Finite Element Simulation of Double-Stent Parallel Thrombectomy at Y-Shaped Bifurcation of Internal Carotid Artery / 医用生物力学

Objective To study the process of single stent and double-stent thrombectomy at the Y-shaped bifurcation of the ideal internal carotid artery by finite element simulation, analyze the stent-thrombus-vessel interaction during the thrombectomy process based on the simulation results, and provide guidance for improving the effect of stent thrombectomy at the bifurcation. Methods The CAD software was used to build the model and the finite element analysis software was used to simulate the process of single stent and double-stent thrombectomy. Results Thrombectomy was unsuccessful in single stent model and successful in double-stent model, and the maximum stress of thrombus during embolus retrieval was twice that of single stent, the maximum strain was 1.12 times that of single stent, and the maximum contact pressure on the surface of vessel was approximately twice that of single stent. Conclusions Double Solitaire stents can effectively prevent thrombus displacement at the bifurcation and successfully retrieve the thrombus, but there is a risk of fracture due to the high stress level in the middle section of the thrombus. The contact pressure of the vessel on the anterior artery side is higher during thrombectomy, and the risk of vessel damage is greater. Therefore, it is necessary to optimize the design of the stent-retriever to improve its flexibility.

Computational Study of Fenestration and Parallel Grafts Used in Aortic Arch Lesion / 医用生物力学

Objective To explore hemodynamics of the aortic arch and supraarch vessels after thoracic endovascular aortic repair with fenestration and parallel grafts techniques, and compare the differences of these techniques. Methods Four patients with aortic arch lesions whose supraarch vessels were reconstructed by different surgical techniques (fenestration, chimney and periscope) were studied, and three-dimensional (3D) geometric models were established based on postoperative image data. The physiological flow obtained from two dimensional (2D) phase contrast magnetic resonance imaging were imposed on the ascending aorta inlet and the supraarch vessels outlets. The pressure waveform of 3-element Windkessel model was imposed on the descending aorta outlet. Through computational fluid dynamics ( CFD ) simulations, the hemodynamic parameters were obtained, including the pressure of supraarch vessels, the velocity vector of the stent inlet, and the relative residence time. Results The pressure change of the periscope stent was the largest, followed by the fenestration stent, and the pressure change of the chimney stent was the smallest. The velocity of the fenestration and periscope stent inlet was uneven, which might form vortex. The velocity of the chimney stent inlet was even. The high relative residence time concentrated in distal end of the fenestration stent outer wall, the ‘gutter’ part, and the place where the chimney and periscope stent adhered to the vessel wall. Conclusions The pressure difference between the inner and outer walls of the fenestration and periscope stent was high, so it was recommended to use the balloon-expandable stent. The pressure difference between the inner and outer walls of the chimney stent was low, so it was recommended to use the self-expanding stent. The predicted location of thrombosis was consistent with the clinical follow-up data, so it may be used for surgical planning and risk assessment of interventional treatment of aortic arch lesions.

Finite Element Analysis and in vitro Hemodynamic Testing of Polyester Textile Valves with Nitinol Wires / 医用生物力学

Objective To study mechanical properties of polyethylene terephthalate (PET)-based textile valves woven with nickel-titanium (NiTi) wires by finite element method, and combined with in vitro hemodynamic testing, to analyze the effect of wire quantity and woven position on hemodynamic performance of PET textile valve. Methods The three-dimensional (3D) geometric models of PET valves without wires and models of PET valves with wires by different numbers and distributions in radial direction were constructed using modeling software. Material properties of PET valves and wires were given based on the literature and experimental data. The transvalvular pressure difference curves of PET valves obtained from in vitro pulsatile flow experiments were used as boundary conditions. Stress distributions of the valve during peak systole and diastole were studied by finite element analysis software. Hydrodynamic performance of the valve with wires was evaluated by in vitro pulsatile flow experiments. ResultsThe finite element analysis results showed that the radially woven NiTi wires could enhance support for the PET textile valve, and support force and area of the valve in belly region of the valve leaflet with evenly distributed metal wires increased with the number of metal wires. The situation of support force was similar for silk distributions on both sides of the belly. The weaving of wires reduced stress concentration on the PET textile valve to a certain extent. The pulsatile flow experiment results showed that the stability of opening and closing shapes, effective opening area (EOA), regurgitation fraction (RF) and transvalvular pressure differences for two kinds of the PET valves with woven wires were better than those of the PET valves without wires. Conclusions Weaving metal wires in radial direction of the PET textile valve can effectively reduce stress concentrations on the PET textile valve during the cardiac cycle, and reduce tearing possibility of the valve leaflet. The woven metal wires can improve opening and closing stability of PET textile valve in in vitro hydrodynamic test, increase EOA and reduce RF and transvalvular pressure difference of the PET valve.

