Narrative Review of Risk Assessment of Abdominal Aortic Aneurysm Rupture Based on Biomechanics-Related Morphology.

CLINICAL IMPACT: Studies have shown that the biomechanical indicators based on multi-scale models are more effective in accurately assessing the rupture risk of AAA. To meet the need for clinical monitoring and rapid decision making, the typical morphological parameters associated with AAA rupture and their relationships with the mechanical environment have been summarized, which provide a reference for clinical preoperative risk assessment of AAA.

Proanthocyanidins Promote Endothelial Cell Viability and Angiogenesis.

ABSTRACT: Botanic drugs are reportedly effective in treating ischemic conditions by improving vascular circulation. However, it has been very rare for biomaterial researchers to look into the possibility of using such products in the context of tissue regeneration. This work studied 4 botanic drugs to explore their effects on vascular endothelial cell growth. Human umbilical endothelial cells were cultured in the presence of different doses of astragalus powder extract, astragalus injection, puerarin injection, and proanthocyanidin (PAC). Among the 4 drugs, PAC showed a potent effect on cell viability and stimulated cell growth in a dose-dependent manner. In particular, the PAC under test was able to maintain a high level of cell viability/proliferation comparable with the cells supplemented with the endothelial cell growth medium, at both low and normal serum conditions. Blocking either endothelial cell growth factor receptors or epithelial cell growth factor receptors was ineffective in reducing the stimulatory effect. The PAC released from polyvinyl alcohol cryogels stimulated HUVECs proliferation. The chick embryo chorioallantoic membrane model was further used to test the angiogenicity of PAC, showing that this botanic drug was potent in stimulating vasculature development. This work therefore demonstrates for the first time that PAC is capable of upregulating endothelial cell activity and growth in vitro in the absence of growth factors and that PAC can be loaded and released from drug carriers and can stimulate angiogenesis. These findings suggest the application of PAC in angiogenesis and tissue regeneration.

Effects of reverse deployment of cone-shaped vena cava filter on improvements in hemodynamic performance in vena cava.

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.

A new way to reduce flow disturbance in endovascular stents: a numerical study.

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.

Hemodynamic performance of a sutureless anastomosis device (the Graft Connector): a numerical study.

Sutureless anastomosis devices have been developed to facilitate arterial bypass surgery on the beating heart. However, these devices can significantly alter the hemodynamics at the end-to-side anastomosis and in the host artery, leading to the formation of thrombus or/and intimal hyperplasia (IH). In this study, a numerical analysis was performed on the hemodynamic performance of the Graft Connector (GC), a sutureless anastomosis device, under pulsatile flow conditions. The results showed that blood flow was severely disturbed in the GC model with the formation of vortices and flow stagnation at the bed and the toe, and distal to each of the stent struts, which led to low wall shear stresses and high oscillating shear indices in these regions. This may cause severe IH in the host artery and compromise the performance of the device. Based on the numerical study, suggestions were proposed for the design of the GC to improve its performance.

[Electrical stimulation enhances viability of osteoblasts on conductive biodegradable material].

This study was aimed at exploring the viability of osteoblasts on conductive tissue engineering material. Conductive biodegradable Polyprrole/Polylactide (PPy/PLA) was prepared by emulsion polymerization. Scanning electron microscope (SEM) and spectroscopy showed evenly dispersed PPy in PLA. PPy/PLA membrane was found being able to keep conductive stability for more than one month to provide electric circumstances (ECs) for osteoblasts. SEM displayed that osteoblasts adhered and spread well on PPy/PLA. ECs of 12.5, 25, 50, 75, 100, 125, 150, 175, 200 microA/cm2 were separately used to stimulate osteoblasts for 24h, 48h, 72h and 96h. Methyl-thiazole-tetrazolium (MTT) assay after 24h revealed that 50 microA/cm2 evidently accelerated osteoblasts proliferation. Alkaline phosphatase (ALP) activity assay revealed that, 48h later, 50 microA/cm2, and 75 microA/cm2 promoted osteoblasts differentiation. 50 microA/cm2 enhanced osteoblasts mineration. Conclusively, 50 microA/cm2 can strengthen osteoblasts' function and promote their viability.

Gender differences of morphological and hemodynamic characteristics of abdominal aortic aneurysm.

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.

An S-type bypass can improve the hemodynamics in the bypassed arteries and suppress intimal hyperplasia along the host artery floor.

