Occluding the round window causes no change in threshold, but an increase in hearing loss following noise exposure.
OBJECTIVE
To assess the effects of occluding the round window on the degree of hearing loss following exposure to broad band noise.


METHODS
Following opening of the middle ear bulla in both ears of ten sand rats, auditory nerve-brainstem evoked response (ABR) thresholds were determined in each ear separately using an insert earphone. The round window of one ear was then occluded with super-glue. The opposite ear was sham-operated. ABR thresholds were again assessed immediately. The animals were then exposed to 113 dB SPL broad band noise for 12 hours. 24 hours after the round window was occluded, which was 8-10 hours after the end of the noise exposure, ABR thresholds were again determined in each ear. In four control animals, the round window was blocked, but they were not exposed to noise.


RESULTS
Following the noise exposure, the mean ABR threshold elevation in the round window blocked ears (54.5 +/- 5.5 dB) was significantly (p < 0.004) greater than that in the sham-operated ear (40.5 +/- 8.6 dB). In the four control ears, there was no change in ABR threshold 24 hours after the round window was occluded.


CONCLUSIONS
Occluding the round window was not accompanied by a threshold elevation, but following noise exposure, the noise induced hearing loss was increased, probably by reducing the efficacy of an inherent protective mechanical mechanism.
Department of Otolaryngology and Head & Neck Surgery, Shaare Zedek Medical Center, Jerusalem, Israel.
Ronen
R
Perez
Cahtia
C
Adelman
Jean Yves
JY
Sichel
Haim
H
Sohmer
D000818:Animals; D001309:Auditory Threshold; D016057:Evoked Potentials, Auditory, Brain Stem; D005849:Gerbillinae; D006317:Hearing Loss, Noise-Induced / Q000503:physiopathology*; D013997:Time Factors