The noise protection effect of the stapedius reflex

The purpose was to estimate the attenuation and protection effect of the acoustic stapedius reflex on the inner ear. The acoustic stapedius reflex was recorded by means of extratympanic manometry (ETM). This method was used, as it is able to differ between the stapedius and the tensor reflex. Patients with unilateral Bell's palsy were investigated during palsy time and after recovery. The amplitude of the contralateral acoustic stapedius reflex was used as a relative measure of the excitation of the cochlea on the affected side. The attenuation effect, 20 dB above the reflex threshold, was approximately 15 dB for all tested patients. After the ETM investigation a temporary threshold shift was shown on the affected side (average 34 dB). The hearing threshold on the healthy side was unchanged. Thus the attenuation effect of the acoustic stapedius reflex protects the inner ear from an acoustic damage. A protection effect of the tensor tympani was not demonstrated.