ObjectiveBy comparing the difference between different stenosed degree of aortic valve in flow field uniformity and turbulent shear stress (TSS), to explore the relation between flow field uniformity and different stenosed degree of aortic valve, and probe the clinical value for deciding the operation timing, and analyze the possible role of TSS in the progress of the disease.MethodsThe flow field uniformity values and TSS in parasternal long axis plane and apical five cavity plane on each point were measured and calculated by pulse wave Doppler echocardiography technique for 33 patients with different stenosed degree of aortic valve.ResultsThere were significant difference between the different stenosed degree of aortic valve in maximal velocity difference(ΔV max )and TSS( P lt;0.05, 0.01). The more severe the aortic stenosis was, the worse the flow field uniformity was, the lower the TSS was.ConclusionsThere are significant difference between the patients of different stenosed degree of aortic valve in flow field uniformity. Flow field uniformity has important value in classifying the degree of aortic stenosis and deciding the timing of operation. The more severe the aortic stenosis is ,the lower TSS is. It can be thought that low TSS distribution has important role in pathological process of constriction in cardiovascular system diseases.
Fluid shear stress (FSS) caused by interstitial fluid flow within trabecular bone cavities under mechanical loading is the key factor of stimulating biological response of bone cells. Therefore, to investigate the FSS distribution within cancellous bone is important for understanding the transduction process of mechanical forces within alveolar bone and the regulatory mechanism at cell level during tooth development and orthodontics. In the present study, the orthodontic tooth movement experiment on rats was first performed. Finite element model of tooth-periodontal ligament-alveolar bone based on micro computed tomography (micro-CT) images was established and the strain field in alveolar bone was analyzed. An ideal model was constructed mimicking the porous structure of actual rat alveolar bone. Fluid flow in bone was predicted by using fluid-solid coupling numerical simulation. Dynamic occlusal loading with orthodontic tension loading or compression loading was applied on the ideal model. The results showed that FSS on the surface of the trabeculae along occlusal direction was higher than that along perpendicular to occlusal direction, and orthodontic force has little effect on FSS within alveolar bone. This study suggests that the orientation of occlusal loading can be changed clinically by adjusting the shape of occlusal surface, then FSS with different level could be produced on trabecular surface, which further activates the biological response of bone cells and finally regulates the remodeling of alveolar bone.
Vena cava filter is a filter device designed to prevent pulmonary embolism caused by thrombus detached from lower limbs and pelvis. A new retrievable vena cava filter was designed in this study. To evaluate hemodynamic performance and thrombus capture efficiency after transplanting vena cava filter, numerical simulation of computational fluid dynamics was used to simulate hemodynamics and compare it with the commercialized Denali and Aegisy filters, and in vitro experimental test was performed to compare the thrombus capture effect. In this paper, the two-phase flow model of computational fluid dynamics software was used to analyze the outlet blood flow velocity, inlet-outlet pressure difference, wall shear stress on the wall of the filter, the area ratio of the high and low wall shear stress area and thrombus capture efficiency when the thrombus diameter was 5 mm, 10 mm, 15 mm and thrombus content was 10%, 20%, 30%, respectively. Meanwhile, the thrombus capture effects of the above three filters were also compared and evaluated by in vitro experimental data. The results showed that the Denali filter has minimal interference to blood flow after implantation, but has the worst capture effect on 5 mm small diameter thrombus; the Aegisy filter has the best effect on the trapping of thrombus with different diameters and concentrations, but the low wall shear stress area ratio is the largest; the new filter designed in this study has a good filtering and capture efficiency on small-diameter thrombus, and the area ratio of low wall shear stress which is prone to thrombosis is small. The low wall shear stress area of the Denali and Aegisy filters is relatively large, and the risk of thrombosis is high. Based on the above results, it is expected that the new vena cava filter designed in this paper can provide a reference for the design and clinical selection of new filters.
