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Biomedical subjects

G Lewis

Publications and source records attributed to G Lewis.

At least 127 records · Page 7Linked to original sources
PubMed1998

Premorbid adjustment and personality in people with schizophrenia.

BACKGROUND: Schizoid personality and poor social adjustment have been thought of as common antecedents of schizophrenia but the existing literature is inconclusive. We have carried out a large cohort study with improved methodology. METHOD: The premorbid personality and adjustment of 50,054 Swedish men were assessed on entry into the army at the age of 18. Individuals who developed schizophrenia or another psychosis after 15-year follow-up were identified. Odds ratios for variables independently associated with the later development of schizophrenia were calculated, adjusting for potential confounders. RESULTS: Four variables reflecting early problems with interpersonal relationships were strongly associated with later schizophrenia and, to a lesser extent, non-schizophrenic psychoses, but also occurred commonly in the cohort as a whole. These associations with schizophrenia persisted after early-onset cases were excluded, though their predictive value was low (3.0%, 95% CI 1.5-4.5). CONCLUSIONS: Some aspects of premorbid personality and adjustment may act as risk factors for schizophrenia. The results appear to be most consistent with a multi-factorial aetiology for schizophrenia and offer tentative support for a psychological disturbance mediating genetic and environmental effects on the causal pathway to the illness.

Adolescent↗
PubMed1998

Social roles and gender difference in the prevalence of common mental disorders.

BACKGROUND: It is not known why the most common mental disorders, anxiety and depression, are more prevalent among women then men. The aim was to test the hypothesis that this gender difference could be explained by differences between men and women in social role occupancy, after adjusting for age and socio-economic status. METHOD: A cross-sectional survey of 8979 adults aged 16-74 years living in private households in England, Wales and Scotland was carried out. Prevalence of common mental disorders was assessed using the General Health Questionnaire. RESULTS: The gender difference in the prevalence of the common mental disorders (unlike social role occupancy) did not vary with age to a statistically significant degree (unadjusted odds ratio 1.35, 95% CI 1.23-1.48) (P < 0.0001). Although those of either gender occupying the fewest, and women occupying the most social roles (after adjusting for age) had the highest prevalence of common mental disorders, neither number of social roles, occupancy of traditional 'female' caring and domestic roles, nor socio-economic status explained the gender difference in these conditions (adjusted OR 1.26, 95% CI 1.14-1.41) (P < 0.001). CONCLUSIONS: The gender difference in the prevalence of the common mental disorders is not explained by differences between men and women in the number or type of social roles occupied.

Adolescent↗
PubMed1998

Contact stress at articular surfaces in total joint replacements. Part II: Analytical and numerical methods.

In this second part of the series of reviews, attention focuses on analytical and numerical methods that have been used to estimate the magnitude of the contact stress in: models of articular joints; models of total joint replacements, without and with the associated joint; or models of simple physical systems that are deemed to have relevance to conditions at articular surfaces in arthroplasties. Three main recommendations emerge from this review. First, analytical methods should be avoided. Second, for numerical studies, the nonlinear contact finite element method should be used. Third, more work is needed in many areas, an example of which is the effect of the method of sterilization of tibial inserts on the estimated contact stress at the tibiofemoral interface in knee implants.

Alloys↗
PubMed1998

A methodology for examining the plausibility of accelerated aging protocols for UHMWPE components.

In light of the time-intensive nature of using real-time shelf-aged specimens in research into property changes of ultra-high-molecular-weight polyethylene (UHMWPE), accelerated thermal diffusion oxidative aging (usually referred to as accelerated aging) is frequently resorted to. A number of such aging protocols have been reported in the literature, with various claims for their producing changes in the properties of the polymer being the same as or similar to those seen in real-time shelf-aged samples. The thrust of the present work is the presentation of a methodology for examining such claims. The methodology is applied to six properties (% crystallinity, melting temperature, oxidation index, ultimate tensile strength, ultimate tensile elongation, and tensile toughness) of 4150HP UHMWPE grade, sterilized using six different methods, prior to and following the use of a specific accelerated aging protocol (oxygen gas at 70 degrees C and 507 kPa pressure; 14 d.). These six properties have been identified in the literature as being strongly correlated with the clinical wear of UHMWPE articular components. It is shown that the claim for the protocol used in the present work (in terms of the simulated equivalent shelf aging time) is plausible. It needs to be emphasized, however, that this conclusion is tentative given the paucity of the relevant literature results that are currently available and which are vital to the application of the methodology.

