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Biomedical subjects

D Whitaker

Publications and source records attributed to D Whitaker.

At least 55 records · Page 3Linked to original sources
PubMed1996

Comparison of measures of exposure to asbestos in former crocidolite workers from Wittenoom Gorge, W. Australia.

Determinations of exposure-response relationships between crocidolite and the major asbestos-related diseases in the Wittenoom cohort have previously depended on the validity of estimates of airborne exposure to asbestos. This work aims to validate the airborne exposure measurements by obtaining measurements of the concentrations of uncoated crocidolite fibers and asbestos bodies retained in the lungs of individual workers, and to estimate the half-life of crocidolite fibers in the lungs. Samples of lung tissue, excluding tumor, of all former Wittenoom workers known to have died in Western Australia (WA) were sought from teaching hospitals, pathology departments, and the Coroner's pathologist. The lung specimens were processed using Pooley's method with TEM for counts of fibers of all types and using Smith and Naylor's method with conventional light microscopy for asbestos bodies (AB). Multiple linear regression was utilized to examine the associations between crocidolite concentrations in the lung and duration of employment at Wittenoom, time since last employed at Wittenoom, nature of job, estimated average fiber concentration at the worksite, and estimated cumulative crocidolite exposure (CCE) in fiber-years/ml for each subject. Lung tissue from 90 cases was processed and there was good agreement between counts of crocidolite fibers, asbestos bodies, and CCE. Correlations were 0.77 for AB and fibers, 0.54 for AB and CCE, and 0.58 for CCE and fibers, after log transformation. The half-life of crocidolite fibers in the lung was estimated at 92 months (95% CI 55-277 months). Previous estimates of airborne exposure to Wittenoom crocidolite have been reasonably reliable. The relatively simple technique of light microscopy for counting ABs in lung tissue also provides a useful and reliable indication of the level of past occupational exposure to crocidolite in subjects whose exposure has been only to crocidolite. The half-life of crocidolite fibers in the lungs of former Wittenoom workers is about 7-8 years.

Adult↗
PubMed1996

A comparison of word recognition and reading performance in foveal and peripheral vision.

Word recognition thresholds and rapid serial visual presentation (RSVP) reading rates for both unrelated words and meaningful sentences were examined across the visual field. Both word recognition thresholds and RSVP reading rates for unrelated words can be equated across the visual field by an increase in size scale. RSVP reading rates for meaningful sentences cannot be equated across the visual field, with the fovea demonstrating a qualitative superiority over the periphery, irrespective of scale. The results suggest that the early visual machinery which underlies word recognition is the same across the visual field apart from a change in scale, whilst the periphery is qualitatively inferior to the fovea at interpreting sentences with meaning.

Adult↗
PubMed1996

Centroid analysis predicts visual localization of first- and second-order stimuli.

Perceived alignment of asymmetric Gaussian-windowed stimuli was measured in an attempt to differentiate between stimulus characteristics which might underlie visual localization. These asymmetric stimuli have the advantage of being continuous in the spatial domain and of possessing well-defined spatial characteristics in which centroid, points of inflexion and peak can be separated from each other. Results for both luminance- and contrast-defined stimuli are reasonably well described on the basis that the centroid of the stimulus envelope represents the primitive which determines perceived visual location. Centroid location is inherent in the output of filters which are large enough to cover the object of interest.

Contrast Sensitivity↗
PubMed1996

Trial of labor in patients with a previous lower uterine vertical cesarean section.

