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Biomedical subjects

R Thomson

Publications and source records attributed to R Thomson.

At least 19 recordsLinked to original sources
PubMed2002

Critical behavior of a strain percolation model for metals.

Extensive simulations of a strain percolation model for a deforming metal have been performed to examine its strain behavior. We find that the total strain exhibits critical power-law behavior that is well explained by two-dimensional percolation theory. Near the critical point, most of the strained cells organize themselves around a state having the minimum or at least marginally stable strain regardless of the initial conditions. A strain much greater than the minimum stable strain generally decays to a lower value when transmitted to an unstrained cell. The universal behavior of the total strain in the system is a consequence of the self-organizing character of the strain in the critical cluster. Although the probability distributions for the total strain and cluster size appear to exhibit nonuniversal behavior, this may merely represent a transient response before crossover to a true asymptotic, universal behavior occurs. Other critical aspects of the model are also discussed.

Journal Article↗
PubMed2001

A giant multiacinar macroregenerative nodule in an explanted liver.

Macroregenerative nodules (MRN) have been detected with increased incidence in explanted livers since orthotopic liver transplantation (OLTx) has become a routine treatment for end-stage liver disease. Autopsy series suggest that MRN may be more common than once thought, and several studies point to the malignant potential of these lesions. With increasing waiting times for OLTx, the propensity for these premalignant lesions to arise in cirrhotic livers has important implications for the supervision of patients on OLTx waiting lists. We present here a striking example of a MRN and review a topic that is generating considerable interest.

Adult↗
PubMed2001

A novel method for the isolation of motile bacteria using gradient culture systems.

Isolation of motile bacteria from stream water samples was achieved by using Lutrol F127 (poloxamer 407) as a gelling agent in culture media. This block copolymer has the property of repeatedly liquefying and solidifying at low and high temperatures, respectively. The ability of motile bacteria to move through liquid-state Lutrol F127 towards a higher nutrient concentration was exploited. After establishment of the nutrient gradient and inoculation, the system was cooled to liquefy the medium and kept liquid to allow motile bacteria to move. Raising the temperature allowed solidification and prevented further movement. Colonies could be easily removed. The proportion of motile isolates (determined by microscopic observation) increased from 42% in the indigenous population to 100% after isolation using the gradient system.

Bacteria↗
PubMed2001

Implementation and evaluation of local-level priority setting for stroke.

We aimed to develop and evaluate a prioritisation process to combine the evidence base with stakeholder involvement within a stroke programme for a Health Improvement Programme (HImP). Implementation involved: formation of a district stroke group (DSG); review of the evidence; survey of DSG members; survey of other key professionals; consensus within the DSG; consultation with local users of the service. Evaluation was through semi-structured interviews and documentary analysis. The process was accepted as appropriate and valuable by the majority of participants, and a district HImP implementation group allocated pound sterling 100 000 for stroke development as a result of this process. However, some felt that stroke itself had been an imposed, rather than an agreed, local priority. The priority setting process was not clear to all participants and change of personnel, particularly in the NHS trusts, led to some perceived lack of ownership. Professionals from secondary care participated, but later criticised the process when they felt that the priorities in the HImP could limit their ability to access money for other service developments. The user consultation days occurred too late to influence the 1999/2002 HImP. We have shown that it is possible to develop an approach that is broadly accepted by stakeholders and balance the evidence base with local ownership. The participation of stakeholders, clarity of procedures, local ownership and awareness of local politics are important in effective priority setting. The model developed will be of value in other settings.

Evidence-Based Medicine↗
PubMed2001

Hidden need for drug treatment services: measuring levels of problematic drug use in the North West of England.

BACKGROUND: In the North West of England, data on drug users are routinely collected from a variety of agencies including specialist treatment centres, police and probation services. However, the covert nature of drug use means that alone, these conventional monitoring systems cannot provide the epidemiology required to target and develop drug treatment and prevention initiatives. METHODS: Utilizing surveillance data and capture-recapture techniques we estimate the rates of problematic drug users by age and sex in five North West health authorities and one local authority. RESULTS: Analyses show concentrations of problematic drug use in large metropolitan areas (Liverpool and Manchester) with levels as high as 34.5 and 36.5 per 1000 population (ages 15-44), respectively, and, for males, levels exceed 50 per 1000 in three authorities. Patterns of prevalence for those aged 25 and over differed from those in the younger age groups, with disproportionate levels of young users outside metropolitan areas. The proportion of young users already in treatment (21.3 per cent) was lower (older users, 35.3 per cent), with overall proportions in treatment varying between health authorities (range 26.2-46.5 per cent). CONCLUSION: With a multi-agency approach, established monitoring systems can be used to measure hidden populations of drug users. Estimates of the current populations of such users in the North West of England suggest that planned increases of people in treatment by 100 per cent would fail to accommodate even current level of problematic users. A holistic approach to new initiatives must ensure that the high level of relapse once drug users are discharged are reduced and that the needs of young users are addressed before prolonged treatment is required.

