[Numerical study on structural design and mechanical analysis of anti-migration tracheal stent with non-uniform Poisson's ratio].

Stent migration is one of the common complications after tracheal stent implantation. The causes of stent migration include size mismatch between the stent and the trachea, physiological movement of the trachea, and so on. In order to solve the above problems, this study designed a non-uniform Poisson ratio tracheal stent by combining the size and structure of the trachea and the physiological movement of the trachea to improve the migration of the stent, meanwhile ensuring the support of the stent. In this study, the stent corresponding to cartilage was constructed with negative Poisson's ratio, and the stent corresponding to the circular connective tissue and muscular membrane was constructed with positive Poisson's ratio. And four kinds of non-uniform Poisson's ratio tracheal stents with different link lengths and negative Poisson's ratio were designed. Then, this paper numerically simulated the expansion and rebound process of the stent after implantation to observe the support of the stent, and further simulated the stretch movement of the trachea to calculate the diameter changes of the stent corresponding to different negative Poisson's ratio structures. The axial migration of the stent was recorded by applying different respiratory pressure to the wall of the tracheal wall to evaluate whether the stent has anti-migration effect. The research results show that the non-uniform Poisson ratio stent with connecting rod length of 3 mm has the largest diameter expansion in the negative Poisson ratio section when the trachea was stretched. Compared with the positive Poisson's ratio structure, the axial migration during vigorous breathing was reduced from 0.024 mm to 0.012 mm. The negative Poisson's ratio structure of the non-uniform Poisson's ratio stent designed in this study did not fail in the tracheal expansion effect. Compared with the traditional stent, the non-uniform Poisson's ratio tracheal stent has an anti-migration effect under the normal movement of the trachea while ensuring the support force of the stent.

[Structural design of "fitness" and "feasibility" of body-fitted stent and its mechanical analysis].

To address the conflict between the "fitness" and "feasibility" of body-fitted stents, this paper investigates the impact of various smoothing design strategies on the mechanical behaviour and apposition performance of stent. Based on the three-dimensional projection method, the projection region was fitted with the least squares method (fitting orders 1-6 corresponded to models 1-6, respectively) to achieve the effect of smoothing the body-fitted stent. The simulation included the crimping and expansion process of six groups of stents in stenotic vessels with different degrees of plaque calcification. Various metrics were analyzed, including bending stiffness, stent ruggedness, area residual stenosis rate, contact area fraction, and contact volume fraction. The study findings showed that the bending stiffness, stent ruggedness, area residual stenosis rate, contact area fraction and contact volume fraction increased with the fitting order's increase. Model 1 had the smallest contact area fraction and contact volume fraction, 77.63% and 83.49% respectively, in the incompletely calcified plaque environment. In the completely calcified plaque environment, these values were 72.86% and 82.21%, respectively. Additionally, it had the worst "fitness". Models 5 and 6 had similar values for stent ruggedness, with 32.15% and 32.38%, respectively, which indicated the worst "feasibility" for fabrication and implantation. Models 2, 3, and 4 had similar area residual stenosis rates in both plaque environments. In conclusion, it is more reasonable to obtain the body-fitted stent by using 2nd to 4th order fitting with the least squares method to the projected region. Among them, the body-fitted stent obtained by the 2nd order fitting performs better in the completely calcified environment.

Computational fluid dynamics study of the effect of transverse sinus stenosis on the blood flow pattern in the ipsilateral superior curve of the sigmoid sinus.

OBJECTIVE: To investigate the effect of different types of transverse sinus stenosis on blood flow patterns in the ipsilateral superior curve of the sigmoid sinus. METHODS: According to the morphology of transverse and sigmoid sinus sections in pulsatile tinnitus patients, ten idealized models with different degrees and positions of transverse sinus stenosis were constructed. Computational fluid dynamics simulations were performed to compare the hemodynamic characteristics among these models. Follow-up images of previous cases were included, which preliminarily confirmed the hypothesis that bone plate erosion of the sigmoid sinus sulcus is related to blood flow impingement. RESULTS: Blood flow impingement on the superior curve of the sigmoid sinus wall intensified with increasing degree of stenosis and decreased with increasing distance between the stenosis and the sigmoid sinus. The impact zone was generally confined to the anterior and lateral walls of the superior curve of the sigmoid sinus. When the stenosis was located far from the middle of the transverse sinus, the blood flow impingement on the sigmoid sinus wall was very weak. CONCLUSIONS: When stenosis is located far from the sigmoid sinus, the causes of tinnitus should be comprehensively considered instead of assuming that stenosis is the main cause. Bone plate erosion of the sigmoid sinus sulcus was promoted by blood flow impingement. KEY POINTS: • Ten idealized models with different degrees and positions of stenosis were constructed. • The causes of pulsatile tinnitus should be comprehensively considered. • Sigmoid sinus plate dehiscence was promoted by blood flow impingement.

