The Effect of Noise Exposure on Auditory Threshold, Otoacoustic Emissions, and Electrocochleography

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Alyson Butler Lake (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: Noise exposure is the second leading cause of acquired sensorineural hearing loss and is one of the most common occupational and environmental hazards. Examining changes in behavioral thresholds has long been the standard for detection and monitoring of noise-induced hearing loss (NIHL). It has been suggested that electrocochleography (ECochG) could be an additional tool for assessing NIHL. Otoacoustic emissions (OAEs) provide objective information on the integrity of outer hair cell (OHC) function and have also been suggested for evaluating damage due to noise overexposure. The broad experimental question was: What is the effect of short-term narrowband noise exposure, as a function of ear and gender, on cochlear function as measured with behavioral, ECochG, and OAE indices? In Experiment 1, it was of interest to first examine the reliability of ECochG electrode type (i.e., Lilly-TM Wick vs. TIPtrode[TM]) at two stimulus rates (i.e., 7.7/s vs. 77.7/s). Electrode and rate were statistically significant (p [less than] .001) predictors of SP and AP responses (i.e., responses were more apt to be present when recorded with the wick electrode at the slow rate). Test-retest reliability was examined with correlation coefficients, linear mixed model analyses of variance, test-retest differences, and Bland-Altman plots. There were statistically significant correlations (p [less than] .05) between initial test and retest for all ECochG indices (i.e., summating potential [SP] amplitude, action potential [AP] latency, AP amplitude, SP/AP amplitude ratio, and SP/AP area ratio) when using a Lilly TM-Wick electrode and for all ECochG indices except SP amplitude when testing with a TIPtrode[TM]. Amplitude measures were significantly (p [less than] .01) larger when recording with the wick electrode. SP amplitudes were significantly (p [less than] .05) larger for the faster rate. AP latency was significantly (p [less than] .001) longer for the fast rate. AP amplitudes were significantly (p [less than] .05) larger for the slower rate. Both SP/AP amplitude ratio and SP/AP area ratio were significantly (p [less than] .001) larger for the fast rate. There was no statistically significant effect of test on any ECochG indices (p [less than] .05). In Experiment 2, auditory threshold differences were examined as a function of ear, gender, and frequency. Significantly (p [less than] .0001) larger auditory threshold differences were observed for left ears and for 3000 Hz than 2000 Hz, 4000 Hz or 6000 Hz. Additionally, statistically significant correlations between right ear auditory threshold differences at 3000 Hz and right 2000 Hz pure tone acoustic reflex thresholds (p = .04) as well as between left ear auditory threshold differences at 3000 Hz and left 2000 Hz pure tone acoustic reflex thresholds (p = .03) and 2000 Hz narrowband noise acoustic reflex thresholds (p = .01) were found. Statistically significant main effects of level (p [less than] .0001) and frequency (p [less than] .0001) were observed for DPOAE I/O functions in Experiment 3. DPOAE absolute amplitude differences were largest for the L1, L2 level of 55, 40 dB SPL and smallest for the L1, L2 level of 65, 65 dB SPL. DPOAE absolute amplitude differences were also smallest for the f2 frequency of 2051 Hz. A statistically significant gender by frequency interaction (p [less than] .05) was also identified. Females generally had larger DPOAE absolute amplitude differences than males except at the f2 frequency of 4980 Hz. Finally, Experiment 4 revealed a statistically significant interaction of ear and gender (p [less than] .05) for SP amplitude. SP amplitudes were significantly increased for female left ears following noise exposure while female right ears showed essentially no change. Additionally, left ear SP/AP amplitude ratios and SP/AP area ratios were significantly (p [less than] .05) increased following noise exposure. In summary, due to the excellent test-retest reliability and easier identification of ECochG wave components, Lilly-TM Wick electrodes were deemed superior for recording ECochG. Experiments 2, 3, and 4 revealed that behavioral thresholds, DPOAE I/O functions, and ECochG showed measureable changes following a 2000 Hz narrowband noise exposure.

Additional Information

Publication

Dissertation

Language: English

Date: 2016

Keywords

Adult, Temporary Threshold Shift, Otoacoustic Emissions, Electrocochleography, Noise Exposure

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