Biomechanical mechanism and quantitative assessment indices for vulnerable carotid plaques / 医用生物力学

The rupture of carotid atherosclerotic plaques and thrombosis are the main risk factor for ischemic stroke. The risk of carotid plaque rupture is closely related with the local biomechanical situation, morphology, components and biological activity of the carotid plaques. In this article, the research progress on methodology for studying carotid stenosis biomechanics, the risk of vulnerable plaque rupture in carotid stenosis and decision-making in clinical treatment, the animal modeling and experiment on vulnerable carotid plaques, and the components and biological activities of carotid plaques was summarized, the existing problems were analyzed, and the in-depth prospective about the biomechanical mechanism and quantitative assessment indices for vulnerable carotid plaques was also proposed, expecting to provide necessary theoretical guidance for feasible decision-making on the treatment of carotid stenosis.

Application of computational fluid dynamics in clinical treatment of cerebral aneurysms / 医用生物力学

In recent years, computational fluid dynamics (CFD) has been widely used in fundamental and clinical researches of cerebral aneurysms. The research direction involves: ① the hemodynamic risk factors associated with initiation, evolution and rupture of cerebral aneurysms, ② the assessment of flow field changes in cerebral aneurysms after the implantation of coils and stent as well as the effect of such endovascular treatment by establishing the patient-specific models. This review elaborates the research progress in hemodynamics of cerebral aneurysms from 3 aspects: the development of CFD models, the morphological and hemodynamic parameters for rupture risk assessment of aneurysms and the role of CFD in the endovascular treatment of cerebral aneurysms.

Simulation study on expansion process of vascular stent in realistic stenosis model / 医用生物力学

Objective To study the deformation and mechanical characteristics during expansion process of vascular stent in realistic stenosis model, so as to provide scientific references for interventional treatment and stent design. Methods The carotid vessel model and plaque model of patient were built by using 3D reconstruction method, and the stent model with I-shaped link was established by using Pro/E; ABAQUS/Standard was used to simulate the radial expansion (the first stage) and radial contraction (the second stage) of the stent in real stenosis model, and a realistic model of blood vessel with plaque was also established to make contrast test. Results In the first stage, radial expansion of the stent was formed. The maximum contact area was generated between the outer surface of the stent and the inner surface of the plaque/arterial wall, and the maximum stresses on the stent, plague and arterial wall were 515.000, 2.482, 1.053 MPa, respectively. In the second stage, the radial contraction of the stent resulted in “dog-bone” effect. Many gaps between the stent and vessel wall was formed, and the maximum stresses on the stent, plague and arterial wall were 464.500, 0.954, 0.316 MPa, respectively. In contrast test, the maximum stresses on stenotic vessel and stent were 0.9, 414.1 MPa in the second stage. Conclusions Compared with the model in contrast test, the stenosis model differentiating the component of vascular tissues is more consistent with the real situation of stenotic vessels, by more truly showing deformation and mechanical characteristics of the stent and blood vessel. The stent causes the maximum damage to plaque and inner wall of blood vessel in the first stage, while “dog-bone” effect of the stent is an important influencing factor that results in the gaps between the stent, plague and blood vessel. These research findings may provide significant guidance for selecting stent in interventional treatment and improving stent design.

Evaluation of cardiovascular health based on pulse wave detection technology / 医用生物力学

There contains so much physiological/pathological information in pulse wave, which can reflect the early changes in cardiovascular function parameters. Therefore, it would be valuable to quantify the information revealed by pulse wave as important reference for cardiovascular diseases. In this review, the relationship between physiological/pathological information in cardiovascular system and pulse wave was described from the viewpoint of pulse wave formation mechanism, and to explain how the non-invasive detection indexes supplied by pulse wave could be applied in clinical use by analyzing the waveforms. Cardiovascular health evaluation index established by physiological/pathological information from cardiovascular system with pulse wave theory was also discussed. The development of non-invasive detection methods for cardiovascular system based on pulse wave theory can contribute to cardiovascular health care and provide important reference for the early detection, early prevention and early treatment of cardiovascular diseases. Besides, the non-invasive detection method can simplify the process of clinical testing and reduce the costs so as to achieve health assessment on cardiovascular diseases timely and reduce the mortality and disability rates.

