Dacron Vascular Grafts Research Articles

Prefabricated jejunal free-tissue transfer for tracheal reconstruction: an experimental study.

Reconstruction of long-segment tracheal defects is a problem for the reconstructive surgeon. Difficulties arise with the use of prosthetic materials because of their propensity for infection and extrusion. Autologous tissue is limited by poor structural characteristics and technical complexity. We propose a simple composite bioprosthesis that, through a process of prefabrication and subsequent neovascularization, may provide a functional tracheal analogue superior to existing forms of reconstruction. Ten rats had composite flaps constructed by combining an isolated, perfused, mucosectomized segment with an outer covering of a ring-reinforced woven Dacron vascular graft. This unit remained in the intraabdominal milieu for 20 days and was then inspected for viability, incorporation of jejunum and graft, flexibility, and tolerance to negative pressure. Seven experimental animals survived the initial phase. The jejunal bioprostheses in all cases tolerated negative pressures to -200 mmHg, rotation of 180 degrees, and flexion to 90 degrees without collapse of the graft segments. Vascular casts and standard histologic examination showed neovascularization of the Dacron graft and dense fibrovascular ingrowth into the interstices of the graft. We conclude that prefabrication utilizing autologous and prosthetic components to create a single axial flap for transfer is a feasible solution to long-segment tracheal reconstruction. Neovascularization permeates the full thickness of the prosthetic component and is accompanied by dense fibrous ingrowth during the delay period. This neotracheal analogue also possesses structural characteristics similar to those of the native trachea and a durable submucosal layer that can support ingrowth of epithelium.

Experimental study of the antithrombogenic behavior of Dacron vascular grafts coated with hydrophilic acrylic copolymers bearing salicylic acid residues.

The objective of the present work was study of the behavior of active coatings of hydrophilic acrylic polymers bearing salicylic acid residues linked covalently to the macromolecular chains, after their application to woven and knitted Dacron vascular grafts. In vitro tests were carried out under dynamic flow conditions using equipment especially designed to reproduce physiologic conditions, to determine the retention of the coating using a saline solution. Ex vivo tests were carried out in an extracorporeal circuit using the dog as an animal model. The study of the deposition of platelets was followed by labeling of autologous platelets with 111In-oxine, as well as by analysis of the surfaces of the prostheses by scanning electron microscopy. An application of thin coatings of hydrophilic acrylic copolymers improves the antithrombogenicity of the vascular grafts with respect to the uncoated prosthesis. The presence of relatively small amounts of units bearing salicylic acid residues in the copolymer chains (5-20 wt %) gives good results when they are applied to woven and knitten Dacron meshes which have been quantified by analysis of the percentage of radiotracer on the surface of the vascular grafts tested in ex vivo experiments. The salicylic acid residues are released slowly to the medium by hydrolysis of the reversible covalent bonds of this compound to the acrylic macromolecular chains, which provides an additional antiaggregating effect for platelets. The polymeric coating forms a thin active film which improves the antithrombogenic properties of the surface of woven or knitted Dacron vascular grafts in ex vivo experiments.

DEVELOPMENT OF A STAPHYLOCOCCUS EPIDERMIDIS VASCULAR GRAFT INFECTION MODEL IN SHEEP

Staphylococcus epidermidis is an increasingly recognized causative organism of vascular graft infections. To increase our understanding of this problem we have tried to establish Staph. epidermidis vascular graft infection in sheep by direct inoculation. A 2 cm long, 5 mm diameter polytetrafluoroethylene (PTFE) or a gelatin sealed Dacron vascular graft was inserted into the left carotid artery. At the completion of the operation 1 mL of normal saline containing either 10(4), 10(6), or 10(8) colony forming units (cfu) of a slime producing Staph. epidermidis was inoculated directly onto the graft. After 3 weeks the grafts were harvested in a sterile fashion. Swabs were taken of the perigraft tissues and the external and internal aspects of the grafts; a 3-5 mm segment of the graft was incubated in broth medium and a second segment was ground for 5 min and then incubated in broth medium. Note was made of the presence of abscess formation, anastomotic failure or thrombosis. Thirteen sheep received a PTFE graft and 14 received a gelatin sealed Dacron graft. Three sheep died immediately postoperatively. The rate of infection was 40% at 10(4), 67% at 10(6) and 80% at 10(8) cfu Staph. epidermidis. In only four cases were all five cultures positive. In nine cases two or less cultures were positive, the majority of these being the broth cultures. Nine other organisms were isolated from nine mixed infections. Nine out of 13 PTFE and seven out of 11 Dacron grafts were infected.(ABSTRACT TRUNCATED AT 250 WORDS)

