A Comparative Evaluation of two Types of Dacron Vascular Prostheses

The function of two types of Dacron vascular prostheses was evaluated in dogs using the abdominal aorta, inferior vena cava and iliac artery as host vessels. The transplants used were woven and knitted DeBakey prostheses and knitted Cooley prostheses. It is concluded that the function of a prosthesis with a diameter less than 5 mm is unsatisfactory. The same is true of a prosthesis implanted on the venous side, even in a large vein, such as the inferior caval vein, with a high flow. There is no significant difference between the function of DeBakey and Denton Cooley prostheses.     

Three years experience with experimental implantation of fibrous polyurethane microvascular prostheses in the rat aorta

The results of a 3-year study in which a series of 355 implantations of 1-cm-long fibrous polyurethane microvascular prostheses into the infrarenal aorta of the rat (group A) were evaluated with respect to patency and formation, structure, and fate of the neo-intima. Rats were sacrificed at various intervals from 1 day to 2 years in order to obtain a time-related impression of the re-endothelialization and stability of the neo-intima. A second series of 51 implants was done with prostheses 10 cm in length, placed in a 1.5-cm loop in the abdominal aorta (group B). An overall patency rate of 92.7% was achieved in group A. Initially, eight technical failures caused early thrombosis of the prostheses. Sixteen prostheses became infected and subsequently occluded. The overall patency in group B was 52.9%, due to kinking from adhesion formation and normal growth of the rat. In both the long and short prostheses, a continuous multilayered neo-intima developed, growing from the aortic stumps into the prosthesis from both sides. According to the growth rate of 0.3 mm/day, a 1-cm prosthesis was re-endothelialized after +/- 20 days and a 10-cm prosthesis after +/- 9 months. Once developed, the neo-intima, consisting of myofibroblasts and smooth muscle cells covered with a flat endothelium, remained stable and continuous, throughout the observation period. The neo-intima was firmly anchored onto the prosthetic wall by means of cellular protrusions extending between the polyurethane fibres. The significance of rapid healing of an implanted prosthesis is emphasized with respect to preventing (late) hematogenous, endogenous infection of the prosthesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Woven vascular microsurgical prostheses in our experimental practice

The authors have been concerned for six years with the development of woven microsurgical prostheses in experiments on laboratory rats, beagle dogs and domestic white pigs. In rats, in 224 experiments employing 38 types of prostheses with an inner diameter of 2 mm, a reliable prosthesis was selected, described as No. 36, with a 100% patency after insertion of a 1 cm long portion into a defect in the abdominal aorta in 40 experiments. The follow-up of this type of prosthesis lasted 12 months. In large animals this type of prosthesis was implanted into a defect of the radial artery and cephalic vein in dogs and into the femoral artery and the artery of a vascular pedicle of groin and lateral thigh flap. These experiments on large animals are not yet complete and will be the subject of a separate paper.     

The influence of inner wall filamentousness on the performance of small- and large-caliber arterial grafts

Dacron prostheses with differing degrees of inner wall filamentousness were implanted in the canine descending thoracic aorta for 56 days (n = 14) and the carotid arteries for 21 days (n = 40). In the thoracic aorta the healed inner capsule of 8 mm internal velour grafts was approximately three times as thick as the inner capsule of external velour knitted prostheses. However, the early patency and rapidity of healing of these two types of prostheses were essentially the same. In the carotid arteries the patency of the 4 mm external velour prostheses was greater than that of the internal velour prostheses and the mean thrombus-free surface area of the external velour grafts was significantly greater than that of the internal velour grafts. These observations suggest that an internal velour surface is not deleterious to early patency in a large-caliber, high-flow artery but that it may be in a small-caliber, low-flow artery.     