OBJECTIVE: Our purpose was to determine the efficacy and safety of a trial of labor in patients previously delivered at least once by a lower uterine vertical cesarean section. STUDY DESIGN: A retrospective review was performed at a single tertiary perinatal center, The University of Florida Health Science Center, Jacksonville. The medical records of all patients with a previous low vertical cesarean section who underwent a trial of labor during a 72-month period from January 1988 until December 1993 were reviewed. The medical records of the next two patients who did not have a prior uterine incision admitted to labor and delivery after the index case served as the controls. The duration and outcome of labor, including mode of delivery, maternal and perinatal morbidity, and birth trauma were evaluated. RESULTS: Of 77 patients with a previous low vertical cesarean incision, 11 (14.3%) had a repeat operation compared with 14 of 154 patients (9.0%) in the no previous cesarean section group (not significant). No differences were noted in the incidences of operative vaginal deliveries or prolonged duration of the first or second stages of labor, or in the rate or maximum dose of oxytocin infusion between the two groups. One patient in the previous cesarean section group had uterine rupture. The incidence of umbilical artery pH < or = 7.20 was similar. No difference in the number of infants with 1- or 5-minute Apgar scores < or = 7 was noted. CONCLUSION: A trial of labor in women with previous low vertical cesarean sections results in an acceptable rate of vaginal delivery and appears safe for both mother and fetus.

Adult↗
PubMed1996

Effect of a cataract simulation on clinical and real world vision.

AIMS/BACKGROUND: Many reports have indicated that some patients with cataract can retain good visual acuity but complain of significant visual problems. This is the first in a series of papers trying to determine what causes these symptoms and whether other clinical tests can predict the real world vision loss. METHODS: The effect of a cataract simulation with a similar angular distribution of light scatter as real cataract on clinical (visual acuity, contrast sensitivity, and disability glare) and real world vision (face recognition, reading speed, and mobility orientation) was investigated. RESULTS: The simulation had a relatively small effect on visual acuity (6/6 with the simulation), but much larger effects on contrast sensitivity and low contrast acuity with and without glare. The simulation had no effect on high luminance and high contrast real world tasks, such as mobility orientation in room light and optimal reading speed. A small, but significant deterioration was found for the slightly lower contrast task of face and expression recognition. However, under low luminance conditions, substantial defects in mobility orientation were obtained (despite 6/6 acuity). CONCLUSIONS: Although the relative effect of the cataract simulation on acuity and contrast tasks is not typical of the average cataract, it can be found in those cataract patients with visual problems despite good visual acuity. This corroborates the suggestion that it is large amounts of wide angle light scatter (forward and/or backward) which are at least partly responsible for visual disability in cataract patients with good visual acuity. A patient's reported visual disability may depend on the percentage of time he or she spends under low contrast and/or low luminance conditions, such as walking or reading in dim illumination, and walking or driving at night, in fog, or heavy rain.

Adult↗
PubMed1996

Mesothelioma in a community in the north of England.

OBJECTIVES: To find the numbers of mesotheliomas in Calderdale over the period 1966-94 and determine their relation to asbestos exposure, pathology, and mineral fibre burden within the lungs of affected subjects. METHODS: Cases were entered into the study if the subject has been diagnosed with mesothelioma after postmortem and histopathological examinations. Occupational data were obtained mainly from the case records of the Cape Asbestos medical officer, hospital, and medical practitioner and from death certificates. Analyses of the mineral fibres were performed with transmission electron microscopy and energy dispersive x ray spectrometry. RESULTS: 73 mesotheliomas were diagnosed from 1966 to 1994. Forty four were associated with exposure at the Acre Mill factory, which manufactured asbestos products. Concentrations of amphibole asbestos fibres were found to be raised above controls in 31 out of 32 cases associated with Acre Mill exposure, in 10 out of 12 other cases exposed to asbestos and eight out of 17 cases not exposed to asbestos. CONCLUSIONS: There was a high number of mesotheliomas in Calderdale. More than half of the cases were associated with occupation at the Acre Mill factory and were associated with exposure to amphibole asbestos, predominantly crocidolite. No cases associated with neighbourhood exposure to asbestos were identified.

Adult↗
PubMed1996

Relative roles of resolution and spatial interference in foveal and peripheral vision.

The rate of change of visual performance with increasing eccentricity of fixation is known to be task dependent. In order to examine eccentricity-related changes in visual performance when a combination of two different factors influence thresholds, visual acuity in the presence of flanking elements was investigated across the visual field. Interference zones increased in extent with eccentricity at a much faster rate than did resolution thresholds. E2 values, quantifying the eccentricity-related magnification required, were 1-2 degrees for resolution and 0.1-0.2 degrees for spatial interference. E2 values for resolution in the presence of flanks depended on the proximity of the flanks and their 'weighting' in the task. From the results, the magnitude and extent of spatial interference across the visual field can be described quantitatively. Further, the results serve as an example of how observed variations in peripheral threshold gradients might be achieved as a combination of underlying factors with different E2 values.

