UBC Theses and Dissertations
Electrocochleography as a diagnostic tool for noise-induced cochlear synaptopathy Chang, Shiang Ling
PURPOSE: Recent studies suggest synaptic connections between hair cells and the auditory nerve may be more vulnerable to noise-induced damage than the cochlear hair cells. The resulting neuropathy may be associated with an increased difficulty with speech perception in noise than expected from a normal audiogram. This type of hearing loss has been named “hidden hearing loss”. Studies with animal models indicate that suprathreshold wave I auditory brainstem responses are sensitive to the loss of synaptic ribbons in mice, but humans studies remain inconclusive. This work aims to identify the diagnostic potential of tympanic membrane electrocochleography on noise-induced cochlear synaptopathy. DESIGN: We recruited 18 music students (n = 32; mean age = 21.7) with normal hearing (≤ 25 dB, HL 250-8000 Hz) and 19 normal hearing controls (n = 35; mean age = 22.5). Lifetime noise exposure was obtained using the Noise Exposure Structured Interview. Electrocochleography was measured in response to 95 dB nHL broadband click with tympanic membrane electrodes. A factorial ANOVA was used to investigate the effect of music background and sex on the lifetime noise exposure. Mixed model ANOVA was used to analyze effect of noise exposure, sex, and ear on absolute SP and AP amplitudes, SP/AP amplitude ratio, and SP/AP area ratio. RESULTS: There was a trend for higher lifetime noise exposure scores for the music students but the difference did not reach significance. There were no significant group differences on any of the electrocochleography measures. CONCLUSION: In the present study, there is no evidence that AP amplitude, SP/AP amplitude ratio, or SP/AP area ratio are associated with noise exposure. It is possible that the effects of noise exposure may be observed in individuals with greater lifetime noise exposure than the cohort tested within this study. The use of tympanic membrane electrocochleography to assess cochlear synaptopathy in humans remains inconclusive. Additional research would be needed to develop a diagnostic protocol for early cochlear damage that precedes sensory hair cell loss in humans.
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