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Biomedical subjects

R Guidoin

Publications and source records attributed to R Guidoin.

At least 217 records · Page 12Linked to original sources
PubMedDate not supplied

Noninvasive follow-up of tissue encapsulation of foreign materials. Are magnetic resonance imaging and spectroscopy breakthroughs?

The development of sensitive and noninvasive magnetic resonance (MR) techniques for the long- and short-term evaluation of vascular prostheses requires detailed knowledge of the evolutionary trend of the MR properties of the perigraft tissue during the healing process. To characterize changes in water MR properties, the water proton relaxation times, T1 and T2, of the muscle in the vicinity of an implanted polyester material were measured as a function of implantation time. To provide better insight into interpretation of the MR results, we carried out histologic and peripheral blood cell activation studies and tissue water content measurements. The MR results illustrated the sensitivity of the relaxation times to changes in cellular response to the presence of an implant. The evolutionary trend of these MR parameters exhibited two distinct phases. The crossover from phase I to phase II occurred around 10 days postimplantation. This crossover is attributed to the transition in the inflammatory response from the acute phase to the chronic phase. During the acute phase, the very high initial T1 and T2s (the slower relaxing component of the transverse relaxation time) values decreased significantly and steadily. The value of T1 dropped by a factor of 2, whereas T2s went down by a factor of 6. During the same time, the diffusion parameter, beta, remained constant. However, during the chronic phase, the diffusion parameter increased sharply. By 30 days postimplantation, the value of beta had increased by a factor of 10. The relaxation times, on the other hand, increased steadily with implantation time. Because the current MR results provide an in vivo and noninvasive follow-up of the healing process around the polyester implant material, they will be of considerable value in the early detection of vascular graft complications by MR imaging.

Animals↗
PubMedDate not supplied

Can collagen impregnated polyester arterial prostheses be recommended as small diameter blood conduits?

A collagen impregnated graft and its parent preclotted prosthesis were implanted as thoraco-abdominal bypasses in dogs for periods ranging from 4 hr to 6 months and evaluated for their ease of handling, imperviousness, and healing behavior in terms of luminal surface thrombogenicity using labeled platelets and fibrinogen, prostacyclin (PGI2) secretion, histomorphometric determination of internal capsule thickness, and histopathologic and scanning electron microscopic studies. The collagen impregnated graft was impervious to blood and both grafts showed excellent handling characteristics. Fibrin uptake was negligible on both grafts; however, platelet uptake was higher on the collagen impregnated graft than on the control graft at 4 and 24 hr. The healing behavior of the collagen impregnated graft was also found to be different than that of the control graft between 1 and 6 months post implantation. The development of a host collagenous internal capsule at the anastomoses, and a confluent endothelial lining, was observed in both grafts at 1 month; in later implantation periods, the healing of the medial region was found to be more irregular in the collagen impregnated grafts, showing a lower mean PGI2 secretion than the preclotted control grafts. Histomorphometric analysis showed the internal capsule on the collagen impregnated grafts to be thicker than on the control grafts for most periods of implantation. The current study illustrates that the healing process of collagen impregnated grafts is delayed and that bovine collagen has a stimulating effect on tissue encapsulation. Current impregnated polyester arterial prostheses therefore cannot be recommended as small diameter blood conduits.

Animals↗
PubMedDate not supplied

Polyester arterial prostheses. Recent developments from the Czech Republic and Poland.

To evaluate recent developments in the design and production of polyester vascular prostheses in eastern Europe, a series of in vitro physical and chemical tests and an in vivo study was performed on three new prototype devices from the Czech Republic and one from Poland. The in vitro results for these four prostheses, referred to as the Ra-1n (warp knitted, uncrimped), Ra-1v (warp knitted, crimped), Mikrofroté (weft knitted, uncrimped), and Dallon (warp knitted, crimped) prostheses, were compared against values for three commercial devices of western origin, namely the Triaxial, the Vasculour II, and the Cooley II grafts. The animal trial involved implanting the four prototype devices as a thoracoabdominal bypass in dogs for eight different periods ranging from 4 hrs to 6 months and undertaking histologic and structural investigations on the retrieved grafts. Because of its poor long-term dimensional stability in vivo, the continued use of a weft knitted structure, like the Mikrofroté prosthesis, is to be deprecated. Conversely, the introduction of a more dimensionally stable warp knitted structure in three prototypes is to be acknowledged. However, the presence of surface contaminants was most likely responsible for the excessive inflammatory reaction generated by all four prostheses during the first month in vivo, which resulted in delayed healing performance. In addition, an unusually high surface carbon-oxygen ratio suggests that the crimping process needs further refinement. Improved cleaning and packaging procedures are essential before these products can complete against existing commercial prostheses of western origin. In conclusion, these new developments illustrate that the technology of warp knitting, which is now spreading worldwide, should be evaluated.

