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Biomedical subjects

L Gonzalez

Publications and source records attributed to L Gonzalez.

At least 37 records · Page 2Linked to original sources
PubMed2002

Characterization of free volume during vulcanization of styrene butadiene rubber by means of positron annihilation lifetime spectroscopy and dynamic mechanical test.

An experimental investigation was performed to study the effect on the free volume of the advance of the cross-linking reaction in a copolymer of styrene butadiene rubber by sulfur vulcanization. The dynamic modulus and loss tangent were evaluated over samples cured for different times at 433 K by dynamic mechanical tests over a range of frequencies between 5 and 80 Hz at temperatures between 200 and 300 K. Using the William-Landel-Ferry relationship, master curves were obtained at a reference temperature of 298 K and the coefficients c(0)(1) and c(0)(2) were evaluated. From these parameters the dependence of the free volume on the cure time is obtained. Positron annihilation lifetime spectroscopy was also used to estimate the size and number density of free volume sites in the material. The spectra were analyzed in terms of continuous distributions of free volume size. The results suggest an increase of the lower free volume size when cross linking takes place. Both techniques give similar results for the dependence of free volume on the time of cure of the polymer.

Journal Article↗
PubMed2002

Long-term cytotoxicity of resin-based dental restorative materials.

Highly filled composites, Ormocers (organically modified ceramics) and 'smart' materials have been developed to overcome the polymerization shrinkage problems of conventional composite materials. The purpose of the current study was to investigate the effect of longer-term (up to 8 weeks) ageing of these resin-based dental restorative materials and determine the effect of post-curing on cytotoxicity. Twelve discs of each material (Colombus/IDR, Definite/Degussa, Ariston pHc/Vivadent) were either light-cured (Lc) or light-cured and post-cured (Pc). For cytotoxicity testing, the discs were placed in contact with cell culture medium (DMEM) and incubated at 37 degrees C. Extracts from composite materials were collected after 24 h and weekly over a time period of 8 weeks. Cytotoxicity of the eluates to cultured fibroblasts (Balb/c3T3) were measured by the succinic dehydrogenase (SDH) activity (MTT assay) and the results expressed in percentage of negative controls (Teflon discs). The results showed that ageing significantly influenced the cytotoxicity of the materials. Except for Ariston pHc, materials were less cytotoxic after 8 weeks of ageing than they were in early intervals and post-curing was not generally useful in reducing cytotoxicity. The Ariston pHc was initially moderately toxic, but then become highly cytotoxic for 5 weeks before returning to initial levels. The current study demonstrated the importance of assessing the cytotoxicity of resin composite materials at multiple times.

3T3 Cells↗
PubMed2001

Glancing-angle diffraction anomalous fine structure of InAs quantum dots and quantum wires.

We have performed Diffraction Anomalous Fine Structure measurements at the As K-edge of self-growth InAs/InP(001) Quantum Wires and InAs/GaAs(001) Quantum Dots. The samples have been grown by Molecular Beam Epitaxy and their equivalent thickness is of 2.5 monolayers. We have measured the (440) and (420) Bragg reflections in glancing-angle scattering geometry, at incidence angles close to the substrate critical angle. We demonstrate the feasibility of the experiment reporting, for the first time. Diffraction Anomalous Fine Structure spectra of such low coverage epitaxial layers, and we show that the analysis of the Diffraction Anomalous Fine Structure lineshape together with the analysis of oscillatory part of the signal, can provide information about composition and strain of the nanostructures.

Journal Article↗
PubMed2001

Helicobacter pylori "test-and-scope" strategy for dyspeptic patients. Is it useful and safe?

AIM: To evaluate outcome of test-and-scope strategy using 13C-urea breath test, Helicobacter pylori IgG serology, and CagA serology. PATIENTS AND METHODS: A series of 100 dyspeptic patients were studied. Biopsies were obtained for histology and rapid urease test (gold standard). Serum samples were obtained for Helicobacter pylori IgG and CagA serology, and 13C-urea breath test was carried out. RESULTS: If endoscopy had not been performed in Helicobacter pylori patients based on 13C-urea breath test, <45 years, without alarm symptoms, and without non-steroidal anti-inflammatory drug use, 15% of endoscopies would have been saved, and one gastric ulcer and two oesophagitis would have been missed. Based on Helicobacter pylori IgG serology, 21% of endoscopies would have been saved. Finally, if endoscopy had been performed only in CagA+ patients, 31% of endoscopies would have been saved, missing one gastric ulcer and two cases of oesophagitis. CONCLUSIONS: In our geographical area, the test-and-scope strategy based on 13C-urea breath test or Helicobacter pylori IgG serology would have saved only 15-20% of endoscopies. Although some relevant pathology would have been missed, it is not of a malignant type. 13C-urea breath test is the preferred non-invasive method to be used in this strategy, while Helicobacter pylori IgG serology is of limited value due to its low accuracy. With the use of CagA serology a larger number of unnecessary endoscopic examinations can be avoided.

