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Biomedical subjects

S Oberg

Publications and source records attributed to S Oberg.

At least 19 recordsLinked to original sources
PubMed2006

E center in silicon has a donor level in the band gap.

It has been an accepted fact for more than 40 years that the E center in Si (the group-V impurity--vacancy pair)--one of the most studied defects in semiconductors--has only one energy level in the band gap: namely, the acceptor level at about 0.45 eV below the conduction band. We now demonstrate that it has a second level, situated in the lower half of the band gap at 0.27 eV above the valence band. The existence of this level, having a donor character, is disclosed by a combination of different transient-capacitance techniques and electronic-structure calculations. The finding seriously questions some diffusion-modeling approaches performed in the past.

Journal Article↗
PubMed2004

Degradation of boron-doped Czochralski-grown silicon solar cells.

The formation mechanism and properties of the boron-oxygen center responsible for the degradation of Czochralski-grown Si(B) solar cells during operation is investigated using density functional calculations. We find that boron traps an oxygen dimer to form a bistable defect with a donor level in the upper half of the band gap. The activation energy for its dissociation is found to be 1.2 eV. The formation of the defect from mobile oxygen dimers, which are shown to migrate by a Bourgoin mechanism under minority carrier injection, has a calculated activation energy of 0.3 eV. These energies and the dependence of the generation rate of the recombination center on boron concentration are in good agreement with observations.

Journal Article↗
PubMed2003

Bone formation after implantation of autolysed antigen extracted allogeneic bone in ovariectomized rabbits.

This study was undertaken to evaluate the bone formation response to AAA bone in healthy and oestrogen deficient animals. Seventeen young healthy New Zealand female rabbits were used. Nine rabbits were subjected to ovariectomy and the remaining eight were sham-operated. Four weeks after ovariectomy standardized round cavities, 5mm in diameter, were made medially in the cortical part of each proximal tibia. To half of the cavities autolysed antigen-extracted allogeneic AAA bone granules were added. After another 8 weeks the animals were sacrificed and sections of the tibial experimental areas were obtained. These were studied in light microscopy and the bone and non-bone areas were measured with computer support. The study showed that the addition of a bone inductive substance such as AAA bone enhances bone formation also in oestrogen deficient animals.

Animals↗
PubMed2003

Heller's esophagomyotomy with or without a 360 degrees floppy Nissen fundoplication for achalasia. Long-term results from a prospective randomized study.

Heller's esophagomyotomy relieves dysphagia but does not restore esophageal peristalsis. The myotomy may induce reflux and the addition of a 360 degrees fundoplication may be hazardous with regard to the remaining aperistaltic esophagus. The aim of this prospectively randomized clinical trial was to compare the outcome for patients with uncomplicated achalasia who underwent an anterior Heller's esophagomyotomy (H group) with or without an additional floppy Nissen fundoplication (H + N group). Between 1984 and 1995, 20 patients were prospectively randomized to one or other of the performed operations, 10 patients per group. Esophagitis including Barrett's esophagus (n = 2) was seen under medical treatment, in 6 of 9 in the H group but none in the H + N group. No patient in the H + N group required postoperative continuous acid-reducing drugs. Twenty-four-hour esophageal pH-studies in median 3.4 years after surgery showed pathological reflux expressed as a percentage of time below pH 4 of 13.1% in the H group compared to 0.15% (P < 0.001) in H + N group. One patient with recurrent dysphagia in the H + N group later had an esophagectomy. The remaining patients reported significant improvement of dysphagia without symptoms of reflux at 8.0 years follow-up. Heller's esophagomyotomy eliminates dysphagia, but can induce advanced reflux that requires medical treatment. The addition of a 360 degrees fundoplication eliminates reflux without adding dysphagia in the majority of patients and can be recommended for most patients with uncomplicated achalasia.

Adult↗
PubMed2001

Thermal double donors and quantum dots.

