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Biomedical subjects

M Edwards

Publications and source records attributed to M Edwards.

At least 127 records · Page 7Linked to original sources
PubMed1996

Role of postreplicative DNA mismatch repair in the cytotoxic action of thioguanine.

It is proposed here that the delayed cytotoxicity of thioguanine involves the postreplicative DNA mismatch repair system. After incorporation into DNA, the thioguanine is chemically methylated by S-adenosylmethionine to form S6-methylthioguanine. During DNA replication, the S6-methylthioguanine directs incorporation of either thymine or cytosine into the growing DNA strand, and the resultant S6-methylthioguanine-thymine pairs are recognized by the postreplicative mismatch repair system. Azathioprine, an immunosuppressant used in organ transplantation, is partly converted to thioguanine. Because the carcinogenicity of N-nitrosamines depends on formation of O6-alkylguanine in DNA, the formation of the analog S6-methylthioguanine during azathioprine treatment may partly explain the high incidence of cancer after transplantation.

Animals↗
PubMed1996

Patient-nurse relationships: using reflective practice.

This article describes how a district nurse used a reflective journal to evaluate her practice when dealing with a tense patient-nurse relationship. Using a model of reflective practice and drawing on much of the theory on the subject, the author describes how the whole experience forced her to revise her perceptions of nursing.

Humans↗
PubMed1996

Global-motion perception: interaction of chromatic and luminance signals.

A global dot-motion stimulus was employed in order to investigate the interaction between luminance and chromatic signals in motion processing. Thresholds are determined by measuring the minimum number of dots which need to move in a coherent fashion in a field of randomly moving dots in order for the observers to be able to determine the direction of coherent motion. We found that: (1) observers could not track an achromatic signal-dot which changes its luminance polarity between frame transitions. The addition of a consistent chromatic signal allowed observers to track such a dot when the dot contained low- (8%) luminance contrast but this ability was impaired as the luminance contrast was increased; (2) the addition of chromatic contrast to a dot which contained consistent low-luminance contrast could result in threshold elevation. For fixed contrast chromatic and luminance signals, the presence and degree of threshold elevation depended upon the spatiotemporal properties of the dot motion; (3) the ability of observers to extract a global-motion signal carried by a group of dots of one colour was impaired by the addition of a number of additional-noise dots of a different colour. These results are interpreted as indicating that: (1) the motion-selective cells that are sensitive to chromatic signals are also sensitive to luminance signals; (2) the combined chromatic and luminance and purely luminance motion cells are pooled to form a single pathway prior to global-motion extraction; and (3) the negative interaction observed between the chromatic and luminance signals is likely to be due to the differences in the processing speeds of the combined luminance and chromatic and the purely luminance sensitive motion cells.

Color↗
PubMed1996

Contrast sensitivity of the motion system.

A number of experiments were conducted to investigate how global-motion performance varies with luminance contrast. When all the dots in the stimulus were the same contrast, performance improved with increasing contrast up to about the 15% level (Experiment 1). Increasing the contrast beyond this level had no additional effect on performance. When the contrast of a subgroup of the dots was varied, differential effects on performance could be obtained for contrasts up to the 80% level (Experiment 2). These results are interpreted as indicating that the performance saturation observed in Experiment 1 was due to the attainment of a performance ceiling at the global-motion level, and not due to contrast-response saturation of the underlying local-motion detectors. The results of earlier studies that have apparently found conflicting results (saturation vs no saturation) are discussed in light of the present results.

Contrast Sensitivity↗
PubMed1996

Development of friable embryogenic callus and embryogenic suspension culture systems in cassava (Manihot esculenta Crantz)

Procedures for the production of a new and highly prolific embryogenic culture system have been developed in cassava. The importance of the basal salts and type of auxin in controlling the development of cassava embryogenic tissues has been demonstrated, with culture on Gresshoff and Doy basal medium in the presence of 4-amino-3,5,6,trichloro-picolinic acid (picloram) inducing the formation of friable embryogenic callus from which highly totipotent embryogenic suspension cultures could be established. Plants have been regenerated from these cultures. The availability of embryogenic suspension cultures is considered to have important implications for the application of genetic transformation and other biotechnologies in the agronomic improvement of cassava.

Culture Techniques↗
PubMed1996

Predictive diagnosis of multiple endocrine neoplasia (MEN 1) in four Australian kindreds.

BACKGROUND: Multiple endocrine neoplasia type 1 (MEN 1) is a tumour predisposition syndrome that usually manifests in the first four decades of life. It has an autosomal dominant mode of inheritance which means that any new member of a MEN1 kindred has roughly a 50% chance of developing the disorder during their lifetime. The localisation of the MEN1 gene to a small region of chromosome band 11q13 has led to the development of DNA-based predictive diagnosis for this disease. AIMS: To establish a polymerase chain reaction (PCR)-based system, using simple tandem repeat polymorphisms (STRPs), to predict gene carriers in four Australian MEN 1 kindreds. METHODS: Six STRP markers flanking the MEN1 region of chromosome band 11q13 were used to screen individuals for a common haplotype in order to determine carrier status. RESULTS: The accuracy of prediction was calculated to be > 95% in informative individuals. CONCLUSIONS: DNA-based presymptomatic detection of affected members of MEN 1 kindreds could facilitate their care and reduce the inconvenience and expense of repeated testing of unaffected members. However, due to occasional recombination events or uninformativeness of markers in certain individuals, carrier status cannot always be predicted.

