Measurement of wall shear stress in a glass model renal bifurcation by a technique that monitors the rate of erosion of an opaque coating layer

Abstract

A novel technique was used to measure wall shear stress in a glass model of an aorto-renal bifurcation. A viscous, white coating material was applied in a thin layer to the inner walls of glass models, and the removal of the layer by steady flow of a dark aqueous dye (Reynolds number 510 and 1000) was recorded on videotape. On playback, a video analyzer produced intensity versus time information at chosen positions. In a calibration experiment using Poiseuille flow, the inverse of the time between 50% and 20% of the total intensity change was linearly related to the calculated wall shear stress (correlation coefficient 0.98, range tested: 0 to 4 dyn/cm²). Measurements were made at 36 positions downstream from the side branch in a 90°-side branch model (main branch and parent = 1.56 cm I.D., side branch = 0.77 cm I.D.) of a renal bifurcation. As anticipated, there was a high shear stress region downstream from the branch but this region had a bilobate shape that was not expected. Similarity principles were used to convert wall shear stresses measured in the model to those which would occur with blood flow. Results indicate that in vivo shear stresses near a bifurcation exceed those reported to cause changes in endothelial cell permeability, and in some cases reach values reported to cause structural damage to endothelial cells.