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Biomedical subjects

A C Fisher

Publications and source records attributed to A C Fisher.

At least 37 records · Page 2Linked to original sources
PubMed1995

In vitro assessment of water vapour transmission of synthetic wound dressings.

The water vapour transmission rate (WVTR) of 14 commercially available wound dressings (11 hydrocolloids, 2 hydrogels and 1 polyurethane film) was evaluated over 24 and 48 h periods using a modified ASTM standard method (ASTM E96-90). For the 48 h studies a novel microcomputer-controlled apparatus was employed. The dressings exhibited a wide range of WVTRs (76-9360 g m-2 d-1 at 24 h under forced air convection of 0.4 m s-1). The influence of air velocity of 0.4 m s-1 was not significant if the WVTR of the dressing was less than 880 g m-2 d-1 when measured under static air conditions. The influence of outer barrier layers and additional bandages on WVTR was also examined.

Bandages↗
PubMed1995

Effect of captopril, enalaprilat and mercaptopropionyl glycine (MPG) on the oxidative activity of human isolated neutrophils.

1. Neutrophil NADPH oxidase produces the superoxide anion (O2-) anion radical from oxygen. The thiol containing ACE inhibitor, captopril has been reported to inhibit isolated NADPH oxidase. The above effect of captopril, if present in intact cells, could contribute to the ability of this drug to alleviate neutrophil-mediated tissue damage. We have, therefore, investigated the effect of captopril on the oxidative activity of intact human isolated neutrophils. 2. The effects of captopril on neutrophil oxidative activity were compared with those of enalaprilat (a non-thiol ACE inhibitor) and N-mercaptopropionyl glycine (MPG) (a simple thiol). 3. The oxidative response of PMA-stimulated neutrophils measured by lucigenin chemiluminescence was not affected by any of these test agents. The thiol captopril and MPG (but not enalaprilat) caused an initial delay in luminol chemiluminescence production by PMA-stimulated neutrophils. 4. Captopril and MPG (but not enalaprilat) increased, rather than decreased oxygen uptake, when added to PMA-stimulated neutrophils. Thiol oxidation was determined to be, at least partly, responsible for the excess oxygen uptake observed. 5. NADPH oxidase activity in intact neutrophils was not affected by captopril, MPG or enalaprilat. The inhibition of NADPH oxidase activity is unlikely to contribute to the therapeutic effects of captopril and other thiols.

Acridines↗
PubMed1995

Does luminol chemiluminescence detect free radical scavengers?

Thiol compounds have been reported to abolish hypoxanthine/xanthine oxidase induced luminol chemiluminescence and this effect has been attributed to scavenging of superoxide (O2-)/(H2O2) produced from hypoxanthine/xanthine oxidase. Yet other workers have reported that thiol compounds have shown little, if any, reactivity towards O2-/H2O2. The aim of this study was to examine the discrepancy between these two sets of findings further. Captopril (a thiol angiotensin-converting enzyme (ACE) inhibitor) and MPG (a simple thiol) were observed to abolish hypoxanthine/xanthine oxidase induced chemiluminescence. The reactivity of captopril and MPG towards O2-/H2O2 was then determined by measurement of thiol oxidation in captopril and MPG after their incubation with hypoxanthine/xanthine oxidase. Incubation (at 10 min, 37 degrees C) with 4 mM hypoxanthine/0.03 u ml-1 xanthine oxidase resulted in 7% and 20% thiol oxidation in captopril and MPG (at 1 mM) respectively. Captopril and MPG, therefore, appeared to be ineffective scavengers of oxidants produced by hypoxanthine/xanthine oxidase. Captopril and MPG also did not affect urate production or oxygen consumption by xanthine oxidase which indicated that captopril and MPG quench luminol chemiluminescence by a mechanism that excludes the inhibition of xanthine oxidase. Hypoxanthine/xanthine oxidase induced luminol chemiluminescence may, therefore, be an unsuitable method for measuring free radical scavenging activity by drugs.

Antioxidants↗
PubMed1994

The effect of angiotensin-converting enzyme inhibitors on human neutrophil chemotaxis in vitro.

