The effect of noise on ears with a hole in the vestibule


Acta Oto-Laryngologica, 2010; 130: 659-664

1Department of Otolaryngology and Head and Neck Surgery, Shaare Zedek Medical Center, 2Speech & Hearing Center, Hadassah University Hospital and 3Department of Physiology, Hebrew University-Hadassah Medical School, Jerusalem, Israel


Conclusion: A hole in the vestibule of the inner ear leads to augmentation of the hearing loss following noise exposure. Further research is needed to ascertain the mechanism. Objectives: The possible effects of a hole in the wall of the inner ear at the vestibule on noise-induced hearing loss were assessed. Methods: The study was conducted on a total of 14 sand rats. Of these 14 animals, 10 underwent baseline auditory nerve and brainstem evoked response (ABR) threshold measurements in each ear separately (insert earphone), opening of middle ear bulla in both ears and drilling of a hole in the vestibule of one inner ear. The other ear was sham-operated. Following immediate re-assessment of ABR threshold, the 10 animals were exposed to 113 dB SPL broadband noise during 4 nights, and 3 days later ABR measurements were repeated. Four additional animals with a hole in one vestibule, not exposed to noise, served as controls. Results: Following noise exposure, ABR thresholds were elevated by 28.5 ± 9.1 dB in the ears with the hole, and by 15.5 ± 7.2 dB in the opposite ear without the hole (significant difference, p < 0.003). In the four control ears, ABR threshold was not elevated a week after drilling the hole. (Bold text emphasis by Martin Braun)


A hole in the vestibule necessarily functions as a pressure outlet during sound exposure via the middle ear. The anatomical reason for this is that the scala vestibuli of the cochlea, where sound pressure enters from the middle ear, has a common perilymphatic fluid chamber with the vestibule. An evident effect of an experimental pressure outlet in the vestibule is that fluid shift that can move the basilar membrane (BM) in the cochlea is reduced.
The finding that a hole in the vestibule leaves the auditory threshold unchanged once again indicates that BM motion apparently is not a relevant stimulus for hair cell excitation.
The finding that a hole in the vestibule increases the damage due to acoustic overload once again indicates that BM motion apparently has the function to damp out excessive acoustic stress for the hair cells. The new results indicate an inhibition of the BM's damping mechanism by drilling a pressure outlet in the vestibule.
The present results that a reduction of the BM traveling wave leaves hearing thresholds unchanged, but increases vulnerability against acoustic overload, are consistent with the recent spectacular observations by Perez et al. (2009). (Comment Martin Braun)

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