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Biomedical subjects

B Walters

Publications and source records attributed to B Walters.

At least 19 recordsLinked to original sources
PubMed2005

"Reference Biospheres" for solid radioactive waste disposal: the BIOMASS methodology.

The BIOMASS Theme 1 project has developed a methodology for the logical and defensible construction of 'assessment biospheres': mathematical representations of biospheres used in the total system performance assessment of radioactive waste disposal. The BIOMASS Methodology provides a systematic approach to decision making, including decisions on how to address biosphere change. The BIOMASS Methodology was developed through consultation and collaboration with many relevant organisations, including regulators, operators and a variety of independent experts. It has been developed to be practical and to be consistent with recommendations from ICRP and IAEA on radiation protection in the context of the disposal of long-lived solid radioactive wastes. The five main steps in the methodology are described in this paper. The importance of a clear assessment context, to clarify intentions and to support a coherent biosphere assessment process within an overall repository performance assessment, is strongly emphasised. A well described assessment context is an important tool for ensuring consistency across the performance assessment as a whole. The use of interaction matrices has been found to be helpful in clarifying the interactions between different habitats within the biosphere system and the significant radionuclide transfer pathways within the biosphere system. Matrices also provide a useful means of checking for consistency.

Program Development↗
PubMed2005

Contractile response to colonic distention is influenced by oscillation frequency.

Static colonic mechanical properties are characterized by stepwise balloon distention. It is unclear whether the state of contractile activation affects frequency-dependent differences in biomechanical properties. Our aim was to investigate the frequency-dependence of colonic mechanical properties by sinusoidal oscillation. A descending colonic balloon was sinusoidally oscillated by 25 mL at 5, 10 and 20 cpm in randomized order for 20 min at each frequency in six healthy subjects before and after neostigmine. Volume oscillation was between 75-100 mL before, and 25-50 mL after neostigmine. Pressure waveforms were most variable shortly after commencing oscillation, reflecting an initial contractile response to distention. Elastance (i.e. pressure response to imposed volume) and hysteresivity were estimated; hysteresivity represents the proportion of energy added to the system during inflation, which cannot be recovered during deflation. Colonic elastance was frequency dependent, being highest and most variable at 10 cpm. In contrast, hysteresivity was not significantly different across frequencies. Neostigmine increased mean colonic elastance at all frequencies, and hysteresivity only at 5 cpm. Thus, colonic mechanical properties, particularly elastance are frequency-dependent. The frequency-dependence of colonic mechanical properties is worthy of future study because it may provide insights into reflex responses in health and disease.

Acetylcholine↗
PubMed2005

Detection of bacterial overgrowth in IBS using the lactulose H2 breath test: comparison with 14C-D-xylose and healthy controls.

UNLABELLED: OBJECTIVES Recent reports suggest bacterial overgrowth is commonly associated with irritable bowel syndrome (IBS) when diagnosed using the lactulose hydrogen breath test (LHBT). We employed this test to examine whether similar findings exist in a geographically distinct population of Rome II positive IBS patients and compared it to the 14C-D-xylose breath test, a test with acknowledged greater specificity for bacterial overgrowth. METHODS: In the first series, Rome II IBS patients underwent a 10 g lactulose breath test and a standardized 1 g 14C-D-xylose breath test and answered IBS symptom questionnaires. A positive test required an elevated breath hydrogen concentration within 90 min, two distinct peaks, and an increase >20 ppm. In a second series, control patients lacking gastrointestinal symptoms underwent a lactulose breath test. A positive test required an elevation of breath hydrogen >20 ppm within 90 or 180 min. These criteria were also applied to lactulose breath tests from IBS cases in series one. RESULTS: The IBS patients were predominantly female (64%) and most reported severe symptoms (80%). The majority had diarrhea predominant symptoms (63%) and only 3% were constipation predominant. In the first series, only 10% of patients had a positive lactulose breath test and 13% had a positive 14C-D-xylose test. In the second series, the number of abnormal LHBTs was much higher but no differences were found between IBS patients and controls. CONCLUSION: The lactulose breath test did not reliably detect a common association between bacterial overgrowth and IBS in our patient population.

Adult↗
PubMed2001

Study of plasma factors associated with neutrophil activation and lipid peroxidation in preeclampsia.