Combined local mode spectroscopy and ab initio modeling are used to demonstrate for the first time that oxygen atoms in thermal double donors (TDD) in Si are in close proximity. The observed vibrational modes in (16)O, (18)O, and mixed isotopic samples are consistent with a model involving [110] aligned oxygen chains made up of an insulating core lying between electrically active ends. The model also explains the minute spin density observed on oxygen in TDD(+) as well as the piezospectroscopic tensors of the donors. The analogy between the thermal donors and quantum dots is emphasized.

Journal Article↗
PubMed2001

Predictive factors of Barrett esophagus: multivariate analysis of 502 patients with gastroesophageal reflux disease.

HYPOTHESIS: Risk factors for the presence and extent of Barrett esophagus (BE) can be identified in patients with gastroesophageal reflux disease (GERD). DESIGN: Case-comparison study. SETTING: University tertiary referral center. PATIENTS: Five hundred two consecutive patients with GERD documented by 24-hour esophageal pH monitoring and with complete demographic, endoscopic, and physiological evaluation, divided in groups according to the presence and extent of BE (328 patients without BE and 174 with BE [67 short-segment BE and 107 long-segment BE]). MAIN OUTCOME MEASURES: Clinical, endoscopic, and physiological data, studied by multivariate analysis, to identify the independent predictors of the presence and extent of BE. RESULTS: Seven factors were identified as predictors of BE. They were abnormal bile reflux (odds ratio [OR], 4.2; 95% confidence interval [CI], 1.9-9.7), hiatal hernia larger than 4 cm (OR, 4.1; 95% CI, 2.1-8.0), a defective lower esophageal sphincter (OR, 2.7; 95% CI, 1.4-5.4), male sex (OR, 2.6; 95% CI, 1.6-4.3), defective distal esophageal contraction (OR, 2.2; 95% CI, 1.4-3.5), abnormal number of reflux episodes lasting longer than 5 minutes (OR, 2.2; 95% CI, 1.1-4.6), and GERD symptoms lasting for more than 5 years (OR, 2.1; 95% CI, 1.4-3.2). Only abnormal bile reflux (OR, 4.8; 95% CI, 1.7-13.2) was identified as a predictor of short-segment BE (baseline, no BE). Three factors were identified as predictors of long-segment BE (baseline short-segment BE). They were hiatal hernia larger than 4 cm (OR, 17.8; 95% CI, 4.1-76.6), a defective lower esophageal sphincter (OR, 16.9; 95% CI, 1.6-181.4), and an abnormal longest reflux episode (OR, 8.1; 95% CI, 2.8-24.0). CONCLUSIONS: Among patients with GERD, specific factors are associated with the presence and extent of BE. Elimination of reflux with an antireflux operation in patients with 1 or more of these factors may prevent the future development of BE.

Adolescent↗
PubMed2001

Short-term outcome after laparoscopic and open 360 degrees fundoplication. A prospective randomized trial.

BACKGROUND: Despite the lack of randomized trials supporting the laparoscopic approach, laparoscopic antireflux surgery has gained widespread acceptance during the last decade. The aim of this study was to compare the short-term symptomatic and objective outcome after laparoscopic and open 360 degrees fundoplication in a prospective randomized clinical trial. METHODS: Sixty patients with GERD were randomized to undergo either laparoscopic (LF) or open 360 degrees fundoplication (OF). Endoscopy, esophageal manometry, 24-h pH monitoring, clinical symptom evaluation, and symptom scoring according to a validated questionnaire (the Gastrointestinal Symptom Rating Scale [GSRS]) was performed preoperatively and 6 months after surgery. RESULTS: Five patients randomized to the laparoscopic group were converted to open surgery. Esophageal acid exposure was restored to normal in all patients. Lower esophageal sphincter length and resting pressure were significantly increased after both laparoscopic and open fundoplication (p < 0.001); there were no differences between the groups. No significant differences were seen in symptomatic outcome, although there was a trend toward a higher rate of mild dysphagia (p = 0.051) after laparoscopic surgery. GSRS revealed a decrease in reflux score (p < 0.001) and abdominal pain score (p < 0.001) postoperatively. There were no significant differences in GSRS scores between the two groups. CONCLUSION: Laparoscopic 360 degrees fundoplication is as effective in treating reflux disease as open fundoplication. Six months postoperatively, no significant differences were seen in symptomatic or objective outcome. Long-term evaluation is needed.

