Papers by oscar gutierrez
Electronics Letters, 2003
ABSTRACT A new interpolation technique to represent the induced current with a very low amount of... more ABSTRACT A new interpolation technique to represent the induced current with a very low amount of sample points and computational cost is presented. The amplitude and phase of the current are represented separately, each one being defined at any point of the scattering surface by an interpolating function, built using Bezier's surfaces.
IEEE Antennas and Propagation Magazine, 1998
The application of se:veral ray-tracing techniques, in combination with GTDKJTD (Geometrical Theo... more The application of se:veral ray-tracing techniques, in combination with GTDKJTD (Geometrical Theory of Diffraction/Uniform Theory of Diffraction), for an efficient analysis of propagation in urban scenarios is presented. The frequency of the analysis is in the UHF band, and a three-dimensional model of the geometry, using flat facets, is considered. After a review of the most commonly used ray-tracing techniques, a new method, called the Angular Z-Buffer (AZ13) technique, is presented. As is shown and validated with results, the AZB appears to be extremely efficient for GTDKJTD applications.
FASPRO is an accurate and extremely efficient tool that is used to perform deterministic analyses... more FASPRO is an accurate and extremely efficient tool that is used to perform deterministic analyses of propagation in urban picocells and microcells. A fully 3D propagation model is considered. The topographical input data are based on a 3D plane-facets model of the urban environment which is given in terms of DXF files. FASPRO is able to read DXF files from AUTOCAD, Microsystem, CADDS and other CAGD and topographical tools. In addition, FASPRO has its own facility which allows it to create new urban scenes. FASPRO visualizes the geometry on the screen as a 2D map of the urban scene or a 3D isoparametric view. The electromagnetic analysis is performed using UTD techniques. First order coupling mechanisms (direct reflected and edge-diffracted rays), second order coupling mechanisms (double reflected diffracted-reflected, diffracted-reflected, double diffracted, etc.) and third order mechanisms (e.g. reflected-diffracted-reflected, etc.) are included. It must be noted that, thanks to the incorporation of diffraction in all the edges of the 3D model, coverage in areas in the deep shadow of the transmitter antenna can be predicted well. A new ray-tracing algorithm is used to speed-up the computations. This ray-tracing algorithm is based on a modification of the Z-Buffer and the “Bounding Volumes” schemes, in which the elements are arranged in an angular map (AZB, Angular Z-Buffer)
Gastroenterology, 1999
The variation in size of Helicobacter pylori CagA is related to repeat sequences in the 3Ј region... more The variation in size of Helicobacter pylori CagA is related to repeat sequences in the 3Ј region of the cagA gene. We investigated whether structural subtypes of the cagA 3Ј region are associated with presentation of the infection or to susceptibility to acid. Methods: We examined 319 cagA-positive H. pylori isolates: 84 isolates from Bogota, Colombia; 83 from Houston, Texas; 24 from Siena, Italy; and 128 from Seoul, Korea. The cagA 3Ј region was amplified by polymerase chain reaction. Gastric histology and susceptibility to pH 3 were evaluated in relation to the number of cagA repeat regions. Results: Strains with more than three repeat regions were associated with significantly higher scores for gastric mucosal atrophy and intestinal metaplasia than those with fewer repeat regions. H. pylori strains with three repeat regions were also significantly more susceptible to pH 3 than isolates with fewer repeat regions. Conclusions: H. pylori strains with more than three repeat regions in the 3Ј region of the cagA gene are associated with enhanced histological injury and with reduced survival in acidic conditions. It is hypothesized that these variants arise within the stomach.
