Otolaryngology - Theses
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ItemImproving the preservation of acoustic hearing for cochlear implant recipients( 2022)Cochlear implants have been widely used to provide an alternative way of hearing for those who have experienced hearing loss, specifically in the high frequencies. Over the years, cochlear implant recipient criteria have expanded to those who are not only classified as severely to profoundly deaf, but also to include those who still have substantial residual hearing, particularly in the low frequencies. The increase in cochlear implant candidacy motivated the development of a new modality for treating patients with residual low-frequency hearing, termed electro-acoustic stimulation. Electro-acoustic stimulation involves electrical stimulation from the implant for mid to high frequencies complementary to low-frequency amplification through hearing aids. The resulting hearing experience has been shown to be advantageous over cochlear implant stimulation alone, allowing for better music appreciation, and improved speech recognition in noise. To achieve electro-acoustic stimulation, the residual low-frequency hearing must be preserved during and following cochlear implantation. Unfortunately, this is not always the case as implantation often results in either immediate or delayed loss of residual hearing loss in the postoperative period in more than half the individuals. Causes for these losses are speculated to be associated with intra-cochlear trauma occurring during electrode array insertion in conjunction with the consequential inflammatory response that ensues. To further improve hearing outcomes in cochlear implantation recipients, the issue currently presented is whether the detection of cochlear injury can be achieved and result in improved hearing preservation rates post-implantation. The investigations in this thesis aim to explore the implementation of a monitoring system, namely impedance, to identify whether an intra-cochlear injury has occurred, such as cochlear wall injury leading to the infiltration of blood into the cochlea. Impedance is a passive electrical measurement that evaluates the resistance and conductivity of the medium surrounding the recording electrodes. Specifically, this thesis will explore relationships between intra-operative impedance measurements and clinical outcomes such as hearing thresholds. Additionally, the impedance will be monitored post-operatively to determine if impedance fluctuations align with physiological events anticipated to occur in the cochlear following implantation that is unfavourable for hearing preservation. Lastly, investigations in this thesis will explore a possible therapeutic intervention for the removal of intra-scalar blood if it were to enter the cochlea during implantation.