Adult↗
PubMed2001

Gastro-esophageal reflux disease confined to the sphincter.

It has been shown previously that patients with gastro-esophageal reflux disease (GERD) do not always have increased esophageal acid exposure on 24 h pH monitoring. The recent recognition of carditis as a sensitive marker for GERD raises the possibility for patients with mild disease to have normal esophageal acid exposure but inflamed cardiac mucosa on biopsies of the cardia, which may be an early sign of GERD. To test this hypothesis, 171 consecutive patients evaluated for symptoms of GERD and no increased esophageal acid exposure, Barrett's esophagus or erosive esophagitis were divided into those with and without carditis. Esophageal acid exposure and lower esophageal sphincter (LES) characteristics were compared between the two groups. Comparisons were done using the Mann-Whitney U-test for non-parametric data. There were 82 patients with histologic evidence of carditis and 89 patients without carditis. Patients with carditis had a more deteriorated sphincter, determined by overall and abdominal length and resting pressure, and significantly higher esophageal acid exposure (P < 0.05). Patients with symptoms of GERD and histologic evidence of carditis may have early or mild reflux disease, which is confined to the sphincter.

Adolescent↗
PubMed2001

Endoscopic surveillance of columnar-lined esophagus: frequency of intestinal metaplasia detection and impact of antireflux surgery.

OBJECTIVE: To quantify the occurrence of intestinal metaplasia in columnar-lined esophagus (CLE) during endoscopic surveillance and to evaluate the impact of antireflux surgery on the development of intestinal metaplasia. SUMMARY BACKGROUND DATA: The malignant potential in segments of CLE is mainly restricted to those containing intestinal metaplasia. Patients with segments of CLE in which no intestinal metaplasia can be detected are rarely enrolled in a surveillance program but may still be at increased risk of developing esophageal adenocarcinoma because intestinal metaplasia may be missed or may develop with time. METHODS: The occurrence of intestinal metaplasia on biopsy samples was determined on repeated endoscopies in 177 patients enrolled in a surveillance program for CLE. The incidence of intestinal metaplasia in patients with no evidence of intestinal metaplasia on the two first endoscopies was evaluated on the subsequent endoscopies and compared in patients with medically and surgically treated gastroesophageal reflux disease. RESULTS: Intestinal metaplasia was found in 53% of the patients (94/177) on their first surveillance endoscopy and was more prevalent in long segments of CLE. The prevalence of intestinal metaplasia increased markedly with increasing number of surveillance endoscopies. Intestinal metaplasia tended to be detected early in patients with long segments of CLE; in patients with shorter segments, intestinal metaplasia was also detected late in the course of endoscopic surveillance. Patients with surgically treated reflux disease were 10.3 times less likely to develop intestinal metaplasia compared with a group receiving standard medical therapy. CONCLUSION: Biopsy samples from a single endoscopy, despite an adequate biopsy protocol, are insufficient to rule out the presence of intestinal metaplasia. Patients in whom biopsy specimens from a segment of CLE show no intestinal metaplasia have a significant risk of having undetected intestinal metaplasia or of developing intestinal metaplasia with time. Sampling error is probably the reason for the absence of intestinal metaplasia in segments of CLE longer than 4 cm, whereas development of intestinal metaplasia is common in patients with shorter segments of CLE. Antireflux surgery protects against the development of intestinal metaplasia, possibly by better control of reflux of gastric contents.

Aged↗
PubMed2000

Is adenocarcinoma following esophagoduodenostomy without carcinogen in the rat reflux-induced?

