P21: Generalized blood rheological model for analyzing thrombus formation in venous valve architecture

Abstract

The health impact of venous thromboembolism (VTE), a major cause of morbidity and mortality, can be appreciated from the large number of people affected, 1 million Americans and > 700,000 Europeans annually. The economic impacts of this have been the focus of several studies, with the annual cost to the US healthcare system of incident VTE being estimated at up to $10 billion. The non-Newtonian, shear-thinning blood rheology plays a major role in determining the shape and duration of stagnant fluid zones arising within the venous valve leaflet pockets where the thrombi occur. It has also been suggested that valve compression treatment ensuring oscillating shear stress at the vein wall within the pocket can prevent the formation of clots. Many models have been proposed for blood rheology, some with yield stress and others not, and these have been used extensively to model wall shear stress in models of coronary arteries, with a view to determining the likelihood of stenoses. In this new work, we propose a new non-Newtonian model whose parameters can be readily determined using a capillary rheometer. The model takes the form σ = σ0 + k εn + µ∞ ε where σ is the shear stress and is the ε shear strain rate. σ0 is the yield stress and the fluid viscosity at a high shear strain rate. This generalizes three of the existing models and eliminates the unphysical characteristics of each individual model. This model incorporates the Herschel-Bulkley, Casson, and K-L models as special cases. The overall aim of the work is to determine the effect of venous valve geometry on the likelihood of clot formation, using a realistic description of blood rheology.