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The patient-specific aortic silicone model was established based on CTA data. The digital particle image velocimetry (DPIV) test method in the modified ViVitro pulsatile flow system was used to investigate the aortic hemodynamic performance and flow field characteristics before and after transcatheter aortic valve replacement (TAVR). The results showed that the hemodynamic parameters were consistent with the clinical data, which verified the accuracy of the model. From the comparative study of preoperative and postoperative effective orifice area (0.33 cm2 and 1.78 cm2), mean pressure difference (58 mmHg and 9 mmHg), percentage of regurgitation (52% and 8%), peak flow velocity (4.60 m/s and 1.81 m/s) and flow field distribution (eccentric jet and uniform jet), the immediate efficacy after TAVR is good. From the perspective of viscous shear stress and Reynolds shear stress, the risk of hemolysis and thrombotic problems was low in preoperative and postoperative patient-specific models. This study provides a set of reliable DPIV testing methods for aortic flow field, and provides biomechanical basis for the immediate and long-term effectiveness of TAVR from the perspective of hemodynamics and flow field characteristics. It has important application value in clinical diagnosis, surgical treatment and long-term evaluation.
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Humans , Transcatheter Aortic Valve Replacement/methods , Aortic Valve/surgery , Heart Valve Prosthesis , Hemodynamics , Aortic Valve Stenosis/diagnosis , Treatment OutcomeABSTRACT
Objective In view of the situation that tracheal atrophy causes the overall airway size to become smaller in the elderly, effects of the airway wall surface on reconstruction of a narrow airway and the airflow field under different respiratory conditions were investigated. Methods A three-dimensional (3D) model of human airway was established by using Mimics, and flow field in the airway was simulated by computational fluid dynamics (CFD) method. The inner wall pressure and the distribution of airflow were analyzed and compared under different breathing states. Results Under different respiratory states, the pressure of endotracheal wall was relatively uniform in the endotracheal wall, but decreased significantly in air inlet of the bronchial stenosis segment, and reached negative pressure near the narrowest area. The airflow velocity decreased from the center of the pipe to the boundary layer, and the velocity reached the maximum at the narrow area. Vortex was generated when airflow passed through the narrow area, and the larger the inlet flow velocity was, the larger the positive pressure and negative pressure were, the more obvious the pressure drop at the narrow area was, and the more obvious the vortex phenomenon was. Conclusions The constriction of the airway stenosis area caused by negative pressure will lead to the patient’s dyspnea, and the eddy current will cause the airway wall to be affected by the aerodynamic shear stress and may damage the airway wall mucosa. Therefore, understanding of the pressure distribution and velocity distribution in the narrow airway can provide references for clinical diagnosis and treatment of such diseased airways.
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@#Parotid obstructions can cause repeated swelling of the glands. Previously, duct stones were thought to be the main cause of obstructions, but salivary gland endoscopy examinations have revealed the absence of stones or foreign bodies in the duct system of the parotid glands with obstructive symptoms. Diseases of the parotid gland with obstructive symptoms include chronic recurrent parotitis, non-stone chronic obstructive parotitis, Sjögren′s syndrome, IgG4-related parotitis and radiation-induced parotitis. The mechanism of obstructions is unknown, and the disease course is prolonged. In this paper, based on a brief analysis of duct stenosis, distortion and mucus emboli, which may lead to parotid obstructions, a new perspective is emphasized: the duct system of the parotid and flowing saliva constitute a microflow field. Based on the principle of fluid mechanics, the flow of saliva in the flow field can be affected by the confluence, diameter changes, and twist of the ducts. This outcome results in changes in the low velocity zone, backflow, counterflow and turbulence; affects saliva flow and normal discharge; and causes symptoms of parotid obstruction. An analysis of the possible mechanisms of parotid obstruction using two variables, duct anatomy and saliva traits, helps explain the causes of nonstone parotid obstructions.
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Objective To investigate the effects of rounding on the prediction of flow field and hemolysis for FDA benchmark blood pumps by using the method of computational fluid dynamics（CFD）. Methods Key properties such as hydraulic characteristics, mean velocity distributions and hemolysis index of FDA benchmark blood pump under three operating conditions were simulated, and the influence of the above simulation result was further compared when the impeller was equipped with or without rounding. Results The rounding of blood pump impeller had impacts on pump head (the maximum percentage difference between the impeller with rounding and without rounding was 57.38%), velocity distributions, which led to a considerable impact on predicted hemolysis levels (the maximum error between the impeller with rounding and without rounding was more than one order of magnitude). Conclusions Impeller with rounding was beneficial for optimization of blood pump performance. The research findings are of great importance for better use of CFD to aid the hemocompatibility design of blood pump.