1. Myocardial 'reperfusion injury' has been partly attributed to the production of free radicals which are cytotoxic towards cells. Neutrophils are recruited by ischaemic tissue and are one source of free radicals. Angiotensin-converting enzyme (ACE) inhibitors can reduce 'reperfusion injury' and we decided to determine if ACE inhibitors might contribute to this effect by inhibiting neutrophil chemotaxis. 2. The effects of captopril (a thiol containing ACE inhibitor) and enalaprilat (a nonthiol ACE inhibitor) and N-mercaptopropionyl glycine (MPG) (a simple thiol) on neutrophil chemotaxis were tested in an in vitro Boyden chamber assay. 3. The chemotactic response of human neutrophils to fMLP was reduced by 27.6% with MPG (n = 8; P < 0.05), by 13.2% with enalaprilat (n = 8; P = 0.075) and by 5.2% with captopril (n = 8; P = 0.66) at 5 microM (therapeutic concentration.) 4. Neutrophil chemotaxis was significantly decreased with 50 microM and 500 microM MPG and enalaprilat and 500 microM captopril. 5. Supratherapeutic concentrations of ACE inhibitors can reduce neutrophil chemotaxis at high concentrations and this effect does not appear to be -SH dependent.

Captopril↗
PubMed1993

Athletic trainers' attitudes and judgments of injured athletes' rehabilitation adherence.

Certified athletic trainers (ATCs) in District 2 (n=187) of the National Athletic Trainers' Association (NATA) were asked to complete a questionnaire that assessed the attitudes and judgments of ATCs concerning numerous factors presumed to influence sport injury rehabilitation. Gender and experience differences in ATCs' attitudes and judgments about rehabilitation adherence were examined. Successful and unsuccessful adherence strategies also were reported. The questionnaire consisted of 60 statements that were categorized into seven scales: athletic trainer's influence, environmental influences, athlete's personality, pain tolerance, selfmotivation, goals and incentives, and significant others. There were no significant differences for either gender or experience of ATCs on any of the seven scales. An analysis of questionnaire item responses revealed the following as factors ATCs deemed important to injury rehabilitation: a) good rapport and communication between the ATC and the injured athlete, b) explanation of the injury and rehabilitation regimen, c) convenience and accessibility of the rehabilitation facility, d) rehabilitation sessions planned around the athletes' busy schedules, e) athletes' beliefs that the program is worth pursuing, f) personal supervision and regular monitoring, g) need for injured athletes to see immediate results, and h) support from significant others. ATCs reported education, goal setting, encouragement, monitoring progress, and support systems as successful strategies. Threats and rehabilitation without monitoring were reported as unsuccessful strategies.

Journal Article↗
PubMed1993

Injured athletes' attitudes and judgments toward rehabilitation adherence.

In a follow-up study to certified athletic trainers' (ATCs') attitudes and judgments toward injury rehabilitation adherence, previously injured and rehabilitated athletes (n=36) were administered the Athletic Injury Rehabilitation Adherence Questionnaire. The purpose of the study was to compare the results collected from athletes with those collected previously from ATCs. The questionnaire consisted of 60 statements, categorized into seven scales: athletic trainers' influence, environmental influences, athlete's personality, pain tolerance, self-motivation, goals and incentives, and significant others. Four additional open-ended questions dealing with successful and unsuccessful rehabilitation strategies also were completed. Athletes' responses were generally similar to those of ATCs. Factors deemed significant to rehabilitation adherence were: (a) good rapport and communication between athletic trainers and injured athletes, (b) support from athletic trainers and coaches, (c) self-motivation on the part of athletes, and (d) convenience, accessibility, and flexibility of the rehabilitation facility and staff. The greatest deviations between athletes' and ATCs' responses were in the areas of self-motivation, pain tolerance, education about injury and rehabilitation exercises, and degree of realistic feedback. Analyses of open-ended question responses reinforced the aforementioned results. The strongest findings derived from these questions were the importance of rapport, communication, and support to rehabilitation adherence. Also, athletes' distastes for threats and scare tactics were quite evident.

Journal Article↗
PubMed1993

Enhancing athletic injury rehabilitation adherence.

Contemporary sports medicine literature has begun to address more centrally the idea that treatment adherence is a complex issue. Not only must certified athletic trainers (ATCs) possess knowledge about injuries and subsequent rehabilitation protocols, they also must be able to deliver essential services in a manner that predisposes treatment success. Effective treatment of athletic injuries necessitates consideration of various psychosocial factors shown to enhance rehabilitation adherence. Detailed explanations of several important ATC-athlete interaction patterns and motivational strategies are offered.

