Search PubMed⌕ Search

Biomedical subjects

A Evans

Publications and source records attributed to A Evans.

At least 73 records · Page 4Linked to original sources
PubMed2003

X-ray refraction effects: application to the imaging of biological tissues.

The purpose of this study was to explore the potential of refraction contrast X-ray imaging of biological tissues. Images of dissected mouse lungs, heart, liver and legs were produced using the medical beamline at the Elettra Synchrotron at Trieste, Italy. The technique used was diffraction enhanced imaging. This utilizes a silicon crystal positioned between the tissue sample and the detector to separate refracted X-rays from transmitted and scattered radiation by Bragg diffraction. The contrast in the images produced is related to changes in the X-ray refractive index of the tissues, resulting in remarkable clarity compared with conventional X-ray images based on absorption effects. These changes were greatest at the boundaries between different tissues, giving a marked edge enhancement effect and three-dimensional appearance to the images. The technique provides a way of imaging a property of biological tissues not yet exploited, and further studies are planned to identify specific applications in medical imaging.

Animals↗
PubMed2003

[Biological banks of the prospective cohort PRIME Study].

BACKGROUND: Cardiovascular disease is the leading cause of mortality in westernized countries. Learning more about the cause of coronary heart disease (CHD) is an essential step in the search for effective CHD prevention, both at the individual and population levels. Prospective cohort studies are particularly well suited to the study of risk markers. However, the high cost of mounting such studies, along with the newer hypotheses generated during the period of follow-up necessitates the use of plasma and serum banks for analyses of many biological parameters. METHODS: The prospective, cohort PRIME Study has recruited 10,592 men, aged 50-59 years in France and Northern Ireland, to establish new risk markers for CHD. A plasma serum bank was established comprising 240,000 samples, either in straws or tubes, which have been stored in liquid nitrogen for over 5 years. The use of straws was required to store the largest number of aliquots in the smallest possible space. Storage validation was carried out for a number of key parameters. The validity of freezing of plasma in straws was established for a number of key measurements under investigation. Simultaneously, a DNA bank was set up to facilitate genetic analyses. In contrast to the DNA bank, which enables the performance of a very large number of analyses on a small amount of material, the plasma/serum bank has to be managed very frugally, requiring laboratories to use the smallest volume possible in each analysis. RESULTS AND CONCLUSION: Problems and difficulties solved during building and use of biological banks are presented. The initial results obtained using this plasma bank have demonstrated its validity.

Blood Banks↗
PubMed2003

Prediction of corneal permeability using artificial neural networks.

The purpose of this study was to develop a simple model for prediction of corneal permeability of structurally different drugs as a function of calculated molecular descriptors using artificial neural networks. A set of 45 compounds with experimentally derived values of corneal permeability (log C) was used to develop, test and validate a predictive model. Each compound was encoded with 1194 calculated molecular structure descriptors. A genetic algorithm was used to select a subset of descriptors that best describe corneal permeability coefficient log C and a supervised network with radial basis transfer function (RBF) was used to correlate calculated molecular descriptors with experimentally derived measures of corneal permeability. The best model, with 4 input descriptors and 12 hidden neurones was chosen, and the significance of the selected descriptors to corneal permeability was examined. Strong correlation of predicted with experimentally derived log C values (correlation coefficient greater than 0.87 and 0.83 respectively) was obtained for the training and testing data sets. The developed model could be useful for the rapid prediction of the corneal permeability of candidate drugs based on molecular structure alone as it does not require experimentally derived data.

Chemical Phenomena↗
PubMed2002

Strategies for the control of catheter encrustation.

