ABSTRACT
Long-term exposure to risk factors will lead to coronary atherosclerosis, which will lead to the formation and progression of coronary plaque. Early identification of high-risk plaque characteristics will help prevent plaque rupture or erosion, thus avoiding the occurrence of acute cardiovascular events. Biomechanical stress plays an important role in progression and rupture of atherosclerotic plaques. In recent years, non-invasive coronary computed tomography angiography (CCTA) computational fluid dynamics (CFD) modeling has made it possible to acquire the corresponding biomechanical stress parameters. These coronary biomechanical stress parameters, especially wall shear stress (WSS), will aid in the development of a more accurate clinical model for predicting plaque progression and major adverse cardiovascular events ( MACE ). In this review, the biomechanical stress and the role of WSS from CCTA in atherosclerosis were introduced, and the researches on the relationship between biomechanical stress from CCTA and coronary artery diseases were discussed.
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Objective To propose a two-way fluid-structure interaction (FSI) method based on real patients with carotid artery stenosis, and analyze the hemodynamic parameters of carotid plaques with different types at the lesion as well as deformation and stress changes of the plaque itself. Methods Three-dimensional ( 3D) modeling was performed based on computed tomography angiography ( CTA) data of patients with moderate carotid artery stenosis. The carotid artery wall model and plaque model were separated, and transient fluid structure coupling calculation was performed. The situation from early stage of carotid atherosclerosis to formation of the plaque was simulated. The plaque types were divided into thickened plaques, lipid plaques, mixed plaques and calcified plaques, among which thickened plaques were regarded as non-plaque conditions for representing the thickening of vascular intima-media. The stenotic carotid arteries with different plaque types were compared and analyzed. Results The plaques with different types had little effect on the overall blood flow, but the wall shear stress of lipid plaques at the lesion was lower than that of other plaques. With thickened plaques as a control, concurrence of the plaque would inhibit artery expansion, and lipid plaques were the most obvious. Calcified plaques had the highest average plaque structure stress, while lipid plaques had the lowest average plaque structure stress. Conclusions The method proposed in this study can analyze fluid area and solid area at the same time. The results can contribute to better understanding the influence of different plaque types on carotid artery diseases.
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Objective To investigate the effects of fluid shear stress on rolling adhesion of neutrophils on immobilized platelets under flows. Methods Experiments were performed at the parallel plate flow chamber. Platelets were adhered to the functionalized flow chamber bottom which were coated with vWF-A1 first, and then washed with PBS under wall shear stress (WSS) of 1 Pa for different time (0 min, 2.5 min, 7.5 min). A high-speed camera was used to observe and record the rolling adhesion events of neutrophils on immobilized platelets under 50 mPa WSS, and the adhesion parameters such as the number of adhesion events, the tether lifetime of cells and rolling velocity. Results Neutrophils could specifically bind to the immobilized platelets on vWF-A1-coated bottom of the flow chamber. Mechanical stimulation on immobilized platelets had no effects on the tether lifetime of neutrophils on the platelets, but up-regulated the adhesive ratio of neutrophils on the platelets and slowed down the rolling of neutrophils on the platelets. Conclusions Mechanical stimulation on the immobilized platelets will significantly make the circulating neutrophils to be captured easily and promote the rolling adhesion of neutrophils on platelets.
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Objective To analyze the hemodynamic parameters of anomalous origin of the right coronary artery from the left coronary artery sinus (AORL) based on computational fluid dynamics (CFD), so as to make an evaluation of the disease. Methods A normal right coronary artery (RCA) case and an AORL case were selected. Two models were reconstructed in Mimics software and imported into ANSYS CFX software for hemodynamics simulation. The hemodynamics of normal RCA model and AORL model were compared. Results AORL model had a smaller volume flow (9.35 cm3/s), which might lead to insufficient blood supply downstream of the RCA; the pressure at the acute corner of AORL model (13.78 kPa) was lower than normal RCA model (14.9 kPa); the wall shear stress (WSS) of AORL model (12.83 Pa) was larger than that of normal RCA model (9.74 Pa); the total deformation of AORL model was relatively large. Conclusions The entrance velocity and pressure of AORL were lower than those of normal RCA, which might lead to ischemic symptoms. The research findings are of theoretical significance for the effective evaluation of ischemia and other diseases in clinic.