FSI simulation of patient-specific aortic dissection and its bypass grafting / 医用生物力学

Objective To investigate the effects of different bypass grafting for treating DeBakey Ⅲ aortic dissection. Methods The patient-specific models of DeBakey Ⅲ aortic dissection based on CT images were reconstructed by using Mimics software, and two bridge models of bypassing between ascending aorta and abdominal aorta (AA), and between left subclavian artery and abdominal aorta (LA) were established by computer-aided method, respectively. Then numerical simulations were performed by using fluid-structure interaction (FSI) method to compare hemodynamic differences of these two models. Results After bypass surgery, the mass flow, mean and maximum velocities of the through lumen models were reduced to different degrees. Meanwhile, both the maximum blood pressures and displacements of the vessel walls of AA models were decreased, but those of LA models were increased. In contrast, all the above-mentioned hemodynamic parameters of the blind lumen models were decreased, especially for AA models. Conclusions The AA bypassing is a better treatment for DeBakey Ⅲ aortic dissection of through lumen and blind lumen. The therapeutic effects can be easily explained through simulation results, to ensure the scientific validity and clinical utility of bypassing.

Invasive detection of blood viscosity and its influencing factors in middle-aged and elderly people with cardiovascular diseases / 医用生物力学

Objective To detect the blood viscosity values and find out the statistically significant influencing factors of blood viscosity and their fitting formulas among the middle aged and elderly people with high incidence of cardiovascular diseases. Methods The subjects’ blood was collected in the hospital, together with their physiological and pathological information, and LG-R-80 series rotary viscometer detector was used to detect blood viscosity. The statistically significant factors of blood viscosity and their fitting formulas were obtained by using SPSS. Results Blood viscosity increased with age and body mass index (BMI) and reached its peak value in 60 year-old males (5.35 mPa•s) and 50 year-old females (4.45 mPa•s), respectively, then the variation of blood viscosity would be stabilized, with no more increase; the blood viscosity values of males in all groups with different ages were significantly higher than those of females, with difference value in the range of 0.28-0.90 mPa•s; the blood viscosity values were obviously higher in hypertension group than those in normal group, with statistically significant differences (P<0.1). Conclusions The blood viscosity distribution in people with high incidence of cardiovascular diseases has certain regular pattern, and the obtained fitting formula between blood viscosity and influencing factors in this study would provide useful references for further study such as variation of blood viscosity under different physiological conditions, effects of different viscosities on some cardiovascular diseases, and non-invasive detection of blood viscosities.

Hemodynamics-based numerical comparison between modified B-T shunt and central shunt / 医用生物力学

Objective Modified B-T shunt (MBTS) and central shunt (CS) are two common surgical procedures for the treatment of tetralogy of fallot (TOF). The purpose is to analyze and compare the hemodynamic features of MBTS and CS. Methods 3D anatomy was reconstructed by medical images obtained from a patient with TOF, and two computational models were generated through virtual operations. A lumped parameter model was constructed to predict the post-operational boundary conditions. Computational fluid dynamics (CFD) was performed for the two models. Results A persistent pulmonary blood perfusion was observed in each model both during the systolic phase and diastolic phase, but the maximum velocities in the shunt were different for the two models. The pressure drop of the shunt in CS model was higher than that in MBTS model. The wall shear stress of the shunt in the MBTS model ranged unevenly from 0.025 to 340 Pa, while the wall shear stress in CS model ranged relatively evenly from 32.2 to 72.6 Pa. Conclusions Pulmonary artery blood was increased effectively for both options. The blood perfusion of right upper extremity was decreased in the MBTS model. More blood was directed into the pulmonary artery in CS model. Attention should be paid to the fact that the pressure gradient was large at the proximal anastomosis in both models in clinic. This study provides important theoretical references for surgeons to make choice from the surgery options in the treatment with TOF.

