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Biomedical subjects

G M Clark

Publications and source records attributed to G M Clark.

At least 523 records · Page 29Linked to original sources
PubMed1978

Sources of potential residue problems in dairy herds.

Drugs and chemicals provide economic benefit to animal and crop production; to derive this benefit they must be used appropriately. Data from the United States Department of Agriculture, Food Safety and Quality Service residue monitoring program indicates certain drugs and chemicals are not being used appropriately by the dairy industry, and residues are occurring in cow carcasses at slaughter. Residues of antibiotics and certain pesticides which are administered intentionally are being found. Dairy cows are also particularly susceptible to inadvertant exposure to chemicals because of certain management practices and physiologic characteristics of dairy cows. Contamination of Michigan dairy cows with polybrominated biphenyls is an example. Methods of controlling both intentional and unintentional exposure of cows to drugs and chemicals will require considerable involvement of producers.

Animals↗
PubMed1977

A multiple-electrode hearing prosthesis for cochlea implantation in deaf patients.

A multiple-electrode hearing prosthesis for cochlea implantation in deaf patients has been developed at the University of Melbourne. It has been designed as a multiple-electrode implant to provide the best chance of enabling patients to understand speech. It has been shown that an electrode array can be threaded along the coills of the inner ear close to residual auditory nerves. Experimental studies have indicated that the long-term implantation of the array will not lead to significant degeneration of auditory nerve fibres. Loss of platinum from the stimulating electrodes can be minimized with a biphasic constant current pulse, where the first phase is negative with respect to ground. The receiver-stimulator component has also been designed to provide 10-15 channels of stimulation. Furthermore, the phase and amplitude of the stimuli to individual electrodes can be varied to enable the localization of the electrical fields to discrete groups of nerve fibres, and the correct method of frequency and intensity coding to be determined. Finally, the device should be used in the first instance for a specially selected group of adults who are post-lingually deaf.

Animals↗
PubMed1977

Changing distribution of primary cancers in the large bowel.

Analysis of the changing distribution of origin site of 1,990 colorectal cancers observed at a large midwestern hospital shows a statistically significant trend of a decreasing percentage of distal (rectum, P=.0192) and an increasing percentage of proximal (cecum, P=.0015) large-bowel lesions during a period of at least 30 years. Mortality data for 11,635 colorectal cancers in the state of Kansas for this period confirm this trend (P less than .0001). The respective decrease and increase may well be the result of more than one factor. Results of digital examination of the rectum and sigmoidoscopy are less likely to diagnose large-bowel cancer as they did 30 years ago. Stool screening for occult blood, barium enema roentgenographic examination, and colonoscopy become more important diagnostic tools in light of this trend.

Colonic Neoplasms↗
PubMed1977

The clinical assessment of cochlear implant patients.

This study outlines the clinical assessment procedures adopted in the Department of Otolaryngology at the University of Melbourne for patients being considered for a cochlear implant. As the procedure is new and requires rigorous evaluation, it is considered preferable only to operate on a limited number of patients, and ensure that they have a thorough evaluation both before and after surgery. This should be carried out by a team whose members have experience in otology, audiology, aural rehabilitation, acoustics and psychology. The indications and contraindications for surgery are also outlined.

Audiometry↗
PubMed1977

A multiple electrode cochlear implant.

The University of Melbourne Departments of Otolaryngology and Electrical Engineering (UMDOLEE) receiving and stimulating component of a multiple-electrode cochlear implant hearing prosthesis produces constant stimulation. It has a stimulating pulse shape that minimizes the production of toxic substances and loss of metal from the electrodes, and this is achieved with a biphasic rectangular waveform where the first phase is negative with respect to ground. The duration of each stimulus phase in 180 msec, which is long enough to allow low levels of current stimulation, and short enough to permit rates of 1000 pulses/second to be achieved. In order to be consistent with our present understanding of the perception of pitch, the device permits the independent stimulation of a number of electrodes. Furthermore, to electrically isolate the stimulus to small areas, there is the capacity to vary the current and set the threshold independently at individual electrodes. The phase and amplitude of the pulses to neighbouring electrodes with also be varied to assist in localizing the current flow. The pattern to stimulation to individual or groups of electrodes can also be altered to enable studies to be carried out to determine ways of conveying frequency and intensity information over a more normal dynamic range.

Animals↗
PubMed1977

The association between fasting hyperbilirubinaemia and serum non-esterified fatty acids in man.

