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  • 1
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The biological heart prostheses present midterm and long term problems owing to the progressive deterioration and calcification of the tissue. In the attempt to study the latter problem, we have compared the effectiveness of anticalcification treatments in calf pericardium samples implanted into female Wistar rats after undergoing the following procedures: Group I, control, treatment with glutaraldehyde; group II, treated with 0.1m Al3+ for 24 h; and group III, subjected to lipid removal by chemical treatment with chloroform/methanol for 1 h. Positive results were obtained with both treatments, but the results after 60 days of implantation were more favourable with lipid removal than with Al3+ treatment.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Poor mechanical properties of biological tissue are known to cause wear, leading to the failure of cardiac bioprostheses made of calf pericardium. Different chemical agents such as sodium dodecyl sulfate (SDS) are presently being tested as possible inhibitors of the calcification process. The objective of this report was to determine the mechanical behavior of calf pericardium treated with SDS for 24 h and the influence of the suture on the mechanical properties of the tissue. Forty-eight samples were tested: 24 subjected to a standard treatment with glutaraldehyde (12 sewn with 4/0 silk suture thread) and 24 incubated with SDS for 24 h (12 sewn with the same suture thread). Each sutured and non-sutured sample was cut into two strips to yield paired samples. All were subjected to tensile stress to breaking point. The mean stress at breaking point in the non-sutured series treated with glutaraldehyde alone was 16.42 and 13.85 MPa depending on the region of the pericardium, while in the sutured samples subjected to glutaraldehyde the mean stress was 7.50 and 7.63 MPa, respectively, differences which were statistically significant (p = 0.03 and p = 0.003, respectively) when the means for non-sutured samples from equivalent regions treated with glutaraldehyde were compared. The stress at breaking point was lower in the SDS-treated series, ranging between 2.60 and 3.56 MPa. The mathematical functions that govern the stress/strain or deformation were obtained. In the series of pericardium treated with SDS, deformations of 10% were produced with stresses of under 0.4 MPa, an outcome that is intolerable from the constructive point of view. We established a regression model that enabled us to determine the mechanical behavior of a sutured sample by testing a contiguous piece of tissue, with a high correlation coefficient (r 〉 0.99). We consider this finding to be of interest in the selection of pericardium for use in the construction of leaflets for cardiac bioprostheses.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The objective of the study was to determine the shearing stress exerted by the suture thread under conditions of normal working stress. Thirty-six samples of calf pericardium, similar to that employed in the manufacture of bioprosthetic cardiac valve leaflets, were subjected to tensile testing. Prior to the trial, a continuous suture was sewn in the central zone of each sample, at a 45° angle to the longest axis of the sample, using commercially-available threads (silk, Gore-Tex, Surgilene and nylon). Application of the Mohr circle for combined wear revealed that the shearing stress ranged between 2.68-fold greater (for samples sewn with silk) and 5.48-fold greater (for samples sewn with nylon) than the working tensile stress in the region of the suture. It is concluded that the shearing stress is responsible for the limited durability of sutured samples of calf pericardium prepared to simulate bioprosthetic cardiac valve leaflets. © 1998 Chapman & Hall
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    European journal of nuclear medicine 10 (1985), S. 203-207 
    ISSN: 1619-7089
    Keywords: Cardiac rejection ; Cardiac transplantation ; 201Tl
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Serial percutaneous endomyocardial biopsy is the standard for diagnosis of cardiac rejection; it is generally done on a weekly basis for the first month and then as indicated by ECG voltage; but, this method is invasive, can be done only in specialized centers, not available for the many patients who return home, requires 18–24 h before a result is obtained, delaying institution of therapy, and it is aggressive for the endomyocardium of the graft. A reliable, rapid, and noninvasive test for detection of cardiac rejection is still not available. The aim of this work was to determine whether 201Tl uptake was significantly correlated with the histological findings presenting in cardiac rejection. Auxiliary heart transplantation was carried out on 60 male rats. Graft viability was evaluated by direct palpation, ECG voltage, and 201Tl uptake during the study (from 4–6 h after transplantation to 1 month). Syngenic rats (without rejection) were used as a control group. Histological studies were done at the end of the isotope study in all animals. The statistical significance of all results was determined by means of Student's t-test. A very significant correlation between the severity of the histological findings of rejection and 201Tl uptake was found (P〈 0.001). Our results have demonstrated that 201Tl uptake detected rejection earlier than ECG voltage; moreover, 201Tl uptake was more sensitive in detecting a mild degree of rejection while ECG only detected a moderate degree. We believe that 201Tl uptake should be the screening method for the followup of cardiac transplantation; it offers to surgeons the opportunity to select patients for endomyocardial biopsy, with a higher accuracy than the other noninvasive methods.