Animals↗
PubMedDate not supplied

Comparison of the in vivo behavior of polyvinylidene fluoride and polypropylene sutures used in vascular surgery.

To find a nonabsorbable suture material that is equivalent to polypropylene in ease of handling and tensile properties, and that has low thrombogenicity and tissue reactivity but improved biostability, some researchers and clinicians see merit in considering the suitability of monofilaments made from polyvinylidene fluoride. The current animal study investigated the relative biocompatibility and biostability of these two suture materials by using them to anastomose a polyester arterial prosthesis in a canine thoracoabdominal bypass model for 10 periods of implantation ranging from 4 hr to 2 years. Biocompatibility was assessed with light and scanning electron microscope examinations of the explanted sutures, and biostability of the cleaned sutures was determined by Fourier transform infrared spectroscopy and scanning electron microscope analysis. The polyvinylidene fluoride and polypropylene sutures were found to have similar handling and healing characteristics. During the first months in vivo, both types of suture experienced a temporary increase in carbonyl group absorption that coincided with the duration of the inflammatory response. After 1 and 2 years in vivo, the explanted polypropylene sutures showed visual evidence of surface stress cracking. This was not found with the explanted polyvinylidene fluoride sutures. These results suggest that polyvinylidene fluoride may be more biostable than polypropylene in the long term.

Animals↗
PubMedDate not supplied

Use of supercritical fluid extraction as a method of cleaning anterior cruciate ligament prostheses: in vitro and in vivo validation.

The process of supercritical fluid extraction (SFE) using carbon dioxide as the mobile phase is finding increasing numbers of applications in a wide variety of industries for the extraction, separation, and cleaning of materials. This study assessed the usefulness of this approach in removing surface contaminants from a knitted polyester anterior cruciate ligament (ACL) prosthesis before packaging and sterilizing the product during manufacture. The physical, dimensional, and chemical properties of SFE treated compared with commercially scoured control samples were characterized using a number of textile test methods: electron spectroscopy for chemical analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry, and solvent extraction analysis. The biocompatibility of the samples was measured in terms of their ability to generate CD18 integrin expression on activated human polymorphonuclear cells, and their inflammatory response when implanted for up to 30 days in the knee joint of rats. SFE treatment was successful in removing most of the nonpolar contaminants from the ACL prosthesis and reducing the amount of residuals to a commercially acceptable level. However, some nitrogen containing compounds and polar salts were not removed by the SFE process. The results from the biocompatibility tests demonstrated that the cleaner SFE treated prosthesis induced significantly lower CD18 expression than the scoured control fabric, and was also associated with a milder inflammatory response and a more rapid rate of healing during the 30 day animal trial. Another effect of SFE processing was to cause the polyester device to shrink and lose porosity because of yarn contraction and modification of the polymer's microcrystalline structure.

Animals↗
PubMedDate not supplied

Development of in vitro performance tests and evaluation of nonabsorbable monofilament sutures for cardiovascular surgery.

There have been reports suggesting that polypropylene (PP) monofilament sutures are associated with mechanical failure. To overcome this problem, a new monofilament suture made from polyvinylidene fluoride, under the trade name of Teflene, has been developed. Few studies have measured the in vitro properties of Teflene sutures, and those that have, have been limited to a few tensile properties of the straight suture such as tensile strength, elongation, and creep behavior. The in vitro performance properties of Teflene sutures were evaluated and compared with those of commercial sutures made from PP such as Prolene and Surgilene in four sizes, 2-0, 3-0, 4-0, and 5-0. The performance properties of sutures included both the physical properties of straight sutures, such as suture diameter, tensile strength, elongation, surface roughness, coefficient of friction, bending stiffness, and tissue drag, and the knot characteristics, such as knot pull strength, knot run-down, and knot security. Existing standard test methods and testing instruments were used if available to measure certain suture properties such as diameter, tensile strength, knot pull strength, and some physical properties. The other novel test methods and unique accessory devices needed to perform the tests for measuring tissue drag, knot run-down, coefficient of friction, and knot security were developed in the authors' laboratories, and the comparative results are reported for the first time. From the test results, Teflene sutures were found in general to possess equivalent characteristics to those of existing PP commercial sutures, but some differences also were observed, such as greater elongation and less knot run-down. These differences may give them a unique feel and handling performance, especially in terms of making a knot, sliding it into position, and causing less damage to adjacent tissue.