Neutrophil activation occurs in women with preeclampsia and is resolved after delivery. The present study examined whether circulating factors in plasma of women with preeclampsia caused neutrophil activation and lipid peroxidation. Twenty-one women with proteinuric preeclampsia were matched for age and gestational age with 19 normal pregnant women. Plasma was collected from all subjects before delivery and at 6 weeks postpartum and incubated with autologous white-cell buffy coat collected at the postpartum visit. Neutrophil activation was assessed by level of CD11b and CD18 expression after incubation with autologous antepartum or postpartum plasma. Lipid peroxidation was assessed by measurement of F(2)-isoprostanes in plasma, plasma-white cell incubates, and urine. Neutrophil CD11b and CD18 expression was not differentially altered by incubation with plasma from either women with preeclampsia or normal pregnant women and was similar between groups when incubation was performed with plasma collected after delivery. In preeclampsia, plasma F(2)-isoprostanes were significantly increased before and after delivery compared with controls. Plasma F(2)-isoprostanes were increased 2-fold after incubation of plasma with buffy coat, but preeclamptic women had higher levels compared with those of controls when either pregnant or postpartum plasma was used. In pregnant preeclamptics, plasma F(2)-isoprostanes were positively correlated with lymphocyte count. Six weeks after delivery, plasma F(2)-isoprostanes in the preeclamptic women were significantly positively associated with lymphocyte count and cholesterol and negatively associated with albumin. In conclusion, the present study does not suggest that a stable circulating factor causes neutrophil activation in preeclampsia. However, lipid peroxidation is elevated before and after delivery in women with preeclampsia, which suggests that these women may have an underlying predisposition to increased oxidative stress that may be driven by or contribute to a persistent low-grade inflammatory response.

Adult↗
PubMed2001

Configural display design techniques considered at multiple levels of evaluation.

Two studies were conducted to examine issues in the design and evaluation of configural displays. Four design techniques (bar graphs/extenders, scale markers/ scale grids, color coding/color layering/color separation, and annotation with digital values) were applied, alone and in combination, to a baseline configural display, forming 10 displays. Two qualitatively different evaluations assessed performance for (A) low-level data probes (quantitative estimates of individual variables) and (B) system control and fault detection tasks. Three of the four design techniques improved performance significantly for low-level data probes (color coding was the exception). A display with digital values only (i.e., no analog configural display) produced the poorest performance for control/fault detection tasks. When both levels of evaluation are considered, a composite display (configural display with all four techniques applied) was clearly the most effective. Overall, the findings obtained in the two experiments provide very limited evidence for the generalization of results between evaluations. The two levels of evaluation, the display manipulations, and the patterns of results are considered in terms of a cognitive systems engineering evaluation framework. General implications for the evaluation of displays and interfaces are discussed. Actual or potential applications include design techniques to improve graphical displays and methodological insights to focus and improve evaluation efforts.

Adult↗
PubMed2000

A randomised controlled trial of dietary energy restriction in the management of obese women with gestational diabetes.

A randomised controlled trial was designed to determine the effect of moderate 30% maternal dietary energy restriction on the requirement for maternal insulin therapy and the incidence of macrosomia in gestational diabetes. Although the control group restricted their intake to a level similar to that of the intervention group (6,845 kiloJoules (kJ) versus 6,579 kJ), the resulting cohort could not identify any adverse effect of energy restriction in pregnancy. Energy restriction did not alter the frequency of insulin therapy (17.5% in the intervention group and 16.9% in the control group). Mean birthweight (3,461 g in the intervention group and 3,267 g in the control group) was not affected. There was a trend in the intervention group towards later gestational age at commencement of insulin therapy (33 weeks versus 31 weeks) and lower maximum daily insulin dose (23 units versus 60 units) which did not reach statistical significance. Energy restriction did not cause an increase in ketonemia.

3-Hydroxybutyric Acid↗
PubMed1998

Increased iron and ferritin content of sputum from patients with cystic fibrosis or chronic bronchitis.

