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Biomedical subjects

Martin Stevens

Publications and source records attributed to Martin Stevens.

At least 19 recordsLinked to original sources
PubMed2007

Preoperative or postoperative self-efficacy: which is a better predictor of outcome after total hip or knee arthroplasty?

OBJECTIVE: Self-efficacy is considered an important determinant of outcome after total hip or knee arthroplasty. Aim of this study is to evaluate the contributions of preoperative and short-term postoperative self-efficacy in predicting long-term outcome. METHODS: Self-efficacy was determined in 103 total hip and knee arthroplasty patients preoperatively and 6 weeks postoperatively with the Self-Efficacy for Rehabilitation Outcome Scale (SER). The 6-month outcome was assessed with a disease-specific and a generic self-report questionnaire and an objective measure of function (walking speed). Multiple linear regression analyses were used to examine the value of preoperative and short-term postoperative self-efficacy in predicting 6-month outcomes. RESULTS: Preoperative self-efficacy was only a significant predictor of long-term postoperative walking speed, with higher self-efficacy resulting in faster walking speed at the long-term measurement (R(2)=0.47). Short-term postoperative self-efficacy was a significant predictor of the long-term postoperative generic outcome measure (physical functioning: R(2)=0.30; mental health: R(2)=0.53) and of walking speed (R(2)=0.66), with higher self-efficacy resulting in a better long-term outcome. CONCLUSION: Short-term postoperative self-efficacy seems a better predictor of long-term outcome after total hip or knee arthroplasty than preoperative self-efficacy. PRACTICE IMPLICATIONS: Interventions should focus on enhancing short-term postoperative rather than preoperative self-efficacy.

Activities of Daily Living↗
PubMed2007

Effectiveness of computer-navigated minimally invasive total hip surgery compared to conventional total hip arthroplasty: design of a randomized controlled trial.

BACKGROUND: Moderate to severe osteoarthrosis is the most common indication for Total Hip Arthroplasty (THA). Minimally Invasive Total Hip Surgery (MIS) and computer-navigated surgery were introduced several years ago. However, the literature lacks well-designed studies that provide evidence of superiority of computer-navigated MIS over a conventional THA technique. Hence, the purpose of this study is to compare (cost)effectiveness of computer-navigated MIS with a conventional technique for THA. It is our hypothesis that computer-navigated MIS will lead to a quicker recovery during the early postoperative period (3 months), and to an outcome at least as good 6 months postoperatively. We also hypothesize that computer-navigated MIS leads to fewer perioperative complications and better prosthesis positioning. Furthermore, cost advantages of computer-navigated MIS over conventional THA technique are expected. METHODS/DESIGN: A cluster randomized controlled trial will be executed. Patients between the ages of 18 and 75 admitted for primary cementless unilateral THA will be included. Patients will be stratified using the Charnley classification. They will be randomly allocated to have computer-navigated MIS or conventional THA technique. Measurements take place preoperatively, perioperatively, and 6 weeks and 3 and 6 months postoperatively. Degree of limping (gait analysis), self-reported functional status and health-related quality of life (questionnaires) will be assessed preoperatively as well as postoperatively. Perioperative complications will be registered. Radiographic evaluation of prosthesis positioning will take place 6 weeks postoperatively. An evaluation of costs within and outside the healthcare sector will focus on differences in costs between computer-navigated MIS and conventional THA technique. DISCUSSION: Based on studies performed so far, few objective data quantifying the risks and benefits of computer-navigated MIS are available. Therefore, this study has been designed to compare (cost) effectiveness of computer-navigated MIS with a conventional technique for THA. The results of this trial will be presented as soon as they become available.

Adolescent↗
PubMed2006

Disruptive contrast in animal camouflage.