Data Interpretation, Statistical↗
PubMed1995

Asbestos bodies in lung tissue following exposure to crocidolite.

A series of 206 necropsies in Western Australia (WA) have had routine counts made of asbestos bodies in samples of lung tissue using conventional light microscopy. Thirty-two cases had worked in the asbestos industry at Wittenoom, WA and (log) counts of asbestos bodies in their lung tissue correlated well with estimates of their (log) cumulative airborne exposure to crocidolite fibers (r = 0.60). There was no association between the number of asbestos bodies and time since exposure to asbestos ceased. In subjects without known exposure to asbestos, there was a weak but nonsignificant increase in number of asbestos bodies with increasing age, with 26% of cases having no asbestos bodies present. It is concluded that the relatively simple technique of light microscopy for counting of asbestos bodies in lung tissue provides a reliable indication of the level of past occupational exposure to crocidolite in subjects whose exposure has been only to crocidolite. This could be extremely useful in follow-up studies of cohorts that lack reliable measures of airborne exposure to crocidolite asbestos.

Adult↗
PubMed1995

Visual acuity changes throughout adulthood in normal, healthy eyes: seeing beyond 6/6.

There are many useful longitudinal and cross-sectional epidemiological studies of how visual acuity (VA) deteriorates with age. However, few studies have evaluated age-related VA changes in normal, healthy eyes. Data from three previous studies that included VA measurements taken with logMAR charts from subjects with normal, healthy eyes were collated and additional data from 42 subjects were added. This provided VA results from 223 subjects (age range 18 to 80 years). Mean logMAR VA improved from -0.13 (Snellen equivalent 6/4.5) in 18- to 24-year-olds to -0.16 (Snellen 6/4(-1)) in 25- to 29-year-olds and then gradually became worse with age to a mean value of -0.02 (Snellen 6/6+1) for subjects over 75 years of age. The inadequacy of 6/6 as a norm value of VA is illustrated. The data show VA levels far superior to the data from the standard references of Pitts (1982) and Weale. (1975, 82) We suggest that this is because we used logMAR charts (providing nontruncated data), the subject's optimal refractive correction (rather than habitual) and strict exclusion criteria ensuring that only subjects with normal, healthy eyes were recruited for the studies.

Adolescent↗
PubMed1995

Assessment of retinal-neural function before neodymium:YAG laser capsulotomy.

PURPOSE: The aim of this study was to evaluate a clinical test of hyperacuity in the assessment of retinal-neural function in patients with posterior capsular opacification. METHODS: Neodymium (Nd):YAG laser capsulotomy was performed on 39 subjects (mean age, 76.72 years +/- 10.41 years). Measurements of refractive error, logMAR acuity, and displacement threshold hyperacuity (DTH) were made before and 3 weeks after Nd:YAG therapy. The DTH task involved measurement of the smallest detectable displacement of an object relative to two stationary references. In addition, an independent fundus examination was performed before and after therapy to determine the presence of retinal disease. By ophthalmoscopic examination, a blind protocol was adopted for the classification of subjects as normal or as having retinal disease. RESULTS: Preoperative measures of logMAR visual acuity were of no value in distinguishing between patients with retinal disease and normals (P > 0.1) and were a poor indicator of postoperative logMAR acuity (r2 = 0.2). Preoperative DTH could be used to distinguish patients with retinal disease from normals (P < 0.005) and were found to be correlated with measures of postoperative logMAR acuity (r2 = 0.4). Preoperative DTH correlated well with postoperative DTH (r2 = 0.7), which is consistent with its resistance to optical image degradation. CONCLUSION: The results of this study indicate that DTH is of value in the presurgical assessment of visual function in patients with media opacification if adequate fundus examination is not possible.

Aged↗
PubMed1995

The statistical interpretation of blue-on-yellow visual field loss.