Adult↗
PubMed2001

Southern Buenos Aires stroke project.

BACKGROUND: Ethnic differences and vascular risk factors are the major determinants of stroke subtypes. Nevertheless, specific data from undeveloped countries is difficult to obtain. Natives from South America may have a higher frequency of penetrating small vessel disease and hemorrhagic stroke. However, there are few studies in South America supporting these findings. OBJECTIVE: We analyze demographic, ethnic, risk factors, clinical characteristics, and stroke subtypes in all patients with acute stroke admitted to our hospital. METHODS: We studied all consecutive acute stroke patients admitted to the Ramos Mejia Hospital in Buenos Aires from 1997 to 1999. Our hospital serves a determined population of Southern Buenos Aires. Data were collected prospectively on patients' admission in a form especially designed for this study including vascular risk factors, clinical features, epidemiological characteristics, and neuroradiological findings. Stroke subtypes were determined according to the TOAST classification. RESULTS: Among 361 acute stroke patients, 31% had hemorrhagic stroke. It was more frequent among Natives (34%) than Caucasians (27%) (P<0.002). Ischemic stroke subtypes were as follows: 105 (42%) patients had lacunar, 31 (12%) atherosclerotic stroke, 53 (21%) cardioembolic infarction, and 16 (6%) other causes of stroke. Forty-five (18%) patients were classified as undetermined. Small vessel disease was higher among Caucasians (35%) than Natives (24%). CONCLUSIONS: Penetrating artery disease (42%) and intracranial hemorrhage (31%) were the most common stroke subtypes, being more frequent than reported in the literature. Natives had significantly higher frequency of hemorrhagic stroke than Caucasians.

Acute Disease↗
PubMed2001

Helicobacter pylori and bleeding duodenal ulcer: prevalence of the infection and role of non-steroidal anti-inflammatory drugs.

BACKGROUND: Several authors have reported low prevalence of Helicobacter pylori infection in patients with upper gastrointestinal bleeding (UGIB). Our aim was to study the prevalence of H. pylori in bleeding duodenal ulcer (DU), with both invasive and non-invasive methods, and to assess the role of non-steroidal anti-inflammatory drugs (NSAIDs). METHODS: Ninety-two patients with bleeding DU were prospectively studied. The use of NSAIDs was evaluated by specific questionnaire. As a control group, 428 patients undergoing outpatient evaluation for the investigation of dyspepsia and found to have a DU at endoscopy were included. At endoscopy, two antral biopsies were obtained (H&E stain). A 13C-urea breath test was carried out in all patients. Breath test was repeated in patients treated with omeprazole during the hospitalization if H. pylori was not detected with the first test. RESULTS: Gastric biopsies could be obtained in 39 patients with UGIB. Three patients with UGIB treated with omeprazole and being H. pylori-negative with the first breath test were finally considered infected with the second test. Overall, 92.4% (95% CI, 85%-96%) of the patients with UGIB were infected (89.7% with histology and 92.4% with breath test (P = 0.15)). Concordance kappa value for both diagnostic tests was 0.64. NSAID intake was more frequent in patients with UGIB (34%) than in those without UGIB (5.6%) (P < 0.001), while H. pylori infection was less frequent in patients with UGIB (92.4% (85%-96%)) than in those without UGIB (99.1% (98%-100%); P < 0.001). Even in patients with UGIB, NSAID intake was the only risk factor in 5% of cases. The proportion of cases without H. pylori infection and without NSAID intake was very low in both bleeding and non-bleeding ulcers (2% and 0.5%, respectively; P = 0.146). H. pylori prevalence in bleeding ulcers was of 84% (67%-93%) in patients with NSAID intake, and 96.7% (89%-99%) when patients taking NSAIDs were excluded. In the multivariate analysis, NSAID intake (odds ratio, 9.8 (5.2-18.4)) correlated with UGIB; however, neither H. pylori status nor the interaction between H. pylori infection and NSAID intake correlated with UGIB. In the multivariate analysis in the subgroup of patients with UGIB, NSAID use was the only variable which correlated with H. pylori prevalence (odds ratio, 0.18 (0.03-0.97)). CONCLUSIONS: The most important factor associated with H. pylori-negative bleeding DU is NSAID use, and if this factor is excluded prevalence of infection is almost 100% (97%), similar to that found in patients with non-bleeding DU (and without NSAID intake). Bleeding DU patients with neither H. pylori infection nor NSAID use are extremely rare (only 2%), which suggests that the pathogenesis of bleeding DU is similar to that of non-complicated DU disease.

