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Biomedical subjects

G Lewis

Publications and source records attributed to G Lewis.

At least 109 records · Page 6Linked to original sources
PubMed1999

A new method of determining the J-integral fracture toughness of very tough polymers: application to ultra high molecular weight polyethylene.

The thrust of the present work was the development of a new modification to the ASTM E813-89 method for determining the J-integral fracture toughness, JIc, of ductile polymers. The advantages and limitations of the modification, vis a vis the ASTM E813-89 and the hysteresis methods, are presented. The modification was then applied to investigate the effect of sterilization method on the JIc of ultra-high-molecular-weight polyethylene (UHMWPE) specimens that were subsequently aged (heated, in a cylindrical pressure vessel, in oxygen gas at 507 kPa and 70 degrees C for 14 d). Relative to the unsterilized material, it was found that gamma-irradiating the polymer leads to a significant drop in its JIc, while sterilization using either ethylene oxide or gas plasma produced no effect on its JIc. The clinical implications of the present results for the in vivo performance of UHMWPE counterfaces, and, hence, hip and knee arthroplasties, are fully discussed.

Hardness Tests↗
PubMed1998

Suicide, deprivation, and unemployment: record linkage study.

OBJECTIVES: To investigate the association between suicide and socioeconomic status, unemployment, and chronic illness. DESIGN: Longitudinal study. SETTING: England and Wales. SUBJECTS: Individuals from the Office for National Statistics longitudinal study for whom 1981 census data were available. The longitudinal study is a representative 1% sample of the population of England and Wales in which census variables are linked to mortality data. MAIN OUTCOME MEASURES: Suicide and undetermined deaths occurring between 1983 and 1992. Odds ratios estimated with logistic regression adjusted for attrition of cohort members. RESULTS: There was a strong independent association between suicide and individuals who were unemployed (odds ratio 2.6; 95% confidence interval 2.0 to 3.4) and permanently sick (2.5; 1.6 to 4.0). Those without access to a car had an increased risk (1.3; 1.0 to 1.5), but other measures of socioeconomic status were not associated with suicide. CONCLUSIONS: The association between suicide and unemployment is more important than the association with other socioeconomic measures. Although some potentially important confounders were not adjusted for, the findings support the idea that unemployment or lack of job security increases the risk of suicide and that social and economic policies that reduce unemployment will also reduce the rate of suicide.

Adolescent↗
PubMed1998

Secretion of D-aspartic acid by the rat testis and its role in endocrinology of the testis and spermatogenesis.

The D-isomer of aspartic acid (D-Asp) has been found in rat testes. In the present study, samples of testicular venous blood plasma, rete testis fluid, interstitial extracellular fluid, luminal fluid from the seminiferous tubules, testicular parenchymal cells, epididymal spermatozoa and peripheral blood plasma were collected and analyzed for D-Asp by two methods, an enzymatic and a chromatographic HPLC method. The two methods gave very similar results for all samples. The highest concentrations of D-Asp (about 120 nmol/ml) were found in testicular venous blood plasma, with slightly lower concentrations in rete testis fluid (95 nmol/ml) and epididymal spermatozoa (80 nmol/g wet weight). Lower levels were found in testicular parenchymal cells (which would comprise mostly spermatids and spermatocytes), luminal fluid from the seminiferous tubules and interstitial extracellular fluid (26, 23 and 11 nmol/ml respectively). However, these values were all higher than those for peripheral blood plasma (6 nmol/ml). It would appear that D-Asp is being secreted by the testis mostly into the venous blood, passing thence into the rete testis fluid and being incorporated into the spermatozoa at the time or after they leave the testis. The distribution of D-Asp is thus quite different from that of testosterone, and its role and the reason for its high concentration in the male reproductive tract remain to be elucidated.

Animals↗
PubMed1998

Functional and molecular characterization of human monoclonal antibody reactive with the immunodominant region of HIV type 1 glycoprotein 41.

