Abstract
BackgroundCochlear implants (CIs) have become important for the treatment of severe-to-profound sensorineural hearing loss (SNHL). Meanwhile, electrically evoked compound action potentials (ECAPs) and electrically evoked auditory brainstem responses (EABRs), which can be examined and evaluated with minimal patient cooperation, have become more reliable for tone measurement and speech recognition postoperatively. However, few studies have compared the electrophysiological characteristics of the auditory nerve using ECAPs and EABRs under different functional states of the auditory nerve (FSANs). We used guinea pig models in which six electrodes were implanted unilaterally with continuous electrical stimulation (ES) for 4 h. The amplitude growth functions (AGFs) of the alternating polarity ECAP (AP-ECAP) and forward-masking subtraction ECAP (FM-ECAP), as well as the EABR waves under “normal” and “abnormal” FSANs, were obtained.ResultsBoth the AP-ECAP and FM-ECAP thresholds were significantly higher than those measured by EABR under both “normal” FSAN and “abnormal” FSANs (p < 0.05). There was a significant difference in the slope values between electrodes 1 and 2 and electrodes 3 and 4 in terms of the AP-ECAP under the “abnormal” FSAN (p < 0.05). The threshold gaps between the AP-ECAP and FM-ECAP were significantly larger under the “abnormal” FSAN than under the “normal” FSAN (p < 0.05).ConclusionsBoth of the ECAP thresholds were higher than the EABR thresholds. The AP-ECAP was more sensitive than the FM-ECAP under the “abnormal” FSAN.
Highlights
Cochlear implants (CIs) have become important for the treatment of severe-to-profound sensorineural hearing loss (SNHL)
The mean gap between the AP-Electrically evoked compound action potential (ECAP) and Electrically evoked auditory brainstem response (EABR) and between the forwardmasking subtraction ECAP (FM-ECAP) and EABRs under the “normal” functional states of the auditory nerve (FSAN) was 42.9 and 38.7 CL, respectively, while for those under the “abnormal” FSAN was 49.4 and 38.4 CL, respectively. These results suggested that the EABR thresholds were lower than the ECAP thresholds with the methods used in the present study
These results indicated that the slope of the alternating polarity ECAP (AP-ECAP) may be more sensitive in reflecting the “abnormal” FSAN
Summary
The average values of the AP-ECAP, FM-ECAP and EABR thresholds under the “normal” FSAN were 159.2, 155.0 and 116.3 CL, while those under the “abnormal” FSAN were 194.1, 183.1 and 144.7 CL, respectively (Table 1). The gaps among the thresholds under the “normal” FSAN and under “abnormal” FSAN were not significantly different for the AP-ECAPs, FM-ECAPs and EABRs (p > 0.05), the mean values of which were 45.2, 44.4 and 44.8 CL, respectively (Table 3, Fig. 3a). The gaps between the AGF slopes of the AP-ECAP and FM-ECAP were not significantly different (p > 0.05), as the mean values were 7.5 and 8.2, respectively (Table 4, Fig. 3b) These results suggested that the threshold gaps in the ECAP and EABR for the “normal” FSAN and “abnormal” FSAN were effective in reflecting the severity of the “abnormal” FSAN. The corresponding slope gaps of the AGF were comparable (p > 0.05), as the mean value was 5.8 under the “normal” FSAN and 2.2 under the “abnormal” FSAN (Fig. 4b) These results suggested that the “abnormal” FSAN augments the difference between the thresholds of the AP-ECAP and FM-ECAP. AP-ECAP is likely more sensitive in detecting changes in ECAP thresholds under the “abnormal” FSAN
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