FLOW VISUALIZATION AND 1-D AND 3-D LASER-DOPPLER-ANEMOMETER MEASUREMENTS IN MODELS OF HUMAN CAROTID ARTERIES

Pulsatile flow, wall distensibility, non-Newtonian flow characteristic s of blood in flow separation regions, and high/low blood pressure wer e studied in elastic silicon rubber models having a compliance similar to human vessels and the same surface structure as the biological int ima models of (1) a healthy carotid artery model, (2) a 90% stenosis i n the ICA, and (3) 80% stenosis in both the internal and external caro tid arteries. Flow was visualized for steady flow and pulsatile studie s to localize flow separation regions and reattachment points. Local v elocity was measured with a 1-, 2-, or 3-D laser-Doppler-anemometer (L DA). Flow in the unstenosed model was Re = 250. In the stenosed models , the Re number decreased to Re = 180 and 213 under the same experimen tal conditions. High velocity fluctuations with vortices were found in the stenosed models. The jet flow in the stenosis increased up to 4 m /s. With an increasing bifurcation angle, the separation regions in th e ECA and ICA increased. Increased flow (Re = 350) led to an increase in flow separation and high velocity shear gradients. The highest shea r stresses were nearly 20 times higher than normal. The 90% stenosis c reated high velocity shear gradients and velocity fluctuations. Downst ream of the stenoses, eddies were found over the whole cross-section. In the healthy model a slight flow separation region was observed in t he ICA at the branching cross-section whereas in the stenosed models, the flow separation regions extended far into the ICA. We conclude tha t a detailed understanding of flow is necessary before vascular surger y is performed especially before artificial grafts or patches are impl anted.