To test the hypothesis that by intentionally inducing swirling flow in an endovascular stent, hemodynamic performance of the stent can be improved, we numerically analyzed the flow characteristics in a simplified model of a stent within a straight segment of an artery in which swirling flow was introduced intentionally. The study was designed with two purposes: 1) to investigate whether swirling flow is beneficial to suppress flow disturbance in the stent; and 2) to determine the minimum helical strength of the swirling flow required in the design of a swirling flow stent. The numerical simulation showed that the swirling flow indeed reduced the size of the disturbed flow zones, enhanced the average wall shear stress, and lowered oscillatory shear index in the stent, which have been believed to be adverse factors involved in the development of arterial restenosis after stent deployment. The minimum inlet helicity density (or strength) of the swirling flow required was approximately 6.5 m/s(2). Based on the study, it is also believed that a stent with a structure that possesses intrinsic characteristics to automatically induce swirling flow in the stent is better than a stent with a front swirling flow inducer in terms of hemodynamics.

The size mismatch in an end-to-end vascular anastomosis between the host vessel and the graft may cause flow disturbance and possibly result in thrombosis. To test the hypothesis that intentionally induced swirling flow in an end-to-end anastomosis could suppress flow disturbance, impeding thrombus formation by affecting platelets adhesion, a comparative study was designed to investigate the effect of swirling flow on the adhesion and activation of platelets in a glass sudden tubular expansion tube coated with calf skin type I collagen. The results revealed that the swirling flow generated in the expansion could reduce the length of the flow recirculation zone distal to the expansion and significantly reduce the total number of adherent platelets in the test tube when compared with that for the normal flow. No significant difference was observed in the activation of platelets between the swirling flow group and the normal flow group. This study therefore suggests that intentionally introduced swirling flow in an end-to-end anastomosis has no adverse effect on platelet activation and may indeed be a solution to improve the patency of end-to-end microvascular anastomoses by suppressing thrombus formation.

Traditional commercial stents are made of wires with square or semi-circular cross-sections that lead to flow disturbance, which plays an important role in the initiation and progression of restenosis. A new stent with streamlined cross-sectional wires was proposed and researched numerically for its hemodynamic performance. Simplified models of stents with square, semi-circular, or streamlined cross-sectional wires were constructed numerically. Blood flows in the three models were simulated using computational fluid dynamics methods, and compared in terms of flow pattern, wall shear stress (WSS), and oscillating shear index (OSI). The results showed that when compared with the two traditional stents, the new stent with streamlined cross-sectional wires induced almost no flow disturbance, significantly enhanced WSS, and reduced the value of OSI within the stent. The present preliminary study indicates that the optimization of the cross-sectional shape of stent wires ought to be considered in the structural design for endovascular stents.

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Background: Gender difference in cardiovascular diseases (CVDs) is an important topic in the field of cardiovascular medicine. In this study, we focused on the mortality difference of abdominal aortic aneurysms (AAA), which is higher for female than that of male. The aim of this study was to verify whether morphological and hemodynamic factors play their roles in this phenomenon. Methods: Patient-specific AAA models of 11 females and 23 males with similar age and body mass index (BMI) have been reconstructed based on clinical computed tomography (CT) data. Firstly, the morphological parameters (diameters, curvature, intraluminal thrombus volume, etc.) of AAA models and lumbar vertebrae models were collected and analyzed. Then, based on statistical results of morphological parameters, uniformed male and female AAA models were reconstructed, and hemodynamic simulations were conducted respectively. In post-processing, the hemodynamic performances induced by gender-different morphological geometries were analyzed and compared. Results: The comparison of morphological parameters revealed that the average curvature of lumbar vertebrae and AAA centerline of female AAA models were obviously higher than that of the male. The amount of intraluminal thrombus in female AAA models was relatively lower than that of the male. According to the hemodynamic simulation, the uniform female AAA model has higher peak pressure, lower oscillatory shear stress index (OSI), and lower relative residence time (RRT) than that of the male model, all of which put female AAA to a relatively higher risk hemodynamic situation. Conclusions: The morphological and hemodynamic features of AAA have very obvious gender differences that would induce higher risk of rupture for female AAA biomechanically. These findings would help to explore the mechanism of gender differences in AAA and draw attention to gender-specific consideration for AAA treatment. More morphological and hemodynamic indictors are suggested to be involved in the future guidelines.