Aged↗
PubMed2001

Approaches to establishing reference levels in interventional radiology.

Reference levels in radiodiagnostics are a requirement stated by the Council Directive 97/43/EURATOM. Reference levels are also relevant for interventional procedures, in accordance with this Directive, which claims special attention to quality assurance programmes, including quality control and patient dose evaluations for special practices such as interventional radiology, to assess the convenience of corrective action depending on the measured doses. The present paper addresses a method of establishing reference levels in interventional radiology, in the framework of optimisation, discussing the ways of putting forward values with a degree of tolerance, to allow for procedure complexity, depending on patient pathology. The need for several estimators used together, namely fluoroscopy time, total number of images per procedure and dose-area product, is also emphasised, proposing a further skin dose estimate in case of risk of deterministic effects. Finally, a brief summary of principles is given for the correct management of reference levels in interventional radiology.

European Union↗
PubMed2001

Training and accreditation in radiation protection for interventional radiology.

Training in radiation protection is a basic aspect of the optimisation of medical exposures. Council Directive 97/43/EURATOM establishes the need for an adequate theoretical and practical training of the staff working in radiological practices, and competence in radiation, for which Member States shall ensure the establishment of appropriate curricula. Keeping in mind the different specialities and professional responsibilities, training curricula must be proposed and endorsed to achieve a common core of knowledge in radiation protection throughout Europe, for different groups of health workers. In interventional radiology, previous initiatives led to the definition of a syllabus of educational objectives and to its testing in a specific course. The present paper presents educational objectives for interventional radiology, developed in the framework of the DIMOND European concerted action.

Accreditation↗
PubMed2001

Olmesartan medoxomil: influence of age, renal and hepatic function on the pharmacokinetics of olmesartan medoxomil.

Olmesartan medoxomil was rapidly absorbed and converted to olmesartan in elderly hypertensive patients, and in patients with renal and hepatic dysfunction. No olmesartan medoxomil itself was detected in plasma. Pharmacokinetic steady state was reached within the first few days after oral dosing. In elderly (65-75 years old), after 80 mg olmesartan medoxomil once daily, and very elderly (> or = 75 years old) hypertensive patients after 10 mg daily, steady-state Cmax and area under the curve (AUC(0-24 h)) values were up to 44% higher compared with young patients (< 46 years). Steady-state elimination half-life values were also longer in elderly (12.8 h) and very elderly patients (16.5 h) compared with young patients (10.6 and 12.3 h, respectively). At steady state after 10 mg olmesartan medoxomil daily in patients with renal impairment, both Cmax and AUC(0-24 h) increased as creatinine clearance (CLCR) decreased, and renal clearance (CLR) decreased with decreasing CLCR. Steady-state Cmax and AUC(0-24 h) values in patients with mild (CLCR, 40-59 ml/min) and moderate (CLCR, 20-30 ml/min) were up to 39 and 82% higher than the values in healthy subjects. After single oral doses of 10 mg olmesartan medoxomil daily to patients with mild (Child-Pugh score < or = 6) and moderate (score 7-9) hepatic impairment, Cmax was generally similar to that in healthy matched subjects, but AUC increased by 30 and 48%, respectively, and was reflected in small increases in absolute bioavailability values compared with healthy subject controls. Excretion of olmesartan in urine also increased with the degree of hepatic impairment, indicating a compensatory excretion mechanism in this disease state. Since the increased plasma concentrations (Cmax and AUC(0-24 h)) in elderly and very elderly patients, and in mild and moderate renal and hepatic impairment, were several-fold lower than plasma concentrations observed in other studies after 80 mg olmesartan medoxomil daily that were well tolerated, a dosing adjustment in these groups is not considered necessary. In patients with severe renal impairment, however, consideration should be given to a lower starting dose, and it is recommended that the daily dose should not exceed 20 mg daily (compared with 40 mg daily for the general patient population).

Aged↗
PubMed2001

Skin dose and dose-area product values for interventional cardiology procedures.