BACKGROUND: A widely used rat model for reflux-induced esophageal adenocarcinoma in the absence of carcinogens involves induction of duodenoesophageal reflux by performance of esophagoduodenostomy. The aim of this study was to test the hypothesis that acid reflux reduces the incidence of adenocarcinoma in this animal model. METHODS: One hundred ninety 8-week-old male Sprague-Dawley rats were studied. The animals were randomly divided into four groups with a different type of reflux established in each group. Group 1 had an esophagoduodenostomy for duodenogastroesophageal reflux (n = 59), group 2 had an esophagoduodenostomy and a total gastrectomy for duodenoesophageal reflux (n = 54), group 3 had an esophagoduodenostomy and a total gastrectomy with acid supplementation with acidified water to control for the effect of the gastrectomy (n = 50), and group 4 had a total gastrectomy with Roux-en-Y reconstruction to eliminate all reflux (n = 25). One hundred eighty-eight surviving animals were sacrificed at 36 weeks of age and the resected esophagi were examined. RESULTS: All animals except the no reflux control group had severe reflux esophagitis. The frequency of tumor development was similar in all study groups. All of the tumors were well-differentiated adenocarcinomas that were located on the external surface of the bowel either at or immediately distal to the esophagoenteric anastomosis. The tumors appeared to arise from the submucosa and did not involve the overlying mucosa. There was no definite evidence of columnar lining of the esophagus but an admixture of squamous and columnar epithelium was found microscopically in all groups. This finding was unrelated to the presence and composition of reflux. CONCLUSIONS: Adenocarcinomas in this animal model are not reflux-induced and do not arise from the mucosa. Despite previous reports to the contrary, we suggest that this model may not be valid for the study of reflux-induced esophageal adenocarcinoma.

Adenocarcinoma, Mucinous↗
PubMed2000

Determinants of intestinal metaplasia within the columnar-lined esophagus.

HYPOTHESIS: The clinical and physiological features of patients with short segments of columnar-lined esophagus (CLE) with and without intestinal metaplasia (IM) are distinct. DESIGN: Retrospective case series. SETTING: University tertiary referral center. PATIENTS: Sixty-five consecutive patients with a 2-cm or shorter length of endoscopically visible CLE. INTERVENTIONS: The type of CLE and the presence of Helicobacter pylori were determined by histopathologic examination of esophageal and gastric antrum biopsy specimens. All patients underwent esophageal manometry and simultaneous 24-hour pH and bilirubin monitoring. MAIN OUTCOME MEASURES: Clinical and physiological data were compared in patients with and without IM. RESULTS: Thirty-six patients had IM and 29 had cardiac-type mucosa without IM in biopsy specimens from the CLE. There was no significant difference in age or sex distribution, but the duration of symptoms was significantly longer in patients with IM (10 vs 5 years; P = .03). Abnormal esophageal acid exposure was found in 30 (83%) of 36 patients with IM and 23 (79%) of 29 patients without IM. The prevalence of abnormal bilirubin exposure was significantly higher in patients with IM (75% [27/36]) than in those without IM (41% [12/29]; P = .01). There was no significant difference in the prevalence of H pylori infection between the 2 groups (8% vs 10%; P >.99). CONCLUSIONS: Patients with short segments of CLE and IM have similar esophageal acid exposure but significantly higher frequency of abnormal bilirubin exposure and longer median duration of reflux symptoms than patients without IM. Therefore, CLE, regardless of histological type, is a manifestation of gastroesophageal reflux disease. The presence of duodenoesophageal reflux and the duration of reflux seem to be important in the pathogenesis of IM.

Barrett Esophagus↗
PubMed2000

Anastomotic diameters and strictures following esophagectomy and total gastrectomy in 256 patients.