Camouflage typically involves colour patterns that match the background. However, it has been argued that concealment may be achieved by strategic use of apparently conspicuous markings. Recent evidence supports the theory that the presence of contrasting patterns placed peripherally on an animal's body (disruptive coloration) provides survival advantages. However, no study has tested a key prediction from the early literature that disruptive coloration is effective even when some colour patches do not match the background and have a high contrast with both the background and adjacent pattern elements (disruptive contrast). We test this counter-intuitive idea that conspicuous patterns might aid concealment, using artificial moth-like targets with pattern elements designed to match or mismatch the average luminance (lightness) of the trees on which they were placed. Disruptive coloration was less effective when some pattern elements did not match the background luminance. However, even non-background-matching disruptive patterns reduced predation relative to equivalent non-disruptive patterns or to unpatterned controls. Therefore, concealment may still be achieved even when an animal possesses markings not found in the background. Disruptive coloration may allow animals to exploit backgrounds on which they are not perfectly matched, and to possess conspicuous markings while still retaining a degree of camouflage.

Animals↗
PubMed2006

Groningen orthopaedic exit strategy: Validation of a support program after total hip or knee arthroplasty.

OBJECTIVE: Validation of the program theory of the Groningen orthopaedic exit strategy (GOES), a theory-driven program aiming to improve the rehabilitation of total hip and knee arthroplasty patients after shortened hospital stay. First part of the program theory is the action theory, hypothesising that the GOES treatment positively influences the mediating variables (self-efficacy, social support, pain-coping). The second part, the conceptual theory, hypothesis a positive relationship between these variables and the outcome variables (ADL functioning, physical activity behaviour, quality of life). METHODS: Patients were randomly assigned to the GOES or control groups. Questionnaires were used to assess mediating and outcome variables in 103 patients (50 GOES, 53 controls) pre-operatively, and 6 and 26 weeks post-operatively. RESULTS: No difference was seen between the two groups in terms of changes between pre-operative and post-operative mediating variables (action theory). Moderate-to-large correlations explaining reasonable amount of variance (22%, 25%, 56%) were found between the mediating and outcome variables (conceptual theory). CONCLUSION: The conceptual theory is supported; however, as the treatment did not influence the mediating variables (action theory), it has no added value in its current form. PRACTICE IMPLICATIONS: The treatment needs to be adjusted; it is discussed that individualised treatment could be more effective.

Academic Medical Centers↗
PubMed2006

Disruptive coloration, crypsis and edge detection in early visual processing.

Many animals use concealing markings to reduce the risk of predation. These include background pattern matching (crypsis), where the coloration matches a random sample of the background and disruptive patterns, whose effectiveness has been hypothesized to lie in breaking up the body into a series of apparently unrelated objects. We have previously established the effectiveness of disruptive coloration against avian predators, using artificial moth-like stimuli with colours designed to match natural backgrounds as perceived by birds. Here, we investigate the mechanism by which disruptive patterns reduce detectability, using a computational vision model of edge detection applied to photographs of our experimental stimuli, calibrated for bird colour vision. We show that, disruptive coloration is effective by exploiting edge detection algorithms that we use to model early visual processing. Thus, 'false' edges are detected within the body rather than at its periphery, so inhibiting successful detection of the animal's body outline.

Animals↗
PubMed2006

The effectiveness of disruptive coloration as a concealment strategy.

Our understanding of camouflage has been developing for over 100 years. Several underlying principles have emerged. Background pattern matching, or crypsis, is insufficient to conceal objects because of edge information. Other strategies exist to disrupt the continuity of extended edges. These strategies are reviewed. We pay particular attention to the theory of disruptive coloration, which predicts that high-contrast elements located at the object edge will mask the perception of a target as belonging to a certain category of object, in spite of the fact that the edge elements are independently visible. Although this strategy has long been assumed to be effective, there has been a lack of supportive data involving the perception of targets by nonhuman animals. We present evidence, from a field study, in support of the notion that disruptive coloration reduces the chances of bird predation of artificial "moths."

Adaptation, Biological↗
PubMed2005

Patient satisfaction at and after discharge. Effect of a time lag.