PURPOSE: Extracellular free iron, or iron bound to ferritin, may promote oxidative injury and bacterial growth in airways of patients with chronic airway inflammation due to cystic fibrosis (CF) or chronic bronchitis (CB). In this study, we assessed sputum content of total iron, ferritin, and transferrin in patients with CF or CB as well as sputum from normal subjects with acute airway inflammation caused by viral upper respiratory tract infections (URTIs). METHODS: Spontaneously produced sputum was obtained from 33 subjects, including 10 subjects with CF, 18 subjects with CB (10 acute exacerbations, 8 with stable CB), and 5 subjects with URTIs (control subjects). After lysing and dilution, total iron concentrations were determined by controlled coulometry, ferritin was measured by radioimmunoassay, and transferrin was measured by enzyme-linked immunosorbent assay. RESULTS: Iron was not present in detectable amounts in control sputums, but ferritin was present (6+/-2 ng/mg protein, mean+/-SE), as was transferrin (2.37+/-0.44 microg/mg). Compared with control subjects, concentrations of iron in sputum were increased in patient groups with higher amounts in CF patients (242+/-47 ng/mg, p<0.01) than CB patients with acute exacerbations or patients with stable CB (98+/-50 and 42+/-12 ng/mg, p<0.05 for both). Ferritin content of sputum was also increased in each group, with CF patients (113+/-22 ng/mg, p<0.001) higher than CB patients (acute, 45+/-10 ng/mg; stable, 87+/-24 ng/mg; p<0.01 for both). Compared with control subjects, sputum transferrin was decreased in CF patients (1.09+/-0.40 microg/mg, p<0.05), but not CB patients. CONCLUSIONS: These findings indicate there are increased airway concentrations of total iron and ferritin-bound iron in patients with CB and, to a greater extent, in patients with CF. Particularly in CF patients who also demonstrated decreased airway concentrations of transferrin, ferritin-bound iron in airways may promote oxidative injury and enhance bacterial growth.

Acute Disease↗
PubMed1998

Usefulness of proton MR spectroscopy in the evaluation of temporal lobe epilepsy.

OBJECTIVE: The purpose of our study was to compare the ability of MR spectroscopy with that of standard presurgical methods to accurately lateralize the abnormal hippocampus in a group of patients with complex partial seizures. SUBJECTS AND METHODS: Ten healthy volunteers (five male, five female) without a history of seizures, significant head trauma, or other neurologic abnormalities were chosen to participate in the study. Twelve consecutive patients (three male, nine female) having intractable temporal lobe epilepsy and undergoing presurgical evaluation for temporal lobectomy were chosen to participate in the study. The condition of all patients was refractory to medications. All patients underwent presurgical examination with interictal and video ictal electroencephalography, ictal single-photon emission computed tomography, interictal positron emission tomography, MR imaging, and neuropsychologic testing. When noninvasive data were inconclusive, depth or grid recordings were performed. The results of MR spectroscopy were also compared with postsurgical seizure control as defined by the Engel classification. RESULTS: Nine (90%) of 10 control subjects showed no significant difference in N-acetyl aspartate. One control subject showed 16% asymmetry in N-acetyl aspartate between sides. The control group showed no statistically significant differences in ratios of N-acetyl aspartate:creatine, N-acetyl aspartate:choline, or creatine:choline when comparing sides (p < .05). All 12 patients showed clearly lateralizing values identified by the index of asymmetry in N-acetyl aspartate (range, 24-93%), with a mean difference of 51% (SD, 22) (p = .01). Additionally, as a group, statistically significant indexes of asymmetry (p = .01) were seen in ratios of N-acetyl aspartate:choline (mean, 42; SD, 22%), N-acetyl aspartate:creatine (mean, 41; SD, 27), and N-acetyl aspartate:creatine + choline (mean, 42; SD, 22). Using an N-acetyl aspartate index of asymmetry of greater than 15%, which represents the mean index of asymmetry of the control subjects +/- two SDs, as our cutoff level for lateralization, the correct side was identified in all patients. When comparing both hippocampi using an asymmetry index of 15% for N-acetyl aspartate:choline + creatine, 11 (92%) of 12 were correctly lateralized. When comparing the unaffected temporal lobes between patients and control subjects, no statistically significant differences were detected in any metabolites or ratios. CONCLUSION: Our study agrees with others in showing decreased N-acetyl aspartate in the hippocampus of seizure patients when compared with control subjects. Using N-acetyl aspartate, N-acetyl aspartate:creatine, N-acetyl aspartate:choline, and N-acetyl aspartate:creatine + choline as our parameters, patients with mesial temporal lobe epilepsy were correctly lateralized with MR spectroscopy when compared with clinical consensus criteria. We consider MR spectroscopy to be complementary to MR imaging. Both studies can be performed as a single integrated examination.

Adult↗
PubMed1994

Analysis of discrete T2 components of NMR relaxation for aqueous solutions in hollow fiber capillaries.