Two general strategies have been adopted to develop catheter materials that resist encrustaion by bacterial biofilms: (a) the incorporation of antimicrobial agents into the polymers and (b) the production of materials with surface properties which prevent the adherence of bacterial cells. Our experience to develop non-adherent surfaces which abstracts design from nature is reported. Compounds based on 2-methacryloloxyethylphosphorylcholine co-polymerised with long-chain alkyl methacrylates have been produced which have structural and surface properties similar to those of the outer membranes of erythrocytes. These PC-coatings have been applied onto catheter base materials where they produce polar surfaces that are extremely hydrophilic. In experiments using a laboratory model of the catheterised bladder we found that the PC-coatings did not reduce colonisation of latex or silicone catheters by crystalline Proteus mirabilis biofilm. There were no significant difference between the amounts of calcium and magnesium salts deposited on coated and non-coated catheters. In a further set of experiments the PC-coatings did not significantly increase the mean times for which catheters drained freely. In a parallel clinical study, the performance of PC-coated ureteral stents was investigated. Scanning electron microscopy and bacteriological analysis on 44 PC-coated stents that had been implanted in patients for 12-week periods and 28 control stents suggested that the PC-coated devices were less vulnerable to encrustation and colonisation by bacterial biofilm than normal stents. It was of interest that in contrast to encrusted catheters, urease producing species such as P. mirabilis were rarely isolated from the stents. The main organisms colonising the stents were enterococci and coagulase-negative staphylococci. These results suggest that the mechanisms of catheter and stent encrustation may be different and require different strategies for control.

Bacteria↗
PubMed2002

Urinary catheter 'deflation cuff' formation: clinical audit and quantitative in vitro analysis.

OBJECTIVE: To investigate reports from district nursing staff of difficulty in removing long-term urinary catheters (LTCs) because of the formation of a 'cuff' on deflating the self-retaining balloon. PATIENTS AND METHODS: Problems experienced by district nurses when removing urethral and suprapubic LTCs were audited, noting the type of problem, the catheter and any action taken. Quantitative in vitro studies were conducted on the deflated self-retaining balloons after incubating a similar range of catheters in saline at 37 degrees C for 6 weeks, using suprapubic profilometry to assess the resistance to withdrawal (retention force). RESULTS: Questionnaires were returned on 154 patients with LTCs; 56% had urethral and 44% suprapubic catheters. The catheters were hydrogel-coated (83%), all-silicone (13%) and PTFE-coated (3%). Twenty-two (14%) of the sample reported problems with catheter removal in the previous year, including 15 (68%) with all-silicone catheters and 15 (68%) with suprapubic catheters; cuff formation was noted in 60%. In the laboratory, 10 of the balloons formed a 'cuff' on deflation, but there was great variability in the effect this had on the retention force, with values of 0.5-3 N for different catheters. CONCLUSIONS: Most problems with catheter removal involved all-silicone and suprapubic catheters. Suprapubic profilometry confirmed increased resistance to withdrawal by formation of a 'cuff' on deflation of the balloon of all-silicone catheters. These results suggest that the first choice of catheter material for long-term urethral and suprapubic use should be hydrogel-coated latex.

Catheterization↗
PubMed2002

Hormone replacement therapy and mammographic screening.

The benefits of hormone replacement therapy (HRT) with oestrogen are well known and have led to widespread usage of HRT in post-menopausal women. There is an increased relative risk of breast cancer with prolonged HRT use of 1.7 at worst and this does not warrant more frequent screening. HRT itself makes mammographic screening less effective by adversely affecting both the sensitivity and specificity of screening mammography.A number of large studies have shown a reduction in the sensitivity of screening mammography of between 7% and 21% in current HRT users. This reduction in sensitivity is seen only in women over the age of 50 and is more marked when using single view mammography. The reduction in sensitivity is largely confined to those women who have a dense mammographic background pattern while on HRT. HRT use is also associated with a reduction in specificity of between 12% and almost 50%. This reduction in specificity is mainly found at incident screens. What can be done to minimize the adverse effects of HRT on mammographic screening? The imminent introduction of two views at all screens within the National Health Breast Screening Programme will be helpful. Short-term cessation of HRT use may deter attendance for screening by HRT users and is unproven. Combined oestrogen and progesterone preparations taken continuously appear to be particularly associated with adverse breast screening performance, while tibolone may have little effect on mammographic density. Manipulation of the type of HRT preparations used may allow the adverse effects of HRT on breast screening to be reduced.

Breast Neoplasms↗
PubMed2002

Temporomandibular joint synovial fluid sampling: estimation of dilution factor using calcium ion concentration.

