RELATION OF EVOKED OTOACOUSTIC EMISSION TO STRUCTURAL DAMAGE AFTER ACOUSTIC OVERSTIMULATION IN CAT

Abstract

Evoked otoacoustic emissions (e-OAE) at a 2 kHz tone burst were measured in 37 ears of 21 cats. The e-OAE responses were detectable in 30 ears of 19 cats. In most cats (26 out of 30 ears) nonlinear behavior could be identified and saturated above 15 to 20 dBnHL. The responses had very short latencies (to their peak pressures) of 5.53 ms to 7.28 ms.
Scanning electron microscopy (SEM) was used to examine feline cochleas for structural damage after exposure to a 2 kHz pure tone (105 dBSPL and 125 dBSPL). Following a 105dB exposure for 30 min acoustic response recovered to normal levels at 120 min after exposure with no significant loss of hair cell stereocilia. Fatigue induced changes in outer hair cell activity may be relevant to the production of TTS. The loss of stereocilia on outer hair cell row 1 and on inner hair cells was seen between 6 and 9 mm from the apex after exposure to a 125dBSPL, 2 kHz pure tone for 30 min and e-OAE disappeared after overstimulation in all these cases. We found that e-OAE was affected by minimal cochlear damage.