Objective To establish an ideal model of the mitral valve,including the left heart and blood,and study the motion characteristics of the mitral valve in blood flow using the fluid-structure interaction(FSI)simulation.Methods Based on anatomical parameters,models of the mitral valve,left heart,and blood were established.The finite-elements combined immersed boundary method was used for FSI to simulate the motion of the mitral valve using the LS-DYNA software.Morphological,mechanical,and hemodynamic parameters were compared with those obtained from structural simulations.Results The morphological results of the mitral valve from the two simulations differed significantly,and the FSI results matched the ultrasound images.The stress distributions of the leaflets in the FSI and structural simulations were consistent.The maximum first principal stresses calculated by FSI and structural simulations were 1.48 MPa and 1.53 MPa,respectively,with a relative error of 3.27％.The fluid field in the left heart was complex with vortex structures,and the maximum mitral flow velocity was 1.02 m/s during diastole,consistent with the physiological data of healthy humans(0.89±0.15 m/s).Conclusions The morphological results of the mitral valve obtained from the FSI simulation were closer to those in the physiological state.FSI simulations can provide flow patterns that are indispensable for clinical diagnosis.Structural simulations are more efficient for studying leaflet stress distribution.

Objective To noninvasively assess the cerebral ischemic status using the velocity profile of the carotid and vertebral arteries measured by Doppler ultrasound and a neural network model.Methods Imaging data were collected from patients who underwent computed tomography perfusion(CTP)and Doppler ultrasound.Hemodynamic parameters were extracted from the ultrasound images.These parameters were used to train a fully connected neural network model.The model was validated using the CTP results.Results Sixty-two eligible patients were included;44 were randomly selected as the training dataset and 18 were designated for validation.In the training set,the area under the curve(AUC)of the receiver operating characteristic,sensitivity,specificity,and accuracy were 0.95,0.833,0.923,and 0.886,respectively.In the test set,the AUC,sensitivity,specificity,and accuracy were 0.860,0.714,1.000,and 0.889,respectively.Conclusions The model based on Doppler ultrasound and neural network was clinically verified and had good accuracy for assessing cerebral ischemia,showing its clinical potential for the early screening of cerebral ischemia.

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.

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.

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.
Computer Simulation ; Finite Element Analysis ; Humans ; Stents ; Stress, Mechanical

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.

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.
China ; Flail Chest/surgery* ; Fracture Fixation, Internal ; Humans ; Retrospective Studies ; Rib Fractures/surgery* ; Ribs

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.

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.
Arteries ; Blood Vessel Prosthesis Implantation ; Cardiovascular Diseases ; Computer Simulation ; Finite Element Analysis ; Humans ; Prosthesis Design ; Stents

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.