Reconstruction of rat femoral veins with microvascular prostheses

Synthetic conduits have not been suitable for microvascular reconstruction owing primarily to their high thrombogenicity. Vein replacements are the most vulnerable to thrombosis because of their low shear rates and low pressure. Experimental replacement of microvenous segments with prosthetic segments has shown little success. Recent technological advances in biomaterials and control of thrombogenesis provide the potential for success in the development of venous prostheses. The purpose of this study was to assess the use of nonbiodegradable composite polyurethane microvascular prostheses for reconstruction of rat femoral veins. Rat femoral venous defects of 10 mm were reconstructed with autogenous vein (n = 12), unprocessed plain polyurethane (n = 5), and nonbiodegradable composite polyurethane (n = 31). Patency was evaluated by direct observation and proximal venous milking tests. The patency rate of composite grafts was not significantly different from that of isotopic vein (p = 0.5, Fisher's exact test), and both had higher patency than unprocessed polyurethane (p less than 0.01). Composite grafts were examined sequentially using light and scanning electron microscopy. Grafts were fully endothelialized between the first and third months. The neointimal, neomedial, and neoadventitial layers could be seen more distinctly over time. New opportunities in reconstructive microsurgery may be opened by microvascular prostheses that are complaint and thromboresistant.     

Expanded polytetrafluoroethylene as a microvascular graft: a study of four fibril lengths

The utility for a prosthetic microvascular graft is well demonstrated, but previous studies have been inconclusive. Expanded polytetrafluoroethylene (Gore-Tex) has been most widely tested as a prosthetic graft. Polytetrafluoroethylene is composed of transverse nodules connected by long fibrils. This study evaluates the effect of fibril length on observed patency in a 1-mm inner-diameter system. Fibril lengths tested were 30, 60, 90, and 120 micron. One-hundred and sixty-three grafts were implanted in the abdominal aorta of Sprague-Dawley rats by a single surgeon using a standardized technique. No anticoagulants were used. Grafts were harvested at predetermined times and evaluated macroscopically, by scanning electron microscope, and by standard histology. The highest patency observed was 97.7 percent in the 90-micron fibril-length grafts. Fibril morphology also affected patency. Increased patency was associated with an amorphous fibril pattern. The graft functioned as a matrix for the formation of a pseudoartery, complete with monocell-thick intima and smooth-muscle media. A foreign-body reaction was observed in the 60-micron fibril-length graft only. Expanded polytetrafluoroethylene does show promise as a microvascular graft. Both fibril length and morphology affect observed patency.     

Experimental microvascular anastomoses in radiated vessels: a study of the patency rate and the histopathology of healing.

A study of microvascular surgery in radiated tissue is presented. The radiation damage to the vessels and its consequence on the histopathology of blood vessel healing is discussed. The main difficulty encountered was the radiation-induced fibrosis in the perivascular tissues. The patency rate in ther arterial anastomoses was unaltered by prior radiation, but the patency rate in the venous anastomoses fell to 54 percent after high doses of prior radiation.     

Human saphenous vein and coronary bypass surgery: ultrastructural aspects of conventional and "no-touch" vein graft preparations

Coronary artery bypass graft surgery (CABG) is routinely used to restore blood flow to diseased cardiac muscle due to coronary artery disease. The patency of conventional grafts decreases with time, which is due to thrombosis and formation of neointima. A primary cause of graft failure is the mechanical damage inflicted to the graft during harvesting, including removal of surrounding tissue accompanied by high pressure saline distension to overcome vasospasm (both causing considerable mechanical trauma). The aim of this study was to compare the ultrastructural features of human saphenous vein (SV) grafts harvested conventionally and grafts prepared using an atraumatic 'no-touch' harvesting technique introduced by Souza (1996). The results of this study showed a better preservation of the lumenal endothelium and medial vascular smooth muscle (SM) in 'no-touch' versus conventional grafts. A 'fast' (within 30 min) response of SM cells to conventional harvesting was noted where features of both SM cell division and apoptosis were observed. It is concluded that the 'preserved' nature of the 'no-touch' aortocoronary SV grafts renders them less susceptible to thrombotic and atherosclerotic factors than grafts harvested conventionally. These features are suggested to contribute to the improved early patency rate described using the no-touch technique of SV harvesting.     

