Further technical considerations of the sleeve microanastomosis

In sleeve anastomoses, stenoses at the suture site have been the main concern. Mechanical dilatation is one way to prevent the stenosis, as suggested by Lauritzen. In the present study, 50 vessels (femoral and carotid) and 10 veins were used for sleeve anastomoses and the same numbers of vessels were used for conventional anastomoses (as control) to evaluate the effect of mechanical dilatation using resin corrosion cast (Mercox) because the Mercox cast facilitates three-dimensional stereoscopic views. Gradual dilatations around the suture sites were observed in seven carotid arteries, and three of seven resulted into aneurysm formation due to weakening of the inner vascular wall in the sleeve anastomosis. No dilatation or aneurysm was observed in the femoral arteries. Newly proliferating capillaries formed on the endothelial surfaces of the inner vascular walls around the suture sites after 4 weeks in the sleeve anastomoses. Operative time and endothelial trauma were markedly reduced with sleeve anastomoses. The gradual dilatation and aneurysm formation in the carotid arteries show that sleeve anastomoses should be used carefully for high-pressure arteries in clinical practice if mechanical dilatation is performed.     

Bipolar anastomosis technique with removable instruments: an easy, fast, and reliable technique for vascular anastomosis

The interrupted suture technique is most commonly used for microsurgical vascular anastomosis. For several reasons (e.g., exposure of suture material to blood, time needed), many attempts have been made to find other solutions. This article describes a new means of performing a microsurgical vascular anastomosis. The aim of this study was to show the feasibility and possible advantages of this new technique. The basic components at work here are a modified cuff and electrically generated heat used to unite the vessel walls. In this way, both endothelial layers are adapted without manipulating the inside of the vessel or leaving behind foreign matter. Various energy/coagulation time settings were used to perform arterial anastomoses (n = 42) in an isogeneic abdominal aorta interposition model in the rat. The quality of anastomosis was evaluated at days 1, 10, 21, and 120. Immediately after the welding process all anastomoses (n = 42) were patent. No stenosis was found at any observation time. Anastomosis time ranged from 3 to 18 minutes (average, 11 minutes). This new technique permits a vascular anastomosis to be performed easily and reliably with a high patency rate. With this technique, the authors are convinced that a skilled surgeon can create a high-quality anastomosis in a fraction of the time needed to sew an anastomosis.     

External-beam radiation therapy for improved dialysis access patency: feasibility and early safety.

Rectenwald, J. E., Pretus, H. A., Seeger, J. M., Huber, T. S., Mendenhall, N. P., Zlotecki, R. A., Palta, J. R., Li, Z. F., Hook, S. Y., Sarac, T. P., Welborn, M. B., Klingman, N. V., Abouhamze, Z. S. and Ozaki, C. K. External-Beam Radiation Therapy for Improved Dialysis Access Patency: Feasibility and Early Safety. Radiat. Res. 156, 53-60 (2001).Prosthetic dialysis access grafts fail secondary to neointimal hyperplasia at the venous anastomosis. We hypothesized that postoperative single-fraction external-beam radiation therapy to the venous anastomosis of hemodialysis grafts can be used safely in an effort to improve access patency. Dogs (n = 8) underwent placement of expanded polytetrafluoroethylene grafts from the right carotid artery to the left jugular vein. Five dogs received single-fraction external-beam photon irradiation (8 Gy) to the venous anastomosis after surgery. Controls were not irradiated. Shunt angiograms were completed 3 and 6 months postoperatively. Anastomoses, mid-graft, and the surrounding tissues were analyzed. Immunohistochemistry for smooth muscle cell alpha-actin, proliferating cellular nuclear antigen (PCNA), and apoptosis was performed. Incisions healed well, though all animals developed wound seromas. One control suffered graft thrombosis 4 months postoperatively. Angiography/histology confirmed severe neointimal hyperplasia at the venous anastomosis. The remaining seven dogs developed similar amounts of neointimal hyperplasia. PCNA studies showed no accelerated fibroproliferative response at irradiated anastomoses compared to controls. Skin incisions and soft tissues over irradiated anastomoses revealed no radiation-induced changes or increase in apoptosis. Thus we conclude that postoperative single-fraction external-beam irradiation of the venous anastomosis of a prosthetic arteriovenous graft that mimics the situation in humans is feasible and safe with regard to early wound healing.     