The Effect of Torsion of Blood Vessel after Stent Implantation on Mechanical State of Stent / 中国医疗器械杂志

OBJECTIVE@#In daily life, the movement of the neck will cause certain deformation of the blood vessel and the stent. This study explores the quantitative influence of the torsion deformation of the blood vessel on the mechanical properties of the stent.@*METHODS@#In the finite element simulation software Abaqus, the numerical simulation of the crimping and releasing process of the stent, the numerical simulation of the torsion process of the blood vessel with the stent, and the numerical simulation of the pressure loading process of the outer wall of the blood vessel were carried out.@*RESULTS@#After the stent was implanted, when a load was applied to the outer surface of the blood vessel wall, when the applied load did not change, as the torsion angle increased, the smallest cross-sectional area in the blood vessel decreased.@*CONCLUSIONS@#After the stent is placed, when the external load is fixed, the radial support capacity of the stent will decrease as the torsion angle increases.

The Effect from Elastic Modulus of Vessels on Fractional Flow Reserve of Carotid Artery Stenosis / 医用生物力学

Objective To explore the feasibility of applying fractional flow reserve (FFR) into the assessment of carotid stenosis, and analyze the effects from elastic modulus of vessel wall on hemodynamic parameters of carotid artery stenosis model and FFR calculation results. Methods The standard models of carotid bifurcation and stenosis models with different stenosis rates were established by computer-aided design software. Assuming that the vessel wall was linear elastic material and the blood was incompressible Newtonian fluid, the fluid-structure coupling simulation of blood flow in carotid artery stenosis model under the pulsating flow was carried out by finite element analysis, and the relevant hemodynamic parameters were obtained, and the corresponding FFR was calculated. Results When the elastic modulus was fixed, the FFR for narrow part of the model decreased gradually with the increase of the stenosis rate, and the relative difference between the FFR of elastic wall and rigid wall increased with the increase of the stenosis rate; when the stenosis rate was fixed at 70%, the FFR decreased gradually with the increase of elastic modulus. Conclusions The effect of vascular wall elasticity should be considered in the process of functional assessment on carotid stenosis with FFR; the larger stenosis rate will lead to the greater influence from elastic modulus of vessel wall on FFR.

Clinical Application and Mechanical Analysis of the Treatment of Multiple Rib Fractures and Flail Chest Using Three-wings Rib Plate / 中国医疗器械杂志

This research evaluated the clinical efficacy of three-wings rib plate in the treatment of multiple rib fractures and flail chest with mechanical analysis and clinical verification. The model of rib and three-wings rib plate was reconstructed. The contact simulation with pretension stress was applied to the plate's fixation, and it was found that the bearable stress of the rib fractures after fixation increased from the result which indicated a good fixation efficacy of the plate. Clinical data of 53 cases of rib fractures and flail chest treated with three-wings rib plate in Shanghai Pudong Hospital of Fudan University were retrospectively analyzed. After the operation, the pain of the patients was relieved. Postoperative CT reconstruction of the chest showed good restoration of the rib fractures, which verified the clinical efficacy of three-wings rib plate. The three-wings rib plate showed a high value in clinical use for treatment of rib fractures.

Finite element simulation of stent implantation and its applications in the interventional planning for hemorrhagic cardio-cerebrovascular diseases / 生物医学工程学杂志

Numerical simulation of stent deployment is very important to the surgical planning and risk assess of the interventional treatment for the cardio-cerebrovascular diseases. Our group developed a framework to deploy the braided stent and the stent graft virtually by finite element simulation. By using the framework, the whole process of the deployment of the flow diverter to treat a cerebral aneurysm was simulated, and the deformation of the parent artery and the distributions of the stress in the parent artery wall were investigated. The results provided some information to improve the intervention of cerebral aneurysm and optimize the design of the flow diverter. Furthermore, the whole process of the deployment of the stent graft to treat an aortic dissection was simulated, and the distributions of the stress in the aortic wall were investigated when the different oversize ratio of the stent graft was selected. The simulation results proved that the maximum stress located at the position where the bare metal ring touched the artery wall. The results also can be applied to improve the intervention of the aortic dissection and the design of the stent graft.