Experimental comparison of the thrombogenicity of fibrin and PTFE flow surfaces

Two types of 4 mm ID prostheses were studied in the carotid arteries of the dog. These were noncrimped polypropylene-supported filamentous velour knitted Dacron (PPSFV) and expanded polytetrafluoroethylene (e-PTFE, Gore-Tex). Thrombus-"Free" Surface TFS) areas and patency rates were determined at the end of the implant periods. One series of implants was subjected to controlled low flow rates for six hours; another was exposed to physiologic flow rates and observed at seven days, 14 days, and 12 weeks. At six hours the filamentous Dacron, preclotted according to a specific regimen utilizating heparin, performed as well as, and possibly better than, e-PTFE. The Gore-Tex developed surface coagulum in an irregular fashion which was related to graft wetting and blood soakage. Seven-day TFS scores and patency rates of the two graft types were comparable at physiologic flow rates. At two weeks, TFS scores and patency rates of the two graft types were comparable at physiologic flow rates. At two weeks, TFS scores and patency rates dropped. This was sufficiently marked in the case of e-PTFE that longer-term implants were not done. However, PPSFV grafts were implanted for 12 weeks, and all grafts examined at that time had closed. It appears that patency of 4 mm ID grafts of this construction will not be reliably attained in the dog carotid artery without the use of platelet-inhibitory drugs until complete healing has occurred.     

Long-term patency of regenerated neoaortic wall following the implant of a fully biodegradable polyurethane prosthesis: Experimental lipid diet model in pigs

The degradation of a polyurethane vascular prosthesis, the time course and characteristics of tissue ingrowth and prosthesis replacement, and the incidence of thrombosis have been investigated in 50 young pigs. A 6-7 cm long cone-shaped prosthesis was implanted in the infrarenal aorta of 50 young growing pigs which were sacrificed at intervals from 60 to 365 days. Ten animals were controls, 25 were given aspirin 10 mg/kg of body weight/day, and 15 were fed with cod liver oil. Aortography, done at 30, 60, and 90 days, showed 100% of implants were thrombosed in the surviving controls, 55% of the aspirin group had patent grafts, and 100% of animals in the lipid diet group had patent grafts. At final graft retrieval, the aspirin group showed only three patencies, while in the lipid diet group seven out of nine animals were patent. The laboratory and morphological studies indicated that all patent prostheses were lined with tissue that resembled the intima of native aorta with a layer of smooth muscle cells which appeared complete at 180 days. From these data we conclude that the biodegradable polyurethane vascular prosthesis is reliable for experimental implants in a pig model. The lipid-rich diet of polyunsaturated fatty acids potentiates long-term patency, perhaps by preventing platelet aggregation and thrombosis, and allowing the growth of a neoendothelium and neomedia within the lumen of the prosthesis, which slowly degrade towards fatty tissue and form neoadventitia.     

Experimental studies on application of small-caliber vascular prosthesis produced by polyurethane.

It has been suggested that a microporous structure enhances fast and complete endothelialization. For long-term patency, antithrombogenicity and microporous structure are very important factors. In this paper, we have developed a new technique to give a micro-porous structure to small-caliber vascular prosthesis produced by polyurethane which has favorable antithrombogenecity. A mixed solution (tetrahydrofuran: dimethylformamide = 1:1) containing 13 wt% of segmented polyurethane and a variable amount of calcium carbonate (mean particle size of 8 mm in diameter) was dip-coated on a glass mandril of 3 mm and 6 mm in diameter and placed into distilled water for 24 hours. After the glass mandrill was removed, this polyurethane tube was placed into 1 mmol hydrochloric acid for 1 hour, and a microporous polyurethane vascular prosthesis of 20 mm in length was completed. These prostheses of 3 mm and 6 mm in diameter were implanted into the femoral and the carotid arteries, and the abdominal aorta of the dogs, respectively. Patency was recognized by arteriography and Duplex scanning and the removed grafts were inspected macro- and microscopically. Greater hydraulic permeability of this graft was obtained with an increase in the quantity of calcium carbonate mixed with polyurethane. In elasticity, this graft was more similar to the canine jugular vein than the polytetrafluoroethylene graft. Patency was observed 8 weeks after implantation on the arteriogram, and neointima was observed microscopically on the smooth and lustrous lumen. The new polyurethane vascular prosthesis we developed might provide a potential prosthesis for small-caliber vascular reconstruction.     

New prostheses for venous substitution

In 81 Beagle dogs, 6 cm long segments of the inferior vena cava were replaced end-to-end by artificial vascular grafts (10 mm in diameter) without an av-fistula and anticoagulant drugs. Different graft materials have been used, such as various e-PTFE (30-90 microns fiber length) and polyurethane with low and increased microporosity. e-PTFE with 75 microns fiber length and polyurethane with increased porosity showed the best tissue incorporation, complete endothelialization of the whole length and a high patency rate of 80-85% after a follow-up of 12 months. In contrast to other commercially available vascular grafts (textile woven or knitted, e-PTFE 30 microns) tested in previous series, polyurethane and e-PTFE with increased microporosity had already achieved complete endothelialization after 6-12 weeks. Therefore, these optimized prostheses should be introduced into clinical practice for large venous substitution. Thereafter, an adjunctive av-fistula as protection is probably no longer necessary.     

