 24 anesthetized, open-chest dogs. Blood from the coronary sinus and from the pulmonary artery reflected the uptake of 86-Rb by myocardium and the total body, respectively, and extractions were computed from the relative arteriovenous differences (A-V/A). While the arterial concentration of 86-Rb was constant, EM varied from 0.66 plus or minus .02 (SE) at 2-2.5 min to 0.65 plus or minus 0.02 at 5-5.5 min, and ETB varied from 0.63 plus or minus 0.01 to 0.58 plus or minus 0.01 over the same interval. Mean extractions were similar statistically at 2-2.5 min, but individual differences as great as 30% were encountered at the 95% confidence level. After 3 min of 86-Rb administration, EM significantly exceeded ETB (P is less than 0.05) due to the more rapid decline with time of ETB. The similarity of the early extractions of 86-Rb by myocardium and by the total body supports, in general, the use of the radiorubidium uptake method for measuring coronary blood flow. However, the administration of the indicator should be brief, and rather large errors in individual estimates must be anticipated.