Threshold Shifts and Cochlear Injury in Chinchillas Exposed to Octave Bands of Noise Centered at 63 and 1000 HZ for 9 Days

Abstract : The use of A-weighted sound pressure levels in hearing conservation criteria is based on scant data from low frequency exposures. This study contributes additional data from exposure to low frequency noise and attempts to relate it to damage risk criteria. Audiograms were obtained on 16 binaural chinchillas using a shuttle box avoidance procedure. The chinchillas were then exposed in groups to one of the following noise conditions for 9 days. Eight animals were exposed to an octave band noise centered at 1000 Hz: four were exposed at an intensity level of 85 dB SPL (85 dBA) and four at an intensity level of 95 dB SPL (95 dBA). The 85-dB exposure produced a temporary threshold shift at an intensity level of 85 dB SPL (85 dBA) and four at an intensity level of 46 dB at 1.4 kHz with no permanent threshold shift. The 95-dB exposure produced a compound threshold shift of 60 dB at 1.4 kHz and a peak permanent threshold shift of 2B at 2.0 kHz. The eight remaining animals were exposed to an octave band noise centered at 63 Hz: four were exposed to an intensity level of 110 dB (84 dBA) and four at an intensity level of 120 dB SPL (94 dBA). The 110-dB exposure produced a compound threshold shift of 23 dB at 2.0 kHz with a peak permanent threshold shift of 7 dB at 2.0 kHz. The 120-dB exposure produced a compound threshold shift of 45 dB at 2.0 kHz and a peak permanent threshold shift of 19 dB at 2.0 kHz. (Author)