Experimental Model for Shear Stress Measurement in Vascular Circulation by Micro Particle Image Velocimetry

The present study investigated the basic architectonics of a micro particle image velocimetry (PIV) system and measured shear stress in a model of hepatic microcirculation for the purpose of understanding mechanical stress in small-for-size graft liver transplantation. The flow velocity was measured using a micro PIV system in a straight confluence, with bifurcation channels of the hepatic sinusoid model made of a clear acrylics that was 300μm in width and 100μm in height. In the micro PIV system, two strobes as a light source illuminated an object from underneath, and its visual flow images were recorded into a computer using a high-resolution CCD camera. The flow visualization was performed by adding distilled water to proper nylon tracer particles of 1μm in diameter (specific gravity: 1.02). The experimental velocity profile measured by this micro PIV system was in good accordance with both the results obtained using the three-dimensional Navier-Strokes equations on a square tube and Hagen-Poiseulle equations on a circular tube, which confirmed the suitability of this measurement system. The flow velocity after both confluence and branching in the model of hepatic circulation very rapidly became similar to that of the straight flow. The wall shear stress was calculated using an equation of τ=μヤu/dy, based on the measured mean velocity distribution. The measurement data of shear stress in the straight flow was accurate with an error of 6%. This micro PIV system had sufficient reliability for measuring the shear stress in hepatic microcirculation and serve as a new instrument for understanding pathological conditions in hepatic microcirculation in small-for-size liver transplantation.