Venous Prostheses Research Articles

Search for an Optimal Design of a Bioprosthetic Venous Valve: In silico and in vitro Studies

Valve incompetence is a progressive disease of the venous system that may eventually lead to venous hypertension, pain, and ulcers. There is a need for a venous valve prosthesis to replace incompetent valves. Computational and experimental investigations on venous valve design and associated haemodynamics will undoubtedly advance prosthesis design and treatments. Here, the objective is to investigate the effect of venous valve on the fluid and solid mechanics. The hypothesis is that there exists a valve geometry that maximises leaflet shear stress (LSS) but minimises leaflet intramural stress (LIS; i.e., minimise stress ratio=LIS/LSS). To address the hypothesis, fully dynamic fluid-structure interaction (FSI) models were developed. The entire cycle of valve opening and closure was simulated. The flow validation experiments were conducted using a stented venous valve prosthesis and a pulse duplicator flow loop. Agreement between the output of FSI simulations and output of pulse duplicator was confirmed. The maximum flow rates were within 6% difference, and the total flow during the cycle was within 10% difference. The simulated high stress ratio region at the leaflet base (five times the leaflet average) predicted the disease location of the vast majority of explanted venous valves reported in clinical literature. The study found that the reduced valve height and leaflet dome shape resulted in optimal performance to provide the lowest stress ratio. This study proposes an effective design of venous prostheses and elaborates on the correlations of venous valve with clinical observations.

Prosthetic venous valve patient selection by validated physics-based computational models.

There is significant interest in a venous prosthesis to replace insufficient valves. The aim of the current study was to select the patients with hemodynamic conditions most likely to benefit from a valve implant. The hypothesis is that the venous valve prosthesis is most suitable for patients with significant reflux, such as in chronic venous insufficiency (CVI), right heart hypertrophy (RHH), and right heart failure (RHF). Conversely, a prosthetic valve is likely to be of least benefit for deep venous thrombosis (DVT) patients with low flow. To address this hypothesis, fully coupled fluid and solid mechanics computational models were developed and validated in five acute canine implants. The animal-validated simulations were then carried out for the CVI, RHH, RHF, and DVT patients based on literature hemodynamic data. A mechanical stress ratio of leaflet wall stress to fluid wall shear stress was defined to combine the effects of both fluid mechanics and solid mechanics on leaflet function, for which a lower stress ratio is hemodynamically desirable. The simulation results of mean valve flow velocity and percentage valve opening were found to be within 10% of the measurements in canines. The simulations show that the patients in the CVI classes 4 to 6, RHH patients, and RHF patients may have a significant reduction in stress ratio with virtual implant of a prosthetic valve. The DVT patient simulations demonstrate a minimal reduction in the stress ratio. After thrombus removal where flow is restored, however, the prosthetic valve may be helpful for post-thrombotic patients. For patient selections of the venous valve prosthesis, the most suitable patients are the CVI classes 4 to 6, RHH, and RHF patients. The least suitable patients are the DVT patients because a valve is not effective under low-flow conditions. The present study demonstrates a physics-based approach to patient selection that can be tested in future clinical trials.

Varying levels of 6-keto-prostaglandin F1α and thromboxane B2 in serum and endothelialization and hyperplasia in small-diameter grafts seeded with CD34+ bone marrow cells in canines.

