Effects of three noise exposure patterns with equivalent sound energy on the auditory system of chinchilla

Author

William Scott Wood

Date of Award

6-1981

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Speech and Hearing Science

Major Professor

David M Lipscomb

Committee Members

Anna Nabelek, Igor Nabelek, James Lawler

Abstract

Review of the literature concerned with the equal energy hypothesis and the use of equivalent sound level as a descriptor for assessing oto-hazardous noise exposures was found to lack information regarding long-term noise exposures which simulated a 40-hour work-week schedule. The purpose of this study was to investigate the effects upon the chinchilla's auditory system of three noise exposure patterns with equivalent 24-hour sound levels (Leq₂₄).

Three groups of six animals each were exposed to a one-third octave band noise, centered at 4.0 kHz and set to achieve an Leq₂₄ of 85 dB. Group C received a continuous 8-hour exposure of 90 dBA. Groups E and F had time-varying 8-hour exposures such that their mean high sound levels and durations were 105 dBA for 15 minutes and 94.1 dBA for 4 hours, respectively. A 6-month exposure schedule (consisting of 27 weeks of 5-day 8-hour exposures and 2-day, 24-hour quiet periods) was used.

Auditory thresholds were measured by averaging electrical responses from the brain stem elicited by tone bursts. Temporary threshold shifts after the first, fifth, and final 8-hour exposures revealed no statistically significant differences among groups. Threshold shifts measured 30 days after the last exposure (permanent threshold shifts) indicated a statistically significant difference among the three exposure groups for the 4.0 kHz stimulus.

After final auditory thresholds were measured, animals were decapitated. Cochleas were dissected by the surface preparation technique and auditory sensory cell damage was assessed by interference-contrast microscopy. Results indicated a statistically significant difference for the mean percent of missing hair cells among exposure groups. In addition, there appeared to be no relationship between the percent of missing hair cells for specific regions and the amount of permanent threshold shift for frequencies primarily stimulating those regions.

Recommended Citation

Wood, William Scott, "Effects of three noise exposure patterns with equivalent sound energy on the auditory system of chinchilla. " PhD diss., University of Tennessee, 1981.
https://trace.tennessee.edu/utk_graddiss/13556