The prevalence of anastomotic strictures in esophageal anastomoses provides us with limited information about the anastomotic healing process. This prospective study evaluates the exact esophageal anastomotic diameters in 256 patients who underwent esophagectomy and esophagogastrostomy without pyloroplasty (n = 107) or total gastrectomy and Roux reconstruction (n = 149). No perioperative chemoradiotherapy was given. Anastomotic strictures and diameters were assessed during endoscopy by a separately inserted (inflated to the anastomotic width) balloon catheter. The anastomotic diameters increased significantly during the first postoperative year in the esophagectomy (p = 0.001) and gastrectomy (p < 0.001) groups. The anastomoses in the gastrectomy group were significantly wider than those in the esophagectomy group 3 (25.7 versus 19.9 mm), 6 (28.5 versus 22.0 mm), and 12 (30.5 versus 23.3 mm) months after surgery (p < 0.001). Neither the anastomotic site (neck or chest) in the esophagectomy group (p = 0.176) nor that in the gastrectomy group (abdomen or chest) (p = 0.577) influenced the anastomotic diameter. Benign anastomotic strictures were most frequently found after 3 months and after esophagectomy. Esophagojejunostomies performed with 2 linear stapling devices or cartridge size 28 mm showed the widest anastomoses with only 1 stricture. Esophagogastric anastomoses following esophagectomy are narrower and develop more strictures than esophagojejunal anastomoses after total gastrectomy, but both dilate during the first year.

Adult↗
PubMed2000

Invasive group A streptococcal infections in Sweden in 1994 and 1995: epidemiology and clinical spectrum.

A nationwide study of invasive group A streptococcal (GAS) infections in Sweden during 1994-1995 was carried out. All Swedish microbiological laboratories were asked to report isolates of GAS from normally sterile sites. During the study period they were also asked to send their isolates for T typing. Questionnaires were sent to the physicians in charge of each patient. The incidence, serotype, clinical presentation, symptoms and outcome were recorded. Clinical data were obtained for 468 of 556 patients with GAS bacteraemia. The lethality rate was 16%, but was much higher (37%) in the 113 patients who developed streptococcal toxic shock syndrome (STSS). Streptococci of serotype T1 dominated during the study period and were linked to the increase in invasive GAS infections. They also carried an increased risk of causing STSS. Invasive streptococcal disease with STSS most often has an unknown primary focus or is associated with soft tissue infections. Invasive streptococcal disease not associated with STSS most often has a skin infection as portal of entry or else an unknown focus.

Adolescent↗
PubMed2000

Cerebrospinal fluid and plasma viral load in HIV-1-infected patients with various anti-retroviral treatment regimens.

Highly active anti-retroviral therapy (HAART) effectively decreases HIV-1 RNA in cerebrospinal fluid (CSF) and plasma in controlled clinical trials. To study the virological effect in CSF and plasma achieved in routine practice, HIV-1 RNA levels were analysed retrospectively in 27 patients on mono-nucleoside reversed transcriptase inhibitor (NRTI) treatment, 27 on dual-NRTI-treatment and 45 on HAART using a Roche Amplicor HIV-1 monitor quantitative PCR. A significant difference was found in the proportion of patients with a CSF viral load below 20 copies/ml between patients treated with 1 (0%) and 2 NRTIs (41%) as well as between those treated with 2 NRTIs and HAART (69%). The proportion of patients with plasma viral load below 20 copies/ml differed significantly between patients on HAART (47%) and those on 2 NRTIs (0%), but not between those with 1 (0%) or 2 NRTIs. In multivariate regression analysis, treatment regimen and prior anti-retroviral experience (but not treatment time) were independently associated with the CSF viral load. Plasma viral load was independently associated with treatment regimen and treatment time, but not with anti-retroviral experience. Dual-NRTI-treatment affects the CSF viral load substantially, while HAART is required to achieve an essential decline in plasma viral load.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Definition of histopathologic changes in gastroesophageal reflux disease.

