Neural health in cochlear implant users with ipsilateral residual hearing
Studies in cochlear implant (CI) users have shown a correlation between neural health and speech reception performance. Recently, electrically evoked compound action potentials (eCAP) with varying interphase gaps (IPG) have been used to estimate neural health. In the present study, we investigated eCAP characteristics in CI users with ipsilateral residual hearing (electric-acoustic stimulation, EAS). We hypothesized that neural health is better in apical areas in EAS users than in basal areas, due to increased hair cell survival. Amplitude growth functions (AGF) with varying IPGs of 2.1 and 10 μs were measured in 19 MED-EL Flex recipients with residual hearing. The eCAP characteristics slope, N1 latency and stimulus level at 50% maximum eCAP amplitude were investigated for the effect of IPG across electrode positions and were correlated to speech perception outcomes and duration of hearing loss. CI users without residual hearing were used as a control group to compare the patterns of slope, latency and 50% maximum amplitude between both IPGs. IPG showed a significant effect on the eCAP characteristics. The change in stimulus level for the 50% maximum amplitude showed a significant difference between electrode 1 and 3 as well as 1 and 4 in EAS users, maybe indicating impaired neural health in the medial region and validating the measurement in EAS users.
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