Intra-Operative Electrophysiological Measures and Applications in Cochlear Implants

Since the introduction of a cochlear implant back-telemetry channel in 1991, use of this feature has greatly expanded. This paper reviews existing and emerging back-telemetry measures.

Electrode contact impedance was the first back-telemetry measure, used initially to ensure that an intact stimulation pathway existed and later to maintain stimulation within the current sources’ compliance while optimizing power consumption. Extending the impedance matrix allowed Electrical Field Imaging to assess current spread within the cochlea, including applications such as tip-fold-over detection. The recording of eCAPs through Neural Response Imaging helped quantify the availability of neural tissue for stimulation, assisted in fitting and through spread of excitation and recovery function can guide electrode set and stimulation rate choice. More of the auditory pathway can be examined through recording eABR and improved correlation with M-levels through the use of an integrated eSRT measure. More recently electrocochleography, involving acoustic stimulation and electrical recording via the implant opens up a new range of applications: real-time monitoring of electrode insertion, objective audiogram estimation, scalar place determination, detection of electrode extrusion and general cochlear health.

Results will be shown that confirm the use of all the measures listed above, demonstrating that this raft of electrophysiological measures add an enormous amount to our knowledge of what is happening within the cochlea.

With the evolution seen in the past there is every reason to believe that further insights will be possible into the electrically stimulated cochlea, allowing improved structure preserving surgery, individualized fitting and optimization of outcome.