[Structural design and biomechanical numerical analysis of body-fitted stent in stenotic vessels].

To solve the problem of stent malapposition of intravascular stents, explore the design method of intravascular body-fitted stent structure and to establish an objective apposition evaluation method, the support and apposition performance of body-fitted stent in the stenotic vessels with different degrees of calcified plaque were simulated and analyzed. The traditional tube-mesh-like stent model was constructed by using computational aided design tool SolidWorks, and based on this model, the body-fitted stent model was designed by means of projection algorithm. Abaqus was used to simulate the crimping-expansion-recoil process of the two stents in the stenotic vessel with incompletely calcified plaque and completely calcified plaque respectively. A comprehensive method for apposition evaluation was proposed considering three aspects such as separation distance, fraction of non-contact area and residual volume. Compared with the traditional stent, the separation distances of the body-fitted stent in the incompletely calcified plaque model and the completely calcified plaque model were decreased by 21.5% and 22.0% respectively, the fractions of non-contact areas were decreased by 11.3% and 11.1% respectively, and the residual volumes were decreased by 93.1% and 92.5% respectively. The body-fitted stent improved the apposition performance and was effective in both incompletely and completely calcified plaque models. The established apposition performance evaluation method of stent considered more geometric factors, and the results were more comprehensive and objective.

[Review of studies on the biomechanical modelling of the coupling effect between stent degradation and blood vessel remodeling].

The dynamic coupling of stent degradation and vessel remodeling can influence not only the structural morphology and material property of stent and vessel, but also the development of in-stent restenosis. The research achievements of biomechanical modelling and analysis of stent degradation and vessel remodeling were reviewed; several noteworthy research perspectives were addressed, a stent-vessel coupling model was developed based on stent damage function and vessel growth function, and then concepts of matching ratio and risk factor were established so as to evaluate the treatment effect of stent intervention, which may lay the scientific foundation for the structure design, mechanical analysis and clinical application of biodegradable stent.

Mechanical analysis of a novel biodegradable zinc alloy stent based on a degradation model.

BACKGROUND: Biodegradable stents display insufficient scaffold performance due to their poor Young's Modulus. In addition, the corresponding biodegradable materials harbor weakened structures during degradation processes. Consequently, such stents have not been extensively applied in clinical therapy. In this study, the scaffold performance of a patented stent and its ability to reshape damaged vessels during degradation process were evaluated. METHODS: A common stent was chosen as a control to assess the mechanical behavior of the patented stent. Finite element analysis was used to simulate stent deployment into a 40% stenotic vessel. A material corrosion model involving uniform and stress corrosion was implemented within the finite element framework to update the stress state following degradation. RESULTS: The results showed that radial recoiling ratio and mass loss ratio of the patented stent is 7.19% and 3.1%, respectively, which are definitely lower than those of the common stent with the corresponding values of 22.6% and 14.1%, respectively. Moreover, the patented stent displayed stronger scaffold performance in a corrosive environment and the plaque treated with patented stents had a larger and flatter lumen. CONCLUSION: Owing to its improved mechanical performance, the novel biodegradable zinc alloy stent reported here has high potential as an alternative choice in surgery.

[Influence of valve height on the opening/closure performance of transplanted aortic valve].

Valve transplantation is often used in the treatment of aortic valve insufficiency. However, after surgery, the reconstructed aortic roots have an expansion phenomenon, in which the lack of valve height causes the aortic valve to close again. In this paper, the effects of different aortic valve height design on valve opening and closing performance were studied. The optimal surgical plan was obtained by in vitro numerical simulation, providing technical support and theoretical basis. In this paper, six groups of three-dimensional geometric models with a valve height increment of ± 0.5 mm were established with a root diameter of 26.0 mm and a valve height of 14.0 mm. Through the structural mechanics calculation and analysis of the parameters such as maximum stress, valve area and contact force of the model, reasonable geometrical dimensions are obtained. The study found that the maximum stress values of the six groups of models ranged from 640 to 690 kPa, which was consistent with the results of the literature; the three-group models with valve heights of 13.5 mm, 14.0 mm, and 14.5 mm were within a reasonable range. The contact force value of the 6 groups of leaflets increased with the increase of valve height. Studies have shown that the height of the aortic valve has an effect on the aortic valve closure performance. A valve height that is too small or too large will reduce the aortic systolic valve area and affect the aortic function.