1. The concentrations of plasma total and unconjugated bilirubin and of serum nonesterified fatty acids (NEFA) have been measured in two healthy subjects during fasts of up to 21 h. 2. Fasting was either continuous or interrupted by various procedures that altered the concentrations of NEFA and total bilirubin. 3. When NEFA concentrations were increased by the administration of noradrenaline, heparin or caffeine, bilirubin concentrations also rose. 4. When NEFA concentrations were lowered by insulin, bilirubin concentrations fell. 5. Meals of 3-138 kJ and more, taken during the fasting period, lowered total bilirubin and NEFA concentrations in both subjects, whereas the effects of smaller meals were less consistent. 6. These studies demonstrate a statistically significant correlation between total bilirubin and NEFA during uninterrupted fasting and an association between these variables under other experimental conditions. They suggest that the control of bilirubin concentrations in the blood is linked to lipid metabolism.

Bilirubin↗
PubMed1977

An evaluation of per-scalar cochlear electrode implantation techniques. An histopathological study in cats.

This study was carried out to evaluate the effects of infection and trauma on the organ of Corti and spiral ganglion cells following per-scalar cochlear electrode implantations in cats. The results showed that the incidence of infection with a per-scalar electrode inserted through an opening made directly into the apical and middle turns is low, provided the procedure is carried out aseptically with an antibiotic cover. Trauma could also be kept to a minimum by inserting the electrode into the scala tympani, taking care to insert the electrode without applying force, and ensuring that the first insertion is the only one. Furthermore, the tip of the electrode should be blunt, and its diameter smaller than the width of the scala tympani. It was noted that damage to the organ of Corti, and loss of spiral ganglion cells only occurred as a local phenomenon, and its extent was related to the severity of the damage to the Reissner's and basilar membranes. The insertion of an electrode through the round window and along the scala tympani was not free of risk, as infection which led to a marked loss of spiral ganglion cells occurred, particularly in the basal turn. On the other hand when the size of the electrode was small in relation to the cross sectional area of the scala tympani, and it was not inserted far along the length of the basal turn, the evidence of trauma was minimal. Tissue reaction to the teflon-coated platinum electrode was also not observed.

Animals↗
PubMed1976

A multiple-electrode array for a cochlear implant.

A satisfactory multiple-electrode array for a cochlear implant has been developed. This can be passed around the turns of the cochlea if it is first introduced into the scala tympani through an opening in the apical turn.

Cochlea↗
PubMed1975

A surgical approach for a cochlear implant: an anatomical study.

This study has demonstrated the anatomical relations of the cochlea to structures in the medial wall of the tympanum, and has shown that surgical access can be obtained to the terminal auditory nerve fibres supplying the basal, middle and apical turns of the cochlea. It is suggested that a cochlear implantation should be carried out in two stages. The first stage should be modified radical mastoidectomy, and in the second stage electrode arrays should be implanted into the three cochlear turns through openings made in the proximal and distal portions of the basal turn, and the distal portion of the middle turn.

Cochlea↗
PubMed1975

Histopathological findings in cochlear implants in cats.

This histopathological study on cats has shown that electrodes may be implanted into the cochlea through the round window or an opening drilled over the middle and apical turns without loss of the spiral ganglion cells or auditory nerve fibres. It has also shown that infection, leading to a labyrinthitis, was more likely to occur when an opening was drilled in the cochlea, and this could lead to a marked destruction of the cochlear structures, and loss of the spiral ganglion cells.

Animals↗
PubMed1975

A cochlear implant electrode.

This study has shown that an electrode array can be passed along the hold length of the cochlea if it is inserted through and opening in the scala tympani of the apical turn. The electrode must have the appropriate mechanical properties and some of these were stiffness and extensibility. The electrode and operative approach should be helpful in stimulating the terminal auditory nerve fibres on a place basis, which is desirable if patients with severe sensorineural deafness are to be helped with a cochlear implant.

Cochlea↗
PubMed1974

Evaluation of methods for isolating Salmonella and Arizona organisms from pet turtles.

Two methods for isolating Salmonella and Arizona organisms from turtles, blending and excretion, were evaluated, and the percentage of isolates obtained by each method was compared with the percentage of isolates obtained by culture of turtle organs. The blending and excretion methods were equally effective in detecting the overall incidence of Salmonella and Arizona infections in turtles. The percentage of isolates obtained by specific organ culture, however, was less than the percentage obtained by the other two methods. The blending method detected a greater number of turtles with Arizona infections than did the excretion method, but there was no difference in the number of Salmonella infections detected by the two methods. The frequency of isolation of Arizona organisms from organs other than the small intestine and colon was higher than that of Salmonella.

Animals↗