Cardiovascular Surgical Procedures↗
PubMedDate not supplied

Theoretical prediction of the hemodynamic performance of slow resorbing polyester protein impregnated arterial prostheses after implantation: a plea for fast resorption of the coating.

The clinical literature cites cases where slow, incomplete, or nonuniform protein resorption from protein impregnated arterial prostheses produces undesirable localized internal capsule proliferation leading to a significant reduction of the internal diameter of the prosthesis. In an attempt to describe the hemodynamic response to this phenomenon, the blood flow in such stenotic regions was simulated and characterized numerically using FIDAP computational fluid dynamics software to determine the Navier-Stokes and continuity equations for simple channel flow. To simulate various stages of internal capsule development, numeric computations were made in an idealized tubular expansion at stenosis ratios ranging from 0.9 to 0.5 and stenosis length ratios from 10 to 40. The results indicated that a triangular annular ring vortex was formed immediately distal to the stenosis at all Reynolds numbers (Re) studied. The size of the vortex increased almost linearly with the Reynolds number. The pressure drop through the stenosis was affected by blood flow rate, severity, and stenosis length. When the stenosis ratio was low, the pressure drop through the stenosis increased gradually and almost linearly with blood flow rate. In a severe stenosis, the pressure drop was no longer a linear function of flow rate, but increased significantly with increasing flow rate. In conclusion, satisfactory healing of the internal capsule requires fast resorption of any impregnated protein. If the resorption is slow, incomplete, or nonuniform, there is a tendency for the lumen to narrow, causing stenosis, an increased pressure drop through the narrowed graft and disturbed flow distal to the stenosis. This phenomenon therefore constitutes a major limitation for using this type of graft in small diameter arterial reconstruction.

Absorbable Implants↗
PubMedDate not supplied

Phonocardiogram spectral analysis simulator of mitral valve prostheses.

Spectral analysis of sounds produced in vitro by mitral valve prostheses placed in a specially designed flow simulator has been carried out using a short-time Fourier representation of the recorded signal. Time variations of power spectra are displayed as a three-dimensional plot. Sounds produced by three types of valves, namely ball and cage, tilting disk and porcine valves, were analysed. Each valve type produced a characteristic spectrogram, and, for a given valve, spectrograms were reproducible to within a margin of 5 dB. The simulator may be used to detect structural deficiencies and functional abnormalities of prosthetic heart valves. In addition to quantifying the noise level of mechanical valves, the system may be used for quality control purposes to identify faulty valves.

Equipment Design↗
PubMedDate not supplied

Use of myxalin for improving vascular graft healing: evaluation of biocompatibility in rats.

Myxalin is a glycopeptide extracted recently from a gram-negative bacterium. It has blood anticoagulant properties and can enhance endothelial cell growth. With the ultimate objective of using this bioactive molecule to promote vascular graft healing, this study assessed its biocompatibility in vivo by comparing the cellular and immunological responses of gelatin-coated knitted polyester grafts with and without myxalin following implantation in the peritoneal cavity of rats for prescheduled periods of 3 days and 1, 2, and 4 weeks. A nongelatin-coated virgin polyester graft was included as the reference material. The biological response to gelatin alone was characterized by a slower rate of cellular infiltration into the implant, reduced collagen synthesis, and higher levels of acid phosphatase and esterase activity in the surrounding tissue. The addition of myxalin to this coating resulted in a significant reduction of hydrolase secretion in the tissue surrounding the implant and an enhancement of cellular ingrowth.

Acid Phosphatase↗
PubMedDate not supplied

A novel microporous polyurethane blood conduit: biocompatibility assessment of the UTA arterial prosthesis by an organo-typic culture technique.

