A Highly Scalable Boundary Integral Equation and Walk-on-Spheres (BIE-WOS) Method for the Laplace Equation with Dirichlet Data

In this paper, we study a highly scalable communication-free parallel domain boundary decomposition algorithm for the Laplace equation based on a hybrid method combining boundary integral equations and walk-on-spheres (BIE-WOS) method, which provides a numerical approximation of the Dirichlet-to-Neumann (DtN) mapping for the Laplace equation. The BIE-WOS is a local method on the boundary of the domain and does not require a structured mesh, and only needs a covering of the domain boundary by patches and a local mesh for each patch for a local BIE. A new version of the BIE-WOS method with second kind integral equations is introduced for better error controls. The effect of errors from the Feynman-Kac formula based path integral WOS method on the overall accuracy of the BIE-WOS method is analyzed for the BIEs, especially in the calculation of the right hand sides of the BIEs. For the special case of flat patches, it is shown that the second kind integral equation of BIE-WOS method can be simplified where the local BIE solutions can be given in closed forms. A key advantage of the parallel BIE-WOS method is the absence of communications during the computation of the DtN mapping on individual patches of the boundary, resulting in a complete independent computation using a large number of cluster nodes. In addition, the BIE-WOS has an intrinsic capability of fault tolerance for exascale computations. The nearly linear scalability of the parallel BIE-WOS method on a large-scale cluster with 6400 CPU cores is verified for computing the DtN mapping of exterior Laplace problems with Dirichlet data for several domains.     

Interior Penalty Discontinuous Galerkin Based Isogeometric Analysis for Allen-Cahn Equations on Surfaces

We propose a method that combines Isogeometric Analysis (IGA) with the interior penalty discontinuous Galerkin (IPDG) method for solving the Allen-Cahn equation, arising from phase transition in materials science, on three-dimensional (3D) surfaces consisting of multiple patches. DG ideology is adopted at patch level, i.e., we employ the standard IGA within each patch, and employ the IPDG method across the patch interfaces. IGA is very suitable for solving Partial Differential Equations (PDEs) on (3D) surfaces and the IPDG method is used to glue the multiple patches together to get the right solution. Our method takes advantage of both IGA and the IPDG method, which allows us to design a superior semi-discrete (in time) IPDG scheme. First and most importantly, the time-consuming mesh generation process in traditional Finite Element Analysis (FEA) is no longer necessary and refinements, including h-refinement and p-refinement which both maintain the original geometry, can be easily performed at any level. Moreover, the flexibility of the IPDG method makes our method very easy to handle cases with non-conforming patches and different degrees across the patch interfaces. Additionally, the geometrical error is eliminated (for all conic sections) or significantly reduced at the beginning due to the geometric flexibility of IGA basis functions, especially the use of multiple patches. Finally, this method can be easily formulated and implemented. We present our semi-discrete IPDG scheme after generally describe the problem, and then briefly introduce the time marching method employed in this paper. Theoretical analysis is carried out to show that our method satisfies a discrete energy law, and achieves the optimal convergence rate with respect to the $L^2$ norm. Furthermore, we propose an elliptic projection operator on (3D) surfaces and prove an approximation error estimate which are vital for us to obtain the error estimate in the $L^2$ norm. Numerical tests are given to validate the theory and gauge the good performance of our method.     

Regional Anesthesia and Pain Targeted thoracic epidural blood patch placed under electrical stimulation guidance (Tsui test)

PURPOSE: This case report describes the use of electrical epidural stimulation (Tsui test) to confirm accurate placement of a thoracic epidural catheter when administering an epidural blood patch for headache management in a patient suffering from spontaneous intracranial hypotension. CLINICAL FEATURES: A 41-yr-old female presented to the Chronic Pain Clinic with a history of postural headache symptoms worsening in severity over several years. Two previous blood patches performed at T11-12 and T10-11 respectively provided short-term relief only. The presumed diagnosis of a spontaneous dural tear was confirmed by a nuclear flow test to be at T2-T4. The epidural site was accessed at T6 with a Tuohy needle. To accurately place the epidural blood patch at the level of the dural tear, the Arrow catheter with electrode adapter was advanced under nerve stimulation guidance to T4. Ten millilitres of autologous blood injected through the catheter was confirmed on magnetic resonance imaging, one hour postprocedure, to lie between T3 and T9. Sustained headache relief was achieved. CONCLUSION: The use of electrical stimulation guidance may be useful when precise epidural blood patch placement is required.     