The C-seal: A Biofragmentable Drain Protecting the Stapled Colorectal Anastomosis from Leakage

Colorectal anastomotic leakage (AL) is a serious complication in colorectal surgery leading to high morbidity and mortality rates¹. The incidence of AL varies between 2.5 and 20% ^2-5. Over the years, many strategies aimed at lowering the incidence of anastomotic leakage have been examined^{6, 7}.The cause of AL is probably multifactorial. Etiological factors include insufficient arterial blood supply, tension on the anastomosis, hematoma and/or infection at the anastomotic site, and co-morbid factors of the patient as diabetes and atherosclerosis⁸. Furthermore, some anastomoses may be insufficient from the start due to technical failure.Currently a new device is developed in our institute aimed at protecting the colorectal anastomosis and lowering the incidence of AL. This so called C-seal is a biofragmentable drain, which is stapled to the anastomosis with the circular stapler. It covers the luminal side of the colorectal anastomosis thereby preventing leakage.The C-seal is a thin-walled tube-like drain, with an approximate diameter of 4 cm and an approximate length of 25 cm (figure 1). It is a tubular device composed of biodegradable polyurethane. Two flaps with adhesive tape are found at one end of the tube. These flaps are used to attach the C-seal to the anvil of the circular stapler, so that after the anastomosis is made the C-seal can be pulled through the anus. The C-seal remains in situ for at least 10 days. Thereafter it will lose strength and will degrade to be secreted from the body together with the gastrointestinal natural contents.The C-seal does not prevent the formation of dehiscences. However, it prevents extravasation of faeces into the peritoneal cavity. This means that a gap at the anastomotic site does not lead to leakage.Currently, a phase II study testing the C-seal in 35 patients undergoing (colo-)rectal resection with stapled anastomosis is recruiting. The C-seal can be used in both open procedures as well as laparoscopic procedures. The C-seal is only applied in stapled anastomoses within 15cm from the anal verge. In the video, application of the C-seal is shown in an open extended sigmoid resection in a patient suffering from diverticular disease with a stenotic colon.     

The use of prostacyclin analogue-containing suture for the prevention of postoperative venous thrombosis in the rat

The ability of prostacyclin analogue incorporated into a controlled-release suture to prevent postoperative venous thrombosis was investigated. Thirteen rats underwent bilateral transection and anastomosis of the common femoral vein. In each animal, polycaprolactone suture containing 0.25 micrograms/cm of the prostacyclin analogue Iloprost (Schering Ag, Berlin, West Germany) was used to perform the anastomosis on one vessel. Similar suture without prostacyclin analogue was used on the contralateral vessel, which served as a control. Functional patency and luminal surface morphology were assessed 24 hours postoperatively. All anastomoses performed using suture containing prostacyclin analogue were patent. Among controls, five anastomoses were patent and eight were occluded. This difference was highly significant (p less than 0.005). All anastomoses performed with prostacyclin analogue-containing suture exhibited a uniform absence of thrombosis. In contrast, eight control veins exhibited a dense, well-organized fibrinous clot that filled the entire lumen, effectively sealing off the vessel. These results suggest that the prostacyclin analogue released from the suture was highly effective in inhibiting thrombus formation without adversely affecting the vessel's ability to achieve hemostasis.     

Mechanical remodeling of small-intestine submucosa small-diameter vascular grafts--a preliminary report

