Noninvasive measurement of intrarenal blood flow distribution: kinetic model of renal 123I-hippuran handling.

A new technique for noninvasive measurement of intrarenal blood flow distribution over cortex and medulla is proposed. The technique involves analysis of 123I-labeled hippuran renography, according to a kinetic model that describes the flow of 123I-hippuran from the heart (input) through the renal cortex and medulla to the bladder (output). The method is validated and compared with the standard microsphere injection technique in anesthetized dogs. Changes in intrarenal blood flow distribution were induced by infusion of placebo (n = 6), angiotensin I (n = 5), or atrial natriuretic factor (n = 5). Baseline percentage medullary blood flow in the left kidney was 12 +/- 1% of total renal blood flow measured with microspheres and 15 +/- 1% with renography. During infusion of the placebo, medullary blood flow decreased slightly compared with baseline, as measured with both methods, by 2 +/- 6 (microspheres) and 1 +/- 8% (renography). Infusion of angiotensin I caused a marked fall in medullary blood flow by 42 +/- 11 (microspheres) and 57 +/- 8% (renography). In contrast, infusion of atrial natriuretic factor caused a small rise in medullary blood flow as measured with both methods (9 +/- 3 and 12 +/- 11%, respectively). The absolute and percent changes in medullary blood flow measured with renography correlated with those measured with microspheres (left kidney: r = 0.67, P = 0.005; r = 0.71, P = 0.003, respectively; right kidney: r = 0.62, P = 0.01; r = 0.68, P = 0.004, respectively). We conclude that the proposed kinetic model of renal 123I-hippuran handling can be used to measure changes in intrarenal blood flow distribution and, because of its noninvasive character, may be of use in clinical studies.