Revascularized periosteal grafts--a new method to produce functional new bone without bone grafting

Rib periosteum was transplanted to the groins of 9 dogs. In half of the periosteal grafts, no microvascular anastomoses were done (free grafts); at 6 weeks after grafting they had become resorbed. The other periosteal grafts were revascularized by microvascular anastomoses of the intercostal vessels to local muscular vessels; at 6 weeks those with confirmed vascular patency had all formed substantial amounts of new bone. Five cm, full-thickness defects were created in the tibias of 10 dogs. The control animals (without grafting) did not heal in two months. However, the experimental dogs, with vascularized periosteal grafts in the defects regenerated their tibias with healthy new bone by 6 weeks--and were walking on them then.     

Experimental microvascular polytetrafluoroethylene grafts: 6-month patency

The efficacy of 1-mm internal-diameter polytetrafluoroethylene as a microvascular prosthesis is unclear. In this study, 8-mm-long segments of this material were implanted into the femoral arteries of 30 rats. Animals were examined every 2 weeks up to 6 months by Doppler ultrasound. Cumulative patency by the life-table method was 86.7 percent at 6 months. There were 26 patent grafts, 2 occlusions, and 2 deaths. Intimal hyperplasia adjacent to the anastomoses was seen in the native arteries. The pseudointima lining the grafts was cellular near the anastomoses but usually acellular in midgraft regions. It is concluded that if early failure does not occur, then good long-term patency is possible with 1-mm polytetrafluoroethylene in this setting and that patency is not dependent on development of a cellular pseudointima. Longer graft segments should be evaluated in future studies.     

Anastomosis of vessels of unequal diameter using an interpositional vein graft

In this study, 100 rabbits were used to assess the efficacy of five different methods of microvascular anastomosis where a vessel diameter discrepancy of 5:1 existed. The inferior vena cava of the rabbit was used as a graft in the femoral artery. In 50 percent of the rabbits the graft was reversed to assess the effects on flow. When explored between 7 and 10 days after anastomosis, an overall patency rate of 96 percent was recorded. Three grafts were not patent in the reversed group and one was not patent in the nonreversed group. There was no significant statistical difference in patency rates between any of the groups, as calculated by the Fisher's exact probability test. The tapered end-to-end and side-to-end anastomoses were found to be the most rapid and simplest methods to perform.     

Tubo-ovarian transplantation in the treatment of sterility. Experimental research]

Microsurgical transposition of fallopian tube and ovary has the potential of being an efficient therapeutic treatment in patients with tubal sterility. The Authors present their experience of microsurgical adnexal transplantation in rabbit by two different techniques: the first procedure by microvascular anastomosis of the ovarian vessels, the second one without vascular pedicle. Function is evaluated at various time after grafting by: exploratory laparotomy on day 30 to establish whether circulation to the grafts was still maintained; macroscopic and microscopic examination of ovaries and fallopian tubes. The microvascular techniques prove highly reliable in terms of immediate vascular patency rate but it is disappointing that 50% of the autografts has failed with blocked vessels by day 30. Perhaps this is due to the difficult techniques in anastomosing the ovarian vessels of small caliber. In spite of these outcomes the vascularized autografts were viable and functional after transplantation in contrast with the non-vascularized tubo-ovarian grafts which all failed. This experience encourages to believe that the microsurgical technique could be employed for homograft transplantation in woman with extensive ovarian and tubal damages.     

Tubular silk scaffolds for small diameter vascular grafts

Vascular surgeries such as coronary artery bypass require small diameter vascular grafts with properties that are not available at this time. Approaches using synthetic biomaterials have been not completely successful in producing non-thrombogenic grafts with inner diameters less than 6 mm, and there is a need for new biomaterials and graft designs. We propose silk fibroin as a microvascular graft material and describe tubular silk scaffolds that demonstrate improved properties over existing vascular graft materials. Silk tubes produced using an aqueous gel spinning technique were first assessed in vitro in terms of thrombogenicity (thrombin and fibrinogen adsorption, platelet adhesion) and vascular cell responses (endothelial and smooth muscle cell attachment and proliferation) in comparison with polytetrafluoroethylene (PTFE), a synthetic material most frequently used for vascular grafts. Silk tubes were then implanted into the abdominal aortas of Sprague-Dawley rats. At time points of 2 weeks and 4 weeks post implantation, tissue outcomes were assessed through gross observation (acute thrombosis, patency) and histological staining (H&E, Factor VIII, smooth muscle actin). Over the 4-week time period, we observed graft patency and endothelial cell lining of the lumen surfaces. These results demonstrate the feasibility of using silk fibroin as a vascular graft material and some advantages of silk tubes over the currently used synthetic grafts.     