PURPOSE: To evaluate short-wavelength-sensitive perimetry in the detection of glaucomatous field loss. METHODS: The sample consisted of 27 normal subjects, 24 patients with primary open angle glaucoma (POAG), and 27 patients with ocular hypertension (OHT). Blue-on-yellow (B-Y) and standard (W-W) perimetry was undertaken with a modified Humphrey Field Analyzer 640 on one eye of each subject and patient. The B-Y data were corrected for individual ocular media absorption. Results were compared to an age-matched normal database of 50 subjects (age range, 60 to 82 years; mean age, 70.0 years; SD, 6.4 years). Visual field indices and total and pattern deviation probability maps were calculated for both W-W and B-Y fields. RESULTS: The B-Y normal database exhibited increased between-subject variability compared to the W-W normal database (P < 0.001). The greater variability increased with the increase in eccentricity (P < 0.001) and with the increase in age (P = 0.032). All patients with POAG exhibited B-Y field loss; 11 demonstrated greater B-Y loss than the corresponding W-W field. In advanced POAG, the B-Y and the W-W fields were similar. Twenty-five of the 27 normal subjects exhibited normal B-Y fields. Five of the 27 patients with OHT manifested B-Y focal abnormality and a normal W-W field: in two, W-W focal loss subsequently developed. CONCLUSIONS: Short-wavelength-sensitive perimetry can identify visual field loss before that detected by W-W perimetry. However, the increased between-subject variability necessitates stringent statistical analysis in the definition of abnormality.

Aged↗
PubMed1994

Monoclonal antibody Ber-EP4: its use in the differential diagnosis of malignant mesothelioma and carcinoma in cell blocks of malignant effusions and FNA specimens.

Formol sublimate-fixed cell blocks derived from 129 malignant pleural (and some peritoneal) effusions, 8 benign effusions with reactive mesothelial cells, and 23 FNA specimens, were immunostained with monoclonal antibody Ber-EP4 to assess its ability to distinguish malignant mesothelioma (MM) from carcinoma. Only 2 of 44 (4%) well-characterized MM were Ber-EP4+, while none of 8 benign mesothelial proliferations reacted with the antibody. Fifty-seven percent of 23 pulmonary adenocarcinomas (AC) and 60% of 43 pulmonary carcinomas of all other histological types were Ber-EP4+. Of 40 metastatic AC originating from breast, gastrointestinal tract, ovary, endometrium, and kidney, 80% were Ber-EP4+. The predictive value of positive Ber-EP4 staining in distinguishing AC from MM was 96%. The predictive value of a negative Ber-EP4 in excluding MM was 70%, when the differential diagnosis was adenocarcinoma. These results suggest that Ber-EP4 is helpful in differentiating MM and AC if used together with other discriminating antibodies.

Antibodies, Monoclonal↗
PubMed1994

Effects of luminance and external temporal noise on flicker sensitivity as a function of stimulus size at various eccentricities.

We studied how the dependence of flicker sensitivity on stimulus size was affected by the eccentricity of the stimulus at high luminance, at low luminance (with quantal noise), and at high luminance with the addition of pure white temporal noise. Flicker sensitivity was measured as a function of stimulus size for temporal frequencies of 1-30 Hz with uniform sinusoidally flickering spots. Sensitivity first increased with increasing stimulus size but then the increase saturated. At high luminance the saturation took place at larger stimulus sizes with increasing eccentricity. Without externally added temporal noise the maximum sensitivity was higher at the fovea than in the periphery at temporal frequencies of 1-10 Hz, but at 30 Hz this situation reversed. Therefore only the ascending parts of the spatial integration curves from various eccentricities could be superimposed by size scaling. E2, the eccentricity at which the spatial scale doubles, was found to be 2.2-2.7 deg for 1-10 Hz but 4.4 deg for 30 Hz. When enough temporal noise was added, performance at all stimulus sizes studied could be made independent of eccentricity by spatial scaling, since noise reduced maximum sensitivities to a constant level at all eccentricities. E2 was found to be 4.1 deg for 3 Hz and 7.2 deg for 30 Hz. When light level was reduced by 3 log10 units, foveal and peripheral flicker sensitivity functions almost superimposed at all stimulus sizes studied. Hence, at 1 and 3 Hz E2 was very large, about 70 and 22 deg, respectively. At 10 and 30 Hz no size scaling was needed and E2 was therefore infinite.

