Assessment of stenosis in vascular access grafts

The major complication that occurs with grafts used as vascular access for hemodialysis, is stenosis at the venous anastomosis or in the draining vein. 75% area stenosis is considered significant as thrombotic occlusion may occur. The aim of this experimental study was to evaluate invasive and noninvasive indices to detect significant stenoses in a vascular access graft. A compliant underarm loop graft in vitro model was built and studied with 50, 65, 80, and 90% stenosis at flow rates of 500, 1000, and 1500 mL/min. Flow in the system was pulsatile. Velocity was measured with ultrasound Doppler and the pressure was measured invasively. The resistance index (RI), p(venous line)/MAP, and the newly introduced pressure ratio (PR) were calculated and compared. A stenosis can be suspected when a high frequency ultrasound velocity signal develops at the venous anastomosis. RI > 1 confirms a very severe stenosis (90%). The parameter PR < 8% confirms significant stenoses showing its clinical relevancy.     

Effects of vascular endothelial growth factor on nerve regeneration in acellular nerve grafts

The purpose of this study was to evaluate the effects of human recombinant vascular endothelial growth factor (VEGF-165) on peripheral nerve axonal sprouting and elongation following peripheral nerve injury and repair. Two-centimeter nerve gaps were created in rat peroneal nerves and repaired with either peripheral nerve autografts, acellular peripheral nerve isografts, or VEGF-165-treated acellular peripheral nerve isografts. Four months postoperatively, the peroneal nerves were harvested and histomorphometric analysis was performed. The reinnervated extensor digitorum longus (EDL) muscles were harvested and weighed. At the proximal nerve gap coaptation site, there was a statistically significant increase in the total number of axons and percent neural tissue in the VEGF-treated acellular nerve graft group, compared with the acellular peripheral nerve isograft and autograft groups. At the distal coaptation site, however, the total number of axons and percent neural tissue was similar in the acellular and VEGF-treated groups, which was significantly less than the autograft group. VEGF-165 treatment of acellular nerve grafts resulted in greater EDL muscle masses than acellular nerve grafts alone. VEGF treatment of acellular peripheral nerve isografts enhances axonal sprouting, resulting in an increased number of axons and percent neural tissue at the proximal nerve graft coaptation site. In the absence of any cellular elements, VEGF-impregnated acellular peripheral nerve grafts do not demonstrate enhanced axonal elongation, as noted by relatively few axons at the distal nerve graft coaptation site.     

Cavernous nerve regeneration using acellular nerve grafts

INTRODUCTION: The restoration of erectile function following complete transection of nerve tissue during surgery remains challenging. Recently, graft procedures using sural nerve grafts during radical prostatectomy have had favorable outcomes, and this has rekindled interest in the applications of neural repair in a urologic setting. Although nerve repair using autologous donor graft is the gold standard of treatment currently, donor nerve availability and the associated donor site morbidity remain a problem. In this study, we investigated whether an "off-the-shelf" acellular nerve graft would serve as a viable substitute. We examined the capacity of acellular nerve scaffolds to facilitate the regeneration of cavernous nerve in a rodent model. MATERIALS AND METHODS: Acellular nerve matrices, processed from donor rat corporal nerves, were interposed across nerve gaps. A total of 80 adult male Sprague-Dawley rats were divided into four groups. A 0.5-cm segment of cavernosal nerve was excised bilaterally in three of the four groups. In the first group, acellular nerve segments were inserted bilaterally at the defect site. The second group underwent autologous genitofemoral nerve grafts at the same site, and the third group had no repair. The fourth group underwent a sham procedure. Serial cavernosal nerve function assessment was performed using electromyography (EMG) at 1 and 3 months following initial surgery. Histological and immunocytochemical analyses were performed to identify the extent of nerve regeneration. RESULTS: Animals implanted with acellular nerve grafts demonstrated a significant recovery in erectile function when compared with the group that received no repair, both at 1 and 3 months. EMG of the acellular nerve grafts demonstrated adequate intracavernosal pressures by 3 months (87.6% of the normal non-injured nerves). Histologically, the retrieved regenerated nerve grafts demonstrated the presence of host cell infiltration within the nerve sheaths. Immunohistochemically, antibodies specific to axons and Schwann cells demonstrated an increase in nerve regeneration across the grafts over time. No organized nerve regeneration was observed when the cavernous nerve was not repaired. CONCLUSION: These findings show that the use of nerve guidance channel systems allow for accelerated and precise cavernosal nerve regeneration. Acellular nerve grafts represent a viable alternative to fresh autologous grafts in a rodent model of erectile dysfunction.     