Small-intestine submucosa (SIS) is cell-free, 100-mu-thick collagen derived from the small intestine. It has been used as a vascular graft and has the highly desirable ability to be remodeled to become histologically indistinguishable from native adjacent artery. To date there has been limited reporting of its preimplantation and explant mechanical properties as a vascular graft. In this study, compliance, elastic modulus, and burst pressure were measured on preimplant-tested 5- and 8-mm SIS grafts and two 60-day remodeled grafts. Seven prefabricated grafts were implanted in the carotid (n = 7) in dogs, which were sacrificed after 55-63 days. The animals (n = 4) weighed from 22 to 27 kg. One dog received a unilateral carotid graft, and 3 dogs received bilateral carotid grafts. The fabrication technique employed hand-suturing with either nonresorbable or resorbable sutures. None of the grafts had a patency failure. Angiograms taken at 1 month and just before explantation showed uniform flow and no dilation. At the time of explantation, all carotid grafts were found to be encased in fibrous tissue. The grafts made with nonresorbable sutures showed thicker tissue growth at the suture line compared with those made with the resorbable sutures. Along the suture line, the grafts made with resorbable sutures exhibited a more natural color than those sutured with nonresorbable sutures. When the explanted carotid grafts were slit open, the lumen was white, shiny, and glistening. The grafts sutured with nonresorbable sutures exhibited small areas of fibrin and red blood cells when the suture was within the lumen. The resorbable-sutured grafts did not exhibit this response. The mean compliance (percent diameter increase for a pressure rise from 80 to 120 mm Hg) was on average 4.6% (range, 2.9%-8.6%) for the 5-mm preimplant-tested grafts. For the 8-mm preimplant-tested grafts, the increase in diameter for the same pressure rise was 8.7%, on average (range, 7.2% to 9.5%). For comparison, the small-diameter SIS graft at the time of implantation was about one half as compliant as the adjacent dog carotid artery, about 4 times more compliant than a typical vein graft, and more than 10 times more compliant than synthetic vascular grafts. The compliance measured on two 60-day carotid grafts was 10.5% and 7.2%, respectively. This is midway between the original compliance value and the compliance of a typical canine carotid artery (14%), indicating that mechanical remodeling occurred. The modulus of elasticity (E) increased exponentially with increasing pressure according to E = E0e alpha P, where E0 is the zero-pressure modulus and alpha is the exponent that describes the rate of increase in E with pressure; the unit of measure for variables E, E0, and P is g/cm2. The mean value for E0 was 4106 gm/cm2 (range, 1348-5601). The mean value for alpha was 0.0059 (range, 0.0028-0.0125). At 100 mm Hg, the mean value for E was 8.03 x 10(6) dynes/cm2 (range, 4.95-15.7 x 10(6)). For a 60-day SIS graft implant, the elastic modulus at 100 mm Hg decreased from a high value at implant time to twice that of a typical native canine carotid artery. The mean burst pressure for 5.5-mm grafts was 3517 mm Hg (range, 2069-4654). The burst pressure of the remodeled carotid grafts averaged 5660 mm Hg. The burst pressure for a typical carotid artery is about 5000 mm Hg. The results of this preliminary study complement those of previous SIS-vascular-graft studies and add a new factor, namely that the mechanical properties of the remodeled graft approach those of the vessel it replaces.     

Use of the vascular closure staple clip applier for microvascular anastomosis in free-flap surgery

We report our initial experience using the vascular closure staple clip applier (a nonpenetrating titanium clip applied in an interrupted, everting fashion) for microvascular anastomosis in free-flap surgery. In total, 153 anastomoses were performed in 87 free flaps (174 potential anastomoses) using the vascular closure stapler between October of 1997 and June of 1999. In 66 flaps, both the arterial and venous anastomosis were performed with the clip applier, whereas in 21 flaps only the venous anastomosis was performed using the clips. A total of 146 anastomoses were performed in an end-to-end fashion, and seven were performed end-to-side. Of the 87 flaps there were 53 TRAM flaps, seven bilateral TRAM, five latissimus dorsi, four gastrocnemius, three rectus abdominis, two radial forearm fibula, and four Rubens fat-pad flaps. Seventy flaps were used for breast reconstruction, seven flaps for lower limb reconstruction, four flaps for head and neck reconstruction, and six flaps for chest wall/trunk reconstruction. There were no postoperative anastomotic complications of bleeding, thrombosis, or need for revision (100 percent patency rate), with a significantly reduced time for completion of anastomoses. The clip applier is a safe, reliable method for performing microvascular anastomoses, allowing reduced operating time and possible cost savings in free-flap surgery.     

Microvascular anastomoses in irradiated vessels: a comparison between the Unilink system and sutures

A new mechanical device (the Unilink system) was compared to conventional suture anastomoses in irradiated microvessels. Twenty rabbits received a single radiation dose of 20 Gy from a 7-MeV electron source through an anterior neck field. One and 6 months following irradiation, the carotid arteries and facial veins were divided and anastomosed on one side with the Unilink system and on the other side with suture technique. At sacrifice 4 weeks postoperatively, all vessels were evaluated for patency and histologic changes associated with radiation and anastomotic trauma. Histology disclosed severe radiation changes. Also, intimal hyperplasia was consistently found at the anastomotic sites in the arteries, while it was totally absent in the venous anastomoses. Occlusive thrombosis was found in two arteries, one anastomosed with the Unilink system and one sutured. Two other arteries, one from each group, had subtotal occlusions at the anastomotic site. No occlusions occurred in any of the venous anastomoses. The overall patency in this study was 97.5 percent, with no difference between the two techniques.     