In vivo study of a model tissue-engineered small-diameter vascular bypass graft

Conventionally used vascular grafts such as polyester (Dacron) or expanded polytetrafluoroethylene perform inadequately as small-diameter vascular bypass grafts (SDBGs). SDBGs, which can maintain long-term patency and those that could potentially evolve with the somatic growth, are highly desirable in vascular surgery and thus research into tissue-engineered blood vessels (TEBVs) is of keen interest. A TEBV was developed by seeding endothelial cells onto a collagen matrix that was cross-linked and contracted by smooth muscle cells (SMCs). A polyester graft served as a scaffold. Recovery studies (12 TEBVs and seven controls) were carried out to assess in vivo endothelialization and long-term patency of TEBVs. Hemodynamic observations indicated para-anastomotic turbulences and high shear stress at anastomosis. Recovery studies demonstrated confluent endothelialization, thrombus-free surfaces, and patent TEBVs in all cases. Graft incorporation and neovascularization of the scaffold occurred in both hybrid and control grafts. However, thickened neointima formation occurred in TEBV grafts, which was most likely caused by the rigidity of polyester scaffold. Significant perigraft inflammatory changes could be observed in both TEBVs and control grafts at 1, 4, and 8 weeks. In conclusion, the TEBVs demonstrated satisfactory performance as an infra-renal-aortic graft in a porcine model. The TEBV serves as a promising model and facilitates the development of a TEBV in a clinical setting, potentially with human stem cells and with more biocompatible, biodegradable scaffolds that are mechanically more compliant with natural vessels.     

64层螺旋CTA在冠状动脉搭桥术后桥血管评价中的临床应用

目的：评价64层螺旋CTA在冠状动脉搭桥术后桥血管评价中的应用价值。方法：收集67例冠脉搭桥术后64层螺旋CTA资料,回顾性分析其成像条件、心电编辑软件对图像质量的影响;薄层容积图像及VR、CPP、MIP等后处理方法对桥血管的显示情况,并观察桥血管通畅状态。结果：67例CTA容积图像质量均满足诊断要求,其中15例经B受体阻滞剂控制心率;27例经过心电编辑软件后处理;检出正常桥血管107支,占74_31％（107／144）;异常静脉桥血管32支,22．22％（32／144）,包括近端吻合口尖角状闭塞13支,钙化斑块7支,软癍块8支,混合斑块1支;远端吻合口狭窄3支;正常动脉桥血管35支,24-31％（35／144）;异常动脉桥血管5支,3．47％（5／144）,包括闭塞内乳动脉桥血管4支,远端吻合口狭窄1支。上述多种后处理方法有助于多角度、多方位显示桥血管近、远端吻合口、桥血管行程及其与毗邻结构关系、有无斑块及管腔狭窄程度等。结论：64层螺旋CTA是冠脉搭桥术后评估桥血管状态准确、安全及简便的影像学检查方法。     

Comparison of the thrombogenicity of internationally available fibrin sealants in an established microsurgical model.

Previous studies comparing the thrombotic complications of cryoprecipitated fibrin sealant containing bovine thrombin on microvascular venous anastomoses in a rat epigastric free flap model revealed deleterious outcomes regarding flap survival with higher concentrations of topical bovine thrombin. This study was designed to compare three internationally available fibrin sealants, one experimental fibrin monomer sealant that does not require thrombin, and human thrombin alone as to their effects on the survival of an established rat epigastric free flap model. Ninety Sprague-Dawley rats (400 to 600 g) were prepared for abdominal surgery, and an epigastric-based skin flap was raised. The single vein draining the flap was clamped, divided, and reconnected using standard microvascular suturing techniques. Before release of the clamps, the chosen additive was applied precisely to the anastomosis. Additional material was then added to the raw surface of the flap. The animals were divided into seven treatment groups, each receiving 1 ml of commercial or investigational fibrin sealant or human thrombin alone: one control group receiving no additive treatment, four fibrin sealant groups receiving treatment with commercial or investigational fibrin sealant preparations, and two groups receiving different concentrations (500 IU/ml and 1000 IU/ml) of human thrombin applied to the anastomoses and the surrounding tissue. Flap survival was assessed at 7 days postoperatively. This study supports the contention that microvascular free flap survival based on microvascular venous anastomotic patency was adversely effected by high concentrations of thrombin. Lower concentrations (500 IU/ml and less) of thrombin did not seem to affect flap survival. One test product was composed of a fibrin monomer sealant, which obviates the need for the thrombin additive. This group's survival rate was not statistically different from that of the control group. Thus, for microvascular anastomoses, lower concentrations of thrombin or a sealant devoid of thrombin seem to be best for microvascular anastomotic patency.     

