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The coincidence counting technic was used to measure the clearance equivalent of rubidium-84 as a function of coronary flow by the human heart in vivo. This technic makes possible a distinction of radioactivity of the heart muscle from the surrounding tissue, eliminates lead collimation, and is more sensitive than the singles technic. In experiments on isolated dog heart it was found that changes in rate of perfusion of the coronary arteries failed to influence the myocardial extraction ratio of rubidium-84. Alterations in heart rate were also without effect. Nitroglycerin increased the clearance equivalent of rubidium-84 in patients without coronary heart disease. In patients with coronary artery disease the drug led to fall in clearance equivalent. The method has been helpful in distinguishing between normal individuals and those with coronary artery disease.
Bing et al. (1964) studied this question.