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Biomedical subjects

D R Williams

Publications and source records attributed to D R Williams.

At least 109 records · Page 6Linked to original sources
PubMed1997

Race and health: basic questions, emerging directions.

PURPOSE: This paper examines the scientific consensus on the conceptualization of race, identifies why health researchers should analyze racial differences in morbidity and mortality and provides guidelines for future health research that includes race. METHODS: Examines scientific dictionaries and reviews the social science, public health and medical literature on the role of race in health. RESULTS: First, this paper reviews the evidence suggesting that race is more of a social category than a biological one. Variation in genotypic characteristics exists, but race does not capture it. Second, since racial categories have historically represented and continue to reflect the creation of social, economic, and political disadvantage that is consequential for well-being, it is important to continue to study racial differences in health. Finally, the paper outlines directions for a more deliberate and thoughtful examination of the role of race in health. CONCLUSIONS: Race is typically used in a mechanical and uncritical manner as a proxy for unmeasured biological, socioeconomic, and/or sociocultural factors. Future research should explore how clearly delineated environmental demands combine with genetic susceptibilities as well as with specified behavioral and physiological responses to increase the risk of illness for groups differentially exposed to psychosocial adversity.

Culture↗
PubMed1997

Pilot-scale extraction of PHB from recombinant E. coli by homogenization and centrifugation.

A new method of poly-beta-hydroxybutyrate (PHB) extraction from recombinant E. coli is proposed, using homogenization and centrifugation coupled with sodium hypochlorite treatment. The size of PHB granules and cell debris in homogenates was characterised as a function of the number of homogenization passes. Simulation was used to develop the PHB and cell debris fractionation system, enabling numerical examination of the effects of repeated homogenization and centrifuge-feedrate variation. The simulation provided a good prediction of experimental performance. Sodium hypochlorite treatment was necessary to optimise PHB fractionation. A PHB recovery of 80% at a purity of 96.5% was obtained with the final optimised process. Protein and DNA contained in the resultant product were negligible. The developed process holds promise for significantly reducing the recovery cost associated with PHB manufacture.

Biotechnology↗
PubMed1997

Measuring social class in US public health research: concepts, methodologies, and guidelines.

Increasing social inequalities in health in the United States and elsewhere, coupled with growing inequalities in income and wealth, have refocused attention on social class as a key determinant of population health. Routine analysis using conceptually coherent and consistent measures of socioeconomic position in US public health research and surveillance, however, remains rare. This review discusses concepts and methodologies concerning, and guidelines for measuring, social class and other aspects of socioeconomic position (e.g. income, poverty, deprivation, wealth, education). These data should be collected at the individual, household, and neighborhood level, to characterize both childhood and adult socioeconomic position; fluctuations in economic resources during these time periods also merit consideration. Guidelines for linking census-based socioeconomic measures and health data are presented, as are recommendations for analyses involving social class, race/ethnicity, and gender. Suggestions for research on socioeconomic measures are provided, to aid monitoring steps toward social equity in health.

Adult↗
PubMed1997

Aberrations and retinal image quality of the normal human eye.

We have constructed a wave-front sensor to measure the irregular as well as the classical aberrations of the eye, providing a more complete description of the eye's aberrations than has previously been possible. We show that the wave-front sensor provides repeatable and accurate measurements of the eye's wave aberration. The modulation transfer function of the eye computed from the wave-front sensor is in fair, though not complete, agreement with that obtained under similar conditions on the same observers by use of the double-pass and the interferometric techniques. Irregular aberrations, i.e., those beyond defocus, astigmatism, coma, and spherical aberration, do not have a large effect on retinal image quality in normal eyes when the pupil is small (3 mm). However, they play a substantial role when the pupil is large (7.3-mm), reducing visual performance and the resolution of images of the living retina. Although the pattern of aberrations varies from subject to subject, aberrations, including irregular ones, are correlated in left and right eyes of the same subject, indicating that they are not random defects.

Humans↗
PubMed1997

Supernormal vision and high-resolution retinal imaging through adaptive optics.

Even when corrected with the best spectacles or contact lenses, normal human eyes still suffer from monochromatic aberrations that blur vision when the pupil is large. We have successfully corrected these aberrations using adaptive optics, providing normal eyes with supernormal optical quality. Contrast sensitivity to fine spatial patterns was increased when observers viewed stimuli through adaptive optics. The eye's aberrations also limit the resolution of images of the retina, a limit that has existed since the invention of the ophthalmoscope. We have constructed a fundus camera equipped with adaptive optics that provides unprecedented resolution, allowing the imaging of microscopic structures the size of single cells in the living human retina.