The aim of the present study was to investigate the serum levels of 6-keto-prostaglandin (PG)F1α and thromboxane (TX)B2, as well as the endothelialization and hyperplasia of polytetrafluoroethylene (PTFE) and Dacron prostheses seeded with CD34+ cells in medium-term observation. A total of 24 crossbred dogs were randomly distributed into PTFE or Dacron groups. CD34+ cells were isolated from bone marrow aspirate and collected using an immunomagnetic bead-based system. The PTFE or Dacron prostheses were implanted into the abdominal aortic artery and inferior vena cava of the dogs. In each group, 8 dogs were implanted with prostheses that had been seeded with CD34+ cells, while 4 dogs were implanted with prostheses that had been seeded with autogenous blood as a control. Serum concentrations of 6-keto-PGF1α and TXB2 were determined at days 0, 10, 30 and 60 following surgery. The grafts were removed and examined at days 10, 30, 60 and 100 following surgery. Finally, CD34 factor staining was used to identify endothelial cells, while light and electron microscopy were applied to examine endothelialization and patency. The results revealed that confluent endothelial cells appeared on the neointima of prostheses seeded with CD34+ cells at day 30 following surgery. In the control groups compared with the experimental groups, there were fewer endothelial cells and the neointima was significantly thicker in the arterial (PTFE, 174±1.41 vs. 117±2.83 μm, respectively; P=0.001; Dacron, 187.5±3.5 vs. 100±1.41 μm, respectively; P<0.001) and venous (PTFE, 230.5±6.36 vs. 135±5.66 μm, respectively; P=0.001; Dacron, 249±2.83 vs. 121.5±3.54 μm, respectively; P<0.001) prostheses. In the experimental groups, intimal hyperplasia in the venous prostheses (PTFE, 135±5.66 μm; Dacron, 121.5±3.54 μm) was more severe compared with that in the arterial prostheses (PTFE, 117±2.83 μm; Dacron, 100±1.41 μm) at day 60. Compared with the 6-keto-PGF1α concentrations in the experimental groups, those in the control groups were significantly lower on day 10 (PTFE, 135±6.01 vs. 80.5±4.35 pg/l, respectively; P=0.001; Dacron, 145±6.54 vs. 81.2±5.10 pg/l, respectively; P<0.001) and were then maintained at a lower level. By contrast, the TXB2 concentration, following marked increases on day 10 in the experimental and control groups (PTFE, 635±32.8 vs. 1,256±63.5 pg/l, respectively; P<0.001; Dacron, 652±30.9 vs. 1,136±53.2 pg/l, respectively; P=0.001), remained at a high level in the control groups. Therefore, the results of the present study indicate that it is possible to achieve rapid endothelialization in PTFE or Dacron prostheses by implanting CD34+ cells. Endothelialization inhibited the reduction in the concentration of 6-keto-PGF1α and the increase in the concentration of TXB2. In addition, endothelialization inhibited excessive intimal hyperplasia and thrombosis. Thus, CD34+ cell seeding provides a theoretical basis for the clinical application of artificial vessel endothelialization.

Sténose des veines pulmonaires après radiofréquence pour fibrillation atriale

Pulmonary vein stenosis is a rare condition with a high mortality. With the advent of radiofrequency ablation for atrial fibrillation a new cause of pulmonary vein stenosis has emerged. We report two cases of severe pulmonary vein stenosis. In the first case the diagnosis was obtained rapidly and balloon angioplasty with stent implantation was performed in the two left pulmonary veins. Recurrent occlusion occurred within the stents, extensive pulmonary infiltrates resembling pulmonary venous infarction developed and the patient died. In the second case the diagnosis was missed initially because the clinical picture suggested thrombo-embolic disease or infection. Balloon angioplasty with stent implantation was performed later. Restenosis occurred after 18 months. These two cases illustrate the frequency with which percutaneously inserted venous prostheses thombose. Clinicians should be familiar with the possibility of the development of pulmonary vein stenosis after radiofrequency ablation for atrial fibrillation. Pulmonary vein stenosis remains a difficult condition to manage. The pulmonary infarction should probably be considered as an urgent indication for surgical resection or even transplantation.

Fluid dynamics of venous valve closure.

