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Biomedical subjects

G Lewis

Publications and source records attributed to G Lewis.

At least 73 records · Page 4Linked to original sources
PubMed2001

Effect of crosslinking UHMWPE on its tensile and compressive creep performance.

The in vitro quasi-static tensile and compressive creep properties of three sets of GUR 1050 ultra-high-molecular-weight polyethylene (UHMWPE) specimens were obtained. These sets were: control (as-received stock); "low-gamma" (specimens were crosslinked using gamma radiation, with a minimum dose of 5 Mrad); and "high-gamma" (specimens were crosslinked using gamma radiation, with a minimum dose of 15 Mrad). The % crystallinity (%C) and crosslink density (rho(x)) of the specimens in the three sets were also obtained. It was found that, in both tension and compression, crosslinking resulted in a significant depreciation in the creep properties, relative to control. The trend in the creep results is explained in terms of the impact of crosslinking on the polymer's %C and rho(x). The present results are in contrast to literature reports that show that crosslinking enhances the wear resistance of the polymer. The implications of the present results, taken together with the aforementioned literature results, are fully discussed vis-a-vis the use of crosslinked UHMWPE for fabricating articular components for arthroplasties.

Biocompatible Materials↗
PubMed2001

Intravenous apoA-I/lecithin discs increase pre-beta-HDL concentration in tissue fluid and stimulate reverse cholesterol transport in humans.

The extent to which plasma HDL concentration regulates reverse cholesterol transport (RCT) is not known. The principal acceptors of unesterified cholesterol (UC) from cultured cells are small pre-beta-HDL, which we have shown increase in plasma during intravenous infusion of apolipoprotein A-I/phosphatidylcholine (apoA-I/PC) discs in humans. We have now examined the effects on tissue fluid HDL and RCT. ApoA-I/PC or proapoA-I/PC discs were infused into 16 healthy males. Eleven had been given intravenous radiocholesterol to label tissue pools; in 12 prenodal leg lymph was collected throughout; and in 8 all feces were collected. The rise in small pre-beta-HDL in plasma was associated with increases in 1) pre-beta-HDL concentration in lymph (all subjects), 2) the size of other lymph HDL (four of four subjects), 3) the cholesterol content of lymph lipoproteins relative to plasma lipoproteins (P < 0.01, n = 4), 4) cholesterol-specific radioactivity in lymph (five of nine subjects), 5) plasma lathosterol (P < 0.004, n = 4), 6) plasma cholesterol esterification rate (P < 0.001, n = 4), and 7) fecal bile acid excretion (P < 0.001, n = 8). These results support the hypothesis that small pre-beta-HDL generated in plasma readily cross endothelium into tissue fluid, and thereby promote efflux of UC from peripheral cells. After delivery to the liver, peripheral cholesterol appears to be utilized more for bile acid synthesis than for biliary cholesterol secretion in humans.

Adult↗
PubMed2000

Relative roles of cement molecular weight and mixing method on the fatigue performance of acrylic bone cement: Simplex P versus Osteopal.

The weight-average molecular weight (MW(w)) of a cement and the method used to mix its powder and liquid monomer constituents have been identified in the literature as key variables that affect mechanical properties of the fully polymerized cement that are relevant to its performance as a grouting agent in cemented arthroplasties. The goal of the present work was to identify which of these two variables exerts the greater effect in the case of fully reversed tension-compression fatigue performance. A judicious choice of cement brands, Surgical Simplex P and Osteopal, and the use of hand versus vacuum mixing, permitted this identification to be achieved. Three key observations were made in this work. First, for a given cement, the fatigue performance of vacuum-mixed specimens is far superior to that of hand-mixed ones, which may be a consequence of the substantially lower percentage areal porosity of the former specimens. Second, regardless of the mixing method, the fatigue performance of Osteopal outstrips that of Simplex P, a result that is attributed to the much higher MW(w) of the former cement. Third, hand-mixed Osteopal outperforms vacuum-mixed Simplex P (especially at low alternating stress levels), indicating that MW(w) of a bone cement is more influential than mixing method on its fatigue performance.