Coronary angiography and percutaneous transluminal coronary angioplasty procedures performed in four different facilities were monitored in the present study by measuring maximum skin dose, dose-area product and other operational parameters. Radiographic slow film, thermoluminescent dosemeters and transmission ion chambers were used to measure dose related quantities. Values of 107-711 mGy for maximum skin dose and 27.3-370.6 Gy cm2 for dose-area product were found, together with cumulative skin dose estimates of 110-3706 mGy. A discussion of the relationship of measured dose-area product and skin dose values is made using a field concentration factor defined as a way to interpret the findings. No general correlation was observed between dose-area product and maximum skin dose. Cumulative skin dose estimates throughout a procedure should be discarded as a realistic method for assessing deterministic risk in cardiology procedures. Slow film in addition to thermoluminescent dosemeters for measurement of maximum skin dose is a good alternative, especially for complex interventional procedures. For repeated procedures, combining film and dose-area product monitoring favours optimization of radiation protection for the patient.

Angioplasty, Balloon, Coronary↗
PubMed2001

Skin radiation injuries in patients following repeated coronary angioplasty procedures.

This study investigates the incidence of skin injuries and retrospectively estimates skin doses in a sample of patients who had multiple coronary angiographies and who underwent more than four percutaneous transluminal coronary angioplasties (PTCAs), performed primarily by the same team of cardiologists in a university hospital. A database of 7824 PTCAs performed during the last 14 years was analysed. Patients were selected and reviewed by a cardiologist and two radiotherapists with experience in radiation-induced skin injuries. A retrospective analysis of skin doses was performed using data from the patients' files and from the quality assurance (QA) programme of the hospital, which includes periodic patient dose measurements. 14 patients were included in the study. Each patient had undergone between 4 and 14 coronary angiographies and between 5 and 10 PTCAs, performed over a period of 2-10 years. The estimated mean dose-area product per procedure was 46 Gy cm(2) for coronary angiography and 82 Gy cm(2) for PTCA. Mean values of maximum skin dose per procedure were 217 mGy for the diagnostic studies and 391 mGy for the PTCAs. Only a slight radiation skin injury was clinically demonstrated in one patient with a history of 10 coronary angiographies and 10 PTCAs (estimated maximum skin dose 9.5 Gy). Another patient who underwent 14 coronary angiographies and 10 PTCAs (estimated maximum skin dose 7.3 Gy) showed a slight telangiectasia and discrete pigmentation. Another patient with a cutaneous lupus erythematosus showed pigmentation in the area of the radiation field following seven coronary angiographies and six PTCAs (estimated maximum skin dose 5.6 Gy), as expected bearing in mind that skin tolerance to high doses may be altered for patients with this pathology. Each of the remaining 11 patients with no skin injuries had undergone between 5 and 7 PTCAs and between 5 and 14 additional angiographies. None of the 14 patients reported acute skin injuries and no necrosis or radiodermatitis was observed.

Adult↗
PubMed2001

Characterization of PknC, a Ser/Thr kinase with broad substrate specificity from the cyanobacterium Anabaena sp. strain PCC 7120.

Eukaryotic-like protein Ser/Thr and Tyr kinases have only recently been discovered in prokaryotes. In most cases, their biochemical properties have been poorly characterized. The nitrogen-fixing and heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120 houses a family of eukaryotic-like Ser/Thr kinases. Some of these enzymes are required for cell growth or development under certain conditions. None of them, however, has been shown experimentally to possess Ser/Thr kinase activity. A gene, pknC, encoding a novel putative Ser/Thr kinase was isolated from Anabaena sp. PCC 7120. The recombinant PknC was shown to be phosphorylated on a Thr residue. This phosphorylation was probably due to the autophosphorylation activity of PknC itself because mutation of two amino acid residues within the subdomain II of its catalytic domain eliminated the phosphorylation of PknC. PknC displayed also a Ser kinase activity towards several nonspecific substrates, and the two residues needed for PknC autophosphorylation was equally required for the phosphorylation of other substrates. PknC is thus a Ser/Thr kinase with broad substrate specificity. The activity of PknC is likely to be regulated in vivo in order to limit the spectrum of its substrate specificity.

Amino Acid Sequence↗
PubMed2001

An intent of correlating clinical manifestations and ultrastructural lung changes in mice inoculated with Tityus discrepans (Buthidae) venom.