New small-caliber antithrombotic vascular prosthesis: experimental study

Vascular prostheses with the inner diameter smaller than 1 mm were implanted to the common carotid artery of rats, and their patency was examined. Four types of tubes were prepared for this purpose in Experiment 1: polyethylene (PE), poly-(acrylic acid)-grafted polyethylene (PE-AA), polyacrylamide-grafted polyethylene (PE-AAm), and poly(vinyl alcohol) (PVA) tubes. Comparative studies made using nonsuture anastomosis revealed that the PE-AAm and PVA tubes were antithrombotic, although disconnection was noted at the anastomotic sites within 1 week and 1 month, respectively. Thereafter in Experiment 2, the PVA tubes were implanted to the common carotid artery of 20 rats using conventional anastomosis. Neither anticoagulants nor fibrinolytic agents were used in both series of experiments. Patency of the PVA tubes was 80% after 1 week and 70% after 1 month. In patent cases after 1 month, the luminal surfaces of the prostheses and the host arteries were examined using scanning electron microscopy. The lumen of the arteries and anastomotic sites was covered with endothelial cells, while the lumen of the PVA tubes was free from thrombi and there was no neointima formation. So far, there has been reported no manmade material that has completely antithrombotic property in vivo. However, our studies disclosed that PVA is antithrombotic and one of the most promising materials for the inner surface of small vascular prostheses.     

Long-term evaluation of a new selectively biodegradable vascular graft coated with polyethylene oxide-polylactic acid for right ventricular conduit. An experimental study

Low-porosity woven Dacron grafts have been used extensively as an extracardiac conduit in the surgical treatment of congenital and acquired heart diseases involving total heparinization. Caution is still warranted in their use, however, because of long-term complications, including calcification and development of obstructive fibrous peel. In contrast, high-porosity grafts offer much better tissue anchorage and healing but cannot be used under heparinization. We have developed a compound vascular prosthesis in which a knitted Dacron graft is coated with a polymeric biodegradable sealant. Polyethylene oxide-polylactic acid-segmented copolymers comprised the degradable component of the graft. In vitro studies showed that the coated prosthesis exhibited a highly flexible elastomer-like mechanical response. The prostheses were completely watertight, and significant degradation started after 1 week, with absorption completed after 3 weeks. Seven woven and six knitted polyethylene oxide-polylactic acid-coated Dacron grafts used as extracordiac conduits (16 mm), connecting the right ventricle and the pulmonary artery were implanted in dogs. The dogs were killed after 12 to 18 months, and the results are reported. Scanning electron microscopy examination showed peel detachment and nonhomogenous intimal surface with fenestrations in the woven graft group, but complete healing and incorporation of the pseudointima with homogenous, thin lining of the luminal surface in the polyethylene oxide-polylactic acid-coated group. Histologic studies indicated much superior healing and anchorage of the periprosthetic tissue and the pseudointima in the polyethylene oxide-polylactic acid-coated grafts. The biodegradable polymer was fully degraded and exhibited a complete incorporation of the compound vascular prosthesis. This study indicates the superior healing properties of these selectively biodegradable grafts, which might increase long-term patency and decrease complications of right ventricular conduits.     

Heat-denatured albumin-coated Dacron vascular grafts: physical characteristics and in vivo performance