Mechanical analysis on treatment of vertebral artery stenosis by stents with different links / 医用生物力学

Objective To investigate the mechanical effect of stents with different links on the treatment of vertebral artery stenosis, and provide scientific guidelines for the design of stent structure and clinical procedure of stenting intervention. Methods Models of three kinds of stents with different types of links (namely, L-stent, V-stent and S-stent according to the shape of links) and vertebral artery with stenosis were established by using Pro/Engineering, then the same boundary conditions were exerted on the three models to simulate the stent deployed in the vertebral artery by finite element analysis using ABAQUS. Results Compared with L-stent and V-stent, S-stent had a better compliance, generating smaller stress in the arterial wall, causing relatively weak vascular straightening. Due to smaller stress and axial shortening generated in the stent strut, S-stent made less lesion on the arterial wall. Conclusions The therapeutic effect of S-stent is the best among the three kinds of stents, which could reduce in-stent-restenosis, and has good prospect in clinical application.

Recent development and application of hemodynamics / 医用生物力学

The study of hemodynamics, which refers to dynamics inside the blood circulation, mainly includes the flow rate, flow resistance, pressure, shear stress, disturbed flow, as well as their associations in between. Therefore, with its important significance in the clinical treatments of vessel curvature, arterial stenosis or occlusion, pathological artery branches and aneurism, study about hemodynamics is essential to human health. Currently, extensive researches on hemodynamics have been conducted with respect to artery bypass, coronary arterial stenosis, abdominal aortic aneurysm, atherosclerosis, cerebral aneurysm and swirling flow. With the development of such research on hemodynamics, surgical planning and interventional therapy have improved rapidly. The influence mechanism of hemodynamic parameters, including pressure, flow resistance, flow rate, wall shear stress, blood viscosity, flow separation, turbulent flow, vortex on the post-operation complications could be deeply explored with the help of more and more clinical apparatus and have gained some achievements.

Hemodynamic simulation of vertebral artery stenosis treated by stents with different links / 医用生物力学

Objective To investigate the hemodynamic effect of stents with different types of links on treating vertebral artery stenosis, and provide scientific guidelines for the design of stent structure and the clinical procedure of stent intervention. Methods Models of vertebral artery with stenosis and three kinds of stents with different types of links (named as L-stent, V-stent and S-stentaccording to the shapes) were constructed by using Pro/Engineering. The expansions of these stents in the stenotic vertebral artery were simulated using ABAQUS, and three finite element models of the stented vertebral artery were then established for fluid flow analysis, and hemodynamic simulation was performed using ANSYS-CFX. Results Compared with V-link and S-link stent, L-link stent had smaller area of low wall shear stress distributions and smaller blood stagnation area. Conclusions With better hemodynamic effect, L-stent can potentially reduce the possibility of in-stent restenosis and provide scientific references for the choice of stent, the design of stent structure and surgical planning of stent intervention.

Fluid structure interaction analysis based on patient-specific internal carotid artery aneurysm model / 医用生物力学

Objective To analyze the distribution characteristics of blood flow and wall shear stress with the consideration of elasticity of the artery wall and to investigate the biomechanical factors inducing aneurismal rupture. Methods The three-dimensional patient-specific internal carotid artery aneurysm model was constructed based on two-dimensional medical scan images. The artery wall model was created based on the statistical data of human body. According to the condition of the pulsatile blood flow in human body, hemodynamics in internal carotid aneurysm with fluid structure interaction was simulated using finite volume method and finite element method. Results An obvious vortex flow in aneurismal cavity was found with the direction unchanged during a cardiac cycle. There was a region at the aneurismal neck and aneurismal dome where the value of wall shear stress was relatively high. It also found two regions in the aneurismal neck and the aneurismal dome where the value of Von Mises Stress reached the maximum locally. In view of the material strength, it should be easy to have aneurismal rupture in these areas. Conclusions The distribution characteristics of vascular wall stress can be obtained by the calculation of fluid structure interaction to further predict the possible position of aneurismal rupture.

Fluid-structure interaction numerical simulation of bypassed DeBakey Ⅲ aortic dissection / 医用生物力学

Objective To investigate the mechanical mechanism of bypass graft for the treatment of DeBakey III aortic dissection and explore the valid surgical planning. Methods Patient-specific models of DeBakey III aortic dissection, including the models of through lumen and blind lumen, before and after bypassing between ascending aorta and abdominal aorta, between left subclavian artery and abdominal aorta, were constructed, and then numerical simulations were performed using computational fluid dynamics (CFD) method under physiological flow conditions based on fluid-structure interaction (FSI). Results Blood flow velocity, pressure, vessel wall displacement of the false lumen after bypass graft were reduced by 38.86%, 15.347 kPa and 39.46% on average, respectively. Conclusions Bypass graft is an effective surgical method for the treatment of DeBakey III aortic dissection under specific conditions with good prospects in clinical application.

