Differential Intracochlear Sound Pressure Measurements in Normal Human Temporal Bones

Abstract

We present the first simultaneous sound pressure measurements in scala vestibuli and scala tympani of the cochlea in human cadaveric temporal bones. The technique we employ, which exploits microscale fiberoptic pressure sensors, enables the study of differential sound pressure at the cochlear base. This differential pressure is the input to the cochlear partition, driving cochlear waves and auditory transduction. In our results, the sound pressure in scala vestibuli (P SV ) was much greater than scala tympani pressure (P ST ), except for very low and high frequencies where P ST significantly affected the input to the cochlea. The differential pressure (P SV − P ST ) is a superior measure of ossicular transduction of sound compared to P SV alone: (P SV −P ST ) was reduced by 30 to 50 dB when the ossicular chain was disarticulated, whereas P SV was not reduced as much. The middle ear gain P SV /P EC and the differential pressure normalized to ear canal pressure (P SV − P ST )/P EC were generally bandpass in frequency dependence. At frequencies above 1 kHz, the group delay in the middle ear gain is about 83 μs, over twice that of the gerbil. Concurrent measurements of stapes velocity produced estimates of cochlear input impedance, the differential impedance across the partition, and round window impedance. The differential impedance was generally resistive, while the round window impedance was consistent with compliance in conjunction with distributed inertia and damping. Our technique of measuring differential pressure can be used to study inner ear conductive pathologies (e.g., semicircular dehiscence), as well as non-ossicular cochlear stimulation (e.g., round window stimulation and bone conduction)-situations that cannot be completely quantified by measurements of stapes velocity or scala vestibuli pressure by themselves.

Finite element modelling of human auditory periphery including a feed-forward amplification of the cochlea

“…The model results were compared with the experimental data measured in human temporal bones by several groups. Middle-ear sound pressure gain reached the maximum value at frequencies of 1 -2 kHz predicted by the FE model and measured in temporal bones by Aibara et al (2001), Nakajima et al (2009) and Puria and Allen (1991). The good agreement between the model-predicted middle-ear transfer function and that measured in human temporal bones in acoustic pressure transmission is shown in Figure 6.…”

“…As shown in Figure 6(A), the pressure gain from the TM to the SV has a maximum magnitude of approximately 23 dB. The FE model well predicted the middle-ear pressure gain over frequencies of 0.2-8 kHz compared to the results measured from human cadaver ears by Aibara et al and Puria et al The magnitude curve of model was about 4 dB higher than the results reported by Nakajima et al (2009) above 1 kHz.…”

“…Figure 6 shows the FE model-derived middle-ear pressure gain (solid line), which is defined as the ratio of SV pressure near the OW to the ear canal sound pressure at the surface of the TM. The modelling results were also compared with published data by Aibara et al (2001), Nakajima et al (2009) and Puria and Allen (1991). As shown in Figure 6(A), the pressure gain from the TM to the SV has a maximum magnitude of approximately 23 dB.…”

Pressures in the human cochlea during bone conduction

“…methods used to measure ear-canal pressure and velocities (e.g., stapes, round window, promontory, etc.) have been described in earlier publications [1,3]. The cartilaginous ear canal was removed in our preparation, thus the contribution of ear canal compression (occusion effect) of BC that would have occurred was presumably reduced in these experiments.…”

“…Because the highest voltage before significant distortion occurred was approximately 71 mV RMS , an input voltage of about 40 mV RMS across all frequencies was used. Intracochlear pressure measurements were made using 150-160 m diameter fiberoptic pressure sensors developed by Olson [1]. Cochleostomies (~200 m in diameter) were drilled by hand under fluid to prevent entrance of air into the cochlea.…”