Arthroplasty, Replacement↗
PubMed2000

Toward standardization of methods of determination of fracture properties of acrylic bone cement and statistical analysis of test results.

A succinct critical review of the literature on the fatigue, fatigue crack propagation, and fracture toughness (herein collectively termed "fracture properties") of acrylic bone cement is presented, whereby it is pointed out that a plethora of test conditions have been used. This situation precludes meaningful interstudy comparisons and mitigates against a definitive delineation of the effect of a named variable on a specified fracture property. A case for standardization of test conditions is thus made, culminating in the presentation of a recommended set of such conditions. In addition, it is shown that many literature parametric studies employed inappropriate statistical methods for performing pairwise comparisons, and all these studies have not addressed the issue of possible interactions between the parameters being investigated. A methodology for addressing these deficiencies is presented in the present report, and its use is illustrated with a set of notional fatigue test results.

Acrylates↗
PubMed2000

Selective serotonin reuptake inhibitors versus tricyclic and heterocyclic antidepressants: comparison of drug adherence.

BACKGROUND: Selective serotonin reuptake inhibitors are thought to have better discontinuation rates (i.e. less people dropping out) than tricyclic and heterocyclic antidepressant drugs. It is important to quantify the drop-out rates of different antidepressant drugs in order to have a better understanding of the relative tolerability of these drugs. OBJECTIVES: To assess the comparative tolerability of selective serotonin reuptake inhibitors and tricyclic/heterocyclic antidepressant drugs. SEARCH STRATEGY: We searched the Cochrane Collaboration Depression, Anxiety and Neurosis Controlled Trials Registers (1997 to 1999), MEDLINE (1966 to 1999), EMBASE (1974 to 1999) We also searched specialist journals, the reference lists of relevant papers and previous systematic reviews, conference abstracts and government documents. Representatives of the pharmaceutical industry were contacted. SELECTION CRITERIA: Parallel group randomised controlled trials comparing selective serotonin reuptake inhibitors with tricyclic or heterocyclic antidepressants in people with depression. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and a third reviewer checked any cases of disagreement. MAIN RESULTS: We included 136 trials. The selective serotonin reuptake inhibitors showed less participants dropping out compared to the tricyclic/heterocyclic group (odds ratio 1.21, 95% confidence interval 1.12 to 1.30). A statistically significant difference was found in total drop-outs between the selective serotonin reuptake inhibitors and the old tricyclics as well as the newer tricyclics. When the selective serotonin reuptake inhibitors were compared to the heterocyclic antidepressants, there was a non significant difference favouring the selective serotonin reuptake inhibitors. The poor tolerability profile of the old tricyclics was explained by differences in drop-outs for side-effects, but not for inefficacy. REVIEWER'S CONCLUSIONS: Whilst selective serotonin reuptake inhibitors do appear to show an advantage over tricyclic drugs in terms of total drop-outs, this advantage is relatively modest. This has implications for pharmaco-economic models, some of which may have overestimated the difference of drop-out rates between selective serotonin reuptake inhibitors and tricyclic antdepressants. These results are based on short-term randomised controlled trials, and may not generalise into clinical practice.

Antidepressive Agents↗
PubMed2000

Psychiatric disorder and dysfunction in the UK National Survey of Psychiatric Morbidity.

