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Determination of Myocardial Blood Flow in the Anesthetized Dog after a Bolus of ⁸⁴Rb

John A. Hartford Foundation Laboratory, Wayne State University School of Medicine and Harper Hospital, Detroit, Michigan

Correspondence: For reprints contact: R. J. Bing, Wayne State University School of Medicine, 1400 Chrysler Freeway, Detroit, Mich. 48207.

ABSTRACT

The myocardial blood flow in the anesthetized dog using the coincidence-counting system in connection with a bolus injection of the isotope ⁸⁴Rb was investigated. The validity of the method was tested by comparing myocardial blood flow with myocardial clearance of ⁸⁴Rb; flow was calculated with the Fick principle and clearance was obtained by dividing precordial uptake of the isotope by the integrated arterial concentration of the first circulation.

The average coronary blood flow in 44 dogs was 170.0 cc/mm/whole heart; the average myocardial clearance was 179.0 cc/mm/whole heart. The difference was 6.6% and statistically significant (P < 0.02). It could be demonstrated, however, that over a wide range of flows (91–362 cc/mm/whole heart) there is a linear and direct relationship between myocardial blood flow and clearance in the resting dog.

The effects of isoproterenol and norepinephrine on both myocardial blood flow and clearance of ⁸⁴Rb were examined. Isoproterenol did not change the relationship between clearance and flow, but a high dose of norepinephrine caused a proportional greater increase in flow than in clearance. It is likely that this is due to an alteration of the myocardial extraction ratio of rubidium. The results demonstrate that myocardial clearance of ⁸⁴Rb is primarily flow dependent under these experimental conditions and that the factors which can alter clearance were not a major influence.

The advantages and disadvantages of the bolus method as compared to the constant infusion method were discussed.