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Biomedical subjects

R Guidoin

Publications and source records attributed to R Guidoin.

At least 163 records · Page 9Linked to original sources
PubMed1984

[The Sparks-Mandril arterial prosthesis. An ingenious concept, a total failure. What can we learn from it?].

In spite of its ingenuity, the Sparks-mandril concept has failed to generate a satisfactory arterial substitute. Pathological analysis of prostheses retrieved from humans and explanted from dogs as part of a controlled laboratory study has demonstrated that the tissue laid down during the autogenous generation stage contains neither elastin fibers nor smooth muscle cells capable of providing the required dimensional stability of a blood vessel. The supporting polyester mesh tube has been found to stretch in vivo, resulting in dilation and lengthening of the prosthesis and the formation of aneurysm and thrombosis. It is recommended that the use of devices relying on the Sparks-mandril concept not to be reintroduced until such time as the mechanism of growth promoting factors for angiogenesis are fully understood.

Adult↗
PubMed1984

Textile Teflon arterial prostheses: how successful are they?

Today the woven and knitted Teflon vascular prostheses developed over 25 years ago by Edwards are of only minor clinical interest. The literature contains a chronology of postoperative complications critical of textile Teflon as a prosthetic material, and this led to its discontinuance as a commercial product. Recent evidence from pathologic and material analyses of three grafts removed from patients after implantation for 11, 19 and 19 years, respectively, suggests that the previously reported complications were more likely to have been related to the use of silk sutures, the fraying and ravelling of the woven and weft-knitted constructions and local or systemic reactions than to degradation of the Teflon. Experimental studies of grafts implanted in the thoracic and abdominal aortas of dogs for periods of up to 6 months support these findings. Because of the apparent long-term stability of textile Teflon as an implantable material, the authors see merit in its reintroduction as a warp-knitted vascular prosthesis.

Aged↗
PubMed1984

[Progressive complications associated with the use of a bovine heterograft for vascular access].

Three bovine carotid heterografts, used for vascular access, were analysed after removal following the development of aneurysms in two cases and thrombosis in one. The first prosthesis was implanted in a 17-year-old man who suffered from myasthenia gravis and was undergoing plasmapheresis. It became notably dilated several months after implantation, and resection was necessary 14 months after insertion. The second graft was placed in a 31-year-old woman being treated for a severe chronic potassium insufficiency. It was removed 16 months after insertion because of thrombosis. The third bovine carotid heterograft was inserted in a 48-year-old patient on long-term hemodialysis and was removed 3.5 months later because of aneurysmal dilatation adjacent to the arterial anastomosis. These evolutionary and degenerative changes associated with the bovine carotid heterograft illustrate the limitations of this material as an interpositional limb for arteriovenous fistulas in angioaccess therapy. Small weaknesses have sometimes been noted in the microstructure of the graft material studied before implantation.

Adolescent↗
PubMed1984

[First contact between blood and the arterial prosthesis. Study of the retention of the blood elements].

In order to characterize the nature of the interaction between arterial prostheses and their initial contact with blood, we propose the use of an in vitro test using labelled platelets and fibrinogen to measure the amount of the thrombotic matrix that is entrapped by the wall of the graft. The results have been confirmed by scanning electron microscopy. Polyester prostheses, whose healing process depends on the reorganisation of the thrombotic matrix, retains considerably more blood cells than the polytetrafluoroethylene microporous prostheses or the treated biological devices, whose fate, following implantation, maintains almost complete passivity.

Biocompatible Materials↗
PubMed1984

[Venous homografts as femoro-popliteal bypasses or as vascular access routes in chronic hemodialysis].

Saphenous vein homografts preserved by freezing at 40 degrees C in the presence of antibiotics for periods of as much as six months were implanted as part of a clinical evaluation program. Candidates included one requiring femoro-popliteal reconstruction with two separate bypass procedure and reoperations for thrombosis and false aneurysm in the left limb as well as 23 maintenance hemodialysis patients (32 arteriovenous blood access shunts for a total of 424 patient-months). Explanted veins used as femoro-popliteal bypasses were examined after collection incidental to reoperations and autopsy. In-vivo dwell time varied between 7 and 51 months. The femoro-popliteal by-passes exhibited calcification and sclerosis. The dialysis access shunts had average service lives of about a year; 21 were replaced because of thrombosis, 10 were stenosed, 7 had aneurysms and necrosis was present in six. Although this implant provides a workable alternative approach to vascular reconstruction, the rapid degeneration of such veins in vivo is a limitation.

