首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 93 毫秒
1.

Introduction  

The success of vascular stents in the restoration of blood flow is limited by restenosis. Recent data generated from computational fluid dynamics (CFD) models suggest that the vascular geometry created by an implanted stent causes local alterations in wall shear stress (WSS) that are associated with neointimal hyperplasia (NH). Foreshortening is a potential limitation of stent design that may affect stent performance and the rate of restenosis. The angle created between axially aligned stent struts and the principal direction of blood flow varies with the degree to which the stent foreshortens after implantation.  相似文献   

2.

Background

Recent clinical studies have shown that recanalization rates are lower in stent-assisted coil embolization than in coiling alone in the treatment of cerebral aneurysms.

Objective

This study aimed to assess and compare the hemodynamic effect of stent struts and straightening of vessels by stent placement on reducing flow velocity in sidewall aneurysms, with the goal of reducing recanalization rates.

Methods

We evaluated 16 sidewall aneurysms treated with Enterprise stents. We performed computational fluid dynamics simulations using patient-specific geometries before and after treatment, with or without stent struts.

Results

Stent placement straightened vessels by a mean (±standard deviation) of 12.9°±13.1° 6 months after treatment. Placement of stent struts in the initial vessel geometries reduced flow velocity in aneurysms by 23.1%±6.3%. Straightening of vessels without stent struts reduced flow velocity by 9.6%±12.6%. Stent struts had significantly stronger effects on reducing flow velocity than straightening (P = 0.004, Wilcoxon test). Deviation of the effects was larger by straightening than by stent struts (P = 0.01, F-test). The combination of stent struts and straightening reduced flow velocity by 32.6%±12.2%. There was a trend that larger inflow angles produced a larger reduction in flow velocity by straightening of vessels (P = 0.16).

Conclusion

In sidewall aneurysms, stent struts have stronger effects (approximately 2 times) on reduction in flow velocity than straightening of vessels. Hemodynamic effects by straightening vary in each case and can be predicted by inflow angles of pre-operative vessel geometry. These results may be useful to design a treatment strategy for reducing recanalization rates.  相似文献   

3.

Background  

The process of restenosis after a stenting procedure is related to local biomechanical environment. Arterial wall stresses caused by the interaction of the stent with the vascular wall and possibly stress induced stent strut fracture are two important parameters. The knowledge of these parameters after stent deployment in a patient derived 3D reconstruction of a diseased coronary artery might give insights in the understanding of the process of restenosis.  相似文献   

4.

Background

Stacking cross-sectional intravascular images permits three-dimensional rendering of endovascular implants, yet introduces between-frame uncertainties that limit characterization of device placement and the hemodynamic microenvironment. In a porcine coronary stent model, we demonstrate enhanced OCT reconstruction with preservation of between-frame features through fusion with angiography and a priori knowledge of stent design.

Methods and Results

Strut positions were extracted from sequential OCT frames. Reconstruction with standard interpolation generated discontinuous stent structures. By computationally constraining interpolation to known stent skeletons fitted to 3D ‘clouds’ of OCT-Angio-derived struts, implant anatomy was resolved, accurately rendering features from implant diameter and curvature (n = 1 vessels, r2 = 0.91, 0.90, respectively) to individual strut-wall configurations (average displacement error ~15 μm). This framework facilitated hemodynamic simulation (n = 1 vessel), showing the critical importance of accurate anatomic rendering in characterizing both quantitative and basic qualitative flow patterns. Discontinuities with standard approaches systematically introduced noise and bias, poorly capturing regional flow effects. In contrast, the enhanced method preserved multi-scale (local strut to regional stent) flow interactions, demonstrating the impact of regional contexts in defining the hemodynamic consequence of local deployment errors.

Conclusion

Fusion of planar angiography and knowledge of device design permits enhanced OCT image analysis of in situ tissue-device interactions. Given emerging interests in simulation-derived hemodynamic assessment as surrogate measures of biological risk, such fused modalities offer a new window into patient-specific implant environments.  相似文献   

5.
Frequency domain optical coherence tomography (FD-OCT) has become one of the important clinical tools for intracoronary imaging to diagnose and monitor coronary artery disease, which has been one of the leading causes of death. To help more accurate diagnosis and monitoring of the disease, many researchers have recently worked on visualization of various coronary microscopic features including stent struts by constructing three-dimensional (3D) volumetric rendering from series of cross-sectional intracoronary FD-OCT images. In this paper, we present the first, to our knowledge, "push-of-a-button" graphics processing unit (GPU)-accelerated framework for intracoronary OCT imaging. Our framework visualizes 3D microstructures of the vessel wall with stent struts from raw binary OCT data acquired by the system digitizer as one seamless process. The framework reports the state-of-the-art performance; from raw OCT data, it takes 4.7 seconds to provide 3D visualization of a 5-cm-long coronary artery (of size 1600 samples x 1024 A-lines x 260 frames) with stent struts and detection of malapposition automatically at the single push of a button.  相似文献   

6.