Saline aspirates have been commonly used in the biochemical investigations of temporomandibular joint (TMJ) pathology. However, due to presence of adhesions in the diseased temporomandibular joint, full equilibration between the injected saline and the synovial fluid may not be achieved in all cases. We measured calcium ion concentration in the saline aspirates and the plasma to assess the degree of dilution of the synovial fluid by the injected media. Saline aspirates obtained prior to the arthroscopic examination of 17 patients with painful TMJs not responding to 3 months of conservative treatment were analysed for their calcium content by a highly sensitive spectrophotometric autoanalyser. In 10 patients with unilateral symptoms, the contralateral asymptomatic side was used as a control. Using a concentration volume equation the amount of the synovial fluid in the saline aspirates was calculated. The yield of the saline aspirates was variable ranging from 330 to 1000 microl. The mean calcium level was 0.787 mg/dl in the symptomatic group (C.I. 95% 0.337-1.237 mg/dl) and 0.512 mg/dl (C.I. 95% 0.235-0.797) in the asymptomatic group. Using a Student t-test there was no significant difference between the two groups. Furthermore, there was no demonstrable correlation between the volume of the aspirate and its synovial fluid content. This study confirms that the saline aspirate may not be a representative sample of the TMJ synovial fluid, and that expression of the results of the biochemical assays per volume of the aspirate may be misleading.

Adult↗
PubMed2002

PGE(2) receptors and synthesis in human gastric mucosa: perturbation in cancer.

Recent evidence suggests that prostanoids are an important participant in the pathobiology of gastric adenocarcinoma, but the location and identity of cells in tumor-adjacent gastric mucosa able to synthesize and/or bind specific prostanoids is not clear. Using probes for cyclooxygenase 1 and 2 mRNA and protein as well as for the EP family of PGE(2) receptors, we sought to define the biology of prostanoids in adjacent human gastric mucosa at the site of tumor invasion. In mucosa adjacent to an invasive gastric adenocarcinoma, expression of cyclooxygenase was prominent, with COX 1 primarily in mucosal T lymphocytes surrounding nests of tumor cells. Densitometry showed these tumor-adjacent cells had substantial levels of COX 1 immunoreactive protein (relative intensity, 3.2). Cyclooxygenase 2 was newly expressed among these cells as well, but was limited in number (<25% of cyclooxygenase-positive T lymphocytes) in tumor-adjacent mucosa. Further, CD3(+) mononuclear cells, adjacent to tumor, strongly expressed prostanoid receptor EP(4) (relative intensity, 8.0), but cells with this receptor were not evident in the tumor itself. In contrast, normal gastric mucosa showed a consistent and structured expression of cyclooxygenase and PGE(2) receptor immunoreactive protein among mucosal cells. Cyclooxygenase 1 and PGE(2) receptor EP(4) were expressed on mucosal CD3(+) T lymphocytes in the lumenal (upper) third of gastric mucosa; and prostanoid receptors EP(2), EP(3) and EP(4), on gastric epithelia lining gastric pits. In situ hybridization with COX cDNAs confirmed these findings, and neither COX 2-specific mRNA nor protein was detected in normal gastric tissue. Our studies suggest that synthetic machinery and receptors for PGE(2), prominently expressed by T lymphocytes in gastric mucosa at the boundary of normal mucosa with tumor cells, may play a central role in prostanoid-driven tumorigenesis of this tissue.

Antibodies↗
PubMed2002

Pigtail catheter drain in the treatment of empyema thoracis.

We compared the outcome of children with empyema managed either through thoracotomy with pleural debridment, conventional stiff chest drain, or pigtail chest drain. Compared to conventional drain, children who received either thoracotomy or pigtail catheters had a significantly decreased period of drain in situ, were afebrile earlier, were clinically improved earlier, and were discharged earlier.

Catheterization, Peripheral↗
PubMed2001

Should stroke subtype influence anticoagulation decisions to prevent recurrence in stroke patients with atrial fibrillation?