大鼠颈部自体静脉移植模型两种吻合方法的比较

目的比较间断吻合和连续吻合法建立静脉桥狭窄动物模型的优劣。方法SD大鼠20只,分成两组（间断吻合组和连续吻合组）,取颈外静脉与颈总动脉行端端吻合。术后4周取下静脉桥,观察桥管通畅性,分析新生内膜与中膜的厚度、面积比。结果连续组与间断组相比手术时间更短,出血更少,但桥管通畅率低,两组内膜增生程度没有显著差异。结论连续吻合用时短,出血少,对术者要求更高,较易形成吻合口狭窄。两者造模效果一样。     

Comparison of the hemodynamics in 6mm and 4-7 mm hemodialysis grafts by means of CFD

The aim of our study is to investigate with computational fluid dynamics (CFD) whether different arterial anastomotic geometries result in a different hemodynamics at the arterial (AA) and venous anastomosis (VA) of hemodialysis vascular access grafts. We have studied a 6mm graft (CD) and a 4-7 mm graft (TG). A validated three-dimensional CFD model is developed to simulate flow in the two graft types. Only the arterial anastomosis (AA) geometry differs. The boundary conditions applied are a periodic velocity signal at the arterial inlet and a periodic pressure wave at the venous outlet. Flow rate is set to 1,000 ml/min. The time dependent Navier-Stokes equations are solved. Wall shear stress (WSS), wall shear stress gradient (WSSG) and pressure gradient (PG) are calculated. Anastomotic flow is asymmetric although the anastomosis geometry is symmetric. The hemodynamic parameters, WSS, WSSG and PG, values at the suture line of the arterial anastomosis of the TG are at least twice as much as in the CD. Comparing the parameters at the two AA indicate that little flow rate increase introduces the risk of hemolysis in the TG whereas the CD is completely free of hemolysis. The hemodynamic parameter values at the venous anastomosis of the CD are 24 till 35% higher compared to the values of the TG. WSS values (> 3 Pa) in the VA are in the critical range for stenosis development in both graft geometries. The zones where the parameters reach extreme values correspond to the locations where intimal hyperplasia formation is reported in literature. In all anastomoses, the hemodynamic parameter levels are in the range where leucocytes and platelets get activated. Our simulations confirm clinical results where TG did not show a better outcome when compared to the CD.     

Is there a haemodynamic advantage associated with cuffed arterial anastomoses?

The development of intimal hyperplasia at arterial bypass graft anastomoses is a major factor responsible for graft failure. A revised surgical technique, involving the incorporation of a small section of vein (vein cuff) into the distal anastomosis of PTFE grafts, results in an altered distribution of intimal hyperplasia and improved graft patency rates, especially for below-knee grafts. Numerical simulations have been conducted under physiological conditions to identify the flow behaviour in a typical cuffed bypass model and to determine whether the improved performance of the cuffed system can be accounted for by haemodynamic factors. The flow patterns at the cuffed anastomosis are significantly different to those at the conventional end-to-side anastomosis. In the former case, the flow is characterised by an expansive, low momentum recirculation within the cuff. Separation occurs at the graft heel, and at the cuff toe as the blood enters the recipient artery. Wall shear stresses in the vicinity of the cuff heel are low, but high shear stresses and large spatial gradients in the shearing force act on the artery floor during systole. In contrast, a less disturbed flow prevails and the floor shear stress distribution is less adverse in the conventional model. In conclusion, aspects of the anastomotic haemodynamics are worsened when the cuff is employed. The benefits associated with the cuffed grafts may be related primarily to the presence of venous material at the anastomosis. Therefore, caution is advised with regard to the use of PTFE grafts, pre-shaped to resemble a cuffed geometry.     

Sequential venous anastomosis design to enhance patency of arterio-venous grafts for hemodialysis

Arterio-venous grafts (AVGs), the second best option as long-term vascular access for hemodialysis, face major issues of stenosis mainly due to development of intimal hyperplasia at the venous anastomosis which is linked to unfavorable hemodynamic conditions. We have investigated computationally the utility of a coupled sequential venous anastomotic design to replace conventional end-to-side (ETS) venous anastomosis, in order to improve the hemodynamic environment and consequently enhance the patency of AVGs. Two complete vascular access models with the conventional and the proposed venous anastomosis configurations were constructed. Three-dimensional, pulsatile blood flow through the models was simulated, and wall shear stress (WSS)-based hemodynamic parameters were calculated and compared between the two models. Simulation results demonstrated that the proposed anastomotic design provides: (i) a more uniform and smooth flow at the ETS anastomosis, without flow impingement and stagnation point on the artery bed and vortex formation in the heel region of the ETS anastomosis; (ii) more uniform distribution of WSS and substantially lower WSS gradients on the venous wall; and (iii) a spare route for the blood flow to the vein, to avoid re-operation in case of stenosis. The distinctive hemodynamic advantages observed in the proposed anastomotic design can enhance the patency of AVGs.     

