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Biomedical subjects

T Rivera

Publications and source records attributed to T Rivera.

At least 19 recordsLinked to original sources
PubMed2005

Large B-cell lymphoma with Hodgkin's features.

AIMS: To describe the features of a series of nine cases of diffuse large B-cell lymphoma (DLBCL) showing morphological and immunophenotypic features that are intermediate with Hodgkin's lymphoma (HL). METHODS AND RESULTS: Most cases (6/9) presented as mediastinal tumours affecting young males, while the other three cases arose in extramediastinal locations. Histopathologically, tumours showed diffuse large cell areas in a polymorphous background, with pleomorphic cytology and the common presence of Hodgkin's and Reed-Sternberg cells. Immunophenotypically, tumours shared features of DLBCL and classical HL, with expression of CD30, CD15 (6/9), and a full B-cell profile including CD45RB, CD20, CD79a and OCT2. Epstein-Barr virus-latent membrane protein expression was found in 2/9 cases. The majority of tumours had immunohistochemical features consistent with activation of the NF-(kappa)B pathway, including nuclear location of the c-REL/p65 subunit, overexpression of phosphorylated I(kappa)B(alpha), and overexpression of NF-(kappa)B targets. Finally, 2/9 cases showed 3q27 (BCL6) rearrangement, and 1/9 had p53 gene mutations, both of which are rarely detected in classical HL. CONCLUSIONS: These findings suggest that DLBCLs with HL features constitute a distinctive subgroup of aggressive lymphomas whose neoplastic growth and peculiar characteristics could be facilitated by a particular microenvironment found in the mediastinum.

Adult↗
PubMed2002

Preparation and thermoluminescence properties of aluminium oxide doped with europium.

There is little information concerning the use of rare earths as dopants of Al2O3. This paper presents the preparation method and the results of studying the thermoluminescence characteristics of Al2O3:Eu exposed to ultraviolet light. Phosphor powder was obtained by the evaporation method. Optimum dopant concentration was 10% at an evaporation temperature of 700 degrees C. The powder obtained was submitted to thermal treatments at high temperatures in order to stabilise the traps. Diffraction patterns showed amorphous powder up to 500 degrees C; as the temperature was raised crystalline phases of Al2O3 appeared. The photoluminescence spectrum induced by 250 nm UV light exhibited four well defined peaks characteristic of the Eu3+ ion. The glow curve exhibited two peaks at 180 and 350 degrees C. The sensitivity of Al2O3:Eu was 10 times lower than Al2O3:C. The thermoluminescence response was linear from 2.4 to 3000 microJ.cm(-2) of spectral irradiance, and the fading 2% in a month. From these results it can be concluded that Al2O3:Eu has potential as an UV dosemeter.

Aluminum Oxide↗
PubMed2002

Thermoluminescent response of ZrO2 + PTFE prepared in Mexico to 90Sr/90Y beta particles.

Results of studying the thermoluminescent response of undoped ZrO2 + PTFE pellets irradiated with 90Sr/90Y beta particles are presented. Previously, TL characteristics of ZrO2 films doped with rare earths were studied. Phosphor powder was obtained by evaporating a solution of zirconium nitrate in ethanol. In order to stabilise the traps in ZrO2 this phosphor was submitted to different thermal treatments. Optimal thermal treatment consisted in heating at 1100 degrees C for 24 h. With this powder. pressing at room temperature a mixture (2:1) of ZrO2 and polytetrafluoroethylene (PTFE), pellets of 5 mm diameter and 0.8 mm thickness were made. The glow curve of ZrO2 + PTFE pellets exhibited two peaks at 200 and 250 degrees C: its TL response as a function of beta particles dose was linear in the range from 2 to 60 Gy. Repeatability over 10 cycles was 1.8%. Fading at room temperature was 3.8% per month.

Beta Particles↗
PubMed2001

Kashin-Beck disease and iodine deficiency in Tibet.

We evaluated iodine and selenium status in 575 children between 5 and 15 years with Kashin-Beck disease from endemic and non-endemic areas. Of these 267 (46%) children had goiter. The proportion of subjects with goiter was higher in the villages with Kashin-Beck disease than in the control village. In the villages with Kashin-Beck disease, 105 (23%) of the subjects had a serum thyrotropin greater than 10 mU/l as compared with 3 (4%) in the control village. The percentages of low serum thyroxine values and low serum tri-iodothyronine were greater in the villages where Kashin-Beck disease was endemic than in the control village. The percentages of low urinary iodine concentration were significantly greater in the subjects with Kashin-Beck disease. The results suggest that in areas where severe selenium deficiency is endemic, iodine deficiency is a risk factor for Kashin-Beck disease.