The immunoreactivity, functional activity, and molecular features of a human monoclonal antibody (HMAb), F240, from an HIV-1-infected individual have been studied. Flow cytometric analysis demonstrated that F240 is reactive with cells infected with a broad range of laboratory isolates but not with uninfected cells. Reactivity of F240 is greatly enhanced by preincubation of infected cells with soluble CD4, and to a much lesser extent, with F105, an HMAb reactive with the CD4-binding site of gp120. This enhancement is temperature dependent, with maximum enhancement observed at 37 degrees C, and suggests that the F240 epitope may be more accessible after gp120 has bound to CD4 in vivo. Immunoblot analysis reveals antigen specificity of F240 for gp41 or its precursor gp160. F240 specificity is mapped to the immunodominant region of the gp41 ectodomain by Pepscan analysis. This epitope has been implicated in eliciting nonprotective antibodies that enhance infection in the presence of complement. Consistent with this, F240 failed to neutralize laboratory isolates and enhanced viral infection in a complement-dependent manner. The F240 VH demonstrates extensive somatic mutations compared with the product of its closest homologous germline gene VH3-3.11. Most amino acid substitutions occur in CDR2, characteristic of an antigen-driven response, and in FR3, a phenomenon observed in other anti-HIV-1 envelope HMAbs. Primary structure analysis of the F240 heavy chain revealed strong homology in the CDR domains to an HMAb (3D6) reactive with the same gp41 region, which suggests that these HMAbs could define a potential human antibody clonotype.

Amino Acid Sequence↗
PubMed1998

Socioeconomic status, standard of living, and neurotic disorder.

BACKGROUND: Evidence on the association between socioeconomic status and the prevalence of neurotic disorder is contradictory. We studied the association between three elements of socioeconomic status and the prevalence of neurotic psychiatric disorder in a representative sample of adults aged 16-64 living in private households in the UK. METHODS: A cross-sectional survey of 10,108 adults aged 16-65 resident in private households in the UK was selected by a multi-stage, clustered, random-sampling design. Neurotic disorders were defined using a standardised interview, the revised clinical interview schedule (CIS-R). Data for 9570 people were available for this study. FINDINGS: We used housing tenure and access to cars as measures of standard of living; both were associated with the prevalence of neurotic disorder even after adjustment for other socioeconomic and demographic variables, including Registrar General's Social Class and educational attainment. Those people with no access to a car had an odds ratio for neurotic disorder of 1.4 (95% CI 1.1-1.7), compared with those who had access to two or more cars. People who rented their homes were also at increased risk (1.3 [1.1-1.5]). We estimated that about 10% of the neurotic disorder in the UK could be attributed to the increased prevalence of those without cars who rented their homes. There was a complex interaction between Registrar General's Social Class and sex, and there was no independent association with educational attainment. INTERPRETATION: There is an independent association between low standard of living and the prevalence of neurotic psychiatric disorder. The UK has experienced one of the largest increases in income inequality within western market economies over the past 20 years, and this inequality may have had adverse consequences for the mental health of the population.

Adolescent↗
PubMed1998

Poverty, unemployment, and common mental disorders: population based cohort study.

OBJECTIVE: To determine whether poverty and unemployment increase the likelihood of or delay recovery from common mental disorders, and whether these associations could be explained by subjective financial strain. DESIGN: Prospective cohort study. SETTING: England, Wales, and Scotland. SUBJECTS: 7726 adults aged 16-75 living in private households. MAIN OUTCOME MEASURES: Common mental disorders were assessed using the general health questionnaire, a self assessed measure of psychiatric morbidity. RESULTS: Poverty and unemployment (odds ratio 1.86, 95% confidence interval 1.18 to 2.94) were associated with the maintenance but not onset of episodes of common mental disorders. Associations between poverty and employment and maintenance of common mental disorders, however, were much smaller than those of cross sectional studies. Financial strain at baseline was independently associated with both onset (1.57, 1.19 to 2.07) and maintenance (1.86, 1.36 to 2.53) even after adjusting for objective indices of standard of living. CONCLUSIONS: Poverty and unemployment increased the duration of episodes of common mental disorders but not the likelihood of their onset. Financial strain was a better predictor of future psychiatric morbidity than either of these more objective risk factors though the nature of this risk factor and its relation with poverty and unemployment remain unclear.

