Evaluation of the Bimodal Benefit in a Large Cohort of Cochlear Implant Subjects Using a Contralateral Hearing Aid

Objective: To investigate the benefit of contralateral residual hearing in a large group of cochlear implant recipients with different degrees of residual hearing. Patients: One hundred and forty-one adult patients (age in years: mean 58.82, min 16.27, max 88.20) wearing a cochlear implant and a contralateral hearing aid, bimodal. Intervention: Rehabilitative. Main Outcome Measures: All 141 patients underwent speech perception testing in quiet and noise with cochlear implant (CI) alone, and with CI and hearing aid (HA). Additionally, pure-tone air conduction threshold levels were measured in all subjects. The bimodal benefit was analyzed and correlations to the hearing threshold for different audiometric frequencies were calculated. Results: Comparison between the scores for CI alone and CI + HA showed statistically significant advantages (p < 0.0001) in all four tests. The benefit for sentences in noise to each individual patient showed a negative correlation with the hearing threshold level of 125 Hz and 250 Hz, using a linear regression analysis applying the Spearman's rho correlation coefficient (r = -0.32, -0.232), and a significant difference at p = 0.006, p = 0.007. The correlations involving speech understanding in sentences in noise, and the hearing level of 500 Hz and above, are not significant for the benefit obtained with a contralateral hearing aid. Conclusion: The benefit of combined electric and acoustic hearing in bimodally fitted subjects depends mainly on residual hearing in the low-frequency range below 500 Hz. For bimodal fitting to yield significant benefits, hearing loss in the contralateral ear should not exceed 80 dB HL in the low frequencies.