Distribution of shear stress over smooth muscle cells in deformable arterial wall
Department of Energy and Environmental Technology, Lappeenranta University of Technology, Lappeenranta, Finland. Medical & Biological Engineering & Computing
(Impact Factor: 1.73).
08/2008; 46(7):649-57. DOI: 10.1007/s11517-008-0338-7
A biphasic, anisotropic model of the deformable aortic wall in combination with computational fluid dynamics is used to investigate the variation of shear stress over smooth muscle cells (SMCs) with transmural pressure. The media layer is modeled as a porous medium consisting of SMCs and a homogeneous porous medium of interstitial fluid and elastin, collagen and proteoglycans fibers. Interstitial fluid enters the media through fenestral pores, which are distributed over the internal elastic lamina (IEL). The IEL is considered as an impermeable barrier to fluid flow except at fenestral pores. The thickness and the radius of aortic wall vary with transmural pressure ranging from 10 to 180 mm Hg. It is assumed that SMCs are cylinders with a circular cross section at 0 mm Hg. As the transmural pressure increases, SMCs elongate with simultaneous change of cross sectional shape into ellipse according to the strain field in the media. Results demonstrate that the variation of shear stress within the media layer is significantly dependent on the configuration and cross sectional shape of SMCs. In the staggered array of SMCs, the shear stress over the first SMC nearest to the IEL is about 2.2 times lower than that of the square array. The shear stress even over the second nearest SMC to the IEL is considerably higher (about 15%) in the staggered array. In addition to configuration and cross sectional shape of SMCs, the variation of structural properties of the media layer with pressure and the sensitivity of the local shear stress to the minimum distance between SMCs and the IEL (reducing with transmural pressure) between SMCs and the IEL are studied. At 180 mm Hg, the ratio of the local shear stress of the nearest SMC to that of the second nearest SMC is 4.8 in the square array, whereas it reduces to about 1.8 in the staggered array. The importance of the fluid shear stress is associated with its role in the biomolecular state of smooth muscle cells bearing the shear stress.
Available from: Payman Jalali
- "However, some of studies neglected the three major of branches of aortic arch. Towfiq  and Dabagh et al.  have shown that the aorta size is subjected to change with blood pressure. But no attention has been made on studying the corresponding influence on the blood flow features. "
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ABSTRACT: A three-dimensional computer model of human aortic arch with three branches is reproduced to study the pulsatile blood flow with Finite Element Method. In specific, the focus is on variation of wall shear stress, which plays an important role in the localization and development of atherosclerotic plaques. Pulsatile pressure pulse is used as boundary condition to avoid flow entry development, and the aorta walls are considered rigid. The aorta model along with boundary conditions is altered to study the effect of hypotension and hypertension. The results illustrated low and fluctuating shear stress at outer and inner wall of aortic arch, proximal wall of branches, and entry region. Despite the simplification of aorta model, rigid walls and other assumptions results displayed that hypertension causes lowered local wall shear stresses. It is the sign of an increased risk of atherosclerosis. The assessment of hemodynamics shows that under the flow regimes of hypotension and hypertension, the risk of atherosclerosis localization in human aorta may increase.
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ABSTRACT: The interstitial flow through a deformable media layer of thoracic aorta wall is simulated in a three-dimensional model to study the variation of shear stress over the surface of smooth muscle cells (SMCs) with pressure. A biphasic, anisotropic model assuming the radius, thickness, and hydraulic conductivity of vessel wall as functions of transmural pressure is introduced to numerical simulations. The deformable media layer is modeled as a heterogeneous medium composed of SMCs, which are arranged in squared or staggered configurations, embedded in a continuous porous extracellular matrix composed of elastin, proteoglycan, and collagen fibers. The media layer is compressed according to the strain field dictated by the pressure increase from 0 to 180 mmHg. Smooth muscle cells are assumed as cylindrical objects with circular cross section at 0 mmHg. They follow the compression of media so that their cross sections change from circles into ellipses. Results show that the local shear stress over the surface of the nearest SMC to the internal elastic lamina (IEL) depends on the pressure and the arrangement of SMCs. It could be twenty five times larger than the shear stress on SMCs far away from the IEL when the leading edge of the SMC is located in front of the fenestral pore. It is in contrast to earlier studies that suggested in a normal artery with intact IEL, the innermost layer of SMC at the intimalmedial border is biochemically the most active layer due to elevated shear stress.
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ABSTRACT: The sensitivity of shear stress over smooth muscle cells (SMCs) to the deformability of media layer due to pressure is investigated in thoracic aorta wall using three-dimensional simulations. A biphasic, anisotropic model assuming the radius, thickness, and hydraulic conductivity of vessel wall as functions of transmural pressure is employed in numerical simulations. The leakage of interstitial fluid from intima to media layer is only possible through fenestral pores on the internal elastic lamina (IEL). The media layer is assumed a heterogeneous medium containing SMCs embedded in a porous extracellular matrix of elastin, proteoglycan, and collagen fibers. The applicable pressures for the deformation of media layer are varied from 0 to 180 mmHg. The SMCs are cylindrical objects of circular cross section at zero pressure. The cross sectional shape of SMCs changes from circle to ellipse as the media is compressed. The local shear stress over the nearest SMC to the IEL profoundly depends on pressure, SMCs configurations, and the corresponding distance to the IEL. The consideration of various SMC configurations, namely the staggered and square arrays, mimics various physiological conditions that can happen in positioning of an SMC. The results of our simulations show that even the second nearest SMCs to the IEL can significantly change their functions due to high shear stress levels. This is in contrast to earlier studies suggesting the highest vulnerability to shear stress for the innermost layer of SMCs at the intimal-medial interface.
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