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

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.

Direct Acoustic Stimulation at the Lateral Canal: An Alternative Route to the Inner Ear?

“…Other studies have showed that the vibrations measured at the center of the RWM increase linearly with acoustical stimulation level in the range of 50 to 110 dB SPL [ 25 ]. As mentioned by Grossöhmichen et al [ 26 ], the constancy of the vibration pattern allows a relative estimation of stimulation efficiency in forward stimulation, moreover for the comparison of different coupling situations. Hence, similarly [ 26 ] the position of the reflective tape on the RWM was kept constant approximately at an anterior-central position of the RWM throughout each of the experiments.…”

Feasibility of Round Window Stimulation by a Novel Electromagnetic Microactuator

“…Compared to the available systems in the market [7, 9], the actuator showed a good performance. Concerning speech relevant frequencies of 0.5–4 kHz the achieved SPLs were within 85–105 dB HL [15].…”

“…Although Spindel et al demonstrated already in 1995 successfully the stimulation of the RWM using an implantable device [1], it took a decade before this approach was clinically applied to patients [3–5]. Since then, the round window (RW) stimulation has developed to a successful treatment of mixed hearing losses [6, 7]. Due to the still high variability in the outcomes, research focusses on the investigation and optimization of the coupling between the implantable device and the RWM [8, 9].…”

Hearing Aid Treatment for Patients with Mixed Hearing Loss. Part II: Speech Recognition in Comparison to Direct Acoustic Cochlear Stimulation

“…As a consequence, the gain and maximum output of this device are not limited by the ABG. Furthermore, measurements have shown that the DACI actuator can provide a broad bandwidth and high MPO [Grossöhmichen et al, 2015].…”