Adolescent↗
PubMed1998

Accidental nuclear war--a post-cold war assessment.

BACKGROUND: In the 1980s, many medical organizations identified the prevention of nuclear war as one of the medical profession's most important goals. An assessment of the current danger is warranted given the radically changed context of the post-Cold War era. METHODS: We reviewed the recent literature on the status of nuclear arsenals and the risk of nuclear war. We then estimated the likely medical effects of a scenario identified by leading experts as posing a serious danger: an accidental launch of nuclear weapons. We assessed possible measures to reduce the risk of such an event. RESULTS: U.S. and Russian nuclear-weapons systems remain on a high-level alert status. This fact, combined with the aging of Russian technical systems, has recently increased the risk of an accidental nuclear attack. As a conservative estimate, an accidental intermediate-sized launch of weapons from a single Russian submarine would result in the deaths of 6,838,000 persons from firestorms in eight U.S. cities. Millions of other people would probably be exposed to potentially lethal radiation from fallout. An agreement to remove all nuclear missiles from high-level alert status and eliminate the capability of a rapid launch would put an end to this threat. CONCLUSIONS: The risk of an accidental nuclear attack has increased in recent years, threatening a public health disaster of unprecedented scale. Physicians and medical organizations should work actively to help build support for the policy changes that would prevent such a disaster.

Disasters↗
PubMed1998

Dynamic thermomechanical properties and crystallinity of ultrahigh molecular weight polyethylene tibial inserts.

A dynamic thermomechanical analysis method was used to determine the values of the viscoelastic parameters, storage modulus (E') and the tangent of the loss angle (tan delta) of samples taken from the near surface and core regions of ultrahigh molecular weight polyethylene (UHMWPE) bar stock specimens that had been aged in ambient laboratory air for 12 months (the control group) and UHMWPE tibial inserts that had been subjected to the following treatments: gamma sterilization followed by shelf aging in ambient laboratory air for between 56 and 112 months or ethylene oxide (EtO) gas sterilization followed by shelf aging in ambient laboratory air for 73 months. Differential scanning calorimetry was used to determine the melt temperature and percentage crystallinity (%C) of these samples. There were three main findings. First, EtO sterilization produced no statistically significant effect on the values of E' or tan delta (relative to those for the control group), but the values of these parameters were markedly affected by gamma sterilization. Second, for gamma-irradiated samples, E' increased with an increase in the shelf aging time. Third, there was a strong direct association between E' and % C. The various potential uses of this association are described, paying special attention to its likely role in predicting the in vivo wear of UHMWPE tibial inserts.

Biocompatible Materials↗
PubMed1998

What's in a name? A comparison of four psychiatric assessments.

The Hamilton Depression Rating Scale, Beck Depression Inventory, Clinical Interview Schedule and General Health Questionnaire have been designed to detect and measure severity of psychiatric disorders in different settings. We aimed to determine the relationship between each assessment within a mixed primary care population. The questionnaires and interviews were administered to a sample of 49 patients attending an urban general practice. The total score for each scale correlated closely with every other one (correlation coefficients = 0.70-0.79). Factor analysis suggested that all of the scales were measuring a single underlying construct with reliabilities of 0.68-0.78. The implications of these findings are discussed in relation to the assessment of severity of depression and other neurotic symptoms. We suggest that the Clinical Interview Schedule is a feasible alternative to the Hamilton Rating Scale for Depression and discuss reasons why it might be preferable within clinical trials of depression.

Adolescent↗
PubMed1998

Electromyogram-triggered neuromuscular stimulation for improving the arm function of acute stroke survivors: a randomized pilot study.

