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Biomedical subjects

D Taylor

Publications and source records attributed to D Taylor.

At least 37 records · Page 2Linked to original sources
PubMed2004

A history of the optic nerve and its diseases.

We will trace the history of ideas about optic nerve anatomy and function in the Western world from the ancient Greeks to the early 20th century and show how these influenced causal theories of optic nerve diseases. Greek and Roman humoral physiology needed a hollow optic nerve, the obstruction of which prevented the flow of visual spirit to and from the brain and resulted in blindness. Medieval physicians understood that the presence of a fixed dilated pupil indicated optic nerve obstruction, preventing the passage of visual spirit, and that cataract surgery in such cases would not restore sight. During the Renaissance, the organ of vision was transferred from the lens to the optic nerve, which was generally believed to be on the axis of the eye. The acuity of central vision (at the optic disc) was explained by the concentration of visual spirit where the optic nerve met the retina. The growth of anatomy and influence of mechanical philosophy from the 17th century led to visual spirit being replaced with the concept of nerve force, which later became associated with electricity travelling along nerve fibres. This coincided with discourse about the nature of the nervous system and a shift in orientation from understanding illness holistically in terms of an individual's humoral imbalance to the concept of organ-based diseases. Both the microscope and the ophthalmoscope allowed visualisation of the optic nerve, but problems of interpretation persisted until conceptual transformations in medical science were made.

Greek World↗
PubMed2004

Interferon-alpha-2b and oral cytarabine ocfosfate for newly diagnosed chronic myeloid leukaemia.

BACKGROUND: Treatment with interferon and subcutaneous cytarabine produces superior cytogenetic responses in chronic myeloid leukaemia (CML) than treatment with interferon alone, but at the expense of greater toxicity. Cytarabine ocfosfate (YNK01) is an oral precursor of cytarabine that may overcome some of the inconvenience and toxicities associated with subcutaneous cytarabine administration. PATIENTS AND METHODS: We studied the efficacy and tolerability of combination therapy with interferon-alpha-2b and YNK01 in patients with newly diagnosed, untreated CML. Forty patients were treated with interferon-alpha-2b (5 MU/m2/day) plus monthly courses of YNK01 (600 mg/day for 10 days) for 1 year. RESULTS: The 6-month complete haematological response rate was 63% and the 1-year major cytogenetic response rate was 30%, with 10% of cytogenetic responses being complete. With a median follow-up of 57 months, the estimated 5-year overall survival was 86% (95% confidence interval 70% to 94%). Treatment tolerability was poor, with toxicity leading to discontinuation of one or both drugs in 60% of cases. The median daily dose of interferon alpha-2b was 7.75 MU and the median dose of YNK01 was 600 mg/day for each 10-day treatment cycle. CONCLUSIONS: Interferon-alpha-2b and YNK01 produce cytogenetic responses comparable to those achieved with interferon-alpha-2b and parenteral cytarabine, although toxicity was excessive. Alternate dosing strategies may enhance the tolerability of YNK01.

Administration, Oral↗
PubMed2004

A dynamic clinical dental relational database.

The traditional approach to relational database design is based on the logical organization of data into a number of related normalized tables. One assumption is that the nature and structure of the data is known at the design stage. In the case of designing a relational database to store historical dental epidemiological data from individual clinical surveys, the structure of the data is not known until the data is presented for inclusion into the database. This paper addresses the issues concerned with the theoretical design of a clinical dynamic database capable of adapting the internal table structure to accommodate clinical survey data, and presents a prototype database application capable of processing, displaying, and querying the dental data.

Database Management Systems↗
PubMed2004

Obesity, dyslipidaemias and smoking in an inpatient population treated with antipsychotic drugs.