The impeller profile, which is one of the most important factors, determines the creation of shear stress which leads to blood hemolysis in the internal flow of centrifugal blood pump. The investigation of the internal flow field in centrifugal blood pump and the estimation of the hemolysis within different impeller profiles will provide information to improve the performance of centrifugal blood pump. The SST κ-ω with low Reynolds correction was used in our laboratory to study the internal flow fields for four kinds of impellers of centrifugal blood pump. The flow fields included distributions of pressure field, velocity field and shear stress field. In addition, a fast numerical hemolysis approximation was adopted to calculate the normalized index of hemolysis (NIH). The results indicated that the pressure field distribution in all kinds of blood pump were reasonable, but for the log spiral impeller pump, the vortex and backflow were much lower than those of the other pumps, and the high shear stress zone was just about 0.004%, and the NIH was 0.0089.
Objective To investigate the effects of flow shear stress and mass transport on the construction of largescale tissue engineered bone using a perfusion bioreactor. Methods Bone marrow (20 mL) was harvested from the il iac crestof the healthy volunteer, and then hBMSCs were isolated, cultured and identified. The hBMSCs at passage 3 were seeded on the critical-size β-TCP scaffold and cultured in a perfusion bioreactor for 28 days. Different flow shear stress (1 ×, 2 × and 3 ×) and different mass transport (3, 6 and 9 mL/min) were exerted on the cells seeded on the scaffold by changing the viscosity of media or perfusion flow rate. The cell prol iferation and ALP activity of cells seeded on the scaffold were detected, and histology observation and morphology measurement of cell/scaffold complex were conducted. Results When the perfusion flow rabe was 3 mL/min, the cell viabil ity of 2 × group was higher than that of other groups (P lt; 0.05). When the flow shear stress was 3 ×, no significant differences were found among 3, 6 and 9 mL/min in cell viabil ity (P gt; 0.05). When the perfusion flow rate was 3 mL/min, the activity of ALP of 2 × and 3 × groups was higher than that of 1 × group (P lt; 0.05). When the flow shear stress was 3 ×, the activity of ALP of 6 mL/min group was the highest (P lt; 0.05). After 28 days of perfusion culture, the ECM of all the groups distributed throughout the scaffold, and the formation and mineral ization of ECM was improved with the increase of flow shear stress when the perfusion flow rate was 3 mL/min. However, the increase of perfusion flow rate decreased the mineral ization of ECM when the flow shear stress was 3 ×. Conclusion As two important fluid dynamics parameters affecting the construction of large-scale tissue engineered bone, the flow shear stress and the mass transport should be measured duringthe process of constructing large-scale tissue engineered bone so as to maximize their roles.
ObjectiveTo discuss the feasibility of establishment of animal model of "functional" bicuspid aortic valve with swine and observe its effect on the wall shear stress inside the aorta. MethodsFour common Shanghai White Swine with body weight between 50 kg to 55 kg were selected. Under general anesthesia and cardiopulmonary bypass, the aortic transverse incision approach was used, continuous suture with 6-0 polypropylene to align the left and right coronary valve leaflets to create a bicuspid valve morphology. After the operation, echocardiography was used to observe the aortic valve morphology and the hemodynamic changes of the aortic valve orifice. The effect on the wall shear stress inside the aorta was studied with 4D-Flow magnetic resonance imaging (MRI). ResultsA total of 4 swine "functional" bicuspid aortic valve models were established, with a success rate of 100.0%. Echocardiography showed that the blood flow velocity of the aortic valve orifice was faster than that before the operation (0.96 m/s vs. 1.80 m/s). 4D-Flow MRI showed abnormally increased wall shear stress and blood flow velocity in the aorta of the animal models. After the surgery, in model animals, the maximal wall shear stress inside the ascending aorta was greater than 1.36 Pa, and the maximum blood flow velocity was greater than 1.4 m/s. ConclusionEstablishment of the animal model of "functional" bicuspid aortic valve in swine is feasible, scientific and reliable. It can be used in researches on evaluating the pathophysiological changes.