An organotypic culture assay has been used to assess the biocompatibility and cytotoxicity of an arterial prosthesis developed at the University of Texas-Arlington (the UTA graft) from a structurally modified polyurethane (PU) elastomer (Tecoflex). The cell culture test was applied to the UTA graft after sterilization by ethylene oxide and by gamma radiation in two separate series. First, small specimens of the prosthesis were incubated for 7 days on a semisolid nutrient medium with their luminal surface in direct contact with endothelium explanted from the aorta of chick embryos. Second, the possibility of cytotoxic contaminants being leached from the polyurethane was assessed by immersing the biomaterial in the liquid culture medium for 5 days at 37 degrees C prior to conducting the organo-typic culture assay on a standard control surface. The structure of the UTA polyurethane prosthesis is porous, but the graft wall is impervious because it contains closed (i.e., noncommunicating) pores. In addition, four other vascular prostheses were included in the study for comparison. They were the Hydrophilic Mitrathane PU graft with a similar impervious, closed pore structure, an experimental Hydrophobic Mitrathane PU graft with a fibrous, open pore structure, and the commercial Impra and Reinforced Goretex expanded PTFE grafts. Following 7 days of cell culture, the biocompatibility and cytotoxicity of the various biomaterials were measured in terms of the area of migrating cells, the density of cells surrounding the explants, and the level of cell adhesion. Comparison of the results against control cultures demonstrated that the UTA graft, along with the other four prostheses, does not release cytotoxic extractables. Microscopic observations of its cultured surface indicated that the UTA graft promotes a high density of cell growth over a limited area, similar to the Hydrophilic Mitrathane graft. This level of biocompatibility is considered inferior to that of the two PTFE and the Hydrophobic Mitrathane prostheses, which promote more extensive cell migration, greater cell adhesion, and cell growth in a continuous single layer.

Animals↗
PubMedDate not supplied

A novel microporous polyurethane vascular graft: in vivo evaluation of the UTA prosthesis implanted as infra-renal aortic substitute in dogs.

A novel microporous polyurethane blood conduit developed at the University of Texas at Arlington was implanted as an infra-renal substitute in dogs. The prosthesis was fabricated by precipitating a solution of the polymer with dry nitrogen onto a rotating mandrel. The grafts were sterilized either by gamma radiation (series I) or ethylene oxide (series II); they were implanted for the following prescheduled periods: 4, 24, 48 hours, and 1 week (short-term) and 2, 4 weeks, 3 and 6 months (medium-term). The thrombohematological characteristics of each animal were evaluated prior to implantation and confirmed that the index of blood coagulability was normal. In the short-term group, five out of eight grafts were patent and three were partially occluded; four grafts in the medium-term group were patent; one was partially occluded; and three were thrombosed at retrieval. One week after implantation, the prostheses were surrounded by an external capsule, which was present mainly at the two anastomoses. The external capsule covered the entire graft at 3 months. No kinking of the grafts was observed and the presence of a mild yellow stain related to bilirubin uptake was detected at 2 weeks, 1, 3, and 6 months. Histological studies have revealed the formation of a thin internal capsule at both anastomoses, 2 weeks postimplantation, which was not anchored to the graft wall. In the medium-term group, the thrombosed grafts failed to develop an internal capsule, whereas the patent graft exhibited a thick internal capsule made of neocollagenous tissue over the entire graft. This new microporous polyurethane prosthesis did not perform satisfactorily as an infra-renal substitute in dogs and its in vivo stability requires further assessment. Thus, the concept of a polyurethane with closed pores does not achieve what was anticipated.

Animals↗
PubMedDate not supplied

Longitudinal forces acting on a knitted polyester arterial prosthesis when implanted as a thoracic aorta substitute in the dog.