Biological vascular grafts

Biological bypass graft material has been used as an alternative to autogenous vein since the first lower extremity revascularization procedures were performed. Both immunogenicity and biodegradation can contribute to the failure of these grafts and must be addressed. Cryopreservation at ultralow temperatures (-196 degrees C) after pretreatment with dimethylsulfoxide has been successful in preserving viable vein graft endothelium. Both rejection and deterioration of the cellular elements may contribute to the relatively high failure rates. The umbilical vein graft has become an effective alternative to autogenous material. The glutaraldehyde tanning procedure increases tensile strength, masks antigenicity, and sterilizes the tissue. Recent results with excellent 5-year patency (67%) and cumulative limb salvage (80%) confirm the utility of this graft.     

Catheterization of synthetic vascular grafts

One hundred nine percutaneous catheterizations of synthetic vascular grafts in 89 patients who had angiographic procedures were reviewed to determine the risk of major complications. Ninety-six of the catheterizations were inserted into the inguinal portion of aortofemoral grafts. There were no instances of hematoma, graft infection, aneurysm formation, suture line disruption, or embolic events distal to the puncture site. One local thrombus developed within a vascular graft that was corrected by a simple thrombectomy performed with a surgical catheter. One puncture site required 2 hours of compression to maintain hemostasis. Because of the extremely low risk of complications from catheterization of synthetic vascular grafts, it is the preferred route for angiographic procedures when the native femoral arterial route is unavailable.     

无细胞的异体神经修复鼠坐骨神经缺损

目的 通过化学萃取同种异体神经,去除髓鞘和雪旺细胞,形成无细胞基膜管后桥接鼠坐骨神经缺损,研究神经再生效果。方法 正常鼠坐骨神经用非变性生物剂处理后得到无细胞的基膜管,桥接鼠坐骨神经20mm缺损。实验分3组:无细胞基膜管移植组(A组),自体神经移植组(B组)和异体神经移植组(C组)。术后进行肌电图、光镜、电镜及图象分析仪检查。结果 A组再生神经有大量轴突通过移植体,术后2个月电生理检测再生神经的潜伏期及波幅低于B组(P<0.05),术后3个月2组差异无显著意义。髓鞘厚度在术后3个月时亦低于B组,差异有显著意义(P<0.05)。轴突直径及数目两组无差异。C组因无神经再生,结果无法测量。结论 这种无细胞基膜管移植体能支持轴突的生长和雪旺细胞的迁移,是一种良好的神经移植替代材料。     

Tissue engineered small-diameter vascular grafts

Arterial occlusive disease remains the leading cause of death in western countries and often requires vascular reconstructive surgery. The limited supply of suitable small-diameter vascular grafts has led to the development of tissue engineered blood vessel substitutes. Many different approaches have been examined, including natural scaffolds containing one or more ECM proteins and degradable polymeric scaffolds. For optimal graft development, many efforts have modified the culture environment to enhance ECM synthesis and organization using bioreactors under physiologic conditions and biochemical supplements. In the past couple of decades, a great deal of progress on TEVGs has been made. Many challenges remain and are being addressed, particularly with regard to the prevention of thrombosis and the improvement of graft mechanical properties. To develop a patent TEVG that grossly resembles native tissue, required culture times in most studies exceed 8 weeks. Even with further advances in the field, TEVGs will likely not be used in emergency situations because of the time necessary to allow for cell expansion, ECM production and organization, and attainment of desired mechanical strength. Furthermore, TEVGs will probably require the use of autologous tissue to prevent an immunogenic response, unless advances in immune acceptance render allogenic and xenogenic tissue use feasible. TEVGs have not yet been subjected to clinical trials, which will determine the efficacy of such grafts in the long term. Finally, off-the-shelf availability and cost will become the biggest hurdles in the development of a feasible TEVG product. Although many obstacles exist in the effort to develop a small-diameter TEVG, the potential benefits of such an achievement are exciting. In the near future, a nonthrombogenic TEVG with sufficient mechanical strength may be developed for clinical trials. Such a graft will have the minimum characteristics of biological tissue necessary to remain patent over a period comparable to current vein graft therapies. As science and technology advance, TEVGs may evolve into complex blood vessel substitutes. TEVGs may become living grafts, capable of growing, remodeling, and responding to mechanical and biochemical stimuli in the surrounding environment. These blood vessel substitutes will closely resemble native vessels in almost every way, including structure, composition, mechanical properties, and function. They will possess vasoactive properties and be able to dilate and constrict in response to stimuli. Close mimicry of native blood vessels may aid in the engineering of other tissues dependent upon vasculature to sustain function. With further understanding of the factors involved in cardiovascular development and function combined with the foundation of knowledge already in place, the development of TEVGs should one day lead to improved quality of life for those with vascular disease and other life-threatening conditions.     