Evolution of autologous graft interface in rats: experimental study

With purpose to study the evolution of autologous venous graft interface, an experimental model utilizing an autologous venous patch to repair an infrarenal abdominal aortic defect in rats was developed. A small piece of both the jugular vein and the aorta were first excised. After implantation and reestablishment of blood flow, the animals were subsequently sacrificed in groups of 3 at the following intervals: 10 seconds, 1 minute, 10 minutes, 30 minutes, 1 hour, 6 hours, 12 hours, 24 hours, 7 days, 30 days and 90 days. All the patches and adjacent aortae were collected and studied using scanning electron microscopy, with the following results: 1) the endothelial lining of both the autologous vein patch and the adjacent aorta is destroyed before implantation due to operative manipulation; 2) after blood flow reestablishment, the patch and adjacent aortic interfaces are reactive to platelets and other blood cells; 3) New endothelial lining begins to appear from the 7th day after implantation, but the regeneration is not complete at 3 months. From the model, it is deducted that the endothelial repair of autologous venous patch and its adjacent aorta involves a very slow process.     

Current usage and future directions for the bovine pericardial patch

Bovine pericardium (BP) is widely used in surgery and is commonly used as a patch after arteriotomy in cardiovascular surgery. BP patches have several advantages compared with prosthetic patches, including superior biocompatability, easy handling, less suture line bleeding, and possibly reduced rates of infection. These advantages of BP have led to its common use during carotid endarterectomy (CEA). However, long-term clinical results reported after CEA have suggested several issues that may be related to the patch, including restenosis, pseudoaneurysm formation, infection, fibrosis, calcification, and thrombosis. These complications may diminish the long-term efficacy of CEA and suggest potential areas for improvement of surgical patches. Understanding the mechanisms by which BP heals after patch angioplasty may lead to next generation tissue-engineered patches.     

A Two-Dimensional Second Order Conservative Front-Tracking Method with an Original Marker Advection Approach Based on Jump Relations

A two-dimensional front-tracking method is developed for handling complex shape interfaces satisfying the volume conservation. In order to validate the proposed front-tracking method, a complete convergence study is carried out on several analytical test cases for which the interface is widely stretched and deformed. Comparisons to different existing approaches show that our front-tracking method is second order accurate in space with lower errors than existing interface tracking techniques of the literature.We also propose an original marker advection method which takes into account the jump relations valid at interface in order to deal with the contrast of physical properties encountered in two-phase flow simulations. The conservative front-tracking method computed in this work is shown to be able to describe interfaces with high accuracy even for poorly resolved Eulerian grids.     

A Front Tracking Method for the Simulation of Compressible Multimedium Flows

A front tracking method combined with the real ghost fluid method (RGFM) is proposed for simulations of fluid interfaces in two-dimensional compressible flows. In this paper the Riemann problem is constructed along the normal direction of interface and the corresponding Riemann solutions are used to track fluid interfaces. The interface boundary conditions are defined by the RGFM, and the fluid interfaces are explicitly tracked by several connected marker points. The Riemann solutions are also used directly to update the flow states on both sides of the interface in the RGFM. In order to validate the accuracy and capacity of the new method, extensive numerical tests including the bubble advection, the Sod tube, the shock-bubble interaction, the Richtmyer-Meshkov instability and the gas-water interface, are simulated by using the Euler equations. The computational results are also compared with earlier computational studies and it shows good agreements including the compressible gas-water system with large density differences.     

生物补片在疝与腹壁外科的临床应用进展

目前人工合成补片在疝与腹壁外科中应用广泛,并取得良好的效果,但是合成补片具有难以避免的缺点,如补片感染、慢性疼痛、肠粘连、甚至肠瘘等,一旦补片感染则需要移除补片。此外,因合成补片可能增加手术部位感染的概率,故目前不推荐其应用于存在明确污染或感染部位的手术中。生物补片正是针对人工合成补片存在的缺陷而研发出来,它具有耐感染性好、良好组织相容性、完全可吸收等优势。研究证明生物补片可以安全应用于潜在污染或感染部位的疝修补术中。目前生物补片已应用于各种腹壁疝以及腹壁肿瘤、感染或创伤后的腹壁重建等手术中。然而,现阶段有关生物补片的循证医学证据等级较低,不同研究报道生物补片的应用效果差异较大,尚无共识形成,故针对生物补片的临床应用尚需要持谨慎态度。我们期待前瞻性的临床研究来进一步论证生物补片的长期疗效。本文针对生物补片临床应用现状和进展进行简要综述。     

