Direct-Drive Acoustic Amplification Using a Tympanostomy Tube

Objectives: Determine whether a tympanostomy tube with a ferromagnetic cap can be actuated to deliver sound to the cochlea. Methods: A ferromagnetic mixture of nickel powder and epoxy was glued to the outer flange of an Armstrong V Grommet tympanostomy tube. The tube was then placed into the pars tensa portion of a cadaveric temporal bone. The Direct-Drive Hearing Device (DHD), a completely-in-the-canal hearing aid prototype developed in our lab, was coupled to the nickel-epoxy flange and fixed inside the ear canal. The displacements of the posterior crus of the stapes were then measured using a Laser Doppler Vibrometer. The range of displacements induced by the device was compared to those of natural sound. Results: A 200 mV input to the device produced a range of displacements equivalent to those of sound at 70 dB sound pressure level (SPL; mean 0.44 nm; range 0.01-2.80). A 400 mV input produced a range of displacements equivalent to those of sound at 80 dB SPL (mean 1.34 nm; range 0.02-8.87). Conclusions: DHD, a small completely-in-the-canal hearing aid prototype, is capable of actuating the TM through a ferromagnetic tympanostomy tube and producing range of displacements equivalent to moderate to severe levels of hearing loss.