The longitudinal forces under which arterial prostheses are held in situ are of great importance. The tension caused by the longitudinal force may be one of the factors involved in the formation of anastomotic false aneurysms. In order to measure the changes in the longitudinal force at both proximal and distal end-to-end anastomoses over different periods of implantation, we devised an experimental study in which the changes in length of a warp-knitted polyester VP1200K (Vascutek Ltd., Inchinnan, Scotland) arterial prosthesis, used as a thoracic aorta substitute in the dog, were recorded photographically at implantation and removal. The longitudinal forces acting at the two sites were then calculated using a linear relationship between the longitudinal force and the changes in length of a virgin prosthesis, which was found experimentally in vitro using a computerized laser calibration system. One-tailed Student's t-test showed no significant difference between the length indicator values at the two anastomotic sites at different periods of implantation except during the 1-month period. Textile analysis of the explanted prostheses and histopathologic observations confirmed this similar behavior at the two anastomotic sites. These observations were contrary to the theoretic prediction regarding the effect of forces applied by drag and tissue ingrowth. Nevertheless, analysis of variance confirmed that there was no difference evident at the two sites between different implantation periods. These observations may explain why the formation of anastomotic false aneurysms is less common at end-to-end anastomoses.

Animals↗
PubMedDate not supplied

Fresh venous allografts as arterial substitutes in dogs: the importance of donor-recipient tissue compatibility.

Fresh venous allografts were investigated in dogs matched according to donor-recipient tissue compatibility, either originating from the same litter or chosen at random (pound dogs). Five centimeter long segments of femoral vein were interposed as carotid substitutes in an autografting and allografting manner between paired dogs. During a 5-month implantation period, donor-specific antibody development was measured in the recipient serum by a flow-cytometric assay using cultured donor vascular endothelial cells. Autografts and allografts were investigated in terms of patency, histopathology, and endothelial cell function. Fifteen of 16 autografts remained patent. Allografts between littermate dogs, whether compatible or incompatible, showed no donor-specific antibody development and were all patent at retrieval. Compatible and incompatible allografts in littermates did not show any difference in prostacyclin (PGI2)/thromboxane A2 (TXA2) ratios. In pound dogs, both compatible allografts were patent and one dog developed donor-specific antivascular endothelial cell antibodies. Among incompatible dogs, antibody formation was detected at 1 month in five of six recipients and graft patency was as follows: two partial thromboses, two stenoses, and two patent grafts. The PGI2/TXA2 ratio was significantly lower in incompatible allografts than in compatible ones (p = .028). These results show the importance of donor-recipient histocompatibility matching in improving the outcome of vein allografts.

Animals↗
PubMedDate not supplied

Pumpless respiratory assistance using a membrane oxygenator as an artificial placenta: a preliminary study in newborn and preterm lambs.

Newborns suffering from severe respiratory difficulties and not responding to conventional methods have been successfully treated by extracorporeal circulation with a membrane oxygenator (ECMO). However, the technique needs a highly specialized staff, excellent laboratory support, and continuous surveillance of the procedure to prevent complications. In a series of experiments on newborn and preterm lambs, we have investigated a relatively simpler technique of respiratory support that involves a pumpless arteriovenous bypass by cannulating both umbilical arteries and the umbilical vein. A highly efficient microporous membrane oxygenator (MO) with very low resistance was selected. This type of perfusion that mimics the placental circulation, besides providing an additional amount of oxygen to the blood, has proven to be very effective for CO2 extraction. Before its application in humans, however, improvements in the catheters to be inserted in the umbilical vessels, some modifications in the design of the MO, and improvements in the blood compatibility of all foreign surfaces in contact with blood are needed.

Animals↗
PubMedDate not supplied

Longitudinal forces acting at side-to-end and end-to-side anastomoses when a knitted polyester arterial prosthesis is implanted in the dog.

In a previous study, which investigated the tensions at the proximal and distal end-to-end anastomoses of a vascular prosthesis, no significant differences were found in the longitudinal forces between the two anastomotic sites after different periods of implantation. The present follow-up study was devised to study the longitudinal forces at a proximal side-to-end and a distal end-to-side anastomosis using a warp knitted polyester prosthesis implanted as a canine thorocoabdominal bypass. The external surface of the prosthesis contained a specially printed "tension indicator" design, which enabled changes in length to be assessed photographically at the two anastomoses at the time of implantation and at sacrifice. The longitudinal force at each site was then calculated using a relationship obtained experimentally between the total longitudinal force and the changes in length of the virgin graft in vitro. The in vitro measurements on the prosthesis were performed using a computer-controlled laser calibration system. Although the results showed a tendency toward a gradual loss in longitudinal force at both anastomoses over 7 months in situ, statistical analysis showed no significant difference in the longitudinal force at the two anastomotic sites after any period of implantation. Histopathological and textile analysis also showed that the characteristics of the prostheses were similar at both anastomotic sites. This does not mean, however, that the intramural stress concentrations experienced by the two sites were the same. While comparing the level of the longitudinal forces measured in this study with those observed in the previous thoracic aorta study using end-to-end anastomoses, no significant differences were observed due to the different types of anastomoses. It would appear that the longitudinal force is not one of the main etiological factors that cause the formation and localization of anastomotic failure.

