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Biomedical subjects

M A Pérez

Publications and source records attributed to M A Pérez.

At least 19 recordsLinked to original sources
PubMed2006

Random-walk models of cell dispersal included in mechanobiological simulations of tissue differentiation.

Computational models have shown that biophysical stimuli can be correlated with observed patterns of tissue differentiation, and simulations have been performed that predict the time course of tissue differentiation in, for example, long bone fracture healing. Some simulations have used a diffusion model to simulate the migration and proliferation of cells with the differentiating tissue. However, despite the convenience of the diffusion model, diffusion is not the mechanism of cell dispersal: cells disperse by crawling or proliferation, or are transported in a moving fluid. In this paper, a random-walk model (i.e., a stochastic model), with and without a preferred direction, is studied as an approach to simulate cell proliferation/migration in differentiating tissues and it is compared with the diffusion model. A simulation of tissue differentiation of gap tissue in a two-dimensional model of a bone/implant interface was performed to demonstrate the differences between diffusion vs. random walk with a preferred direction. Results of diffusion and random-walk models are similar with respect to the change in the stiffness of the gap tissue but rather different results are obtained regarding tissue patterning in the differentiating tissues; the diffusion approach predicted continuous patterns of tissue differentiation whereas the random-walk model showed a more discontinuous pattern-histological results are not available that can unequivocally establish which is most similar to experimental observation. Comparing isotropic to anisotropic random walk (preferred direction of proliferation and cell migration), a more rapid reduction of the relative displacement between implant and bone is predicted. In conclusion, we have shown how random-walk models of cell dispersal and proliferation can be implemented, and shown where differences between them exist. Further study of the random-walk model is warranted, given the importance of cell seeding and cell dispersal/proliferation in many mechanobiological problems.

Animals↗
PubMed2005

Dynamic left ventricular outflow tract obstruction secondary to catecholamine excess in a normal ventricle.

Hypertrophic cardiomyopathy (HCM) is the most common cause of left ventricular outflow tract (LVOT) obstruction. The LVOT obstruction is a consequence of the asymmetric septal hypertrophy and the mitral systolic anterior motion (SAM), causing both of them a dynamic gradient in LVOT. LVOT obstruction has been observed also in other conditions like hypertensive hypertrophy, dehydration, sepsis, vasodilatation, excessive sympathetic stimulation, pericardial tamponade, and after mitral valve repair and aortic valve replacement for aortic stenosis. We report in this document the case of two patients who developed a significant gradient at LVOT in the context of amine treatment during their admission into the intensive unit care. In both, cases there were no gradient, significant hypertrophy or SAM at baseline cardiac evaluation. We have met only one case reported in the literature matching those conditions. In order to treat this type of patients properly, it is essential to take in consideration this pathology.

Aged↗
PubMed2005

A comparative FEA of the debonding process in different concepts of cemented hip implants.

Debonding of the stem-cement interface and damage accumulation in the cement mantle are basic events that contribute to the long-term failure of cemented hip reconstructions. In this work, a numerical study with these two processes coupled is presented. On the one hand, debonding of the stem-cement interface was simulated by means of a cohesive surface theory that was implemented into an interface finite element. This interface model includes a tensile-shear behavior law, the fatigue failure of the interface, and the friction evolution between both surfaces. On the other hand, damage accumulation in the cement was formulated through the theory of continuum damage mechanics, considering cement damage due to tension, creep under compression, crack closure effects, non-linear damage accumulation and cement residual stresses appearing during polymerisation. This methodology was applied to simulate and compare the degradation process of the cement and stem-cement interface in four different concepts of design: Exeter, Charnley, Elite Plus and ABG II stems. As the actual mechanical properties of the surface of each specific prosthesis are not known, we assumed the same for all of them, distinguishing between polished and matt surfaces. With this assumption, the predicted results showed that the debonding process is very different for each implant depending on the stem geometry. Lower cement deterioration was obtained for the Exeter and ABG II stems, while the lowest stem-cement interface debonding was produced in the Exeter and the Elite Plus stems.