OBJECTIVE: Patient satisfaction is an important outcome measure for evaluating the quality of medical care. It is remarkable that consistently high satisfaction ratings have been reported over the last 30 years. There are indications that the time point of administration of a patient satisfaction questionnaire has an influence on satisfaction ratings. This study aimed at investigating whether the assessment of patient satisfaction at different time points resulted in different outcomes. METHODS: Patient satisfaction was measured twice. The sample consisted of 152 orthopedic patients who filled in the questionnaire at hospital discharge and one to 12 months after discharge. RESULTS: At follow-up, satisfaction ratings decreased significantly. Satisfaction with postoperative information decreased the most after discharge. CONCLUSION: The results of this study indicate that the time point of administration of a patient satisfaction questionnaire does influence satisfaction ratings. PRACTICE IMPLICATIONS: Patient satisfaction outcomes collected during hospitalization and after discharge may not be interpreted similarly.

Female↗
PubMed2005

The unsuitability of HTML-based colour charts for estimating animal colours--a comment on Berggren and Merilä (2004).

BACKGROUND: A variety of techniques are used to study the colours of animal signals, including the use of visual matching to colour charts. This paper aims to highlight why they are generally an unsatisfactory tool for the measurement and classification of animal colours and why colour codes based on HTML (really RGB) standards, as advocated in a recent paper, are particularly inappropriate. There are many theoretical arguments against the use of colour charts, not least that human colour vision differs markedly from that of most other animals. However, the focus of this paper is the concern that, even when applied to humans, there is no simple 1:1 mapping from an RGB colour space to the perceived colours in a chart (the results are both printer- and illumination-dependent). We support our criticisms with data from colour matching experiments with humans, involving self-made, printed colour charts. RESULTS: Colour matching experiments with printed charts involving 11 subjects showed that the choices made by individuals were significantly different between charts that had exactly the same RGB values, but were produced from different printers. Furthermore, individual matches tended to vary under different lighting conditions. Spectrophotometry of the colour charts showed that the reflectance spectra of the charts varied greatly between printers and that equal steps in RGB space were often far from equal in terms of reflectance on the printed charts. CONCLUSION: In addition to outlining theoretical criticisms of the use of colour charts, our empirical results show that: individuals vary in their perception of colours, that different printers produce strikingly different results when reproducing what should be the same chart, and that the characteristics of the light irradiating the surface do affect colour perception. Therefore, we urge great caution in the use of colour charts to study animal colour signals. They should be used only as a last resort and in full knowledge of their limitations, with specially produced charts made to high industry standards.

Journal Article↗
PubMed2005

Six-month effects of the Groningen active living model (GALM) on physical activity, health and fitness outcomes in sedentary and underactive older adults aged 55-65.

OBJECTIVE: To determine the effects on energy expenditure, health and fitness outcomes in sedentary older adults aged 55-65 after 6-month participation in the GALM program. METHODS: In three Dutch communities, subjects from matched neighbourhoods were assigned to an intervention (n = 79) or a waiting-list control group (n = 102). The GALM program consisted of fifteen 60 min sessions once a week emphasising moderate-intensity recreational sports activities. RESULTS: The intervention group showed significant increases in energy expenditure for recreational sports activities, other leisure-time physical activity, health indicators, and perceived and performance-based fitness. Contrary to our expectations, the same increases were found for the control group. Consequently, only significant between-group differences, favouring the intervention group, were obtained for sleep, diastolic blood pressure, perceived fitness score and grip strength. CONCLUSION: The increases in energy expenditure for physical activity from the GALM program, especially for the more intensive recreational sports activities, look promising and are in line with the expected amounts necessary to improve health. Further research is needed to evaluate long-term effects of participation in the GALM program. PRACTICE IMPLICATIONS: These results underline that GALM can be considered successful in stimulating leisure-time physical activity and improving health and fitness in older adults.

Age Factors↗
PubMed2005

Disruptive coloration and background pattern matching.

