Graeme Clark Collection

Permanent URI for this collection

Search Results

Now showing 1 - 10 of 34
  • Item
    No Preview Available
    Can we prevent cochlear implant recipients from developing pneumococcal meningitis?
    Wei, BPC ; Robins-Browne, RM ; Shepherd, RK ; Clark, GM ; O'Leary, SJ (Oxford University Press (OUP), 2008-01-01)
    The restoration of hearing to persons with severely or profoundly impaired hearing by means of a cochlear implant is one of the great achievements of bionics applied to medicine. However, pneumococcal meningitis in implant recipients has received high profile public attention as a result of the US Food and Drug Administration's public health notification and recent media attention. Worldwide, 118 of the 60,000 people who received cochlear implants over the past 20 years have acquired meningitis, causing deep concern in the international medical community. This review provides answers to pediatricians, internists, and infectious diseases doctors who have patients with cochlear implants and who have questions about the safety of the cochlear implant from both the clinical and scientific research perspectives. Both clinical and laboratory research support the notion that pneumococcal meningitis is more likely in patients who receive cochlear implantation, and that the surgical insertion technique and the cochlear implant design should be nontraumatic, and that all cochlear implant recipients should be offered vaccination against Streptococcus pneumoniae.
  • Item
    Thumbnail Image
    Promoting neurite outgrowth from spiral ganglion neuron explants using polypyrrole/BDNF-coated electrodes
    Evans, AJ ; Thompson, BC ; Wallace, GG ; Millard, R ; O'Leary, SJ ; Clark, GM ; Shepherd, RK ; Richardson, RT (WILEY, 2009-10-01)
    Release of neurotrophin-3 (NT3) and brain-derived neurotrophic factor (BDNF) from hair cells in the cochlea is essential for the survival of spiral ganglion neurons (SGNs). Loss of hair cells associated with a sensorineural hearing loss therefore results in degeneration of SGNs, potentially reducing the performance of a cochlear implant. Exogenous replacement of either or both neurotrophins protects SGNs from degeneration after deafness. We previously incorporated NT3 into the conducting polymer polypyrrole (Ppy) synthesized with para-toluene sulfonate (pTS) to investigate whether Ppy/pTS/NT3-coated cochlear implant electrodes could provide both neurotrophic support and electrical stimulation for SGNs. Enhanced and controlled release of NT3 was achieved when Ppy/pTS/NT3-coated electrodes were subjected to electrical stimulation. Here we describe the release dynamics and biological properties of Ppy/pTS with incorporated BDNF. Release studies demonstrated slow passive diffusion of BDNF from Ppy/pTS/BDNF, with electrical stimulation significantly enhancing BDNF release over 7 days. A 3-day SGN explant assay found that neurite outgrowth from explants was 12.3-fold greater when polymers contained BDNF (p < 0.001), although electrical stimulation did not increase neurite outgrowth further. The versatility of Ppy to store and release neurotrophins, conduct electrical charge, and act as a substrate for nerve-electrode interactions is discussed for specialized applications such as cochlear implants.