An analysis is presented of proton NMR T2 relaxation times measured for aqueous solutions in simple bundles of hollow fibers. The relaxation times are calculated with a two-compartment diffusive exchange model using the known relaxation times of the aqueous solutions and the fiber geometry. When the relaxation time outside the fibers is short (approximately 1 ms), three or more relaxation components are observed from this two compartment system, in agreement with the calculation. The amplitude and relaxation times of the third component are consistent with those of a diffusion-mediated mode, as suggested theoretically by Brownstein and Tarr (Phys. Rev. A 19, 2446 (1979)). The possible contribution of such modes to the multicomponent relaxation observed in tissues is discussed.

Animals↗
PubMed1994

An investigation of spinal bone mineral density measured laterally: a normal range for UK women.

A UK normal range for 250 volunteers was established for bone mineral density (BMD) of the lumbar spine (L2-L4) measured laterally in the decubitus position. Two software defined regions of interest ("Body" and "Mid") within the vertebral body were analysed throughout. As expected, a negative correlation of BMD with age was found for Body (r = -0.55, p < 0.001) and Mid (r = -0.56, p < 0.001). The age related bone loss from young to old (20-80 years) was 40% in L3 (Body) and 45% in L3 (Mid). In 22% of the cases only L3 could be measured owing to the influence of rib over L2 and interference of the iliac crest over L4. Age related normal ranges (+/- 2 standard deviations) for the three lumbar vertebra L2, L3, L4 for young normals (age 19-39 years) were found to be 0.54 to 1.02, 0.49 to 1.05 and 0.5 to 1.14 g cm-2 respectively for the Body region and 0.49 to 0.97, 0.45 to 1.01 and 0.45 to 1.13 g cm-2 respectively for the Mid region. These ranges can now be used as reference values for patients with suspected osteoporosis and possibly for future fracture prediction. The in vivo precision in 19 volunteers was found to be 4.2% and 5.6% on Body and Mid respectively. The short term (less than 1 week) in vitro precision was 3.1% and 2.7% respectively. From these data it appears that there is a greater measured age related drop in BMD in the vertebral body (measured laterally) than in the entire vertebra (measured anterior-posteriorly) indicating that the lateral measurement may prove to be more sensitive in predicting fracture. The precision of these results indicates that lateral measurements of the spine are not yet useful for monitoring individuals over short term periods and are less useful for studying the effects of drug treatment than the more traditional anterior-posterior measurement of the spine and femur.

Absorptiometry, Photon↗
PubMed1993

Nosocomial outbreak due to Enterococcus faecium highly resistant to vancomycin, penicillin, and gentamicin.

In October 1990, Enterococcus faecium that was highly resistant to glycopeptides, penicillins, and aminoglycosides was isolated from the peritoneal dialysis fluid from a patient in an intensive care unit. Over the following 6 months, multiresistant E. faecium organisms were isolated from cultures of blood, urine, or surgical wound specimens from eight additional patients. Surveillance cultures of groin and/or rectal swabs were positive for eight of 37 patients and four of 62 employees at risk. Restriction endonuclease digestion of chromosomal DNA from outbreak isolates was consistent with dissemination of a single strain throughout the intensive care unit. Strict infection control interventions contained the outbreak after several weeks. Review of patient charts suggested that renal insufficiency, length of hospital stay, duration of antibiotic treatment, and prior treatment with vancomycin were risks for infection due to multiresistant E. faecium. The emergence of multiple-drug-resistant enterococci presents serious infection control and therapeutic dilemmas.

Aged↗
PubMed1993

Human uptake of 137Cs in mutton.

The uptake of radiocesium from mutton contaminated by fallout from the Chernobyl reactor accident has been studied in eight healthy male volunteers. Each subject consumed, on adjacent days, two meals prepared from the mutton containing a total of 0.8 kBq 137Cs. The elevation and subsequent decline in whole-body content were determined from body radioactivity measurements prior to the meals and at intervals up to 15 wk afterwards. Clearance of 137Cs between 1 and 15 wk showed a biological half-time of 102 +/- 24 (SD) d, (range 84-154 d). The fraction cleared with this half-time was 80 +/- 4% (range 72-85%). No attempt was made to determine the early retention and excretion but, if the ICRP's assumption of 10% clearance with a 2-d half-life were valid, the data would indicate an average uptake (f1) of 89%, i.e., marginally lower than the value of 100% assumed in setting limits on intake.

Accidents↗