title: The floating mass transducer at the round window: direct transmission or bone conduction?
abstract: The round window placement of a floating mass transducer (FMT) is a new approach for coupling an implantable hearing system to the cochlea. We evaluated the vibration transfer to the cochlear fluids of an FMT placed at the round window (rwFMT) with special attention to the role of bone conduction. A posterior tympanotomy was performed on eleven ears of seven human whole head specimens. Several rwFMT setups were examined using laser Doppler vibrometry measurements at the stapes and the promontory. In three ears, the vibrations of a bone anchored hearing aid (BAHA) and an FMT fixed to the promontory (pFMT) were compared to explore the role of bone conduction. Vibration transmission to the measuring point at the stapes was best when the rwFMT was perpendicularly placed in the round window and underlayed with connective tissue. Fixation of the rwFMT to the round window exhibited significantly lower vibration transmission. Although measurable, bone conduction from the pFMT was much lower than that of the BAHA. Our results suggest that the rwFMT does not act as a small bone anchored hearing aid, but instead, acts as a direct vibratory stimulator of the round window membrane.
authors.affiliation: University Department of ENT, Head and Neck Surgery, Inselspital, University of Bern, Switzerland. andreas.arnold@insel.ch
authors.forename: Andreas
authors.initials: A
authors.lastname: Arnold
authors.forename: Martin
authors.initials: M
authors.lastname: Kompis
authors.forename: Claudia
authors.initials: C
authors.lastname: Candreia
authors.forename: Flurin
authors.initials: F
authors.lastname: Pfiffner
authors.forename: Rudolf
authors.initials: R
authors.lastname: Häusler
authors.forename: Christof
authors.initials: C
authors.lastname: Stieger
mesh_terms: D000161:Acoustic Stimulation; D000368:Aged; D000369:Aged, 80 and over; D001299:Audiometry; D001844:Bone Conduction / Q000502:physiology*; D002102:Cadaver; D005260:Female; D006310:Hearing Aids; D034381:Hearing Loss / Q000503:physiopathology / Q000601:surgery; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D009998:Ossicular Prosthesis; D012405:Round Window, Ear / Q000503:physiopathology* / Q000601:surgery*; D014159:Transducers; D014732:Vibration