BACKGROUND: Psychiatric symptoms are wide-spread in the general population, but have little effect on performance. Deficits in performance and psychiatric symptoms may be the end point of processes common to both, or they may be caused by quite different factors. In this paper we examine the epidemiological distribution of psychiatric symptoms and performance deficits, as indicated by difficulties in activities of daily living (ADL). We hypothesised that ADL difficulties are partly independent of psychiatric symptoms, and that this is reflected in a different demographic distribution. METHOD: The household component of the National Surveys of Psychiatric Morbidity was based on a sample of around ten thousand subjects selected at random from the population of Great Britain. Psychiatric symptoms were elicited by lay interviewers using the revised Clinical Interview Schedule. Performance was assessed by asking about difficulties experienced in performing seven types of everyday activity. In this paper, our chosen variables were overall symptom and ADL deficit scores, and these were related to standard demographic variables. RESULTS: There were significant differences in the epidemiological distribution of psychiatric symptoms and ADL difficulties. In particular, men experienced more ADL difficulties at a given symptom level than women. There were also differences in relation to social class, employment status, marital status, ethnic group and age. CONCLUSIONS: ADL deficits and psychiatric symptoms are related in the general population, and this probably represents common factors in their origin. However, discrepancies in the social distribution of these phenomena suggest there are also aetiological differences. These do not appear to be the result of the impact of physical illness on activities of daily living. Our results emphasise that ADL difficulties should be studied separately, particularly in investigations of treatment seeking.

Activities of Daily Living↗
PubMed2000

Correlation between impact strength and fracture toughness of PMMA-based bone cements.

The thrust of the work involved determining the impact strength, IS (in kJ m(-2)) [using non-ASTM-sized Charpy-type specimens and an in-house impact tester] and fracture toughness, K1c (in MPa square root(m)) [using ASTM-sized rectangular compact tension specimens] of Surgical Simplex P and three variants of Palacos R acrylic bone cements. The attractions and drawbacks of this method for determining IS are detailed. The best fit to the K1c and IS results yielded a power relationship K1c = 0.795(IS)(0.59). The usefulness and limitations of this relationship are detailed.

Biomechanical Phenomena↗
PubMed2000

Unequal access and unmet need: neurotic disorders and the use of primary care services.

BACKGROUND: In this paper we use data from the National Survey of Psychiatric Morbidity to examine how many people with neurotic disorders receive professional evaluation, and how this is affected by clinical and sociodemographic differences. We hypothesized that psychiatric symptoms and attendant dysfunctions would both have an effect on contacting, and that key demographic variables would not. METHOD: The household component of the British National Surveys of Psychiatric Morbidity was based on a random sample of > 10,000 subjects. Psychiatric symptoms and ICD-10 diagnosis were established by lay interviewers using the CIS-R. Social dysfunction was tapped by asking about difficulties in performing seven types of everyday activity. We examined symptom score, ADL deficit score and demographic variables in relation to contact with primary care physicians for psychiatric symptoms. RESULTS: The major determinant of contacting a primary care physician was severity, mainly due to the level of psychiatric symptoms, but with an independent contribution from social dysfunction. There were also significant contributions from sex, marital status, age, employment status and whether the subject had a physical condition as well. CONCLUSIONS: The major influence on whether people seek the help of their family doctors for mental health problems is the severity of disorder. Although there are some social inequalities in access to family doctors, these are less important. The most salient finding from our study is that even people suffering from high levels of psychiatric symptoms very often do not have contact with professionals who might help them.

Activities of Daily Living↗
PubMed2000

Neurotic disorders and the receipt of psychiatric treatment.

BACKGROUND: Access to psychiatric treatment by people with neurotic disorders in the general population is likely to be affected both by the severity of disorder and by sociodemographic differences. METHOD: In the household component of the National Surveys of Psychiatric Morbidity > 10,000 subjects in Great Britain with psychiatric symptoms were interviewed using the CIS-R. They were also asked about difficulties experienced in performing seven types of everyday activity. All subjects classed as having an ICD-10 disorder were questioned about their experience of treatment with antidepressants, hypnotics, and counselling or psychotherapy. RESULTS: Less than 14% of people with current neurotic disorders were receiving treatment for them. Within the previous year, only a third had made contact with their primary care physician for their mental problem: of these < 30% were receiving treatment. Overall, 9% of people with disorders were given medication and 8% counselling or psychotherapy. A diagnosis of depressive episode was that most associated with antidepressant medication. Treatment access was affected by employment status, marital status, and age, but the major determinant was symptom severity. Neither sex nor social class influenced which people received treatment. CONCLUSIONS: People with psychiatric disorders seldom receive treatment, even when they have consulted their primary care physician about them. In many cases, this must represent unmet needs with a strong claim on health resources. There are also inequalities in the receipt of treatment, although the major influence is the severity of disorder.