In vitro experiment was performed on a stented bovine jugular vein valve (VV, 14 mm I.D. x 2 cm long) and a stentless bovine jugular vein valve conduit (10 mm I.D. x 6 cm long) in a hydraulic flow loop with a downstream oscillatory pressure source to mimic respiratory changes. Simultaneous measurements were made on the valve opening area, conduit and sinus diameter changes using a specially designed laser optic system. Visualization of flow fields both proximal and distal to the venous valve, and the valve opening area were simultaneously recorded by using two video cameras. Laser Doppler anemometer surveys were made at three cross sections: the valve inlet, the valve exist, and 2 cm downstream of the venous valve to quantity flow reflux at valve closure. The experiment confirmed that the VV is a pressure-operated rather than a flow-driven device and that little or no reflux is needed to close the valve completely. The experiment further demonstrated that the VV sinus expands rapidly against back pressure, a critical character to consider in venous prosthesis design.

In vitro endothelialization of a mesosystemic shunt: A clinical case report

The existence of a confluently covering endothelium that is free of any thrombotic appositions can be proved 30 days after clinical implantation of an in vitro endothelialized expanded polytetrafluoroethylene graft. The recipient of the mesosystemic H-graft was a 69-year-old man who had a thrombosed portal vein following pancreatitis. Autologous endothelial cells were obtained from the external jugular vein under local anesthesia, applying the in situ cannulation technique. After low-density plating, first-passage mass cultures of 1.22 x 10(6) endothelial cells were obtained 14 days after vein excision. After precoating was accomplished with fibrinolytically inhibited fibrin glue, a 10 mm expanded polytetrafluoroethylene graft was confluently lined with the autologous endothelial cells at a seeding density of 1.2 x 10(5) cells/cm2. After a maturation period of an additional 9 days and the microbiologic exclusion of a possible infection, an 11 cm graft segment was implanted between the superior mesenteric vein and the inferior vena cava. In spite of a patent shunt the patient had a repeat bleeding episode, needed parenteral nutrition, and died of sepsis on day 30. Immediately after the graft had been taken out, specimens were processed by scanning electron microscopy and light microscopy for the immunohistochemical proof of the endothelial nature of the surface-covering cell layer. The entire graft surface displayed a confluent cell lining that was free of any thrombotic appositions. A strongly positive stain result for both factor VIII-related antigen and the fixation-resistant CD34 molecule identified these cells as endothelial. No alpha-actin-positive cells could be detected. The underlying protein matrix was well preserved and unaltered in thickness and appearance, compared with preimplantation samples. None of the specimens showed any evidence of infection. This human demonstration of an intact endothelium on a patent venous prosthesis further establishes in vitro lining as a method that actually creates a persistent and functioning endothelium on a synthetic graft surface.

Ultrastructural analysis of pseudo-intimal hyperplasia of polytetrafluoroethylene prostheses implanted into the venous and arterial systems

To evaluate and compare the pathogenesis of pseudo-intimal hyperplasia (PH) of venous and arterial prostheses, a segment of the inferior vena cava (n = 16) or abdominal aorta (n = 16) was substituted by a 3 mm internal diameter polytetrafluoroethylene tube graft (PTFE, 3 cm long, 30 microns in nodal distance) in albino rabbits. At designated time intervals (3-28 days) after the replacement, graft patency was examined and the dry weights of the intraluminal deposits measured as an indicator of the degree of PH. The harvested grafts were then subjected to an ultrastructural analysis by means of light microscopy (LM), and scanning electron and transmission electron microscopy (SEM, TEM). All the grafts remained patent during the entire observation period. The PH judged by the dry weight was significantly more extensive in the venous than in the arterial prostheses. The PH on day 28, observed by light microscopes was apparently most extensive in the mid-portion of venous prostheses but in the arteria prostheses it was mostly seen at the anastomotic sites. The lining of the intraluminal surface of the prostheses with endothelial-like cells observed by SEM was faster and more extensive in venous than in arterial prostheses. The process of PH in venous prostheses observed by TEM may be divided into the following steps: early thrombosis, phagocytosis of the thrombus, appearance of fibroblasts, growth of endothelial-like cells, appearance of smooth muscle cells, and pseudointimal thickening and proliferation of fibroblasts producing collagen fibrils. The process in arterial prostheses was essentially identical to that in venous prostheses but was much slower and less extensive. From these observations, it was concluded that the formation of PH occurs much faster in venous than in arterial prostheses, although the mechanism of PH is mostly identical in venous and arterial prostheses.