The development of distal end-to-side anastomotic intimal hyperplasia (IH) has been attributed to the flow disturbance and abnormal wall shear stress (WSS) distribution there. The geometry of the bypass has a strong influence on the flow pattern and WSS distribution. Using a canine model of end-to-side anastomosis, a 45 degrees S-type bypass was compared with 60 degrees , 45 degrees and 30 degrees conventional bypasses in the term of IH along the host artery floor. Numerical blood flow simulations were also carried out to characterize the flow patterns at the distal parts of the bypassed arteries for the 4 models. The results showed that the averaged intima thicknesses of the host artery floors for the 4 bypass models were 119.50+/-10.30 microm (60 degrees ), 65.56+/-6.53 microm (45 degrees ), 45.26+/-5.99 microm (30 degrees ) and 47.64+/-4.85 microm (S-type), respectively, vs. 9.81+/-1.88 microm in the control group (without bypass surgery). Compared with the control group, neointima thickness in all 4 bypass models was significantly increased, but the neointima thickness of the 45 degrees S-type bypass was apparently much better than its 45 degrees conventional counterpart, and was as good as the 30 degrees conventional bypass. The numerical simulation revealed an apparent swirling flow pattern in the S-type bypass, which was very different than the flow patterns in the 3 conventional bypass models. This swirling flow altered the overall flow pattern in the distal part of the bypassed artery and eliminated the low WSS zone along the host artery floor. The improvement in the term of IH for the S-type bypass is most likely due to the alteration of the overall flow pattern and WSS distribution by the geometrical configuration of the S-type bypass.

Characterization of an endovascular prosthesis using the 3Bs rule (biocompatibility, biofunctionality and biodurability): a recommended protocol to investigate a device harvested at necropsy.

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.

[Time-frequency analysis of ventricular fibrillation and the effects of amiodarone].

This study is to quantify time-varying dominant frequencies in electrocardiogram (ECG) during the ventricular fibrillation (VF). Orthogonal ECG (sagittal, x; transverse, y; and longitudinal, z) and the transvenous two-leads defibrillation systems were set in 19 dogs. Time-frequency analysis was used to assess changes in the dominant frequency within ECG recorded in dogs during trials of 10-30 s of VF. In 4 additional dogs, the dominant frequencies were compared during 10 s of VF before and after administration of amiodarone. Results showed that in the 427 trials of 10 s VF and 335 trials of 30 s VF, average variation in the dominant frequency was considerable, between +/- 12%-18%. The frequencies orthogonal ECG during 10 s VF were distributed symmetrically above and below the mean frequency like a normal distribution. In the 79 trials with administration of amiodarone during 10 s VF in all three ECG, the mean frequencies decreased from 6.5 (x), 7.4 (y) and 7.0 Hz (z) to 6.1, 6.4 and 6.3 Hz (P < 0.01), respectively, and the variation in dominant frequencies decreased from 1.18, 1.38 and 1.19 to 0.98, 1.11 and 1.02 Hz (P < 0.05) respectively. The results confirmed that the frequencies of 10-30 s VF in ECG vary considerably and continuously, and amiodarone decreases this variation.

[Effects of extracts from different parts of Folium perillae (L.) Britt. on Hemorrheological parameters in rats].

In order to provide experimental data for the development and application of drug in clinic, we determined the effects of extracts from different parts of folium perillae (L. ) Britt. on hemorheological parameters, extracted from leaves (folium perillae), seeds (fructus perillae) and peduncles (caulis perillae). The results showed that all extracts from different parts of folium perillae (L. ) Britt. can significantly reduce the whole blood viscosity at low shear rate (10 s(-1)), erythrocyte aggregation index, erythrocyte electrophoresis index (P<0.05), and the whole blood reductive viscosity at low shear rate (10 s(-1)) (P<0.01). Extracts from folium perillae and caulis perillae can significantly decrease erythrocyte deformation index (P<0.05), whereas extracts from fructus perillae can not. Extracts from fructus perillae and caulis perillae can significantly decrease plasma viscosity at low shear rate(10 s(-1)), but extracts of folium perillae can not. Aspirin can only decrease the whole blood reductive viscosity at low shear rate and plasma viscosity (P<0.05). All extracts from different parts of folium perillae (L. ) Britt. had no significant effects on hematocrit, erythrocyte rigidity index, fibrinogen concentration , the whole blood viscosity and the whole blood reductive viscosity at middle and high shear rate (60 s(-1),120 s(-1)).

Does lower limb exercise worsen renal artery hemodynamics in patients with abdominal aortic aneurysm?

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.

The beneficial effect of swirling flow on platelet adhesion to the surface of a sudden tubular expansion tube: its potential application in end-to-end arterial anastomosis.

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.

Swirling flow can suppress flow disturbances in endovascular stents: a numerical study.

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 effect of rhubarb ethanol-extract on hyperlipidemia and liver fatty in rabbits].

AIM: To observe the effect of rhubarb ethanol-extract on hyperlipidemia and liver fatty in rabbits. METHODS: Thirty healthy male white rabbits were divided randomly into five groups, six rabbits in each group. The rabbits in control group were fed with common forage. The rabbits in model group were fed with high lipid forage. The rabbits in three different rhubarb groups were fed with high lipid forage and treated with different level rhubarb ethanol-extract (REE). In the process of experiment, periodically measured serology index of the rabbits and observed common physiology index. The rabbits were killed at the end of tenth week, liver fatty degeneration degree and liver coefficient were measured and compared. RESULTS: REE could decrease serum total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C), and increase serum high density lipoprotein cholesterol (HDL-C), and reduce liver fatty de generation and protect liver cell function. And the dose-effect relation was showed among different dose REE groups. CONCLUSION: REE can significantly reduce blood lipid, prevent and treat hyperlipidemia and liver fatty.