Experimental Investigation of Bone Conduction Pathways: Stimulation Site and Coupling Type Dependence

Objectives: Investigation of bone conduction sound propagation by the osseous and non-osseous pathways and their interaction depending on stimulation site and coupling method of the bone conduction hearing aid (BCHA).

Methods: Experiments were conducted on five Thiel embalmed whole head cadaver specimens. The electromagnetic actuators from a commercial BCHA (Baha® Cordelle and BoneBridge®) were used to provide stepped sine stimulus (0.1-10 kHz). Osseous pathways were sequentially activated by mastoid stimulation via a percutaneously implanted screw, Baha® Attract transcutaneous magnet and a 5-Newton steelband. Non-osseous were activated by stimulation on the eye, neck, and dura via a 5-Newton steelband, and compared with equivalent stimulation on mastoid or forehead. Motions of the ipsi- and contra-lateral promontory were measured with a three-dimensional laser Doppler vibrometer system. Intracranial pressure (ICP) in central, anterior, posterior, ipsilateral and contralateral temporal regions of the cranial space. Promontory motion was measured with.

Results: Direct dura and eye stimulation induce comparable or even higher (at frequencies below 1 kHz) ICP, relative to percutaneous (via implant BI300) mastoid stimulation. Phase data indicates lower phase delays for ICP when stimulated via non-osseous means (i.e. eye, dura) versus osseous means (i.e., mastoid, forehead). 3D LDV data indicates that the promontory undergoes complex spatial motion with similar contributions from all motion components, under all stimulation modes.

Conclusion: Comprehensive experiments, including simultaneous motion and pressure measurements, with various stimulation positions and coupling methods, allow for detailed exploration and differentiation of the individual contributions of the various bone conduction pathways.