BACKGROUND AND PURPOSE: Long-term anticoagulation is routinely used for secondary stroke prevention in atrial fibrillation, often regardless of stroke subtype. Although the role of warfarin in cardioembolic stroke is established, it may not prevent recurrence in other stroke subtypes, even in the presence of atrial fibrillation. METHODS: This was a 2-year, prospective, intervention study conducted in a district general hospital. Participants included 386 acute stroke patients with atrial fibrillation. Subjects were characterized for stroke subtype on clinical, neuroimaging, carotid ultrasonographic, and echocardiographic criteria. Eligible patients were treated with adjusted-dose warfarin (international normalized ratio, 2.0 to 3.0). Aspirin (75 to 300 mg/d) was used in patients with contraindications or those who refused anticoagulation. The main outcome measures were rate of recurrent stroke by subtype and major and minor bleeding complications. RESULTS: The aspirin group (n=172) was comparable to the warfarin group (n=214) in terms of age, sex, risk factors, and initial stroke subtype. The rate of recurrent stroke was higher (9.5% versus 4.9%, P<0.02) but that of major bleeding was lower (0.6% versus 2.5%, P<0.05) with aspirin. The increased stroke rate with aspirin was due predominantly to cardioembolic recurrence in patients presenting initially with cardioembolic stroke (8.4% versus 1.9%, P<0.01). The recurrence rate in aspirin-treated patients who presented with lacunar stroke and atrial fibrillation was similar to that seen in patients receiving warfarin (8.8% versus 8.9%). CONCLUSIONS: In this cohort of stroke patients with atrial fibrillation, anticoagulation was superior to aspirin in preventing cardioembolic but not lacunar recurrence. Determination of stroke subtype may be important in anticoagulation decisions for secondary prevention, and further studies are required.

Aged↗
PubMed2001

Different alcohol drinking and blood pressure relationships in France and Northern Ireland: The PRIME Study.

To assess the effect of alcoholic beverages consumed on blood pressure levels by day of the week, baseline data from the Prospective Epidemiological Study of Myocardial Infarction (PRIME), including 6523 male subjects who drank at least once a week (5156 in France and 1367 in Northern Ireland), were analyzed. In France, alcohol consumption was rather homogeneous throughout the week, with a slight increase during weekends, whereas in Northern Ireland, Fridays and Saturdays accounted for 66% of total alcohol consumption. After adjustment for age, body mass index, heart rate, tobacco smoking, educational level, marital status, and professional activity, blood pressure levels were higher in Northern Irish drinkers on Monday and decreased until Thursday, whereas blood pressure levels were constant throughout the week for French drinkers (day x country interactions, P<0.05). Conversely, no between-day differences were found regarding teetotalers in both countries. In drinkers, between-day differences and day x country interactions were suppressed after adjustment for the average alcohol consumption of the third day before measurement. We conclude that the binge-drinking pattern observed among Northern Irish drinkers leads to physiologically disadvantageous consequences regarding blood pressure levels, whereas no such fluctuations in blood pressure levels are found for regular consumption.

Alcohol Drinking↗
PubMed2001

p73 is over-expressed in vulval cancer principally as the Delta 2 isoform.

p73 was studied in squamous cancers and precursor lesions of the vulva. Over-expression of p73 occurred commonly in both human papillomavirus (HPV)-positive and -negative squamous cell cancers (SCC) and high-grade premalignant lesions. Whereas expression in normal vulval epithelium was detected only in the basal and supra-basal layers, expression in neoplastic epithelium increased with grade of neoplasia, being maximal at both protein and RNA levels in SCC. p73 Delta 2 was the principal over-expressed isoform in the majority of cases of vulval SCC and often the sole form expressed in SCC. Over-expression of p73 was associated with expression of HPV-encoded E7 or with hypermethylation or mutation of p16(INK4a) in HPV-negative cases. There was a close correlation between expression of p73 and p14(ARF) in cancers with loss of p53 function. The frequent over-expression of p73 Delta 2 in neoplastic but not normal vulval epithelium, and its co-ordinate deregulation with other E2F-1 responsive genes suggests a role in the oncogenic process.

Cyclin-Dependent Kinase Inhibitor p16↗
PubMed2001

Can differences in management processes explain different outcomes between stroke unit and stroke-team care?

BACKGROUND: Stroke units reduce mortality and dependence, but the reasons are unclear. We have compared differences in management and complications of patients with acute stroke who were admitted to a stroke unit or to a general ward as part of a previously reported randomised trial. METHODS: 304 patients had been randomly assigned to stroke units (n=152) or to general wards supported by a specialist stroke team (152). We used a structured format to gather prospective data on the frequency of prespecified interventions in each of the major aspects of stroke care. Observations were undertaken daily for the first week and every week for the next 3 months by independent observers. The effect of differences in management on outcome at 3 months was assessed with the modified Rankin score, dichotomised to good (0-3) and poor (4-6) outcome. FINDINGS: Patients in the stroke unit were monitored more frequently (odds ratio 2.1 [1.3-3.4]) and more patients received oxygen (2.0 [1.3-3.2]), antipyretics (6.4 [1.5-27.5]), measures to reduce aspiration (6.0 [2.3-15.5]), and early nutrition (14.4 [5.1-40.9]) than those in general wards. Complications were less frequent in patients in the stroke unit than those in general wards (0.6 [0.2-0.7]), with fewer patients having progression of stroke, chest infection, or dehydration. Measures to prevent aspiration, early feeding, stroke unit management, and frequency of complications independently affected outcome. INTERPRETATION: Differences in management and complications between the stroke unit and general wards differ substantially, even when specialist support is provided. Such differences could be responsible for the more favourable outcome seen in patients on stroke units than those on general wards.

