EFFECT OF OCCLUDING THE ROUND WINDOW ON NOISE INDUCED HEARING LOSS

Sichel J Y (1), Perez R (1), Freeman S (2), Sohmer H (2).

(1) Dept. of Otolaryngology and Head and Neck Surgery, Shaare Zedek Medical Center; (2) Dept. of Physiology, Hebrew University-Hadassah Medical School, Jerusalem, Israel.

Objective/Hypothesis: It has been suggested that at high stimulus intensities, the passive basilar membrane traveling wave may provide overload protection of the delicate and fragile hair cells from excessive vibrations. In a previous study conducted by our group, we have shown that introduction of a hole in the vestibule of the sand rat, which was then exposed to noise, lead to an increased auditory nerve and brainstem response (ABR) threshold elevation in response, supporting the protection theory. In the present experiment, in order to further substantiate this theory, we occluded the sand rats’ round window (RW) before exposure to loud noise. Occluding the RW could possibly compromise the generation of the passive basilar membrane traveling wave in these animals.

Methods: Ten sand-rats underwent baseline ABR measurements followed by bilateral opening of the bulla and occluding the RW with glue in one ear. Subsequently, the animals were exposed to broadband noise (113 dB SPL) for 12 hours and on the following day (24 hours after the round window was occluded) ABR measurements were repeated. Four additional animals not exposed to noise served as control.

Results: Occluding the RW did not induce significant change in ABR threshold. ABR thresholds were elevated by 54±9 dB in the ears with the occluded RW and by 40±9 in the contralateral ears (p<0.004). In the 4 control ears, there was no change in ABR threshold 24 hours after the round window was occluded.

Conclusion: These results show that occluding the RW had a clear effect on the responses of the inner ear to high intensity noise exposure. This further validates the theory that the passive basilar membrane traveling wave may serve to protect the inner ear from high intensity noise.

E-mail: sicheljy@yahoo.com