Mechanical anastomosis of small arteries and veins with the unilink apparatus: a histologic and scanning electron microscopic study

A new method for mechanical anastomosis of small vessels--the Unilink device--has been tested in 23 rabbits. A total of 81 arterial and venous anastomoses were performed. One of the arterial anastomoses were thrombotized, while the remaining 80 anastomoses were fully patent at 2 or 16 weeks. The repair process at the anastomotic site was very rapid both in arteries and veins. The endothelialization was complete at 2 weeks, but a marked atrophy of the media was noted in the arterial anastomoses. The same phenomenon was observed in the venous anastomosis, but to a much lesser degree. Thrombus formation was extremely rare, and the atrophy of the media did not seem to affect the patency rate. The experiment has confirmed that the Unilink method provides a very safe, fast, and simple way to perform microvascular anastomoses.     

兔颈动、静脉移植桥血管狭窄模型的建立及其电镜观察

目的：建立兔颈动、静脉移植血管桥动物模型,观察移植桥血管内膜增生和狭窄的电镜下表现。方法：通过兔双侧颈动脉进行动脉桥和静脉桥的移植,形成双侧移植血管桥再狭窄动物模型。在第8周施行血管桥移植手术的同时留取右侧颈动静脉标本作为对照血管,再分别于第12周、16周和第20周分别处死模型兔,采集移植桥血管标本,在光镜下测量其内膜厚度、面积、狭窄度,并进行电镜观察。结果：颈动脉和颈静脉桥移植后,随着时间的延长,桥血管的出现平滑肌迁移,脂质沉积,内膜增生,血管狭窄等改变,且以静脉桥血管的病理改变更为明显。结论：在兔形成动脉粥样硬化病变基础上,进行双侧颈动脉血管桥的移植,建立兔双侧颈动脉移植血管桥再狭窄动物模型,有利于设立自身对照,研究术后动静脉桥再狭窄差异机制;建立动、静脉桥后,位于血管中膜的平滑肌细胞出现向血管内膜迁移现象,说明中膜平滑肌细胞迁移进入内膜导致新内膜形成是血管再狭窄的重要环节。     

Sutureless microvascular anastomoses by a biodegradable laser-activated solid protein solder.

A new sutureless technique to successfully anastomose the abdominal aorta of rats (1.3 mm in diameter) by using a fully biodegradable, laser-activated protein solder is presented. A total of 90 rats were divided into two groups randomly. In group one, the anastomoses were performed by using conventional microsuturing technique, whereas in group two, the anastomoses were performed by using a new laser welding technique. In addition, each of the two groups were divided into five subgroups and evaluated at different follow-up periods (10 minutes, 1 hour, 1 day, 1 week, and 6 weeks). At these intervals, the anastomoses were evaluated for patency and tensile strength. Three anastomoses in each subgroup were processed for light and electron microscopy. All anastomoses were found to be patent. The mean clamp time of the anastomoses performed with conventional suturing was 20.6 minutes compared with 7.2 minutes for the laser-activated welded anastomoses (p < 0.001). The strain measurements showed a stronger mechanical bond of the sutured anastomoses in the initial phase. However, at 6 weeks the tensile strength of the laser-welded anastomoses was higher compared with the conventional suture technique. Histologic evaluations revealed a near complete resorption of the solder after 6 weeks. The junction site of the vessel ends cannot be determined on the luminal side of the artery. In conclusion, a resorbable protein used as a solder, activated by a diode laser, can provide a reliable, safe, and rapid arterial anastomosis, which could be performed by any microsurgeon faster than conventional suturing after a short learning curve.     