OBJECTIVE: To assess the efficacy of electromyogram (EMG)-triggered neuromuscular stimulation (EMG-stim) in enhancing upper extremity motor and functional recovery of acute stroke survivors. DESIGN: A pilot randomized, single-blinded clinical trial. SETTING: Freestanding inpatient rehabilitation facility. PATIENTS: Nine subjects who were within 6 weeks of their first unifocal, nonhemorrhagic stroke were randomly assigned to either the EMG-stim (n = 4) or control (n = 5) group. All subjects had a detectable EMG signal (>5 microV) from the surface of the paretic extensor carpi radialis and voluntary wrist extension in synergy or in isolation with muscle grade of <3/5. INTERVENTION: All subjects received two 30-minute sessions per day of wrist strengthening exercises with EMG-stim (experimental) or without (control) for the duration of their rehabilitation stay. MAIN OUTCOME MEASURES: Upper extremity Fugl-Meyer motor assessment and the feeding, grooming, and upper body dressing items of the Functional Independence Measure (FIM) were assessed at study entry and at discharge. RESULTS: Subjects treated with EMG-stim exhibited significantly greater gains in Fugl-Meyer (27.0 vs 10.4; p = .05), and FIM (6.0 vs 3.4; p = .02) scores compared with controls. CONCLUSION: Data suggest that EMG-stim enhances the arm function of acute stroke survivors.

Activities of Daily Living↗
PubMed1998

The apparent fracture toughness of acrylic bone cement: effect of three variables.

In cemented arthroplasties, pores are almost invariably present at one or more of the so-called 'weak-link' zones (namely, the bone-cement interface, the cement mantle and the cement-implant interface). In the clinical milieu, arthroplasties are frequently subjected to cyclical loading. These conditions underscore the significance of the apparent fracture toughness (KISR) of the cement. The present work is an investigation of the effect of three variables on KISR of three commercial formulations of bone cement (namely, CMW3, PalacosR and Osteopal) measured using straight-sided chevron notched short rod specimens. For CMW3, the effect of mixing method was studied, with all cement constituents having been stored at ambient laboratory environment prior to being mixed. The highest KISR was obtained from material that was obtained from exposing the cement constituents to a passive vacuum for 20 s and then mixing them in a machine that subjected them to simultaneous mechanical mixing and centrifugation. For Palacos R, the effects of two variables [storage temperature of the cement constituents prior to being mixed (4 degrees C versus 21 degrees C) and mixing method (hand mixing versus vacuum mixing)] (taken individually) were studied. It was found that only mixing method exerts a significant effect on KISR. When room-temperature stored constituents were vacuum mixed, the KISR values for a low-viscosity cement (Osteopal) and a medium-viscosity cement of very similar composition (Palacos R) are not significantly different, indicating that the fracture resistance of bone cement is influenced more by its composition than its viscosity.

Acrylic Resins↗
PubMed1998

The influence of age and sex on the prevalence of depressive conditions: report from the National Survey of Psychiatric Morbidity .

BACKGROUND: Women are consistently reported to have a greater prevalence of depressive disorders than men. The reason for this is unclear, and is as likely to be social as biological. There is some evidence that the excess of depression is greater during women's reproductive lives. Data from the National Survey of Psychiatric Morbidity were used to test the hypothesis that the excess disappeared in the post-menopausal years and that obvious social explanations for this were inadequate. METHOD: Subjects (N = 9792) from a random sample of the British population provided data for the analysis. Psychiatric assessment was carried out by lay interviewers using the CIS-R. Subjects with ICD-10 depressive episode or mixed anxiety/depression were compared with the remainder. Social variables that were likely to contribute to a post-menopausal decline in depressive disorders were controlled in logistic regression analyses. RESULTS: There was a clear reversal of the sex difference in prevalence of depression in those over age 55. This could not be explained in terms of differential effects of marital status, child care, or employment status. CONCLUSIONS: This large and representative survey adds considerably to the increasingly held view that the sex difference in prevalence of depression is less apparent in later middle age. This may be linked to the menopause, and our attempts to explain it in terms of obvious conditions among social variables were not successful. More specific studies are required to clarify the finding.