Blood compatibility of venous prosthesis made of textile or non-textile material

To study blood compatibility of venous prosthesis made of textile or non-textile material, the inferior vena cava of 37 rabbits was partly replaced by 3 mm internal diameter synthetic tube graft made of textile material (T: woven tetron) or non-textile material (P: polytetrafluoroethylene). At designated time intervals after the replacement (5 hours to 4 weeks), graft patency was examined and the dry weight of intraluminal deposits was measured. The harvested grafts were then subjected to light and scanning electron microscopy. All the T-grafts were occluded as early as 5 hours after grafting but when ticlopidine was administered prior to the grafting, all the grafts were patent. All the P-grafts were patent up to 4 weeks after grafting, though the amount of intraluminal deposits was increased in a time related manner, narrowing the lumen of the grafts. The luminal surface of the P-grafts harvested at 5 hours after grafting was covered by piles of fibrin networks entrapping erythrocytes without an association of platelet aggregates, which resembles the finding in the T-grafts harvested from the ticlopidine treated rabbits. In the P-grafts, both the proximal and distal luminal surfaces near the anastomosis were fully covered with endothelial cells by 2 weeks and the entire luminal surface was covered with these cells by 4 weeks. From these results, the following conclusions were obtained; (1) P-graft was superior to T-graft for venous prosthesis, which is mainly due to the inertness of P against platelet activation. (2) Though the luminal surface of the P-grafts was completely covered with endothelial cells by 4 weeks after grafting, the lumen was markedly narrowed by intimal hyperplasia.

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.

The pathogenesis of thrombosis in venous prostheses

To evaluate the pathogenesis of thrombosis formation in synthetic venous grafts, the inferior vena cava of rabbits were replaced by woven Tetron (polyethylene terephtalate) grafts. Six animals were assigned as controls without medication (Group A), and 48 animals were randomly assigned to experimental groups as follows: ticlopidine hydrochloride (100 mg/kg/day) was administered orally from 5 days prior to operation to the end of the experiment (Group B); warfarin sodium (0.33 mg/kg/day) was given orally for the same period (Group C); and a combination of ticlopidine hydrochloride (50 mg/kg/day) and warfarin sodium (0.16 mg/kg/day) was administered for the same period (Group D). All the grafts in group A occluded within 3 h. All grafts harvested from groups B and D remained patent at least until the twenty-eighth day after grafting but the lumen was narrowed by intimal hyperplasia. Although the grafts from group C were patent at the seventh day, all grafts occluded with intimal hyperplasia on day 14 and day 28. The dry weight of thrombus in the graft in group B and group D was 39 +/- 3 mg and 30 +/- 2 mg, respectively on day 28. These figures were significantly lower than that of the control group 59 +/- 9 mg at 5 h after the initial heparinisation. Ultrastructural studies with scanning electron microscopy showed that the thrombus in the graft of the control group was composed of platelet aggregates anchored to synthetic fibres and of erythrocytes entrapped in the fibrin network. By day 7, in the groups modified with drugs, sheets of endothelial-like cells extended across both suture lines from the host stumps and extended to the middle of the graft thereafter. Light microscopy revealed that the initimal hyperplasia in groups B, C and D on day 28 were mainly composed of fibroblasts, myoblasts, collagenous fibres and micro-capillaries.(ABSTRACT TRUNCATED AT 250 WORDS)