Investigation of the pathogenesis of human pulmonary damage caused by the toxic aggression by Tityus discrepans venom relies to a considerable extent upon the use of animal models. In this work, authors examine the correlation of clinical manifestations and changes in the organisation of cellular and subcellular pulmonary components in the murine model that probably resembles the damage found in envenomed humans. To evaluate lung subcellular response to Tityus discrepans venom, male C57/Bl adult mice were randomised into two groups: envenomed mice were intraperitoneally injected at a dose of 5 mg/Kg of weight and controls received saline solution. Lung samples were processed by electronic microscopy techniques and observed in a Hitachi-300. Ultrastructural findings in pulmonary tissue showed a partial denudation of its epithelial cells; the basal membrane was irregular and swollen. In the interstice there were fibroblasts with multiple cytoplasmatic projections and abundant extracellular material. Adjacent to the interstice bronchiolar areas with cells showing disperse nuclear chromatin were appreciated. There were losses of the intercellular unions and a clear separation among the cellular plasmatic membranes was observed. In conclusion, we suggest that some of the clinical manifestations of scorpion envenoming may be determined by ultrastructural lung damage produced by toxins present in this venom.

Animals↗
PubMed2000

Activation of AMPA receptors inhibits prolactin and estradiol secretion and delays the onset of puberty in female rats.

Previous experiments have evidenced the neuroendocrine role of AMPA receptors. Present studies were carried out to obtain information on the role of these receptors in the control of the onset of puberty. To this end, female rats were i.c.v. injected with vehicle or AMPA (agonist of AMPA receptors: 0.1 or 0.5 nmol/day) between 26 and 30 days (Experiment 1), or 30 and 34 days (Experiment 2) of age. Serum concentrations of PRL, LH and estradiol were measured before drug administration, 10 min after the last injection, at vaginal opening (VO) and at first estrus (FE) presentation. In both experiments, AMPA administration inhibited PRL and estradiol secretion without affecting LH release. When AMPA was administered between 26 and 30 days a significant delay in the day of vaginal opening was observed. These results confirmed the inhibitory effect of AMPA on PRL secretion and suggests a role of AMPA receptors in the control of puberty onset.

Age Factors↗
PubMed2000

Medial prefrontal transection enhances social interaction. II: neurochemical studies.

Medial prefrontal cortex (MPFC) transection enhances social interaction in an open arena test. Social interaction enhances dopaminergic activity in the nucleus accumbens (NAC). In the present set of experiments, microdialysis probes were implanted in the NAC, and glutamate, gamma-aminobutyric acid (GABA) and dopamine (DA) were measured during electrical stimulation of the MPFC, after coronal transection caudal to the MPFC and after a systemic injection of amphetamine in transected rats. Electrical stimulation of the MPFC caused a transient enhancement of glutamate release in the NAC, no change in GABA levels and a long lasting increase in DA levels. Medial prefrontal transection did not change basal glutamate or GABA levels in the NAC, but increased basal DA levels. Amphetamine administration decreased GABA levels in medial prefrontal transected rats, had no effect on glutamate and increased DA levels more than in controls. The experiments suggest that glutamatergic activity in the accumbens decreases dopamine release. Medial prefrontal transection reduces glutamatergic tone and enhances dopamine release, which probably decreases GABAergic activity in the NAC. Presumably, GABA inhibition in the NAC enhances social interaction.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2000

Effect of sub-lethal concentrations of HEMA (2-hydroxyethyl methacrylate) on THP-1 human monocyte-macrophages, in vitro.

OBJECTIVE: Resin monomers such as HEMA (2-hydroxyethyl methacrylate) can be released from restorative materials and diffuse into the tooth pulp over long periods of time. Although the short-term toxicity of resin monomers has been well documented, little is known about the risk for chronic toxicity resulting from low concentrations of resins. Thus, the hypothesis tested in this study was that sub-lethal concentrations of HEMA alter the functions of macrophages after long-term exposure. METHODS: Human THP-1 monocyte-macrophages were exposed to concentrations of HEMA between 0 and 1.5 mmol/l for up to 6 weeks. Cellular proliferation was measured by a hemocytometer with trypan-blue dye exclusion. Mitochondrial activity was measured by the MTT assay, and total cellular protein was measured using the bicinchoninic acid assay. RESULTS: Macrophage proliferation was inhibited 40-50% (significant, p < 0.05) by as little as 0.75 mmol/l after 1 week of exposure. Inhibition of proliferation remained constant after 1 week. The total protein per cell increased by as much as 80% (significant, p < 0.05) after 2 weeks and remained elevated through 6 weeks. Mitochondrial activity per cell increased 60-80% (significant, p < 0.05) after 2 weeks, then decreased. However, mitochondrial activity remained significantly elevated above controls through 6 weeks. SIGNIFICANCE: Findings from the current study indicate that 6-week exposures of monocytes to HEMA alter their proliferation and other activities at concentrations substantially lower than previously reported. This is particularly relevant in light of evidence that such concentrations have been previously shown to come through dentin by diffusion.

Analysis of Variance↗