A Four-Hour Infusion of Recombinant Hirudin Results in Long-Term Inhibition of Arterial-Type Thrombosis in Baboons

Intravenous recombinant (r)-hirudin has a potent antithrombotic effect in aspirin- and heparin-resistant platelet-dependent thrombus formation in baboon models. However, these thrombi reform when therapy is stopped after 60 minutes. To determine if 4 hours of therapy can produce a lasting antithrombotic effect, we investigated the extent of deposition of 111In-labeled platelets onto 0.5-cm2 segments of Dacron vascular grafts for 53 hours. These grafts had been incorporated into exteriorized permanent femoral arteriovenous shunts in baboons. Platelet deposition in eight untreated animals was generally sigmoidal. Maximum platelet deposition, 1.7% +/- 0.9% of injected labeled platelets, was reached after approximately 4 hours. Deposition then gradually decreased to 0.4% +/- 0.2% of injected labeled platelets after 53 hours. After a thrombus was allowed to form for 15 minutes in six animals, intravenous treatment with r-hirudin at a dose of 20 nmol (0.14 mg)/kg-min-1 (aPTT > 300 seconds) was started and maintained for 4 hours. Platelet deposition was interrupted during treatment. After infusion was stopped, platelets accumulated again, but not as much as in the untreated animals. Maximum platelet deposition, 0.7% +/- 0.2% of injected labeled platelets, was significantly less (P < .01), and was reached after approximately 23 hours. Thereafter, deposition decreased to 0.4% +/- 0.2% at 53 hours. The shunts in all of the untreated animals occluded at some stage during the study, while only one shunt occluded in the treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolonged Inhibition of Acute Arterial Thrombosis by High Dosing of a Monoclonal Anti-platelet Glycoprotein IIb/IIIa Antibody in a Baboon Model

The in vivo activity of MA-16N7C2, the first monoclonal antibody that contains an echistatin-like RGD-sequence and inhibits platelet glycoprotein (GP)IIb/IIIa function, was determined in baboons. A dose-finding study assessing haemostatic variables such as bleeding time and ex vivo platelet aggregation showed that doses of as low as 0.2-0.3 mg/kg resulted in a pronounced effect. The effects were dose-dependent and lasted for several days, implying that MA-16N7C2 is a potent and long-acting GPIIb/IIIa inhibitor. Following the initial studies, the antithrombotic effect of 0.1 and 0.3 mg/kg of the antibody, given as a bolus, was determined in a baboon model of platelet-dependent, arterial-type thrombus formation. In these studies, a thrombogenic device consisting of Dacron vascular graft material was inserted as extension segments into a permanent arteriovenous shunt. The results confirmed the potent and long-lasting antithrombotic effect of MA-16N7C2. Surprisingly, the antithrombotic effect was stronger 48 h after a dose of 0.3 mg/kg administration than on the day of treatment with 0.1 mg/kg, despite the fact that comparable numbers of GPIIb/IIIa receptors were occupied on resting platelets. We postulate that with the high dose of MA-16N7C2 and after an extended period, occupied GPIIb/IIIa may be internalised by the platelets. Upon platelet activation, these receptors become reexposed but are unable to participate in thrombus formation. This is in contrast to unoccupied internal GPIIb/IIIa receptors early after a low dose of MA-16N7C2.

Effects of neurolytic concentrations of alcohol and phenol on Dacron and Gore-Tex vascular prosthetic grafts.