OBJECTIVE: The prevalence of cardiovascular disease in people with schizophrenia is known to be above population norms. In addition, many antipsychotic drugs have been associated with weight gain and some with dyslipidaemia. Our aims were to determine the apparent and actual prevalence of the modifiable risk factors for cardiovascular disease: obesity, hyperlipidaemia and smoking, in hospitalized patients treated with antipsychotic drugs. METHOD: (i) Survey of clinical notes. (ii) Direct measurement of fasting lipids, body mass index and waist : hip ratio. RESULTS: Lipids were rarely monitored and body weight often not recorded making the apparent prevalence of these cardiovascular risk factors low. Smoking status was recorded. When directly measured, the actual prevalence of obesity was above population norms and two-thirds of patients had a dyslipidaemia. CONCLUSION: Routine screening for these modifiable risk factors followed by active intervention where appropriate could significantly reduce morbidity and mortality in this patient group.

Adolescent↗
PubMed2004

Is early surgery for congenital cataract a risk factor for glaucoma?

AIMS: To estimate the risk of aphakic glaucoma after lensectomy for congenital cataract and its association with surgery within the first month of life. METHOD: A retrospective case notes review was conducted of all patients who had lensectomy for congenital cataract during their first year of life at Great Ormond Street Hospital between 1994 and 1997. Patients with pre-existing glaucoma, anterior segment dysgenesis, and Lowe syndrome were excluded. The risk of aphakic glaucoma after surgery was estimated using Kaplan-Meier survival analysis. RESULTS: 80 patients, undergoing 128 lensectomies were eligible. Of these, six patients (nine eyes) were lost to follow up. Based on eye count, the risk of glaucoma by 5 years after lensectomy was 15.6% (95% CI 10.2 to 23.4). Based on patient count, the 5 year risk of glaucoma in at least one eye following bilateral surgery was 25.1% (95% CI 15.1 to 40.0). The incidence of glaucoma remained at a constant level for the first 5 years after surgery. After early bilateral lensectomy, within the first month of life, the 5 year risk of glaucoma in at least one eye was 50% (95% CI 27.8 to 77.1) compared to 14.9% (95% CI 6.5 to 32.1) with surgery performed later (log rank test, p = 0.012). There was no significant difference (Kolmogorov-Smirnov test: unilateral lensectomy p = 0.587, bilateral lensectomy p = 0.369) in 5 year visual outcomes between eyes operated before and after 1 month of age. CONCLUSION: Bilateral lensectomy during the first month of life is associated with a higher risk of subsequent glaucoma than with surgery performed later. The reason for this is unclear but it may be prudent, in bilateral cases, to consider delaying surgery until the infant is 4 weeks old. As the incidence of glaucoma is similar for each year after surgery, long term glaucoma surveillance is mandatory.

Age Factors↗
PubMed2003

The cellular transducer in damage-stimulated bone remodelling: a theoretical investigation using fracture mechanics.

This paper reports on some theoretical work which used fracture mechanics concepts to draw conclusions about the nature of the so-called 'cellular transducer': the means by which bone cells detect the presence of damage and thus initiate remodelling and adaptation activities. Using analytical and numerical methods, we estimated the strains and displacements around cracks of the typical size, shape and orientation that normally occur in compact bone. We predicted that it is not possible for osteocytes or their processes to be fractured as a result of direct tensile strains, because the strains generated are much less than the expected failure strains of cellular material. We proposed a new failure mechanism by which osteocyte processes spanning the crack are cut by shearing motions between the crack faces. We predicted that failures of this type can occur. Failures begin to occur if crack lengths become greater than normal (100 microm), so this could act as a signal to initiate repair processes for individual cracks. Very large numbers of cell processes (greater than 1000) will fail if the crack length and/or applied stress reach dangerous levels (300 microm and 60 Mpa, respectively) at which point bone deposition may be required to prevent stress fractures. Similar results also occurred if we proposed a different mechanism of damage detection, involving cells' ability to detect the high levels of strain that occur near crack tips. This work, though based on theoretical mechanics considerations, suggests some biological experiments which might confirm our findings.