Adult↗
PubMed1994

Age-related effects of glare on luminance and color contrast sensitivity.

PURPOSE: To determine the effect of disability glare (DG) upon luminance and color contrast sensitivity for young and elderly subjects. METHODS: DG was defined as the difference in contrast sensitivity with and without the presence of a glare source. Isoluminant color gratings were modulated either along a red-green (R-G) or blue-yellow (B-Y) axis. RESULTS: Without glare the effect of age on sensitivity to both luminance and R-G color-modulated gratings was small and did not reach statistical significance (P > 0.1). However, the reduction in sensitivity for B-Y color modulation was highly significant (P < 0.01). For both age groups, DG was greatest for the R-G stimulus and least for the B-Y. DG in the elderly increased relative to the young observers for both R-G and luminance-modulated gratings (P < 0.01) but not for B-Y (P > 0.01). CONCLUSIONS: The precise effect of a glare source on color discrimination depends upon a complex interaction between the chromaticity of the glare source and that of the stimulus. In certain circumstances, such as in our R-G stimulus, glare can dramatically reduce chromatic discrimination ability by desaturating the component colors.

Adult↗
PubMed1994

Role of mast cells in early epithelial target cell injury in experimental acute graft-versus-host disease.

The skin is a major target organ for graft-versus-host disease (GVHD), the principal complication of allogeneic bone marrow transplantation. The purpose of the present study was to test whether mast cell degranulation might be related to early target cell injury in the development of acute GVHD. We employed two irradiated murine strain combinations, one in which disease was mediated by CD4+ effector T cells (B10.D2-->DBA/2), and the other by CD8+ effector T cells (B10.BR-->CBA). As compared to controls, both models exhibited mast cell degranulation of differing extents and patterns, as well as dyskeratosis in the epidermis before the influx of effector lymphocytes. These results suggested that factors produced and released by degranulated dermal mast cells might contribute to early target cell injury. Accordingly, the possible role of tumor necrosis factor (TNF)-alpha, a cytokine recently discovered in mast cell granules, was investigated by the injection of anti-TNF-alpha antibody during the course of disease mediated by either CD4+ or CD8+ T cells. Although overall survival of recipients undergoing CD4+ T-cell-mediated GVHD was only slightly improved and the extent of mast cell degranulation was not affected by anti-TNF-alpha antibody treatment, the skin exhibited a significant diminution in the number of dyskeratotic cells/linear mm at 3-4 weeks post-transplantation. In contrast, anti-TNF-alpha antibody failed to enhance survival or reduce the number of dyskeratotic cells in the skin during CD8+ T-cell-mediated disease. Finally, to determine whether CD8+ T-cell-mediated GVHD was at all dependent upon mast cell involvement, the C3H.SW-->B6WWv strain combination was utilized, in which recipients were genetically deficient in mast cells. Onset of GVHD was significantly delayed in B6WWv mice and was clearly correlated to the appearance and increase of de novo mast cells at later time points.

Animals↗
PubMed1994

Spatial summation of the differential light threshold as a function of visual field location and age.

Static differential light thresholds were measured as a function of stimulus size (Goldmann sizes I-V) along four visual field meridia (75, 165, 255 and 345 degrees) with the Humphrey Field Analyzer 640. Data were obtained for both young (n = 10, age 23.6 +/- 2.9 years) and elderly (n = 10, age 72.0 +/- 5.2 years) normal subjects. The resulting peripheral spatial summation curves could be equated to the foveal data simply by a change in size scale, which increased linearly with eccentricity. E2 values, expressing the eccentricity at which stimulus size must double for performance to remain comparable to the fovea, were in the order of 3-9 degrees. Whilst the rate of scale change is approximately the same for both young and elderly observers, differences in performance can be explained by a combination of lower sensitivity and a bias in sensitivity towards larger stimulus sizes with increasing age.

Adult↗