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Objective To study mechanical properties of the bone scaffold with different structure and its internal flow field distributions,so as to provide a direct comparison and judgment on model structure and offer an effective guidance for bone scaffold structure design.Methods Bone scaffold with natural,woven and spherical pore structure were reconstructed respectively by using Pro/Engineer and Mimics.The effective elastic modulus for three kinds of scaffolds,as well as their stress distributions and internal flow field distributions under three-dimensional perfusion culture system were analyzed with the finite element method.Results The bone scaffold with natural structure showed smaller effective elastic modulus,smaller peak stress and more uniform stress distributions under the same pressure.With the same initial velocity and fluid viscosity,the bone scaffold with natural structure showed smaller internal velocity,wall shear stress and wall pressure.Conclusions The bone scaffold with natural structure has better biomechanical properties,which corresponds to the design criteria of bone scaffold in bone tissue engineering.
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Objective To study mechanical properties of the bone scaffold with different structure and its internal flow field distributions,so as to provide a direct comparison and judgment on model structure and offer an effective guidance for bone scaffold structure design.Methods Bone scaffold with natural,woven and spherical pore structure were reconstructed respectively by using Pro/Engineer and Mimics.The effective elastic modulus for three kinds of scaffolds,as well as their stress distributions and internal flow field distributions under three-dimensional perfusion culture system were analyzed with the finite element method.Results The bone scaffold with natural structure showed smaller effective elastic modulus,smaller peak stress and more uniform stress distributions under the same pressure.With the same initial velocity and fluid viscosity,the bone scaffold with natural structure showed smaller internal velocity,wall shear stress and wall pressure.Conclusions The bone scaffold with natural structure has better biomechanical properties,which corresponds to the design criteria of bone scaffold in bone tissue engineering.
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Objective To study mechanical properties of the bone scaffold with different structure and its internal flow field distributions,so as to provide a direct comparison and judgment on model structure and offer an effective guidance for bone scaffold structure design.Methods Bone scaffold with natural,woven and spherical pore structure were reconstructed respectively by using Pro/Engineer and Mimics.The effective elastic modulus for three kinds of scaffolds,as well as their stress distributions and internal flow field distributions under three-dimensional perfusion culture system were analyzed with the finite element method.Results The bone scaffold with natural structure showed smaller effective elastic modulus,smaller peak stress and more uniform stress distributions under the same pressure.With the same initial velocity and fluid viscosity,the bone scaffold with natural structure showed smaller internal velocity,wall shear stress and wall pressure.Conclusions The bone scaffold with natural structure has better biomechanical properties,which corresponds to the design criteria of bone scaffold in bone tissue engineering.
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Objective To investigate the application of wall shear stress (WSS) in the carotid sinus of type 2 diabetes mellitus (T2DM) patients,and analyze the spatial distribution of WSS with contrast enhanced flow field (CEFF) quantita tive visualization analysis software.Methods Totally 47 T2DM patients and 25 healthy subjects were investigated.According to the intima-media thickness (IMT) of common carotid artery (CCA),the T2DM patients were divided into IMT normal group (n=21) and IMT thickening group (n=26).WSS in the carotid sinus was calculated by CEFF analysis soft ware,the corresponding spatial distribution maps of WSS were designed.WSS of the posterior wall of internal carotid artery (ICA) was recorded and statistical analysis.Results Both in the carotid sinus of healthy subjects and T2DM patients,there were two low WSS regions and one high WSS region.There were a large region of low WSS at the posterior wall of CCA and ICA,a small region of low WSS at the anterior wall of CCA,and a high WSS region at the anterior wall of ICA.The WSS at the posterior wall of ICA both in the IMT normal group [(3.39 ± 0.60)dynes/cm2] and IMT thickening group [(2.58±0.46)dynes/cm2] were significantly lower than that in control group ([3.74±0.53]dynes/cm2,both P＜0.05).WSS in IMT thickening group was lower than that in IMT normal group (P＜0.05).Conclusion CEFF quantitative visu alization analysis might constitute an approach to assess the presence of early-stage arteriosclerosis by measuring the WSS in the carotid sinus.