Numerous endovascular stent grafts to treat intrarenal aortic aneurysms are now commercially available, and many new concepts are currently in development worldwide. In order to objectively quantify their outcomes, we propose a detailed protocol to examine a reference device that was harvested from a patient who died a few hours after endovascular stent-graft deployment for an abdominal aortic aneurysm according to the 3Bs rule (biocompatibility, biofunctionality, and biodurability). Relevant patient history of this 63-year-old man included radiotherapy treatment for lung cancer. Following the patient's death, the device was harvested en bloc together with the aneurysmal sac. The analysis of the device was conducted using nondestructive testing (X-rays, CT scan, magnetic resonance imaging [MRI], and endoscopy) and destructive testing (dissection, histology, and fabric and wire component analyses). Results from the gross examination demonstrated that the outer layer of the aneurysm sac was white, stiff, and continuous without any disruption. The Xray analysis, CT scan, and MRI confirmed that the device together with its modular segments was properly deployed at implantation. Endoscopy showed that the device was deployed securely immediately distal to the renal arteries. As anticipated, thin scattered mural thrombi at the blood/foreign material interface were observed on the blood tight flow surface. There were no tears in the fabric, and the dimensions and textile structure were well preserved. The metallic wires were intact. This fatality had no association with the stent graft as the patient's death was caused by the rupture of the pulmonary artery following intensive radiotherapy. In conclusion, autopsy, nondestructive testing, and destructive testing are therefore the necessary steps to validate any explanted endovascular stent graft in terms of biocompatibility, biofunctionality, and biodurability. In this specific case, the endovascular device fulfills the 3Bs rule. The authors recommend this protocol to investigate explanted endovascular devices.

Renal artery stenosis (RAS) and renal complications emerge in some patients after endovascular aneurysm repair (EVAR) to treat abdominal aorta aneurysm (AAA). The mechanisms for the causes of these problems are not clear. We hypothesized that for EVAR patients, lower limb exercise could negatively influence the physiology of the renal artery and the renal function, by decreasing the blood flow velocity and changing the hemodynamics in the renal arteries. To evaluate this hypothesis, pre- and post-operative models of the abdominal aorta were reconstructed based on CT images. The hemodynamic environment was numerically simulated under rest and lower limb exercise conditions. The results revealed that in the renal arteries, lower limb exercise decreased the wall shear stress (WSS), increased the oscillatory shear index (OSI) and increased the relative residence time (RRT). EVAR further enhanced these effects. Because these parameters are related to artery stenosis and atherosclerosis, this preliminary study concluded that lower limb exercise may increase the potential risk of inducing renal artery stenosis and renal complications for AAA patients. This finding could help elucidate the mechanism of renal artery stenosis and renal complications after EVAR and warn us to reconsider the management and nursing care of AAA patients.

Background Cone-shaped vena cava filters (VCFs) are widely used to treat venous thromboembolism. However, in the long term, the problem of occlusion persists even after the filter is deployed. A previous study hypothesized that the reverse deployment of a cone-shaped VCFs may prevent filter blockage. Methods To explore this hypothesis, a comparative study of the traditional and reverse deployments of VCFs was conducted using a computational fluid dynamics approach. The distribution of wall shear stress (WSS) and shear stress-related parameters were calculated to evaluate the differences in hemodynamic effects between both conditions. In the animal experiment, we reversely deployed a filter in the vena cava of a goat and analyzed the blood clot distribution in the filter. Results The numerical simulation showed that the reverse deployment of a VCF resulted in a slightly higher shear rate on the thrombus, and no reductions in the oscillating shear index (OSI) and relative residence time (RRT) on the vessel wall. Comparing the traditional method with the reversely deployed cases, the shear rate values is 16.49 and 16.48 1/s, respectively; the minimal OSI values are 0.01 and 0.04, respectively; in the vicinity of the VCF, the RRT values are both approximately 5 1/Pa; and the WSS is approximately 0.3 Pa for both cases. Therefore, the reverse deployment of cone-shaped filters is not advantageous when compared with the traditional method in terms of local hemodynamics. However, it is effective in capturing thrombi in the short term, as demonstrated via animal experiments. The reversely deployed cone-shaped filter captured the thrombi at its center in the experiments. Conclusions Thus, the reverse deployment of cone-shaped filters is not advantageous when compared with the traditional method in terms of local hemodynamics. Therefore, we would not suggest the reverse deployment of the cone-shaped filter in the vena cava to prevent a potentially fatal pulmonary embolism.