Adolescent↗
PubMed2000

A new ESR dosimeter based on polytetrafluoroethylene

A new electron spin resonance (ESR) dosimetry system based on the ESR response of polytetrafluoroethylene is presented. The dose response of these dosimeters irradiated with 60Co gamma radiation was linear in the range from 6 x 10(2) up to 1.5 x 10(5) Gy, having a repeatability of +/-1% and a high degree of reliability (Cf = 1.054). The persistence of the signal was monitored over a period of one month. ESR signal decay was 5-7% in the temperature range from room temperature up to 40 degrees C.

Journal Article↗
PubMed2000

Stromal tumors of the stomach. Review of our experience and reclassification of a series of patients.

OBJECTIVE: To retrospectively review a series of 12 patients operated on in our department for stromal tumor of the stomach. Clinical and morphological data, and the patients' postoperative course, were analyzed. METHODS: Medical records for 12 patients (mean age 63.3 years) were retrospectively reviewed to obtain data on clinical presentation, diagnosis and treatment. Surgical morbidity and mortality were analyzed. A pathologist reviewed the resected specimens to determine the morphological factors of prognostic value. The biological nature of the tumor was reclassified based exclusively on mitotic index, and all tumors were staged according to the TGM system. Recurrence and survival rates were also calculated. RESULTS: The most frequent clinical presentation was abdominal pain and gastrointestinal bleeding. The most sensitive diagnostic methods were computerized tomography and echographic endoscopy. Operability and resectability rates were 100% and 91.6% respectively. Local resection was done in 5 patients, partial gastrectomy in 5, and extended total gastrectomy in 1. Histologically, 6 cases were muscular tumors (2 leiomyomas, 3 low-grade leiomyosarcomas and 1 high-grade leiomyosarcoma), 2 were gastrointestinal autonomic nerve (GAN) tumors, and 4 were pure stomal tumors. The morbidity rate was 33.3% and the mortality rate was 8.3% (1 patient). All patients were followed up: 1 patient each died after 9 months and 4 years, 1 developed liver metastases after a disease-free interval of 14 months, and the other 9 patients were still alive and free of disease after intervals ranging from 4 months to 7 years. CONCLUSIONS: Stromal tumors include a group of tumors which may present muscular differentiation (the most frequent type), neural differentiation (GAN tumors) or no differentiation at all (pure stromal tumors). The mitotic index is the most valid parameter to determine biological nature, considering that classification as a benign tumor requires the total absence of mitoses. Treatment was mostly surgical, and local resection with adequate safety margins was effective. Prognosis was relatively good, but long-term follow-up is needed to assess the malignant potential of these tumors.

Adult↗
PubMed2000

[Correlation of clinical, radiologic, and histopathologic findings in laryngeal, hypopharyngeal, and oropharyngeal cancer].

The correct staging of the tumors has important consequences in the planning of the treatment in the patients with cancer of larynx, hypopharynx and oropharynx. The objective of this paper is to study the correlation of the clinical, radiologic and pathologic staging with the purpose to evaluate if the computed tomography (CT) is effective in the diagnostic of the stage in the different tumoral findings. We did a retrospective study in 34 patients with pharynx and larynx cancer in the "Hospital Universitario Príncipe de Asturias" between the years 1994-1998. The method was: 1. Clinical history and ENT examination. 2. Head and neck CT. 3. Direct laryngoscopy and biopsy. 4. Surgical treatment and posterior pathologic staging of the removed specimen. The lesions were studied according the TNM-UICC classification with the T and N stage. The first thing to do was the clinical stage then the radiologic stage and at last compare it with the pathologic stage after surgical removal. The results are presented in percentages and confirm that the clinical and radiologic combined information improve the correlation between clinical and pathologic staging in the cancer of larynx, hypopharynx and oropharynx.

Humans↗
PubMed1998

Synthesis and evaluation of compounds that facilitate the gastrointestinal absorption of heparin.

A family of novel compounds (delivery agents) that promote the gastrointestinal absorption of USP heparin in rats and primates has been discovered. The delivery agents in combination with heparin were administered either orally or intracolonically in an aqueous propylene glycol solution and caused dramatic increases in both plasma heparin concentrations (anti-Factor Xa) and clotting times (APTT). Using one of the most effective delivery agents in this series, an estimated relative bioavailability of 8% can be achieved following oral administration to cynomolgus monkeys. To establish a correlation between the in vivo data and an in vitro parameter, immobilized artificial membrane (IAM) chromatography was performed. Log relative k' values were correlated to the efficiency of oral heparin delivery.

Amino Acids↗
PubMed1998

Acylated non-alpha-amino acids as novel agents for the oral delivery of heparin sodium, USP.