[Effect of sinus diameter on the opening and closing performance of aortic valve under the expansion of aortic root].

This study aims to explore the effect of aortic sinus diameter on aortic valve opening and closing performance in the case of no obvious disease of aortic valve and annulus and continuous dilation of aortic root. A total of 25 three-dimensional aortic root models with different aortic sinus and root diameters were constructed according to the size of clinical surgical guidance. The valve sinus diameter DS is set to 32, 36, 40, 44 and 48 mm, respectively, and the aortic root diameter DA is set to 26, 27, 28, 29 and 30 mm, respectively. Through the structural mechanics calculation with the finite element software, the maximum stress, valve orifice area, contact force and other parameters of the model are analyzed to evaluate the valve opening and closing performance under the dilated state. The study found that aortic valve stenosis occurs when the DS = 32 mm, DA = 26, 27 mm and DS = 36 mm, DA = 26 mm. Aortic regurgitation occurs when the DS = 32, 36 and 40 mm, DA = 30 mm and DS = 44, 48 mm, DA = 29, 30 mm. The other 15 models had normal valve movement. The results showed that the size of the aortic sinus affected the opening and closing performance of the aortic valve. The smaller sinus diameter adapted with the larger root diameter and the larger sinus diameter adapted with the smaller root diameter. When the sinus diameter is 40 mm, the mechanical performance of the valve are good and it can well adapt with the relatively large range of aortic root dilation.

[Research on the cardiovascular function evaluation system based on noninvasive detection indices].

Based on the noninvasive detection indeices and fuzzy mathematics method, this paper studied the noninvasive, convenient and economical cardiovascular health assessment system. The health evaluation index of cardiovascular function was built based on the internationally recognized risk factors of cardiovascular disease and the noninvasive detection index. The weight of 12 indexes was completed by the analytic hierarchy process, and the consistency test was passed. The membership function, evaluation matrix and evaluation model were built by fuzzy mathematics. The introducted methods enhanced the scientificity of the evaluation system. Through the Kappa consistency test, McNemer statistical results ( P = 0.995 > 0.05) and Kappa values (Kappa = 0.616, P < 0.001) suggest that the comprehensive evaluation results of model in this paper are relatively consistent with the clinical, which is of certain scientific significance for the early detection of cardiovascular diseases.

[Numerical simulation of the effect of virtual stent release pose on the expansion results].

The current finite element analysis of vascular stent expansion does not take into account the effect of the stent release pose on the expansion results. In this study, stent and vessel model were established by Pro/E. Five kinds of finite element assembly models were constructed by ABAQUS, including 0 degree without eccentricity model, 3 degree without eccentricity model, 5 degree without eccentricity model, 0 degree axial eccentricity model and 0 degree radial eccentricity model. These models were divided into two groups of experiments for numerical simulation with respect to angle and eccentricity. The mechanical parameters such as foreshortening rate, radial recoil rate and dog boning rate were calculated. The influence of angle and eccentricity on the numerical simulation was obtained by comparative analysis. Calculation results showed that the residual stenosis rates were 38.3%, 38.4%, 38.4%, 35.7% and 38.2% respectively for the 5 models. The results indicate that the pose has less effect on the numerical simulation results so that it can be neglected when the accuracy of the result is not highly required, and the basic model as 0 degree without eccentricity model is feasible for numerical simulation.

[Noninvasive numerical simulation of coronary fractional flow reserve based on lattice Boltzmann method].

In order to investigate the application of lattice Boltzmann method (LBM) in the numerical simulation of computed tomography angiography-derived fractional flow reserve (FFR CT), an idealized narrowed tube model and two coronary stenosis arterymodels are studied. Based on the open source code library (Palabos), the relative algorithm program in the development environment (Codeblocks) was improved. Through comparing and analyzing the results of FFR CT which is simulated by LBM and finite element analysis software ANSYS, and the feasibility of the numerical simulation of FFR CT by LBM was verified . The results show that the relative error between the results of LBM and finite element analysis software ANSYS is about 1%, which vertifies the feasibility of simulating the coronary FFR CT by LBM. The simulation of this study provides technical support for developing future FFR CT application software, and lays the foundation for the calculation of clinical FFR CT.

