Intracochlear Recordings of Cochlear Microphonics in Hearing Preservation Cochlear Implantees

Objectives: The objectives of this study were: 1) to identify the most sensitive frequency for recording of cochlear microphonics (CM) in cochlear implant users with a wide degree of hearing abilities and deep electrode insertion; 2) to identify the optimum location within the cochlea for recording of intracochlear potentials.

Methods: Eight females and 8 males were implanted with Flex 20 (n=1); Flex 24 (n=8); Flex 28 (n=1); Flex Soft (n=5); Medium (n=1) and Standard electrode array with cochlear implants Pulsar, Concerto or Sonata, Med-El Corp. Intracochlear acoustically evoked potentials (AEPs) were recorded from the cochlear implant electrodes.

Results: The mean degree of electrode insertion for tone pips of frequency at 250, 500, 1k, 2k and 4 kHz and for the 1 ms click at the location within the cochlea where the maximum CM peak-to-peak amplitudes and peak-to-peak amplitudes occurred were: 312.2 ±198.5, 294.4 ±182.1, 248.4 ±181.0, 171.6 ±149.6, 152.8 ±129.2, and 295.3 ±218.2 μV, respectively, and the mean maximum ACMpp amplitudes were: 109.5 ±116.2, 154.3 ±151.8, 161.3 ±170.2, 148.1 ±229.5, 106.1 ±147.6, and 166.4 ±171.2 μV, respectively.

Conclusion: Among the tone pips of various frequencies, 1k or 500Hz were the most sensitive for cochlear implant users. The most sensitive place in the cochlea to record the CM potentials depended on the tone frequency used. The deeper into the cochlea the mean maximum CM peak-to-peak amplitude was measured, the lower the stimulating tone frequency was.