Biocompatible Materials↗
PubMed1998

Effect of material property representation on stresses in endoprostheses.

The present study sought to examine if, and to what extent, the representation of the elastic properties of material(s) in a model of an endoprosthesis per se or a construct that includes an endoprosthesis affects the stresses in the model, when the finite element analysis method is used to obtain these stresses. For this purpose, two models were examined. One was of an elastomeric metacarpophalangeal joint implant, with the material being assumed to have isotropic elastic properties in one case while it was represented as hyperelastic in the other. The model used in the second study case was that of a construct comprising the tibial component of a total knee replacement, the associated tibial insert, the resected bones, and the acrylic bone cement layer. In one analysis of this model, all the materials were taken to have isotropic elastic properties, while in the other analysis, the cortical bone was represented as transversely isotropic, with all other materials being considered to have isotropic elastic properties. The result show that, in both study cases considered, there is a strong effect of the representation of the elastic properties of material(s) on the stresses in the models.

Elasticity↗
PubMed1998

Contact stress at articular surfaces in total joint replacements. Part I: experimental methods.

It is now widely accepted that both the design and the operating conditions at articular surfaces in total joint replacements influence the magnitude of the contact stress at those surfaces. In turn, such stress plays a pivotal role in the clinical performance of the prosthesis. Hence, a plethora of methods have been used by many workers not only to determine or estimate this stress but also to identify the main influencing factors. This literature is critically reviewed in the present study, which is in two parts. In this first part, the focus is on experimental methods. Two main recommendations emerge from this review. First, the pressure-sensitive film should be used. Second, more work is needed in many areas, an example of which is the effect of the method of sterilization of tibial inserts on the contact stress at the tibiofemoral interface in knee implants.

Arthroplasty, Replacement↗
PubMed1997

Crystallization and preliminary X-ray studies on Candida cylindracea lipase.

As part of the programme to understand the mechanism and specificity of lipase enzymes used in biotransformation reactions, the lipase from Candida cylindracea has been purified and crystallized. This lipase has been widely used by organic chemists for hydrolysis and esterification reactions. Crystals were obtained using polyethylene glycol 6000 as a precipitant and grew to 0.6 mm in the maximum dimension. The enzyme crystallized in the space group P2(1) with unit-cell dimensions a = 94.3, b = 117.0, and c = 114.2 A with beta = 109.2 degrees. Calculations indicate that there are four molecules in the asymmetric unit. The crystals diffract to at least 2.5 A resolution and the structure has been solved by molecular replacement using the lipase from Geotrichum candidum as a search model.

Journal Article↗
PubMed1997

Developmental precursors of affective illness in a general population birth cohort.

BACKGROUND: Recent evidence suggests that neurodevelopmental impairment may be a risk factor for later affective disorder. METHODS: Associations between childhood developmental characteristics and affective disorder were examined in a prospectively studied national British birth cohort of 5362 individuals born between March 3 and March 9, 1946. Mental state examinations by trained interviewers performed at ages 36 and 43 years identified 270 case subjects with adult affective disorder (AD). Teachers' questionnaires completed at age 13 and 15 years identified 195 case subjects who had shown evidence of childhood affective disturbance (CAD). RESULTS: Female gender and low educational test scores at ages 8, 11, and 15 years were a risk factor for AD, CAD, and AD without CAD. In addition, attainment of motor milestones was later in the CAD group (odds ratio [OR] = 1.2; 95% confidence interval [CI], 1.1-1.3), followed by, and independent of, greater risk for speech defects between the ages of 6 and 15 years (OR = 2.0; 95% CI, 1.3-3.0), decreased psychomotor alertness on medical examination between ages 4 and 11 years (OR = 4.6; 95% CI, 2.2-9.7), and an excess of twitching and grimacing motor behaviors in adolescence (OR = 3.9; 95% CI, 2.5-6.1). Persistent CAD was strongly associated with persistent AD (OR = 7.8; 95% CI, 2.6-23.2). CONCLUSION: The findings give credence to the suggestion that affective disorder, especially its early-onset form, is preceded by impaired neurodevelopment.

Adolescent↗
PubMed1997

Polyethylene wear in total hip and knee arthroplasties.