生物血管异种移植的初步研究

目的为了寻求一种新的小口径血管代用品,建立异种移植的动物实验模型,以观察异种移植物的安全性、可靠性、通畅性及组织学改变。方法共采用17只杂种雌性犬,实验组10只,植入经环氧化物处理的猪血管移植物;对照组7只,植入人造血管。手术方法为右侧股动静脉瘘。术后通过超声和血管造影方法来观察移植血管的通畅性,并在术后3月将移植物取出,进行病理学检查,观察移植前后移植物的组织学改变。结果术后第一周、二周行Doppler超声检查结果,两组动静脉瘘均通畅,2周内血管通畅率为100%。术后3个月动脉造影检查后,生物血管组(PG)通畅5只,通畅率62.5%,e-PTFE组通畅4只,通畅率66.7%。两组数据统计学处理,差异无显著性(P>0.05)。术后3月对移植物取材,进行光镜及扫描电镜病理学检查,通畅的生物血管吻合口无狭窄,吻合部位有新的内膜覆盖,周围组织无钙化,有新生的内皮细胞覆盖。结论经环氧化物处理的猪的血管移植物(PG)生物血管作为异种移植物,生物相容性好,具有一定的可行性。     

Indications, technique, and results in 336 tibioperoneal reconstructions

At the University of Erlangen-Nürnberg, a retrospective study was done of 336 femorotibial bypasses for limb salvage, with a follow-up of 7 years. The indication for arterial reconstruction was severe ischemia in 80.7%. Early good results were obtained in 89.6%, and the mortality rate was 1.5%. The best bypass grafts were the autologous vein and the composite graft, with patency rates of 92%. Five and 7 years after surgery, the cumulative patency rates were 50.7% and 49.1% respectively.     

Hydroxyapatite ceramics in multilevel cervical interbody fusion - is there a role?

The aim of this study is to evaluate the efficacy of hydroxyapatite grafts in multilevel cervical interbody fusion during the one year follow-up. A total of 86 patients with degenerative cervical disc disease underwent all together 224 cervical interbody fusion procedures in which either Smith-Robinson or Cloward type hydroxyapatite grafts were used. The surgeries included radiculopathy in 38 cases, myelopathy in 20 cases and myeloradicuopathy in 28 patients. In 65 out of 86 patients, fusion was followed by an anterior instrumentation (plating). Postoperatively, patients were followed for a mean of 15.64 (range 11-23.3) months. All patients underwent radiography to evaluate fusion and the axis curvature. Excellent clinical results (86%), described as a complete or partial relief of symptoms with full return to preop activity, were obtained in patients with radiculopathy. There were 5 grafts mobilizations and one graft fracture. Two grafts extruded in non-instrumented patients and required repeated surgery. There were other three reoperations due to the hardware problems. One year fusion rate was obtained at 86% for two-level surgery, 80.1% for three-level surgery and 74% for four-level surgery. The mean (SD) hospital stay was 3.8 (0.7) days. A hydroxyapatite cheramic can be a very effective synthetic material for multilevel cervical interbody fusion. It is characterized by a high fusion rate and a small percentage of graft-related complications, especially when fusion procedure is followed by plating.     

End-to-end versus end-to-side microvascular anastomosis patency in experimental venous repairs

In this experimental study, venous end-to-end and end-to-side microvascular anastomoses in similar and diameter-discrepant vessels were compared. In 50 rats, end-to-end microvascular repair of the divided epigastric vein and end-to-side repair of the epigastric vein into the femoral vein showed 5-day patency rates of 75 and 88 percent, respectively. These data are not statistically different. In 20 rats, microvascular repair of end epigastric to end femoral veins (size discrepant) and end epigastric to side femoral veins showed 5-day patency rates of 50 and 85 percent, respectively. These data are statistically different (p less than 0.05). We conclude from these experimental data that end-to-side venous repairs may be useful in lowering the anastomosis thrombosis rate seen when size-discrepant veins are repaired.     

