Gruenwald, Jill M.

Objective: 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. Patients: Adult candidates for CI. Interventions: 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. Main outcome measures: 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. Results: 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. Conclusions: 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.

Objectives A small number of cochlear implant (CI) users experience facial nerve stimulation (FNS), which can manifest as facial twitching. In some patients, this can be resolved by adjusting the electrical stimulation parameters. However, for others, facial stimulation can significantly impair CI outcomes or even prevent its use. The exact mechanisms underlying FNS are unclear and may vary among patients. Design Transimpedance measurements were used to assess lateral and longitudinal spread of current within 15 cochlea of nucleus CI recipients with FNS (13 unilateral recipients and 1 bilateral recipient). We compared the transimpedance measurements with programming parameters from clinical visits and pre- and postoperative temporal bone computed tomography (CT) scans to identify factors that may contribute to FNS in each CI ear. Results In nine ears, transimpedance curves showed inflection, which suggests a localized current sink within the cochlea. This indicates a low-impedance pathway through which current exits the cochlea and stimulates the labyrinthine segment of the facial nerve canal. Electrodes near this current sink were disabled or underfit to minimize facial stimulation. In the other seven ears, current flow peaked toward the basal end of the cochlea, suggesting that current exits through the round window or other structures near the basal end of the cochlea, stimulating the tympanic segment of the facial nerve. Conclusions Objective transimpedance measurements can be used to elucidate the mechanisms of FNS and to develop strategies for optimizing electrical stimulation parameters and speech coding to minimize or eliminate FNS in a small subset of CI users.