Loudness Adaptation Among Cochlear Implant Candidates to Inform Hearing Preservation During Awake Cochlear...

Cochlear implantation (CI) under local anesthesia facilitates intraoperative behavioral patient feedback to potentially improve acoustic hearing preservation and limit intracochlear trauma. Patient feedback during electrode insertion is potentially confounded by loudness adaptation, a perception of tone decrease despite stable presentation, or insufficient intensity discrimination, a failure to detect a change in hearing despite one actually occurring. Both loudness adaptation and intensity discrimination are critical factors for awake CI and have not been systematically studied in the CI candidate population.

Adult candidates for CI.

Under routine audiometric testing conditions in a soundproof booth, a standard behavioral audiogram, audiogram obtained in recorded ambient operating room (OR) noise, loudness adaptation to sustained suprathreshold (+10 and +20 dB) pure tones at 500, 1000, 2000, and 4000 Hz in both quiet and in ambient OR noise, and intensity discrimination to sustained suprathreshold (+10 and +20 dB) pure tones at 500, 1000, 2000, and 4000 Hz were performed.

Pure tone average (PTA) in quiet and in ambient OR noise, proportion of patients reporting loudness adaptation at different suprathreshold levels and frequencies, and reliability of intensity discrimination.

In total, 20 ears were included for study. The median PTA was similar between testing in quiet (68 dB, IQR: 63 to 73) and in ambient OR noise (68 dB, IQR: 62 to 73). Most participants (n = 11, 55%) reported loudness adaptation when testing at +10 dB suprathreshold intensity, with a decreased proportion (n = 8, 40%) demonstrating adaptation at the higher tone intensity (+20 dB suprathreshold). Loudness adaptation varied among frequencies, with a trend toward increasing adaptation at higher frequencies at both testing intensities. Participants demonstrated excellent intensity discrimination, detecting a 5 dB difference when testing at +10 dB both in quiet and with background OR noise in 82 of the 85 (96%) tests performed across the frequency range, although with lower intensity discrimination at +20 dB, particularly in background OR noise.

For CI candidates, pure tone audiometric performance did not significantly differ in background OR noise, confirming the reliability of intraoperative audiometric testing. For optimal tone presentation, there is decreasing loudness adaptation with increased tone presentation (+20 dB suprathreshold) and in lower frequencies of tone presentation. Intensity discrimination was reliable at a 5 dB increment across a range of testing parameters.