Intrarenal flow of microspheres and red blood cells: skimming in slit and tube models

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Abstract
Microspheres (MS) provide somewhat erroneous estimates of intrarenal blood flow distribution due to a variable MS skimming. The errors were computed from two sets of model experiments. Skimming of 3.5-, 10-, and 15-micron MS and normal and hardened red blood cells (RBC and HRBC, respectively) were studied in a slit model simulating an interlobular artery (ila) with variable diameter from 40 to 160 micron, having as a side branch of constant diameter one afferent arteriole with variable fractional flow. The corresponding afferent arteriole capture zones in the ila were determined in a tube model. All particles except 3.5-micron MS were skimmed, RBC having an effective diameter of 5 micron compared with 8 micron for HRBC. Skimming was greater in tubes than in slits at a given afferent arteriole flow fraction and was predominantly determined by the particle-to-ila diameter ratio. Intrarenal MS and RBC skimming in dog and rat kidneys was predicted on the basis of the number of afferent arterioles along the ila, ila diameter and tapering. The predictions agreed fairly well with available in vivo data. In conclusion, previously observed redistribution of MS, induced by vasodilation and vasoconstriction in the dog kidney, may be quantitatively ascribed to changes in the ila diameters and MS skimming in the inner cortex without redistribution of fractional blood flow between deep and superficial renal zones.