Biomechanical Phenomena↗
PubMed2005

Ellipsometric study of dissolution of anodic WO3 films in aqueous solutions. 2. Reaction mechanism.

The present work demonstrates that the dissolution of anodic WO3 can be described in terms of general mechanisms already used to account for the physicochemical processes involved in the dissolution of oxides of other metals. The chemical dissolution of anodic WO3 films is characterized by in situ ellipsometry, which has proven to be a suitable technique for studying the processes taking place.(1) The capability of ellipsometry for distinguishing between thickness decrease and hydration and generation of porosity/roughness helps to analyze the thickness range within which reliable kinetic information can be obtained. The dissolution rate law found for anodic WO3 does not depend on the oxide thickness. The dissolution of anodic WO3 films includes hydration and roughening, besides thickness decrease, and is kinetically controlled by the OH- concentration at the oxide/electrolyte interface. Apart from OH-, the specific nature of electrolyte anions seems to play no kinetic role, except in promoting porosity/roughness.

Journal Article↗
PubMed2005

Probabilistic analysis of the influence of the bonding degree of the stem-cement interface in the performance of cemented hip prostheses.

The long-term behavior of the stem-cement interface is one of the most frequent topics of discussion in the design of cemented total hip replacements, especially with regards to the process of damage accumulation in the cement layer. This effect is analyzed here comparing two different situations of the interface: completely bonded and debonded with friction. This comparative analysis is performed using a probabilistic computational approach that considers the variability and uncertainty of determinant factors that directly compromise the damage accumulation in the cement mantle. This stochastic technique is based on the combination of probabilistic finite elements (PFEM) and a cumulative damage approach known as B-model. Three random variables were considered: muscle and joint contact forces at the hip (both for walking and stair climbing), cement damage and fatigue properties of the cement. The results predicted that the regions with higher failure probability in the bulk cement are completely different depending on the stem-cement interface characteristics. In a bonded interface, critical sites appeared at the distal and medial parts of the cement, while for debonded interfaces, the critical regions were found distally and proximally. In bonded interfaces, the failure probability was higher than in debonded ones. The same conclusion may be established for stair climbing in comparison with walking activity.

Cementation↗
PubMed2005

Properties of galactocerebroside layers transferred to glassy carbon electrodes: effect of an applied electric field.

Galactocerebroside films deposited onto glassy carbon electrodes have been previously studied through the electrochemical response of a redox couple present in solution. Those experiments indicated that the film is inhomogeneous and that there are lipid-free places. In this work, we present experimental results indicating that those bare regions are formed when the electrode is introduced in an aqueous solution, and that the size and/or amount of uncovered domains increase when negative potentials are applied to the film. The experimental techniques employed for these findings are epifluorescence microscopy and ellipsometry.

Carbon↗
PubMed2004

Statistical normal values of visual parameters that characterize binocular function in children.

A wide range of visual parameters used to evaluate binocular function were evaluated in a paediatric population (1056 subjects aged 6-12 years). Mean values are provided for these ages in optometric tests that directly assess the vergence system, horizontal phorias for near and far vision (measured by a modified version of the Thorington method), negative and positive vergence amplitude for near and far vision (step vergence testing), vergence facility (flippers 8 Delta BI/8 Delta BO), and near-point of convergence (penlight push-up technique and red-lens push-up technique), as well as stimulus accommodative convergence/accommodation ratio and stereoacuity (Randot test) which provide an overall evaluation of the vergence, accommodative and oculomotor systems. A statistical comparison (anova and Bonferroni post hoc test) of these values between ages was performed. The differences, although statistically significant, were not clinically meaningful, and therefore we identified two trends in the behaviour of these parameters. For all parameters, except for vergence facility, we established a single mean reference value for the age range studied. The difference between the means for vergence facility indicated the need to divide the population into two age ranges (6-8 and 8-12 years). This study establishes statistical normal values for these parameters in a paediatric population and their means are a valuable instrument for separating children with binocular anomalies from those with normal binocular vision.

Aging↗
PubMed2003

Evolution of accommodative function and development of ocular movements in children.

