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Biomedical subjects

K Davey

Publications and source records attributed to K Davey.

13 recordsLinked to original sources
PubMed2000

Magnetic stimulation coil and circuit design.

A detailed analysis of the membrane voltage rise commensurate with the electrical charging circuit of a typical magnetic stimulator is presented. The analysis shows how the membrane voltage is linked to the energy, reluctance, and resonant frequency of the electrical charging circuit. There is an optimum resonant frequency for any nerve membrane depending on its capacitive time constant. The analysis also shows why a larger membrane voltage will be registered on the second phase of a biphasic pulse excitation [1]. Typical constraints on three key quantities voltage, current, and silicone controlled rectifier (SCR) switching time dictate key components such as capacitance, inductance, and choice of turns.

Biomedical Engineering↗
PubMed1999

Changes as the result of ageing in extraocular muscles: a post-mortem study.

BACKGROUND: Extraocular muscles differ from typical skeletal muscle in many respects such as smaller fibre size, high mitochondrial content, unusual contractile/innervation patterns and highly developed microvascular bed. Changes in typical skeletal muscle with ageing have been well documented yet the reports on ageing changes in extraocular muscles is limited. The aim of this study was to examine these changes. METHODS: The right inferior and medial rectus muscles were removed at post-mortem from patients with no history of prior ocular or neuromuscular disease. These included 25 patients aged between 23 and 88 years (14 male, 11 female). The median age of the patients was 69 years and 72% of patients were aged older than 66 years. The median post-mortem interval was 28 h, RESULTS: In young adults between 20 and 30 years of age, the muscle fibres were regular, of fairly uniform size with minimal endomysial connective tissue and no lipofuscin was detected in fibres. In adults between 40 and 50 years of age, a small amount of subsarcolemmal lipofuscin was detected. Between 50 and 60 years of age, a few fibres with reduced density of myofibrils were noted. All patients over 65 years had definite changes of ageing and those between 70 and 80 years of age showed similar features to those between 60 and 80 years of age. These changes included variation in fibre size, increased endomysial fibrous tissue and increased endomysial adipose tissue, and loss of myofibrils with some fibres devoid of fibrils and comprising 'bags' of mitochondria. There was increased lipofuscin in a number of fibres, increased 'degenerative' changes such as vacuolation of fibres, scattered 'eosinophilic intracytoplasmic bodies' and increased numbers of 'ringbinden'.

Adult↗
PubMed1998

The Heimann-Bielscholwsky phenomenon: dissociated vertical nystagmus.

BACKGROUND: The Heimann-Bielschowsky phenomenon (HBP) is a unilateral vertical nystagmus with coarse, slow pendular movements that typically occurs in an eye with profound visual loss. There are no sinister neurological implications. METHODS: Symptoms and signs on presentation and the subsequent course are described in detail in 10 patients. Eye movements were recorded for one patient. RESULTS: Three patients had corrected vision of 6/24 or better. Strabismus was seen in eight patients. Symptoms of diplopia and oscillopsia were infrequent. CONCLUSIONS: We believe that the HBP may be a reasonably common condition, although very under diagnosed. This condition may be similar to Central Fusion Disruption. Patients with HBP appear to have lost the potential for fusion.

Adolescent↗
PubMed1997

Effect of acute pentoxifylline treatment in an experimental model of colitis.

BACKGROUND: The effect of acute pentoxifylline treatment in an experimental model of colitis was assessed using the trinitrobenzene sulphonic acid (TNBS)-induced rat model of colitis. METHODS: Animals were treated with intracolonic injection (250 microliters) of TNBS (50 mg in 50% ethanol) to induce inflammation and ulcers. Animals received pentoxifilline (100 mg/kg intracolonically) or saline 24 and 48 h following TNBS treatment. Five days following TNBS treatment, colons were dissected and scored according to the morphology damage score. The colons were then rolled longitudinally, fixed in formalin and embedded in paraffin. The collagen content of colonic sections were determined by a Sirius red-Fast green technique. RESULTS: Animals treated with TNBS alone had significantly higher gross morphology damage scores compared to animals treated with saline. Pentoxifylline significantly reduced the gross morphology damage score in animals receiving TNBS. Colonic collagen levels were significantly elevated in TNBS-treated animals compared to animals receiving saline. Pentoxifylline treatment did not alter the collagen content of colons from TNBS-treated animals. CONCLUSION: TNBS treatment significantly elevates morphology damage score compared to controls. The results also suggest that colonic collagen was significantly elevated in animals treated with TNBS compared to controls. Pentoxifylline treatment was not sufficient to reduce the elevation in colonic collagen, although pentoxifylline treatment was sufficient to reduce the pathological changes due to TNBS, thus bringing the morphology damage score down to control levels.

Animals↗
PubMed1995

The feeding stimulus in Rhodnius prolixus is transmitted to the brain by a humoral factor

Neurosecretory cells in the brain of Rhodnius prolixus are known to be the source of an ovulation hormone released at feeding. They were selected to test the hypothesis that feeding brings about the release of another hormone in the abdomen which is transported forward to activate the neuroendocrine axis in the brain, and that severing the aorta interferes with this transport. These cells have previously been shown to exhibit an increase in action potential frequency at the time of release of their hormone. In normal females, the spike frequency of the cells increased after feeding and remained high over at least the next 24 h. In females with the dorsal vessel severed, the spike frequency remained low, at levels near those of unfed females, except for a transitory increase 4 h after feeding. The spike frequency of the neurosecretory cells in females with the dorsal vessel severed increased when hemolymph from fed normal females or from those with their dorsal vessel severed was placed directly on the brains of the test females. Hemolymph taken from unfed females did not produce this response. The activity in the hemolymph was heat-stable and disappeared after pronase or trypsin digestion. Similar activity was present in the fused thoracico-abdominal ganglionic mass, but absent from fore-, mid- and hindgut and from the abdominal neurosecretory organs.