A series of 71 patients with multiple measured biopsies of the gastroesophageal junctional region permitting assessment of the presence and length of different glandular epithelial types is presented. All but nine of 53 patients in whom a 24-hour pH study was performed had abnormal reflux, suggesting that endoscopic recognition of an abnormal columnar mucosa at the gastroesophageal junction sufficient to precipitate multiple-level biopsies indicates a high probability of abnormal reflux. All patients had cardiac mucosa (CM) or oxyntocardiac mucosa (OCM). CM was present in 68 of 71 patients. The prevalence of intestinal metaplasia increased with increasing CM+OCM length, and was present in all 22 patients with a CM+OCM length >2 cm and in 20 of 49 patients with a CM+OCM length <2 cm. Patients with a CM+OCM length >2 cm had a markedly higher acid exposure than patients with a CM+OCM length <2 cm. The findings suggest that the presence of CM and OCM in the junctional region are predictive of abnormal acid exposure, and that increasing OCM+CM length correlates strongly with the amount of acid exposure. The histologic finding of CM and OCM represents a sensitive histologic criterion for gastroesophageal reflux rather than normal epithelia. These diagnostic criteria represent the first useful histologic definitions for assessing the presence and severity of reflux.

Gastric Mucosa↗
PubMed1999

Helicobacter pylori is not associated with the manifestations of gastroesophageal reflux disease.

HYPOTHESIS: Helicobacter pylori is not associated with gastroesophageal reflux disease and its complications, including adenocarcinoma of the esophagus and the gastroesophageal junction (GEJ). DESIGN: Retrospective analysis. SETTING: University tertiary referral center. PATIENTS: Two hundred twenty-nine patients with symptoms suggestive of foregut disease underwent esophageal manometry, 24-hour pH monitoring, and upper gastrointestinal tract endoscopy, with biopsy specimens obtained from the gastric antrum, the GEJ, and the distal esophagus. In these and in an additional 114 patients with adenocarcinoma of the esophagus and the GEJ, the presence of H. pylori was determined by Giemsa stain. The presence of gastroesophageal reflux disease, defined by abnormal esophageal acid exposure, and its manifestations (carditis, erosive esophagitis, intestinal metaplasia limited to the GEJ, Barrett esophagus, and adenocarcinoma of the esophagus and GEJ) were correlated with the presence of H. pylori. RESULTS: Helicobacter pylori was found on the biopsy specimens of the gastric antrum in 14.0% (32/229) of the patients with benign disease. It was not related to the features of gastroesophageal reflux disease, including abnormal esophageal acid exposure, erosive esophagitis, or Barrett esophagus. The presence of inflamed cardiac mucosa at the GEJ or carditis was inversely related to H. pylori infection and strongly associated with increased esophageal acid exposure. There was no association between the presence of intestinal metaplasia and H. pylori infection. Helicobacter pylori was found in 22 (19.3%) of the 114 patients with esophageal adenocarcinoma, which was not different from the prevalence of H. pylori in patients with benign disease. CONCLUSION: Helicobacter pylori plays no role in the pathogenesis of gastroesophageal reflux disease or its complications.

Adolescent↗
PubMed1999

The pattern of esophageal acid exposure in gastroesophageal reflux disease influences the severity of the disease.

HYPOTHESIS: There is an independent association between the different patterns of esophageal acid exposure in gastroesophageal reflux disease and the severity of the disease. DESIGN: Case-comparison study. SETTING: Department of surgery at a university hospital. PATIENTS: A group of 401 patients with increased esophageal acid exposure divided into 4 groups according to the pattern of reflux: postprandial (n = 41), upright (n = 74), supine (n = 129), and bipositional (n = 157). MAIN OUTCOME MEASURES: The prevalence of mucosal injury and the status of the lower esophageal sphincter and esophageal motility were assessed in each group. RESULTS: The likelihood of having indicators of the severity of gastroesophageal reflux disease increases progressively from postprandial to upright, supine, and bipositional reflux. CONCLUSIONS: The pattern of esophageal acid exposure in gastroesophageal reflux disease is an objective predictor of the severity of disease and could be used for therapeutic decisions.

Case-Control Studies↗