Anastomosis, Surgical↗
PubMedDate not supplied

Can the infusion of elastase in the abdominal aorta of the Yucatán miniature swine consistently produce experimental aneurysms?

The intraluminal elastase perfusion model has been proved to be potentially effective in producing abdominal aortic aneurysm in rodents, but it produced unpredictable results in larger animals. The purpose of this study was to explore the potential ability of such a model to produce experimental aneurysm consistently in the Yucatán miniature swine. Six Yucatán miniature swine received infusion with porcine elastase into an isolated segment of the infrarenal aorta. The excised arterial segments were examined macroscopically to assess the luminal surface characteristics and histologically to describe the different pathologic injuries induced by the elastase treatment on the intima, media, and adventitia of the arterial wall. Histologic examination revealed that the elastic network of the media was destroyed. In the first week after perfusion, altered smooth muscle cells were located in the intima and innermost layer of the media in juxtaposition with the occlusive thrombus. Infiltration of inflammatory cells was observed in these regions of elastic network and smooth muscle cell alterations. In the arterial segments of swine sustained for 3 weeks, a reduction of smooth muscle cells was noted in some areas. An important number of necrotic lesions was observed, and they were associated with the development of calcium deposits. Significant intimal hyperplasic reaction was identified at day 19 and again at day 21. However, no aneurysmal development was observed. This study constituted the first experiment with infusion of porcine elastase in the Yucatán miniature swine infrarenal aorta. The present experimental protocol induced important elastic network and smooth muscle cell alterations leading to severe necrotic lesions associated with calcium deposition, but it produced no aneurysmal dilatation. This model requires further testing to obtain a more complete degradation of the elastic network in both the media and adventitia and more significant collagenolysis without early thrombotic events.

Animals↗
PubMedDate not supplied

Experimental modifications to a canine infrarenal aortic aneurysm model for the validation of endovascular stent-grafts: an exploratory study.

The intraluminal elastase perfusion model has been proven to be potentially effective in producing abdominal aortic aneurysms (AAA) in rodents, yet has produced unpredictable results in larger animals. The purpose of this study was to explore different variations to an existing elastase perfusion model in the dog in the hopes of producing a consistent AAA for endovascular graft validation. The elastase perfusion canine model was modified as follows: (1) inflation of a balloon catheter in the infrarenal aorta (IA) of 3 dogs following elastase perfusion with doses of 2800 U for 40 min; (2) perfusion of the IA of 5 dogs with various elastase doses ranging from 2800 U to 8400 U for 2 h; and (3) perfusion of the IA of 2 dogs with elastase and collagenase for 2 h. The dogs were sacrificed at 4, 7, and 29 weeks. Prior to sacrifice, the treated aortic segments were either examined in vivo by x-ray angiography or by ultrasonography to measure aneurysmal dilation. The aortas were examined macroscopically postmortem to assess the luminal surface characteristics, and under light microscopy and scanning electron microscopy to reveal any pathological injuries induced by the various treatments on the aortic wall. Perfusion of the aorta with 2800 U elastase for 40 min followed by balloon catheter inflation either immediately or 3 weeks after perfusion produced no dilation. Perfusion for 2 h with either elastase alone or in combination with collagenase showed an increased aortic diameter averaging 65.6+/-20.8%, with an irregular dilation of the aortic wall. Histological examination revealed partially digested elastic network of the intima, media, and adventitia, as well as a reduction in the number of smooth muscle cells. An intimal hyperplasic reaction was observed in some of the dogs. Located sparingly within the intima were extravasated erythrocytes associated with recent hemorrhages, intramural thrombi in reorganization, and occasional necrotic lesions. The various modifications brought to the elastase perfusion model failed to produced an aneurysmal dilation with enough expansion to make it a reliable model for endovascular graft validation.

Animals↗