Contrast Sensitivity↗
PubMed1996

Photopigment transmittance imaging of the primate photoreceptor mosaic.

We introduce a new technique for classifying many photoreceptors simultaneously in fresh, excised primate retina on the basis of their absorptance spectra. Primate retina is removed from the pigment epithelium and illuminated under a microscope from the same direction as in the intact eye. To facilitate the guiding of light into the receptor outer segments, the optical axes of the photoreceptors are oriented parallel to the optical axis of the microscope. Photoreceptor outer-segment tips are imaged on a charge-coupled device array, which provides radiometric measurements of the light passing through each photoreceptor. These images are acquired sequentially at three wavelengths chosen to maximize the absorptance differences among the three cone photopigments. After the photopigment is bleached, a second set of three images is acquired. The ratios of the images before and after bleaching at each wavelength are photopigment transmittance maps of the retina. These are combined into a single trichromatic image showing the distribution of photopigment if the retina could be viewed directly in white light without bleaching. We have found patches of receptors in peripheral macaque retina where the measured absorptance at the wavelength of maximum absorptance is consistent with the predicted axial absorptance of th photopigment. The cones in these patches cluster into two groups corresponding to the middle wavelength-sensitive (n = 53, mean absorptance = 0.28) and the long wavelength-sensitive (n = 63, mean absorptance = 0.30) cones. The mean absorptances of 273 macaque and 183 human rods were 0.51 and 0.41, respectively.

Animals↗
PubMed1996

Patterns of in and out-patient activity for diabetes: a district survey.

The objective was to describe, by means of a retrospective study of three years' routine District information (financial years 1991/92 to 1993/94), the in- and out-patient activity for patients with diabetes, and compare this with the non-diabetic population. The clinical resource usage by patients with diabetes relative to those without was estimated by (a) their relative probability of admission by specialty, (b) attendance rates at out-patient clinics, (c) primary diagnosis, and (d) operations and procedures. The setting was a District Health Authority with a population of 408 000. All in-patient and out-patient records were reclassified as attributable to a patient with or without diabetes by cross-referral to routine records of patients with identified diabetes from separate hospital databases. The main outcome measures were: (a) relative frequency, and crude and age-specific relative probability of admission by specialty, ICD9 primary diagnosis, and OPCS4 primary operation and procedure, and (b) out-patient attendance rates by specialty. Patients with diabetes were responsible for 5.5% of admissions and 6.4% of out-patient attendances. However, because of increased length of stay, patients with diabetes occupy 9.4% of bed days. The relative risk of admission for diabetes related complications was: coronary heart disease 11.8 (95% CI = 11.4-12.3), cerebrovascular disease 11.8 (10.8-12.8), neuropathy and peripheral vascular disease 15.6 (13.6-17.9), eye complications 10.4 (9.3-11.7), and renal disease 14.7 (12.6-17.3). Recognised diabetes related vascular (9.3-11.7), and renal disease 14.7 (12.6-17.3). Recognised diabetes related vascular complications accounted for at least 23% of admissions of patients with diabetes. The relative risk of admission for diagnoses and procedures not known to be related to diabetes were similar for non-diabetic and diabetic patients. The pattern of out-patient activity mirrored that of the relative probability of admission. It is concluded that previous estimates of the proportion of NHS resources used for the treatment of patients with diabetes had been significantly underestimated. Patients with diabetes were found to occupy 1 in 10 non-obstetric, non-psychiatric beds. Many of these admissions were for diagnoses and procedures that are known to be related to diabetes.

Age Factors↗
PubMed1996

Geographical mapping of childhood diabetes in the northern English county of Yorkshire.

This study aimed to highlight geographical differences in childhood Type 1 (insulin dependent) diabetes mellitus (IDDM) by mapping incidence at 3 different geographical scales, within the northern English county of Yorkshire. Mapping techniques are applied to incident cases from a population-based regional register of childhood IDDM. The Yorkshire Children's Diabetes Register (YCDR) comprises 1310 children (0-14 years) diagnosed with IDDM from 1978-1990. Age standardized incidence rates (cases/100000/year) are given for administrative county, standardized incidence ratios (SIRs) are mapped by local government district and electoral ward. Heterogeneity between areas was assessed by a chi 2 test. At county level, incidence is 25% higher in Humberside (16.82 per 100000 per year) compared to West Yorkshire (12.21 per 100000 per year) (p < 0.001). SIRs for the 22 districts display significant heterogeneity (p < 0.001) with deficits in the urban areas of Kirklees (70 95% CI 57-85) and Bradford (81 95% CI 68-95) and significant excesses in the rural districts of Ryedale (147 95% CI 106-198), Beverley (149 95% CI 113-193), Holderness (166 95% CI 112-237) and Boothferry (186 95% CI 134-250). At the smallest scale, variation between wards is significant (p < 0.001) and low incidence in urban areas is notable. Geographical variation in the incidence of childhood IDDM may provide strong clues to its aetiology. Within Yorkshire, geographical distribution shows significant heterogeneity at three different scales. The magnitude of the variation is not explained by ethnic or genetic differences in the population and underlines the important influence of environmental factors in disease aetiology.

