The Evaluation of Frequency Specific Cochlear Damage: Measurement of Low Frequency Hearing Function

• Author / Creator

  Yu, YongQiang

• Abstract Background Sensorineural hearing loss is a highly prevalent condition. A common cause of this type of loss is noise exposure (noise-induced hearing loss; NIHL). Effective management is available for NIHL, however, appropriate management depends on accurate diagnosis. Three tests commonly used to make a clinical diagnosis of hearing loss are distortion product otoacoustic emissions (DPOAE), auditory brainstem responses (ABR), and the cochlear microphonic (CM). In general, these tests are more sensitive to hearing loss at higher frequencies than at lower frequencies. The evaluation of lower frequency hearing function is as important as that of higher frequency hearing function; however, the use of these tests in diagnosing low frequency hearing loss has not been adequately addressed in the research literature. To address this gap in knowledge, the current study was conducted. Research Questions 1. What are the response patterns of the auditory system tests in the presence of normal hearing (Group 1) and NIHL? 2. What are the differences in the three tests as a function of NIHL, specifically the following: a. low frequency band-noise exposure (Group 2) b. high frequency band-noise exposure (Group 3) c. a sequence of low then high frequency band-noise exposure (Group 4), and, d. a sequence of high then low frequency band-noise exposure (Group 5)? 3. What is the relationship between the CM measured at the round window (RW) and the CM measured at the ear canal (EC) in the presence of normal hearing and NIHL? 4. What are the differences in the morphology and number of outer hair cells (OHCs) as a result of NIHL? Methods Fifteen guinea pigs were equally allocated into five groups (i.e., normal control and four kinds of noise exposure). DPOAE, ABR, and CM (at RW and EC) were used to evaluate hearing function in the five groups. Each test was measured at 0.5 kHz, 2 kHz, 4 kHz, 6 kHz and 8 kHz. After the tests were completed, the animals were euthanized, the cochlea were removed for silver nitrate staining, and the hair cells were examined under microscope. Results Research questions 1 and 2. Response patterns of the auditory system tests were compared in the presence of normal hearing and NIHL. The highest signal-to-noise ratio (SNR) of DPOAE and the highest amplitudes of ABR and CM occurred in the control group. At 0.5 kHz and 2 kHz, there were significant reductions in SNR of DPOAE and in the amplitudes of ABR and CM in groups 2, 4, and 5. At 6 kHz and 8 kHz, there were significant reductions in the SNR of DPOAE and the amplitudes of ABR and CM in groups 3, 4, and 5. There was no significant difference in hearing loss between single and double frequency band noise exposure. At 0.5 and 2 kHz, there were no significant difference between groups 2, 4, and 5; at 6 and 8 kHz, there was no significant difference between groups 3, 4, and 5. Research question 3. There was a statistically significant association between CM RW and CM EC in all test groups at all frequencies. Research question 4. There were no significant differences in the total number of missing OHCs between the five groups. Slight morphological changes were observed in the noise exposure groups. Discussion The evaluation of low frequency hearing function, particularly the successful recording of 0.5 kHz DPOAE and CM, is an important contribution to the literature on evaluation of low frequency hearing function. The significant correlation between the CM EC and CM RW indicates that the CM EC preserved the essential characteristics of CM RW, providing support for EC recording in clinical applications. The lack of a statistically significant difference between one and two frequency band-noise-exposure may be because relatively high levels of noise intensity and longer durations of exposure than were used in the current study are required to produce significant effects on hearing function. Finally, the lack of a statistically significant difference in the total number of missing OHCs as a function of noise may be explained by the time, i.e., not enough time had passed after the experiment and before the animals were euthanized to see significant changes in numbers of hair cells.

• Subjects / Keywords

  • Low frequency hearing function

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3KW57W7X

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.