The Determination of Coronary Flow Equivalent with Coincidence Counting Technic.

THE measurement of organ blood flow in the intact animal and man is limited primarily to methods relying either on the Fick principle or on the dye-dilution method.'-3 Measurement of coronary flow in man has been accomplished by the uptake of an inert diffusing gas, nitrous oxide, by the heart muscle.4 This method requires that a state of equilibrium between the coronary circulation and the myocardium exists for the period of observation. The disadvantages are that only mean flow over a period of minutes can be determined, and sudden and transient flow changes are not recorded. In addition, some of the gas may traverse the coronary arteriovenous precapillary anastomosis. Finally, the procedure necessitates the intubation of the coronary sinus. Radioisotopes have been employed in the measurement of coronary flow by a series of investigators. Based on the similarity in potassium and rubidium turnover rates, Love and Burch 5 used myocardial rubidium-86 uptake as an indicator of coronary blood flow. They assumed that the percentage extraction of rubidium-86 by the heart was constant and that the myocardial uptake had a complementary exponential relationship with time. These authors also found that Pitressin and l-norepinephrine produced changes in rubidium-86 uptake that were in the same direction as their known effect on the rate of coronary flow.5