Background  

All animals possess some type of tissue repair mechanism. In some species, the capacity to repair tissues is limited to the healing of wounds. Other species, such as echinoderms, posses a striking repair capability that can include the replacement of entire organs. It has been reported that some mechanisms, namely extracellular matrix remodeling, appear to occur in most repair processes. However, it remains unclear to what extent the process of organ regeneration, particularly in animals where loss and regeneration of complex structures is a programmed natural event, is similar to wound healing. We have now used the sea cucumber Holothuria glaberrima to address this question.  相似文献   

7.

Background  

The success of stent implantation in the restoration of blood flow through areas of vascular narrowing is limited by restenosis. Several recent studies have suggested that the local geometric environment created by a deployed stent may influence regional blood flow characteristics and alter distributions of wall shear stress (WSS) after implantation, thereby rendering specific areas of the vessel wall more susceptible to neointimal hyperplasia and restenosis. Stents are most frequently implanted in curved vessels such as the coronary arteries, but most computational studies examining blood flow patterns through stented vessels conducted to date use linear, cylindrical geometric models. It appears highly probable that restenosis occurring after stent implantation in curved arteries also occurs as a consequence of changes in fluid dynamics that are established immediately after stent implantation.  相似文献   

8.

Background:

The multifunctional transforming growth factor beta (TGF-β) is a glycoprotein that exists in three isoforms. TGF-β3 expression increases in fetal wound healing and reduces fibronectin and collagen I and III deposition, and also improves the architecture of the neodermis which is a combination of blood vessels and connective tissue during wound healing. Fibroblasts are key cells in the wound healing process. TGF-β3 plays a critical role in scar-free wound healing and fibroblast actions in the wound healing process. The aim of this study was to express the TGF-β3 gene (tgf-b3) in human foreskin fibroblasts (HFF’s).

Methods:

We obtained HFF’s from a newborn and a primary fibroblast culture was prepared. The cells were transfected with TGF-β3-pCMV6-XL5 plasmid DNA by both lipofection and electroporation. Expression of TGF-β3 was measured by enzyme-linked immunosorbent assay (ELISA).

Results:

The highest TGF-β3 expression (8.3-fold greater than control) was obtained by lipofection after 72 hours using 3 µl of transfection reagent. Expression was 1.4-fold greater than control by electroporation.

Conclusions:

In this study, we successfully increased TGF-β3 expression in primary fibroblast cells. In the future, grafting these transfected fibroblasts onto wounds can help the healing process without scarring.Key Words: Fibroblasts, Gene expression, TGF-β3  相似文献   

9.

Background  

Angiogenesis is a crucial process in follicular development and luteogenesis. The nerve growth factor (NGF) promotes angiogenesis in various tissues. An impaired production of this neurotrophin has been associated with delayed wound healing. A variety of ovarian functions are regulated by NGF, but its effects on ovarian angiogenesis remain unknown. The aim of this study was to elucidate if NGF modulates 1) the amount of follicular blood vessels and 2) ovarian expression of two angiogenic factors: vascular endothelial growth factor (VEGF) and transforming growth factor beta 1 (TGFbeta1), in the rat ovary.  相似文献   

10.

Background and Methods

It is important to ensure that blood flow is modelled accurately in numerical studies of arteries featuring drug-eluting stents due to the significant proportion of drug transport from the stent into the arterial wall which is flow-mediated. Modelling blood is complicated, however, by variations in blood rheological behaviour between individuals, blood’s complex near-wall behaviour, and the large number of rheological models which have been proposed. In this study, a series of steady-state computational fluid dynamics analyses were performed in which the traditional Newtonian model was compared against a range of non-Newtonian models. The impact of these rheological models was elucidated through comparisons of haemodynamic flow details and drug transport behaviour at various blood flow rates.

Results

Recirculation lengths were found to reduce by as much as 24% with the inclusion of a non-Newtonian rheological model. Another model possessing the viscosity and density of blood plasma was also implemented to account for near-wall red blood cell losses and yielded recirculation length increases of up to 59%. However, the deviation from the average drug concentration in the tissue obtained with the Newtonian model was observed to be less than 5% in all cases except one. Despite the small sensitivity to the effects of viscosity variations, the spatial distribution of drug matter in the tissue was found to be significantly affected by rheological model selection.