Effective camouflage renders a target indistinguishable from irrelevant background objects. Two interrelated but logically distinct mechanisms for this are background pattern matching (crypsis) and disruptive coloration: in the former, the animal's colours are a random sample of the background; in the latter, bold contrasting colours on the animal's periphery break up its outline. The latter has long been proposed as an explanation for some apparently conspicuous coloration in animals, and is standard textbook material. Surprisingly, only one quantitative test of the theory exists, and one experimental test of its effectiveness against non-human predators. Here we test two key predictions: that patterns on the body's outline should be particularly effective in promoting concealment and that highly contrasting colours should enhance this disruptive effect. Artificial moth-like targets were exposed to bird predation in the field, with the experimental colour patterns on the 'wings' and a dead mealworm as the edible 'body'. Survival analysis supported the predictions, indicating that disruptive coloration is an effective means of camouflage, above and beyond background pattern matching.

Adaptation, Biological↗
PubMed2005

A Dutch translation of the Self-Efficacy for Rehabilitation Outcome Scale (SER): a first impression on reliability and validity.

Self-efficacy is a relevant factor during rehabilitation after total hip or knee arthroplasty. Research was done into the reliability and validity of a Dutch translation of the Self-Efficacy for Rehabilitation Outcome Scale (SER). One hundred and forty-one persons filled in the SER questionnaire and the Self-Efficacy Expectation Scale (SES) as a control scale. Research was done into reliability and into construct- and criterion-related validity. Factor analysis yielded two factors. Pearson's correlation between the two factors was 0.61 (P < 0.01). To assess criterion-related validity, the Pearson's correlation coefficient was calculated between the sum score of the SER and the SES. The scales had a correlation of 0.62 (P < 0.01). Internal consistency resulted in a Cronbach's coefficient alpha of 0.94 for the entire SER scale, and 0.94 and 0.87 for the first and second factors. It is concluded that for the time being the Dutch version of the SER can be considered a reliable and valid questionnaire.

Arthroplasty, Replacement, Hip↗
PubMed2005

The role of eyespots as anti-predator mechanisms, principally demonstrated in the Lepidoptera.

Eyespots are found in a variety of animals, in particular lepidopterans. The role of eyespots as antipredator mechanisms has been discussed since the 19th Century, with two main hypotheses invoked to explain their occurrence. The first is that large, centrally located eyespots intimidate predators by resembling the eyes of the predators' own enemies; the second, though not necessarily conflicting, hypothesis is that small, peripherally located eyespots function as markers to deflect the attacks of predators to non-vital regions of the body. A third possibility is also proposed; that eyespots intimidate predators merely because they are novel or rarely encountered salient features. These hypotheses are reviewed, with special reference given to avian predators, since these are likely to be the principal visually hunting predators of the lepidopterans considered. Also highlighted is the necessity to consider the potential influence of sexual selection on lepidopteran wing patterns, and the genetics and development of eyespot formation.

Animals↗
PubMed2004

The Groningen Orthopedic Exit Strategy (GOES): a home-based support program for total hip and knee arthroplasty patients after shortened hospital stay.

The number of total hip and knee arthroplasty patients in The Netherlands will increase progressively in the coming decades. A reaction to this trend is a shortening of hospital stays. This however should not result in uncertainty, lack of information and unnecessary medical consumption by patients at home. Based on insights from social cognitive theory, an exit strategy is described to support patients during their rehabilitation at home. It is our hypothesis that patients who participate in such a support program will be able to resume activities of daily living more quickly and effectively, and will reach higher levels of physical activity compared to patients who only follow the shortened program. To determine the effectiveness of the exit strategy, mediating variables (self-efficacy, social support and pain coping) and outcome variables (activities of daily living, physical activity behavior, health-related quality of life and gait analysis) will be measured.

Activities of Daily Living↗
PubMed2004

Groningen Orthopaedic Social Support Scale: validity and reliability.