Dacron fabrics with a wide range of porosities were autoclaved for 3 minutes after being soaked in serum, 5% albumin, or 25% albumin. Porosity of compound Dacron grafts made with 25% albumin was less than 1 ml/min/cm2 regardless of the fabric base, whereas porosity of grafts made with serum or 5% albumin was proportional to the porosity of the base fabric. Porosity of the compound grafts remained stable for more than 48 hours and to pressure greater than 450 mm Hg, if the grafts were kept moist. Tubes of Marlex mesh coated with heat-denatured albumin, implanted as infrarenal aortic replacements in dogs, showed complete albumin absorption by 3 weeks. However, perigraft tissue reaction and graft incorporation were minimal and extensive false aneurysm formation resulted. Knitted filamentous Dacron 6 mm tubes coated with heat-denatured albumin were implanted as iliofemoral bypass grafts in 12 dogs, with blood-preclotted knitted filamentous Dacron grafts implanted as contralateral control grafts. Comparison of the albumin-coated grafts with the blood-preclotted control grafts showed no differences in healing or patency at 4 to 6 months. Heat-denatured 25% albumin forms a strong and hemostatic coating regardless of fabric base. Albumin-Dacron compound grafts are easily and rapidly made in the operating room, handle well, and are suitable for large and medium-sized arterial replacements without changes in healing or patency. Because of slow tissue incorporation, however, albumin-coated knitted Dacron grafts should be avoided in patients who require long-term anticoagulation therapy.     

Haemodynamic aspects of lower limb arterial reconstruction using Dacron and Goretex prostheses

We have studied some haemodynamic consequences of vascular grafts of less than 8 mm diameter by animal studies on dogs before and after aortofemoral bypass with either knitted Dacron 5 mm internal diameter (6 dogs) or Goretex 6 mm internal diameter (7 dogs) prostheses between 17 and 24 cm in length. Both materials gave an increased velocity of pulse wave transmission for pressure and flow and an increase in resistance to pulsatile flow. The effects were more severe with Dacron than with Goretex. Pressure index and pressure pulsatility were not significantly altered, but flow pulsatility index, peak flow rate, and peak flow acceleration were all significantly reduced after both implants. These results are due to mismatching of mechanical properties leading to an increased impedance to pulsatile flow.     

Clinical Trial of New Polyurethane Vascular Grafts for Hemodialysis: Compared with Expanded Polytetrafluoroethylene Grafts

Abstract: We developed a new polyurethane vascular access graft coated with gelatin and reinforced with knitted polyester fibers (PE-PEUG). Advantages over expanded-polytetrafluoroethylene graft (E-PTFEG) were previously reported in experimental studies. Between May 1990 and August 1992, 39 PE-PEUGs including 34 loop and 5 straight and 18 E-PTFEGs including 18 loop were implanted to create arteriovenous (AV) fistulas in a total of 52 adult patients on maintenance hemodialysis (HD). They were followed up until October 1994. Hemostasis on the suture line was achieved within 3 min in all patients implanted with PE-PEUGs. Bleeding from the needle holes of PE-PEUG stopped within 10 min with gentle finger pressure. Minimal local edema developed in only a few patients implanted with PE-PEUG while most patients implanted with E-PTFEG developed moderate lo cal edema. One seroma formation was found in an E-PTFE case. Aneurysmal dilatations were observed twice in a PE-PEUG patient 9 and 17 months after the implantation and once in a E-PTFEG patient 2 years after the implantation. The cumulative patency rate at 1 year in the PE-PEUG and E-PTFEG groups were 53.2 and 70.8%, respectively. Our clinical study showed that the PE-PEUG had several advantages over E-PTFEG: prompt hemostasis, no persistent edema and no formation of seroma, no change in elasticity, and sufficient mechanical strength. However, the cumulative patency rate was inferior to that with E-PTFEG implanted in our series. Further modifications are therefore necessary to improve the patency rate.     

骨髓CD34~+干细胞种植人工血管应用于血管置换后内皮化和通畅率的研究

目的:探讨骨髓CD34+细胞分别种植于常用膨体聚四氟乙烯(expanded polytera fluoroethylone,ePTFE)人工血管和涤纶人工血管的内皮化程度和通畅率.方法:选杂种犬16条,依人工血管不同分为ePTFE血管实验组(6条)和涤纶皿管实验组(6条)及ePTFE对照组(2条)和涤纶对照组(2条),实验犬采自体骨髓,提取CD34+细胞种植覆膜人工血管,对照犬采用单纯自体血预凝人工血管,将ePTFE或涤纶人工血管分别植入所有实验犬的下腔静脉和腹主动脉.术后第30、60、100天取标本,观察通畅率,并分别用光学显微镜、电子显微镜和免疫组织化学方法观察新生内膜表面内皮化情况.结果:对照组静脉全部阻塞.实验组第30天人工血管腔面新生内膜内皮细胞密度自吻合口向中间方向逐渐减少,第60天的人工血管内皮基本覆盖管壁,第100天人工血管腔面内膜内皮细胞排列均匀完整,而对照组内膜表面无内皮细胞覆盖.结论:经纯化的CD34+细胞种植于ePTFE和涤纶人工血管较未种植的人工血管中远期有较好的内皮化和通畅率.     