Adolescent↗
PubMed2000

Clarifying the relationship between unexplained chronic fatigue and psychiatric morbidity: results from a community survey in Great Britain.

OBJECTIVE: The study examined the associations between several sociodemographic and psychosocial variables and unexplained chronic fatigue in the community before and after adjustment for psychiatric morbidity and determined the prevalence of fatigue and rate of disability resulting from fatigue in the general population. METHOD: The study is a secondary analysis of 1993 data from a household survey of psychiatric morbidity conducted by the Office for Population Censuses and Surveys in Great Britain. The survey included 12,730 subjects age 16-64 years. Unexplained chronic fatigue was used as the dependent variable in a logistic regression analysis, with various sociodemographic and psychosocial variables and psychiatric morbidity as the independent variables. Psychiatric morbidity was assessed by using the Revised Clinical Interview Schedule. Fatigue was measured by using the fatigue section of the Revised Clinical Interview Schedule. RESULTS: A total of 10,108 subjects agreed to cooperate (79.4% participation rate). The prevalence of unexplained chronic fatigue was 9%. Subjects with psychiatric morbidity had higher rates of fatigue. Adjustment for psychiatric morbidity had a minor effect on the associations between sociodemographic factors and chronic fatigue. After adjustment, older subjects, women, and couples with children had higher rates of fatigue. Single subjects, widowed subjects, adults living with parents, and economically inactive subjects had lower rates of fatigue. Fatigue was associated with considerable disability, but most of this disability was explained by the association between fatigue and psychiatric morbidity. CONCLUSIONS: Unexplained chronic fatigue is a common condition, strongly associated with psychiatric morbidity. The close relationship between fatigue and psychiatric morbidity should not obscure the possibility of differences as well as similarities in their etiologies.

Activities of Daily Living↗
PubMed2000

Non-psychotic psychiatric disorder and subsequent risk of schizophrenia. Cohort study.

BACKGROUND: Those with schizophrenia often give a history of premorbid non-psychotic psychiatric disorder. AIMS: To investigate the association between non-psychotic psychiatric disorders and the later development of schizophrenia. METHOD: Men aged 18 or 19 years, conscripted to the Swedish army in 1970 (n=50 054) were linked to the Swedish National Psychiatric Case Register. RESULTS: There was an increased risk of schizophrenia in those with ICD-8 diagnoses of neurosis (OR=4.6,95% Cl 3.2-6.9), personality disorder (OR=8.2, 95% Cl 5.4-12.3), alcohol abuse (OR=5.5, 95% Cl 1.7-17.5) or substance abuse (OR=14.0, 95% Cl 7.8-25.0) at age 18. Of those who developed schizophrenia, 38% (95% Cl 32-45) received a diagnosis of non-psychotic psychiatric disorder at age 18. Only those with personality disorder had a significantly increased risk of schizophrenia (OR=2.4, 95% Cl 1.1-5.2) with onset after age 23. CONCLUSIONS: Personality factors could represent an underlying vulnerability to schizophrenia. Other diagnoses occurring before schizophrenia may reflect a prodromal phase of the illness.

Adolescent↗
PubMed2000

Relationship between fracture toughness and impact strength of acrylic bone cement.

This work involved determining the fracture toughness, KIc (in MPa(square root)m) (using rectangular compact tension specimens) and impact strength, IS (in kJ/m2) (Charpy type specimens) of Surgical Simplex P and three variants of Palacos R acrylic bone cements. The best fit to these results yielded a power relationship KIc = 0.795(IS)0.59. The usefulness of this relationship is detailed, especially for the purpose of performing quality control checks on bone cements.

Biocompatible Materials↗