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Biomedical subjects

G Téllez

Publications and source records attributed to G Téllez.

At least 19 recordsLinked to original sources
PubMed2006

Durability of a cardiac valve leaflet made of calf pericardium: fatigue and energy consumption.

We studied the mechanical behavior of membranes of calf pericardium, similar to those employed in prosthetic valve leaflets, when subjected to tensile fatigue. The objective was to assess its durability, as a fundamental property of cardiac bioprosthesis, and analyze the energy consumption. For this purpose, the authors built a hydraulic simulator to subject a spherical valve leaflet made of calf pericardium to cyclic stress mimicking cardiac function. A total of 522 assays were performed in 40 samples, subjected to cyclic pressures greater than 6 atm, and 482 subjected to pressures ranging between 2 and 6 atm. The mathematical expression that establishes the relationship between the pressure exerted and the frequency was obtained. If we assume that the function is continuous, this equation provides the range of fatigue tolerated for a given number of cycles. Using the optimal values (the five highest values per series), the expression was found to be y = 9.95x(-0 1214) (R(2) = 0.955), where x represents the frequency in cycles per second and y the pressure in atmospheres. In addition, we established the mathematical relationship between the energy consumed and the frequency, which was a function of the pressure exerted, regardless of the region or zone from which the samples had been obtained. The methods of manual and morphology-based selection employed produced widely dispersed results. When a mechanical criterion was included, the similarity in the energy consumed during fatigue testing markedly improved the correlation, with a coefficient of determination between paired samples of R(2) = 0.7477. A mechanical criterion, such as energy consumption, can help to improve sample selection and produce more consistent results. Finally, we obtained the mathematical expression that relates the energy consumed to the pressure exerted and the number of cycles per second to which the valve leaflet was subjected. This procedure enables us to establish the limit to the energy that a biomaterial can consume over a period of time during which it is subjected to a working pressure and, thus, calculate more precisely its durability.

Animals↗
PubMed2005

Effect of prebiotic on gut development and ascites incidence of broilers reared in a hypoxic environment.

Modern broilers have been genetically selected for an increased growth rate and improved feed conversion, but they are also more susceptible to ascites. Ascites occurs when there is an imbalance between available oxygen and the oxygen demand of the broiler. We hypothesized that promoting neonatal gut development with a prebiotic, such as Aspergillus meal (Prebiotic-AM), would enhance gut efficiency, decrease the oxygen demand of the gut, and reduce ascites incidence. In this study, we compared the effect of Prebiotic-AM on ascites incidence and gut development in commercial broilers reared at a local altitude (390 m above sea level) and a simulated high altitude (2,900 m above sea level). Half of the birds received a National Research Council recommended corn-soybean ration, and the other half received the same ration supplemented with 0.2% Prebiotic-AM. These 2 groups were further divided into a local altitude group and a simulated high altitude group for a total of 4 treatment combinations. Tissues were collected on d 1, 3, 7, 14, and 21 from the duodenum and lower ileum and placed in 10% buffered formalin for morphometric analysis. At a simulated high altitude, ascites incidence was 68% for birds fed the Prebiotic-AM supplement compared with 92% ascites incidence in birds given the control feed. The simulated high altitude decreased (P < 0.05) gut development, but prebiotic-treated birds reared in hypoxic conditions had similar gut development to control birds reared at local altitude. These data suggest that a feed ration supplemented with Prebiotic-AM may reduce the effect of hypoxia on broiler gut development and ascites incidence.

Altitude↗
PubMed2005

Resistance and stability of a new method for bonding biological materials using sutures and biological adhesives.

The valve leaflets of cardiac bioprostheses are secured and shaped by sutures which, given their high degree of resistance and poor elasticity, have been implicated in the generation of stresses within the leaflets, contributing to the failure of the bioprostheses. Bioadhesives are bonding materials that have begun to be utilized in surgery, although there is a lack of experience in their use with inert tissues or bioprostheses. Tensile testing is performed until rupture in samples of calf pericardium, a biomaterial employed in the manufacture of bioprosthetic heart valve leaflets. One hundred and thirty-two trials are carried out in three types of samples: intact or control tissue (n = 12); samples transected and glued in an overlapping manner with a cyanoacrylate (n = 60); and samples transected, sewn with a commercially available suture material and reinforced at the suture holes with the same cyanoacrylate (n = 60). Seven days after their preparation, 12 samples from each group, including the controls, are subjected to tensile testing until rupture and the findings are compared. In the stability study, groups of 12 each of the remaining 48 glued and 48 sutured and glued samples underwent tensile testing until rupture on days 30, 60, 90, and 120, after their preparation. The results show that bonding with the adhesive provided a resistance ranging between 1.04 and 1.87 kg, probably insufficient for use in valve leaflets, but also afforded a high degree of elasticity. After 120 days, both the glued and the sutured and glued series show excellent elastic behavior, with no rigidity or hardening of the pericardium. These samples present reversible elongation, or strain, when they surpass their elastic limit at rupture. This finding may be due to a load concentration that is damaging to the pericardium, to the behavior of the tissue as an amorphous material, or perhaps to both circumstances. These results need to be confirmed in future studies as they may be of value in the design and manufacture of cardiac bioprostheses.

