Numerical Simulation of In-Plane Crack Propagation in Aortic Dissection / 医用生物力学

Objective Based on interface damage, a numerical simulation method for in-plane propagation of false lumen (FL) was proposed to explore the regular pattern of in-plane propagation of the initial cavity. Methods Three interface damage modes were characterized by bi-linear traction separation law, and the damage parameters were calibrated by simulating peeling and shearing tests. The damage interface was introduced into the ideal double-layer cylindrical tube aortic model by means of cohesive zone model (CZM) to simulate the in-plane propagation of FL. The control variable method was used to establish several computational models to investigate the influence of cavity geometric parameters on propagation direction, critical pressure and interface damage mode. Results The interface damage was mainly opening mode (Mode I) in axial propagation and sliding mode (Mode II) in circumferential propagation. With radial depth of the initial cavity increasing, the propagation of the FL changed from circumferential direction to axial direction, the critical pressure decreased, and the axial damage tended to be pure opening mode. With circumferential angle and axial length of the initial cavity increasing, the critical pressure decreased and the circumferential damage tended to be pure sliding mode. The critical pressure of single damage was lower than that of mixed damage. Conclusions The CZM can effectively characterize interface damage behavior of elastic lamellae within the media, and it applies to numerical simulation of in-plane propagation of the FL. The results of this study is helpful to understand the complex pathophysiological process of dissection crack propagation.

Fluid-Structure Interaction Simulation of Multiple Overlapping Uncovered Stent Intervention in Aortic Dissection / 医用生物力学

Objective To propose a one-way fluid-structure interaction (FSI) method based on an idealized aortic dissection model, so as to analyze the hemodynamics and wall stress in the false lumen (FL) under the influence of multiple overlapping uncovered stents (MOUS). Methods Upon establishment of the numerical model, the models were divided into two categories according to whether the model involved FL perfused branch artery. The characteristics of hemodynamics and wall stress state in the post-operative scenarios were simulated under different surgical strategies. The wall stress state of the FL before and after thrombosis formation was also compared and analyzed. ResultsThe release process of the stents had little influence on wall stress of the FL. The high velocity and high wall shear stress (WSS) area in the FL could not be reduced by using the MOUS alone. If only the proximal entry tear was blocked with a covered stent-graft, the distal end would maintain a region of high flow rate and high WSS. The combination of covered stent-graft and MOUS would result in a region of low flow rate and low WSS, as well as reduced wall pressure and wall stress in the FL. Compared with the model with FL perfused branch arteries, the model without it was more likely to form a region of low flow rate and low WSS after surgery. However, blood pressure in the FL was relatively higher. The formation of thrombus in the FL could greatly reduce wall stress in the area covered by the thrombus. Conclusions The method proposed in this study can simultaneously investigate hemodynamics and wall stress characteristics of the FL, and provide support for studying mechanical mechanism of FL thrombolysis induced by MOUS and the post-operative aortic expansion.