Design optimization of stent and its dilatation balloon using kriging surrogate model.

BACKGROUND: Although stents have great success of treating cardiovascular disease, it actually undermined by the in-stent restenosis and their long-term fatigue failure. The geometry of stent affects its service performance and ultimately affects its fatigue life. Besides, improper length of balloon leads to transient mechanical injury to the vessel wall and in-stent restenosis. Conventional optimization method of stent and its dilatation balloon by comparing several designs and choosing the best one as the optimal design cannot find the global optimal design in the design space. In this study, an adaptive optimization method based on Kriging surrogate model was proposed to optimize the structure of stent and the length of stent dilatation balloon so as to prolong stent service life and improve the performance of stent. METHODS: A finite element simulation based optimization method combing with Kriging surrogate model is proposed to optimize geometries of stent and length of stent dilatation balloon step by step. Kriging surrogate model coupled with design of experiment method is employed to construct the approximate functional relationship between optimization objectives and design variables. Modified rectangular grid is used to select initial training samples in the design space. Expected improvement function is used to balance the local and global searches to find the global optimal result. Finite element method is adopted to simulate the free expansion of balloon-expandable stent and the expansion of stent in stenotic artery. The well-known Goodman diagram was used for the fatigue life prediction of stent, while dogboning effect was used for stent expansion performance measurement. As the real design cases, diamond-shaped stent and sv-shaped stent were studied to demonstrate how the proposed method can be harnessed to design and refine stent fatigue life and expansion performance computationally. RESULTS: The fatigue life and expansion performance of both the diamond-shaped stent and sv-shaped stent are designed and refined, respectively. (a) diamond-shaped stent: The shortest distance from the data points to the failure line in the Goodman diagram was increased by 22.39%, which indicated a safer service performance of the optimal stent. The dogboning effect was almost completely eliminated, which implies more uniform expansion of stent along its length. Simultaneously, radial elastic recoil (RR) at the proximal and distal ends was reduced by 40.98 and 35% respectively and foreshortening (FS) was also decreased by 1.75%. (b) sv-shaped stent: The shortest distance from the data point to the failure line in the Goodman diagram was increased by 15.91%. The dogboning effect was also completely eliminated, RR at the proximal and distal ends was reduced by 82.70 and 97.13%, respectively, and the FS was decreased by 16.81%. Numerical results showed that the fatigue life of both stents was refined and the comprehensive expansion performance of them was improved. CONCLUSIONS: This article presents an adaptive optimization method based on the Kriging surrogate model to optimize the structure of stents and the length of their dilatation balloon to prolong stents fatigue life and decreases the dogboning effect of stents during expansion process. Numerical results show that the adaptive optimization method based on Kriging surrogate model can effectively optimize the design of stents and the dilatation balloon. Further investigations containing more design goals and more effective multidisciplinary design optimization method are warranted.

[Experimental study of the effects of sinotubular junction taper on artificial bioprosthesis valve in pulsatile flow condition].

The aim of the present experimental study is to determine the effects of sinotubular junction diameter on artificial bioprosthesis valves. An experimental study was performed for aortic root models with different sinotubular junction taper under pulsatile flow condition. The sinotubular junction diameters were modified to create four models with different sinotubular junction tapers with 0, 1, 3 and 5 degrees, respectively, using three dimensional printing techniques. After installing the testing bioprosthesis valve on the aortic root models, we conducted experiments of the pulsatile flow testing with different stroke volume in the pulsatile circulation simulation system. The testing condition was set at the pulse frequency of 70 beats/min and the stroke volume of 2-7 L/min. The status of the valves in 10 continuous pulse cycles was tested and the average results were obtained for each stroke volume. The results of testing showed that the mean transvalvular pressure gradients agreed well with the national standard, and all smaller than 10 mm Hg. The sinotubular junction taper had an influence on regurgitation fraction of the artificial bioprosthesis valve. The smaller sinotubular junction taper showed beneficial effect to decrease the regurgitation fraction. In the case of smaller stroke volume, the smaller sinotubular junction taper was beneficial to increase the effective valve orifice area. In the case of larger stroke volume, the larger sinotubular junction taper was beneficial to increase the effective valve orifice area. This study indicates that a doctor should consider the smaller sinotubular junction taper in the case of smaller stroke volume more. In the case of larger stroke volume, the doctor should consider the larger sinotubular junction taper more.