Adolescent↗
PubMed1998

Suicide acceptability in African- and white Americans: the role of religion.

Rates of suicidal behavior are lower among African- than white Americans. We analyzed the association of suicide acceptability with religious, sociodemographic, and emotional variables in representative samples of African- and white Americans (1990). Adjusted for ethnic response bias, the former were less accepting of suicide than the latter (odds ratio .60; 95% confidence interval .41, .88). Orthodox religious beliefs and personal devotion predicted rejection of suicide best; this effect was equally strong in both groups. The comparatively low level of suicide acceptability among African-Americans was mostly attributable to their relatively high levels of orthodox religious beliefs and devotion, as opposed to practice and affiliation, although sociodemographic and emotional differences contributed as well. These results are interpreted using the cognitive dissonance model. Given rapid secularization among the young in the United States, these findings may help explain the rising suicide rates among white and, especially, African-American young people.

Black or African American↗
PubMed1998

Geometrical properties and torsional fatigue life of a tibial interlocking intramedullary nail segment.

OBJECTIVES: The first goal was to present details of a methodology for selecting the cross-sectional geometry and associated dimensions for a tibial interlocking intramedullary (i.m.) nail segment, given a set of candidate geometries. The second goal was to study the effect of four variables on the torsional fatigue life of specimens that constitute a segment of a tibial i.m. nail. METHODS: For the cross-sectional geometry study, the geometric element modeling and analysis method was used to obtain the areas (A) and moments of inertia (I and J) of each of the cross-sectional geometries in the set considered. In the fatigue tests, a specimen was subjected to a load at the end of a lever arm, through an actuator, at a fixed frequency. RESULTS: On the basis of the values of the A, I, and J and consideration of compatibility with the biological envelope, the hourglass cross-section geometry was selected as the best compromise. The cannulation, fillet radius, and main radius of this hourglass were determined to be 3.96, 1.02, and 4.06 millimeters, respectively. Fatigue test specimens fabricated from Ti-6Al-4V and having three sets of additional characteristics performed equally well as those fabricated from 316L stainless steel. These sets of characteristics are hourglass cross-section and mill annealed only; hourglass cross-section and mill annealed, followed by machining and anodization to give a gray coating; and cloverleaf cross-section and mill annealed, followed by machining and anodization to give a gray coating. CONCLUSION: Tibial IM nails with hourglass cross-sectional shape and fabricated of Ti-6Al-4V or Ti-13Nb-13Zr alloy, having appropriate mechanical, thermal, and surface treatments, may be competitive with the current "gold standard" (namely cloverleaf cross-section and fabricated of 316L stainless steel in the cold-worked state).

Bone Nails↗
PubMed1998

Material standard of living, social class, and the prevalence of the common mental disorders in Great Britain.

STUDY OBJECTIVE: To test the hypothesis that poor material standard of living is independently associated with the prevalence of the common mental disorders after adjusting for occupational social class, and to estimate the population impact of poor material standard of living on the prevalence of these disorders. DESIGN: Cross sectional survey. Prevalence of the common mental disorders was assessed using the General Health Questionnaire, a self administered measure of psychiatric morbidity. PARTICIPANTS: 9064 adults aged 16-75 living in private households in England, Wales, and Scotland. MAIN RESULTS: The common mental disorders were significantly associated with poor material standard of living, including low household income (OR 1.24, 95% CI 1.00, 1.54) and not saving from income (OR 1.29, 95% CI 1.15, 1.45), after adjusting for occupational social class and other potential confounders. An independent association was also found with occupational social class of the head of household among women, but not men, after adjusting for material standard of living. The adjusted population attributable fraction for poor material standard of living (using a five item index) was 24.0%. CONCLUSIONS: Like mortality and physical morbidity, common mental disorders are associated with a poor material standard of living, independent of occupational social class. These findings support the view that recent widening of inequalities in material standards of living in the United Kingdom pose a substantial threat to health.

Adolescent↗