Journal Article↗
PubMed1994

Toward functional magnetic stimulation (FMS) theory and experiment.

This paper examines the use of magnetic fields to functionally stimulate peripheral nerves. All electric fields are induced via a changing magnetic field whose flux is entirely confined within a closed magnetic circuit. Induced electric fields are simulated using a nonlinear boundary element solver. The induced fields are solved using duality theory. The accuracy of these predictions is verified by saline bath experiments. Next, the theory is applied to the stimulation of nerves using small, partially occluded ferrite and laminated vanadium permendur cores. Experiments demonstrate the successful stimulation of peripheral nerves in the African bullfrog with 11 mA, 153 mV excitations. These results offer a new vista of possibilities in the area of functional nerve stimulation. Unlike functional electric stimulation (FES), FMS does not involve any half cell reactions, and thus would not have the commensurate FES restrictions regarding balanced biphasic stimulation, strength duration balances, and oxidation issues, always exercising care that the electrodes remain in the reversible operating regime.

Action Potentials↗
PubMed1993

Is post-cataract mydriasis necessary?

We report the results of a randomised prospective trial of post-operative cyclopentolate in patients who had uncomplicated endocapsular cataract extraction. We found no significant difference in visual acuity, intraocular lens centration or pupil area achieved after dilatation with tropicamide. There was a marked increase in the incidence of posterior synechiae in the group receiving cyclopentolate (33% vs. 13%).

Aged↗
PubMed1992

A method for assessing the accuracy of surgical technique in the correction of astigmatism.

Surgical results can be assessed as a function of what was aimed for, what was done, and what was achieved. One of the aims of refractive surgery is to reduce astigmatism; the smaller the postoperative astigmatism the better the result. Determination of what was done--that is, the surgical effect, can be calculated from the preoperative and postoperative astigmatism. A simplified formulation is described which facilitates the calculation (magnitude and direction) of this surgical effect. In addition, an expression for surgical accuracy is described, as a function of what was aimed for and what was achieved.

Astigmatism↗
PubMed1988

Microcomputer analyses of clinical ERG, EOG, and other tests of retinal function.

The electroretinogram (ERG) and electro-oculogram (EOG) are two of the most frequently used visual electrodiagnostic tests of retinal function. The ERG and EOG are easily measured, but there are many engineering difficulties in processing their signal data because the response amplitudes are relatively small, and the relevant signals are buried in electromagnetic and biologic noise. These tests tend to be time consuming, so they lend themselves to automatic control. This article describes the engineering designs relative to a microprocessor-based electrophysiologic laboratory at Emory University Clinic to perform ERG, EOG, and other clinical tests of retinal function. A comparable system that offered both the ability to accept data from a variety of transducers and the flexibility to permit all of the planned testing protocols was not available from any commercial source.

Computers↗
PubMed1986

Chronic polyarticular gout in the elderly: a report of six cases.

This report describes six elderly patients with previously undiagnosed and untreated chronic polyarticular gout, five of whom were seen at a Geriatric Rehabilitation and Assessment Unit within a 3-month period. All were on long-term diuretic therapy. Four patients had coexisting osteoarthritis. Three patients were unable to recall any prior history of attacks of acute arthritis and four patients were significantly disabled from gout. Chronic polyarticular gout in these patients was previously misdiagnosed and inadequately treated, resulting in otherwise preventable disability.

Aged↗
PubMed1985

Hydrogen sulphide poisoning: associated with pelt processing.

Four cases of poisoning with hydrogen sulphide (H2S) were admitted to Ashburton Hospital within a period of one week following accidental exposure to H2S at a freezing works. We review the clinical presentation of these four cases, their management, follow up and the circumstances which led to their accidental exposure.

Accidents, Occupational↗
PubMed1975

Cardiac lesions in rats fed rapeseed oils.

Fully refined rapeseed oils containing different amounts of erucic acid (1.6%, 4.3% and 22.3%) were fed, at 20% by weight of diet, to weanling male and female Sprague-Dawley rats for periods up to 112 days. Transient myocardial lipidosis characterized by accumulation of fat droplets in myocardial fibers was marked in male and female rats fed oxidized and unoxidized rapeseed oil containing 22.3% erucic acid, moderate with rapeseed oil containing 4.3% erucic acid and very slight in rats fed rapeseed oil containing 1.6% erucic acid. Peak intensity of myocardial lipidosis occurred at three to seven days and regressed thereafter. Focal myocardial necrosis and fibrosis occurred in male rats fed rapeseed oils containing different levels of erucic acid for 112 days. The incidence of myocardial necrosis and fibrosis was markedly lower in female rats, and the incidence of these lesions in either sex was not affected by the state of oxidation of these oils. In a second experiment, male rats were fed diets containing crude, partially refined or fully refined rapeseed oils. There was no correlation between the number of foci of myocardial necrosis and fibrosis and the state of refinement of the oils, but there were generally fewer lesions in rats fed those oils having the lowest levels of erucic acid.

Animals↗