Fundamental flow studies in models of human arteries

Atherosclerosis is the principal cause of myocardial and cerebral infarction. Atherosclerotic lesions are present in localized regions of the vasculature where abrupt changes in vessel geometry occur, such as bends and bifurcations. In order to develop features of the risk profile, flow systems which simulate closely the pertinent anatomy and surface properties of the human vasculature are used with test fluids which mimic the physicochemical properties of blood. Analysis of the flow regimes were made by one-, two- or three-dimensional laser Doppler anemometry. Rigid and elastic model vessels with simple flow geometry as well as true-to-scale models of human arterial casts were used. Viscous pseudoplastic and viscoelastic fluid suspensions were employed under both steady and pulsatile flow. From the measured velocity profiles, the shear rates were estimated and with the local viscosity the shear stresses calculated. Flow behaviour was visualized using dyes and birefringent solutions. It was found that the geometry and flow rate ratio at bifurcations greatly influence the flow separation zones. It is also important to consider elasticity, pulsatility and non-Newtonian flow behavior in large blood vessels in zones where secondary flow is developed and flow separation zones are formed.