Bone Remodeling↗
PubMed2003

Morphological studies on the extracellular structure of the midgut of a tick, Haemaphysalis longicornis (Acari: Ixodidae).

In the present study, morphological observations on the extracellular structures found on the apical surface of the midgut epithelium, known as the peritrophic membrane (PM) or glycocalyx, are described in Haemaphysalis longicornis females and larvae. These structures have been hypothesized to provide protection to the microvilli of epithelial cells of the digestive tract. Our aim was to determine whether the extracellular structures are important in the digestion of the blood meal and/or as a protection against infection or injury. The PM was detectable in the midgut of engorged larvae by electron microscopy, but not in engorged females. However, a PM-like structure, stainable with toluidine blue, was observed in females by light microscopy. From the results of confocal laser scanning and electron microscopic observations with wheat germ agglutinin (WGA lectin) staining for chitin of the PM, however, the structure was clearly recognized. The structure in the female is likely to be PM because staining with WGA lectin in the presence of GlcNAc indicates the presence of chitin and various morphologies of PM have been reported in insects and ticks. These results show morphologically that different types of PM-like structure are formed in larvae and females of H. longicornis.

Animals↗
PubMed2003

Multicriteria optimization of gluconic acid production using net flow.

The biochemical process industry is often confronted with the challenge of making decisions in an atmosphere of multiple and conflicting objectives. Recent innovations in the field of operations research and systems science have yielded rigorous multicriteria optimization techniques that can be successfully applied to the field of biochemical engineering. These techniques incorporate the expert's experience into the optimization routine and provide valuable information about the zone of possible solutions. This paper presents a multicriteria optimization strategy that generates a Pareto domain, given a set of conflicting objective criteria, and determines the optimal operating region for the production of gluconic acid using the net flow method (NFM). The objective criteria include maximizing the productivity and concentration of gluconic acid, while minimizing the residual substrate. Three optimization strategies are considered. The first two strategies identify the optimal operating region for the process inputs. The results yielded an acceptable compromise between productivity, gluconic acid concentration and residual substrate concentration. Fixing the process inputs representing the batch time, initial substrate concentration and initial biomass equal to their optimal values, the remaining simulations were used to study the sensitivity of the optimum operating region to changes in the oxygen mass transfer coefficient, K(L) a, by utilizing a multi-level K(L) a strategy. The results show that controlling K(L) a during the reaction reduced the production of biomass, which in turn resulted in increased productivity and concentration of gluconic acid above that of a fixed K(L) a.

Journal Article↗
PubMed2003

The fatigue strength of compact bone in torsion.

We have conducted a series of fatigue tests on samples of bovine compact bone loaded in cyclic torsion. The fatigue strength (i.e. the range of stress needed to cause failure in a given number of cycles) was found to be lower than the fatigue strength of the same material in compression by more than a factor of two. We also tested intact chicken metatarsals and found a similar reduction in strength compared to compression testing of chicken tibiae. These results were predicted using a theoretical model in which fatigue failure was assumed to be dependent on the growth of microcracks, oriented approximately parallel to the bone's longitudinal axis but having misorientation angles of up to 30 degrees. An effective stress range was derived which is a function of the normal and shear stresses, and thus of the Mode I and Mode II stress intensities experienced by the crack. These results may have important consequences for the understanding of fatigue in bone in vivo; relatively small amounts of longitudinal shear stress, which are often ignored in analysis, may contribute significantly to fatigue failures. This may shed light on the phenomenon of stress fractures and on the need for repair and adaptation in living bone.

Animals↗
PubMed2003

Dynamic and static tests of balance and postural sway in boys: effects of previous wrist bone fractures and high adiposity.

Ninety-three males aged 10-21 years undertook the Bruininks-Oseretsky balance test and two computerized posturography tests to evaluate the effects of (a) previous forearm fracture and (b) high body weight on balance and postural sway. Body composition was measured by dual energy X-ray absorptiometry. Fracture history did not affect balance measures. However, Bruininks-Oseretsky balance scores were negatively correlated with body weight, body mass index, percentage fat and total fat mass. Overweight subjects (n=25) had lower scores (P<0.05) than boys of healthy weight (n=47), supporting the view that overweight adolescents have poorer balance than those of healthy weight.

