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Biomedical subjects

R K Shepherd

Publications and source records attributed to R K Shepherd.

87 records · Page 5Linked to original sources
PubMed1987

The University of Melbourne--nucleus multi-electrode cochlear implant.

To summarize, our preliminary results indicate that some prelingually deaf patients may get worthwhile help from a multiple-electrode cochlear implant which extracts formants. They can understand words and running speech better when using the cochlear implant with lip-reading compared to lip-reading alone. It has been encouraging that these improvements can occur in young adults and teenagers. It has also been encouraging that some can recognize place pitch as well as rate pitch. There are, however, considerable variations in performance and this may be due to the following factors: whether they have had some hearing after birth, the method of education used, the motivation of the patient and age at implantation. In conclusion it is important to emphasize that deaf children are severely disadvantaged however good their teacher of the deaf. Research on cochlear implants offers hope for profoundly-totally deaf children. These developments will not replace the caring, competent educators but complement their skills. There is also a greater need than ever for an interdisciplinary approach to these children.

Animals↗
PubMed1986

The distribution and prevalence of stephanofilariasis in cattle in Queensland.

A total of 10,543 cattle from 1,386 farms throughout Queensland was examined at abattoirs and the presence of stephanofilarial lesions was related to property of origin, sex, breed, and age of the slaughtered cattle and season of slaughter. The mean prevalence was 38% and within the infected area this varied from less than 5% in south east Queensland to 95% on Cape York Peninsula. The prevalence of lesions was higher in bulls than in steers [corrected] and was least in cows [corrected]. Bos indicus animals had a lower prevalence than B. taurus. Prevalence increased with age. The distribution of the disease closely matched that of the buffalo fly, Haematobia irritans exigua.

Animals↗
PubMed1985

Scanning electron microscopy of chronically stimulated platinum intracochlear electrodes.

Platinum electrodes were examined for evidence of corrosion using a scanning electron microscope (SEM). In vivo electrodes, stimulated using charge-balanced biphasic pulses for periods of up to 2000 h at charge densities of 0.18-0.32 microC mm-2 geom. per phase, were compared with in vitro electrodes stimulated in inorganic saline using similar stimulus parameters, and with in vivo control electrodes. The in vitro stimulated electrodes showed evidence of platinum corrosion at high charge density and aggregate charge injection. Significantly, the in vivo stimulated electrodes showed no evidence of stimulus induced corrosion. Indeed, their surfaces were similar to the in vivo control electrodes. In vitro electrochemical studies have demonstrated that proteins play a significant role in the inhibition of platinum dissolution: the present study has demonstrated an inhibitory effect in vivo. This may be due to the presence of proteins.

Animals↗
PubMed1985

Susceptibility of Bos indicus and Bos taurus to Anaplasma marginale and Babesia bigemina infections.

The reaction of Bos taurus and pure-bred Bos indicus heifers to infection with the intraerythrocytic parasites Anaplasma marginale and Babesia bigemina was studied. B. bigemina infection at 18 months and A. marginale infection at 13 or 24 months resulted in slightly less severe reactions in pure-bred Bos indicus cattle than in Bos taurus. In both breeds, the reaction to A. marginale infection was more severe in older cattle. The severity of B. bigemina infection was not affected by a previous infection with A. marginale.

Age Factors↗
PubMed1985

Progressive ototoxicity of neomycin monitored using derived brainstem response audiometry.

Progressive hearing loss following the systemic administration of neomycin was investigated using derived brainstem response audiometry. Cats were given three to five times the maximum recommended clinical dose of neomycin over a period of 10 days. Their hearing was monitored prior to and during the administration of the drug, and periodically following its completion. The results of this study showed that the induced hearing loss generally proceeded from high to low frequencies as an advancing lesion, with regions apical to the lesion functioning normally. Although considerable variability in response to the drug existed among animals, the evoked responses from both ears of each animal showed close bilateral symmetry during the deafening process. Furthermore, the present results highlight the long-term ongoing ototoxicity associated with neomycin, and the importance of monitoring high frequencies for initial signs of an aminoglycoside induced hearing loss.

Animals↗
PubMed1984

Implanted material tolerance studies for a multiple-channel cochlear prosthesis.