Adolescent↗
PubMed2001

Where is the gender in gendered language?

The purpose of these studies was to examine how women and men react and accommodate to gender-preferential language in e-mail messages. In Experiment 1, participants wrote messages to two assigned "netpals." These netpals were actually one of the experimenters. For each participant, one netpal used female-preferential language and the other used male-preferential language. Analyses revealed that the netpals' language style, and not the participants' gender, predicted the language used by participants in their e-mail replies. Female and male participants used the gender-preferential language that matched the language used by their netpals. In Experiment 2, the gender labels and language styles of netpals were independently manipulated. As before, linguistic style had the greatest impact on participants' language use. These results have implications for how people think about gendered behavior, and highlight how gendered language is constructed in social interaction.

Adult↗
PubMed2001

Variability in patient preferences for participating in medical decision making: implication for the use of decision support tools.

While there is an increasing emphasis on patient empowerment and shared decision making, evidence suggests that many patients do not wish to be involved in decisions about their own care. Previous research has found patient preferences for involvement in decision making to vary with age, socioeconomic status, illness experience, and the gravity of the decision. Furthermore, there is evidence that certain patients may experience disutility from being involved in decision making about the treatment of their health problems. We discuss the implications of these findings for the use of decision support tools and the difficulties of targeting their use towards those patients most likely to benefit. We argue that patients may be ill informed about what participation in decision making actually entails and unaware of the benefits they stand to gain by articulating their preferences to their clinician. Furthermore, clinicians are not good at accurately assessing patients' preferences, while patients may have unrealistic expectations about their clinician's ability to "know what is best" for them. Further research is required to understand variations in patients' preferences for information and involvement in decision making, and the factors that influence them.

Communication↗
PubMed2001

How patients with atrial fibrillation value different health outcomes: a standard gamble study.

BACKGROUND AND PURPOSE: The assessment of any health care intervention should consider both risks and benefits and take patients' preferences about these into account. The study reported in this paper aimed to elicit patient valuations of health states relevant to assessment of the prevention of stroke by warfarin anticoagulation therapy for patients with atrial fibrillation. METHODS: A sample of patients over the age of 60 years with atrial fibrillation from three family practices in North-East England was interviewed. Their health state values were elicited using the standard gamble method for general practitioner (GP)-managed warfarin treatment, hospital-managed warfarin treatment, major bleed, mild stroke and severe stroke. RESULTS: Of 180 patients, 69 (38%) agreed to participate, of whom 57 (83%) completed interviews. Median (mean) utility values were for GP-managed warfarin treatment 0.986 (0.948), hospital-managed warfarin treatment 0.984 (0.941), major bleed 0.880 (0.841), mild stroke 0.675 (0.641) and severe stroke 0 (0.189). There was wide variation in values between patients and the distributions were highly skewed. CONCLUSIONS: The results are of value in applying decision analysis to groups of patients. They should be used with caution in reaching decisions about appropriate treatment for individual patients, but may provide a starting point for necessary further exploration of those patients' individual preferences.

Anticoagulants↗
PubMed2001

Predicting gender from electronic discourse.

There is substantial evidence of gender differences in face-to-face communication, and we suspect that similar differences are present in electronic communication. We designed three studies to examine gender-preferential language style in electronic discourse. In Expt 1, participants sent electronic messages to a designated 'netpal'. A discriminant analysis showed that it was possible to successfully classify the participants by gender with 91.4% accuracy. In Expts 2 and 3, we wanted to determine whether readers of e-mails could accurately identify author gender. We gave participants a selection of messages from Expt 1 and asked them to predict the author's gender. It was found that for 14 of the 16 messages used, the gender of author was correctly predicted. In the third experiment, six messages about gender-neutral topics were composed. Using a subset of the variables identified in Expt 1, female and male versions of each message were created. When participants were asked to rate whether a female or a male wrote these messages, their ratings differed as a function of the message version. These findings establish that people use gender-preferential language in informal electronic discourse. Furthermore, readers of these messages can use these gender-linked language differences to identify the author's gender.

Adolescent↗
PubMed2001

Medical decision support via the internet: PROforma and Solo.

This paper describes the development and application of an integrated technology to support the authoring of intelligent medical knowledge services, such as decision and guideline support, and disseminate them over the Internet. Decision support and guideline enactment are provided by the PROforma technology which is described in detail elsewhere. Solo is a communications infrastructure that supports the delivery of PROforma services over the Internet using a web browser. The PROforma-Solo technology brings together techniques from knowledge engineering and artificial intelligence with software engineering and the Internet to flexibly support decision making and patient management at the point of care. A variety of clinical applications have been implemented and are briefly described.