Species differences in the infectability of vascular grafts

The susceptibility of different species to bacteremia may influence the results of studies on vascular graft infection. The present study compares prosthetic graft infection in canine and porcine models. Thirty-four mongrel dogs and 38 Yorkshire pigs underwent replacement of the infrarenal aorta with a 3-cm segment of a woven Dacron prosthesis. At the time of closure, each animal received an intravenous inoculum of 10(2) to 10(8) Staphylococcus aureus (S. aureus). Graft cultures at 1 week produced a predictable infection rate in dogs, while pigs developed only random infections (dogs: 23/34; pigs: 7/38; p = .0001). The median infective dose (ID50) in dogs was 10(2.9) but pigs did not develop enough infections to determine this value. Electron microscopy revealed a smooth fibrin surface in grafts explanted from pigs, while grafts from dogs demonstrated bacteria enmeshed in an irregular fibrinous lining. Prosthetic vascular grafts in dogs are more susceptible to hematogenous infection than those in pigs. Because hematogenous infection in humans is a rare event, the swine model may be a more appropriate representation of the clinical situation.     

膀胱无细胞基质移植物重建同种异体兔膀胱的研究

目的探讨膀胱无细胞基质移植物（BAMG）重建同种异体兔膀胱的效果。方法制备兔BAMG,用一半膀胱大小的BAMG对已行半个膀胱切除的25只同种异体兔做原位移植。8周时测定重建膀胱的容量、压力和顺应性,行膀胱造影;于术后1,2,4,8,12和16周,分别行重建膀胱的光镜和电镜观察。结果同种异体兔膀胱重建术后,肉眼可见BAMG结构上逐渐再生完全。术前与术后8周膀胱最大流出压（Pves,mas）、膀胱最大容量（VOlmax）和顺应性（VOlmax／Pves,mas）比较,差异均无统计学意义（P均〉0．05）。重建膀胱X线造影显示膀胱形态恢复正常。膀胱重建后1周时,在原膀胱和BAMG的交界处有上皮细胞、炎症细胞和毛细血管出现;2周时,BAMG有平滑肌和多层上皮细胞形成;4周后,在BAMG内可见短小的神经,各种成分以BAMG为支架继续再生;16周时,移植的无细胞基质与原膀胱在组织学上无区别。结论应用BAMG重建同种异体兔膀胱后,其结构上和功能上的再牛是以BAMG为支架逐步完成的。     

血管脱细胞细胞外基质制备的实验研究

目的 :研究脱除犬血管细胞获取完整血管基质的方法。方法 :采用不同浓度的去垢剂和蛋白酶 ,以及不同温度和时间的效果比较 ,并通过组织学检查 ,确定犬血管脱细胞细胞外基质的较好方法。结果 :经低渗 /高渗溶液加去垢剂和蛋白酶抑制剂处理 ,犬血管的细胞全部脱除 ,细胞外基质保持完好。结论 :制备血管脱细胞细胞外基质时去垢剂脱细胞的效果最佳     

Assessment of the antimicrobial properties of maggots

Chronic bacterial colonisation or infection of wound is one of the major factors interfering proper wound healing, especially in diabetic foot ulcers. This study assesses the potential antimicrobial properties of maggots in vitro. This is a prospective randomised experimental study. Complete lysis of methicillin‐resistant Staphylococcus aureus, Pseudomonas aeruginosa, vancomycin‐resistant Enterococcus and Candida albicans cultures in the area of maggot application was observed 24 hours after application of live maggots in all culture plates and was confirmed by Gram staining. This lysis persisted for more than 5 days after the maggot application. Complete lysis of the bacterial or fungal cultures in the area of maggot application provides convincing evidence for the antimicrobial property of maggots. This effect has a significant implication in management of diabetic foot ulcers and vascular ulcers.     

Biomaterials in the development and future of vascular grafts

Recent developments in the field of tissue engineering have re-invigorated the quest for more suitable biomaterials that are applicable to novel cardiovascular devices, including small-diameter vascular grafts. This review covers both commercially available and relevant newly developed experimental materials, including elastic polymers (polyurethane), the biodegradable and bioresorbable materials, and the naturally occurring materials, focusing on their potential applications in the development of future vascular substitutes.