Biomed Res Int. 2017;2017:7023078.

Fluid-Structure Interaction in Abdominal Aortic Aneurysm: Effect of Modeling Techniques.

Lin S1, Han X2, Bi Y2, Ju S3, Gu L4.
1 School of Civil Engineering and Architecture, Xiamen University of Technology, Xiamen, China; Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0656, USA.
2 Department of Interventional Radiology, The First Affiliated Hospital, Zhengzhou University, Henan Province, China.
3 Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0656, USA.
4 Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0656, USA; Nebraska Center for Materials and Nanoscience, Lincoln, NE 68588-0656, USA.

Abstract

In this work, the impact of modeling techniques on predicting the mechanical behaviors of abdominal aortic aneurysm (AAA) is systematically investigated. The fluid-structure interaction (FSI) model for simultaneously capturing the transient interaction between blood flow dynamics and wall mechanics was compared with its simplified techniques, that is, computational fluid dynamics (CFD) or computational solid stress (CSS) model. Results demonstrated that CFD exhibited relatively smaller vortexes and tends to overestimate the fluid wall shear stress, compared to FSI. On the contrary, the minimal differences in wall stresses and deformation were observed between FSI and CSS models. Furthermore, it was found that the accuracy of CSS prediction depends on the applied pressure profile for the aneurysm sac. A large pressure drop across AAA usually led to the underestimation of wall stresses and thus the AAA rupture. Moreover, the assumed isotropic AAA wall properties, compared to the anisotropic one, will aggravate the difference between the simplified models with the FSI approach. The present work demonstrated the importance of modeling techniques on predicting the blood flow dynamics and wall mechanics of the AAA, which could guide the selection of appropriate modeling technique for significant clinical implications.

PMID: 28321413; DOI:10.1155/2017/7023078

 

Supplements:

Abdominal aortic aneurysms (AAA) are local dilations of the infrarenal aorta. If left untreated, it may continue to expand which eventually rupture. The rupture is a mechanical failure when the stress at the vessel wall exceeds its strength. To determine whether the aneurysm needs to be operated or not, the traditional approach is solely based on its maximum transversal diameter. When the maximum transversal diameter exceeds 55 mm the surgery is normally recommended as current clinical practice. However, small aneurysms can also rupture and has a high mortality rate [1]. Thus, the decision to repair an aneurysm should not be determined by the maximum transversal diameter alone but a more reliable criterion which taking more factors into account. Since aneurysm rupture is a mechanical failure, a criterion associated with the mechanical performance of the AAA such as peak wall stress and strength is proposed by Fillinger et al. [2].

 

Finite element analysis (FEA) is an effective tool for determining the stress distribution on the aneurysm wall [2]. Currently there are three types of models which have been widely used to model the mechanical behavior of the AAA, (i) computational solid stress (CSS) model [3] which only consider the aneurysm wall only and pressure is uniform along the inner surface; (ii) computational fluid dynamics (CFD) [4, 5] model used to estimate wall shear stress which assume the aneurysm wall as rigid; (iii) fluid-structure interaction (FSI) [6, 7]model which couples the flow the inside the aneurysm and the motion of the aneurysm wall together. However, each technique has its own advantages and disadvantages, a detailed comparison between different modeling techniques is made in current study to help people choosing when they have different goals.

 

Results show that the FSI approach is preferred for presurgical planning of the AAA. Compared with FSI, CFD predicted that flow dynamics within AAA might underestimate the development of vortices and overestimate the shear stress. A softer wall material will aggravate the differences between these two modeling approaches. In addition, the CSS model might underestimate the wall stresses unless the pressure profile within the aneurysm could be adopted. The present work demonstrates the differences of three popular modeling techniques on predicting the AAA behaviors, which can be used to provide a fundamental understanding of the AAA behavior, especially blood flow dynamics and wall mechanics, to guide the selection of appropriate modeling technique for preclinical planning and to illuminate the possibilities for exploiting their potential to prevent AAA rupture.

 

 

Figure 1: Aneurysm wall behavior at peak systolic pressure in FSI model. 

 

Figure 2: Flow streamlines colored by velocity magnitude (top) and wall shear stress distribution (bottom) at four different time points for FSI model with anisotropic material property

 

Reference

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