Artificial Intelligence↗
PubMed2001

Publets: clinical judgement on the web.

The Internet is now a major channel for publishing medical research data and documents, including clinical practice guidelines. It is now possible to capture guidelines in a computer interpretable form opening up the capability of using the internet (and intra/extranets etc.) to deliver patient-specific advice and other services. A development lifecycle and technology for publishing and delivering services at the point of care ("publets") are described. As with all new technologies, however, these new methods entail risks as well as opportunities. The paper closes with a discussion of quality requirements and an argument that publets should include a safety case as an integral part of their content.

Internet↗
PubMed2000

Recent common ancestry of human Y chromosomes: evidence from DNA sequence data.

We consider a data set of DNA sequence variation at three Y chromosome genes (SMCY, DBY, and DFFRY) in a worldwide sample of human Y chromosomes. Between 53 and 70 chromosomes were fully screened for sequence variation at each locus by using the method of denaturing high-performance liquid chromatography. The sum of the lengths of the three genes is 64,120 bp. We have used these data to study the ancestral genealogy of human Y chromosomes. In particular, we focused on estimating the expected time to the most recent common ancestor and the expected ages of certain mutations with interesting geographic distributions. Although the geographic structure of the inferred haplotype tree is reminiscent of that obtained for other loci (the root is in Africa, and most of the oldest non-African lineages are Asian), the expected time to the most recent common ancestor is remarkably short, on the order of 50,000 years. Thus, although previous studies have noted that Y chromosome variation shows extreme geographic structure, we estimate that the spread of Y chromosomes out of Africa is much more recent than previously was thought. We also show that our data indicate substantial population growth in the effective number of human Y chromosomes.

Biological Evolution↗
PubMed2000

Decision analysis and guidelines for anticoagulant therapy to prevent stroke in patients with atrial fibrillation.

BACKGROUND: Clinical guidelines are needed on whether or not to use anticoagulant therapy to prevent stroke in patients with non-valvular atrial fibrillation. We did a Markov decision analysis to model decision-making with regard to warfarin treatment in patients with atrial fibrillation, and used the model to develop evaluative guidelines. METHODS: The decision analysis involved a systematic literature review supplemented by patients' estimates of the quality of life associated with different states of health, secondary analysis of stroke-registry data, and estimation of service costs; it also incorporated a sensitivity analysis. The derived guidelines were subsequently applied to a cohort of patients with atrial fibrillation. FINDINGS: We constructed decision tables for 12 age and sex groups. For most risk combinations, warfarin treatment would have decreased health-care costs and increased quality-of-life years, although the clinical decision was sensitive to patients' preferences and to the estimate of warfarin's effectiveness. 97% of women with atrial fibrillation older than 75 years, and 69% aged 65-74 would have been recommended for treatment; for men, the corresponding figures would have been 75% and 53%. With the upper quartile for the loss of quality of life associated with being on warfarin treatment (1.00), all but two of the 116 patients without contraindications would have been treated, whereas with the lower quartile (0.92), only 27 of 116 would have been treated. INTERPRETATION: Decision analysis is useful in the incorporation of complex probabilistic data into informed decision-making, the identification of factors influencing such decisions, and the subsequent development of evaluative guidelines.

Aged↗
PubMed2000

Decision analysis in evidence-based decision making.

Many real world decisions have to be made on a limited evidence base, and clinical decisions are at best problematic. We explored some of the reasons why decision making in health care is so complex, and examined how decision analytic techniques might contribute to problem structuring and to implementation of evidence-based practice. We argued that decision analysis could, to some extent, overcome complexity of decision making by a clear structuring of the problem and a formal analysis of the implications of different decisions. Decision-analytic techniques can guide the management of individual patients or can be used to address policy questions about the use of treatment for groups of patients. However, decision analysis is not without its criticisms, e.g. problems are narrowly defined, replacing judgement and dehumanizing care, neglect of process utility and lack of primary data to develop decision analytic models. The development of evidence-based guidelines is a key component of the UK Government's quality strategy led by the National Institute for Clinical Excellence (NICE). However, the guidelines approach may lead to conflict when assessments of the effectiveness of interventions for individuals (whether or not supported by a formal decision analysis) conflict with the recommendations made by NICE for cost and clinical effectiveness for aggregate groups of patients. Decision analysis may or may not help with this but if guidelines are derived from a decision analysis, then the implications of patient preferences should be made clearer. However, decision analysis-derived guidelines will make general recommendations that may not be appropriate for all individuals. Nonetheless, decision analysis does make such implications explicit and propose that the guidelines should be supported by some mechanism for determining individual patient preferences. It will now need to consider whether some of NICE resources should be directed beyond evidence-based guidelines into decision analysis-derived guidelines and into decision analytical techniques to provide support for clinical and cost effective decision making within the patient-clinician encounter.

Decision Making↗