Neurolytic nerve block, using either alcohol (A) or phenol (P), is frequently used to treat intractable pain. However, these agents may disrupt the integrity of prosthetic vascular grafts. To investigate this possibility, the tensile strength of Dacron (Meadox Medicals, Oakland, NJ) and Gore-Tex (W.L. Gore Associates, Flagstaff, AZ) vascular grafts was determined after in vitro exposure to various clinically used concentrations of A or P. Segments of Dacron and Gore-Tex graft were placed in the following solutions: saline (S), 6% and 9% P, and 25%, 50%, 75%, and 100% A, and stored at 23 degrees +/- 1 degree C for 72 hours. Axial maximum load (in kilonewtons, KN) and strain (in mm/mm) were determined with an Instron universal testing machine (Instron Corporation, Camden, MA). Samples from the S, 9% P, and the 100% A groups were evaluated using a scanning electron microscope. Dacron tensile strength decreased a maximum of 23% after exposure to 50%, 75%, and 100% A. Dacron strain capacity decreased after exposure to A (50%, 75%, 100%) and P (6%, 9%). Scanning electron microscope of both P and A showed significant degradation. No changes were found in the Gore-Tex group after exposure to P or A, however, scanning electron microscope of the 100% A sample showed moderate fiber degradation. The study shows that Dacron woven grafts are degraded by concentrations of A of at least 50%, and to a lesser extent, concentrations of at least 6%, while Gore-Tex had only minimal changes. While neurolytic block offers distinct advantages in patients with terminal cancer pain, the findings suggest that the use of more conservative modalities, such as oral medication regimens, be considered for the treatment of intractable pain in patients with vascular prosthetic grafts that are proximate to the proposed site of neurolysis.

Proof of fallout endothelialization of impervious dacron grafts in the aorta and inferior vena cava of the dog

Purpose: The purpose of this study was to prove directly whether cells from the blood stream contribute to endothelialization of isolated, impervious Dacron vascular grafts in the dog.Methods: We designed an 18 cm, three-component graft with two parallel central Dacron limbs; one was made impervious with silicone rubber, and the other was preclotted. This model was implanted in the canine descending thoracic aorta with 30 μm polytetrafluoroethylene grafts anastomosed at each end. An 8 cm, three-component graft completely coated with silicone rubber was implanted in the canine abdominal aorta and inferior vena cava. Implant periods ranged from 4 to 12 weeks. Flow surfaces were studied by use of stereomicroscopy after being stained with silver nitrate, and by use of scanning and transmission electron microscopy, the inner wall and flow surface were studied by light microscopy after hematoxylin-eosin and immunocytochemical staining (the latter for endothelial and smooth muscle cells), and the full wall was studied by light microscopy after hematoxylin-eosin staining.Results: Effective prevention of pannus and transmural ingrowth into the impervious central test grafts was achieved, and scattered islands of endothelial cells were conclusively demonstrated on flow surfaces in each of the three implant sites 4 weeks after implantation. In the descending thoracic aorta, where these grafts were also implanted for 8 and 12 weeks, α-actin-positive cells and microvessels were found beneath some of the endothelial islands.Conclusion: Fallout endothelialization of Dacron vascular grafts occurs in both the arterial and venous systems of the dog.

Repair of pectus excavatum using a dacron vascular graft strut

Long-term follow-up was obtained for 161 patients who underwent a modified Ravitch repair of pectus excavatum. In all cases, the substernal strut was fashioned from a Dacron vascular graft. Follow-up was done by telephone (most cases) and also by office visit (43 cases). The follow-up period was 12 months to 21.5 years. One hundred thirty-three patients (83%) had satisfactory chest contour; 17 had a fair result, and 11 had frank recurrence. Risk factors for poor contour were an asymmetrical defect, a severe defect, and associated congenital anomalies. Of the three patients with Marfan's syndrome, all had recurrence. One hundred thirty (81%) had a satisfactory scar, and 31 had hypertrophic scars. Risk factors for hypertrophic scar formation were increasing age and weight, and tripod internal fixation used early in the series. Factors not contributing to clinical outcome include the sex of the patient, positive family history, perioperative complications, year of surgery, surgeon, and type of incision. The use of a Dacron strut is relatively easy and complication-free. It can be left permanently in situ. Long-term results have been good, except in patients with an extensive or asymmetrical deformity, and in those with other congenital anomalies, especially Marfan's syndrome.