We have performed a number of temporal bone and animal studies in order to evaluate the histopathological effects of intracochlear electrode implantation and chronic electrical stimulation. Our results indicate that (a) the insertion of a free-fit scala tympani array results in minimal damage to the membranous labyrinth; (b) the materials used in the electrode array evoke mild tissue reactions when implanted subcutaneously, in muscle, or within the scala tympani; (c) intracochlear electrical stimulation for periods of 500 to 2000 hours, using carefully controlled biphasic pulses, does not adversely affect the population or neural activity of the primary auditory neurones; (d) labyrinthine infection severely reduces the number of viable spiral ganglion cells; (e) an adequate fibrous tissue seal of the round window can prevent the spread of infection from the bulla to the implanted cochlea in cats, following inoculation of the bulla cavity with bacteria; (f) bone growth is not associated with electrical stimulation per se; (g) the electrode arrays show minimal platinum dissolution and no apparent degradation of the Silastic carrier following periods of long-term intracochlear electrical stimulation.

Animals↗
PubMed1983

Chronic electrical stimulation of the auditory nerve in cats. Physiological and histopathological results.

The ability of spiral ganglion cells to survive long-term electrical stimulation is a precondition for the success of cochlear prostheses. In this study 10 cats were implanted bilaterally with bipolar scala tympani electrodes, and stimulated for periods of up to 2029 hours using charge balanced biphasic current pulses. The status of the auditory nerve was monitored periodically by recording electrically evoked auditory brainstem responses. At the conclusion of the stimulation program, spiral ganglion cell survival was assessed for stimulated and control cochleas; comparison of the two groups showed no statistically significant difference. The results of this study indicate that long-term intracochlear electrical stimulation, using carefully controlled biphasic pulses, does not adversely affect the spiral ganglion cell population.

Animals↗
PubMed1982

Effect of calving supervision upon the calving performance of Hereford heifers.

The calving performance of 268 two-year-old Hereford heifers was studied in 2 commercial herds and at a research station to compare supervision and non-supervision during calving. Supervision in the 3 herds involved twice-daily paddock inspections of calving heifers using a vehicle and the provision of obstetrical aid to those in difficulty. The unsupervised controls were inspected once weekly and were not assisted. The supervised heifers experienced a higher incidence of live-natural births and fewer dead calves compared with the unsupervised heifers. Dam survival rates were significantly (p less than 0.05) increased in all supervised treatments. Calving supervision was justified by higher survival of both heifers and calves as well as humans considerations. It was endorsed as a worthwhile management practice in commercial herds with significant levels of dystocia in calving heifers.

Animals↗
PubMedDate not supplied

Deafness-induced changes in the auditory pathway: implications for cochlear implants.

A profound sensorineural hearing loss induces significant pathological and atrophic changes within the cochlea and central auditory pathway. We describe these deafness-induced morphological and functional changes following controlled lesions of the cochlea in experimental animals. Such changes are generally consistent with the limited number of reports describing deafness-induced changes observed in human material. The implications of these pathophysiological changes within the auditory pathway on cochlear implant function are discussed. Finally, the plastic response of the deafened auditory system to electrical stimulation of the auditory nerve is reviewed in light of the clinical implications for cochlear implant recipients.

Animals↗
PubMedDate not supplied

Surgery for an improved multiple-channel cochlear implant.

An improved multiple-channel cochlear implant has been developed. The titanium container with enclosed electronics, the receiver coil, and the connector are embedded in medical-grade Silastic. The upper half of the implant has a diameter of 35 mm and a height of 4.5 mm, and the lower half a diameter of 23 mm and a height of 5 mm. The electrode array has also been designed to reduce the possibility of breakage due to repeated movements over many years. The surgery involves drilling a bed in the mastoid bone for the receiver-stimulator, and fixing the proximal electrode under the mastoid cortex. Gentle insertion of the electrode array through the round window and along the scala tympani is achieved with a specially designed microclaw .

Cochlear Implants↗
PubMedDate not supplied

Banded intracochlear electrode array: evaluation of insertion trauma in human temporal bones.

A banded free-fit scala tympani array was inserted into the basal turn of nine human cochleas to evaluate the trauma produced by the procedure. These nine cochleas, together with five nonimplanted controls, were serially sectioned and examined microscopically for damage to the membranous labyrinth, in particular the spiral ligament, the basilar and Reissner's membranes, the stria vascularis, and the osseous spiral lamina. The severity and location of any trauma along the cochlear spiral were recorded. The results indicate that the insertion of the banded scala tympani array resulted in minimal mechanical damage, occurring primarily to a localized region of the spiral ligament. This would not result in significant neural degeneration, and therefore would not compromise the efficacy of the multichannel cochlear prosthesis.

Aged↗