Late Thrombogenicity of Grafts in the Venous System

Although some previous experiments have demonstrated encouraging early results with venous vascular prosthesis, the long-term results have not been sufficiently investigated. The late thrombogenicity of 12 autogenous vein grafts and eight polytetrafluoroethylene (PTFE) grafts, three of which had been subjected to endothelial seeding, was evaluated 6 months after implantation in the canine venous system by determination of the survival time of the indium-labelled autogenous platelets and of the light and electron microscopic appearance of the graft-to-blood interface. Twelve dogs receiving autogenous vein grafts had a platelet half-life of 64 ± 13 (mean ± s.d.) hours and a completely thrombus-free internal graft surface covered by a smooth endothelium. The platelet half-life in five dogs with non-seeded PTFE grafts was significantly ( P &lt; 0.01) shorter (44 ± 11h). The PTFE-to-blood interface consisted of a 100- to 170-μm-thick pseudointima with a thrombus-free surface area of 25-90% and substantial endothelial coverage in only two animals. Three dogs receiving endothelial-seeded PTFE grafts had a platelet half-life of 38, 46 and 53h, respectively, a 10- to 80-μm-thick pseudointima covered with typical endothelium, and a thrombus-free surface area of 90-100%. Our results demonstrate that PTFE grafts are still thrombogenic at 6 months following implantation in the canine venous system. Therefore, additional measures are required to maintain graft patency. Our limited experience with endothelial seeding does not allow any definite conclusions, but our findings indicate that this procedure might be beneficial.

Patency in canine inferior vena cava grafting: Effects of graft material, size, and endothelial seeding

We studied 117 inferior vena cava (IVC) replacements in dogs to determine the effects of graft material, graft size, endothelial seeding, and cultured endothelial linings on graft patency. As a control, the IVC was removed and reimplanted in 11 dogs. Dacron (n = 7) and expanded polytetrafluoroethylene (e-PTFE) grafts (n = 12) were seeded immediately with the use of enzymatically derived autogenous jugular vein endothelium. Cultured linings were prepared for e-PTFE grafts (n = 9) by inoculating the graft with jugular endothelium and nurturing the lining in tissue culture for 14 to 30 days before implantation. Unseeded grafts (n = 27) were prepared according to the manufacturer's recommendations. These six methods of preparation were tested in grafts measuring 6 mm I.D. and 60 mm in length. Other sizes were tested with a Latin square study design. After 30 to 60 days the grafts were perfusion fixed and studied with light and transmission electron microscopy. Patency was determined by contrast cavography after 7 and 30 days. Patency in the IVC reimplantation was 100% compared with 28.0% of the e-PTFE (p = 0.001) and none of the Dacron grafts that measured 6 mm I.D. and 60 mm long. e-PTFE and Dacron graft patency also differed significantly (p = 0.035). Seeded and culture-lined e-PTFE grafts in that same size were patent in 31.6% compared with 16.7% of unseeded e-PTFE. With grafts measuring 80 mm long, three of the five e-PTFE grafts were patent between 3 and 7 days. All progressed to occlusion by 30 days and compared poorly with all other graft sizes tested (2.6% progression to occlusion [p = 3 × 10−8]). Recanalization was not seen in 10 occluded grafts that were followed for 60 days. The histologic features of seeded grafts differed remarkably from grafts previously studied in the arterial circulation and from culture-lined and unseeded venous prostheses in that 60% had prominent large, random, endothelium-lined channels within the inner capsule. Larger graft diameters (p = 0.009) and the omission of an endothelial surface treatment (p = 0.004) were associated with anastomotic subendothelial fibrous hyperplasia. We conclude that graft material is the major determinant of patency in IVC replacements, that an extensive endothelial surface promotes patency, but that simply seeding e-PTFE or Dacron grafts with 105 endothelial cells does not provide sufficient endothelium to alter early patency. Graft dimensions are also critical to long-term patency and the development of subendothelial fibrous hyperplasia. Graft recanalization is not a major feature in the healing of synthetic venous replacements.