Association of simultaneously measured four-limb blood pressures with cardiovascular function: a cross-sectional study.

BACKGROUND: Simultaneous measurement of four-limb blood pressures can improve the accuracy of cardiovascular disease diagnosis. This study aims to investigate the association of simultaneously measured four-limb blood pressures with cardiovascular function as the non-invasive diagnostic method of cardiovascular disease in primary care. METHODS: 229 subjects (62 males, mean age, 63.50 ± 11.13 years; 167 females, mean age, 59.47 ± 7.33 years) were enrolled. Four-limb blood pressure measurements were simultaneously performed using a blood pressure and pulse monitor device in the supine position. Cardiac functional parameters were also measured by using a cardiac hemodynamic detector in the same position. Data were statistically analyzed with SPSS15.0. RESULTS: The mean age of the 229 subjects was 60.56 ± 8.68 years. Cardiovascular functional parameters decreased with age and body mass index (BMI), only the total peripheral resistance (TPR) was in contrast. Age, BMI, left ankle diastolic pressure (LADP), high arm mean arterial pressure (HARMAP), left arm diastolic pressure (LARDP) and right ankle diastolic pressure (RADP) were significantly correlated with cardiovascular functional parameters. Cardiovascular functional parameters have significant differences with inter-arm difference in systolic blood pressure (SBP) between ≥10 and <10 mmHg, inter-ankle difference in SBP between ≥15 and ≥20 mmHg, inter-ankle difference in SBP between ≥15 and <10 mmHg and right ankle brachial index (RABI) between ≤0.9 and ≥1.0. After excluding 99 hypertensive patients, a part of cardiovascular functional parameters has still significant differences with inter-arm difference in SBP between ≥10 and ≥15 mmHg and RABI between ≤0.9 and ≥1.0. CONCLUSION: Age, BMI, LADP, HARMAP, LARDP and RADP were the determinants of cardiovascular functional parameters. In addition, a part of cardiovascular functional parameter is associated with inter-arm difference in SBP ≥10 mmHg, inter-ankle difference in SBP ≥15 mmHg and RABI ≤0.9, while these differences still existed after excluding 99 hypertensive patients. Hence, simultaneous measurement of four-limb blood pressures has become feasible and useful approach to the non-invasive diagnostic method of cardiovascular disease in primary care.

Numerical simulation of closure performance for neo-aortic valve for arterial switch operation.

BACKGROUND: Modeling neo-aortic valve for arterial switch surgical planning to simulate the neo-aortic valve closure performance. METHODS: We created five geometrical models of neo-aortic valve, namely model A, model B, model C, model D and model E with different size of sinotubular junction or sinus. The nodes at the ends of aorta and left ventricle duct fixed all the degrees of freedom. Transvalvular pressure of normal diastolic blood pressure of 54 mmHg was applied on the neo-aortic valve cusps. The neo-aortic valve closure performance was investigated by the parameters, such as stress of neo-aortic root, variation of neo-aortic valve ring as well as aortic valve cusps contact force in the cardiac diastole. RESULTS: The maximum stress of the five neo-aortic valves were 96.29, 98.34, 96.28, 98.26, and 90.60 kPa, respectively. Compared among five neo-aortic valve, aortic valve cusps contact forces were changed by 43.33, -10.00% enlarging or narrowing the sinotubular junction by 20% respectively based on the reference model A. The cusps contact forces were changed by 6.67, -23.33% with sinus diameter varying 1.2 times and 0.8 times respectively. CONCLUSIONS: Comparing with stress of healthy adult subjects, the neo-aortic valve of infant creates lower stress. It is evident that enlarging or narrowing the sinotubular junction within a range of 20% can increase or decrease the maximum stress and aortic valve cusps contact force of neo-aortic valve.

Multi-objective optimization of coronary stent using Kriging surrogate model.