Gastroenterology, 2002
Background & Aims: Disease-associated virulence factors of Helicobacter pylori may not be indepen... more Background & Aims: Disease-associated virulence factors of Helicobacter pylori may not be independent of one another. The aim was to determine which H. pylori virulence factor(s) was the most important predictor of severity of gastric inflammation or clinical outcome. Methods: cag Pathogenicity island (PAI), vacA, babA2, and iceA status were determined by polymerase chain reaction (PCR). oipA functionality was based on switch status determined by PCR-based sequencing. A backward stepwise multiple regression analysis was performed to determine which factor(s) was the most discriminating for clinical outcome as well as the relationship to mucosal histology (H. pylori density, neutrophil infiltration, intestinal metaplasia, and gastric atrophy) and mucosal interleukin 8 (IL-8) production. Results: H. pylori were obtained from 247 patients (86 with gastritis, 86 with duodenal ulcer, and 75 with gastric carcinoma). Although oipA status was closely linked to specific cag PAI, vacA, and babA2 genotypes, only oipA status remained in the final model to discriminate duodenal ulcer from gastritis (adjusted odds ratio [OR] ؍ 5 and 95% confidence interval [CI ] ؍ 2.1-11.9). Among the factors, only a functional oipA was significantly associated with high H. pylori density, severe neutrophil infiltration, and high mucosal IL-8 levels (P < 0.001). oipA status had no relationship to gastric atrophic changes. Conclusions: oipA functional status was related to clinical presentation, H. pylori density, and gastric inflammation. cag PAI, babA2, or vacA status appear important only as surrogate markers for a functional oipA gene.
American Journal of Gastroenterology, 2002
OBJECTIVE: Different types of chronic gastritis, including antral predominant, corpus predominant... more OBJECTIVE: Different types of chronic gastritis, including antral predominant, corpus predominant, and multifocal pangastritis, are associated with Helicobacter pylori infection. Specific patterns of H. pylori gastritis that might characterize individuals with family histories of noncardia gastric cancer (GC) were investigated.
Gut, 2006
Background and aims: A number of Helicobacter pylori outer membrane proteins (OMPs) undergo phase... more Background and aims: A number of Helicobacter pylori outer membrane proteins (OMPs) undergo phase variations. This study examined the relation between OMP phase variations and clinical outcome. Methods: Expression of H pylori BabA, BabB, SabA, and OipA proteins was determined by immunoblot. Multiple regression analysis was performed to determine the relation among OMP expression, clinical outcome, and mucosal histology. Results: H pylori were cultured from 200 patients (80 with gastritis, 80 with duodenal ulcer (DU), and 40 with gastric cancer). The most reliable results were obtained using cultures from single colonies of low passage number. Stability of expression with passage varied with OipA . BabA . BabB . SabA. OipA positive status was significantly associated with the presence of DU and gastric cancer, high H pylori density, and severe neutrophil infiltration. SabA positive status was associated with gastric cancer, intestinal metaplasia, and corpus atrophy, and negatively associated with DU and neutrophil infiltration. The Sydney system underestimated the prevalence of intestinal metaplasia/atrophy compared with systems using proximal and distal corpus biopsies. SabA expression dramatically decreased following exposure of H pylori to pH 5.0 for two hours. Conclusions: SabA expression frequently switched on or off, suggesting that SabA expression can rapidly respond to changing conditions in the stomach or in different regions of the stomach. SabA positive status was inversely related to the ability of the stomach to secrete acid, suggesting that its expression may be regulated by changes in acid secretion and/or in antigens expressed by the atrophic mucosa.
PCR for vacA and cagA genotypes of Helicobacter pylori using DNA isolated from infected gastric b... more PCR for vacA and cagA genotypes of Helicobacter pylori using DNA isolated from infected gastric biopsy specimens was approximately equal to genotyping using bacterial DNA from cultures. Inconsistent results were associated with low H. pylori density in biopsies. A higher proportion of mixed infection was found when biopsies were used.
Alimentary Pharmacology & Therapeutics, 1997
American Journal of Gastroenterology, 1999
OBJECTIVE: Previous studies have reported variable rates of microsatellite instability (MSI) in g... more OBJECTIVE: Previous studies have reported variable rates of microsatellite instability (MSI) in gastric cancer. We investigated the frequency of MSI in invasive gastric carcinoma of patients from three geographic regions.
