Flow dynamics in a stenosed carotid bifurcation model--Part I: Basic velocity measurements.

A model of the human carotid artery bifurcation has been constructed and tested under mean physiologic flow conditions (fluid viscosity = 0.035 poise; mean Re inlet = 400; unconstricted flow split = 70:30, internal carotid artery:external carotid artery). Smooth, axisymmetric constrictor plugs with 0, 20, 40, 60, and 80% diameter reduction are placed in the simulated proximal internal carotid artery to provide a range of flow conditions similar to those found clinically. Axial velocity measurements are made at sites +/- 0.625 radius within the lumen of the tube at distances of 0, 1, 3, 5 and 10 diameters downstream of the constrictor throat using H2 bubble markers and a 7.5 MHz ultrasound pulse Doppler. Measurement of mean, mode -3 dB down high and low and -9 dB down high and low velocities are made from selected fast-Fourier transform (FFT) spectra. The flow field downstream of the 0% diameter reduction is entirely laminar, exhibiting a peak skewed toward the flow divider along the entire 10 diameters downstream and having a consistently narrow bandwidth. Obstruction of the flow channel produces increased axial velocity at the constrictor (20%), an oscillatory jet extending approximately 5 diameters downstream (40%), a transitional jet extending approximately 5 diameters downstream (60%) and a turbulent jet extending approximately 3 diameters downstream (80%). Velocity bandwidth (both -3 dB and -9 dB) increases with degree of constriction and low velocity flow patterns exist between the center line and both tube walls. Presence of constriction produces characteristic downstream flow patterns which are distinctive for each degree of diameter reduction.