BACKGROUND: In stent design optimization, the functional relationship between design parameters and design goals is nonlinear, complex, and implicit and the multi-objective design of stents involves a number of potentially conflicting performance criteria. Therefore it is hard and time-consuming to find the optimal design of stent either by experiment or clinic test. Fortunately, computational methods have been developed to the point whereby optimization and simulation tools can be used to systematically design devices in a realistic time-scale. The aim of the present study is to propose an adaptive optimization method of stent design to improve its expansion performance. METHODS: Multi-objective optimization method based on Kriging surrogate model was proposed to decrease the dogboning effect and the radial elastic recoil of stents to improve stent expansion properties and thus reduce the risk of vascular in-stent restenosis injury. Integrating design of experiment methods and Kriging surrogate model were employed to construct the relationship between measures of stent dilation performance and geometric design parameters. Expected improvement, an infilling sampling criterion, was employed to balance local and global search with the aim of finding the global optimal design. A typical diamond-shaped coronary stent-balloon system was taken as an example to test the effectiveness of the optimization method. Finite element method was used to analyze the stent expansion of each design. RESULTS: 27 iterations were needed to obtain the optimal solution. The absolute values of the dogboning ratio at 32 and 42 ms were reduced by 94.21 and 89.43%, respectively. The dogboning effect was almost eliminated after optimization. The average of elastic recoil was reduced by 15.17%. CONCLUSION: This article presents FEM based multi-objective optimization method combining with the Kriging surrogate model to decrease both the dogboning effect and radial elastic recoil of stents. The numerical results prove that the proposed optimization method effectively decreased both the dogboning effect and radial elastic recoil of stent. Further investigations containing more design goals and more effective multidisciplinary design optimization method are warranted.

[Correlations between Fractional Flow Reserve and Coronary Artery Stenosis Based on the Stenosis Position and Coronary Dominant Type].

For coronary artery diseases,imaging diagnosis is usually used to guide the treatment.However,it can only reflect the geometric characteristics of the disease but does not determine the hemodynamically significant stenosis.This study was aimed to investigate the relationship between angiographic and functional severity of coronary artery stenosis and to improve the diagnostic value of imaging.39 patients with 55 stenosis vessels were included in this study.The correlation between FFR and stenosis rate was analyzed with the medical statistical analysis method,and the influence of the position of stenosis and coronary dominant type on the correlation was discussed.By regression analysis,the stenosis rate of left anterior descending artery of right dominant type showed a significant correlation with FFR value(r≈0.79,P<0.000 1)after grouping with position and the dominant type.Due to the significance of a value of the FFR<0.80 in determining inducible ischemia,the diagnostic accuracy of myocardial ischemia by the stenosis rate increased from 70.9% to 82.8% after grouping.Sensitivity(from 72.2% to 78.6%)and specificity(from 70.3%to 86.7%)were also significantly improved.This study indicates that the position of stenosis and the coronary dominant type are significant influence factors on the correlation between FFR and stenosis rate.Consideration of these two factors in the diagnosis of myocardial ischemia by imaging will be helpful to improve the effectiveness of diagnosis.

Finite element analysis of mechanics of neovessels with intraplaque hemorrhage in carotid atherosclerosis.

BACKGROUND: Intraplaque hemorrhage is a widely known factor facilitating plaque instability. Neovascularization of plaque can be regarded as a compensatory response to the blood supply in the deep intimal and medial areas of the artery. Due to the physiological function, the deformation of carotid atherosclerotic plaque would happen under the action of blood pressure and blood flow. Neovessels are subject to mechanical loading and likely undergo deformation. The rupture of neovessels may deteriorate the instability of plaque. This study focuses on the local mechanical environments around neovessels and investigates the relationship between the biomechanics and the morphological specificity of neovessels. METHODS: Stress and stretch were used to evaluate the rupture risk of the neovessels in plaque. Computational structural analysis was performed based on two human carotid plaque slice samples. Two-dimensional models containing neovessels and other components were built according to the plaque slice samples. Each component was assumed to be non-linear isotropic, piecewise homogeneous and incompressible. Different mechanical boundary conditions, i.e. static pressures, were imposed in the carotid lumen and neovessels lumen respectively. Finite element method was used to simulate the mechanical conditions in the atherosclerotic plaque. RESULTS: Those neovessels closer to the carotid lumen undergo larger stress and stretch. With the same distance to the carotid lumen, the longer the perimeter of neovessels is, the larger stress and the deformation of the neovessels will be. Under the same conditions, the neovessels with larger curvature suffer greater stress and stretch. Neovessels surrounded by red blood cells undergo a much larger stretch. CONCLUSIONS: Local mechanical conditions may result in the hemorrhage of neovessels and accelerate the rupture of plaque. The mechanical environments of the neovessel are related to its shape, curvature, distance to the carotid lumen and the material properties of plaque.

