Assessment of the Effects of Different Sound Pressure Levels on Distortion Product Otoacoustic Emissions (DPOAEs) in Rats

Abstract

Excessive exposure to noise can lead to Noise-Induced Hearing Loss. Otoacoustic emissions affect the microscopic biomechanical activities of healthy outer hair cells. The present study aimed at assessing the influence of various sound pressure levels on Distortion Product Otoacoustic Emissions (DPOAEs) in rats. To this end, 27 adult male rats with an age range of 3 to 4 months and a weight of 200 ± 50 g were randomly divided into nine groups of three. Three groups were considered as the control groups and the rest (i.e. Six groups) as the case groups. Rats of the case groups were exposed to sound pressure levels of 85, 95, and 105 dBA. White noise was used as the noise to which the rats were exposed. The signal to noise ratio (SNR) of otoacoustic emissions of rats’ ears was measured at different frequencies in an acoustic room using a DPOAE machine (4000 I/O manufactured by Homoth of Germany). The collected data were analyzed by the use of Statistical Package for Social Sciences (SPSS) version 18. The results of SNR measurement indicated that over 90% of the data had SNR values of 6dB or more. Furthermore, sound pressure level had a significant negative correlation with SNR, i.e. as the sound pressure level increased, the SNR declined (p<0.001). There was also a significant negative correlation between exposure time and SNR, meaning that increase in the exposure time led to decline in the SNR (p=0.008). It is thus concluded that higher sound pressure levels result in decrease in DPOAE levels