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  • 5
    ISSN: 1573-2568
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In order to evaluate whether an antiendotoxin agent can inhibit the action of endotoxin ofEscherichia coli on biliary flow, we used 18 models of isolated perfused pig liver divided into four groups: (A) five perfused livers (control), (B) five perfused livers with 2 mg/100 ml of endotoxin added, (C) five perfused livers with 2 mg/100 ml of endotoxin added and treated with 1,500,000 IU of colistin, and (D) three perfused livers with 1,500,000 IU of colistin with no endotoxin. The livers were isolated and perfused according to a technique previously described by our laboratory. The viability of the perfusions was controlled by means of the mitochondrial respiration test. Transaminase and LDH levels were measured in the perfusion circuit. A significant reduction of the biliary flow was found in the group with endotoxin ofEscherichia coli (P〈0.002). There was no reduction of biliary flow after addition of 1,500,000 IU of colistin (P〈 0.001). No significant changes were observed in the other parameters measured, and no increase of the bile flow was observed in the colistin group. From our results we conclude that colistin is an inhibitorin vitro of the diminished biliary flow induced by endotoxin ofEscherichia coli.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A material subjected to traction stress increases in length; if we maintain the elongation constant, the stress varies over a period of time. This phenomenon has been referred to as relaxation. The purpose of this study was to define a mathematical law that relates the variation in stress to time when elongation remains constant in bovine pericardium. The mathematical function obtained after assaying 34 samples to the point of relaxation, subjected to initial stresses ranging from 0.17-10.07 MPa, responds to the following equation: y = -0.0252 + 0.953 α - (0.0165 + 0.015 α)lnt, where γ is the stress withstood at an instant in time, t, after initial stress α. A normogram, validated by assays of up to 6,340 min duration (4.40 days), is presented for graphic calculation, permitting the computation of the loss of stress due to relaxation of this biomaterial, with initial stresses ranging from 1-10 MPa. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0021-9304
    Keywords: biomaterial ; bioprostheses ; suture ; pericardium ; heart valves ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The mechanical behavior of calf pericardium employed in the manufacture of cardiac bioprostheses was assessed according to the region from which it was selected. For this purpose, selected samples of the tissue were sewn with different types of commercially available sutures and subjected to tensile testing, the results of which were compared with the findings in selected, but not sutured, tissue used as a control. The results confirm a loss of resistance - that is, a reduction of the capacity of sutured samples of the biomaterial to withstand breakage stress compared with control samples. Taking into account the marked resistance to breakage of the suture thread, this phenomenon can only be explained as a consequence of the deleterious mechanical interaction between the suture and chemically treated pericardium. This interaction is illustrated by the shearing force which is responsible for the loss of resistance in the tested samples. These trials demonstrate that the results can be improved and the deleterious interaction diminished, although not eliminated, when the pericardium is selected from a given region. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 568-574, 1998.
    Additional Material: 5 Ill.
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  • 8
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The mechanoelastic behavior of calf pericardium employed in cardiac bioprostheses was compared with that of three types of thread (Nylon, Prolene, and silk) used to suture this biological tissue. The elastic limit (EL) of each material was determined by means of tensile tests and the mathematical functions that govern the stress/strain curves within the EL have been described. The first derivative of these functions for each point to the curves allowed the immediate calculation of the elastic modulus (EM), which was considered the best parameter for comparing the elasticities of the materials being assessed. It was observed that the deformation of the pericardium produced by the working stress of a pericardial leaflet was approximately 1000 times greater than that produced in the surgical threads. When the elasticities were compared on the basis of the EM, that of pericardium was 749.06, 626.95, and 1253.17 times greater than that of the Nylon, Prolene, and silk suture threads, respectively. These results demonstrate that the interaction between these materials (pericardium and the threads) could be generating detrimental forces that can diminish the durability of the leaflets of the bioprostheses constructed of calf pericardium. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 9
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: An ex vivo shunt, established in dogs between both femoral arteries and right atrium, has been used to quantify the platelet deposition on six prosthetic materials used in the construction of cardiovascular prostheses: highly porous knitted Dacron (intervascular HP 800, 1400 mL/cm2/min/120 mm Hg), low-porosity woven Dacron (intervascular LP 200, 200 mL/cm2/min/120 mm Hg), double velour knitted Dacron, Avcothane 51 elastomere, and the mesothelial and epipericardial surfaces of bovine pericardium. In the search for a method to prevent platelet thrombi formation on these materials, we studied four groups of dogs: group 1 (control), group 2 (5 mg/kg body weight (BW)/day acetylsalicylic acid), group 3 (20 mg/kg BW/day acetylsalicylic acid), and group 4 (5 mg/kg BW/day acetylsalicylic acid plus 5 mg/kg BW/day dipyridamole). Platelets were labeled with 111In-oxine. The least thrombogenic material was Avcothane 51 elastomere. The only effective treatment for reduction of platelet deposition on the six materials was 5 mg/kg BW/day of acetylsalicylic acid. The dose used in group 3 only decreased the deposition of platelets on three of the six materials studied. The treatment employed in group 4 did not significantly reduce the deposition of platelets on any of the materials when compared with the control group. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 10
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Since the development of cardiac bioprostheses, numerous chemical treatments have been assayed to prevent mineralization. The effectiveness of chemical treatments that eliminate lipids from the tissue was tested by combining two models. First, handmade bovine pericardial bioprostheses, subjected to chemical treatment with chloroform/methanol and glutaraldehyde or treated with glutaraldehyde alone for use as controls, were subjected to mechanical stress in a heart valve, accelerated wear tester (100 × 106 consecutive cycles). Then, the bioprostheses were unstitched and tissue samples were taken from the portion subjected to maximal stress (P1) and from that surrounding the sewing ring, which had not been subjected to mechanical stress (P2), for subcutaneous implantation. After 21 and 60 days of implantation, we observed calcification of the samples subjected to mechanical stress, even after delipidating treatment, with no significant differences with respect to the control group. However, the treated samples from the portion not subjected to mechanical stress presented a slighter accumulation of calcium after 60-day implantation (5.60 ± 3.09 mg Ca2+/g dry weight of tissue) versus the control group (47.17 ± 20.4 mg Ca2+/g dry weight of tissue), the difference of which was statistically significant (p 〈 0.01). At the time of these medium-term studies, marked calcification was observed in tissue subjected to delipidating treatment in the zones that underwent mechanical stress. © 1996 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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