The Computational Fluid Dynamics Rupture Challenge 2013--Phase II: Variability of Hemodynamic Simulations in Two Intracranial Aneurysms.

With the increased availability of computational resources, the past decade has seen a rise in the use of computational fluid dynamics (CFD) for medical applications. There has been an increase in the application of CFD to attempt to predict the rupture of intracranial aneurysms, however, while many hemodynamic parameters can be obtained from these computations, to date, no consistent methodology for the prediction of the rupture has been identified. One particular challenge to CFD is that many factors contribute to its accuracy; the mesh resolution and spatial/temporal discretization can alone contribute to a variation in accuracy. This failure to identify the importance of these factors and identify a methodology for the prediction of ruptures has limited the acceptance of CFD among physicians for rupture prediction. The International CFD Rupture Challenge 2013 seeks to comment on the sensitivity of these various CFD assumptions to predict the rupture by undertaking a comparison of the rupture and blood-flow predictions from a wide range of independent participants utilizing a range of CFD approaches. Twenty-six groups from 15 countries took part in the challenge. Participants were provided with surface models of two intracranial aneurysms and asked to carry out the corresponding hemodynamics simulations, free to choose their own mesh, solver, and temporal discretization. They were requested to submit velocity and pressure predictions along the centerline and on specified planes. The first phase of the challenge, described in a separate paper, was aimed at predicting which of the two aneurysms had previously ruptured and where the rupture site was located. The second phase, described in this paper, aims to assess the variability of the solutions and the sensitivity to the modeling assumptions. Participants were free to choose boundary conditions in the first phase, whereas they were prescribed in the second phase but all other CFD modeling parameters were not prescribed. In order to compare the computational results of one representative group with experimental results, steady-flow measurements using particle image velocimetry (PIV) were carried out in a silicone model of one of the provided aneurysms. Approximately 80% of the participating groups generated similar results. Both velocity and pressure computations were in good agreement with each other for cycle-averaged and peak-systolic predictions. Most apparent "outliers" (results that stand out of the collective) were observed to have underestimated velocity levels compared to the majority of solutions, but nevertheless identified comparable flow structures. In only two cases, the results deviate by over 35% from the mean solution of all the participants. Results of steady CFD simulations of the representative group and PIV experiments were in good agreement. The study demonstrated that while a range of numerical schemes, mesh resolution, and solvers was used, similar flow predictions were observed in the majority of cases. To further validate the computational results, it is suggested that time-dependent measurements should be conducted in the future. However, it is recognized that this study does not include the biological aspects of the aneurysm, which needs to be considered to be able to more precisely identify the specific rupture risk of an intracranial aneurysm.

Modeling study of aortic root for ross procedure: a structural finite element analysis.

BACKGROUND AND AIM OF THE STUDY: The Ross procedure involves replacing the diseased aortic valve with the patient's own pulmonary valve (autograft) to form the neoaortic valve, reimplanting the coronary arteries, and inserting a cadaveric homograft into the pulmonary position. METHODS: In order to model a neoaortic root for the Ross procedure in patients with aortic valve disease, the three-dimensional geometry of a reference aortic valve was reconstructed (reference model A). The diameters of the sinotubular junction (STJ) and maximum sinus were then modified to create four geometric models named B, C, D, and E, with different dimensions. The mechanical behavior of the aortic root was simulated, and the performance of the aortic leaflets assessed in terms of maximum geometric orifice area (GOA) during all cardiac cycle and leaflet contact pressure during closing phase. RESULTS: The neoaortic valve model showed a maximum GOA of 274.4 mm2 and a maximum leaflet stress of 682 kPa. For models B and C, the leaflet contact pressure was increased by 27.4% and decreased by 4.42%, with STJ diameter increased 1.1-fold and decreased 0.9-fold compared to reference model A. The leaflet contact pressure in models D and E was increased by 3.04% and decreased by 11.5%, while the sinus diameter was increased 1.1-fold and decreased 0.9-fold compared to model A. CONCLUSION: Increasing the STJ and sinus diameters within a range of 10% can increase the leaflet contact pressure for the aortic root, and vice versa. This may be the reason why neoaortic valve insufficiency occurs long after patients have undergone the Ross procedure.