Conclusions/Significance

These results may be used to guide blood rheological model selection in future numerical studies. The clinical significance of these results is that they convey that the magnitude of drug uptake in stent-based drug delivery is relatively insensitive to individual variations in blood rheology. Furthermore, the finding that flow separation regions formed downstream of the stent struts diminish drug uptake may be of interest to device designers.  相似文献   

11.

Aim

Variations in treatment are the result of differences in demographic and clinical factors (e.g. anatomy), but physician and hospital factors may also contribute to treatment variation. The choice of treatment is considered important since it could lead to differences in long-term outcomes. This study explores the associations with stent choice: i.e. drug-eluting stent (DES) versus bare-metal stents (BMS) for Dutch patients diagnosed with stable or unstable coronary artery disease (CAD).

Methods & results

Associations with treatment decisions were based on a prospective cohort of 692 patients with stable or unstable CAD. Of those patients, 442 patients were treated with BMS or DES. Multiple logistic regression analyses were performed to identify variables associated with stent choice. Bivariate analyses showed that NYHA class, number of diseased vessels, previous percutaneous coronary intervention, smoking, diabetes, and the treating hospital were associated with stent type. After correcting for other associations the treating hospital remained significantly associated with stent type in the stable CAD population.

Conclusions

This study showed that several factors were associated with stent choice. While patients generally appear to receive the most optimal stent given their clinical characteristics, stent choice seems partially determined by the treating hospital, which may lead to differences in long-term outcomes.
  相似文献   

12.

Background  

In-stent restenosis rates have been closely linked to the wall shear stress distribution within a stented arterial segment, which in turn is a function of stent design. Unfortunately, evaluation of hemodynamic performance can only be evaluated with long term clinical trials. In this work we introduce a set of metrics, based on statistical moments, that can be used to evaluate the hemodynamic performance of a stent in a standardized way. They are presented in the context of a 2D flow study, which analyzes the impact of different strut profiles on the wall shear stress distribution for stented coronary arteries.  相似文献   

13.
Following the deployment of a coronary stent and disruption of an atheromatous plaque, the deformation of the arterial wall and the presence of the stent struts create a new fluid dynamic field, which can cause an abnormal biological response. In this study 3D computational models were used to analyze the fluid dynamic disturbances induced by the placement of a stent inside a coronary artery. Stents models were first expanded against a simplified arterial plaque, with a solid mechanics analysis, and then subjected to a fluid flow simulation under pulsatile physiological conditions. Spatial and temporal distribution of arterial wall shear stress (WSS) was investigated after the expansion of stents of different designs and different strut thicknesses. Common oscillatory WSS behavior was detected in all stent models. Comparing stent and vessel wall surfaces, maximum WSS values (in the order of 1Pa) were located on the stent surface area. WSS spatial distribution on the vascular wall surface showed decreasing values from the center of the vessel wall portion delimited by the stent struts to the wall regions close to the struts. The hemodynamic effects induced by two different thickness values for the same stent design were investigated, too, and a reduced extension of low WSS region (<0.5Pa) was observed for the model with a thicker strut.  相似文献   

14.

Objectives

Recent clinical trials suggest an LDL-independent superiority of intensive statin therapy in reducing target vessel revascularization and peri-procedural myocardial infarctions in patients who undergo percutaneous coronary interventions (PCI). While animal studies demonstrate that statins mobilize endothelial progenitor cells (EPCs) which can enhance arterial repair and attenuate neointimal formation, the precise explanation for the clinical PCI benefits of high dose statin therapy remain elusive. Thus we serially assessed patients undergoing PCI to test the hypothesis that high dose Atorvastatin therapy initiated prior to PCI mobilizes EPCs that may be capable of enhancing arterial repair.

Methods and Results

Statin naïve male patients undergoing angiography for stent placement were randomized to standard therapy without Atorvastatin (n = 10) or treatment with Atorvastatin 80 mg (n = 10) beginning three days prior to stent implantation. EPCs were defined by flow cytometry (e.g., surface marker profile of CD45dim/34+/133+/117+). As well, we also enumerated cultured angiogenic cells (CACs) by standard in vitro culture assay. While EPC levels did not fluctuate over time for the patients free of Atorvastatin, there was a 3.5-fold increase in EPC levels with high dose Atorvastatin beginning within 3 days of the first dose (and immediately pre-PCI) which persisted at 4 and 24 hours post-PCI (p<0.05). There was a similar rise in CAC levels as assessed by in vitro culture. CACs cultured in the presence of Atorvastatin failed to show augmented survival or VEGF secretion but displayed a 2-fold increase in adhesion to stent struts (p<0.05).

