Intracochlear Sound Pressure Measurements in Normal Human Temporal Bones During Bone Conduction Stimulation

Abstract

Bone conduction (BC) is heavily relied upon in the diagnosis and treatment of hearing loss, but is poorly understood. For example, the relative importance and frequency dependence of various identified BC sound transmission mechanisms that contribute to activate the cochlear partition remain unknown. Recently, we have developed techniques in fresh human cadaveric specimens to directly measure scalae pressures with micro-fiberoptic sensors, enabling us to monitor the input pressure drive across the cochlear partition that triggers the cochlear traveling wave during air conduction (AC) and round-window stimulation. However, BC stimulation poses challenges that can result in inaccurate intracochlear pressure measurements. Therefore, we have developed a new technique described here that allows for precise measurements during BC. Using this new technique, we found that BC stimulation resulted in pressure in scala vestibuli that was significantly higher in magnitude than in scala tympani for most frequencies, such that the differential pressure across the partition-the input pressure drive-was similar to scala vestibuli pressure. BC (stimulated by a Bone Anchored Hearing Aid [Baha]) showed that the mechanisms of sound transmission in BC differ from AC, and also showed the limitations of the Baha bandwidth. Certain kinematic measurements were generally proportional to the cochlear pressure input drive: for AC, velocity of the stapes, and for BC, low-frequency acceleration and high-frequency velocity of the cochlear promontory. Therefore, our data show that to estimate cochlear input drive in normal ears during AC, stapes velocity is a good measure. During BC, cochlear input drive can be estimated for low frequencies by promontory acceleration (though variable across ears), and for high frequencies by promontory velocity.

Investigation of Mechanisms in Bone Conduction Hyperacusis With Third Window Pathologies Based on Model Predictions

“…The model-predicted sound pressures with BC excitation are shown in Figures 3C,D together with experimentally obtained BC stimulated intra-cochlear sound pressures in Stieger et al ( 37 ) and Mattingly et al ( 38 ). The scala vestibuli side intra-cochlear sound pressures in relation to the cochlear promontory velocity are shown in Figure 3C .…”

“…The sound pressure at position A is relatively close to the experimentally obtained sound pressures while the sound pressure at position B is around 5 dB lower than the position A sound pressure. The model based sound pressure predictions and the Mattingly et al ( 38 ) experimental data indicate an overall 20 dB/decade rise while the Stieger et al ( 37 ) data show a steeper rise at frequencies below 1.5 kHz and a near flat response with frequency at the higher frequencies. The BC model predictions of the scala tympani sound pressure in Figure 3D is relatively similar to the Stieger et al ( 37 ) measurements while the Mattingly et al ( 38 ) sound pressures are 5 to 10 dB greater compared to the model predictions.…”

“… Predictions of intra-cochlear sound pressures with AC stimulation and experimentally measured intra-cochlear sound pressures in Nakajima et al ( 36 ) and Niesten et al ( 14 ) in (A) the vestibular side and (B) scala tympani. Predictions of intra-cochlear sound pressures with BC stimulation and experimentally measured intra-cochlear sound pressures in Stieger et al ( 37 ) and Mattingly et al ( 38 ) in (C) the vestibular side and (D) scala tympani. Positions (A–D) refer to position in the model schematics in Figure 1 .…”

“…Position A is in the center of the vestibule, position B is at the border between the vestibule and scala vestibuli close to the stapes footplate, position C is at the center of scala vestibuli, and position D is at the center of scala tympani. According to the descriptions of the experiments in the temporal bones, the probe positions were close to positions B and D in the model ( 14 , 36 , 37 ). The exact position of the pressure sensors were not equally well-defined in the Mattingly et al ( 38 ) study.…”

“…First, the model itself is validated against experimental data in the normal condition. This is accomplished by comparing intra-cochlear pressures in the model with measurements in cadaveric temporal bones with AC stimulation ( 14 , 36 ) and BC stimulation ( 37 ) and also with BC stimulation in whole human cadaver heads ( 38 ). In the experimental datasets the scala vestibuli and scala tympani pressures were measured by small pressure probes inserted into the scalae through tiny holes that were sealed during the measurements ( 14 , 36 – 38 ).…”