BACKGROUND: Social support is an important factor in the rehabilitation process, as it has a positive influence on patients' health, functioning and recovery. In particular, perceived social support and instrumental support are important after total hip or knee arthroplasty. However, nursing staff often appear to estimate the amount of support available to patients by number of visitors. Until now, no suitable Dutch-language scale was available to measure social support in orthopaedic patients. AIM: The aim of this paper is to describe the development and initial validity and reliability testing of the Groningen Orthopaedic Social Support Scale, a self-report questionnaire to measure social support in patients after total hip or knee arthroplasty. METHODS: A total of 119 people who had had arthroplasty completed the Groningen Orthopaedic Social Support Scale and a control scale. The reliability and validity of the questionnaire were analysed. RESULTS: Reliability of the Groningen Orthopaedic Social Support Scale can be considered satisfactory, with a Cronbach's alpha of 0.89. Analysis of construct validity by means of factor analysis yielded two factors: perceived social support and instrumental support. A Pearson's correlation between these subscales was moderate (r = 0.61 and statistically significant). Concurrent validity can be considered satisfactory, with a Pearson correlation of 0.72 (P < 0.001) between the Groningen Orthopaedic Social Support Scale and the control list. CONCLUSIONS: The Groningen Orthopaedic Social Support Scale can be considered suitable for measuring social support. It can be used to help nursing staff determine if a patient's need for social support is fulfilled, and to advise family and friends on the basis of the results. The questionnaire can also be used to establish the role of social support as a factor in supportive interventions during and after hospital stay.

Arthroplasty, Replacement, Hip↗
PubMed2003

Speed versus accuracy in collective decision making.

We demonstrate a speed versus accuracy trade-off in collective decision making. House-hunting ant colonies choose a new nest more quickly in harsh conditions than in benign ones and are less discriminating. The errors that occur in a harsh environment are errors of judgement not errors of omission because the colonies have discovered all of the alternative nests before they initiate an emigration. Leptothorax albipennis ants use quorum sensing in their house hunting. They only accept a nest, and begin rapidly recruiting members of their colony, when they find within it a sufficient number of their nest-mates. Here we show that these ants can lower their quorum thresholds between benign and harsh conditions to adjust their speed-accuracy trade-off. Indeed, in harsh conditions these ants rely much more on individual decision making than collective decision making. Our findings show that these ants actively choose to take their time over judgements and employ collective decision making in benign conditions when accuracy is more important than speed.

Animal Communication↗
PubMed2003

Groningen Active Living Model (GALM): stimulating physical activity in sedentary older adults; validation of the behavioral change model.

BACKGROUND: A significant proportion of older adults in The Netherlands do not participate regularly in leisure-time physical activity. The Groningen Active Living Model (GALM) was developed to change this situation for the better. Longitudinal results of the validation of the GALM behavioral change model are presented. METHODS: We obtained data on potentially mediating variables of physical activity behavior change (self-efficacy, social support, perceived fitness, and enjoyment) from 96 participants in a prospective study during the 18 months the GALM strategy lasted. RESULTS: Prospective analyses revealed significant differences in several potentially mediating variables, although some of these differences were contrary to our hypothesis. Discriminant analysis resulted in canonical correlations of 0.50 after 6 months and 0.66 after 18 months of program participation between adherers and nonadherers, respectively; 73.8 and 80.0% of the subjects were classified correctly. CONCLUSIONS: Based on the results, it can be concluded that we partially succeeded in manipulating the potentially mediating variables by means of our GALM strategy. Several mediating variables were identified that reliably discriminated long-term adherers from nonadherers, expanding the generalizability of social cognitive theory-driven variables to a Dutch population.

Aged↗
PubMedDate not supplied

Diabetic neuropathy and oxidative stress.

This review will focus on the impact of hyperglycemia-induced oxidative stress in the development of diabetes-related neural dysfunction. Oxidative stress occurs when the balance between the production of reactive oxygen species (ROS) and the ability of cells or tissues to detoxify the free radicals produced during metabolic activity is tilted in the favor of the former. Although hyperglycemia plays a key role in inducing oxidative stress in the diabetic nerve, the contribution of other factors, such as endoneurial hypoxia, transition metal imbalances, and hyperlipidemia have been also suggested. The possible sources for the overproduction of ROS in diabetes are widespread and include enzymatic pathways, auto-oxidation of glucose, and mitochondrial superoxide production. Increase in oxidative stress has clearly been shown to contribute to the pathology of neural and vascular dysfunction in diabetes. Potential therapies for preventing increased oxidative stress in diabetic nerve dysfunction will be discussed.

Antioxidants↗