Biosynthetic Nanostructured Cellulose Patch for Chest Wall Reconstruction: Five-Month Follow-up in a Porcine Model

Purpose: Ideal approaches and materials for reconstruction of large chest wall defects remain a topic of debate. We sought to explore the suitability of a reinforced nanostructured cellulose (NC) patch for chest wall reconstruction in an animal model. Materials and Methods: In four domestic pigs, a standardized 10 × 10 cm chest wall defect was created by resecting three rib segments. Subsequently the defect was reconstructed via a biosynthetic NC patch (16 × 12 cm) reinforced by polytetrafluoroethylene mesh. After 1, 2, 4, and 5 months respectively, gross examination of NC patches was performed following sacrifice of the animals. Specimens of NC patches and surrounding connective tissue underwent histological examinations after staining with Hematoxylin-eosin and Elastica van Gieson. Results: All animals survived their observation period without encountering major adverse events. On gross examination all NC patches were intact and well integrated into the surrounding tissue. Histological examination showed clearly demarked zones of foreign body reaction at the patch/host-tissue interface. After 5 months a slight increase in foreign body reaction, fibrous capsule formation and cellular infiltration were observed. No signs of fibroblast proliferation or neovascularization were seen within NC patches at any point. Conclusions: Our findings suggest a quick healing process and good overall biocompatibility following NC patch implantation.NC might prove an efficient and suitable biomaterial for complex chest wall reconstruction.     

A healable filamentous Dacron surgical fabric. Experimental studies and clinical experience

A strong, lightweight, highly compliant Dacron surgical fabric of warp-knit, velour construction has been developed as an outgrowth of research on filamentous tubular vascular prostheses. This material has excellent suturability and conformability, high preclotting efficiency, and is imprinted with calibration marks at 2 cm intervals. Experimentally, iliac artery and descending thoracic aorta patch grafts of this material were completely healed 28 days after implantation in dogs. Light and electron microscopy showed excellent healing. This paper reports clinical results of 119 patches implanted in 109 patients who have been followed for a mean of 26.4 months (range: 16--34 months). Of these, 20 patches were used in arterial reconstructions, and 99 were used in the heart for repair of 95 congenital and four acquired defects. The 20 patch angioplasties were performed in the carotid artery (four patches), subclavian artery, (one patch), common femoral artery, profunda femoris artery, or superficial femoral artery (10 patches), and in the popliteal artery (five patches). This new surgical fabric is easily adaptable to complex angioplasties and for repair of intracardiac abnormalities. No complications intrinsic to the surgical fabric have been observed in clinical use of this material in 109 patients.     

Numerical Simulation of Compressible Vortical Flows Using a Conservative Unstructured-Grid Adaptive Scheme

A two-dimensional numerical scheme for the compressible Euler equations is presented and applied here to the simulation of exemplary compressible vortical flows. The proposed approach allows to perform computations on unstructured moving grids with adaptation, which is required to capture complex features of the flow-field. Grid adaptation is driven by suitable error indicators based on the Mach number and by element-quality constraints as well. At the new time level, the computational grid is obtained by a suitable combination of grid smoothing, edge-swapping, grid refinement and de-refinement. The grid modifications—including topology modification due to edge-swapping or the insertion/deletion of a new grid node—are interpreted at the flow solver level as continuous (in time) deformations of suitably-defined node-centered finite volumes. The solution over the new grid is obtained without explicitly resorting to interpolation techniques, since the definition of suitable interface velocities allows one to determine the new solution by simple integration of the Arbitrary Lagrangian-Eulerian formulation of the flow equations. Numerical simulations of the steady oblique-shock problem, of the steady transonic flow and of the start-up unsteady flow around the NACA 0012 airfoil are presented to assess the scheme capabilities to describe these flows accurately.     