There is continuing interest in identifying Helicobacter pylori virulence factors that might pred... more There is continuing interest in identifying Helicobacter pylori virulence factors that might predict the risk for symptomatic clinical outcomes. It has been proposed that iceA and cagA genes are such markers and can identify patients with peptic ulcers. We compared H. pylori isolates from four countries, looking at the cagA and vacA genotypes, iceA alleles, and presentation of the infection. We used PCR to examine iceA, vacA, and cagA status of 424 H. pylori isolates obtained from patients with different clinical presentations (peptic ulcer, gastric cancer, and atrophic gastritis). The H. pylori isolates examined included 107 strains from Bogota, Colombia, 70 from Houston, Tex., 135 from Seoul, Korea, and 112 from Kyoto, Japan. The predominant genotype differed among countries: the cagA-positive iceA1 vacA s1c-m1 genotype was predominant in Japan and Korea, the cagA-positive iceA2 vacA s1b-m1 genotype was predominant in the United States, and the cagA-positive iceA2 vacA s1a-m1 genotype was predominant in Colombia. There was no association between the iceA, vacA, or cagA status and clinical outcome in patients in the countries studied. iceA status shows considerable geographic differences, and neither iceA nor combinations of iceA, vacA, and cagA were helpful in predicting the clinical presentation of an H. pylori infection.
Journal of Clinical Microbiology, 2002
The BabA, cagA, and vacA statuses of 827 Helicobacter pylori isolates were used in logistic regre... more The BabA, cagA, and vacA statuses of 827 Helicobacter pylori isolates were used in logistic regression models to discriminate duodenal ulcer from gastritis. Only BabA was a candidate for a universal virulence factor, but the low c statistic value (0.581) indicates that none of these factors were helpful in predicting the clinical presentation.
American Journal of Gastroenterology, 2003
Helicobacter pylori (H. pylori) may colonize gastric mucosa wherever it is found in the GI tract.... more Helicobacter pylori (H. pylori) may colonize gastric mucosa wherever it is found in the GI tract. Heterotopic gastric mucosa in the upper esophagus (inlet patch) is a potential site for H. pylori infection and may provide a reservoir for oral-oral transmission or a niche where antibiotics might have difficulty reaching. The aim of this study was to analyze the intensity and distribution of H. pylori in the inlet patch.
Febs Letters, 2002
We present a molecular epidemiologic study, based on an analysis of vacA, cagA and cag right end ... more We present a molecular epidemiologic study, based on an analysis of vacA, cagA and cag right end junction genotypes from 1042 Helicobacter pylori isolates, suggesting that H. pylori was present in the New World before Columbus. Eight Native Colombian and Alaskan strains possessed novel vacA and/or cagA gene structures and were more closely related to East Asian than to non-Asian H. pylori. Some Native Alaskan strains appear to have originated in Central Asia and to have arrived after strains found in South America suggesting that H. pylori crossed the Bering Strait from Asia to the New World at different times. ß 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.
Epidemiology and Infection, 2000
The predominant H. pylori strain circulating among geographic locations differs with regard to th... more The predominant H. pylori strain circulating among geographic locations differs with regard to the genomic structure. This study determined whether structural subtypes of the cagA 3h repeat region could be used to identify the population of origin of H. pylori isolates. We examined 600 cagA-positive H. pylori (
Scandinavian Journal of Gastroenterology, 1997
For more than 30 years it has been known that gastric acid secretion is inversely related to the ... more For more than 30 years it has been known that gastric acid secretion is inversely related to the extent and severity of corpal gastritis. We therefore evaluated the effect of cure of Helicobacter pylori infection on basal and pentagastrin-stimulated acid secretion. Basal acid output (BAO) and maximal acid output (MAO) were assessed in 11 H. pylori-infected dyspeptic patients (8 women and 3 men; mean age, 28 years) before and after successful anti-H. pylori therapy. The gastritis index was significantly lower after therapy and was associated with an increase in both BAO and MAO after cure of the H. pylori infection (BAO from 0.3 mmol/h and MAO from 4.8 mmol/h to 19 mmol/ h). Basal and stimulated acid concentrations also increased (29.1 +/- 36.6 to 54 +/- 31 mmol/l and 72.5 +/- 46 to 120.1 +/- 30 mmol/l, respectively, for basal and stimulated acid concentrations; P &amp;amp;amp;amp;amp;amp;lt; 0.05 for peak and MAO, P = 0.07 for BAO). Gastric acid secretion increased into the normal range after successful treatment of H. pylori infection, suggesting that gastric function can recover to normal or almost normal after cure of H. pylori infection.
