Multifrequency immittancemetry in experimentally induced stapes, round window and cochlear lesions.

Abstract

OBJECTIVES: To establish that admittance (Y) and susceptance (B) conductance (G) tympanograms at 2 kHz can reflect the status of the annular ligament and the cochlear pressure. METHODS: Seven experiments were set up in 22 guinea pigs: ventilation of the bulla, blockage of the stapes and round window membrane (RWM), fistula, fluid removal from the cochlea, injection of saline in the scala tympani and acoustic trauma. Resonance frequency, Y, B and G at 2 kHz and curve shapes were analyzed before and after lesions. RESULTS: A supplementary peak was observed in Y/G tympanograms in all RWM fistulas and in some cases of acoustic trauma; injection of saline into the scala tympani induced constant, immediate and reproducible changes; RWM and stapes blockages induced foreseeable peaking at 2 kHz; fluid removal from the cochlea induced multiple peak curves. CONCLUSION: Experimentally induced modifications at the AL result in noticeable, constant and reproducible changes in tympanogram curves at 2 kHz and seem to reflect inner ear pressure.