Aged↗
PubMed1984

[Radioisotope evaluation of the interaction between blood and vascular prostheses. Preliminary results].

In order to illustrate the phenomena which occur at the first contact between arterial prostheses and blood, an in vitro test is suggested which may be used to quantify the retention of the cruoric matrix using labelled compounds and confirming the nature by scan electron microscopy. Reorganisation of the cruoric matrix is dependent upon the scarring of polyesters which retain considerably more blood substances than microporous polytetrafluoroethylenes or the biological models dealt with, the course of which after implantation is closer to passivation.

Bioprosthesis↗
PubMed1983

Polyester prostheses as substitutes in the thoracic aorta of dogs. I. Evaluation of commercial prostheses.

Using canine models, a representative selection of polyester or Dacron vascular prostheses, including woven, knitted, and velour types, were evaluated for their relative healing characteristics and for their structural changes during implantation. Following residence periods ranging from 4 h to 6 months at the site of the thoracic aorta, the dogs were sacraficed, and the grafts were excized for measurement of the thrombogenicity of the flow surface and for pathological examination by light microscopy and SEM. The kidneys were also removed and examined for infarcts caused by any trapped circulating emboli. The extent of healing, the presence of embolizing nuclei, and the thrombogenicity and morphology of the lumen surface were also assessed. The healing characteristics of each type of device proved similar. Velour fabrics exhibited more extensive encapsulation, but frequently their internal capsules failed to incorporate all the fibers. In all cases, cellular development on the lumen was limited to areas contiguous to the anastomoses. The initial porosity of the devices as measured by water permeability did not appear to influence the healing sequence to a significant extent. The grafts did exhibit differences in structural stability depending on whether they were of a knitted or woven construction. We suggest that users consider these different mechanical and structural properties when making their choice of a graft. Despite these differences, we believe that the healing process is far more host dependent than graft dependent.

Angiography↗
PubMed1983

Experimental colonization of vascular grafts with Staphylococcus aureus.

In an attempt to solve the problem of infection of arterial grafts, the authors designed an experimental model to reproduce, in vitro, hematogenous seeding of grafts with Staphylococcus aureus. The inoculum, containing an average of 10(7) viable bacterial cells per millilitre, was circulated through grafts of various types. Normal dog aortas were used as controls. They entrapped a mean of 8 bacteria/cm2. The prosthetic grafts, previously placed in dogs as femorofemoral arteriovenous bypasses for 2 hours, trapped many more cells: expanded polytetrafluoroethylene, 23 cells/cm2; bovine heterograft, 607 cells/cm2 and Dacron velour, 2801 cells/cm2. All cell counts were significantly (p less than 0.001) different from control values. Thoracoabdominal aortic bypass grafts implanted in dogs 2 months previously gave the following mean numbers of trapped bacteria: expanded polytetrafluoroethylene, 19 122 cells/cm2; bovine heterograft, 863 cells/cm2 and Dacron velour, 3500 cells/cm2. Polytetrafluoroethylene had significantly (p less than 0.001) higher numbers of trapped bacteria than any other type of prosthesis. The bacteria were located mainly on irregular fibrin strands and on surface defects of the grafts. The addition of cefazolin during the seeding process at concentrations 10 to 25 times the minimal inhibitory concentration did not decrease the numbers of bacteria in any graft. Bacterial colonization of prosthetic arterial grafts depends on the graft material and on the duration of implantation, but this study provided no answer to the controversial question of how to prevent arterial graft infections with antimicrobial agents in patients who undergo vascular procedures that expose them to bacteremia.

Animals↗
PubMed1982

New alternatives in the preparation of chemically fixed human umbilical veins as arterial substitutes.