Animals↗
PubMed2004

Typing of Haemophilus paragallinarum strains by using enterobacterial repetitive intergenic consensus-based polymerase chain reaction.

The enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) technique was used for fingerprinting of reference strains and Mexican isolates of Haemophilus paragallinarum. A total of nine ERIC patterns were given by the nine serovar reference strains of this bacteria. Two Modesto (C-2) reference strains from different sources showed the same ERIC pattern. Seventeen ERIC patterns were obtained among 29 Mexican isolates included in the study, belonging to serovars prevalent in Mexico (A-1, A-2, B-1, and C-2). Obtained results indicate that the ERIC-PCR technique could be used as a molecular laboratory tool for subtyping of H. paragallinarum.

Animals↗
PubMed2002

Mechanical behavior of chemically treated ostrich pericardium subjected to uniaxial tensile testing: influence of the suture.

The mechanical behavior of sutured ostrich pericardium was studied by uniaxial tensile testing. One hundred forty-four tissue specimens were assessed: 96 sutured samples (48 in which a centrally located suture was placed at an angle of 90 degrees with respect to the longitudinal axis, whereas in the remaining 48, a centrally located suture was placed at a 45 degrees angle to the longitudinal axis, in sets of 12 samples each, sewn with sutures made of Gore-Tex, nylon, Prolene, or silk), and 48 unsutured controls. Each group of 24 samples sewn at one angle or the other with the different suture materials was assayed together with a corresponding control group of 12 unsutured samples. The mean tensile strengths in the unsutured controls ranged between 30.16 MPa and 43.42 MPa, whereas those of the sutured sets ranged from 14.68 MPa to 21.91 MPa. The latter presented a statistically significant loss of resistance (p < 0.01) when compared with the unsutured tissue samples. The angle of the suture with respect to the longitudinal axis influenced the degree of shear stress produced by the suture, as well as the behavior of the different suture materials used. The set of samples sewn with Prolene appeared to be that most sensitive to changes in the angle of the suture, whereas tissue sewn at a 45 degrees angle with Gore-Tex presented lower shear stress values in comparison with samples in which the other three materials were used. A method of tissue selection based on morphological and mechanical criteria was used to ensure the homogeneity of the results in such a way that the coefficients of determination (R2) for the stress/strain curve fitting equation ranged between 0.888 and 0.995. This excellent fit made it possible, applying regression analysis, to predict the mechanical behavior of a specimen by determining that of a contiguous tissue sample. Thus, it should be possible, at least theoretically, to characterize the behavior of a specific region or zone of the biomaterial. In conclusion, ostrich pericardium exhibits strong resistance to rupture, even when sutured. The selection method used ensures the homogeneity of the samples and, thus, of the results. The angle of the suture with respect to the longitudinal axis, where the load is centered, determines the shear stress produced by the suture and the mechanical behavior of each suture material.

Animals↗
PubMed2002

Gastric gross and microscopic lesions caused by the UNAM-97 variant strain of infectious bronchitis virus after the eighth passage in specific pathogen-free chicken embryos.