Journal Article↗
PubMed1992

Calcification and stress distribution in bovine pericardial heart valves.

There is a strong relationship between mechanical stress and calcification in biological prosthetic heart valves. A dynamic in vitro calcification test has been used to study the relationship between stress distributions in the leaflets of bovine pericardial valves and the deposition of calcium over the leaflet surfaces. Intuitive stress regions have been defined over the leaflet surfaces. Calcium uptake by the leaflets has been assayed directly by ashing of leaflet material and analysis of the ash by atomic absorption spectrophotometry. Calcium and phosphorus distribution over the leaflet surface has been analyzed using energy-dispersive x-ray analysis by scanning electron microscope and data points assigned to the appropriate stress region. The uptake of calcium is assessed by comparing stress regions, surfaces, and the degree of calcification of the valve. Differences between stress regions and surfaces are significant. Uptake of calcium in these valves appears to be strongly related to the degree and type of stress present in the valve leaflets.

Bioprosthesis↗
PubMed1992

Development of a digital adaptive control system for PO2 regulation in a membrane oxygenator.

Regulation of gas exchange in artificial lungs (oxygenators) during cardiopulmonary bypass is normally achieved by manual control of the gas composition and flow in response to intermittent sampling of the arterial partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2). Manual control often results in abnormal blood gases which have been implicated in patient morbidity as well as influencing perfusion safety. Fine control of PaO2 and PaCO2 may be achieved by a combination of an in-line blood gas monitoring system and a membrane type oxygenator which is automatically regulated. The overall dynamics of the oxygenation process and control system components are complex and have nonlinear, multivariable and time-varying characteristics. Consequently, an adaptive control system approach is necessary. The implementation of a digital self-tuning control regime for PaO2 is described here. The controller is based on an explicit Linear Quadratic Gaussian (LQG) self-tuning control design which is presented using a polynomial equation approach. The controller performance was investigated in in vitro experiments. The self-tuner performed satisfactorily with various sensor/oxygenator combinations for blood flow and temperature load disturbances. In contrast, a nonadaptive (proportional-integral, PI) type of control system was found to be unsuitable.

Carbon Dioxide↗
PubMed1992

Chemical modification of bovine pericardium and its effect on calcification in the rat subdermal model.

Specific modification of functional groups in collagen has been used to investigate their influence on calcification and thermal stability of bovine pericardium. Pretreatment of pericardium with iron (III) citrate reduced calcification in the rat subcutaneous implant model, as did acyl azide activation of carboxyl and amide groups. Chondroitin sulphate had no significant effect, while cyanamide treatment was mainly effective in combination with iron (III) citrate. Glutaraldehyde pretreatment restricted reaction with other modifying agents, but, as a post-fixation treatment, improved the thermal stability of other agents. Glutaraldehyde post-fixation had no significant relationship to the calcification rate.

Animals↗
PubMed1992

Calcification modelling in artificial heart valves.

This study has examined a range of methods of studying the calcification process in bovine pericardial and polyurethane biomaterials. The calcification methods include static and dynamic, in vitro and in vivo tests. The analytical methods include measurement of depletion rates of calcium and phosphate from in vitro calcifying solutions, analysis of tissue contents of calcium, histological staining of tissue sections for calcium, X-ray elemental analysis, by scanning electron microscopy, of calcium and phosphorus distributions over valve leaflets calcified in vitro under dynamic conditions. Bovine pericardium, in all test settings, calcified to a much greater degree than polyurethane biomaterials. Polyurethane extracts calcified to a greater degree than bulk polyurethanes. The test protocol used allows progress through increasingly demanding calcification tests, with the possibility of eliminating unsuitable materials with tests of limited complexity and expense.

Animals↗
PubMed1991

An automatic matching technique for patient alignment.

An automatic system of patient alignment is required in order to monitor changes that occur in the period between magnetic resonance scans. For each scan of the patient a prime requisite is to register the images with respect to each other. The orthogonal relationship between the sagittal and transverse images should, in principle, identify a single common line at the intersection of the two image planes. The basis of the comparison requires spatial registration of the two images to correct for the probable translational and rotational tilts as well as for the geometrical and intensity distortions. This paper describes a number of automatic techniques which compare, pixel-by-pixel, first two synthetic images, and then their application to real images obtained separately from the same head and neck object field. The robustness, computational cost and effectiveness of the techniques presented are discussed, and computed results on real data for the most promising technique based on the Ratio Absolute Difference algorithm are presented.