Following reports of the successful use of chemically processed human umbilical veins as medium and small diameter arterial substitutes, the development of new and improved techniques for the preparation, fixation and storage of these bioprostheses has been attempted. A series of physical and "in vitro" tests was undertaken to predict the "in vivo" performance of these devices. The results indicate that the new techniques are not only technically feasible but may provide a more convenient, versatile and effective surgical product.

Arteries↗
PubMed1982

[Analysis of silicone testicular implants after explantation].

Two juvenile size silicone testicular prostheses were analyzed following replacement by adult size devices after 72 and 99 months in situ. Scanning electron microscopy and electron microprobe studies were carried out on the explanted silicone prostheses and their attached tissue capsules. The material at the surface of the prostheses gave no evidence of biodeterioration. However, localized sites of calcification were observed. The adjacent tissue capsule consisted of two distinct concentric layers with different morphologies; the one adjacent to the prosthesis consisted of dense arrays of collagen fibres oriented parallel to the silicone surface and extending outward to a thickness of 100-120 microns. The outer layer was less dense, more disordered and was uneven in thickness. It contained numerous discrete particles of silicon-rich material. Technical and clinical implications of these results are discussed.

Adolescent↗
PubMed1982

[The use of jugular veins as carotid artery substitutes in dogs: a comparison between cryopreservation techniques and the tanning process of vein preservation (author's transl)].

Improved surgical techniques and an aging population have allowed surgeons the opportunity to implant vascular prostheses in patients where the run-off bed is somewhat compromised. We have considered the possibility of homograft venous preservation either by tanning or cryopreservation and now report our preliminary experience in the canine model jugular veins of large mongrel dogs were excised and treated in one of two manners. These veins were preserved for either seven or thirty days and inserted as functional segments in the carotid vessels: each dog received a tanned vein on one side and one which has been cryopreserved on the other side, as either an autograft or allograft. After three months the twenty one dogs were sacrified and the grafts recovered and examined for patency and histology. There appeared to be no difference in patency between the autograft and the allograft groups but there were striking differences in patency between the tanned grafts (8/21) and the cryopreserved grafts (19/21). Tanned grafts showed a fibrous hyperplasia at the anastomotic suture line that seemed to be the causative factor for graft thrombosis. Cryopreserved grafts showed sclerotic degeneration in the midportion of the graft: it was found to be more pronounced in the 30 day preservation specimens. The relatively good results, regarding patency, in the cryopreserved group has sparked our interest to investigate further into this process.

Animals↗
PubMed1982

Hormonally induced formation of extracellular biomatrix in cultured normal and neoplastic liver cells. Effect of dexamethasone.

We have examined by scanning electron microscopy the cell surface of rat hepatocytes (HEP), propagable liver epithelial (CE) cells, Morris # 7777 and # 7795 hepatoma (MH) cells at different times after seeding onto fibronectin-precoated substratum in presence of a defined medium. Upon seeding, HEP exhibited numerous microvilli and at later times, the cells flattened and lost most of these structures. When HEP were cultured in presence of dexamethasone (DEX), numerous microfibrils were observed extending into the substratum and on the cells and formed elaborate extracellular matrices. By indirect immunofluorescence we have demonstrated that these extracellular matrices are composed of fibronectin and collagens (type I, III). In contrast to HEP, sparse or confluent CE cells showed few microvilli and only very low amount of extracellular matrices were observed at confluency, even in presence of DEX. Growing or confluent MH # 7777 cells exhibited some microvilli while MH # 7795 cells showed a lower number of these surface structures at confluency. These hepatoma cell lines produced little extracellular matrices in absence or presence of DEX. Tyrosine aminotransferase (TAT), a liver specific intracellular protein, was inducible in HEP and MH but not in CE cells. Thus, these data demonstrate that the hormonal induction of a liver specific function is accompanied by the production of extracellular matrix only in the case of normal hepatocytes (HEP), but not in the case of cancerous (MH) or epithelial (CE) cells.

Animals↗
PubMed1981

Effects of traumatic manipulations on grafts, sutures, and host arteries during vascular surgery procedures. Experiments on dogs.

