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腹主动脉瘤的孔隙超弹性有限元建模

Porohyperelastic finite element modeling of abdominal aortic aneurysms.

作者信息

Ayyalasomayajula Avinash, Vande Geest Jonathan P, Simon Bruce R

机构信息

Department of Aerospace and Mechanical Engineering, University of Arizona, P.O. Box 210119, Tucson, AZ 85721-011, USA.

出版信息

J Biomech Eng. 2010 Oct;132(10):104502. doi: 10.1115/1.4002370.

Abstract

Abdominal aortic aneurysm (AAA) is the gradual weakening and dilation of the infrarenal aorta. This disease is progressive, asymptomatic, and can eventually lead to rupture--a catastrophic event leading to massive internal bleeding and possibly death. The mechanical environment present in AAA is currently thought to be important in disease initiation, progression, and diagnosis. In this study, we utilize porohyperelastic (PHE) finite element models (FEMs) to investigate how such modeling can be used to better understand the local biomechanical environment in AAA. A 3D hypothetical AAA was constructed with a preferential anterior bulge assuming both the intraluminal thrombus (ILT) and the AAA wall act as porous materials. A parametric study was performed to investigate how physiologically meaningful variations in AAA wall and ILT hydraulic permeabilities affect luminal interstitial fluid velocities and wall stresses within an AAA. A corresponding hyperelastic (HE) simulation was also run in order to be able to compare stress values between PHE and HE simulations. The effect of AAA size on local interstitial fluid velocity was also investigated by simulating maximum diameters (5.5 cm, 4.5 cm, and 3.5 cm) at the baseline values of ILT and AAA wall permeability. Finally, a cyclic PHE simulation was utilized to study the variation in local fluid velocities as a result of a physiologic pulsatile blood pressure. While the ILT hydraulic permeability was found to have minimal affect on interstitial velocities, our simulations demonstrated a 28% increase and a 20% decrease in luminal interstitial fluid velocity as a result of a 1 standard deviation increase and decrease in AAA wall hydraulic permeability, respectively. Peak interstitial velocities in all simulations occurred on the luminal surface adjacent to the region of maximum diameter. These values increased with increasing AAA size. PHE simulations resulted in 19.4%, 40.1%, and 81.0% increases in peak maximum principal wall stresses in comparison to HE simulations for maximum diameters of 35 mm, 45 mm, and 55 mm, respectively. The pulsatile AAA PHE FEM demonstrated a complex interstitial fluid velocity field the direction of which alternated in to and out of the luminal layer of the ILT. The biomechanical environment within both the aneurysmal wall and the ILT is involved in AAA pathogenesis and rupture. Assuming these tissues to be porohyperelastic materials may provide additional insight into the complex solid and fluid forces acting on the cells responsible for aneurysmal remodeling and weakening.

摘要

腹主动脉瘤(AAA)是肾下腹主动脉逐渐变弱和扩张的疾病。这种疾病具有渐进性、无症状性,最终可能导致破裂,这是一种灾难性事件,会导致大量内出血甚至可能死亡。目前认为AAA中存在的力学环境在疾病的起始、进展和诊断中很重要。在本研究中,我们利用多孔超弹性(PHE)有限元模型(FEMs)来研究如何使用这种建模更好地理解AAA中的局部生物力学环境。构建了一个具有优先向前凸出的三维假设性AAA,假设腔内血栓(ILT)和AAA壁均作为多孔材料。进行了参数研究,以探讨AAA壁和ILT水力渗透率在生理上有意义的变化如何影响AAA内的管腔间质液速度和壁应力。还进行了相应的超弹性(HE)模拟,以便能够比较PHE和HE模拟之间的应力值。通过在ILT和AAA壁渗透率的基线值下模拟最大直径(5.5厘米、4.5厘米和3.5厘米),研究了AAA大小对局部间质液速度的影响。最后,利用循环PHE模拟研究生理搏动性血压导致的局部流体速度变化。虽然发现ILT水力渗透率对间质速度影响最小,但我们的模拟表明,由于AAA壁水力渗透率增加和降低1个标准差,管腔间质液速度分别增加28%和降低20%。所有模拟中的间质速度峰值出现在与最大直径区域相邻的管腔表面。这些值随着AAA大小的增加而增加。与HE模拟相比,对于最大直径分别为35毫米、45毫米和55毫米的情况,PHE模拟导致最大主壁应力峰值分别增加19.4%、40.1%和81.0%。搏动性AAA的PHE有限元模型显示了一个复杂的间质液速度场,其方向在ILT管腔层内外交替。动脉瘤壁和ILT内的生物力学环境都参与了AAA的发病机制和破裂。假设这些组织为多孔超弹性材料可能会为作用于负责动脉瘤重塑和弱化的细胞的复杂固体和流体力提供额外的见解。

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