Venous prostheses: Improved patency with external stents

A uniformly successful prosthesis for replacement in the venous system has not been developed. This study assesses the effect of external stents on the patency of polytetrafluoroethylene (PTFE) grafts in the infrarenal vena cava. Under general anesthesia, 21 mongrel dogs underwent midline laparotomy. The infrarenal vena cava was resected and replaced by a standard segment (8 cm × 10 mm) of stented PTFE (12 dogs) and nonstented PTFE (9 dogs). Patency was assessed by contrast venography and the results compared between the two groups. The 7-, 30-, and 90-day patency was 12 12 , 10 12 , and 9 12 , respectively, for stented PTFE and 6 9 , 2 9 , and 2 9 , respectively, for nonstented PTFE. The patency of externally stented PTFE at 30 and 90 days was significantly better than grafts fashioned from PTFE alone ( P < 0.05 by chi-square analysis). These data demonstrate that external stenting improves the early patency of PTFE prostheses in the infrarenal vena cava. Consideration should be given to the clinical use of externally stented PTFE when prosthetic replacement in the venous system is required.

Inferior vena cava replacement: The role of antiplatelet therapy

To evaluate the effect of ibuprofen on early thrombus formation following inferior vena cava (IVC) replacement, a 4-cm segment of IVC was replaced with a 5-cm (10-mm-i.d.) segment of reinforced polytetrafluoroethylene (PTFE) graft in 12 dogs. Autologous platelets and canine fibrinogen were labeled with 111In and 125I, respectively, and injected into each animal 24 hr prior to vena cava replacement. Six dogs served as controls and six were treated with 12.5 mg/kg ibuprofen intravenously 1 hr preoperatively. All dogs were heparinized with 100 U/kg intravenous heparin prior to crossclamping the IVC: heparin was not reversed at the end of the procedure. Three hours after normal circulation was restored, the grafts were removed and counts of radioactivity made. All grafts were patent. The mean platelet count for the control group was 12.8 X 10(6)/mm2, while in the grafts from the treated group it was 0.960 X 10(6)/mm2. The decreased platelet deposition was significant in all graft segments (P less than 0.01). Fibrin deposition was reduced from 3.38 micrograms/mm2 to 0.25 micrograms/mm2 (P less than 0.01) by ibuprofen. Although fibrin and red blood cells are the major constituents of venous thrombi, platelet aggregation appears to play an important role if prosthetic material is implanted into the venous system. Ibuprofen not only reduced platelet deposition by 13.5-fold, but also reduced fibrin deposition by 13.5-fold. The ratio of platelets to fibrin in control and treated animals was similar (3.84 and 3.79, respectively). These data suggest that antiplatelet medication combined with heparin therapy might decrease early thrombus formation in venous prostheses.

Jugular venous prosthesis on the horse: A preliminary report

Woven dacron vascular prosthesesa were implanted in 6 horses to replace segments of external jugular veins. Anticoagulant therapy using sodium heparin and coumadin was done postoperatively. Clotting profiles and red blood cell counts were determined by measuring activated partial thromboplastin time (APTT), one stage prothrombin time (OSPT), and packed cell volume (PCV). The horses were observed postoperatively for 4 to 38 days. Real time ultrasonography was used to monitor patency of the prostheses. All grafts remained patent during the observation period, although 3 cases of septic thrombosis were seen at necropsy.

