Influence of Oscillating Flow on LDL Transport and Wall Shear Stress in the Normal Aortic Arch

Lipid accumulation in the aortic wall is an important factor in the development of atherosclerosis. The Low Density Lipoprotein (LDL) at the surface of the endothelium in relation to Wall Shear Stress (WSS) in the normal human aortic arch under unsteady, normal flow and mass conditions was computationally analysed. Concave sides of the aortic arch exhibit, relatively to the convex ones, elevated LDL levels at the surface of the endothelium for all time steps. At the peak systolic velocity, the LDL level reaches a value 23.0% higher than that at entrance in the ascending-descending aorta region. The corresponding LDL levels at the surface of the endothelium for the near minimum entrance velocity instant reaches 26.0%. During the cardiac cycle, the highest area averaged normalized LDL taken up as compared to the lowest one is 0.69%. WSS plays an important role in the lipid accumulation. Low WSS regions are exposed to high LDL levels at the surface of the endothelium. Regions of elevated LDL levels do not necessarily co-locate to the sites of lowest WSS. The near wall paths of the velocities might be the most important factor for the elevated LDL levels at the surface of the endothelium

The Need for Stump-Socket Interface Pressure Measurment during Bidirectionally Perturbed Stance In Transtibial Amputees

Recent studies show significant reduction of postural stability in transtibial amputees (TTAs) especially when a perturbation is applied. However, no record has been seen on the consequences of such perturbation on the Stump-Socket Interface Pressure (SSIP). Our objective was to investigate whether such perturbation impose excessive pressures on the stump. We were also interested on the type of the response and direction in which TAs may face more difficulties. A 52-year-old TA participated in the study. The trial was performed using a custom bidirectional perturbing mechanism in the pitch and roll axes of ankle. Center of Pressure and were recorded by two force platforms and five resistive pressure sensors respectively. Right and anterior perturbations imposed the maximum SSIP while several CoP measures were considerably greater for the prosthetic leg just in left perturbations. This supports the necessity of measurement of SSIP as well as CoP to provide a better understanding about the new situations of TAs in postural stabilit