Finite Element Analysis of Aortic Dissection Treated with Stent Graft / 医用生物力学

Objective To study the process of stent graft implantation into the aortic dissection model by finite element simulation, calculate the stress distribution at different locations of the aorta after the implantation, and analyze the biomechanical mechanism of new lesions for implantation of stent grafts. Methods Based on the computed tomography angiography (CTA) image data of the aorta, a three-dimensional geometric model of patient-specific aortic dissection was established with image segmentation and reconstruction. The wall thickness and material properties of the aortic dissection of the computational models were set according to the literature data. Stent grafting rings with different geometric parameters were designed in a computer-aided design (CAD) software, and the procedure of stent graft implantation was simulated by a finite element analysis software. Results When the implanted stent graft reached a steady-state, the maximum Von Mises stress of the aorta was markedly related to the position of the stent graft and located at the bare stent or small nickel-titanium alloy ring. In the long-term, this force might cause a new tear to appear at the treated aorta. Conclusions The position of the stent graft had a weak effect on the distribution of the maximum Von Mises stress of the aorta, but there was an obvious effect on the Von Mises stress of the aorta. These research outcomes may provide significant guidance for selecting the position of the stent graft.

Finite Element Analysis of Effect of Key Dimension of Nitinol Stent on Its Fatigue Behaviour / 生物医学工程学杂志

To evaluate the fatigue behavior of nitinol stents, we used the finite element method to simulate the manufacture processes of nitinol stents, including expanding, annealing, crimping, and releasing procedure in applications of the clinical treatments. Meanwhile, we also studied the effect of the crown area dimension of stent on strain distribution. We then applied a fatigue diagram to investigate the fatigue characteristics of nitinol stents. The results showed that the maximum strain of all three stent structures, which had different crown area dimensions under vessel loads, located at the transition area between the crown and the strut, but comparable deformation appeared at the inner side of the crown area center. The cause, of these results was that the difference of the area moment of inertia determined by the crown dimension induced the difference of strain distribution in stent structure. Moreover, it can be drawn from the fatigue diagrams that the fatigue performance got the best result when the crown area dimension equaled to the intermediate value. The above results proved that the fatigue property of nitinol stent had a close relationship with the dimension of stent crown area, but there was no positive correlation.

A five-element lumped-parameter model for cerebral blood flow autoregulation / 生物医学工程学杂志

Utilizing the third-order polynomial curve fitted to the experimental data, which represents the relationship between cerebral blood flow (CBF) and mean artery blood pressure (MABP), we constructed a lumped-parameter dynamic model with 5 elements. In this model; the resistance is not constants it is determined by the fitted curve. We simulated the process of CBF autoregulation numerically by solving the govern equation of this model and got quite accurate results. Furthermore, we studied the influence of hemodynamic parameters on the CBF autoregulation by this model and proved that the characteristic resistance is the most important factor.

A dynamic model describing lymphatic circulation / 生物医学工程学杂志

Based on the morphology and function of lymphatic vessel, and on the achievements of researches in the regulatory mechanism of lymphatic circulation, we fully considered the dynamic interaction of blood, interstitial fluid and lymph fluid; then we imitated and used Sungawa's method of analyzing the heart output, and finally set up a dynamic model for describing lymphatic circulation. Comparison of our calculating results with the data from Ikomi's experiment showed that they were identical, thus indicating that our model is of value in explaining the dynamic mechanism of lymphatic circulation. In this paper is especially calculated the relationship between lymph flow and massage frequency, which is useful for analyzing the effect of massage on the lymph flow rate with respect to this model.

A hemodynamics model describing cardiac deficiency of qi(vital energy) / 生物医学工程学杂志

Cardiac deficiency of qi(vital energy) is one of the main syndromes in terms of TCM (Traditional Chinese Medicine). Based on our analysis of blood-tissue fluid circulation, we set up a hemodynamics model describing cardiac deficiency of qi. The model's theoretical results can reflect the manifestations of cardiac deficiency of qi, and are identical to those of clinical experimental discoveries, therefore it has substantiated our theory-cell's abnormal physiological function caused by undernourishment of tissue fluid is the reason of qi-deficiency.