Maps created using a new objective procedure (C-NRT) correlate with behavioral, loudness-balanced maps: a study in adult cochlear implant users

In uncooperative patients, electrical compound action potential (ECAP) thresholds are reliable in predicting T-levels, but are not in determining the C-level profile. The present study aims to assess if the C-level profile can be predicted by a new objective procedure (C-NRT) which uses the amplitude growth function (AGF) and is based on the assumption that equal ECAP amplitudes elicit equal loudness percepts. This is a correlational study conducted in five tertiary care referral hospitals with 21 post-lingually deaf adult cochlear implant users. Two maps were created: a behavioral, bitonal balanced (BB) map and an objective map, in which T-levels were the same as in the BB map, and C-levels were obtained with C-NRT. C-NRT consisted of performing the AGF of nine electrodes, and of setting the current level eliciting a 100 μV ECAP amplitude as C-level in the map. AutoNRT was also measured. Main outcome measures were correlation between behavioral C-profile level, objective C-profile level, behavioral T-profile level and objective T-profile (AutoNRT) level; disyllabic word recognition scores in quiet and in noise conditions (SNR = + 10 and 0) with both maps. A strong correlation was found between behavioral and C-NRT-derived C-levels (mean per electrode correlation: R = 0.862, p < 0.001). C-NRT could predict behavioral C-levels with a greater accuracy than AutoNRT. Word recognition was significantly better with BB maps only in the quiet condition (p = 0.002). C-NRT is more accurate than AutoNRT in predicting the C-level profile in adult cochlear implant users. This finding encourages future application in uncooperative patients, especially in very young children.