Occluding the round window causes no change in threshold, but an increase in hearing loss following noise exposure

Ronen Perez*, Cahtia Adelman‡, Jean Yves Sichel*, Haim Sohmer§

Journal of Basisc & Clinical Physiology & Pharmacology, 2009, Vol 20, No 3, 197-205

*Department of Otolarynglogy and Head & Neck Surgery, Shaare Zedek Medical Center,
‡Speech and Hearing Center, Hadassah University Hospital,
§Department of Physiology, Hebrew University - Hadassah Medical School, Jerusalem, Israel


Aim: To assess the effects of occluding the round window on the degree of hearing loss following exposure to broad band noise.
Design: 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 ears (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.
Conclusion: 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. (Bold text emphasis by Martin Braun)


Immobilization of the round window reduces, or even abolishes, a local motion of the basilar membrane (BM) toward the scala timpani upon sound exposure. The reason is that a volume shift in the scala timpani is impeded, or even made impossible, if the round window membrane can no longer bulge outwards. Therefore, a sound induced BM traveling wave along the cochlea must necessarily be greatly reduced under this condition.
The findings that a reduction of the BM traveling wave leaves hearing thresholds unchanged, but increases vulnerability against acoustic overload, constitute a direct experimental confirmation of a completely new theory of cochlear functions that was first published 16 years ago. (Comment Martin Braun)

ask for a PDF of the full paper by Perez et al. (2009)

Confirmed by Perez et al. (2010)

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