Adolescent↗
PubMed1996

Off-axis optical quality and retinal sampling in the human eye.

Using the double pass procedure, Navarro et al. (1993; Journal of the Optical Society of America A, 10, 201-212) measured the monochromatic modulation transfer function (MTF) of the human eye as a function of retinal eccentricity. They chose conditions as similar as possible to those encountered in natural viewing. We report new measurements obtained with conditions chosen instead to optimize retinal image quality: we paralyzed accommodation, used a 3 mm pupil, and corrected defocus and oblique astigmatism at each retinal location. MTFs were estimated at the tangential focus, circle of least confusion, and sagittal focus produced by oblique astigmatism. Though optical blur is well-known to have little effect on peripheral visual acuity, it can nonetheless substantially reduce aliasing by receptoral and post-receptoral spatial sampling.

Adult↗
PubMed1996

Images of cone photoreceptors in the living human eye.

Though the photoreceptor mosaic has been imaged through the intact optics of the eyes of several species, it has not been clear whether individual photoreceptors can be resolved in the living human eye. We have constructed a high-resolution fundus camera and have resolved cones with a spacing as small as 3.5 microns in single images of the fundus. The high contrast of these images implies that almost all the light returning from the retina at this wavelength (555 nm) has passed through the apertures of foveal cones. The average power spectra of our retinal images show that it is possible to recover spatial frequencies as high as 150 c/deg in eyes with normal optical quality, a conclusion that was confirmed with estimates of the optical quality of these eyes obtained with a Hartmann-Shack wavefront sensor. These results emphasize the superiority of the eye's optics over the spatial sampling limits of the retina when the eye's optical quality is optimized. They also show that it would be possible to routinely resolve retinal structures as small as photoreceptors in the normal living eye if its aberrations could be corrected.

Adult↗
PubMed1996

Binocular rivalry with isoluminant stimuli visible only via short-wavelength-sensitive cones.

To test whether the binocular contour rivalry mechanism is tritanopic, we presented isoluminant, rival stimuli visible only via the short-wavelength-sensitive (S) cones. We stimulated only the S cones with violet gratings superimposed on a bright yellow field that adapted the responses of the middle- and long-wavelength-sensitive (M and L) cones. We found that an S-cone grating presented to one eye rivalled with an orthogonal grating presented to the other. Rivalry persisted over a range of luminances and contrasts of the S-cone stimuli, and was greater than could be accounted for by nonrival fading. The spatial spread of rivalry from S-cone stimuli is similar to that for the same stimuli when visible also to the M and L cones (luminance stimuli). We found that an S-cone stimulus would rival with a luminance stimulus, and exploited this to determine the equivalent luminance contrast of S-cone stimuli by putting them in a rivalry competition with luminance stimuli. For rivalry, the equivalent luminance contrast of isoluminant, S-cone stimuli is much less than their S-cone contrast. The existence of rivalry with isoluminant stimuli, along with earlier evidence that such stimuli can support stereopsis, challenges the view that an achromatic channel alone drives certain higher level functions such as depth perception.

Contrast Sensitivity↗
PubMed1996

The spatial grain of motion perception in human peripheral vision.

Motion reversal effects (the apparent reversal of the direction of motion of a high frequency sinusoidal grating) have been attributed to aliasing by the cone mosaic [Coletta et al. (1990). Vision Research, 30, 1631-1648] and postreceptoral layers [Anderson & Hess (1990). Vision Research, 30, 1507-1515] in human observers. We present data and a new model which suggest that at least two sampling arrays of different densities affect direction discrimination out to 30 degrees eccentricity. The first sampling layer matches anatomical estimates of the cone density. The second sampling layer is too dense to be the parasol cells alone; midget ganglion cells certainly contribute to this task. This is further evidence that motion perception is not mediated exclusively by the magnocellular stream.

Discrimination, Psychological↗
PubMed1996

Effects of actual waiting time, perceived waiting time, information delivery, and expressive quality on patient satisfaction in the emergency department.