Herein we report a description of gross and microscopic lesions found in specific pathogen-free chicken embryos caused by UNAM-97 infectious bronchitis virus (IBV) variant strain after the eighth passage. Embryos were divided into three groups and were inoculated in the chorioallantoic sac with 0.2 mL of UNAM-97, Mass 41 IBV (positive control), or sterile PBS (negative control). Forty-eight hours later the allatoic fluid was taken and used to start a cycle of eight passages through 9-d-old embryos. Seven days after the last passage, embryos were harvested and macroscopic lesions in all organs were recorded. Proventriculus and gizzard samples were obtained from all embryos and routinely processed for microscopic and ultrastructural examinations. The UNAM-97 IBV variant strain caused two macroscopic lesions uncommon for Mexican strains: thin-walled proventriculus and gizzard, as well as urate accumulation within an extra-embryonic peritoneal sac, leaving the body through the umbilical duct and accompanied by the yolk sac. At microscopic level, two relevant findings were observed to be produced by this variant. In the proventriculus, there was a decrease in the gland papillary branching, while the gizzard showed a significant reduction in mucosa thickness and tubular-to-proliferative-cell ratio, as well as an absence of hyaline secretion in the lumen. Electrodense material scattered in proventricular and gizzard cells was observed, with a structure consistent with that of coronaviruses. These pathological chicken embryo findings have not been reported as being caused by other IBV strains in Mexico.

Animals↗
PubMed2001

Porcine pericardial membrane subjected to tensile testing: preliminary study of the process of selecting tissue for use in the construction of cardiac bioprostheses.

The durability of cardiac bioprostheses is limited fundamentally by structural failure due to mechanical fatigue and calcification. In the present report, we analyze, using an in vitro hydraulic simulator to test tensile strength, the mechanical behavior of porcine pericardium for the purpose of establishing the criteria for selecting the biomaterial, taking into account both morphological criteria (thickness and homogeneity of the specimens) and mechanical criteria (stress at breaking point), using the epidemiological model of paired samples. The stress at breakage was found to range widely from 24.07 MPa to 100.29 MPa, although we observed no statistically significant differences when comparing the mean results in the different regions and zones of the pericardium being studies. The application of the selection criteria in the present series resulted in an excellent mathematical fit in terms of the stress/elongation (R2 > 0.95), making it possible to establish, by means of linear regression, the prediction of the tensile strength in one zone on the basis of the values observed in its paired specimen.

Journal Article↗
PubMed2001

Histological evaluation of immune organs in chicken embryos inoculated with Marek's disease virus and lymphokines.

The aim of the present study was to evaluate the presence of lymphocytes and granulocytes in different stages of embryonic development and on the first posthatching day. The lymphocytes present in the bursa of Fabricius and thymus were evaluated by histological analysis of the yolk sac, bursa of Fabricius, thymus, liver and bone marrow of 100 chicken embryos divided into groups and treated with: (I) Marek's disease vaccine as viral antigen, (II) Marek's disease vaccine plus lymphokines, (III) lymphokines, and (IV) vaccine diluent. Group V was not treated. Samples were taken on days 14, 17 and 20 of incubation and on the first posthatching day. An increase in the number of epithelial matrix as precursors of lymphoid follicles was observed in the bursa of Fabricius of embryos inoculated with lymphokines compared to embryos in all the other groups (p < 0.05). In addition, a higher amount of granulocytes was found in the yolk sac and liver of embryos inoculated with lymphokines than in the embryos of all other groups (p < 0.05). In the bone marrow, no significant difference was observed among the treated groups concerning the amount of granulocytes. The results suggest that administration of antigens or protein molecules at an early stage of embryonic development increases the presence of granulocytes in the liver and granulopoiesis in the yolk sac, and also increases the number of epithelial matrixs in the bursa of Fabricius.

Animals↗
PubMed2000

The influence of chemical treatment and suture on the elastic behavior of calf pericardium utilized in the construction of cardiac bioprostheses.

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 nonsutured 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 nonsutured 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 nonsutured 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\gt 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.

Journal Article↗
PubMed2000

The influence of chemical treatment and suture on the elastic behavior of calf pericardium utilized in the construction of cardiac bioprostheses.

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 \gt 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.

Journal Article↗
PubMed1999

Pulmonary hydatidosis: surgical treatment and follow-up of 240 cases.

