Ossicular Mechanics of a Low Frequency Ear and Implications for Bone-Conducted Hearing.

摘要 哺乳动物的耳朵包含三块称为听小骨的中耳骨，它们通过空气传导(AC)。 从鼓膜到内耳的声音和从头骨到内耳的骨传导(BC)振动。这个 有三个听小骨来传递声音的功能意义尚不完全清楚，但它们的 两个灵活的关节周围不同的形状、质量分布和关节结构可以保护内部 耳朵受到静态压力和耳道中出现的交流脉冲声的影响，会降低对 由头部运动、咀嚼等引起的自我产生的BC振动可能同时分散注意力 随着时间的推移，听小骨也可能改善低频下的AC和BC听力。在这项研究中，我们建议测试 听小骨形状、质量和质量分布以及柔韧性对三维听小骨运动和运动的影响 人和大象颞骨对AC和BC的反应向耳蜗声传导 正常和修改条件下的刺激。尽管存在显著的解剖学差异，但人类和 大象在重叠的20赫兹-11千赫频率范围内表现出非常相似的听力图，尽管 大象可以听到20赫兹以下的声音，人类可以听到11千赫以上的声音。中耳骨与头骨大小成比例， 因此，大象的听骨(陆地哺乳动物中最大的)大约重7倍 比人类的要多。研究表明，使用质量负载来提高BC的听力在100赫兹以下 模拟更大的听骨质量，我们对大象的初步测量表明，它们更重的 在低频下，听骨会产生比人类好一个数量级的BC听力。卑诗省听证会在 大象也可能因为一个部分融合的砧踝关节而变得更强壮。因此， 量化人耳与大象耳之间的结构-功能关系和质量负荷可以 提高我们对中耳内部可能的优化和权衡的理解。最直接的 本研究的目的是定量比较人类和大象的听骨链形态和 通过使用µCT测量听小骨形状和质量分布来进行与耳蜗骨输入相关的运动 成像；以及使用3D激光多普勒测量对AC和BC刺激的3D听骨运动 振动测量，适用于增加质量和降低听骨关节柔韧性的正常和改良病例。这个 运动测量将用于制作听小骨的µCT重建的动画，这些结果将被 比较使用惯性矩(MOI)来量化物种间结构的功能含义 在以下方面的改进的差异和效果：1)从耳道到耳蜗的声音传输， 尤其是在较低的频率下；2)听小骨的相对运动；以及3)声音通过 骨传导。通过这种物种间的比较揭示的结构-功能关系可能 在专门的被动式和主动式中耳假体修复装置的设计中产生了影响 人类的听觉。

Abstract The mammalian ear contains three middle-ear bones called ossicles that transmit both air-conducted (AC) sound from the eardrum to the inner ear and bone-conducted (BC) vibrations of the skull to the inner ear. The functional significance of having three ossicles to transmit sound is not completely understood, yet their varied shapes, mass distributions, and articulation around two flexible joints could serve to protect the inner ear from static pressure and impulsive AC sounds presented in the ear canal, and could reduce sensitivity to potentially distracting self-generated BC vibrations caused by head movement, chewing, etc. At the same time, ossicles might also improve AC and BC hearing at low frequencies. In this study, we propose to test the role that ossicular shape, mass and mass distribution, as well as flexibility play on 3D ossicular motion and sound transmission into the cochlea for both human and elephant temporal bones in response to AC and BC stimulation under normal and modified conditions. Despite significant anatomical differences, humans and elephants exhibit very similar audiograms over their overlapping 20 Hz–11 kHz frequency range, although elephants can hear below 20 Hz and humans can hear above 11 kHz. Middle-ear bones scale with skull size, such that elephant ossicles (the largest among terrestrial mammals) are approximately seven times heavier than those of humans. Studies suggest that BC hearing is enhanced below 100 Hz using mass-loading to simulate greater ossicular mass, and our preliminary measurements on elephants suggest that their heavier ossicles should yield an order of magnitude better BC hearing than humans at low frequencies. BC hearing in elephants might also be enhanced due to what appears to be a partially fused incudo-malleolar joint. Thus, quantifying the structure–function relationships and mass loading within human versus elephant ears could improve our understanding of the possible optimizations and trade-offs within the middle ear. The immediate goal of this investigation is to quantitatively compare human and elephant ossicular-chain morphology and motion as it relates to input to the cochlea by measuring ossicular shape and mass distributions using µCT imaging; and measuring 3D ossicular motions in response to AC and BC stimulation using 3D laser Doppler vibrometry, for the normal and modified cases with added mass and reduced ossicular-joint flexibility. The motion measurements will be used to animate µCT reconstructions of the ossicles, and these results will be compared using moments of inertia (MOI) to quantify the functional implications of the inter-species structural differences and effects of modifications in terms of: 1) sound transmission from the ear canal to the cochlea, especially at lower frequencies; 2) the relative motion of the ossicles; and 3) the transmission of sound via bone conduction. The structure–function relationships revealed through this inter-species comparison may have ramifications in the design of specialized passive and active middle-ear prosthetic devices for restoring human hearing.