Comparative study on effects from three kinds of stents with different cross-section on aneurismal hemodynamics / 医用生物力学

Objective To propose and numerically simulate a novel stent with triangular wire cross-section so as to compare the hemodynamic effect of endovascular stents in aneurysm with circular, rectangular and triangular cross section, respectively. Methods Three aneurysm models were constructed by implanting 3 kinds of stents separately, including one with bare circular wire cross-section stent (named CM), and one with bare rectangular wire cross-section stent (named RM), and one with bare triangular cross-section stent (named TM). An unstented aneurysm model was also constructed to serve as the control (named UM). Four models were preformed with numerical simulation of fluid-structure interaction under the same boundary conditions using finite element method. Results Compared with TM and CM, RM showed lower velocity, higher flow resistance and longer turn over time, which demonstrated that the effect of blood flow pattern on three stents was decreased in the order of RM, TM, CM. RM could reduce the magnitude and fluctuation of wall shear stress (WSS) more significantly than that of TM and CM. However, the pressure rise of TM and CM was lower than that of RM. WSS distribution and deformation results indicated the possibility of aneurysm development along the distal wall was higher than that along the proximal wall, and the top of aneurysm was in the highest risk of rupture. Conclusions Three kinds of stents show differences of hemodynamics in aneurysm treatment, which provides significant references for the structural design and optimization of endovascular stent.

Research progress in biomechanics of in-stent restenosis / 医用生物力学

Stent intervention has become one of the most effective ways in treating cardiac and cerebral vascular stenosis. However, postoperative in-stent restenosis remains a major unsettled issue. The occurrence of in-stent restenosis is related not only to the mismatch between stent and artery, as well as the stress induced by mechanical support of the stent struts on arterial wall, but also to the intimal hyperplasia induced by the hemodynamic change. Recent literatures on biomechanics of the stented artery were reviewed in this paper. In particular, from the view of solid mechanics and hemodynamics, the research progress of stented artery in biomechanical simulation was given detailed discussion; moreover, the biomechanical factors associated with in-stent restenosis were analyzed and summarized. Numerical simulation is a good method for investigating the relationship between stent intervention and in-stent restenosis, and it also provides a scientific guideline for the design of stent structure and clinical procedure of stent intervention.

Hemodynamics analysis of vertebral artery ostium stenosis treated with stent implantation undergoing different protrusion distances / 医用生物力学

Objective To investigate the influence of different protrusion distance of stent strut into the subclavian artery on local hemodynamics of the vertebral artery (VA) ostium.Methods Five models of the VA were established. Model 1 was without stent implantation, Model 2 to 5 was with stent protruding into the subclavian artery for 0, 1, 2, 3 mm, respectively. Computational fluid dynamics analysis was performed to study the differences of hemodynamics in these models. Results After stent implantation, the wall shear stress and the blood flow velocity at the stent segment in the Model 2 was reduced by 85.33% and 35.36%, respectively. The phenomenon of swirling flow disappeared. For models with different protrusion distance, the maximum difference of wall shear stress of VA was 0.76%, and the maximum difference of blood flow velocity is 0.45%. ConclusionsStent implantation can improve the hemodynamics of vertebral artery ostium stenosis, while the protrusion distance of stent strut has no obvious influence on the blood flow velocity and wall shear stress.

Optimization of baseline on stent with trapezoidal cross-section for intracranial aneurysm / 医用生物力学

Objective To optimize the baseline on the trapezoidal cross section of stent wires, so as to reduce the risk of intracranial saccular aneurysm rupture after the implantation of such stents. Methods Thirty-eight trapezoidal cross-section wire stents with different baselines were constructed to establish the finite element models. Numerical simulation by fluid-solid interaction method was conducted to calculate 38 maximum pressure gradients on the aneurysm wall. GRNN (general regression neural network) and GA (genetic algorithm) were used to optimize the baseline on the cross-section of stents with trapezoidal cross-section wire so as to minimize the maximal pressure gradient on the aneurysm wall. Results Compared with the traditional stent with rectangular cross-section wire, the maximal pressure gradient on the a neurysm wall was reduced by 7.86% after the implantation with the optimized stent with trapezoidal cross-section wire. Conclusions The combination of GRNN and GA is an effective approach for stent optimization.