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Objective To study mechanical properties of the bone scaffold with different structure and its internal flow field distributions, so as to provide a direct comparison and judgment on model structure and offer an effective guidance for bone scaffold structure design. Methods Bone scaffold with natural, woven and spherical pore structure were reconstructed respectively by using Pro/Engineer and Mimics. The effective elastic modulus for three kinds of scaffolds, as well as their stress distributions and internal flow field distributions under three dimensional perfusion culture system were analyzed with the finite element method. Results The bone scaffold with natural structure showed smaller effective elastic modulus, smaller peak stress and more uniform stress distributions under the same pressure. With the same initial velocity and fluid viscosity, the bone scaffold with natural structure showed smaller internal velocity, wall shear stress and wall pressure. Conclusions The bone scaffold with natural structure has better biomechanical properties, which corresponds to the design criteria of bone scaffold in bone tissue engineering.
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Objective To study the effects of different pressure boundary conditions and breathing patterns on the airflow of upper airway and related physiological status of the obstructive sleep apnea hypopnea syndrome (OSAHS) patient at sleep stage with eupnea and apnea, respectively. Methods The CT scan data of an OSAHS patient during natural sleep in supine position were acquired and used to reconstruct a three-dimensional finite element model of upper airway. Meanwhile the pressure changes in laryngeal cavity of the OSAHS patient were clinically measured and then used as the boundary conditions, and four typical breathing patterns (nasal inhaling and nasal exhaling, nasal inhaling and oral exhaling, oral inhaling and nasal exhaling, oral inhaling and oral exhaling) were considered for computational fluid simulation. Results The airflow of the OSAHS patient during sleep was an unstable, whorled and bidirectional flow, which was significantly affected by pressure boundary conditions and breathing patterns. Compared with nasal breathing, the maximum velocity of airflow by mouth breathing was increased, resulting in an increase of pressure drop in oral cavity, with was about 30% in inspiration and 100% in expiration. Conclusions It is significant to use CT data of an OSAHS patient during natural sleep for model reconstruction and the clinically measured pressure in laryngeal cavity as boundary conditions for finite element simulations, and the results will contribute to understand the characteristics of flow field in upper airway of the OSAHS patient during real natural sleep.
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Objective To study effects from sand therapy of Uyghur medicine on hemodynamics in femoral artery branch and stress, so as to further discuss the functions and mechanisms of Uyghur sand therapy for treatment of femoral artery thrombosis formation. Methods Uyghur sand therapy was conducted on the subjects by indoor Uyghur sand therapy system. The peak values of blood flow velocity, inner diameter and resistance index (RI) of femoral artery before and after receiving Uyghur sand therapy were measured by the ultra-portable Doppler Diagnostic Ultrasound System for statistic analysis. Three-dimensional fluid-solid coupling model of femoral artery branch was reconstructed, and blood flow velocity, pressure, wall shear stress in the flow field as well as the equivalent stress, strain, total displacement on femoral artery wall were simulated and analyzed by the ANSYS Workbench. Results After receiving Uyghur sand therapy, the mean peak values of blood flow velocity and inner diameter of femoral artery increased by 32.43% and 2.68%, while the mean values of RI decreased by 4.88%, which showed it had the statistical difference(P0.05).Besides, the maximum values of blood flow velocity, pressure and wall shear stress increased by 29.91%，68.51%,46.54%,respectively, while the maximum values of equivalent stress, equivalent strain, total displacement on femoral artery wall increased by 65.85%，45.45%，44%, respectively, after receiving Uyghur sand therapy. Conclusions Uyghur sand therapy can increase blood flow velocity and decrease RI obviously，and help to expand the inner diameter of femoral artery to make blood circulation inside improved. With Uyghur sand therapy, the shear stress, blood flow velocity, pressure as well as the stress, strain, total displacement on femoral artery walls also increase, meanwhile，high pressure area on femoral artery branch reduces to some extent, which shows it plays a certain positive role in reducing atherosclerosis and thrombus formation inside femoral artery.