The role that ultrahigh molecular weight polyethylene (UHMWPE) wear at bearing surfaces in total hip and knee arthroplasties plays in the clinical life of these implants cannot be overemphasized. This subject has therefore been attracting enormous research attention on both fundamental and technological levels. Given this, it is important to detail the main features of the knowledge base and describe research directions that may culminate in the production of new and/or improved varieties of UHMWPE material and components. These aspects are the subject of the present review.

Biocompatible Materials↗
PubMed1997

Properties of acrylic bone cement: state of the art review.

Acrylic bone cement occupies a distinctive place in the hierarchy of synthetic biomaterials, because it is the only material currently used for anchoring the prosthesis to the contiguous bone in a cemented arthroplasty. However, the cement is not without its drawbacks. The main one is the role that it has been postulated to play in the aseptic loosening and, hence, clinical life of the arthroplasty. In turn, this role is directly related to the mechanical properties of the cement, especially the resistance to fracture of the cement in the mantle at the cement-prosthesis interface or the cement-bone interface. The present work is a detailed critical review of the recent literature on the properties of bone cement that are considered germane to its use in the stated application. The relevant properties are identified and a case is made for including each of them. Compilations of the values of these properties, obtained under clearly identified conditions, are presented for the six commercial formulations of bone cement in current popular orthopedic use. The gaps and unresolved questions in the current data base, efforts that should be made to address these issues, and research directions are covered.

Acrylates↗
PubMed1997

Effect of mixing method on selected properties of acrylic bone cement.

The present study was an investigation of the effect of the method of mixing the constituents of CMW3 bone cement on selected physical and mechanical properties of the fully polymerized cement. Five such methods were used: hand mixing; "active" vacuum mixing; mixing in a machine that allowed simultaneous mechanical mixing and centrifugation; mixing using this machine followed by application of a "passive" vacuum; and application of a passive vacuum followed by mixing in the machine. It was found that the best overall results were obtained from cement that had been mixed using the second and fifth methods and the values of the properties were: density, 1220 to 1246 kg/m3; areal porosity, 0.02 to 7.04%; ultimate compressive strength, 84 to 112 MPa; ultimate compressive strain, 5.1 to 6.4%; and compressive modulus of elasticity, 2249 to 2877 MPa.

Acrylates↗
PubMed1997

Crystallization of 5-aminolaevulinic acid dehydratase from Escherichia coli and Saccharomyces cerevisiae and preliminary X-ray characterization of the crystals.

5-Aminolaevulinic acid dehydratase (ALAD) catalyzes the formation of porphobilinogen from two molecules of 5-aminolaevulinic acid. Both Escherichia coli and Saccharomyces cerevisiae ALADs are homo-octameric enzymes which depend on Zn2+ for catalytic activity and are potently inhibited by lead ions. The E. coli enzyme crystallized in space group I422 (unit cell dimensions a = b = 130.7 A, c = 142.4 A). The best crystals were obtained in the presence of the covalently bound inhibitor laevulinic acid. The yeast enzyme (expressed in E. coli) crystallized in the same space group (I422) but with a smaller unit cell volume (a = b = 103.7 A, c = 167.7 A). High resolution synchrotron data sets were obtained from both E. coli and yeast ALAD crystals by cryocooling to 100 K.

Crystallography, X-Ray↗
PubMed1997

Do socio-economic risk factors predict the incidence and maintenance of psychiatric disorder in primary care?

In a prospective cohort study of consecutive primary care attenders in south London, the estimated prevalence of non-psychotic psychiatric disorder was 45.6%, using the Revised Clinical Interview Schedule (CIS-R). The estimated 12-month incidence rate was 15.7%. Extremely high stability was found in CIS-R scores over 12 months (r = 0.65) and 68.8% of cases at baseline were also cases 12 months later. A clear difference emerged in the types of risk factor which were associated with the incidence and maintenance of disorder in the study population: while socio-economic variables, especially low household income and not having a partner were associated with a worse outcome among prevalent cases at baseline, such variables were only weakly associated with the incidence of psychiatric disorder after adjusting for potential confounders. The latter, notably family psychiatric history and the severity of psychiatric symptoms at baseline were independently associated with the incidence of psychiatric disorder after adjusting for other risk factors, including measures of previous psychiatric disorder.

Adolescent↗
PubMed1997

The National Psychiatric Morbidity surveys of Great Britain--initial findings from the household survey.

