Regional blood flow by fractional distribution of indicators.

SAPIRSTEIN, LEO. A. Regional blood Jaw by fractional distribution of indicators. Am. J. Physiol. 193(1): 161-168. 1958.---K~~ Cl, Rb86C1 and iodoantipyrine (P31) 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. KWl and RbVl 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 thah 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 RbE6 and K42 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 K42 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. I T WAS SHOWN elsewhere (I) that between findings in other species. The brain values were 5 and 60 seconds after the intravenous exceedingly low. It was suggested that though administration of K42C1 to rats, the manthe low cerebral values might be genuine, they ner in which K42 was distributed among the might have resulted from a fall in K42 content organs did not change demonstrably with of the brain preceding the first observation. time. It was argued from this that the fracThe present study was undertaken to investitional distribution of K42 corresponded to the gate this possibility. In the course of the fractional distribution of the cardiac output. study, the techniques employed were modified The blood flow values obtained for other and the theoretical basis of the method was organs than the brain were in fair agreement revised and expanded. The application of the with accepted values based in most cases on method to the dog has made possible comReceived for publication August 12, 1957. parison of the results obtained with blood flow l Supported in part by a contract between the U. S. values obtained by other methods in the same Air Force School of Aviation Medicine, Randolph species. Field, Tex. and The Ohio State University Research METHODS Foundation. This work was also supported in part by grants-in-aid from the Central Ohio Heart Association The rats used in these studies were young and the American Heart Association. female albinos (225-275 gm) of uniform stock. 161 by 10.0.33.6 on July 1, 2017 http://ajple.physiology.org/ D ow nladed fom ~62 LEO A, SAPIRSTEIN The animals were fasted for 18 hours before use, but were allowed free access to water. Nine healthy mongrel females were used in the dog experiments. These animals were selected for uniformity in weight (6-8 kg). Obviously immature, obviously old, pregnant and lactating animals were rejected. No other precautions were taken to insure uniformity in the experimental group. The animals were fasted for 18 hours before use, but allowed free access to water. The three indicator substances employed were K42Cl, Rb@Cl and 4-iodoantipyrine (I131). Isotopic potassium and rubidium were obtained from the Oak Ridge National Laboratories. Iodoantipyrine was obtained from Abbott Laboratories. The K42Cl shipments were dried and taken up in a volume of 0.85 % NaCl sufficient to bring their K3g concentration to 4-5 mEq/l. In rats the injected dose given in a volume of 0.4-0.5 ml contained S-IO PC of K42. In the dog experiments, the solution was similarly prepared, but 25-50 pc was given in a volume of 2.0-2.5 ml. Rb86C1 shipments were dried and taken up in 0.85 % NaCl. Five-microcurie doses in 0.5 ml were used. Iodoantipyrine was made up in the same manner as Rb86Cl but without preliminary drying. The injected solution contained 5 pc/o.s ml. In the rat organ experiments, the animals were anesthetized with 40 mg/kg of pentobarbital sodium by the intraperitoneal route. A femoral vein was exposed, and the isotope injected using a o.s-ml tuberculin syringe. The injection time was less than 0.5 seconds. The animals were killed by cutting through the thorax just below the axillae with a mallet driven axe. The timing was accurate to &I second. Other rats of the same stock were used for the construction of arterial curves of indicator dilution. The technique was the usual one used in indicator dilution determinations of cardiac output, modified for application to the rat as follows: the indicator was injected in the femoral vein in a volume of o. 1-0.2 ml containing o.p-1.0 PC of the indicator. Carotid arterial blood samples were collected through a PE 20 polyethylene catheter, 15 cm in length, which delivered into a sample collector which permitted 90 collections to be made per minute (2). The bleeding rate was 25-30 pi/collection. The points used in the construction of the portion of the curve employed in the calculation of the cardiac output were obtained within 8 seconds after the injection of indicator. In the calculation of the cardiac output, the observed concentrations of indicator in the arterial blood were summated up to the time of the first recirculation (identified as the first recognizable deviation from rectilinearity on the semilog plot of concentration). To this value was added the sum of the converging geometric series of values extrapolated from the rectilinear