  • Item
    No Preview Available
    Polypyrrole-coated electrodes for the delivery of charge and neurotrophins to cochlear neurons
    Richardson, RT ; Wise, AK ; Thompson, BC ; Flynn, BO ; Atkinson, PJ ; Fretwell, NJ ; Fallon, JB ; Wallace, GG ; Shepherd, RK ; Clark, GM ; O'Leary, SJ (ELSEVIER SCI LTD, 2009-05-01)
    Sensorineural hearing loss is associated with gradual degeneration of spiral ganglion neurons (SGNs), compromising hearing outcomes with cochlear implant use. Combination of neurotrophin delivery to the cochlea and electrical stimulation from a cochlear implant protects SGNs, prompting research into neurotrophin-eluting polymer electrode coatings. The electrically conducting polypyrrole/para-toluene sulfonate containing neurotrophin-3 (Ppy/pTS/NT3) was applied to 1.7 mm2 cochlear implant electrodes. Ppy/pTS/NT3-coated electrode arrays stored 2 ng NT3 and released 0.1 ng/day with electrical stimulation. Guinea pigs were implanted with Ppy/pTS or Ppy/pTS/NT3 electrode arrays two weeks after deafening via aminoglycosides. The electrodes of a subgroup of these guinea pigs were electrically stimulated for 8 h/day for 2 weeks. There was a loss of SGNs in the implanted cochleae of guinea pigs with Ppy/pTS-coated electrodes indicative of electrode insertion damage. However, guinea pigs implanted with electrically stimulated Ppy/pTS/NT3-coated electrodes had lower electrically-evoked auditory brainstem response thresholds and greater SGN densities in implanted cochleae compared to non-implanted cochleae and compared to animals implanted with Ppy/pTS-coated electrodes (p<0.05). Ppy/pTS/NT3 did not exacerbate fibrous tissue formation and did not affect electrode impedance. Drug-eluting conducting polymer coatings on cochlear implant electrodes present a clinically viable method to promote preservation of SGNs without adversely affecting the function of the cochlear implant.
  • Item
    Thumbnail Image
    Stiffness properties for nucleus standard straight and contour electrode arrays
    Kha, H. N. ; Chen, B. K. ; Clark, Graeme M. ; Jones, R. ( 2004)
    Trauma and damage during insertion of electrode arrays into the human cochlea are strongly related to the stiffness of the array. The stiffness properties of electrode arrays, which were determined by three-point flexural bending and buckling tests, are reported in this paper. To date there has been limited publication on mechanical properties of these electrode arrays. Previous studies mainly focused on characterizing the stiffness of the tip of the Nucleus straight array with little emphasis on characterizing the stiffness of its whole length. In this study, stiffnesses of the Nucleus straight and contour electrode arrays have been determined along their length. Young’s modulus of elasticity of the Nucleus straight array has been found to increase from the tip (182 MPa) to the rear end (491 MPa), whereas the stiffness of the contour array is greatest near the tip (480 MPa) and is fairly uniform in the middle and rear sections of the electrode array (380-400 MPa). Buckling experiments have shown that the contour array has much higher critical buckling load (about four times) than the Nucleus straight array. The results from three-point flexural bending and buckling experiments provide significant data for the development of electrode arrays, from which new array designs with improved flexibility can be developed. The results of stiffness properties are also important input for use in finite element models to predict the trajectories during insertion and to help evaluate the effects of different electrode array designs on damage sustained during insertion.
  • Item
    Thumbnail Image
    Bionic ears: their development and future advances using neurotrophins and inherently conducting polymers
    Clark, Graeme M. ; Wallace, Gordon ( 2004)
    The development of the multiple-channel bionic ear for hearing and speech understanding in profoundly deaf people is the result of integrating biological and physical sciences with engineering. It is the first clinically successful restoration of sensory and brain function, and brings electronic technology into a direct functional relationship with human consciousness. It presently transmits essential place and coarse temporal information for the coding of frequency, but the fine temporal and place excitation of groups of nerve fibres is inadequate for high-fidelity sound. This is required for adequate musical appreciation and hearing in noise. Research has demonstrated that nerve growth factors preserve the peripheral processes of the auditory nerves so that an electrode array placed close to these fibres could produce this fine temporal and spatial coding. The nerve growth factors can be incorporated into inherently conducting polymers that are part of the array so the peripheral processes can be preserved at the same time as they arc electrically stimulated.