Conclusions

High dose Atorvastatin therapy pre-PCI improves EPC number and CAC number and function in humans which may in part explain the benefit in clinical outcomes seen in patients undergoing coronary interventions.  相似文献   

15.

Background  

Rotator cuff tears are a common and frequent lesion especially in older patients. The mechanisms of tendon repair are not fully understood. Common therapy options for tendon repair include mini-open or arthroscopic surgery. The use of growth factors in experimental studies is mentioned in the literature. Nanofiber scaffolds, which provide several criteria for the healing process, might be a suitable therapy option for operative treatment. The aim of this study was to explore the effects of nanofiber scaffolds on human tendon derived fibroblasts (TDF's), as well as the gene expression and matrix deposition of these fibroblasts.  相似文献   

16.

Background  

SPARC is a matricellular protein involved in cell-matrix interactions. From expression patterns at the wound site and in vitro studies, SPARC has been implicated in the control of wound healing. Here we examined the function of SPARC in cutaneous wound healing using SPARC-null mice and dermal fibroblasts derived from them.  相似文献   

17.

Background  

β-catenin and transforming growth factor β signaling are activated in fibroblasts during wound healing. Both signaling pathways positively regulate fibroblast proliferation during this reparative process, and the effect of transforming growth factor β is partially mediated by β-catenin. Other cellular processes, such as cell motility and the induction of extracellular matrix contraction, also play important roles during wound repair. We examined the function of β-catenin and its interaction with transforming growth factor β in cell motility and the induction of collagen lattice contraction.  相似文献   

18.

Background  

The aim of the study was to investigate the effect of acupuncture on wound healing after soft tissue or orthopaedic surgery in dogs.  相似文献   

19.

Objectives

To assess biodegradable nasal packing effectiveness for improving postoperative symptoms and mucosal healing after endoscopic sinonasal surgery as compared with conventional/non-packing groups.

Methods

Relevant articles were searched on PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials. We included randomized controlled trials (RCTs) that compared biodegradable packings with conventional packings or no packing, reporting postoperative symptoms and/or mucosal healing outcomes.

Results

This review included 19 studies, of which 11 compared biodegradable packings with conventional packings. Meta-analysis found that biodegradable packings significantly improved postoperative symptoms: bleeding at removal, pain at removal, pain in situ, and nasal blockage. Mucosal healing outcomes were inconsistent within studies, with no data could be pooled. Eight studies compared biodegradable packings with non-packing group. Postoperative symptom data in this comparison could not be pooled: A protective or equal effect on postoperative bleeding was reported in different studies; no difference was reported in pain status and nasal blockage. As for mucosal healing, meta-analysis showed that two arms of comparison had similar effect on synechiae, edema, infection and granulation at each time point.

Conclusion

The limiting evidence suggests that biodegradable nasal packings are statistically better than conventional packings in postoperative symptoms, and probably comparable to non-packing group, as in this comparison we could not carry out meta-analysis. No beneficial or detrimental effect on postoperative mucosal healing could be determined based on existing evidence.  相似文献   

20.

Background

Chronic wounds present a major challenge in modern medicine. Even under optimal conditions, the healing process may lead to scarring and fibrosis. The ability of mesenchymal stem cells (MSCs) to differentiate into other cell types makes these cells an attractive therapeutic tool for cell transplantation. Both tissue-engineered construct and MSC therapy are among the current wound healing procedures and potential care. Chitosan has been widely applied in tissue engineering because of its biocompatibility and biodegradability.

Aim

The aim of the current work was to compare the efficiency of MSCs and chitosan dressing, alone or in combination treatment on wound healing.

Methods

This study was conducted on 15 rabbits, which were randomly divided in 3 groups based on the type of treatment with MSCs, chitosan dressing and combination of both. A full–thickness skin defect was excised from the right and left side of the back of each animals. Defects on right sides were filled with treatments and left side defects were left as control. Evaluation of the therapeutic effectiveness was performed through a variety of clinical and microscopical evaluations and measurements of the process of wound healing on days 7, 14, 21, and 28. Histological evaluation of wound healing was classified by different scoring systems.

Results

The data indicated that wounds treated with bone marrow derived MSC had enhanced cellularity and better epidermal regeneration. During the early stages of wound healing, the closure rate of bone marrow derived MSC-treated wounds were significantly higher than other treatments (P < 0.05). Although the MSCs in the wound edges enhance the healing of the full–thickness wound, the healing process of chitosan treatment was slower than the control group.

Conclusion

This study revealed advanced granulation tissue formation and epithelialization in wounds treated with MSCs, and may suggests this treatment as an effective applicant in wound healing process. Chitosan scaffold dressings, whether alone or in combination with MSCs, have worsened the wound healing as compared to the control group.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号