Antithrombotic effects of thrombin-induced activation of endogenous protein C in primates.

The effects on thrombosis and hemostasis of thrombin-induced activation of endogenous protein C (PC) were evaluated in baboons. Thrombosis was induced by placing into arteriovenous shunts a segment of Dacron vascular graft, which generated arterial platelet-rich thrombus, followed by an expansion region of low-shear blood flow, which in turn accumulated fibrin-rich venous-type thrombus. Thrombosis was quantified by 111In-platelet imaging and 125I-fibrinogen accumulation. Intravenous infusion of alpha-thrombin, 1-2 U/kg-min for 1 h, increased baseline activated PC levels (approximately 5 ng/ml) to 250-500 ng/ml (P < 0.01). The lower thrombin dose, which did not deplete circulating platelets, fibrinogen, or PC, reduced arterial graft platelet deposition by 48% (P < 0.05), and platelet and fibrin incorporation into venous-type thrombus by > 85% (P < 0.01). Thrombin infusion prolonged the activated partial thromboplastin clotting time, elevated fibrinopeptide A (FPA), thrombin-antithrombin III complex (T:AT III), and fibrin D-dimer plasma levels (P < 0.01), but did not affect bleeding times. Thrombin's antithrombotic effects were blocked by infusing a monoclonal antibody (HPC-4) which prevented PC activation in vivo, caused shunt occlusion, increased the consumption of platelets and fibrinogen, elevated plasma FPA and T:AT III levels, and reduced factor VIII (but not factor V) procoagulant activity (P < 0.05). We conclude that activated PC is a physiologic inhibitor of thrombosis, and that activation of endogenous PC may represent a novel and effective antithrombotic strategy.

Interruption of vascular thrombus formation and vascular lesion formation by dietary n-3 fatty acids in fish oil in nonhuman primates.

Because of discrepant claims regarding the relative biological effects of n-3 fatty acids (n-3FAs), we have concurrently measured the effects of dietary n-3FAs on blood and vascular lipid composition, hemostatic function, blood thrombotic responses, vascular thrombus formation, and vascular lesion formation in baboons. Dietary n-3FAs displaced n-6FAs in plasma, platelets, blood vessels, and corresponding urinary eicosanoid metabolites (p < 0.01 in all cases) within weeks after initiation of a semipurified diet containing 1 g/kg per day n-3FA-ethyl ester concentrate (composed of two thirds eicosapentanoic acid and one third docosahexanoic acid). Coincidentally, platelet hemostatic function became minimally impaired (template bleeding times prolonged from 4.3 +/- 0.5 minutes to 7.6 +/- 1.3 minutes, p = 0.039); concentrations of collagen producing half-maximal platelet aggregation increased (from 6.4 +/- 2.1 to 8.5 +/- 2.5 micrograms/mL, p = 0.045); and tissue factor expression by endotoxin-stimulated blood monocytes fell (from 6.5 +/- 1.2 to 1.7 +/- 0.14 mU/10(6) cells, p < 0.005). Dietary n-3FAs decreased deposition of platelets onto thrombogenic segments of Dacron vascular graft incorporated into chronic exteriorized femoral arteriovenous (AV) shunts, a thrombotic process resistant to the effects of both aspirin and heparin (111In-labeled platelet deposition decreased from 14.1 +/- 1.4 x 10(9) platelets/5-cm segment at 40-60 minutes with occlusion to 7.5 +/- 0.8 x 10(9) platelets/5-cm segment without occlusion; p < 0.001). Platelet deposition onto segments of endarterectomized homologous normal aorta in the AV shunts of n-3FA-treated animals was similarly reduced (from 4.4 +/- 0.9 to 1.8 +/- 0.4 x 10(9) platelets; p < 0.01). Dietary n-3FAs interrupted vascular thrombus formation at sites of surgical carotid endarterectomy (platelet deposition, 1.5 +/- 0.4 versus 4.4 +/- 1.0 x 10(9) platelets in untreated controls; p < 0.001). Moreover, endarterectomized aortic segments (EASs) from n-3FA-treated donors exhibited little capacity to induce thrombus formation when tested in the AV shunts of control recipient animals (0.24 +/- 0.10 versus 4.4 +/- 0.90 x 10(9) platelets). However, in the converse crossover experiments, EASs from control animals actively accumulated platelets when studied in the AV shunts of n-3FA-treated animals (1.8 +/- 0.4 x 10(9) platelets; p < 0.01 versus n-3FA-treated EASs in shunts of normal animals). Dietary n-3FAs also abolished vascular lesion formation at sites of carotid endarterectomy 6 weeks after surgery (cross-sectional area of neointima 0.048 +/- 0.031 mm2 compared with 0.428 +/- 0.104 mm2 in control arteries; p = 0.010). In nonhuman primates, dietary n-3FAs in high doses eliminate both vascular thrombus formation and vascular lesion formation after mechanical vascular injury while largely sparing hemostatic function and modestly reducing blood thrombotic responses. These effects are attributed to selective n-3FA-dependent alterations in cellular membrane functions.