Pericardium as a thoracic aortic patch: glutaraldehyde-fixed and fresh autologous pericardium

The repair of complex coarctation of the aorta often requires an aortic patch. Prosthetic patches lack growth potential and are associated with an increased incidence of aneurysm formation opposite the patch. We compared buffered glutaraldehyde-fixed patches, used in six animals (group 1), and untreated autologous pericardial aortic patches, used in five animals (group 2). Weanling pigs underwent pericardial patch replacement of a 1 X 2-cm diamond-shaped segment of the lateral wall of the descending thoracic aorta at the level of the aortic isthmus. Six months following patch aortoplasty, the animals were killed and the in situ patch dimensions were measured and compared to the measurements obtained at implantation. The increases in length, recorded as mean percentage change +/- SEM, were 34.7 +/- 3.7% for group 1 and 102.8 +/- 20.3% for group 2 animals; the increases in width were 91.4 +/- 31.7% for group 1 and 192.4 +/- 31.4% for group 2. The percentage changes for both length and width were significantly different between groups (P less than 0.05). Pull strength testing of standard-size patch samples demonstrated no significant difference in tensile breaking load between groups: group 1 = 959 +/- 277 g, group 2 = 795 +/- 86 g. Thoracic aortography revealed no evidence of stenosis or aneurysmal dilation in either group. Autologous pericardium is resilient, strong, and readily available and has expansile potential that makes it an ideal aortic patch material. We conclude that glutaraldehyde fixation does not provide additional strength and limits graft expansile potential when compared to untreated pericardium.     

An Improved Gas-Kinetic Scheme for Multimaterial Flows

The efficiency of recently developed gas-kinetic scheme for multimaterial flows is increased through the adoption of a new iteration method in the kinetic non-mixing Riemann solver and an interface sharpening reconstruction method at a cell interface. The iteration method is used to determine the velocity of fluid interface, based on the force balance between both sides due to the incidence and bounce back of particles at the interface. An improved Aitken method is proposed with a simple hybrid of the modified Aitken method (Aitken-Chen) and the Steffensen method. Numerical tests validate its efficiency with significantly less calls to the function not only for the average number but also for the maximum. The new reconstruction is based on the tangent of hyperbola for interface capturing (THINC) but applied only to the volume fraction, which is very simple to be implemented under the stratified framework and capable of resolving fluid interface in mixture. Furthermore, the directional splitting is adopted rather than the previous quasi-one-dimensional method. Typical numerical tests, including several water-gas shock tube flows, and the shock-water cylinder interaction flow show that the improved gas-kinetic scheme can capture fluid interfaces much sharper, while preserving the advantages of the original one.     

Sandwich technique for closing of the large muscular Swiss-cheese type ventricular septal defects

A 9-year-old girl, who has had a diagnosis as a Taussig-Bing anomary, underwent an original Jatene procedure (o-J) 2 months after birth. This time, she had a diagnosis of the muscular multiple ventricular septal defects (mVSD) and pulmonary stenosis after o-J. The mVSD was Swiss-cheese type and was large from the proximal of the infundibular septum to the apex and posterior of the septum. It was closed by the sandwich technique using a pair of felt patches, which of one was placed at right ventricular side and the other was at left ventricular side, slightly larger than the whole area of the mVSD. The patch fixation was placed with 1 stitch at the center between the patches and a few stitches around the right ventricular side patch to the ventricular septum. Postoperative cardiac function was uneventful regardless of the very large patches placed at the ventricular septum and the cardiac catheterization after 1 year postoperatively showed the pulmonary/systemic blood flow ratio was 1.0. This technique for the closure of the large Swiss-cheese type mVSD can be considered to be very effective.     

In vivo and mechanical properties of peritoneum/fascia as a novel arterial substitute

