The Role of the Middle Ear in Acoustic Trauma from Impulses

The purpose of this experiment was to evaluate the role of the middle ear in acoustic trauma following high‐level impulse noise exposure. Eleven monaural chinchillas were exposed to either 161‐ or 166‐dB peak SPL impulses of 1‐msec “A” duration, presented at the rate of 1 per minute for 50 minutes. Auditory thresholds were measured before and at regular intervals after exposure, using the evoked response technique; middle‐ear status was evaluated by means of impedance tympanometry. At 30 days the animals underwent tympanotomy for middle‐ear examination followed by sacrifice for surface preparation histology. The 161‐dB group showed the widest range of TTS with two animals exhibiting PTS. Tympanometric examination was suggestive of tympanic membrane stress (i.e., double‐peaked tympanograms). The 166‐dB group showed moderate TTS but no PTS; however, all animals had tympanic membrane perforations which required 10 to 30 days to heal. No gross changes were observed in the ossicular chains at tympanotomy. The ...