Scanning electron microscopy was used to diagnose incidents of trauma and the pattern of healing following surgical implantation of microporous blood vessel substitutes. Vascular reconstruction procedures using autogenous or synthetic prosthetic material inflict damage to the adjacent tissues as well as the prosthesis. This affects the thrombotic behavior and healing pattern of the area. The prognosis for long-term success are, as a consequence, directly influenced. Various vessel-occluding devices were evaluated in canine models with respect to their ability to damage blood vessels at the clamped site. The impact of suture needles on tissues and prosthetic materials was also considered. Of the various vessel-clamping devices which are commercially available, those which have elastomeric shields on the clamping components were found to be most satisfactory. The development of less traumatic surgical devices is discussed with the aim of further reducing surgical trauma.

Animals↗
PubMed1981

Thoraco-abdominal bypass as a method of evaluating vascular grafts in the dog.

Seven Vasculour d grafts, five Gore-Tex grafts and seven Solco-graft, 8 mm by 30 cm, implanted as thoraco-abdominal bypasses in dogs. Sixteen were retrieve at two months. Graft size was assessed angiographically in representative dogs of each group prior to sacrifice. Initial examination of the retrieved specimens revealed pannus extensions at both anastomoses on all graft types, and a variable midgraft appearance from smooth and glistening to partially thrombus coated. Histological assessment of graft segments revealed widely differing healing responses on the three graft types. Tissue attachment to both graft surfaces and varying degrees of tissue incorporation were observed in the Vasculour D and Gore-Tex prostheses. The Solco-graft specimens showed no evidence of tissue incorporation of the wall at two months. Tissue on the graft surfaces remains loosely attached and unincorporated. Pannus extensions were thickest on the Solco-graft. Variably thin fibrin is scattered over the luminal surface of the three graft types. Vascularization of the wall particularly the internal capsulae was noted in the Vasculour D grafts. Although biological responses in the dog are difficult to extrapolate to man, the types of comparison testing allowed by the use of the thoraco-abdominal by-pass procedure can provide valuable information of degree of dilation, relative tissue attachment, tissue incorporation into various types of prostheses and kidney infarcts study. The greatest value of the thoraco-abdominal by-pass lies in graft sizes and length without special regard for patency: assessment of graft size post-implantation and structural changes is then made possible.

Abdomen↗
PubMed1981

[Aneurysm formation on dacron prosthesis after 84 months of use. Pathology, structural and chemical evaluation of the explanted device (author's transl)].

A 56 year old patient fitted with a femoro-popliteal Dacron prosthesis (Weavenit-Meadox Medical) 84 months earlier, presented with a severe palpable dilation in the middle part of the graft. The dilated segment of the prosthesis was resected locally and spliced to a new fabric device. The explanted section of prosthesis was analyzed; the dilation was found to extend only over several centimeters near the centre of the prosthesis. The degree of "healing" was found to be satisfactory except in the part which was most distended; this area also revealed mild bacterial colonization. Physico-chemical analysis of the fabric revealed that the dilation had taken place subsequently to hydrolytic degradation of the polyester fibres. Manufacturing conditions may have contributed to predisposing parts of the prosthesis to accelerated biodeterioration in vivo.

Biodegradation, Environmental↗
PubMed1981

[Liquid storage media for vascular prosthesis of biological origins : their impact on biocompatibility (author's transl)].

Unlike synthetic arterial substitutes which are supplied as presterilized, dry-packaged products with potentially indefinite shelf lives, arterial prosthesis of modified biological origin must stored in less convenient liquid preservative media. These preservatives can affect the post-implantation performance and the biocompatibility of the devices. In order to identify the most suitable media, a modified "in vitro" cell culture test method was developed. It makes use of endothelial cells prepared from the aorta of chick embryo. In general, the prosthesis stored in liquid media had a disappointing performance from the point of view of neo-endothelium development and adhesion. Residual cytotoxicity was also noted for most of these currently used prosthesis storage and pre-surgical preparation protocols. Although devices stored in physiologic media showed adequate biocompatibility according to this cell culture test, it appears that neo endothelialization does not proceed concurrently with healing. Cellular development where present, adheres poorly to the substrate and cannot resist the shear forces of normal blood flow. Pre-implantation treatment of such prosthesis with cellular growth-promoting substances may enhance cell-prosthesis adhesion.

Animals↗