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.
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.
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.
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 aim of this study was to investigate whether shear stress could promote function of endothelial progenitor cells (EPCs)with Shexiang Baoxin Pill (SBP) treatment in vitro, and to study whether shear stress contributed to vascular injury repair by EPCs. EPCs were isolated and characterized; EPCs' proliferation, migration, adhesion, tube formation and eNOS protein level in vitro were investigated by culturing confluent EPCs in 4 mg/mL SBP under physiological shear stress (15 dyne/cm2) for up to 24 hours. Afterwards, EPCs were transfused into rats after wire-induced carotid artery injury augmented re-endothelialization. The results showed that, compared to the SBP group, the shear stress+SBP group obviously enhanced EPCs proliferation, migration, adhesion, tube formation and eNOS protein expression in vitro (P<0.01). After one week, immunofluorescence staining showed that endothelial regeneration rate obviously enhanced in shear stress+SBP group (P<0.01). The present study demonstrates that shear stress can promote function of endothelial progenitor cells treated with SBP, which improves the vascular injury repair potentials of EPCs.
Abstract: Objective To investigate the messenger ribonucleic acid (mRNA) expression level of tissue-type plasminogen activator (t-PA) in endothelial cells derived from adult mesenchymal stem cells (MSCs) after fluid shear stress loading which is within the physiological range. Methods After culturing in vitro, bone marrow MSCs of SD rats were seeded on slides.When it come to 80% confluence,26 slides were exposed to 5dyn/cm2 fluid shear stress for 3h in a flow chamber, and then induced to endothelial cells. Among them,13 slides constituted group Ⅰ, and the rest 13 slides set up group Ⅱ, which would be cultured for 3-4d further and passaged in 1∶3. At the same time, control group was set up, which including the cells never exposed to fluid shear stress before the endothelial differentiation. Fluid shear stress were exerting to cells in a specially made flow chamber. The expression level of t-PA mRNA of all groups were measured by real-time fluorescent quantitation reverse transcriptionpolymerase chain reaction (RTPCR). Results After endothelial differentiation for 7 days, the SD rats bone marrow MSCs acquired typical endothelial cell appearance. The t-PA mRNA expression level of group Ⅰ and group Ⅱ have an obviously enhance compared with control group(P＜0.05). The t-PA mRNA expression level of group Ⅱ step down a little (P＞0.05), but it is still significantly higher than that of control group (P＜0.05). Conclusion Fluid shear stress could provide a protective action on the endothelial cells induced from MSCs in vitro, and the effect maintains with the cells passages. This formulates a theoretical foundation to the therapeutics of atherosclerosis and selection of seed cells in vascular tissue engineering.
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.
The development and progression of atherosclerosis and thrombosis are closely related to changes of hemodynamics parameters. Ultrasonic pulse wave Doppler technique is normally used for noninvasively blood flow imaging. However, this technique only provides one-dimensional velocity and depends on the angle between the ultrasound beam and the local velocity vector. In this study, ultrasonic particle image velocimetry method was used to assess whole field hemodynamic changes in normal blood vessels. By using the polynomial fitting method, we investigated the velocity gradient and assessed the shear in different blood flow velocity of 10 healthy rats. It was found that using four polynomial fitting could result in optimal measurement results. The results obtained by ultrasonic particle image velocimetry accorded with the results obtained using Doppler technique. The statistical average of cyclical vessel wall shear stress was positively related to the locational mean velocity. It is proven that ultrasonic particle image velocimetry method could be used to assess directly the real-time whole field hemodynamic changes in blood vessels and was non-invasively, and should be a good prosperous technique for monitoring complex blood flow in stenotic arteries.
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.
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.