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. 2015 Mar 18;10(3):e0119601.
doi: 10.1371/journal.pone.0119601. eCollection 2015.

The Codacs™ Direct Acoustic Cochlear Implant Actuator: Exploring Alternative Stimulation Sites and Their Stimulation Efficiency

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Free PMC article

The Codacs™ Direct Acoustic Cochlear Implant Actuator: Exploring Alternative Stimulation Sites and Their Stimulation Efficiency

Martin Grossöhmichen et al. PLoS One. .
Free PMC article

Abstract

This work assesses the efficiency of the Codacs system actuator (Cochlear Ltd., Sydney Australia) in different inner ear stimulation modalities. Originally the actuator was intended for direct perilymph stimulation after stapedotomy using a piston prosthesis. A possible alternative application is the stimulation of middle ear structures or the round window (RW). Here the perilymph stimulation with a K-piston through a stapes footplate (SFP) fenestration (N = 10) as well as stimulation of the stapes head (SH) with a Bell prosthesis (N = 9), SFP stimulation with an Omega/Aerial prosthesis (N = 8) and reverse RW stimulation (N = 10) were performed in cadaveric human temporal bones (TBs). Codacs actuator output is expressed as equivalent sound pressure level (eq. SPL) using RW and SFP displacement responses, measured by Laser Doppler velocimetry as reference. The axial actuator coupling force in stimulation of stapes and RW was adjusted to ~5 mN. The Bell prosthesis and Omega/Aerial prosthesis stimulation generated similar mean eq. SPLs (Bell: 127.5-141.8 eq. dB SPL; Omega/Aerial: 123.6-143.9 eq. dB SPL), being significantly more efficient than K-piston perilymph stimulation (108.6-131.6 eq. dB SPL) and RW stimulation (108.3-128.2 eq. dB SPL). Our results demonstrate that SH, SFP and RW are adequate alternative stimulation sites for the Codacs actuator using coupling prostheses and an axial coupling force of ~5 mN. Based on the eq. SPLs, all investigated methods were adequate for in vivo hearing aid applications, provided that experimental conditions including constant coupling force will be implemented.

Conflict of interest statement

Competing Interests: This work is part of the doctoral thesis of MG and was supported by Cochlear Ltd. MG and HM received travel support by Cochlear Ltd. to meetings. This does not alter the authors’ adherence to PLOS ONE policies on sharing data and materials.

Figures

Fig 1
Fig 1. Illustration of the implanted Codacs system.
(CC-BY by courtesy of Cochlear Ltd.).
Fig 2
Fig 2. Section view of the Codacs actuator.
(CC-BY by courtesy Cochlear Ltd.).
Fig 3
Fig 3. Stimulation modes tested.
(A) Codacs actuator without AI perpendicular to the RW membrane. (B) Bell prosthesis (BP) crimped to the Codacs actuator AI and coupled to the exposed stapes head. Reflectors were placed on stapes footplate and round window (RW). (C) Omega connector (OC) placed between the remains of the stapes crura (SC) together with the Aerial prosthesis (AP) connected to the actuator AI. (D) K-piston (KP) inserted into the inner ear through a SFP fenestration after immobilization of the SFP by ionomer cement (IC).
Fig 4
Fig 4. SFP displacement responses to sound of TBs used for experiments (N = 10).
The black dashed lines depict the limits given by Rosowski et al. [11].
Fig 5
Fig 5. Eq. sound pressure output level (N = 9) of Codacs stimulation with the Bell prosthesis at the SH for nominally 1 Vrms actuator input voltage.
Fig 6
Fig 6. Eq. sound pressure level output (N = 8) of Codacs stimulation with the Omega/Aerial prosthesis at the SFP for nominally 1 Vrms actuator input voltage.
Fig 7
Fig 7. Eq. sound pressure level output (N = 10) obtained in Codacs stimulation of the RW membrane at nominally 1 Vrms actuator input voltage.
Fig 8
Fig 8. Eq. sound pressure level outputs (N = 10) of Codacs stimulation through a SFP fenestration with a K-piston at nominally 1 Vrms actuator input.
Data having SNRs < 10 dB was omitted (TB12 and TB21 at 125 Hz).
Fig 9
Fig 9. Mean values and standard deviations (error bars) of the equivalent sound pressure levels [eq. dB SPL] generated by Codacs actuator stimulation at 1 Vrms for the four investigated stimulation modes.
At all frequencies the stimulation efficiency of Bell prosthesis stimulation at the stapes head (■) and of Omega/Aerial prosthesis stimulation at the SFP (◆) was statistically significantly higher than direct perilymph stimulation (▲) with the K-piston and direct RW stimulation (●).
Fig 10
Fig 10. Equivalent sound pressure levels obtained by oval window stimulation with the Bell prosthesis using either the RW displacements (■) or the SFP displacements (◆) in response to sound and actuator as reference.
Mean values and standard deviations (error bars) of eq. sound pressure level are shown for nominally 1 Vrms actuator input.

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Grant support

This work is part of the doctoral thesis of MG and was supported by Cochlear Ltd. MG and HM received travel support by Cochlear Ltd. to meetings. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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