Effect on aneurysmal pressure after stent intervention treatment for aneurysm accompanied by stenosis / 医用生物力学

Objective To investigate the effect on aneurysmal pressure after stent intervention treatment for aneurysm accompanied by stenosis. Methods Computational fluid dynamics (CFD) analyses were carried out to make comparative study on aneurysm models with and without stenosis. Three models (M1, M2, M3) were constructed to compare the pressure variations. M1 was the aneurysm model with no stenosis and no stent, M2 was forming from M1 model with a preaneurysm stenosis, and M3 was the M2 model with stent implantation at the place of the aneurysm. Results For comparison between M2 and M1, pressure increase in the aneurismal sac caused by a mild stenosis (50%) was about 1.399 9 kPa(10.3 mmHg) with the peak systole, and the average pressure increase in a cardiac cycle was about 0.572 kPa(4.3 mmHg). For comparison between M2 and M3, pressure increase in the aneurismal sac was about 1.037 kPa(7.8 mmHg) at peak systole in a cardiac cycle, and the average pressure increase in the aneurismal sac in a cardiac cycle was about 0.399 kPa(3 mmHg). Conclusions A mild stenosis could not result in the sharp pressure increase with stent intervention applied to the treatment of aneurysm accompanied by stenosis harbored on a tortuous intracranial artery. The geometry of the parent vessel and its aneurysmal/stenotic diseases do have influence on the pressure variation at the place of aneurysm.

Hemodynamics and its medical application / 医用生物力学

Hemodynamics is closely related with the initiation, development and treatment of neo-cardiovascular diseases. The studies on the hemodynamics in neo-cardiovascular system are the hotspots of biomechanics and biomedical engineering. The research topics, research method, research achievement and its medical application, which are issued in the articles in this special column, were remarked. Emphasis was paid to the review of the research driver, research progress and research tendency of hemodynamics. The application prospect of hemodynamics research on the clinical procedure and healthcare was demonstrated with respect to its multi level application in prevention, diagnosis and treatment.

Hemodynamic effects of stenting on wide-necked intracranial aneurysms / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Stent placement has been widely used to assist coiling in cerebral aneurysm treatments. The present study aimed to investigate the hemodynamic effects of stenting on wide-necked intracranial aneurysms.</p><p><b>METHODS</b>Three idealized plexiglass aneurismal models with different geometries before and after stenting were created, and their three-dimensional computational models were constructed. Flow dynamics in stented and unstented aneurismal models were studied using in vitro flow visualization and computational fluid dynamics (CFD) simulations. In addition, effects of stenting on flow dynamics in a patient-specific aneurysm model were also analyzed by CFD.</p><p><b>RESULTS</b>The results of flow visualization were consistent with those obtained with CFD simulations. Stent deployment reduced vortex inside the aneurysm and its impact on the aneurysm sac, and decreased wall shear stress on the sac. Different aneurysm geometries dictated fundamentally different hemodynamic patterns and outcomes of stenting.</p><p><b>CONCLUSIONS</b>Stenting across the neck of aneurysms improves local blood flow profiles. This may facilitate thrombus formation in aneurysms and decrease the chance of recanalization.</p>

Numerical research of hemodynamic effects on internal carotid aneurysm with five types of stents / 医用生物力学

Objective To investigate effects of endovascular stents with different structures and wire cross section shapes on the treatment of internal carotid aneurysm and its influence on hemodynamics and flexibility. Method Based on the same model of internal carotid aneurysm, five models with different stent intervention treatment were constructed, which had different stent structions or wire cross section shapes while their porosity rates were approximately the same. Numerical simulations were performed using finite volume method to get quantitative information of biomechanics. Results Among the five models, the mean flow rate in aneurismal cavity decreased maximally in the model with stent of rectangular cross section. Wall shear stress in aneurismal dome and aneurismal neck were found to decrease much more in models with circular cross section and rectangular spiral stent. The flexibility of mesh stent was far better than that of the spiral stent. Conclusions Mesh stent with rectangular cross section has better biomechanical influence on the treatment of internal carotid aneurysm. These findings may help clinicians to select a proper stent when treating arterial aneurysm.