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Objective Hemodynamic disorder of the pulmonary artery (PA) is the main cause of pulmonary arterial hypertension related to congenital heart disease (PAH-CHD). To study the hemodynamic characteristics of PA, so as to understand biomechanical factors in the occurrence and development of PAH-CHD. Methods Clinical and imaging data were collected in five PAH-CHD patients and five matched controls (Non-PAH) to reconstruct subject-specific three-dimensional (3D) PA models. Computational fluid dynamics (CFD) was performed to compare the hemodynamic difference of flow patterns, wall shear stress (WSS) and normalized energy loss (E·) in the two groups. Results Hemodynamics-related parameters showed that the velocity and WSS were higher in the left and right PA branches of PAH-CHD patients, with significantly lower WSS in the main PA. The E· significantly increased in PAH-CHD patients and positively correlated with normalized PA diameter and inflow. Conclusions Compared with Non-PAH subjects, PAH-CHD patients have obviously higher velocity and WSS in PA branches, lower WSS in main PA and greater E·, indicating these hemodynamic parameters are related with the PAH-CHD, which can be used as potential biomechanical factors for the clinical evaluation of PAH-CHD.
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Objective To reduce the thrombosis probability and hemolysis risk of the meglev left ventricular assist device (LVAD), so as to increase the efficiency of blood supply. Methods The influences of the pump outlet diameter, exit angle, fillet size between the outlet and the inner wall of the pump, as well as gap between the rotor and the shell on internal flow field of the pump were studied by using the computational fluid dynamics (CFD) method, so as to optimize the internal structure and improve the hydrodynamic performance of the pump. Results Compared with pump of the previous generation, the maximum wall shear stress (WSS) of the pump inner wall, the maximum WSS of the pump rotor, the area with WSS >200 Pa were reduced by 23.6%, 47.4%, 76.2%, respectively, while the outlet flow was increased by 14.4%. Conclusions For the meglev LVAD of the new generation, its internal blood flow tended to be smooth, and the hemodynamic performance of blood flow was improved comprehensively. The research findings provide references for optimization design of the meglev LVAD and related experimental researches in the future.
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Objective To investigate the hemodynamic changes in a tortuous coronary to elucidate the effects of tortuosity on coronary perfusion and wall shear stress (WSS). Methods A single tortuous and non-tortuous patient-specific left anterior descending (LAD) coronary artery cases were selected. Two LAD models with and without coronary tortuosity were reconstructed in Mimics software and then transferred to the ANSYS Fluent software for performing computational fluid dynamics (CFD) simulation. The hemodynamic characteristics of both the LAD models were compared. Results The vessel WSS of the tortuous coronary artery clearly decreased in the bend section where the maximum curvature was larger than 1 mm-1.Such a scenario could led to an inadequate blood supply in the downstream vessels. A low WSS (0-26 Pa) acted on the outer wall of the bend, whereas the inner wall of the bend had a high WSS (>100 Pa). The mean WSS of the non-tortuous and tortuous models was 10.79 Pa and 36.12 Pa, respectively. The overall WSS of the tortuous model was larger compared with that of the non-tortuous model. Conclusions Coronary tortuosity increased the overall WSS, which could delay the progress of coronary atherosclerosis.
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Objective In the computational fluid dynamics software FLUENT, the independently developed user defined function (UDF) dynamic mesh program is called to achieve the mobile update of grid note based on the wall shear stress (WSS). Then this method is applied to simulate the development process of atherosclerosis (AS). Methods The UDF program by secondary development could extract WSS results of every note on the wall during the computing process, and if the threshold value criterion condition was met, the node would be adjusted to a new position. The mesh regeneration method combining with the spring smoothing and the local remeshing was adopted to control the update of the grid, so as to ensure the grid quality during deformation. Results The UDF program successfully extracted the WSS and arranged the corresponding deformation for the grid. The morphology of local extension in the proximal part and restenosis in the distal end were resulted from the vortex in the rear of the initial stenosis. Those features were similar to the indication of clinical angiography. Conclusions The independently developed UDF program has reached the expected effects, depicting the topography characteristics of AS influenced by WSS. In future researches, more influential factors should be considered in dynamic mesh deformation control to provide numerical references for clinical prognosis and risk evaluation of AS.