Expanded polytetrafluoroethylene as the venous prosthesis

Expanded polytetrafluoroethylene as the venous prosthesis

The mechnical behaviors on nonthrombogenecity

Synthetic polymers suitable for use in the cardiovascular system are needed as biomaterials for heart valve prostheses, artificial heart, veins, arteries and extracorporeal circulatory devices as heart-lung and kidney machines. Despite the wide variety of synthetic polymers that are available in the form of plastics or elastomers, none has proven eligible to clinical application for this purpose as a perfectly nonthrombogenic material. Currently, most investigations seem to be directed toward clarification of the blood biomaterial surface interaction, especially the mechanism whereby thrombi are formed in contact with such prosthetic. In many of these studies the surface properties of synthetic materials are being investigated from the angle where the foreign surface: blood interaction is taken as interface reaction, with the attention focused upon hydrophobicity, hydrophilicity and electronegativity of the materials. Findings obtained in our studies aimed at development of antithrombogenic materials have indicated importance of a definite distribution density of hydrophobicity and hydrophilicity for such polymers; namely, it appears unlikely that no surface factor is involved in the biomaterial: blood interface.Supposing, for example, that a synthetic venous prosthesis with a surface of about 15cm2 be introduced into the vascular system, this newly added surface of about 15cm2 undoubtedly would be so slight as to fall within the limits of errors as compared with the entire inner surface of the cardiovascular system and hence as viewed in terms of the concentration of heparin injected for inhibition of the clotting system. Thus it would be rational to introduce into the study the findings on the surface structure of cells exposed to the cardiovacular lumen. Our studies are based on this ground, pursued through physico-chemical analysis of the interface comprised of the prosthetic surface and the circulating plasma surface. By comparative evaluation of various synthetic polymer prostheses in terms of antithrombogencity, the interfacial condition of the vascular inner surface of the organism was determind to consist of γC(Zis.)=20 to 30erg/cm2, γC=68.5erg/cm2 and γSL(H2O)=0erg/cm2, or the surface endowed both with hydrophilicity and it was demonstrated that a synthetic polymer fulfilling the prerequisites of γC(Zis.)=29 to 30erg/cm2, γC=29 to 30erg/cm2 and γSL(H2O)=0erg/cm2 is remarkably antithrombogenic. The results, stress prime importance of the function of interface to protein at a synthetic polymer surface and indicate the presence of biomate rials with minimal bearing upon the clotting system of blood. Further studies aimed at clarification of the interaction with protein will be pursued, using such materials.

The genesis of thromboresistance in expanded polytetrafluoroethylene venous prosthesis and the similarity of its surface properties with those of the cardiovascular endothelial lining

The genesis of thromboresistance in expanded polytetrafluoroethylene venous prosthesis and the similarity of its surface properties with those of the cardiovascular endothelial lining

Surgical treatment of occlusive arterial disease of the legs.

During the period 1959-68, a total of 982 patients were submitted to treatment for arteriosclerotic vascular lesions in the lower limbs in Department M, Bispebjerg Hospital, Copenhagen. Conservative treatment solely was undertaken in 425 cases, while in addition 271 limbs were amputated after varying periods of conservative therapy or observation. Primary lumbar sympathectomy was undertaken in 25 patients. In the remaining 261 patients, indications were found for arterial reconstruction. In 25 cases explorative intervention only was undertaken. In the remaining 236 patients, 255 reconstructive interventions were undertaken during the period. These comprised 113 thrombendarterectomies, 71 of which were in vessels distal to the inguinal ligament, and 142 by-pass operations. In the latter procedures, five bifurcation prostheses were introduced, 40 simple prostheses with proximal anastomosis to the aorta or the iliac arteries, and 53 synthetic prostheses and 44 venous prostheses with proximal anastomoses to the femoral artery. Eight patients (3.4 percent) died postoperatively, while amputation had to be resorted to in 20 (8 percent). On discharge, pulsation distal to the site of operation was found in 61 percent of the patients discharged, one year later in 44 percent of the survivors and five years later in 23 percent. A total of 62 (24 percent) limbs were amputated on an average of 14 months after operation. 224 cases could be assessed after an average of 4 4/12 years. In 58 cases there was definite clinical improvement and pulsation distal to the site of operation. In 44 cases, pulsation had been present after operation and definite clinical improvement, but no pulsation distal to the reconstructed vessel was found at the follow-up examination. In 122 cases no evident beneficial effect of operation could be demonstrated at follow-up examination. The indications for operation and the incidence of operation are discussed, and the results compared with those of previous publications.

Use of copolymer graft developed to serve in venous prostheses.

Use of copolymer graft developed to serve in venous prostheses.