Greene Nathaniel T, Jenkins Herman A, Tollin Daniel J, Easter James R
Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, CO, USA; Department of Otolaryngology, University of Colorado School of Medicine, Aurora, CO, USA.
Department of Otolaryngology, University of Colorado School of Medicine, Aurora, CO, USA.
Hear Res. 2017 May;348:16-30. doi: 10.1016/j.heares.2017.02.002. Epub 2017 Feb 9.
The stapes is held in the oval window by the stapedial annular ligament (SAL), which restricts total peak-to-peak displacement of the stapes. Previous studies have suggested that for moderate (<130 dB SPL) sound levels intracochlear pressure (P), measured at the base of the cochlea far from the basilar membrane, increases directly proportionally with stapes displacement (D), thus a current model of impulse noise exposure (the Auditory Hazard Assessment Algorithm for Humans, or AHAAH) predicts that peak P will vary linearly with D up to some saturation point. However, no direct tests of D, or of the relationship with P during such motion, have been performed during acoustic stimulation of the human ear. In order to examine the relationship between D and P to very high level sounds, measurements of D and P were made in cadaveric human temporal bones. Specimens were prepared by mastoidectomy and extended facial recess to expose the ossicular chain. Measurements of P were made in scala vestibuli (P) and scala tympani (P), along with the SPL in the external auditory canal (P), concurrently with laser Doppler vibrometry (LDV) measurements of stapes velocity (V). Stimuli were moderate (∼100 dB SPL) to very high level (up to ∼170 dB SPL), low frequency tones (20-2560 Hz). Both D and P increased proportionally with sound pressure level in the ear canal up to approximately ∼150 dB SPL, above which both D and P showed a distinct deviation from proportionality with P. Both D and P approached saturation: D at a value exceeding 150 μm, which is substantially higher than has been reported for small mammals, while P showed substantial frequency dependence in the saturation point. The relationship between P and D remained constant, and cochlear input impedance did not vary across the levels tested, consistent with prior measurements at lower sound levels. These results suggest that P sound pressure holds constant relationship with D, described by the cochlear input impedance, at these, but perhaps not higher, stimulation levels. Additionally, these results indicate that the AHAAH model, which was developed using results from small animals, underestimates the sound pressure levels in the cochlea in response to high level sound stimulation, and must be revised.
镫骨通过镫骨环状韧带（SAL）固定于卵圆窗，该韧带限制镫骨的峰 - 峰总位移。先前的研究表明，对于中等强度（<130 dB SPL）的声级，在远离基底膜的耳蜗底部测量的耳蜗内压力（P）与镫骨位移（D）成正比增加，因此当前的脉冲噪声暴露模型（人类听觉危害评估算法，或AHAAH）预测，峰值P将与D呈线性变化，直至达到某个饱和点。然而，在对人耳进行声刺激期间，尚未对D或这种运动期间与P的关系进行直接测试。为了研究D与P对于非常高强度声音的关系，在人尸体颞骨中进行了D和P的测量。通过乳突切除术和扩大的面神经隐窝制备标本，以暴露听骨链。在测量镫骨速度（V）的激光多普勒振动测量（LDV）的同时，测量前庭阶（P）和鼓阶（P）中的P，以及外耳道中的声压级（P）。刺激为中等强度（约100 dB SPL）至非常高强度（高达约170 dB SPL）的低频音调（20 - 2560 Hz）。在耳道声压级达到约150 dB SPL之前，D和P均与声压级成正比增加，高于此值时，D和P均显示出与P的比例关系明显偏离。D和P均接近饱和：D的值超过150μm，这远高于小型哺乳动物所报道的值，而P在饱和点表现出明显的频率依赖性。P与D之间的关系保持不变，并且耳蜗输入阻抗在测试的各个声级之间没有变化，这与先前在较低声级下的测量结果一致。这些结果表明，在这些刺激水平（但可能不是更高水平）下，P声压与D保持由耳蜗输入阻抗描述的恒定关系。此外，这些结果表明，使用小动物结果开发的AHAAH模型低估了耳蜗对高强度声音刺激的声压水平，必须进行修正。