The endothelialization process of a fibrous polyurethane microvascular prosthesis after implantation in the abdominal aorta of the rat. A scanning electron microscopic study

The endothelialization process of a fibrous microvascular polyurethane prosthesis (inner diameter 1.6 mm) was studied by scanning electron microscopy. Forty-seven prostheses (1 cm) were implanted into the abdominal aorta of rats between the left renal artery and the bifurcation. Specimens were taken on day 1, 3, 5, 7, 10, 14, 18, 21 and 25, as well as 6 and 9 months after implantation, to evaluate immediate and delayed response and complications. The patency rate of the implants was 91.2%. After an initial recovery period of five days, endothelial cells started to migrate onto the inner surface of the prosthesis with a velocity of approximately 0.3 mm per day, resulting in a completely endothelialized prosthesis at day 21. A smooth continuous inner lining was achieved. A difference in growth pattern between the proximal and distal growth zone was observed, and may be attributed to the direction of the blood flow through the prosthesis. The endothelial cells advanced in a close arrangement. No cells were seen to settle and grow in between the two growth zones on the fibrin layer. If no immediate complications occur, the endothelialization process (21 days) proceeds uneventfully and no late complications are observed. Though it may be argued that the new cells lack some authentic endothelial features, this study indicates that they are at least of endothelial orgin, and behave morphologically like endothelial cells. It can be concluded that the adequate texture of the prosthesis and the cell anchoring, in combination with both an optimal surgical performance and blood flow, ensure that the microvascular prostheses are rapidly endothelialized and retain high patency rates over long periods of time.(ABSTRACT TRUNCATED AT 250 WORDS)     

Failure to obtain long-term patency after implantation of fibrous polyurethane prostheses in the carotid arteries of rabbits

Fibrous polyurethane prostheses were implanted in the carotid arteries and aortae of New Zealand white (NZW) and Chinchilla (CHIN) rabbits. No immediate post-implantation patency was obtained after implantation in the carotid arteries in NZW rabbits. In CHIN rabbits patency up to 1 week was obtained after carotid implantation. Attempts to increase patency rates by administration of 20 mg/kg body weight/day of both dipyridamol (DIP) and acetyl-salicylic acid (ASA) p.o., starting the week before implantation, had an adverse effect; prostheses became occluded within a few hours after implantation. Coagulation tests (Lee and White, Am J Med Sci 145:495-503, 1913) carried out with blood drawn from CHIN rabbits revealed hypercoaguability after administration of either 10 or 20 mg/kg body weight/day of both DIP and ASA compared to pre-medication values. Prostheses implanted in the aortae of both strains remained patent without anti-platelet-aggregation therapy for a 3-month observation period. It is concluded that in the NZW rabbit carotid implantation was not successful due to severe spasmic reactions and that in CHIN rabbits only very short-term patency could be obtained both with and without administration of 10 or 20 mg/kg body weight/day medication DIP and ASA.     

Influence of luminal pore size on the patency rate and endothelialization of polymeric microvenous prostheses

In microvenous prosthetic surgery a continuous search for better patency rates is necessary to enable a clinical application. In this search for better patencies, modifications in the wall structure are being made. Directions found in the literature suggest that pore size plays an important role in achieving better patencies. Thus far, no study has been conducted to evaluate the influence of pore size on the patency rate of polyurethane microvenous prostheses. Since polyurethane is known to yield good patency rates, we conducted this study in which we compared different luminal pore sizes with regard to patency. Pore size varied from 0.6 to 20 μm in microvenous polyurethane-based prostheses (length 5–6 mm, internal diameter 1 mm). The results showed a favorable patency rate in the pore sizes larger than 5.0 μm (patency 75%) when compared to pore sizes smaller than 2.0 μm (patency 50%). This study demonstrates that microvenous polyurethane-based prostheses with a luminal pore size larger than 5.0 μm may yield better patency rates than prostheses with a luminal pore size smaller than 5.0 μm. Further studies are currently being performed to elucidate the very reasons for this effect. © 1995 Wiley-Liss, Inc.     