Algorithms↗
PubMed1991

Nonparametric tests for interaction and group differences in a two-way layout.

Nonparametric tests of group differences and interaction across strata are developed in which the null hypotheses for these tests are expressed as functions of rho i = P(X > Y) + 1/2P(X = Y), where X refers to a random observation from one group and Y refers to a random observation from the other group within stratum i. The estimator r of the parameter rho is shown to be a useful way to summarize and examine data for ordinal and continuous data.

Drug Therapy↗
PubMed1990

Patient realignment in magnetic resonance imaging of the head: an algorithm using mathematical morphology for feature extraction.

To develop a technique for automatic patient realignment in magnetic resonance imaging (MRI), it is essential to extract key features automatically from the various slices of the head as accurately as possible. Such features include the brain, the brain stem, the pons, the corpus callosum and the cerebellum. A feature extraction algorithm has been developed which is based on thresholding a region to a common grey level and then applying mathematical morphology to produce a binary regular region. In addition, a region-filling algorithm has been developed to obtain the complete feature. The scans derived from the T1 spin-lattice relaxation time, which are the fastest of the MRI scans, are used in patient realignment to provide highly textured images. These are difficult to segment using conventional thresholding or edge enhancement techniques due to their 'grainy' appearance, which makes it difficult to isolate key features from the other components found in the slice. We have developed a method for the accurate extraction of the corpus callosum, the cerebellum and the brain area in a sagittal scan of the head. This is carried out by selective thresholding designed to remove the low texture content and then applying morphological techniques.

Algorithms↗
PubMed1990

Adherence to sports injury rehabilitation programmes.

Many studies have shown that low adherence is a common problem in treatment programmes. Adherence to sports injury rehabilitation is dependent on the personality characteristics of athletes operating in conjunction with particular aspects of their rehabilitation settings and the quality of interactions developed between athletes and their therapists. Any attempt to view treatment adherence as a unitary construct is doomed to fail; a complex construct demands a multidimensional outlook. Taking into account the challenges that injured athletes face during their rehabilitation, strategies can be designed to promote adherence. Self-confidence is the key to enhanced rehabilitation adherence, and the strategies are organised within that framework. Competence strategies include education, treatment efficacy, tailoring, and relapse prevention training. Control strategies include dissociation, self-monitoring, decision-balance sheet, and pain deconditioning. Commitment strategies include shaping, contracting, threats, goal-setting, and social support. Because of the dearth of empirical data on the specific issue of adherence to sports injury rehabilitation programmes, it is necessary to extrapolate from various other areas of treatment adherence (e.g. cardiac rehabilitation). Treatment dropout does not seem to be inevitable, but is in fact preventable. The task for the sports medicine professional is to recognise and acknowledge the salient features of their clients and the rehabilitation demands on them and then to utilise various strategies to enhance the likelihood of treatment adherence.

Athletic Injuries↗
PubMed1989

Human whole-blood granulocyte aggregation in vitro.

1. Aggregation assays are a commonly used technique for the study of granulocyte activation. These studies are usually performed using a pure cell suspension in buffer. This necessitates a separation procedure which is time-consuming and may modify the function of the cells. Interaction between different cell types is precluded. 2. To avoid these disadvantages a method was developed which quantifies granulocyte aggregation in whole blood. Samples drawn from an incubated vessel before and after the addition of a chemotactic stimulus were fixed with formaldehyde to prevent disaggregation. Erythrocytes were then removed by chemical lysis and using an electronic cell-sizing device the number of single cells and aggregates could then be easily measured. 3. Results from a group of volunteers showed a rapid and reversible response to a chemotactic tripeptide, with a fall in single granulocyte count and the appearance of doublets and triplets. Lymphocytes were unaffected. Intra-assay reproducibility was better than +/- 5%. 4. Using this assay, a significant elevation in aggregability was observed in blood from patients after acute myocardial infarction. 5. This novel technique, by avoiding the separation step, is faster, simpler and more physiological than previous methods, and as such is useful for both assays of drug action in vitro and the study of cell activation in disease states.

Adult↗