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OBJECTIVE: To design and construct aset of a symmetric flow field flow fractionation instrument which can be used to separate biomacromolecules, and preliminarily evaluate the instrument performance to provide practical experience for its application to real samples. METHODS: The apparatus was made up of separator and tempered glass. Polycarbonate membrane was used as the accumulated wall of the channel. In order to solve the problem of focusing samples, a novel focus position was developed. The performance of the asymmetric flow field flow fractionation device was preliminarily studied by injecting samples consisting of standard bovine serum albumin and alcohol dehydrogenase. The impacts of three factors at six levels on separation (resolution R) were investigated, including injection/focus time, cross-in flow and cross-out flow. RESULTS: Along with the decrease of focus time and increase of cross-in flow velocity, the resolution increased obviously. CONCLUSION: The self-made asymmetric flow field flow fractionation instrument can successfully separate protein mixtures and it is expected to separate more complex samples.
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objective To observe the influence of hemodynamic changes caused by extracranial carotid stenosis on the plaque stability, and analyze the relationship of cerebral infarction classification,criminal artery stenosis degree and plaque stability to offer evidence for evalu-ating nosogenesis,clinical diagnosis,treatment and prevention of cerebral infarction. Methods CDFI,CTA were performed in 168 patients with acute cerebral infarction,some moderate and severe and occlusive carotid artery which were demonstrated by CTA and CDFI were further checked by DSA during convalescence. Totally 168 acute cerebral infarction patients were divided into 5 groups based on the criminal artery stenosis degree. To evaluate the plaque stability and flow field changes with CDFI and CTA,OCSP clinical classification and brain image clas-sification were finished according to CTA. Patients were classified into 4 subtypes,namely cortical infarction,basal ganglion infarction,corona radiata infarction and posterior infarction,according to the lesion distributions. Observe the changes of flow field and stability of plaque,and compare the relationship between different degree of stenosis and the classification of lesion of infarction. Results Among the 168 criminal arteries,there was 17. 9% of normal,22. 6% of mild stenosis,30. 9% of moderate stenosis,14. 8% of severe stenosis,and 14. 3% of occlu-sion,and the moderate stenosis proportion was the highest. When the stenosis degree was over 50%,it may lead to the changes of flow field, speeding up of blood flow,forming of turbulent flow,and increasing of plaque instability in which lipid plaque and admixture plaque was the highest. PACI is the commonest in all moderate groups. Admixture plaque is usually seen in severe stenosis and occlusion, while fibrous plaque is usually seen in mild stenosis. Conclusion Moderate carotid stenosis may lead to the increase of plaque instability as a result of the changes of flow field,and it may prone to artery-artery embolization.
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Objective To investigate the airflow distribution mode in human upper respiratory tract model for understanding the characteristics of the airflow in human upper respiratory tract, and provide scientific basis for analyzing the diffusion, transition and deposition patterns of aerosol in human upper respiratory tract. Methods PIV（particle image velocimetry）technology was adopted to study flow fields of the real human upper respiratory tract model. The airflow state in oral cavity，pharynx and trachea was analyzed. Results The flow velocity was relatively high at the upper tongue coating and in the middle of the oral cavity; when the airflow reached the pharynx, the velocity was increased rapidly due to the reduction of sectional area; the maximum velocity (10.24 m/s) appeared in the glottis, and the velocity in the anterior wall was higher than that in the posterior wall of the trachea; as the airflow injected at the glottis, the velocity gradient was increased, and the vorticity was concentrated at the anterior and posterior wall of the glottis, resulting in a significantly higher vorticity value at anterior wall of the trachea than that at the posterior wall. Conclusions PIV technology is an effective way to investigate the airflow distribution mode in human upper respiratory tract, and it is of great importance for exploring the harm of toxic aerosol to human body and the therapeutic effect of inhalation drug aerosol, as well as for researching the pathogenesis of respiratory system.