Tight binding of albumin to glow discharge treated polymers

Tetrafluoroethylene (TFE) glow discharge-treated Dacron vascular grafts resist thrombus deposition, embolization and thrombotic occlusion. In addition, albumin adsorbed on TFE-treated surfaces resists elution by sodium dodecyl sulfate (SDS). Since the tight binding of albumin to TFE-treated surfaces may contribute to their thromboresistant character, we decided to examine the mechanism responsible for this tenacious adsorption. We have investigated albumin adsorption and retention (after SDS elution) on a number of untreated and glow discharge-treated surfaces. Fluorocarbon glow discharge-treated polymers retain a larger fraction of the adsorbed albumin than ethylene and hexamethyldisiloxane glow discharge-treated surfaces. Albumin retention by surfaces appears to be closely related to their surface free energy (in air). Low energy surfaces (in air), whether untreated or glow discharge-treated, retain a larger fraction of the albumin adsorbed than higher energy surfaces. The lowest energy surfaces should have the highest interfacial energies in water, with correspondingly high driving forces for adsorption of proteins. This can lead to the formation of multiple binding sites upon adsorption, permitting strong hydrophobic interactions, which leads to the observed strong binding.

In Vivo Inhibition of Acute Platelet-Dependent Thrombosis in a Baboon Model by BAY U3405, a Thromboxane A2-Receptor Antagonist

Bay U3405 is a thromboxane A2 (TxA2)-receptor antagonist that inhibits the binding of TxA2 to its target cells. The aim of this study was to determine if Bay U3405 could be used to inhibit arterial thrombosis. A thrombogenic device, consisting of uncrimped Dacron vascular graft material (0.5 cm2) built into the wall of silicone rubber tubing with 4 mm inside diameter, was exposed to native flowing blood under arterial blood flow conditions (100-140 ml/min) by interposing the devices as extension segments into permanent femoral arteriovenous shunts implanted in baboons. Thrombus formation was quantified in vivo by measuring the deposition of 111In-labelled platelets onto the graft material with a scintillation camera. In six baboons, a bolus injection of Bay U3405, calculated to attain an initial plasma concentration of 300 ng/ml, reduced the maximum thrombus formation measured over a 2 h study period. Platelet deposition was reduced by 33 +/- 14% (SD) at 2 h as compared to control studies done in the same baboons. The accumulation of additional platelets onto a thrombus that was allowed to form for 1 h, was reduced by 58 +/- 28% at 2 h. Ex vivo platelet aggregation in response to ADP, activated partial thromboplastin time (APTT), prothrombin time (PT), and thrombin time (TT) were not affected by the treatment. Ex vivo platelet aggregation in response to collagen was markedly inhibited for 2 h after treatment. The results demonstrated that selective blocking of the TxA2-receptor on platelets reduced platelet-dependent thrombus formation and the accumulation of additional platelets in a freshly formed thrombus.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective factor Xa inhibition by recombinant antistasin prevents vascular graft thrombosis in baboons.