OBJECTIVE: This study evaluates the efficacy of bovine peritoneum/fascia as an arterial substitute. METHODS AND OUTCOME MEASURES: Twelve dogs underwent bilateral femoral artery patch angioplasty with a glutaraldehyde-fixed bovine peritoneal/fascial patch (PFA patch) on one side and polyester patch on the contralateral side. Arteriograms were performed just before vessel harvest at 1 and 6 months, and vessels were evaluated for aneurysms and inflammation. Histologic analysis included intima area, media thickness, and lumen area. Immunofluorescence for CD 34 and Factor VIII was done to evaluate endothelialization and alpha-actin for smooth muscle cell growth. Mechanical strength testing was evaluated in separate PFA patches and compared independently to a commercially available bovine pericardial patch and polyester patch. RESULTS: All vessels examined at both 1 and 6 months were patent with no arteriographic evidence of stenosis. There was no evidence of aneurysm formation in any vessel and no difference between groups in inflammatory reaction. One polyester patch at 1 month developed an infection. Microscopic evaluation of experimental vessels revealed no difference between groups in intima area at 1 month (2.1 +/- 1.2 vs 2.2 +/- 1.2 mm 2 ; P = .5) and at 6 months (1.81 +/- 1.2 vs 1.9 +/- 1.2 mm 2 ; P = .5). There was no difference in media thickness, but the PFA patch group had a greater lumen area at 1 month (8.8 +/- 2.9 vs 9.8 +/- 3.0 mm 2 ; P = .02) and 6 months (10.5 +/- 4.2 vs 11.7 +/- 5.6 mm 2 ; P = .02). Immunofluorescence for CD34 and Factor VIII demonstrated complete re-endothelialization of all patches. The polyester patch had a chronic inflammatory response, but not the PFA patch. Mechanical strength testing demonstrated that compared to pericardium, the PFA patch had superior ( P < .05) failure tension, stiffness, and suture pull-out strength, whereas extensibility, fatigue tension, relax slope, and creep tests were not different. Polyester demonstrated superior suture pull-out, stiffness, relax slope, and failure strain ( P < .05), but it was not different in failure tension and extensibility than the PFA patch. However, the PFA patch had significantly less creep (0.25 +/- 0.25 vs 4.92 +/- 0.84; P < .01). CONCLUSIONS: The PFA patch has similar clot-resistant properties to polyester and is superior to the pericardial patch in mechanical strength. It is a promising endothelial alternative for not only arterial patches but other vascular products. CLINICAL RELEVANCE: The search for an artificial, thromboresistant, and intimal hyperplasia resistant interface between blood and native blood vessels still continues. This study demonstrates the feasibility and proof of concept of the peritoneum's clot-resistant properties. When adding the underlying fascia, it serves as an ideal arterial patch. Other studies are underway evaluating its feasibility as a bypass graft and a "drug coated"-like stent lining.     

Aneurysmal expansion of the visceral patch after thoracoabdominal aortic replacement: an argument for limiting patch size?

INTRODUCTION: Thoracoabdominal aortic replacement requires visceral vessel revascularization and is usually performed with Crawford's inclusion technique or a large Carrel patch. This segment of retained native aorta may be prone to recurrent aneurysmal disease. We reviewed our experience with patients in whom aneurysmal expansion of the visceral patch was detected. METHODS: The records of 107 patients undergoing thoracoabdominal aortic replacement operations performed or followed up at the Johns Hopkins Hospital between 1992 and 2000 were reviewed. All patients had visceral patches created for type II, III, or IV aneurysms. Visceral patches were considered aneurysmal if the maximal diameter of the aortic prosthesis and patch was 4.0 cm or more. RESULTS: Patch aneurysmal expansion (mean, 5.4 cm) was detected in eight patients (7.5%). All three women had connective tissue disorders (mean age, 36 years), and all five men had atherosclerotic disease (mean age, 73 years). Five patients were symptom free with their aneurysms detected by surveillance computed tomography scans; two patients had back pain prompting computed tomography scans; and one patient presented with an emergency patch rupture. Aneurysmal patches were successfully revised in three patients. Two patients died in the operating room, and three patch aneurysms (< 5 cm) are still being observed. The mean time to the detection of aneurysmal expansion was 6.5 years after the original operation. Therapy consisted of replacement of a segment of the thoracoabdominal aortic graft and refashioning a smaller patch, including only the visceral artery orifices with separate attachment of the left and possibly right renal artery. CONCLUSIONS: Although Crawford's inclusion method of visceral patch construction is generally durable, patients undergoing thoracoabdominal aortic replacement require yearly surveillance for the detection of aneurysmal expansion of the visceral patch. We recommend limiting visceral patch size at the original operation by routinely excluding the orifice of the left renal artery. Patients at high risk for recurrent aneurysmal expansion, such as those with connective tissue disorders, will benefit from creating small visceral patches and possibly implanting both renal arteries separately during the original operation.     

