EFFECT OF OTOLOGIC DRILL NOISE ON ABR THRESHOLDS IN A GUINEA-PIG MODEL

The noise generated by the otologic drill has been implicated as a cau se of sensorineural hearing loss after ear surgery. However, clinical studies on this subject are contradictory and difficult to interpret. Therefore a guinea pig model was used to study whether the level of no ise generated by the otologic drill con cause threshold shifts in the auditory brainstem response (ABR). The source noise was a recording ob tained during a human cadaver mastoidectomy using a microphone and an accelerometer. Ten female Topeka-strain guinea pigs were exposed to th e recorded drill noise for a period of 55 minutes. Exposure included b oth air-conducted energy from a speaker and bone-conducted energy from a bone vibrator applied directly to the skull. ABR threshold measurem ents were taken pre-exposure (baseline), immediately after exposure, a nd at weekly intervals thereafter for 3 weeks. Three control animals w ere subjected to the same procedure without the sound exposure. A sign ificant threshold shift (p < 0.0001) was seen for each frequency teste d (2, 4, 8, 16, 20, and 32 kHz) immediately after exposure to noise in all experimental animals. Thresholds returned to baseline within 3 we eks. We conclude that the level of noise generated by the otologic dri ll in mastoid surgery can cause a temporary threshold shift in this gu inea pig model.