A baboon model of high-shear, platelet-dependent vascular graft thrombosis was used to assess the antithrombotic effect of recombinant antistasin (rATS), a 119-amino acid protein with selective, subnanomolar inhibitory potency against coagulation factor Xa. In this model, a Dacron vascular graft segment of a femoral arteriovenous (AV) shunt provided the thrombogenic stimulus. Antithrombotic efficacy of rATS was assessed by continuous monitoring of 111In-labeled platelet and 125I-labeled fibrin(ogen) deposition onto the graft surface and blood flow through the vascular shunt. Systemic intravenous administration of rATS (2 or 4 micrograms/kg.min-1) dose dependently decreased both platelet and fibrin(ogen) deposition onto the graft. Vascular graft thrombus formation was completely inhibited at a systemic dose of rATS of 4 micrograms/kg.min-1. None of the AV shunts in animals receiving rATS at either dose occluded, and blood flow was maintained at 81 +/- 4% (2 micrograms/kg.min-1 rATS) or 96 +/- 3% (4 micrograms/kg.min-1 rATS) of basal flow. Systemic fibrinopeptide A elevations in response to exposure to the Dacron graft segment were completely suppressed by both doses of rATS. The ex vivo activated partial thromboplastin times were extended to greater than 150 seconds during infusion of both doses of rATS; however, even at fully antithrombotic doses, template bleeding times were not significantly increased. Thus, in this baboon model, rATS is a potent antithrombotic agent that inhibits both platelet and fibrin(ogen) deposition onto a Dacron vascular graft segment. Furthermore, these results demonstrate that selective inhibition of coagulation factor Xa by rATS can completely prevent vascular graft thrombus formation without significantly compromising primary hemostasis as measured by template bleeding time.

Experimental comparison of albumin-sealed and gelatin-sealed knitted Dacron conduits

Two high-porosity knitted Dacron vascular grafts sealed with aldehyde cross-linked gelatin or albumin were compared with respect to the following characteristics. Porosity control by the absorbable sealant was assessed with a water porosity meter at 120 mm Hg pressure. Ease of suturing was determined by an objective needle penetration test. Sealant resorption was assessed histologically in a subcutaneous immature rat model as well as in circulatory implants. Gross and microscopic healing characteristics were compared in circulatory implants in the thoracic aorta of sheep with use of a composite conduit in every animal, which allowed direct comparison of the two graft materials and minimized differences in healing between individual animals. Both grafts demonstrated excellent porosity control and better handling characteristics than woven Dacron. Sealant resorption was generally rapid, although residual albumin sealant was often seen adjacent to anastomoses. Residual sealant appeared to result in focally poor healing with focal loss of adhesion of surrounding tissue to graft. We conclude that details of sealant preparation and application can importantly influence the performance of presealed knitted Dacron grafts and should be carefully evaluated in the laboratory before clinical implantation is begun.

Induction of transient neurological dysfunction in baboons by platelet microemboli.

To investigate experimental mechanisms of reversible cerebral dysfunction, we produced transient focal cerebral ischemia in five baboons by unilateral perfusion of internal carotid territories with platelet microemboli generated endogenously. Platelet microemboli were formed by incorporating segments of Dacron vascular graft for 1 hour as unilateral carotid arterio-arterial shunts. Platelet embolization was assessed by ultrasonography and isotopic imaging; cerebral function was evaluated by measurements of somatosensory evoked potentials and clinical motor performance. Platelet microemboli, detected by transcranial Doppler ultrasonography, accumulated rapidly in the shunted carotid hemispheric territory. Indium-111-labeled platelets reached a maximum value of 3.2 +/- 0.8 x 10(9) platelets in the dependent hemisphere of five animals after 20 minutes of carotid blood flow through the grafts when measured in real time by continuous scintillation camera imaging. The retained 111In-platelet microemboli cleared from the cerebral vasculature within 1 hour after removing the grafts. Corresponding blood markers of in vivo thrombus formation, beta-thromboglobulin, platelet factor 4, and fibrinopeptide A, increased eightfold to 20-fold after incorporating graft segments and normalized within 1 hour after removing the grafts. Coincidently, focal neurological function was temporarily impaired, as shown by the ipsilateral loss of somatosensory evoked potentials 5 minutes after initiating platelet microembolization, with restoration 1 hour after removing the grafts in five baboons, and contralateral hemiparesis in two recovered baboons, with complete resolution by 24 hours. Endogenously generated platelet microemboli accumulate transiently in the dependent cerebral circulation and produce corresponding focal neurological dysfunction that resolves within hours after microembolization.

