Cochlear Implant Electrode Effect on Sound Energy Transfer Within the Cochlea During Acoustic Stimulation

Abstract

Hypothesis Cochlear implants (CI) designed for hearing preservation will not alter mechanical properties of the middle and inner ear as measured by intracochlear pressure (PIC) and stapes velocity (Vstap). Background CIs designed to provide combined electrical and acoustic stimulation (EAS) are now available. To maintain functional acoustic hearing, it is important to know if a CI electrode can alter middle or inner ear mechanics, as any alteration could contribute to elevated low-frequency thresholds in EAS patients. Methods Seven human cadaveric temporal bones were prepared, and pure-tone stimuli from 120Hz–10kHz were presented at a range of intensities up to 110 dB SPL. PIC in the scala vestibuli (PSV) and tympani (PST) were measured with fiber-optic pressure sensors concurrently with VStap using laser Doppler vibrometry. Five CI electrodes from two different manufacturers, with varying dimensions were inserted via a round window approach at six different depths (16–25 mm). Results The responses of PIC and VStap to acoustic stimulation were assessed as a function of stimulus frequency, normalized to SPL in the external auditory canal (EAC), in baseline and electrode inserted conditions. Responses measured with electrodes inserted were generally within ~5 dB of baseline, indicating little effect of cochlear implant electrode insertion on PIC and VStap. Overall, mean differences across conditions were small for all responses, and no substantial differences were consistently visible across electrode types. Conclusions Results suggest that the influence of a CI electrode on middle and inner ear mechanics is minimal, despite variation in electrode lengths and configurations.

Stapes displacement and intracochlear pressure in response to very high level, low frequency sounds

“…specimen 48R), similar to previous observations (Nakajima et al 2009). Nevertheless, H Diff was generally consistent with the previous reports (Greene et al 2015; Mattingly et al, 2015; Nakajima et al, 2009) in the range of frequencies tested previously.…”

“…Recent technological advances have allowed direct measurement of intracochlear pressure in response to sound stimulation in intact human temporal bones (Greene et al 2015; Mattingly et al, 2015; Nakajima et al, 2009; Olson, 1998; Olson, 1999). In this report we set out to characterize ossicular motion and intracochlear pressure in response to low frequency and high level sound stimulation, with particular focus on identifying nonlinearities.…”

A Preliminary Investigation of the Air-Bone Gap

“…Data collected from these specimens are illustrated by dashed lines in Figure 2 and were excluded from subsequent analyses. Responses collected from the remaining three specimens were consistent with previous reports [32, 33, 38-40]. Slightly higher than expected stapes velocities are seen at the highest frequencies tested when compared with results from other research groups; higher velocities are likely due to differences in setup or an unknown methodological issue.…”

“…Temporal bone specimens were prepared as previously described by our laboratory [32-37], similar to methods that have been validated by Nakajima et al and Olson et al [38-40]. Figure 1 illustrates the steps of specimen preparation.…”

“…Generation of sound stimuli and recording of responses was performed as described previously [32, 33, 43]. Briefly, stimuli were generated digitally, and presented via a bone conduction oscillator (Cochlear Ltd., Centennial, CO, U.S.A.) or a closed-field magnetic speaker (MF1; Tucker-Davis Technologies Inc., Alachua, FL) coupled directly to the ear with a foam insert altered to accommodate flexible speaker tubing.…”