Regional Blood Flow by Fractional Distribution of Indicators

K 42 Cl, Rb 86 Cl and iodoantipyrine (I 131 ) were given in single intravenous injections to rats. The isotope content of the organs and the arterial blood concentrations were studied as a function of time. K 42 Cl and Rb 86 Cl reached a stable level in all organs other than the brain in 6–9 seconds and maintained this level until 64 seconds. The arterial concentration curves for the isotopes showed that the injected dose was almost completely transferred into the arterial system at about 6–8 seconds. The isotopes showed subsequent recirculation amounting to about 40% of the original dose between the first recirculation and 64 seconds. The organs which displayed stability during the period of recirculation must have had extraction ratios from zero time less than 1.00 but equal to that of the whole body. The fractional uptake of indicator by such organs must therefore have been equal to their blood flow fraction of the cardiac output. The brain reached its maximum content of Rb 86 and K 42 in 5–6 seconds; both isotopes then disappeared rapidly. The brain was thus shown to have a lower extraction ratio toward these isotopes than the body as a whole; its flow fraction could not therefore be measured by their use. Most organs failed to show stability of their iodoantipyrine content between 9 and 64 seconds; this indicator is not suitable for the measurement of the flow fraction of such organs. By combining values for the cardiac output and the fractional uptake of K 42 in dog organs, regional blood flow values were obtained. For those other organs where flow values by other methods are available, the agreement was good. The following blood flow values were obtained in the major organs of the dog: Heart (coronary flow), 1.0 ml/gm/min.; kidney, 3.0 ml/gm/min.; liver, 1.2 ml/gm/min. (0.4 ml/gm/min. hepatic artery, 0.8 ml/gm/min. portal vein); skin, 0.07 ml/gm/min.