Aged↗
PubMed2001

Routine breast screening for women aged 65-69: results from evaluation of the demonstration sites.

Routine programme data and specially designed surveys from 3 demonstration sites were analysed to determine the implications of extending the NHS Breast Screening Programme (NHSBSP), to include routine invitations for women up to 69 years. All women aged 65-69 and registered with GPs in these areas received routine invitations for breast screening along with those aged 50-64. Overall uptake was 71% in women aged 65-69 compared with 78% in younger women, but was > or = 90% in both groups who had previously attended within 5 years. Recall rates were lower for older women, but with a higher positive predictive value for cancer. The percentages of invasive cancer in different prognostic categories were similar in the 2 age groups. Older women took no longer to screen than younger women. The costs per woman invited or per woman screened were also similar to those for women aged 50-64, whilst the cost per cancer detected was some 34% lower in older women. Breast screening is as cost effective for women aged 65-69 as for those aged 50-64, with a higher cancer detection rate balancing shorter life expectancy. The proposed extension to the national programme will have considerable workforce implications for the NHSBSP and require additional resources.

Aged↗
PubMed2001

Apolipoprotein E alleles in nonagenarian subjects in the Belfast Elderly Longitudinal Free-living Ageing Study (BELFAST).

The ApoE gene has three alleles coding for the proteins apoE2, apoE3 and apoE4. E4 has been reported to be associated with hypercholesteraemia, ischaemic heart disease, age-related cognitive decline and Alzheimer's disease. Conversely, the E2 allele has been associated with longevity in French centenarians and their siblings. In this study, we have assessed any shift in the ApoE genotypes in nonagenarian subjects from Belfast where there is a high intrinsic incidence of cardiovascular disease. ApoE phenotypes were determined by electrofocusing and immunoblotting in 114 Senieur-approximated subjects >90 years old and compared with 2071 subjects, 30--65 years of age, recruited from the same geographical area by the MONItoring of CArdiovascular trends study group in Belfast (MONICA). The E4 allele was reduced in the nonagenarian group (X(2)=11.1; P=0.0006), the E3 unchanged and E2 frequency was increased (X(2)=4.0; P=0.047). These results suggest that longevity is negatively associated with the E4 allele and may be associated with carriage of E2.

Adult↗
PubMed2001

A probabilistic atlas and reference system for the human brain: International Consortium for Brain Mapping (ICBM).

Motivated by the vast amount of information that is rapidly accumulating about the human brain in digital form, we embarked upon a program in 1992 to develop a four-dimensional probabilistic atlas and reference system for the human brain. Through an International Consortium for Brain Mapping (ICBM) a dataset is being collected that includes 7000 subjects between the ages of eighteen and ninety years and including 342 mono- and dizygotic twins. Data on each subject includes detailed demographic, clinical, behavioural and imaging information. DNA has been collected for genotyping from 5800 subjects. A component of the programme uses post-mortem tissue to determine the probabilistic distribution of microscopic cyto- and chemoarchitectural regions in the human brain. This, combined with macroscopic information about structure and function derived from subjects in vivo, provides the first large scale opportunity to gain meaningful insights into the concordance or discordance in micro- and macroscopic structure and function. The philosophy, strategy, algorithm development, data acquisition techniques and validation methods are described in this report along with database structures. Examples of results are described for the normal adult human brain as well as examples in patients with Alzheimer's disease and multiple sclerosis. The ability to quantify the variance of the human brain as a function of age in a large population of subjects for whom data is also available about their genetic composition and behaviour will allow for the first assessment of cerebral genotype-phenotype-behavioural correlations in humans to take place in a population this large. This approach and its application should provide new insights and opportunities for investigators interested in basic neuroscience, clinical diagnostics and the evaluation of neuropsychiatric disorders in patients.

Adult↗