New approach for implantable hearing aids: A feasibility study

The objective of this study was to test the feasibility of a new kind of implantable hearing device based on a cerebrospinal fluid hydroacoustic pathway by which sound waves are conducted from the dura mater to the inner ear by cerebrospinal fluid. In this prospective animal study, a piezoelectric bimorph was implanted into 2 guinea pigs and 1 dog between the skull bone and the dura at the parietal area. The bimorph was connected transdermally by wires to a click generator. The auditory brain stem response was recorded after stimulation of the piezoelectric device by the click generator. In the 3 animals, the auditory brain stem response could be recorded in response to a stimulus intensity of 135 dB peak equivalent (pe) sound pressure level (SPL; instrument setting), corresponding to 3.8 V activating the device. The auditory brain stem response disappeared during white noise masking, proving that the origin of the response was in the inner ear. The threshold was 125 and 115 dB pe SPL in the 2 guinea pigs and 135 dB pe SPL in the dog (instrument setting). We conclude that transmission of sound waves by a cerebrospinal fluid hydroacoustic pathway to the inner ear is possible. Such a device would have advantages over more traditional implantable hearing devices: it would not be necessary to couple it to the ossicular chain, and it could be used in patients with infected middle ears.