descending limb. The sum of real and extrapolated concentration values was used as the denominator in the usual equation for the calculation of the cardiac output. The amount of indicator transferred from the venous to the arterial circulation at any time was calculated by multiplying the cardiac output so obtained by the summated arterial concentration constructed from real points up to the time under consideration. It must be stressed that the summated arterial concentration curve used for the calculation of indicator transfer is not identical with the summated arterial concentration used in the calculation of cardiac output. Up to the time of recirculation the former value is smaller, for the extrapolated sum is not included in it; after recirculation, it becomes larger for the real values of arterial concentration are in excess of those extrapolated from the descending limb of the semilogarithmic plot. In the dog experiments, indicator dilution curves were made upon the same animals employed in the organ work. After anesthesia with 30 mg/kg of pentobarbital by the intravenous route the K42C1 was injected into a femoral vein. A Cournand needle in the opposite femoral artery served for the sampling of arterial blood at 30 collections/min. The animals were killed at 20-120 seconds by the rapid intravenous injection of 20 ml saturated KCl. The determination of arterial concentrations of all isotopes was made upon whole blood samples pipetted into planchets and counted with an end window Geiger-Muller tube. Fivetenths-milliliter samples of dog blood and 0.02 by 10.0.33.6 on July 1, 2017 http://ajple.physiology.org/ D ow nladed fom REGIONAL BLOOD FLOW I63 ml samples of rat blood measured in a hemoseconds. The results are similar to those of globin pipette were taken for counting. The three other experiments of the same type. arterial concentrations were plotted on semilog In general, the organs show continued acpaper as a function of time. The initial portion cumulation of K42 and Rbss through the first of the curve was used for the determination 9 seconds, and then stabilize their content of the cardiac output in the usual manner. until 64 seconds. The brain behaves exceptionStandards were made from the injected solually, showing its maximum content of isotope tions. In the case of the short lived K42, standbefore 9 seconds, and declining precipitously, ard counts were made every 15 minutes, and so that between 9 and 64 seconds it contains the blood counts referred to the arithmetic less than 0.2 % of the injected dose, compared mean of the two closest standards. with the maximum value of 0.6-0.8% at 6 The indicator content of dog organs was deseconds. This behavior is more clearly illustermined upon an aliquot of a digest of the trated in figure I which shows the cerebral K42 entire organ. Such digests were made by content as a function of time at I-second covering the organs with 6 N HCl in Mason intervals in another experiment. jars and cooking in a pressure cooker for 3-4 The behavior of the organs toward 4-iodohours at 20 pounds pressure. antipyrine is radically different. Only the The counting of rat organs was simplified brain, skin and carcass show a stable content by the availability of a very large (I 1. caof this indicator. The heart, kidneys and gut pacity) well counter with 4 pi geometry (oball lose the label continuously during the first tainable from The Nucleonic Corp. of America, minute, while the liver accumulates it proBrooklyn, N. Y.). The whole organ was placed gressively. in a Dixie cup and its gamma radiation counted Although no effort was made to collect the after insertion into the well. Despite the low blood spilled when the animals were killed, yield of gamma disintegrations in K42 breakthe recovery of the isotopes in animals killed down and the low efficiency of gamma countbetween 9 and 64 seconds averaged 102% of ing, the counting rate was satisfactorily high the amount administered. From this it would since the whole organ, rather than an aliquot, appear that negligibly small quantities of the was measured. indicators remain in the blood after 9 seconds. RESULTS (This statement should not be interpreted to indicate that the recirculation of indicators is Organ Content of Indicator as a Function of insignificant.) Time: Rat. Table I shows the results of an exOrgan Content of K42 as a Function of Time: periment in which three groups of rats, conDog. Table 2 shows the K42 content of the sisting of 28 animals each, received K42, RbB organs in three groups of dogs killed at 20-39, or iodoantipyrine (1131), and were killed in 40-59 and 60-120 seconds after the administragroups of four at 3, 6, 9, 12, 16, 32 and 64 tion of K42C1. There is no evidence of systemTABLE I. CONTENT OF ~~~~ Rbs6 AND 1131 IN ORGANS OF RATS AT VARYING TIMES AFTER SINGLE INTRAVENOUS INJECTION OF K 42 OR Rb86, Cl OR IODOANTIPYRINE (1131) BY VEIN