Adult↗
PubMed1996

Pressure sore risk calculators: some methodological issues.

Pressure sore risk calculators have assumed a cardinal role in pressure sore prevention and management. Doubts have been expressed as to the extent to which the use of risk calculators should direct care as they have not been found to display high levels of reliability and validity. This paper raises important methodological issues regarding the reliability and validity of risk calculators in order to inform the debate as to the direction of future research in this area.

Bias↗
PubMed1996

Anthropometric measurements and ejection injuries.

BACKGROUND: A previous study examined anthropometric variables to determine possible ejection seat risk factors. It concluded that individuals who weighed below the average body weight or who met the criteria of having a tall, thin physique as measured by body mass index (BMI = kg.m-2) were significantly more at risk for acceleration induced back injuries. HYPOTHESIS: Because of the increased number of female pilots and the potential need to modify ejection seats for lighter aviators, this retrospective analysis of Naval Safety Center data attempted to reproduce and confirm the same results with more current data, covering a 5-yr period from Jan 1989-Dec 1993. METHODS: In this study, the same criteria were used to define back injury, including thoracic or lumbar vertebral fractures and soft tissue injuries, and the same anthropometric variables were used, including weight, height, BMI, and below average weight. Additional categories of injury were examined, including all spinal fractures alone without soft tissue back injuries, all injuries combined, and severity of injury. Sitting height and trunk height were added to the variables. RESULTS: Out of 810 aircrew involved in mishaps, 199 ejected. Of all the ejections, 111 (56%) had some type of injury as a result of the ejection. Severe injuries occurred in 8 (4%) including 4 (2%) fatalities. Back injuries occurred in 44 (22%), and 8 (4%) involved spinal fractures. Although there were no significant risk factors for ejection back injury, weight and height were statistically significant risk factors for severe injury and spinal fracture, respectively. CONCLUSIONS: Aircrew with severe injury were heavier (average weight 88 kg. vs. 79 kg.). In addition, taller aircrew (185 vs. 180 cm.) were at increased risk for any spinal fracture.

Acceleration↗
PubMed1996

Calibration and validity of an eccentric photorefractor.

A new graphical calibration method was developed to convert the photorefractive reflex into refractive error. With this graphical method, the refractive error can be obtained for pupil sizes and for photorefractive reflex sizes which have not been precalibrated. In the conventional method, the refractive error associated with non-precalibrated pupil and reflex sizes is obtained by interpolating between neighbouring precalibrated points. This introduces error because the relationship between refractive error and pupil and reflex size is not linear. Three hundred and sixty-one children aged between 36 and 65 months were clinically examined and photorefracted. The refractive error obtained using retinoscopy and the eccentric photorefractor agreed well with each other, although the photorefractor tended to under-estimate refractive error. Using the referral criteria developed by Chan, O.Y.C. and Edwards, L.M. (Refraction referral criteria for Hong Kong Chinese Children. Ophthal. Physiol. Opt. 14, 259-256, 1994), the photorefractor had a sensitivity of 74.6% and a specificity of 96.4%. All the under-referred cases were borderline, having just failed the referral criteria. All the cases with hyperopia of > + 2.0 D, astigmatism of > 1.25 D and visual acuity of worse than 6/18 were identified.

Calibration↗
PubMed1996

Obesity in primary care patients in Kelantan, Malaysia: prevalence, and patients' knowledge and attitudes.

This study measured the body mass index (BMI), and assessed attitudes and knowledge about obesity, of 197 male and 217 female patients aged 20-59 years attending the primary care clinic of the university hospital in Kelantan, Malaysia. There was no significant difference between the mean BMI of males (23.7) and females (24.2). In the overweight group (BMI 25-29.9) were 60 men (30%) and 66 women (30%). In the obese group (BMI 30 and above) were 12 men (6%) and 22 women (10%). Both diabetes mellitus and hypertension were associated with significantly higher BMI's. Knowledge about obesity was lacking. Sixty-three (15%) failed to recognize that obesity is bad for health. When asked the causes of obesity, 88 (21%) failed to mention either diet or lack of exercise. "Being happy" was suggested as a cause by 32 (8%). When asked if certain foods would cause obesity if eaten in excess, 45 (11%) said "No" for fatty foods, and 164 (40%) said "No" for sweet foods. Concerning appearance, 30 (15%) men regarded an obese man as normal or even handsome, while 49 (23%) women regarded an obese woman as normal or beautiful. Obesity is common among our adult patients, and is associated with some of their common health problems. However, a substantial minority do not regard obesity as unhealthy, do not relate it to diet or lack of exercise, do not recognize important groups of fattening foods, and do not regard obesity as unattractive.

Adult↗