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Objective To analyze and compare hemodynamic features of two different options for modified B-T shunt (MBTS) surgery, namely end-to-side(ETS) and side-to-side (STS), so as to provide references for clinical treatment of single ventricle heart defect syndrome. MethodsThe real geometric model was reconstructed by medical images obtained from a patient with hypoplastic left heart syndrome (HLHS); MBTS surgery was simulated through virtual operations; a lumped parameter model (LPM) was constructed based on physiological data of the patient; the post-operational boundary conditions of computational fluid dynamics (CFD) models (namely STS model and ETS model) were predicted based on the LPM; numerical simulation was conducted on two CFD models by using finite volume method. Results Flow details and wall shear stress distributions were all obtained for two models. The mean oscillatory shear index (OSI) of ETS model and STS model in part of pulmonary arteries was 3.058×10-3 and 13.624×10-3, respectively, while the energy loss was 116.5 and 94.8 mW, respectively, and blood flow rate ratios of left pulmonary artery to right pulmonary artery (RRPA/LPA) were 0.8 and 1.72, respectively. Conclusions There were nearly no differences between two CFD models in energy loss, which led to a relatively small impact on the surgery. The STS model had a more balanced pulmonary artery blood perfusion and a smaller mean OSI in part of pulmonary arteries, therefore, the STS model was superior to the ETS model. This study provides an important theoretical support and reference for treating patients with HLHS.
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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.
ABSTRACT
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.
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Objective Based on time-coupled multiscale coupling algorithm, to simulate the hemodynamics after systemic-pulmonary shunt procedure on single ventricular patient so as to obtain the local three-dimensional (3D) fluid field and global hemodynamic information before and after surgery. MethodsFirstly, the 0D-3D coupled multiscale hemodynamic model of systemic-pulmonary shunt procedure was established based on the lumped parameter model (0D) before surgery and the shunt model (3D), then the 0D-3D interface coupling condition and the time coupling algorithm were discussed. Secondly, the multiscale simulation of 3D CFD (computational fluid dynamics) model coupled with 0D lumped parameter model was realized based on lattice Boltzmann method. Finally, the multiscale simulation results were compared with patient’s 0D simulation results to study the hemodynamic changes before and after surgery. Results The global hemodynamic change and local 3D flow pattern were obtained by this multiscale simulation. The pulmonary blood flow distribution ratio was increased from 32.21% to 57.8%. Conclusions The systemic-pulmonary shunt procedure can effectively increase the blood supply of pulmonary circulation by implanting the shunt between the systematic circulation and pulmonary circulation. The geometrical multiscale method can effectively simulate both the coarse global and detailed local cardiovascular hemodynamic changes, which is of great significance in pre-operation planning of cardiovascular surgery.
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Objective To study the hemodynamics of central shunt (CS) by numerical simulation and investigate the effects of the elastic and rigid vessel wall on distributions of hemodynamic parameters in the vessel. Methods Two idealized CS models were constructed, one with a rigid wall (the rigid model) and the other with an elastic wall (the elastic model). Numerical calculation was conducted by the finite element method, and the elastic model adopted the fluid structure interaction. Results The distribution of flow velocity and pressure in both models were generally the same. About 68.9% of the aortic blood was directed into the pulmonary artery for the rigid model, as compared to 70% for the elastic model. The pressure drops within the shunt for the elastic model and rigid model were about 7.668 8 kPa and 7.222 3 kPa, respectively. The maximum variation in the average cross sections along the shunt was about 2.2% for the elastic model, appearing at the proximal end to side (ETS) anastomosis. The maximum difference of wall shear stress (WSS) between the two models at five key regions of each was about 16.1%. Conclusions Generally, the global flow structure in both the CS models remains unchanged; the elasticity of the vessel wall slightly influenced the flow distributions and pressure drop of the shunt; the effect from elasticity of the vessel wall on average cross sections along the shunt was higher at the proximal ETS anastomosis than that at the distal ETS anastomosis; the hypothesis that the vessel wall is rigid is acceptable in CS numerical simulations for the treatment of tetralogy of Fallot (TOF). However, the coupling of flow dynamics and wall mechanics may lead to a more reliable simulation result in the CS.
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Objective In order to improve the local hemodynamics of coronary artery bypass graft and reduce the incidence of restenosis, a double-bypass-graft design was proposed to alleviate artery stenosis. Methods Based on finite element method, the hemodynamics of the conventional bypass graft model and the double-bypass-graft model was adopted for numerical simulation. The distributions of hemodynamics such as flow field and wall shear stress in the vicinity of anastomosis were calculated. Results This new design provided better hemodynamics near the main anastomosis region, eliminated the vortex and flow stagnation, and increased the wall shear stress at the artery floor. The axial length of vortex near the assistant bypass graft by this new design was only 3 mm, which was shorter than that of 4.5 mm in the conventional design. Nearly 36% of the total blood was directed into the assistant bypass graft. Conclusions The new design could help to reduce the incidence of intimal hyperplasia.
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Objective A blood assist index (BAI), defined as ratio of the output power of LVAD (left ventricular assist device) to the total input power of circulatory system, was proposed in this paper to regulate the energy distribution between LVAD and natural heart. Methods A control strategy based on model free adaptive control (MFAC) algorithm was designed by using BAI as the control variable. The algorithm could track the desired BAI by regulating the pump speed to maintain the measured BAI. A mathematic model of cardiovascular system was used to verify the feasibility of the controller in presence of heart failure, slight physical active and recovery of cardiac function. Results The simulating results demonstrated that the proposed controller could automatically regulate the pump to respond to the reduced peripheral resistance (5 500 r/min vs. 6 000 r/min). When Emax increased from 80 to 240 Pa/mL to simulate the heart recovery, the blood flow rate could increase accordingly from 5 to 8 L/min.Conclusions The proposed control strategy can provide an adjustable and accurate energy distribution between LVAD and native heart by regulating the pump speed, which would be of benefit to promoting left ventricle reverse remodeling.
