Search

Women with abdominal aortic aneurysm (AAA) have a higher incidence of complications after Endovascular aneurysm repair (EVAR), most of which are related to the migration of stent‐graft. The different force acting on the stent‐graft after EVAR caused by different abdominal artery anatomy of male and female AAA patients may be the reason for the sex‐different complications. This article aims to explore the possible biomechanical mechanisms of sex differences by making a comparison of displacement force acting on the stent graft of male and female AAA patients. To explore the effect of different vascular anatomy on stent‐graft migration, the uniformed models were constructed according to the specific vascular anatomy parameters of AAA patients of different sex, which have been measured before. The computational fluid dynamics method was used to quantitate the pulsatile force acting on the stent‐graft after EVAR in a cardiac cycle. Then the displacement force was calculated with the pressure and the wall shear stress, and the total and area‐weighted average of displacement force acting on the stent‐graft were compared respectively. In one cardiac cycle, the wall pressure for the male model is greater than that of the female model (2.7–4.4 vs. 2.2–3.4 N), and the wall shear force for the female model is slightly greater (0–0.0065 vs. 0–0.0055 N). The displacement force is mainly provided by the wall pressure, which is also greater in the male model. However, the area‐averaged displacement force is greater for the female model than that for the male model (180–290 vs. 160–250 Pa). Because of the different vascular anatomies, the impact caused by the pulsating aortic blood flow on the AAA stent‐graft of women after EVAR was greater than that of men. Women's vascular anatomy leads to greater area‐averaged displacement force after stent‐graft implantation, resulting in a greater risk of stent‐graft migration, which might be one of the reasons why women had a higher incidence of complications after EVAR. [ABSTRACT FROM AUTHOR]

To investigate the effect of rotor design configuration on hemodynamic features, hemocompatibility and dynamic balance of blood pumps. Computational fluid dynamics was employed to investigate the effects of rotor type (closed impeller, semi‐open impeller), clearance height and back vanes on blood pump performance. In particular, the Eulerian hemolysis model based on a power‐law function and the Lagrangian thrombus model with integrated stress accumulation and residence time were applied to evaluate the hemocompatibility of the blood pump. This study shows that compared to the closed impeller, the semi‐open impeller can improve hemolysis at a slight sacrifice in head pressure, but increase the risk of thrombogenic potential and disrupt rotor dynamic balance. For the semi‐open impeller, the pressure head, hemolysis, and axial thrust of the blood pump decrease with increasing front clearance, and the risk of thrombosis increases first and then decreases with increasing front clearance. Variations in back clearance have little effect on pressure head, but larger on back clearance, worsens hemolysis, thrombogenic potential and rotor dynamic balance. The employment of back vanes has little effect on the pressure head. All back vanes configurations have an increased risk of hemolysis in the blood pump but are beneficial for the improvement of the rotor dynamic balance of the blood pump. Reasonable back vanes configuration (higher height, wider width, longer length and more number) decreases the flow separation, increases the velocity of blood in the back clearance, and reduces the risk of blood pooling and thrombosis. It was also found that hemolysis index (HI) was highly negatively correlated with pressure difference between the top and back clearances (r = −.87), and thrombogenic potential was positively correlated with pressure difference between the top and back clearances (r =.71). This study found that rotor type, clearance height, and back vanes significantly affect the hydraulic performance, hemocompatibility and rotor dynamic balance of centrifugal blood pumps through secondary flow. These parameters should be carefully selected when designing and optimizing centrifugal blood pumps for improving the blood pump clinical outcomes. [ABSTRACT FROM AUTHOR]