Ten N-acylated, non-alpha-amino acids have been prepared as oral delivery agents and used to demonstrate the oral delivery of heparin in vivo in rats and primates. Following the oral administration of solutions containing a combination of heparin and a delivery agent to rats or primates, significant plasma heparin concentrations were evidenced by APTT and anti-Factor Xa assays. The estimated pharmacodynamic equivalence for an oral dosing solution containing heparin and a delivery agent is 39% in primates. In vitro experiments based on heparin affinity chromatography or heparin/methylene blue complexation were also performed to begin investigation of the mechanism by which these compounds facilitate heparin oral delivery. Results of in vitro studies suggest that absorption of the drug across the gastrointestinal membrane is the result of a non-covalent interaction between heparin and the delivery agent.

Administration, Oral↗
PubMed1997

Prevalence of intestinal parasites in the human population of León, Nicaragua.

Intestinal parasites appear to be prevalent in Nicaragua, which motivated a more extensive prevalence study in which socioeconomic conditions such as degree of crowding, quality of water supply, type of floor and disposal of excretion, were considered. The study was performed on 1267 stool samples from about 8% of the citizens of the city of León. The overall prevalence of intestinal pathogenic parasites among the 1267 individuals was found to be 47.2%. The prevalence of Entamoeba histolytica/dispar was 18.6% followed by Giardia (15.9%) and Ascaris (13.4%). Other helminths such as hookworms and Strongyloides sp. were found at very low rates. Giardia, in contrast to worm infections, was prevalent already in children under 5 years of age. E. histolytica/dispar increased with age and remained high. Of 595 individuals with intestinal parasites 81% were living in 'poor' conditions and in 13 clusters of households, a lower prevalence of parasites was seen in households characterised as having good socioeconomic conditions. However, several variables appear to be important in determining the prevalence of the individual intestinal protozoa and helminths encountered.

Animals↗
PubMed1996

Oral delivery of sodium cromolyn: preliminary studies in vivo and in vitro.

PURPOSE: Herein we report the discovery of a group of derivatized alpha-amino acids that increase the oral bioavailability of sodium cromolyn. METHODS: We prepared three N-acylated alpha-amino acids and used these compounds to demonstrate the oral delivery of cromolyn in an in vivo rat model. In vitro experiments, including permeation studies and near infrared spectroscopy, were also performed to initiate an understanding of the mechanism by which these compounds facilitate cromolyn oral delivery. RESULTS: Following oral administration to rats of solutions containing a combination of cromolyn and the delivery agent, significant systemic plasma concentrations of the drug were detected. In vitro studies suggest that absorption of the drug across the gastrointestinal membrane is a passive process. CONCLUSION: The absolute oral bioavailability of sodium cromolyn in the rat model is estimated to be approximately 5%. Preliminary mechanistic studies suggest that a complex of the cromolyn/delivery agent facilitates permeation across/through the membrane.

Administration, Oral↗
PubMed1993

Rural origin as a risk factor for maternal and child health in periurban Bolivia.

Rapid migration in Latin America is settling rural women and their families next to those of urban origin in sprawling urban settings. Those born and reared in rural areas bring with them knowledge and skills learned and adapted to rural areas; those same skills may be maladaptive in urban areas. Hypothesized is that urban women of rural origin are more likely to have poorer health outcomes for themselves and their children than lifelong urban counterparts. Identification of specific risk factors affecting child and/or maternal health status in peri-urban barrios can assist health workers to target limited resources to those least likely to access available services.

Adolescent↗
PubMed1993

Oral immunization of rats with proteinoid microspheres encapsulating influenza virus antigens.

Influenza virus antigen microspheres were prepared by a pH-dependent process using a protein-like polymer (proteinoid) made by thermal condensation of amino acids. The efficacy of these preparations to induce specific IgG responses when used as oral vaccines in rats was evaluated. A single enteric dose of M1 entrapped in proteinoid microspheres was able to induce a significant IgG response to M1 as early as 2 weeks postdosing, while rats dosed orally with the same M1 total dose (no microspheres) showed no detectable antibody response. An unencapsulated hemagglutinin and neuraminidase (HA-NA) preparation induced a moderate anti HA-NA IgG response. A single enteric dose of HA-NA spheres induced a response in 33% of the rats; this response was up to eight times higher than that observed in the rats dosed with unencapsulated antigen.

Administration, Oral↗
PubMed1991

Alagille syndrome associated with caudal dysplasia sequence.

A 36 day-old male with typical features of Alagille syndrome presented at birth additional features consistent with the diagnosis of caudal dysplasia sequence: imperforate anus, rectourethral fistula, lumbosacral abnormalities, and dysplastic right kidney. The association of these 2 conditions has not been previously reported, and could indicate the existence of an axial mesodermal dysplasia, of variable extension, in the Alagille syndrome.

Abnormalities, Multiple↗