A Phase-Field Model Coupled with Lattice Kinetics Solver for Modeling Crystal Growth in Furnaces

In this study, we present a new numerical model for crystal growth in a vertical solidification system. This model takes into account the buoyancy induced convective flow and its effect on the crystal growth process. The evolution of the crystal growth interface is simulated using the phase-field method. A semi-implicit lattice kinetics solver based on the Boltzmann equation is employed to model the unsteady incompressible flow. This model is used to investigate the effect of furnace operational conditions on crystal growth interface profiles and growth velocities. For a simple case of macroscopic radial growth, the phase-field model is validated against an analytical solution. The numerical simulations reveal that for a certain set of temperature boundary conditions, the heat transport in the melt near the phase interface is diffusion dominant and advection is suppressed.     

人同种心包补片在法洛四联症分期手术中的应用

目的比较人同种心包补片和G ore-tex补片在法洛四联症(tetra logy of F a llot,TOF)分期手术中扩大右心室流出道(righ t ven tricu lar ou tflow tract,RVOT)的效果。方法28例已行一期手术再行分期手术的TOF患者,按不同的二期或三期手术时间分为两组,G ore-tex组:13例,以G ore-tex补片扩大RVOT;人同种心包补片组:15例,以深低温冷冻保存的人同种心包补片扩大RVOT。比较两组术后临床结果和随访结果。结果G ore-tex补片组术中死亡1例(7.7%),人同种心包补片组术后早期死亡1例(6.7%)。人同种心包补片组住ICU时间、呼吸机使用时间和心包腔引流量均少于G ore-tex补片组(P<0.01)。所有患者均获得随访,随访时间0.8~4.5年,超声心动图检查提示G ore-tex补片组患者术后RVOT水平残余梗阻的比率高于人同种心包补片组(P<0.01),胸部X线片未发现钙化影。结论人同种心包组织致密,缝合后不易渗血,止血方便;且具有良好的弹性和顺应性,有助于降低术后RVOT水平的残余梗阻发生,可作为补片材料在心脏外科手术中应用。     

不同斑试材料和加样剂量对斑试皮肤反应结果的影响

目的：评估斑试材料、剂量、时间、抗原、浓度等因素对斑贴试验结果的影响。方法：采用国际标准（国际标准芬兰小室，Fian—chamber）、日本POLA、中国中亚牌三种材料，对男、女各22名受试者背部进行斑贴试验，浓度为十二烷基硫酸钠（2％、1％、0．5％）、丙二醇（20％、10％）、戊二醇（20％、10％）、原浓度腮红，对照物为生理盐水和蒸馏水。结果：Finn-chamber加样剂量为0．015ml／0．015g，阳性率为15．76％；日本POLA加样剂量为0．05mI／0．05g，阳性率为17．69％；中国中亚牌斑试器加样剂量为0．03ml／0．03g，阳性率为14．11％。日本POLA和中国中亚牌斑试器两组间阳性率有显著差别，其余各组间无差别。十二烷基硫酸钠在24h的反应最高，男性阳性反应率较女性高。结论：按不同的加样剂量检测，国际标准Finn—chamber斑试器加样剂量小、敏感性高，斑贴后的观察时间、抗原浓度以及受试者性别等因素对斑试皮肤反应阳性结果也有影响。     

Differences in neointima formation between impervious and porous polytetrafluoroethylene vascular patch material

The aim of this study was to compare the neointima formation and blood loss of an impervious ePTFE with those of the porous ePTFE patch. Ten mongrel dogs were selected for the study. Both the impervious and porous ePTFE patches were implanted into the common iliac arteries in each dog. The blood loss of each patch was recorded and the patches were explanted 30-60 days later for microscopic analysis. The arteries with either the impervious or the porous ePTFE patch were all patent at the end of the study. The impervious ePTFE patch had a significant reduction in blood loss when compared with the porous ePTFE patch (p = 0.04). The neointima covering both patches showed no statistically significant difference in its thickness or in its cellular composition. It has been speculated that wall porosity is essential for tissue ingrowth, endothelial cell proliferation, and neointima formation. In this study, the impervious ePTFE patch did not inhibit neointima formation. Our study shows that graft porosity does not improve neointima formation or patency. Neointimization of the impervious ePTFE patch is the result of pannus ingrowth and deposition of circulating blood elements. There is a statistically significant reduction in blood loss (p = 0.04) with impervious ePTFE patch, compared with that of the porous ePTFE patch.