The evolution of the accommodative function and development of ocular movement are evaluated in a non-clinical paediatric population (1056 subjects) aged 6-12 years, providing means for each age in the optometric tests that evaluate the accommodative amplitude, accommodative facility, accommodative response (lag), and saccadic movements. A comparison of these values between ages (anova) established three distinct trends in the behaviour of these parameters. The accommodative amplitude, measured by modified dynamic retinoscopy, and the evaluation of the saccadic movements by the development of ocular movements [developmental eye movement (DEM)] test showed continuous change with age. The values for monocular and binocular accommodative facility, measured by +/-2.00 D flippers, indicated the need to divide the population into two age groups (6-7 and 8-12 years). Finally, the means of accommodative response, measured by monocular estimation model (MEM) retinoscopy, and the direct observation of saccadic movement revealed no significant differences between ages, establishing a single mean reference value for the age group studied.

Accommodation, Ocular↗
PubMed2001

Evaluation of molecular techniques for the genetic characterization of Saccharomyces cerevisiae strains.

The applicability of different PCR-based techniques, random amplified polymorphic DNA, cleaved amplified polymorphic sequence and SSRs (simple sequence repeats) to genetically identify, typify and discriminate among Saccharomyces cerevisiae strains, was investigated. The analysis and comparison of the genetic profiles obtained for each of the techniques allowed determination of the degree of polymorphism, genetic diversity and relationships among the strains. Consequently, the discriminatory power and usefulness of the molecular techniques assayed was established. SSR analysis was the most effective method due to its high level of polymorphism, the ease of interpretation of the genetic profiles obtained, and the speed of use.

Genetic Techniques↗
PubMed2001

Unusual tolerance to high temperatures in a new herbicide-resistant D1 mutant from Glycine max (L.) Merr. cell cultures deficient in fatty acid desaturation.

The unusual tolerance to heat stress of STR7, an atrazine-resistant mutant isolated from photosynthetic cell-suspension cultures of soybean (Glycine max L. Merr. cv. Corsoy) and characterized previously [M. Alfonso et al. (1996) Plant Physiol 112:1499-1508] has been studied. The STR7 mutant maintained normal growth and fluorescence parameters at higher temperatures than the wild type (WT). The temperature for 50% inactivation of the oxygen-evolving activity of STR7 thylakoids was 13 degrees C higher than in the WT. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis with specific antibodies revealed that the integrity of photosystem II in the STR7 mutant was maintained at higher temperatures than in the WT. This unusual intrinsic tolerance to high temperatures contrasted with the higher sensitivity to heat stress reported as a feature linked to the triazine-resistance trait. The chloroplast membrane of STR7 accumulated an unusually high content of saturated C16:0 and reduced levels of C16:1 and C18:3 unsaturated fatty acids compared with the WT. Among all the lipid classes, chloroplastic lipids synthesized via the prokaryotic pathway (mono-galactosyl-diacyl-glycerol, phosphatidylglycerol and di-galactosyl-diacyl-glycerol), which represented more than 75% of the total lipid classes, showed the most substantial differences in C16:0 and C18:3 levels. In addition, changes in the physicochemical properties of the thylakoid membrane and chloroplast ultrastructure were also detected.

Adaptation, Physiological↗
PubMed2001

Detection, distribution and selection of microsatellites (SSRs) in the genome of the yeast Saccharomyces cerevisiae as molecular markers.

AIMS: The aim of this work was the selection of six polymorphic microsatellite loci for their use as molecular markers in the identification, typification and genetic differentiation of S. cerevisiae strains. METHODS AND RESULTS: The selection was undertaken following a search of the genomic DNA database of Saccharomyces cerevisiae for simple tandem repeat sequences (microsatellites) of di- and trinucleotides. The genetic variability generated by these markers was evaluated in 51 isolates. The discriminatory power produced by combining the information obtained by the six microsatellites was very high. A total of 57 alleles, which generated 44 genotypes, were found. CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY: The multiple analysis of microsatellites proved to be a powerful and agile tool for analysing the genome of S. cerevisiae populations.

Alleles↗
PubMed2001

[Identification of mutation in the gene cystic fibrosis transmembrane regulator (CFTR) in Chilean patients with cystic fibrosis].