Hemolysis is one of the main complications associated with the use of ventricular assist devices. The primary factors influencing hemolysis include the shear stress and exposure time experienced by red blood cells. In addition, factors such as local negative pressure and temperature may also impact hemolysis. The different combinations of hemolysis prediction models and their empirical constants lead to significant variations in prediction results; compared to the power-law model, the OPO model better accounts for the complexity of turbulence. In terms of improving hemolytic performance, research has primarily focused on optimizing blood pump structures, such as adjustments to pump gaps, impellers, and guide vanes. A small number of scholars have studied hemolytic performance through control modes of blood pump speed and the selection of blood-compatible materials. This paper reviews the main factors influencing hemolysis, prediction methods, and improvement strategies for rotary blood pumps, which are currently the most widely used. It also discusses the limitations in current hemolysis research and provides an outlook on future research directions.
To explore the influence of bionic texture coronary stents on hemodynamics, a type of bioabsorbable polylactic acid coronary stents was designed, for which a finite element analysis method was used to carry out simulation analysis on blood flow field after the implantation of bionic texture stents with three different shapes (rectangle, triangle and trapezoid), thus revealing the influence of groove shape and size on hemodynamics, and identifying the optimal solution of bionic texture groove. The results showed that the influence of bionic texture grooves of different shapes and sizes on the lower wall shear stress region had a certain regularity. Specifically, the improvement effect of grooves above 0.06 mm on blood flow characteristics was poor, and the effect of grooves below 0.06 mm was good. Furthermore, the smaller the size is, the better the improvement effect is, and the 0.02 mm triangular groove had the best improvement effect. Based on the results of this study, it is expected that bionic texture stents have provided a new method for reducing in-stent restenosis.
This paper is aimed to investigate the effect of fluid shear stress on the tight junction of laryngeal squamous carcinoma (Hep2) cells and to explore the potential molecular mechanism. Hep2 cells were selected and subjected to the fluid shear stress of 1.4 dyn/cm2 for different time, respectively. The morphological changes of Hep2 cells under shear stress were observed using inverted microscope. The cell-cell junctions were examined by transmission electron microscope (TEM). The expressions of tight junction proteins (including Occludin, Claudin-5 and ZO-1) and the distribution of Claudin-5 were examined by Western blot assay and laser scanning confocal microscope, respectively. The results indicated that Hep2 cells turned to spindle-like shapes after exposed to shear stress, and showed the trend of the recovering to original shapes when the shear stress was cancelled. The cell-cell junctions were tight under the shear flow condition, and the permeability was reduced under the condition of 1.4 dyn/cm2 shear flow. The expressions of tight junction proteins were enhanced with increased duration of shear flow, but reduced after removing shear flow. The result of Claudin-5 expression by immufluorescence assay was consistent with that by Western blot. The Claudin-5 mainly distributed in the cytoplasm under static condition, while it located at the intercellular after shear flow stimulation, and it appeared intercellular and cytoplasm after stopping shear flow stimulation. Therefore, it can be concluded that shear stress changes the morphology of laryngeal squamous carcinoma Hep2 cells, and upregulates the tight junction.
Coronary heart disease is a kind of heart disease that is caused by atherosclerosis.The lipid deposition in the vessel wall results in occlusion of coronary artery and stenosis, which could induce myocardial ischemia and oxygen deficiency. Intervention therapies like percutaneous coronary intervention (PCI) and coronary stent improve myocardial perfusion using catheter angioplasty to reduce stenosis and occlusion of coronary artery lumen. Accordingly, intervention therapies are widely applied in clinic to treat ischemic cardiovascular disease, arterial intima hyperplasia and other heart diseases, which could save the patients′ life rapidly and effectively. However, these interventions also damage the original endothelium, promote acute and subacute thrombosis and intimal hyperplasia, and thus induce in stent restenosis (ISR) eventually. Studies indicated that the rapid reendothelialization of damaged section determined postoperative effects. In this review, reendothelialization of implants after intervention therapy is discussed, including the resource of cells contributed on injured artery, the influences of implanted stents on hemodynamic, and the effects of damaged degree on reendothelialization.