Stent graft repair of visceral artery aneurysms

PURPOSE: The purpose of this study was to compare the efficacy of rifampin-bonded gelatin-sealed and silver acetate/collagen-coated knitted polyester prostheses for the prevention of bacteremic graft infection in an animal model. METHODS: Eighteen 6.0-mm polyester grafts (length, 5.0 cm) were implanted in dogs end-to-end into the infrarenal aorta. The dogs were divided into four groups as a function of type of prosthesis implanted. The dogs in groups I (n = 3) and II (n = 3) received control gelatin-sealed or collagen-coated polyester prostheses, respectively. In group III (n = 6), the dogs received rifampin-bonded gelatin-sealed polyester prostheses. In group IV (n = 6), the dogs received silver/collagen-coated polyester prostheses. Two days after implantation, the grafts were challenged with 6 x 10(9) Staphylococcus aureus intravenously. One week after implantation, the grafts were harvested with sterile technique. Quantitative cultures were obtained from all the harvested grafts. The results were expressed as colony-forming units per cm(2) of graft material. Bacteriologic study was also performed on various tissue samples. The chi(2) test was used to compare the culture proven infection of control and antimicrobial grafts. RESULTS: All the control grafts were infected with S aureus at the time of removal. Five of the six silver/collagen-coated grafts were infected, whereas none of the six rifampin-bonded gelatin-sealed grafts grew S aureus (P <.01). There was no significant difference in the number of positive culture results of organ samples between the different groups of dogs. CONCLUSION: These results indicate that rifampin-bonded gelatin-sealed polyester grafts are significantly more resistant to bacteremic infection than are silver/collagen-coated polyester grafts in a highly challenging model.     

Seeding human arterial prostheses with mechanically derived endothelium: The detrimental effect of smoking

Endothelial healing of Dacron arterial prostheses can be hastened in dogs by seeding autogenous venous endothelium onto the prostheses in a single-staged operation. To determine whether this technique enhances the patency of human grafts, we studied the results of 186 operations on 161 patients performed between February 23, 1978, and December 1, 1982. Alternately allocating patients to treatment with seeded and unseeded Dacron knitted prostheses, we performed axillary-femoral and axillary-femoral-femoral bypasses in 11 patients (six seeded and five unseeded) and femoral-femoral bypasses in 28 (13 seeded and 15 unseeded). By a randomized block method of treatment allocation, femoral-popliteal grafts were installed in 147 limbs (112 vein, 18 seeded, and 17 unseeded). Patency was analyzed by the life-table method. Overall, femoral-femoral and femoral-popliteal bypasses demonstrated no difference between the seeded and unseeded grafts. Patency was somewhat better in seeded than unseeded axillary-femoral bypasses. Nevertheless, nonsmokers with seeded femoral-popliteal Dacron grafts enjoyed a significantly better graft patency than those with unseeded grafts (p = 0.035), whereas a substantial deterioration of seeded Dacron grafts was observed in those patients who smoked (p = 0.008 at 6 months). Vein grafts performed better than either seeded or unseeded Dacron prostheses (p = 0.016). Serum beta-thromboglobulin (BTG) levels varied widely and did not differ among any of the treatment groups. We concluded that endothelial seeding improved the patency of human arterial prostheses but that results were worse if the patient was a smoker. BTG was not a useful measure of the platelet activation induced by an arterial prosthesis. (J VASC SURG 1984;1:279-89.)     

Differentiation of vascular prostheses in dogs with serial tests of in vivo platelet reactivity

Three different vascular prostheses (standard weight knitted Dacron, double velour knitted Dacron, and expanded polytetrafluoroethylene) were implanted in the aortas of dogs, and serial determinations of platelet survival and platelet serotonin were monitored at 12-week intervals for 1 year. Prostheses were then removed and luminal coverage with endothelialized neointima and production of prostacyclin were measured. Changes in platelet survival were correlated with changes in platelet serotonin, and both measurements reflected in vivo platelet reactivity with the vascular prostheses. These changes were unique for each type of prosthesis and were dependent upon physical characteristics and the rate and degree of coverage of the prosthetic surface with endothelialized neointima that produced prostacyclin. Prostheses that reduced platelet survival and platelet serotonin the least as shown by serial evaluation were found at harvest to be the most completely paved with nonthrombogenic neointima. In dogs, these techniques allow differentiation of vascular prostheses and provide a useful animal model for their evaluation.