INFLUENCE OF VASOACTIVE DRUGS ON WALL SHEAR-STRESS DISTRIBUTION IN THE ABDOMINAL AORTIC BIFURCATION - AN IN-VITRO STUDY

The present study compares the wall shear stress (rate) distribution i n a compliant aortic bifurcation model under three different hemodynam ic states: normal state, angiotensin II infusion state (vasoconstricto r), and isoproterenol infusion state (vasodilator). Using a Newtonian blood analog fluid, flow wave forms corresponding to each flow state w ere generated in an in vitro flow loop and a photographic flow visuali zation technique was employed to measure wall shear rate. The results indicate a zone of low mean wall shear stress and highly oscillatory s hear stress on the outer (lateral) wall of the bifurcation. In this zo ne, the mean wall shear stress became negative for all three hemodynam ic states indicating flow separation. However, the spatial extent of t he flow separation zone was not affected significantly by the flow sta te. The study also revealed a large spatial variation of the phase ang le between the hoop strain (circumferential strain due to radial arter y expansion) and the wall shear stress, the two main mechanical stimul i acting on endothelial cells which affect their biology. In the zone of low mean wall shear stress on the outer wall, the two stimuli were more out of phase relative to the mother branch, whereas they were les s out of phase (by about 50 degrees) on the inner wall (flow divider s ide). This phase angle was affected significantly by the flow state. F or angiotensin II, the phase angle reached a maximum of 125 degrees in the low mean shear zone while the maximum was 94 degrees and 66 degre es for the normal and isoproterenol states, respectively. Our observat ion that large phase angles between the hoop strain and wall shear str ess wave forms are localized in the low shear stress region where athe rosclerotic disease occurs suggests the possible physiological relevan ce of this phase angle to the development of atherosclerosis. (C) 1998 Biomedical Engineering Society.