Oscillating LDL accumulation in normal human aortic arch - shear dependent endothelium.

OBJECTIVE: Abnormal mass transfer of blood components to the arterial walls initiates atherosclerosis. Understating the role of mass transfer within the arterial walls requires quantitative analysis. The oscillating lipid accumulation in the aortic wall is examined in the normal human aortic arch with shear dependent endothelium properties. METHODS: A semi-permeable nature of the arterial wall computational model, applied in the normal human aortic arch under unsteady normal flow and mass conditions, is incorporated with hydraulic conductivity and permeability treated as wall shear stress dependent. The coupling of fluid dynamics and solute dynamics at the endothelium was achieved by the Kedem-Katchalsky equation. A typical aortic arch blood flow waveform at resting conditions and lasting 800 msec is applied. RESULTS: With constant values of water infiltration and endothelial permeability the surface vertex average normalized luminal concentration is 4.25 % higher than that at the entrance. With shear dependent values the surface vertex average normalized luminal concentration is 7.3 % higher than at the entrance. The luminal surface concentration at the arterial wall is flow-dependent with local variations due to geometric features. Concave sides of the aortic arch exhibit, relatively to the convex ones, elevated low density lipoprotein at all time steps. CONCLUSIONS: The degree of elevation in luminal surface LDL concentration is mostly affected from the water infiltration velocity at the vessel wall. Shear dependent endothelial values must be taken into account whenever fluid and mass flow within the arterial system is incorporated.

Haemodynamic factors and the important role of local low static pressure in coronary wall thickening.

UNLABELLED: BACKGROUND/STUDY OBJECTIVES: The purpose of our study was to investigate the possible correlation between blood flow physical parameters and the wall thickening in typical human coronary arteries. METHODS: Digitized images of seven transparent arterial segments prepared post-mortem were adopted from a previous study in order to extract the geometry for numerical analysis. Using the exterior outline, reconstructed forms of the vessel geometries were used for subsequent computational fluid dynamic analysis. Data was input to a pre-processing code for unstructured mesh generation. The flow was assumed to be two-dimensional, steady, laminar with parabolic inlet velocity profile. The vessel walls were assumed to be smooth, inelastic and impermeable. Non-Newtonian power law was applied to model blood rheology. The arterial wall thickening was measured and correlated to the wall shear stress, static pressure, molecular viscosity, and near wall blood flow velocity. RESULTS: Wall shear stress, static pressure and near wall velocity magnitude exhibit negative correlation to wall thickening, while molecular viscosity exhibits positive correlation to wall thickening. CONCLUSION: There is a strong correlation between the development of vessel wall thickening and the blood flow physical parameters. Amongst these parameters the role of local low wall static pressure is predominant.