  • Item
    Thumbnail Image
    Cochlear implants
    Clark, Graeme M. (Springer, 2003)
    Over the past two decades there has been remarkable progress in the clinical treatment of profound hearing loss for individuals unable to derive significant benefit from hearing aids. Now many individuals who were unable to communicate effectively prior to receiving a cochlear implant are able to do so, even over the telephone without any supplementary visual cues from lip reading. The earliest cochlear implant devices used only a single active channel for transmitting acoustic information to the auditory system and were not very effective in providing the sort of spectrotemporal information required for spoken communication. This situation began to change about 20 years ago upon introduction of implant devices with several active stimulation sites. The addition of these extra channels of information has revolutionized the treatment of the profoundly hearing impaired. Many individuals with such implants are capable of nearly normal spoken communication, whereas 20 years ago the prognosis for such persons would have been extremely bleak. (From Introduction)
  • Item
  • Item
    Thumbnail Image
    Cognitive processing in children using cochlear implants: the relationship between visual memory, attention, and executive functions and developing language skills
    Surowiecki, Vanessa N. ; SARANT, JULIA ; MARUFF, PAUL ; Blamey, Peter J. ; Busby, Peter A. ; Clark, Graeme M. ( 2002)
    We performed this study to determine whether children using a cochlear implant performed differently from age- and gender-matched hearing aid users on 8 neuropsychological measures of visual memory, attention, and executive functioning. The study also examined whether differences in cognitive skills could account for some of the observed variance in speech perception, vocabulary, and language abilities of hearing-impaired children. In contrast to previous studies, our results revealed no significant cognitive differences between children who use a cochlear implant and children who use hearing aids. Partial correlation analysis indicated that the children’s visual memory skills, i.e., their recognition memory, delayed recall, and paired associative learning memory skills, correlated significantly with their language skills. When examined at a significance level of .01, attention and executive functioning skills did not relate to the children’s developing speech perception, vocabulary, or language skills. The results suggested that differences in visual memory skills may account for some of the variance seen in the language abilities of children using implants and children using hearing aids.
  • Item
    Thumbnail Image
    Speech perception outcomes in older children who use multichannel cochlear implants: Older is not always poorer
    Dowell, RC ; Dettman, SJ ; Hill, K ; Winton, E ; Barker, EJ ; Clark, GM (ANNALS PUBL CO, 2002-05-01)
    Speech perception outcomes for early-deafened children who undergo implantation as teenagers or young adults are generally reported to be poorer than results for young children. It is important to provide appropriate expectations when counseling adolescents and their families to help them make an informed choice regarding cochlear implant surgery. The considerable variation of results in this group makes this process more difficult. This study considered a number of factors in a group of 25 children who underwent implantation in Melbourne between the ages of 8 and 18 years. Each subject completed open-set speech perception testing with Bamford-Kowal-Bench sentences before and after implantation and preoperative language testing with the Peabody Picture Vocabulary Test. Data were collected regarding the type of hearing loss, age at implantation, age at hearing aid fitting, audiometric details, and preoperative and postoperative communication mode. Results were submitted to a stepwise multiple linear regression analysis with postoperative open-set sentence scores as the dependent variables. The analysis suggested that 3 factors have a significant predictive value for speech perception after implantation: preoperative open-set sentence score, duration of profound hearing loss, and equivalent language age. These 3 factors accounted for 66% of the variance in this group. The results of this study suggest that children who have useful speech perception before implantation, and higher age-equivalent scores on language measures, would be expected to do well with a cochlear implant. Consistent with other studies, a shorter duration of profound hearing loss is also advantageous. The mean sentence score for this group, 47%, was not significantly different from the mean result across all children in the Melbourne program.
  • Item
    Thumbnail Image
    Speech perception in children using cochlear implants: prediction of long-term outcomes.
    Dowell, RC ; Dettman, SJ ; Blamey, PJ ; Barker, EJ ; Clark, GM (Maney Publishing, 2002-03)
    A group of 102 children using the Nucleus multichannel cochlear implant were assessed for open-set speech perception abilities at six-monthly intervals following implant surgery. The group included a wide range of ages, types of hearing loss, ages at onset of hearing loss, experience with implant use and communication modes. Multivariate analysis indicated that a shorter duration of profound hearing loss, later onset of profound hearing loss, exclusively oral/aural communication and greater experience with the implant were associated with better open-set speech perception. Developmental delay was associated with poorer speech perception and the SPEAK signal coding scheme was shown to provide better speech perception performance than previous signal processors. Results indicated that postoperative speech perception outcomes could be predicted with an accuracy that is clinically useful.