ON REPRODUCEABILITY OF KR-85 CLEARANCE CURVES . SIMULTANEOUS BLOOD FLOW MEASUREMENTS ON RAT KIDNEY

In experiments on rats the renal cortical blood flow is measured in situ by the Kr-85 clearance method and correlated with the total renal blood flow obtained by simultaneous direct measurement of renal venous outflow. Calculation of the renal cortical blood flow from the washout-curves was made by use of the formulas advanced by Ingvar and Lassen (1962) and Zierler (1965). According to the evaluation of Ingvar and Lassen (1962) the coefficient of correlation is r=0.849, and according to Zierler (1965)r=0.545. Model experiments carried out with an analogous electrical network show that blood flow values determined according to the formula of Ingvar and Lassen (1962) are dependent neither on the duration nor on the form of the so-called input function, the space of time during which the indicator appears within the range of vision of the detector. Blood flow values calculated according to the formula of Zierler (1965), on the other hand, are strongly affected by these factors. The findings of these model experiments do much to explain the variation, according to the method of evaluation used, in reproduceability of blood flow values in rat kidney cortex measured by the Kr-85 washout-technique. Thus it is concluded that the variation of the input function may be regarded as a systematic source of error in the determination of regional blood flow by the inert gas clearance technique. © 1969 Springer-Verlag.