Production of transient ischaemic events by platelet emboli in baboons.

To investigate the pathophysiological process of transient ischaemic events in a clinically relevant model, we produced transient focal cerebral ischaemia in five baboons using endogenously generated platelet microemboli. Thrombogenic segments of Dacron vascular graft were incorporated as unilateral carotid arterio-arterial shunts to produce endogenous platelet microemboli. The embolized microparticles were quantified by isotopic imaging using 111In-platelets and by transcranial Doppler ultrasonography. Platelet microemboli accumulated rapidly in the shunted carotid territory and reached a maximum value of 3.2 +/- 0.8 x 10(9) in the embolized hemisphere 20 min after initiating blood flow through the graft segment. Sixty min after removing the grafts 111In-platelets were largely cleared from hemispheric vasculature. Recovered animals exhibited mild contralateral hemiparesis which disappeared completely within 24 h. We conclude that endogenously generated platelet microemboli accumulate transiently in the dependent cerebral circulation and produce corresponding transient focal neurological dysfunction. This model may be useful in the evaluation of new therapeutic strategies in acute stroke.

In Vitro Endothelialization of Carbon-Coated Dacron Vascular Grafts

Physical vapour deposition is used to coat vascular prostheses with pyrolytic carbon. This coating may facilitate the development of an endothelial monolayer in grafts implanted in laboratory animals. This in vitro study compared the adherence and growth of cultured porcine aortic endothelial cells (EC) seeded in vitro on carbon-coated Dacron, to uncoated prostheses. The cells were incubated at 5 x 10(4) cells/cm2. Progress was monitored at different times (TO + 2 hours, D 1, D 4, D 8) by microscopic observation, when cell counts were made; and by scanning electronic microscopy (SEM) to evaluate morphological EC-graft interactions. Cell adherence was independent of the carbon coating but cellular growth occurred only on carbon-coated Dacron. The SEM observations showed both the shape of the adherent cells, which were rounded on uncoated Dacron and extensively spread on carbon-coated prostheses, and the morphology of the carbon coating.

Antithrombotic effects of combining activated protein C and urokinase in nonhuman primates.

We have determined in vivo the relative antithrombotic efficacy and hemostatic safety of combining low-dose activated protein C (APC) and urokinase (urinary plasminogen activator, u-PA), two natural proteins that regulate thrombogenesis. To model acute thrombotic responses of native blood under conditions of arterial flow, thrombogenic segments of Dacron vascular graft (VG) were incorporated into chronic exteriorized femoral arteriovenous (AV) access shunts in baboons. Thrombus formation on VG was determined by measuring 1) the deposition of autologous 111In platelets using real-time scintillation camera imaging, 2) the accumulation of 125I fibrin, 3) segment patency by Doppler flow analysis, and 4) blood tests for thrombosis, including plasma concentrations of platelet factor 4, beta-thromboglobulin, fibrinopeptide A (FPA), and D-dimer. Treatments consisting of low-dose and intermediate-dose APC (0.07 or 0.25 mg/kg.hr), u-PA (25,000 or 50,000 IU/kg.hr), or the combination were administered for 1 hour by continuous intravenous infusion. In untreated controls, platelets and fibrin accumulated rapidly, reaching plateau values at 1 hour of 15.1 +/- 3.8 x 10(9) platelets and 7.8 +/- 2.2 mg fibrin. Although the low-dose APC or u-PA alone did not decrease either platelet or fibrin deposition significantly, this combination moderately reduced both platelet and fibrin accumulation (7.3 +/- 2.6 x 10(9) platelets, p less than 0.05; 3.9 +/- 0.6 mg fibrin, p less than 0.05). Furthermore, intermediate-dose APC or u-PA reduced thrombus formation by half when administered alone (p less than 0.001 for both platelet and fibrin deposition), and the combination markedly interrupted the accumulation of platelets (3.0 +/- 1.0 x 10(9) platelets, p less than 0.001) and fibrin (1.3 +/- 0.6 mg fibrin, p less than 0.001). During active treatments, all VG segments remained patent. Hemostatic plug forming capability, as measured by template bleeding times, remained normal during all experiments (p greater than 0.05). The T50 clearance time for APC activity was not affected by the concurrent administration of u-PA. u-PA alone increased the plasma levels of D-dimer, FPA, and, interestingly, APC, implying that during pharmacological activation of the fibrinolytic system, thrombin activity was released, and the protein C pathway was activated. A combination of intermediate-dose APC and u-PA produce substantial and efficient antithrombotic effects without impairing hemostatic function.