Absorptiometry, Photon↗
PubMed2003

Behavioural management of antipsychotic-induced weight gain: a review.

OBJECTIVE: Although psychiatrists are aware of weight gain induced by atypical antipsychotics, only few studies on behavioural interventions in this patient group are published. This review aims to summarize the evidence on effectiveness of behavioural interventions for weight gain in the general population and in-patients treated with atypical antipsychotics. METHOD: Medline and Cochrane databases search for evidence on effectiveness of behavioural interventions. RESULTS: In general, behavioural approaches including, diet, exercise and drug treatments may be effective. There were only 13 studies of behavioural interventions for patients taking antipsychotic medication. No study met the criteria for a RCT. Calorie restriction in a controlled ward environment, structured counselling combined with cognitive behavioural therapy and counselling on life style and provision of rewards may potentially lead to weight loss. CONCLUSION: Currently only limited, methodologically flawed, evidence is available that behavioural interventions in overweight patients treated with antipsychotics, although intuitively appealing, actually work.

Antipsychotic Agents↗
PubMed2003

Microdamage and mechanical behaviour: predicting failure and remodelling in compact bone.

This paper reports on the development of a theoretical model to simulate the growth and repair of microdamage in bone. Unlike previous theories, which use simplified descriptions of damage, this approach models each individual microcrack explicitly, and also models the basic multicellular units (BMUs) that repair cracks. A computer simulation has been developed that is capable of making a variety of predictions. Firstly, we can predict the mechanical behaviour of dead bone in laboratory experiments, including estimates of the number of cycles to failure and the number and length of microcracks during fatigue tests. Secondly, we can predict the results of bone histomorphometry, including such parameters as BMU activation rates and the changing ratio of primary to secondary bone during ageing. Thirdly, we can predict the occurrence of stress fractures in living bone: these occur when the severity of loading is so great that cracks grow faster than they can be repaired. Finally, we can predict the phenomenon of adaptation, in which bone is deposited to increase cortical thickness and thus prevent stress fractures. In all cases results compare favourably with experimental and clinical data.

Adaptation, Physiological↗
PubMed2003

Detecting microdamage in bone.

Fatigue-induced microdamage in bone contributes to stress and fragility fractures and acts as a stimulus for bone remodelling. Detecting such microdamage is difficult as pre-existing microdamage sustained in vivo must be differentiated from artefactual damage incurred during specimen preparation. This was addressed by bulk staining specimens in alcohol-soluble basic fuchsin dye, but cutting and grinding them in an aqueous medium. Nonetheless, some artefactual cracks are partially stained and careful observation under transmitted light, or epifluorescence microscopy, is required. Fuchsin lodges in cracks, but is not site-specific. Cracks are discontinuities in the calcium-rich bone matrix and chelating agents, which bind calcium, can selectively label them. Oxytetracycline, alizarin complexone, calcein, calcein blue and xylenol orange all selectively bind microcracks and, as they fluoresce at different wavelengths and colours, can be used in sequence to label microcrack growth. New agents that only fluoresce when involved in a chelate are currently being developed--fluorescent photoinduced electron transfer (PET) sensors. Such agents enable microdamage to be quantified and crack growth to be measured and are useful histological tools in providing data for modelling the material behaviour of bone. However, a non-invasive method is needed to measure microdamage in patients. Micro-CT is being studied and initial work with iodine dyes linked to a chelating group has shown some promise. In the long term, it is hoped that repeated measurements can be made at critical sites and microdamage accumulation monitored. Quantification of microdamage, together with bone mass measurements, will help in predicting and preventing bone fracture failure in patients with osteoporosis.

Animals↗