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Objective To conduct a comprehensive study on pulsatile blood flow in arteries by proposing a convenient theoretical research system for hemodynamics. Methods Based on Womersley algorithm for fully developed pulsatile flow, numerical algorithm was introduced to establish the solving and analytical system of hemodynamics based on flow rate in arteries during one cardiac cycle. The flow rate of carotid artery in pig was measured under three blood flow states: the ideal state with a sinusoidal inflow waveform, the normal physiological state and the enhanced external counterpulsation (EECP) state for comprehensive hemodynamic research. Results Important hemodynamic parameters such as the axial speed vector, the wall shear stress (WSS), and the oscillatory shear index (OSI) during one cardiac cycle under the mentioned three flow states were solved respectively. The waveform of flow rate had a certain effect on WSS distributions and OSI level; the EECP performance obviously resulted in a significant increase in the level of WSS (WSS peak in particular) and OSI. Conclusions The solving system developed in this paper can be used for hemodynamics study conveniently and effectively. One of the most important hemodynamic mechanisms that lead to EECP’s good clinical effect may lie in its promotion to WSS level under physiological state, but the effect of OSI on endothelial function of the artery might much smaller than WSS itself; therefore, OSI may not be an ideal hemodynamic index for predicting the lesion of atherosclerosis.
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Objective To study the hemodynamic characteristics after vascular drug eluting stent (DES) implantation, so as to provide theoretical guidance for clinical application of DES as well as improving the design of DES. Methods The geometry models of vascular lesions implanted with DES were constructed to numerically analyze drug concentration and wall shear stress (WSS) distributions in vessel by computational fluid dynamics (CFD) method. The results were compared with flow characteristics of the model with bare metal stent (BMS) implantation. Results Low WSS accompanied by high drug concentration would occur during blood flow in some areas after DES implantation, and vice versa. The presence of DES significantly reduced appearing such areas as either with low WSS only or with low drug concentration only. Theoretically, DES had more advantages than BMS at the stage of drug release. Conclusions DES could dramatically reduce the ratio of in-stent restenosis. Understanding the regular pattern of blood flow field distributions after DES implantation in detail will be beneficial to improve the design of DES, and further advance the overall performance of the stent, which can provide the theoretical basis for clinical research.
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Objective To compare the differences in the hemodynamic parameters of abdominal aortic aneurysm (AAA) between fluid-structure interaction model (FSIM) and fluid-only model (FM), so as to discuss their application in the research of AAA. MethodsAn idealized AAA model was created based on patient-specific AAA data. In FM, the flow, pressure and wall shear stress (WSS) were computed using finite volume method. In FSIM, an Arbitrary Lagrangian-Eulerian algorithm was used to solve the flow in a continuously deforming geometry. The hemodynamic parameters of both models were obtained for discussion. Results Under the same inlet velocity, there were only two symmetrical vortexes in the AAA dilation area for FSIM. In contrast, four recirculation areas existed in FM; two were main vortexes and the other two were secondary flow, which were located between the main recirculation area and the arterial wall. Six local pressure concentrations occurred in the distal end of AAA and the recirculation area for FM. However, there were only two local pressure concentrations in FSIM. The vortex center of the recirculation area in FSIM was much more close to the distal end of AAA and the area was much larger because of AAA expansion. Four extreme values of WSS existed at the proximal of AAA, the point of boundary layer separation, the point of flow reattachment and the distal end of AAA, respectively, in both FM and FSIM. The maximum wall stress and the largest wall deformation were both located at the proximal and distal end of AAA. Conclusions The number and center of the recirculation area for both models are different, while the change of vortex is closely associated with the AAA growth. The largest WSS of FSIM is 36% smaller than that of FM. Both the maximum wall stress and largest wall displacement shall increase with the outlet pressure increasing. FSIM needs to be considered for studying the relationship between AAA growth and shear stress.