Background: The centrifugal blood pump volute has a significant impact on its hemodynamic performance hemocompatibility. Previous studies about the effect of volute design features on the performance of blood pumps are relatively few. Methods: In the present study, the computational fluid dynamics (CFD) method was utilized to evaluate the impact of volute design factors, including spiral start position, volute tongue radius, inlet height, size, shape and diffuser pipe angle on the hemolysis index and thrombogenic potential of the centrifugal blood pump. Results: Correlation analysis shows that flow losses affect the hemocompatibility of the blood pump by influencing shear stress and residence time. The closer the spiral start position of the volute, the better the hydraulic performance and hemocompatibility of the blood pump. Too large or too small volute inlet heights can worsen hydraulic performance and hemolysis, and higher volute inlet height can increase the thrombogenic potential. Small volute sizes exacerbate hemolysis and large volute sizes increase the thrombogenic risk, but volute size does not affect hydraulic performance. When the diffuser pipe is tangent to the base circle of the volute, the best hydraulic performance and hemolysis performance of the blood pump is achieved, but the thrombogenic potential is increased. The trapezoid volute has poor hydraulic performance and hemocompatibility. The round volute has the best hydraulic and hemolysis performance, but the thrombogenic potential is higher than that of the rectangle volute. Conclusion: This study found that the hemolysis index shows a significant correlation with spiral start position, volute size, and diffuser pipe angle. Thrombogenic potential exhibits a good correlation with all the studied volute design features. The flow losses affect the hemocompatibility of the blood pump by influencing shear stress and residence time. The finding of this study can be used to guide the optimization of blood pump for improving the hemodynamic performance and hemocompatibility. [ABSTRACT FROM AUTHOR]

The importance of vascular cell glycocalyx in mechanotransduction has been demonstrated by many studies. The simulated microgravity induced a region‐dependent adaptation of arterial glycocalyx including its thickness, coverage, and gene expression in conduit arteries of tail‐suspended rats has been reported in our previous studies. Herein, we extended this line of research by quantifying the mRNA levels of three nitric oxide synthase (NOSI, NOSII, and NOSIII) and evaluating the apoptotic rates of endothelial cells (ECs) and smooth muscle cells (SMCs) in the common carotid artery, abdominal aorta, and femoral artery of 3 week tail‐suspended rats. Results indicated that the tail suspension of rats induced about 0.36, 0.22, and 0.33 fold down‐regulation of NOSI, NOSII, and NOSIII in the abdominal aorta, while 3.21, and 3.48 fold up‐regulation of NOSII and NOSIII in the carotid artery and no significant effects on three NOS isoforms in the femoral artery. Moreover, the apoptosis of ECs and SMCs were significantly inhibited in both carotid artery and abdominal aorta, while enhanced in the femoral artery of the tail‐suspended rats. A linear positive correlation exists between the normalized coverage of the glycocalyx and the normalized NOSI and NOSIII mRNA levels. These results indicated that the redistribution of haemodynamics in the conduit arteries of 3 week tail‐suspended rats regulated the glycocalyx, NOS expression, and vascular cell apoptosis in a region‐dependent manner, contributing to the final vascular remodelling under simulated microgravity condition. [ABSTRACT FROM AUTHOR]

Local flow disturbance by arterial stent struts has been shown to play an important role in stent thrombosis. To reduce the local flow disturbance near a stent strut, we proposed a new concept of stent design with small holes in the stent struts. The present study evaluated the new design numerically by comparing it with the traditional stent in terms of local hemodynamic parameters such as flow velocity, flow recirculation area, time-averaged wall shear stress (TAWSS), oscillating shear index (OSI), and relative residence time (RRT). The results demonstrated that when compared with the traditional strut, the new design could significantly enhance flow velocity and reduce the flow recirculation zone in the vicinity of the strut. Moreover, the new design would significantly elevate TAWSS and remarkably reduce OSI and RRT along the host arterial wall. In conclusion, the new design of stent struts with punched holes is advantageous over the traditional one in the aspect of improving local hemodynamics, which may reduce thrombosis formation and promote re-endothelialization after stenting. [ABSTRACT FROM AUTHOR]

The helically distributed ribbons of thrombus, formed in the commercially available SwirlGraft (Veryan Medical, London, UK), are the result of its wall shear stress distribution, which has zonary areas of low wall shear stress. In order to overcome the inherent deficiency of the SwirlGraft, a new helical graft with a noncircular cross section was proposed and compared numerically with the SwirlGraft in terms of wall shear stress distribution, helicity of the swirling flow created, and pressure drop over the grafts. The numerical results showed that due to the modification to the geometrical configuration of the SwirlGraft, wall shear stress in the new helical graft model was enhanced, and the zones of low wall shear stress existing in the SwirlGraft were completely eliminated. The present numerical study also predicted a slightly steeper pressure drop and reduction in helicity in the new helical graft model in comparison with the SwirlGraft model. Based on the study, we believe that the new helical graft with a noncircular cross section may reduce the possibility of acute thrombus formation in the graft because the enhanced wall shear stress can impede the stay and adherence of platelets and leukocytes to the surface of the graft.