STUDY OBJECTIVE: To determine the effects of actual waiting time, perception of waiting time, information delivery, and expressive quality on patient satisfaction. METHODS: During a 12-month study period, a questionnaire was administered by telephone to a random sample of patients who had presented to a suburban community hospital emergency department during the preceding 2 to 4 weeks. Respondents were asked several questions concerning waiting times (ie, time from triage until examination by the emergency physician and time from triage until discharge from the ED), information delivery (eg, explanations of procedures and delays), expressive quality (eg, courteousness, friendliness), and overall patient satisfaction. RESULTS: There were 1,631 respondents. The perception that waiting times were less than expected was associated with a positive overall satisfaction rating for the ED encounter (P < .001). Satisfaction with information delivery and with ED staff expressive quality were also positively associated with overall satisfaction during the ED encounter (P < .001). Actual waiting times were not predictive of overall patient satisfaction (P = NS). CONCLUSION: Perceptions regarding waiting time, information delivery, and expressive quality predict overall patient satisfaction, but actual waiting times do not. Providing information, projecting expressive quality, and managing waiting time perceptions and expectations may be a more effective strategy to achieve improved patient satisfaction in the ED than decreasing actual waiting time.

Adolescent↗
PubMed1996

Clinical economics review: gastroenterology.

In the prevailing climate of cost containment, doctors are increasingly expected to consider the economic consequences of treatment choices. Clinical (or medical) economics attempts to apply economic principles to the description and analysis of the costs of medical interventions, so as to identify how best to spend scarce health care resources. Such economic evaluations may assess the overall financial burden of a disease to society as a whole (macro-economics), or attempt to compare alternative treatment strategies for a specific clinical situation (micro-economics). In addition to expenditure on drugs and investigations (direct medical costs), economic studies may consider a variety of other costs. These include direct costs borne by patients (e.g. prescription charges, travel, food), indirect costs to society owing to lost productivity (resulting from morbidity or premature mortality) and even intangible costs which assign a monetary value to outcomes of disease such as pain, distress and anxiety. Four main types of economic analysis are in current use. Cost-minimization analysis attempts to identify the least expensive option in situations where there are a range of equally effective treatments for a given clinical condition, whereas cost-effectiveness analysis allows management strategies differing both in cost and efficacy to be compared. The cost-effectiveness of health care programmes targeting different disease states may also be compared using cost-utility analysis, in which health benefits are translated into a common utility-based unit of outcome, such as the Quality Adjusted Life Year (QALY). Cost-benefit analysis attempts to quantify health outcomes in monetary terms, so that the net result provides an assessment of value-for-money of health interventions. Gastrointestinal disorders are amongst the commonest of complaints, and considerable health care resources are consumed in treatment. Issues of cost-effectiveness are likely to assume increasing importance in gastroenterology because of the ever expanding range of drug choice, the increasing number of high cost treatments and the development of new therapeutic interventions.

Cost of Illness↗
PubMed1996

A comparison of epidural infusions of fentanyl or pethidine with bupivacaine in the management of postoperative pain.

A double-blind randomised clinical trial was undertaken in 40 patients undergoing major abdominal surgery. Postoperative pain relief was provided using epidural infusions of 0.06% bupivacaine with fentanyl 4 micrograms.ml-1 (n = 20) (group F) or with pethidine 1.5 mg.ml-1 (n = 20) (group P). Postoperative pain scores using a visual analogue scale (0-100 mm) were not significantly different between the two groups. Median pain scores were 0-19 mm at all times of assessment indicating that good analgesia was provided by both regimens. There was no significant difference between the epidural infusion rates in the two groups. The side effects and effect on pulmonary function were similar in each group. Nine patients were withdrawn from the study (four from group F, five from group P) due to failure of the epidural technique or other complications. Fourteen patients, equally distributed, required a total of 24 epidural 'top-ups' by an anaesthetist because of inadequate analgesia. We demonstrated no advantage with epidural pethidine over fentanyl when used by infusion in combination with bupivacaine in the management of postoperative pain.

Abdomen↗
PubMed1996

Race/ethnicity and socioeconomic status: measurement and methodological issues.

This article considers the ways in which race/ethnicity and socioeconomic status (SES) relate to each other and combine to affect racial variations in health status. The author reviews a number of methodological issues concerning the assessment of race in the United States that importantly affect the quality of the available data on racial differences in health. These issues include the discrepancy between self-identification and observer-reported race, changing racial classification categories and racial identification, the difficulties in categorizing persons of mixed racial parentage, and census undercount. In discussing the complex interactions between race and SES, the author first describes the relationship between race and SES and assesses the role of SES in accounting for racial differences in health, then shows how the failure of SES to completely account for racial variations in health status emphasizes the need for health researchers to give more systematic attention to the unique factors linked to race that affect health. These factors include racism, migration, acculturation, and the comprehensive assessment of SES.

Bias↗