Wave Reflection at the Boundary Layer and Initial Factors of Atherosclerosis

The aim is to study the blood flow and vessel wall viscoelastic alterations at the boundary layer. Methods and Results: In 12 healthy men (18 - 52 years of age) at the different sites of the aorta peak velocity, net flow, flow acceleration has been investigated by Magnetic Resonance Angiography. In the aortic arch in the end systole blood flow separates into the opposite directed streams resulting in the wave superposition. At the outer curvature of the isthmus, flow acceleration in the initial diastole is 6.26 times higher than that in systole. Net flow from systole to diastole increases 2.5 ± 0.5 folds. From the end systole to the initial diastole there is a plateau on the net flow graph. At the outer curvature of isthmus, group wave at the boundary reflection, changes in phase at 180o. Herewith, flow wave oscillation frequency at the outer curvature is two times higher (2.5 Hz) than that at the inner (1.25 Hz). Conclusion: During the heart cycle, blood motion at the boundary layer, forms the surface wave and facilitates the blood structural rearrangement and flow. At the end systole, at the outer curvature of the isthmus, pulse pressure at the reflection is in the resonance with the end systolic pressure drop. Amplitude of the wall stress increases. Forming standing wave leads to the dissipation of the wall mechanical energy. Here, in the initial diastole, group wave, due to the wave reflection and frequency dispersion, facilitates the structural rearrangement/denudation of the vessel wall. By the removing resonance oscillation during the end systole/initial diastole between the heart and vessel wall, atherosclerosis can be avoided.

钢板-空气背衬上含空腔粘弹性材料层的声反射特性

本文研究声波从水中入射到粘弹性材料层-钢板-空气上的反射特性,运用分层介质中的波动理论研究粘弹性层均匀情况的声特性,运用有限元方法研究粘弹性层含空气腔结构情况的声特性。结果表明,改变粘弹性材料消声特性需要综合调整材料的弹性参数;粘弹性层内的空腔结构对声特性产生很大影响,改变其谐振特性和反射系数的收敛特性。文中以含圆锥腔、圆台等复合腔的结构粘弹性层为例,计算了其反射系数的频响特性、谐振模态,并分析了结构的影响。