Effects of Skin Thickness on Cochlear Input Signal Using Transcutaneous Bone Conduction Implants

Abstract

Hypothesis Intracochlear sound pressures (PIC) and velocity measurements of the stapes, round window, and promontory (VStap/RW/Prom) will show frequency dependent attenuation using magnet-based, transcutaneous bone-conduction implants (TCBCI) in comparison to direct-connect, skin-penetrating implants (DCBCI). Background TCBCIs have recently been introduced as alternatives to DCBCIs. Clinical studies have demonstrated elevated high-frequency thresholds for TCBCIs as compared to DCBCIs; however, little data exists examining the direct effect of skin thickness on the cochlear input signal using TCBCIs. Methods Using seven cadveric heads, PIC was measured in the scala vestibuli and tympani with fiber-optic pressure sensors concurrently with VStap/RW/Prom via laser Doppler vibrometry. Ipsilateral titanium implant fixtures were placed and connected to either a DCBCI or TCBCI. Soft tissue flaps with varying thicknesses (no flap, 3, 6, and 9 mm) were placed successively between the magnetic plate and sound processor magnet. A bone-conduction transducer coupled to custom software provided pure tone stimuli between 120 to 10240 Hz. Results Stimulation via the DCBCI produced the largest response magnitudes. The TCBCI showed similar PSV/ST and VStap/RW/Prom with no intervening flap, and a frequency-dependent, non-linear reduction of magnitude with increasing flap thickness. Phase shows a comparable dependence on transmission delay as the acoustic baseline, and the slope steepens at higher frequencies as flap thickness increases suggesting a longer group delay. Conclusions Proper soft tissue management is critical to optimize the cochlear input signal. The skin thickness related effects on cochlear response magnitudes should be taken into account when selecting patients for a TCBCI.

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.…”

Intracochlear Measurements of Interaural Time and Level Differences Conveyed by Bilateral Bone Conduction Systems

“…Prior studies by our group evaluated the transfer function magnitudes in response to ipsilateral and contralateral BC stimuli (unpublished data). 16 Figure 2A demonstrates the average transfer function magnitudes in each specimen for ipsilateral and contralateral BC. Comparison of the ipsilateral and contralateral bone conduction transfer functions demonstrated that contralateral stimulation results in a 5–15 dB reduction in transfer function magnitude, primarily with high frequency stimuli (see Figure 2B).…”

“…The method of sound stimuli production and response recording was performed in similar fashion to previously described protocols. 14, 16 Stimuli were generated digitally, presented to the specimen via a bare (i.e., no sound processing) BC transducer or a closed-field magnetic speaker (MF1; Tucker-Davis Technologies Inc., Alachua, FL, U.S.A.) powered by one channel of a stereo amplifier (SA1; Tucker Davis Technologies Inc., Alachua, FL, U.S.A.) and driven by an external sound card (Hammerfall Multiface II; RME, Haimhausen, Germany) modified to eliminate high-pass filtering on the analog output. Stimuli were generated and responses were recorded at a sampling rate of 96,000 Hz and controlled by a custom program in Matlab (MathWorks Inc., Natick, MA, U.S.A.).…”

A MEMS Condenser Microphone-Based Intracochlear Acoustic Receiver

“…In previous studies, ICSP in mammals has been measured with: piezoelectric sensors [9] in cats; piezoresistive sensors [10]- [12] in guinea pigs; and fiber-optic based sensors [5], [13]- [16] in gerbils. In human cadaver heads, ICSP has been quantified with strain gauges [17] and fiber-optic based sound pressure sensors [18], [19]. However, the broader application of existing ICSP measurement methods is limited by laborious sensor preparation, sensor sensitivity changes related to biomaterial deposits on the sensing elements, complexity of the experimental ICSP measurement setup, and low sensor SNR.…”