Viability of the kidney following autovenoplasty of its artery]

A segment of one of the renal arteries of the dog was substituted for a piece of the femoral vein of the same dog. Along the site of vascular anastomoses the kidney was excluded from general blood circulation. The results of the vessel plastics were not always favourable. Inspite of the independence of anastomoses in the course of operation, the lumen of the substituted piece of the renal artery underwent deformity in a number of experiments, the circulation of the kidney was disturbed, the parenchyma of the organ was injured, a part of renal bodies and tubules were atrophied, intraorganic vessels, especially glomeruli were reconstructed. The alterations were of focal character. In general the structure of the kidney was preserved. In most experiments the substitution of the renal artery for the own vein did not cause any disorders. The wall of the transplanted vein was soon reconstructed--artealized, the renal parenchyma kept normal structure. The success of vascular plastics and the full value of blood circulation was controlled by removing the twin organ. Animals with one kidney lived practically unlimited time without obvious disorders, the content of nitrogen in the blood was normal, no alterations were found in intraorganic vessels and the renal parenchyma.     

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.     

A novel technique for loading of paclitaxel-PLGA nanoparticles onto ePTFE vascular grafts

The major cause of hemodialysis vascular access dysfunction (HVAD) is the occurrence of stenosis followed by thrombosis at venous anastomosis sites due to the aggressive development of venous neointimal hyperplasia. Local delivery of antiproliferative drugs may be effective in inhibiting hyperplasia without causing systemic side effects. We have previously demonstrated that paclitaxel-coated expanded poly(tetrafluoroethylene) (ePTFE) grafts, by a dipping method, could prevent neointimal hyperplasia and stenosis of arteriovenous (AV) hemodialysis grafts, especially at the graft-venous anastomoses; however, large quntities of initial burst release have remained a problem. To achieve controlled drug release, paclitaxel (Ptx)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (Ptx-PLGA-NPs) were prepared by the emulsion-solvent evaporation method and then transferred to the luminal surface and inner part of ePTFE vascular grafts through our micro tube pumping and spin penetration techniques. Scanning electron microscope (SEM) images of various stages of Ptx-PLGA-NPs unequivocally showed that micro tube pumping followed by spin penetration effectively transferred Ptx-PLGA-NPs to the inner part, as well as the luminal surface, of an ePTFE graft. In addition, the in vitro release profiles of paclitaxel demonstrated that this new system achieved controlled drug delivery with a reduced initial burst release. These results suggest that loading of Ptx-PLGA-NPs to the luminal surface and the inner part of an ePTFE graft is a promising strategy to ultimately inhibit the development of venous neointimal hyperplasia.     

Experimental studies in animals on the use of a fibrin glue from the human plasma fraction Cohn I in nerve reconstruction

In order to compare the effects of suture and glue direct nerve connections and nerve transplantations in the sciatic nerve in rats were performed. 4, 6 and 12 weeks later, the nerve anastomosis were histologically studied. In the direct nerve connections, despite a single holding suture, dehiscences were frequently detected with the penetration of the adhesive between the nerve ends. Due to the exact adaptation with the aid of inserted nerve grafts, the anastomoses could be repaired sutureless successfully using a fibrin glue cuff. Since histologically, in comparison to suture, no foreign body granulomas were found, the findings in the literature could be confirmed. No cicatricial contractions of the anastomoses could be found. In the interfascicular nerve transplantation, comparatively good results may be obtained using the two-component adhesive on the Cohn I-fraction basis.     

Transitional flow at the venous anastomosis of an arteriovenous graft: potential activation of the ERK1/2 mechanotransduction pathway

We present experimental and computational results that describe the level, distribution, and importance of velocity fluctuations within the venous anastomosis of an arteriovenous graft. The motivation of this work is to understand better the importance of biomechanical forces in the development of intimal hyperplasia within these grafts. Steady-flow in vitro studies (Re = 1060 and 1820) were conducted within a graft model that represents the venous anastomosis to measure velocity by means of laser Doppler anemometry. Numerical simulations with the same geometry and flow conditions were conducted by employing the spectral element technique. As flow enters the vein from the graft, the velocity field exhibits flow separation and coherent structures (weak turbulence) that originate from the separation shear layer. We also report results of a porcine animal study in which the distribution and magnitude of vein-wall vibration on the venous anastomosis were measured at the time of graft construction. Preliminary molecular biology studies indicate elevated activity levels of the extracellular regulatory kinase ERK1/2, a mitogen-activated protein kinase involved in mechanotransduction, at regions of increased vein-wall vibration. These findings suggest a potential relationship between the associated turbulence-induced vein-wall vibration and the development of intimal hyperplasia in arteriovenous grafts. Further research is necessary, however, in order to determine if a correlation exists and to differentiate the vibration effect from that of flow related effects.