BACKGROUND: Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the CFTR gene, that codes for a chloride channel located in the apical surface of epithelial cells. The main role of this protein is the regulation of chloride transport, and secondarily, of sodium and water to the extracellular space. More than 900 gene mutations have been described, and their relative frequency in different populations depends on their ethnic origin. AIM: To report the findings of Chilean patients with cystic fibrosis, in whom the presence of 20 common mutations was analyzed. PATIENTS AND METHODS: Fifty seven patients with established diagnosis or suspicion of CF were studied. The simultaneous identification of 20 mutations and the normal delta F508 allele was done using polymerase chain reactions with a commercial assay. RESULTS: Eight mutations were found. Fifty patients fulfilled diagnostic criteria proposed by the Consensus Panel of the CF Foundation and 66% of alleles were identified in this group. delta F508 mutation was found in 45%. We did not identify mutations in any of the remaining 7 patients. CONCLUSIONS: Our results suggest that the majority of undetected mutations are associated with atypical phenotypes or that some patients in this series could have other diseases. We recommend to include mutation analysis in the evaluation of Chilean patients with CF. It is useful to establish prognosis and genetic counselling.

Adolescent↗
PubMed2000

Alcohol, tobacco, and other psychoactive drug use among high school students in Bogota, Colombia.

This descriptive study identified health behaviors practiced by 10th-grade students enrolled in public schools in Bogotá, Colombia. A modified version of the Youth Risk Behavior Survey assessed the health-related behaviors of 1,730 students. In this paper data for tobacco, alcohol, and psychoactive substances use are discussed. A one-way analysis of variance (ANOVA) was used to determine statistical significance among selected behavioral risk areas and the independent variables that were nominally scaled. Data from the study revealed a high use of gateway substances (tobacco and alcohol) among high school students in Bogotá, but lower usage, when compared to US students, of other mind-altering substance such as marijuana, inhalants, and cocaine.

Adolescent↗
PubMed1998

Primary mycotic aneurysm of the ascending aorta diagnosed by transesophageal echocardiography.

Primary mycotic aneurysms are rare, and they can be difficult to diagnose before rupture. Early diagnosis is the cornerstone to effective management. Preoperative diagnosis has traditionally involved angiography and computed tomography. We report a case of Staphylococcus aureus aortitis with an aortic wall abscess and posterior pseudoaneurysm formation involving the ascending aorta in which transesophageal echocardiography was fundamental in diagnosis and patient management.

Abscess↗
PubMed1991

[Automatic reading of ABO and Rh groups on microplates using FMC medium and an IBG Systems reader].

We present in this paper our experience in the routine use of an automatic reader for microtiter plates (IBG Systems). A total of 2044 samples from blood donors have been tested for ABO (haematic and seric) and Rh (D antigen) blood group typing. The red blood cell samples have been tested against monoclonal anti-A, anti-B, anti-AB and anti-Rh 1 (D) sera (using two different anti-D reagents). As a negative control, 3% albumin solution was employed. In order to determine the seric groups, the plasma samples were tested against A1, A2, B and 0 cells. In all cases the red cells were suspended in Ficoll 400R-Methyl cellulose (FMC), and 0.01 Bromelin was added to red blood cell samples to be typed. The obstacles in the automatic readings were mainly solved by visual reading of the microplates. In the 2,044 samples analysed with the automatic reader, 19 discrepancies (0.94%) were found in ABO typing. In all cases the error was in the seric blood group. Three false positive reactions were found with 0 red cells. Two false negative with B red cells, interpreted by the automatic reader as doubtful results. Three positive readings were detected, in one case the positivity was due to alloantibodies (C + D specificities), the other two cases were autoagglutinations. False negative reactions were found, in 11 cases, 8 of them due to lipaemia and the remaining three were haemolysed plasma samples. It should be stressed that out of 19 cases of discrepancy, only 5 (0.24%) were due to the automatic reader while the remaining were due, to sample troubles.(ABSTRACT TRUNCATED AT 250 WORDS)

ABO Blood-Group System↗