The antithrombogenic potential of a polyhedral oligomeric silsesquioxane (POSS) nanocomposite

We have developed a nanocomposite using a silica nanocomposite polyhedral oligomeric silsesquioxane (POSS) and poly(carbonate-urea)urethane (PCU) for potential use in cardiovascular bypass grafts and the microvascular component of artificial capillary beds. In this study, we sought to compare its antithrombogenicity to that of conventional polymers used in vascular bypass grafts so as to improve upon current patency rates, particularly in the microvascular setting. Using atomic force microscopy (AFM) and transmission electron microscopy (TEM), surface topography and composition were studied, respectively. The ability of the nanocomposite surface to repel both proteins and platelets in vitro was assessed using thromboelastography (TEG), fibrinogen ELISA assays, antifactor Xa assays, scanning electron microscopy (SEM), and platelet adsorption tests. TEG analysis showed a significant decrease in clot strength (one-way ANOVA, p < 0.001) and increase in clot lysis (one-way ANOVA, p < 0.0001) on the nanocomposite when compared to both poly(tetrafluoroethylene) (PTFE) and PCU. ELISA assays indicate lower adsorption of fibrinogen to the nanocomposite compared to PTFE (one-way ANOVA, p < 0.01). Interestingly, increasing the concentration of POSS nanocages within these polymers was shown to proportionately inhibit factor X activity. Platelet adsorption at 120 min was also lower compared to PTFE and PCU (two-way ANOVA, p < 0.05). SEM images showed a "speckled" morphologic pattern with Cooper grades I platelet adsorption morphology on the nanocomposite compared to PTFE with grade IV morphology. On the basis of these results, we concluded that POSS nanocomposites possess greater thromboresistance than PTFE and PCU, making it an ideal material for the construction of both bypass grafts and microvessels.     

Agitation and pressure effects on acetone-butanol fermentation

Batch fermentations were run at varying agitation rates and were either pressurized to 1 bar (15.2 psig) or nonpressurized. Agitation and pressure both affect the level of dissolved hydrogen gas in the media, which in turn influences solvent production. In nonpressurized fermentations volumetric productivity of butanol increased as the agitation rate decreased. While agitation had no significant effect on butanol productivity under pressurized conditions, overall butanol productivity was increased over that obtained in the nonpressurized runs. Maximum butyric acid productivity, however, was found to occur earlier and increased as agitation increased. Peak hydrogen productivity occurred simultaneously with peak butyric acid productivity. The proporation of reducing equivalents used in forming the above products was determined using a redox balance based on the fermentation stoichiometry. An inverse relationship between the final concentrations of acetone and acetoin was found in all fermentations studied. The results show that agitation and pressure are important parameters for solvent productivity in acetone-butanol fermentation.     

Microvascular surgical experimental thrombosis model: rationale and design

The rationale for the design of surgical models of microvascular thrombosis is discussed, and a new model, the arterial inversion graft (AIG), is described and evaluated in the New Zealand white rabbit. Femoral artery segments of predetermined length are excised, gently turned inside-out, and resutured into their native position. Blood flow is restored, and at varying time intervals, vessel patency is assessed through the direct "milking test." In this study, three groups of 20 arterial inversion grafts of 2, 5, and 10 mm in length are created and evaluated for patency at 1 hour and again at 7 days. The incidence of femoral artery occlusion in this model appears to be an increasing function of arterial inversion graft length both at 1 hour--30 percent (2 mm), 80 percent (5 mm), and 100 percent (10 mm)--and at 7 days--65 percent (2 mm), 90 percent (5 mm), and 100 percent (10 mm). This proportionality suggests the arterial inversion graft may be adjusted in length to provide an incidence of vessel occlusion best suited to the needs of any particular experiment.     

Freeze-dried microarterial allografts

Rehydrated freeze-dried microarterial allografts were implanted to bridge arterial defects using New Zealand White rabbits as the experimental model. Segments of artery from the rabbit ear and thigh were harvested and preserved for a minimum of 2 weeks after freeze-drying. These allografts, approximately 1 mm in diameter and ranging from 1.5 to 2.5 cm in length, were rehydrated and then implanted in low-pressure and high-pressure arterial systems. Poor patency was noted in low-pressure systems in both allografts and autografts, tested in 12 rabbits. In the high-pressure arterial systems, allografts that were freeze-dried and reconstituted failed in a group of 10 rabbits with an 8-week patency rate of 30 percent. Gamma irradiation in an effort to reduce infection and antigenicity of grafts after freeze-drying was associated with a patency rate of 10 percent at 8 weeks in this system in another group of 10 rabbits. Postoperative cyclosporin A therapy was associated with a patency rate of 22.2 percent in the high-pressure arterial system in a 9-rabbit group. Control autografts in this system in a group of 10 rabbits showed a 100 percent patency at 8 weeks. Microarterial grafts depend on perfusion pressure of the vascular bed for long-term patency. Rehydrated freeze-dried microarterial allografts do not seem to function well in lengths of 1 to 2.5 cm when implanted in a high-pressure arterial system. Freeze-dried arterial allografts are probably not antigenic.