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Preservation of Hearing in Cochlear Implant Surgery: Advantages of Combined Electrical and Acoustical Speech Processing

Authors

  • Bruce J. Gantz MD,

    Corresponding author
    1. Department of Otolaryngology—Head and Neck Surgery, University of Iowa Roy J and Lucille A Carver College of Medicine, Iowa City, Iowa, U.S.A.
    • Dr. Bruce J Gantz, Department of Otolaryngology—Head and Neck Surgery, University of Iowa Hospitals and Clinics, 200 Hawkins Drive (21201 PFP), Iowa City, IA 52242–1078, U.S.A.
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  • Christopher Turner PhD,

    1. Department of Otolaryngology—Head and Neck Surgery, University of Iowa Roy J and Lucille A Carver College of Medicine, Iowa City, Iowa, U.S.A.
    2. Department of Speech Pathology and Audiology, The University of Iowa, Iowa City, Iowa, U.S.A.
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  • Kate E. Gfeller PhD,

    1. Department of Speech Pathology and Audiology, The University of Iowa, Iowa City, Iowa, U.S.A.
    2. School of Music, The University of Iowa, Iowa City, Iowa, U.S.A.
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  • Mary W. Lowder MA

    1. Department of Otolaryngology—Head and Neck Surgery, University of Iowa Roy J and Lucille A Carver College of Medicine, Iowa City, Iowa, U.S.A.
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  • Supported (in part) by research grants 2 P50 DC00242 and 1 R01 DC 000377 from the National Institutes on Deafness and Other Communication Disorders, National Institutes of Health; grant RR00059 from the General Clinical Research Centers Program, NCRR, National Institutes of Health; the Iowa Lions Sight and Hearing Foundation; and Cochlear Corporation for developing a cochlear implant to our specifications, providing initial devices at no cost, and sharing data from their ongoing clinical trial with the Hybrid implant.

Abstract

Objectives/Hypothesis: This study documents the importance of preserving residual low-frequency acoustic hearing as those with more residual hearing are selected for cochlear implantation. Surgical strategies used for hearing preservation with a short hybrid cochlear implant are outlined. The benefits of preserved residual low-frequency hearing, improved word understanding in noise, and music appreciation are described.

Study Design: Multicenter, prospective, single-subject design.

Methods: Records were reviewed of 21 individuals participating in an Food and Drug Administration (FDA) feasibility clinical trial who have received an Iowa/Nucleus 10 mm electrode. A second group of subjects receiving implants at the University of Iowa that have used the 10 mm device between 2 years and 6 months were also reviewed. Outcome measures included standardized tests of monosyllabic word understanding, spondees in noise, and common melody recognition.

Results: Low-frequency hearing was maintained in all individuals immediately postoperative. One subject lost hearing at 2.5 months postoperative after a viral infection. The group has averaged a loss of −9 dB low-frequency acoustic hearing between 125 and 1,000 Hz. Monosyllabic word understanding scores at 6 months for a group being followed for an FDA clinical trial using the implant plus hearing aids was 69% correct. For the long-term group receiving implants at Iowa, monosyllabic word understanding in those who have used the device between 6 months and 2 years is 79%. Other important findings include improved recognition of speech in noise (9 dB improvement) as compared with standard cochlear implant recipients who were matched for speech recognition in quiet and near normal recognition of common melodies.

Conclusion: The surgical strategies outlined have been successful in preservation of low-frequency hearing in 96% of individuals. Combined electrical and acoustical speech processing has enabled this group of volunteers to gain improved word understanding as compared with their preoperative hearing with bilateral hearing aids and a group of individuals receiving a standard cochlear implant with similar experience with their device. The improvement of speech in noise and melody recognition is attributed to the ability to distinguish fine pitch differences as the result of preserved residual low-frequency acoustic hearing. Preservation of low-frequency acoustic hearing is important for improving speech in noise and music appreciation for the hearing impaired, both of which are important in real-life situations.

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