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Objective To develop a measurement device and provide a platform for researching the characteristics of human upper respiratory tract flow field based on PIV (particle image velocimetry) technology with respect to the characteristics that human upper respiratory tract flow may form the vortex structure, flow shunt and secondary flow. Methods A transparent physical model of human upper respiratory tract was prepared based on the completely scanned medical images. By means of selecting appropriate air pressure system, combined with two-dimensional PIV system, a complete experimental apparatus was established. Based on the apparatus, preliminary experiment on air velocity in human upper respiratory tract flow field was conducted, and the experiment result was compared with the numerical simulation result. Results Under the steady breathing pattern at respiratory flow of 30 L/min, respiratory air flow measured by the experimental apparatus led to the formation of vortex structure in the front part of oral cavity. Air velocity was relatively higher both in the lower part of oral cavity near the upper tongue and in the middle part of oral cavity, while the velocity was relatively lower in the other parts of oral cavity. The results were in accordance with numerical simulation. Conclusions The experimental apparatus for human upper respiratory tract flow measurement based on PIV technology is practical and reliable, which can be applied in the measurement of airflow organization patterns and vorticity distributions in human upper respiratory tract, and realize the verification of numerical simulation results.
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Objective To visualize the process of introcular flow caused by injection into the posterior chamber of the impermeable vitro eyeball with particle image velocimetry (PIV) technology, and calculate the flow fields at different moments, so as to investigate PIV experimental scheme for low-speed flow field measurement in the eye and provide basis for the in vivo measurement of aqueous humor flow under physiological status. Methods In an impermeable vitro eyeball, the introcular flow would be slow enough when the injection pump was driven at the rate of 0.2, 0.4, 0.6, 0.8, 1.0, 1.5 mL/min. Fluorescent particle solution, with a certain concentration and particle diameter of 10 μm, was injected into the posterior chamber of the vitro rabbit eye, and the sheet laser was projected to the medial frontal plane of the eye. Then clear particle images were captured by camera, and the velocity field was recorded and calculated by PIV system. Results The fluid into the posterior chamber first filled in the posterior chamber and the pupil, then passed the pupillary margin and flowed into the anterior chamber, which was consistent with the theoretical flow process of aqueous humor under physiological conditions. Based on analysis of the particle images, the velocity inside an impermeable eyeball was calculated at the magnitude of a few millimeters per second. Conclusions PIV method can be applied to low-speed flow field measurement, and the flow characteristics inside the eyeball can also be measured by PIV method, which contributes to the measurement of aqueous flow under both physical and pathological conditions, provides experimental verification for numerical simulations on aqueous humor field, and offers a new diagnostic and treatment perspective for shear force damage and destructions of corneal endothelial cells, the iris and lens under different flow fields.
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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 To apply the swirling flow mechanism to the design of arterial prostheses with small diameters and the arterial bypass surgery to resolve the acute thrombus in small diameter prostheses after implantation, and lessen the restenosis of bypassed arteries due to the formation of internal hyperplasia. Method The computational fluid dynamics (CFD) method was used to investigate the flow field and wall shear stress distribution of a new graft, an S type bypass and an axis deviated arterial bypass, which all had the swirling flow. In addition, the platelet adhesion under swirling flow and internal hyperplasia in S-type bypass were measured. Results The swirling flow can apparently enhance the wall shear stress (WSS) and suppress the platelet adhesion and internal hyperplasia. Conclusions The swirling flow can significantly improve the flow field in arterial graft and bypass to inhibit the acute thrombus in small diameter prostheses and internal hyperplasia after bypass surgery.
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Objective To study the flow fields of electrolysis oxygen generation with micro-flow-channels of small square cylinders and the key structure factors impacting on the uniform distribution of the water flow in the micro-flow-channels.Methods The low Renault k-? model was used to represent the characteristics of the flow field in the micro-flow-channels.And the simulation results of the flow fields by CFD were calibrated by comparing with that of the particle image velocimetry(PIV) experiments,which showed that the low Renault k-? model was suitable to describe the flow field of the micro-flow-channels.Results The flow fields of variable flow were obtained.Conclusion The flow fields of variable flow rates distribute non-uniformly.The velocity magnitude is 10-3m/s,and the inlet structure of the electrolysis oxygen generation is a key factor impacting on the uniform distribution of the water flow.
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Objective To verify the flow field performance of the air dynamic wind tunnel. Methods The performance of the flow field was evaluated by testing the flow speed of sample-point on the sample-transect of the tunnel. Results Among the flow range of the tunnel, the relative deviations of the speeds of each sample-point on the sample-transect were less than 10%. When the flow rate was set, the relative deviations of the sample-transect average speed in different test period were less than 10%. The ratio of average wind velocity of upper reach to down reach of the tunnel was between 0.92 and 1.03. Conclusion The flow field of the air dynamic wind tunnel is even, stable and coincident.