OBJECTIVE: We review a series of 240 patients treated surgically for pulmonary hydatid cyst in our center between 1966 and 1988, assessing the results with our surgical technique, which involves a novel needle aspiration device designed by Professor D. Figuera, and postoperative treatment protocol. PATIENTS AND METHODS: The majority (60.4%) of the patients were from areas endemic for hydatid disease. The mean age of the patients at the time of the surgical procedure was 31.5 +/- 7.2 years (range: 4-70 years). A trocar-suction device was used for the needle aspiration of 276 (92%) of the 300 cysts encountered in the 240 patients. The remaining 24 cysts were removed integrally by means of different surgical techniques such as cyst enucleation, lobectomy, segmentectomy and atypical pulmonary resection. The residual cavity was treated by pericystectomy and eversion to the pleural surface in 238 cases (86.2%) and by capitonnage in 38 (13.7%). High vacuum suction (-30 cm H2O) was employed in every case. Depending on when the procedure was performed, the patients were treated with mebendazole or albendazole according to the protocol designed by Bekhti. RESULTS: Clinical assessment of the symptoms and plain chest X-ray led to the correct diagnosis in 228 cases (95%). In six (2.5%), imaging studies such as ultrasonography, computed tomography and nuclear magnetic resonance were required, and in the remaining six cases (2.5%), the diagnosis was established intraoperatively or in the subsequent histopathological study. One hundred and seventy patients (70.8%) presented a solitary lung cyst, while the remaining 70 (29.2%) were found to have multiple cysts in one or more lobes of one or both lungs. In addition, 45 patients (18.7%) presented hepatic cysts and 25 (10.4%) had cysts in other locations. After 18 years of follow-up, the survival rate was 94.6%. Of the surviving patients, 98.3% were free of pulmonary hydatid disease and 95.1% were free of hydatid disease. CONCLUSIONS: The trocar-suction device employed here for needle aspiration of hydatid cysts has demonstrated its efficacy in preventing the rupture of the cyst and its possible dissemination. With its use, the parasite is eradicated and the residual cavity can be excised.

Adolescent↗
PubMed1999

[Association of non-syndromic cleft lip and cleft palate with microsatellite markers located in 6p].

BACKGROUND: Nonsyndromic cleft lip with or without cleft palate (NSCLP) is a common craniofacial developmental defect. Association studies have suggested that a clefting locus is located on chromosome 6p at or near two possible loci, Factor 13A (FI3A) in the region 6p 25-24 and HLA at 6p 21.3. AIM: To test the hypothesis on the possible presence of a major gene on chromosome 6p associated with NSCLP. PATIENTS AND METHODS: We carried out an association study on a sample of unrelated NSCLP patients from multiplex (Mx) and simplex (Sx) families, of their unaffected relatives and in control individuals. DNA was analyzed with three PCR markers close to the putative NSCLP locus, dinucleotide repeats at loci D6S89, D6S109 and D6S105. PCR products were resolved by PAGE and visualized by silver staining. Statistical analysis was performed by means of chi 2 log ratio. RESULTS: Significant differences were observed when comparing the allele frequency distribution of D6S89 in patients with NSCLP and controls and in patients with NSCLP-Mx and controls. No significant differences were observed for patients with NSCLP-Sx. D6S109 and D6S105 showed no significant differences in any of the comparisons. CONCLUSIONS: Our results support the hypothesis that a NSCLP locus maps on 6p23 very close to D6S89. Results for D6S109 and D6S105 do not show a clear association. Differences observed between NSCLP-MX and Sx families seem to represent different etiologic entities. The results of the present study, plus those already published for candidate loci, TGFA and MSX1, support the hypothesis that several interacting major genes participate in the etiology of NSCLP.

Alleles↗
PubMed1996

Clinical experience with retrograde lung preservation.

Previous reports and our own experimental work suggest increased vascularity of the tracheobronchial wall when retrograde lung preservation is used. This principle was clinically applied in 21 consecutive lung transplant recipients (10 single and 11 bilateral). Lung preservation was achieved via the left atrial appendage and drainage was obtained through the pulmonary artery. Pneumoplegic preservation was achieved with modified Euro-Collins solution. Cardioplegia was induced by the standard method and the heart, harvested by different teams, did not exhibit left ventricular dilatation. Thirty-two bronchial anastomoses without wrapping were performed. No primary lung graft failure was documented. Cardiopulmonary bypass was instituted in three cases of pulmonary hypertension; however, this was deemed unnecessary in the remainder of the cases of bilateral transplantation while the second organ was being implanted. All bronchial anastomoses were followed between 2 and 28 months. A single instance of bronchial anastomosis dehiscence was observed on the 30th postoperative day. However, no stents were employed in this series, and no strictures or anastomotic granulomas have been reported so far. All the hearts could be used satisfactorily except for one primary graft failure. In conclusion, retrograde lung preservation is feasible in clinical lung transplantation, with simultaneous harvesting of the heart. The impact of retrograde lung preservation on the late clinical outcome remains to be seen.

Anastomosis, Surgical↗