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Objective To conduct the operation of capture and deformation in virtual three-dimensional (3D) environment with force feedback device and simulate the coronary artery bypass operation. Methods Based on data collected from real CT images of the patient with heart disease, digitized visual model of the heart was reconstructed. Then the bypass vessel was built and the vessel model was sculptured by force feedback device to simulate the bypass surgery from pulmonary artery to ventriculus dexter in Fontan operation. Results Space structure of the heart was shown in the virtual 3D reconstructed environment. Bypass vessel with any diameter and angle was transformed to simulate the coronary artery bypass operation. Heart patch with any size was built to repair the heart model. The satisfactory model and parameters of the postoperative model were finally achieved. Conclusions The application of force feedback device in virtual coronary artery bypass operation sets the stage for cardiovascular surgery planning system with mechanical characteristics to simulate multiple modalities of such operation.
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Objective To predict the influence of connecting position between left superior vena cava (LSVC) and pulmonary artery on bilateral bidirectional Glenn (BBDG) shunt by numerical simulation. Methods Firstly, a 3D anatomical geometrical model was reconstructed by the medical images of a hypoplastic left heart syndrome (HLHS) patient with LSVC. Secondly, based on haptic deformations, several computational models were virtually generated, and computational fluid dynamics (CFD) numerical simulations were conducted using finite volume method. Finally, hemodynamic parameters were analyzed and evaluated. Results Flow recirculation was observed in the pulmonary artery between the LSVC and right superior vena cava (RSVC). The diameter of RSVC was defined as D. Varying the distance between LSVC and RSVC from 2D to 3.5D resulted in the least energy dissipation at 3D and the most at 2D. The blood flow rate ratios of left pulmonary artery to right pulmonary artery (LPA/RPA) ranged from 0.65-1.11. Conclusions Too close distance between LSVC and RSVC would bring out unfavorable hemodynamic distributions and consume more energy in the treatment of BBDG shunt. This study is of significance for surgeons to evaluate the optimal Fontan options in the treatment of HLHS accompanied by LSVC.
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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.
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Objective To design a global sliding mode control algorithm for the purpose of eliminating the chattering effect in conventional sliding mode control algorithm on both the controller and controlled plant from the conventional sliding mode control algorithm and regulating the intra aorta pump in response to the demand of blood circulation system in human. Methods A dynamic disturbance compensator was used to estimate the uncertainty of the intra aorta pump control system. Computer simulations and in vitro experiments were also conducted to verify the dynamic characteristics and robustness of the controller. Results As the dynamic disturbance compensator was used to estimate the uncertainty of system, the chattering effect in sliding mode control algorithm was eliminated. When the reference flow rate was set at 5 L/min, the response time was 80 ms without any overshot and static error. When the load torque of the controller was increased to 0.4 N·m, the response time was 25 ms. When the pulsatile signal was input as the reference flow rate, the dynamic response time was 80 ms with the maximum error of flow rate being 0.03 L/min. In the in vitro experiments, as the feedback frequency of flow rate signal and pump speed signal were lower than that in the ideal condition, the controller performance was deteriorative compared with computer simulation. The experimental results demonstrated that when the reference flow rate was set at 5 L/min, the response time was 0.26 s with the error of flow rate being 0.1 L/min. Conclusions The controller provided in this paper can accurately regulate the intra aorta pump according to the reference flow rate. Furthermore, it has a strong robustness for the uncertainty and disturbance of the control system. Due to the use of dynamic disturbance compensator, the chattering effect of the algorithm has been eliminated.
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Objective Try to set up a nonlinear lumped parameter model of intra-aorta pump by studying the relationship between the pressure difference and the blood flow rate at the head of the pump, so as to predict the hemodynamic parameters of the pump. Methods Only the parameters of the pump, without hemodynamic parameters of the circulating system, were used to esfablish the model. It was composed of a speed-controlled current source representing the flow rate driven by impeller, an internal resistant representing the resistance of the radial clearance, an inductance denoting the inertance of the blood. Results The model could simulate the physiological status of the heart under all the situations from pulmonary congestion to ventricular collapse. The characteristic equation of the pump was derived with parameters determined by experimental data in vitro. Conclusions To verify the accuracy of the model, the prediction value calculated from the model was compared with the one recorded from experiment in vitro. The results showed that the error in between was less than 5%, which indicated that this model could predict the pressure difference of the pump accurately.
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Hemodynamics-simulation-based cardiovascular surgical planning.which is the patient-specific surgical hemodynamics optimization based on medical image,is the further development of clinical-applica-tion-oriented computational hemodynamics,it is very helpful for cardiovascular surgical decision-making.The art-in-work of hemodynamics-simulation-based cardiovascular surgical planning in both domestic and over-seas research was reviewed,the key problems and solutions involved were analyzed,and the further develo-ping objectives were presented.
ABSTRACT
Hemodynamics-simulation-based cardiovascular surgical planning.which is the patient-specific surgical hemodynamics optimization based on medical image,is the further development of clinical-applica-tion-oriented computational hemodynamics,it is very helpful for cardiovascular surgical decision-making.The art-in-work of hemodynamics-simulation-based cardiovascular surgical planning in both domestic and over-seas research was reviewed,the key problems and solutions involved were analyzed,and the further develo-ping objectives were presented.