BACKGROUND: This paper describes the Household Survey from the National Survey of Psychiatric Morbidity. This covered a sample drawn at random from the population of Britain, with the exception of the Highlands and Islands of Scotland. METHODS: The Postcode Address file was used as the sampling frame. Nearly 13000 adults aged 16-65 were selected for interview, of whom 10108 (79.4%) were successfully interviewed. Eight per cent could not be contacted and 13% refused interview. Psychiatric assessment was carried out by lay interviewers using the CIS-R. Subjects were also screened for psychosis, and screen-positive individuals were examined by psychiatrists using SCAN. RESULTS: Sixteen per cent of subjects scored above the standard cut-off of 12 on the CIS-R. The overall 1-week prevalence of neurotic disorder was 12.3% in males and 19.5% in females. Unmarried and post-marital groups had high rates of disorder, as did single parents and people living on their own. Respondents in Social Class I had notably lower rates of neurotic disorder than the remainder of the sample. Unemployment was strongly associated with disorder. Subjects living in urban areas had a higher overall prevalence, but there was no significant variation by region. Black respondents had higher rates of disorders that were entirely explained by their age, family type and social class. Individual neurotic disorders were all significantly commoner in women, with the exception of panic disorder. The 1-year prevalence of functional psychoses was 4 per 1000, with no sex difference. Alcohol and drug dependence was considerably more prevalent in men. CONCLUSIONS: For the first time, the survey provides data on the prevalence and correlates of psychiatric disorder on a nationwide sample that can be used to inform equitable and effective national psychiatric services.

Adolescent↗
PubMed1997

The National Psychiatric Morbidity surveys of Great Britain--strategy and methods.

BACKGROUND: This paper describes the rationale and methodology of the first national psychiatric morbidity surveys to be carried out in Great Britain. The objectives of the surveys were to estimate the prevalence of psychiatric morbidity among adults aged 16-64 living in Great Britain; to identify the nature and extent of social disabilities associated with psychiatric morbidity; to describe the use of health and social services by people with psychiatric morbidity and to investigate the association between mental illness and potential environmental risk factors in a household sample. METHODS: Four separate surveys were carried out in order to meet the objectives; a private household sample (N = 10108), a sample of institutions caring for the mentally ill (N = 1191), a sample of homeless people (N = 1166), and a supplementary sample of patients with psychosis living in private households (N = 350). A two-stage assessment procedure was used, in which all subjects were given the Revised Clinical Interview Schedule (CIS-R) administered by lay interviewers to assess neurotic symptoms and disorders and a psychosis screen, including the Psychosis Screening Questionnaire. Those who were positive on the psychosis screen were then interviewed by psychiatrists using the SCAN (incorporating the tenth edition of the Present State Examination). CONCLUSIONS: Large scale national surveys such as this augment the inadequate data on psychiatric morbidity that are routinely available and are, therefore, an important source of information upon which to base policy and generate aetiological hypotheses. These surveys provide a possible model for similar surveys in other countries.

Adolescent↗
PubMed1997

Tolerance of suicide, religion and suicide rates: an ecological and individual study in 19 Western countries.

BACKGROUND: Negative associations between religion and suicide, in individuals and countries, may be mediated by the degree to which suicide is tolerated. METHODS: Linear regression was used to examine ecological associations between suicide tolerance, religion and suicide rates in 19 Western countries in 1989/90. Logistic regression was used to study associations between suicide tolerance and strength of religious belief in 28085 individuals in these countries. The concept of effect modifying function was used to examine whether the strength of the association between suicide tolerance and religious belief in individuals depended on the extent of religious belief in their country. RESULTS: Higher female suicide rates were associated with lower aggregate levels of religious belief and, less strongly, religious attendance. These associations were mostly attributable to the association between higher tolerance of suicide and higher suicide rates. In the 28085 subjects suicide tolerance and the strength of religious belief were negatively associated even after adjustment for other religious and sociodemographic variables and general tolerance levels (odds ratios: men 0.74 (95% CI 0.58-0.94), women 0.72 (95% CI 0.60-0.86)). This negative individual-level association was more pronounced in more highly religious countries but this modifying effect of the religious context was apparent for men only. CONCLUSIONS: Ecological associations between religious variables and suicide rates are stronger for women than men, stronger for measures of belief than observance and mediated by tolerance of suicide. In individuals, stronger religious beliefs are associated with lower tolerance of suicide. Personal religious beliefs and, for men, exposure to a religious environment, may protect against suicide by reducing its acceptability.

Adult↗