American Journal of Gastroenterology, 2001
A strong correlation exists between atrophic gastritis and the intestinal type of gastric carcino... more A strong correlation exists between atrophic gastritis and the intestinal type of gastric carcinoma. Duodenal ulcer disease characteristically has an antral predominant gastritis and a lower risk for gastric cancer. The aim of this study was to investigate the extent and distribution of intestinal metaplasia in duodenal ulcer in countries differing in gastric cancer incidence.
American Journal of Gastroenterology, 2000
The role of intestinal metaplasia in gastric oncogenesis has been demonstrated by both cross-sect... more The role of intestinal metaplasia in gastric oncogenesis has been demonstrated by both cross-sectional and longitudinal studies. This study was designed to determine whether, in a population at high risk for gastric cancer, different topographical patterns and phenotypes of intestinal metaplasia were associated with different degrees of cancer risk. A total of 68 Colombian patients with gastric cancer and 67 controls with nonulcer dyspepsia were studied by an extensive biopsy protocol. Intestinal metaplasia was assessed semiquantitatively by histology and was characterized histochemically. In both patients and controls, the Spearman&amp;amp;amp;amp;amp;amp;#39;s correlation test was applied to the test if the gastric distribution of metaplastic lesions resulted in specific topographical patterns associated with different risks for cancer. Four topographical patterns of intestinalization emerged: 1) &amp;amp;amp;amp;amp;amp;quot;Focal,&amp;amp;amp;amp;amp;amp;quot; in 14 cancer patients and 16 controls; 2) &amp;amp;amp;amp;amp;amp;quot;Antrum-predominant,&amp;amp;amp;amp;amp;amp;quot; in seven cancer patients and six controls; 3) &amp;amp;amp;amp;amp;amp;quot;Magenstrasse&amp;amp;amp;amp;amp;amp;quot; (involving the lesser curvature from cardia to pylorus) in 25 cancer patients and four controls. This pattern was associated with higher cancer risk (OR = 5.7; 95% CI: 1.3-26) than were the two less extensive patterns; and 4) &amp;amp;amp;amp;amp;amp;quot;Diffuse,&amp;amp;amp;amp;amp;amp;quot; involving essentially the entire gastric mucosa with the exception of the fundus, was unique to 13 cancer patients. The OR for cancer was 12.2; 95% CI: 2.0-72.9. Incomplete-type metaplasia significantly correlated with the extent of total metaplasia and was also associated with greater cancer risk. In a population with high risk for gastric cancer, the extension of intestinal metaplasia correlates with the extent of its &amp;amp;amp;amp;amp;amp;quot;incomplete&amp;amp;amp;amp;amp;amp;quot; phenotype and is significantly associated with increased cancer risk. Both the extent and location of intestinal metaplasia along the lesser curvature (from the cardia to the prepyloric zones) identify patients with the highest cancer risk.
American Journal of Gastroenterology, 2002
OBJECTIVE: This study investigated the genetic diversity of the cag pathogenicity island (PAI) in... more OBJECTIVE: This study investigated the genetic diversity of the cag pathogenicity island (PAI) in Helicobacter pylori (H. pylori) in relation to clinical outcome and interleukin (IL)-8 production.
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Papers by oscar gutierrez