Antithrombotic efficacy of recombinant tick anticoagulant peptide. A potent inhibitor of coagulation factor Xa in a primate model of arterial thrombosis.

Tick anticoagulant peptide is a specific, potent inhibitor of blood coagulation factor Xa. The effects of recombinant tick anticoagulant peptide (rTAP) and standard heparin (SH) were compared in an anesthetized baboon model of arterial thrombosis where platelet deposition onto a Dacron vascular graft segment of an arteriovenous (AV) shunt was studied. Animals were randomized to receive systemic administration of SH (10 or 100 U/kg i.v. bolus followed by 0.4 or 1.0 U/kg/min i.v. infusion, respectively) or rTAP (6.25, 12.5, or 25.0 micrograms/kg/min i.v. infusion). rTAP, but not SH, caused a significant (p less than 0.05), dose-dependent reduction of indium-111 labeled platelet and iodine-125 labeled fibrin (ogen) deposition onto the graft. Deposition was not significantly increased from baseline values during infusion of 12.5 or 25.0 micrograms/kg/min of rTAP. Blood flow was maintained at 64 +/- 9, 95 +/- 2, or 97 +/- 2% of baseline following infusion of 6.25, 12.5, or 25.0 micrograms/kg/min of rTAP, respectively. Both SH and rTAP significantly (p less than 0.05) decreased the systemic fibrinopeptide A (FPA) elevation during exposure to the Dacron graft. rTAP was fully antithrombotic at APTT values of 42.6 +/- 2.4 seconds (less than twofold basal value), while SH had no antithrombotic efficacy despite APTT values greater than 150 seconds (greater than fivefold basal value). The demonstrated antithrombotic effect of rTAP in the absence of alterations in primary hemostasis suggests that controlling thrombin generation through inhibition of factor Xa may be a novel and effective pharmacological approach in the prevention of high-shear arterial thrombosis.

Efficacy and duration of antistaphylococcal activity comparing three antibiotics bonded to Dacron vascular grafts with a collagen release system

Type 1 collagen, minimally cross-linked, was used to bind one of three antibiotics (amikacin, chloramphenicol, or rifampin) to double-velour Dacron grafts to develop a prosthesis resistant to infection. Six millimeter disks of graft were placed in separate flasks (specific for each antibiotic) containing albumin in saline and continuously agitated. At daily intervals the solution was changed, and paired graft samples were removed and placed on a blood agar plate confluently streaked with bacteria. The initial zone of inhibition (centimeters squared), the time to 50% reduction of initial inhibition zone, and the overall duration of antibacterial activity were recorded on an exponential model. Grafts bonded with amikacin and chloramphenicol had an overall duration of activity of only 2 and 1 day, respectively, against Staphylococcus aureus. The collagen bonded rifampin grafts had an initial zone of 14.76 cm,2 took 3.92 days to reach 50% of initial inhibition, and had an overall duration of activity of 22.4 days. This was significantly better than grafts preclotted with 1.0 ml of rifampin (60 mg/ml) and 9 ml of blood (10.92 cm,2 1.06 days, and 5.6 days). When tested against a slime-producing Staphylococcus epidermidis (American Type Culture Collection No. 35983), the graft bonded with rifampin had inhibitory activity of up to 27.77 days with a 50% of activity eluted at 4.78 days, significantly better than the preclotted rifampin graft without collagen bonding. These data suggest that rifampin bonded by collagen can protect a vascular graft against infection from S. aureus and S. epidermidis for up to 3 weeks after implantation.