Dirckx Joris J J, Buytaert Jan A N, Decraemer Willem F
Laboratory of Biomedical Physics, Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020, Wilrijk-Antwerpen, Belgium.
J Assoc Res Otolaryngol. 2006 Dec;7(4):339-51. doi: 10.1007/s10162-006-0048-5. Epub 2006 Aug 4.
Due to changes in ambient pressure and to the gas-exchange processes in the middle ear (ME) cavity, the ear is subject to ultra-low-frequency pressure variations, which are many orders of magnitude larger than the loudest acoustic pressures. Little quantitative data exist on how ME mechanics deals with these large quasi-static pressure changes and because of this lack of data, only few efforts could be made to incorporate quasi-static behavior into computer models. When designing and modeling ossicle prostheses and implantable ME hearing aids, the effects of large ossicle movements caused by quasi-static pressures should be taken into account. We investigated the response of the ME to slowly varying pressures by measuring the displacement of the umbo and the stapes in rabbit with a heterodyne interferometer with position decoder. Displacement versus pressure curves were obtained at linear pressure change rates between 200 Pa/s and 1.5 kPa/s, with amplitude +/-2.5 kPa. The change in stapes position associated with a pressure change is independent of pressure change rate (34 microm peak-to-peak at +/-2.5 kPa). The stapes displacement versus pressure curves are highly nonlinear and level off for pressures beyond +/-1 kPa. Stapes motion shows no measurable hysteresis at 1.5 kPa/s, which demonstrates that the annular ligament has little viscoelasticity. Hysteresis increases strongly at the lowest pressure change rates. The stapes moves in phase with the umbo and with pressure, but the sense of rotation of the hysteresis loop of stapes is phase inversed. Stapes motion is not a simple lever ratio mimic of umbo motion, but is the consequence of complex changes in ossicle joints and ossicle position. The change in umbo position produced by a +/-2.5 kPa pressure change decreases with increasing rate from 165 microm at 200 Pa/s to 118 microm at 1.5 kPa/s. Umbo motion already shows significant hysteresis at 1.5 kPa/s, but hysteresis increases further as pressure change rate decreases. We conclude that in the quasi-static regime, ossicle movement is not only governed by viscoelasticity, but that other effects become dominant as pressure change rate decreases below 1 kPa/s. The increasing hysteresis can be caused by increasing friction as speed of movement decreases, and incorporating speed-dependent friction coefficients will be essential to generate realistic models of ossicle movements at slow pressure change rates.
由于环境压力的变化以及中耳（ME）腔内的气体交换过程，耳朵会受到超低频压力变化的影响，这些压力变化比最大声压大许多个数量级。关于中耳力学如何应对这些大的准静态压力变化，几乎没有定量数据，由于缺乏这些数据，几乎无法将准静态行为纳入计算机模型。在设计和模拟听小骨假体及可植入式中耳助听器时，应考虑准静态压力引起的大听小骨运动的影响。我们通过使用带有位置解码器的外差干涉仪测量兔子鼓膜脐部和镫骨的位移，研究了中耳对缓慢变化压力的响应。在200 Pa/s至1.5 kPa/s的线性压力变化率下，获得了位移与压力的曲线，压力幅值为±2.5 kPa。与压力变化相关的镫骨位置变化与压力变化率无关（在±2.5 kPa时峰峰值为34微米）。镫骨位移与压力的曲线高度非线性，对于超过±1 kPa的压力趋于平稳。在1.5 kPa/s时，镫骨运动没有可测量的滞后现象，这表明环状韧带几乎没有粘弹性。在最低压力变化率下，滞后现象强烈增加。镫骨与鼓膜脐部同步且与压力同相移动，但镫骨滞后环的旋转方向相反。镫骨运动不是鼓膜脐部运动的简单杠杆比模拟，而是听小骨关节和听小骨位置复杂变化的结果。由±2.5 kPa压力变化产生的鼓膜脐部位置变化随着速率增加而减小，从200 Pa/s时的165微米降至1.5 kPa/s时的118微米。鼓膜脐部运动在1.5 kPa/s时已经显示出明显的滞后现象，但随着压力变化率降低，滞后现象进一步增加。我们得出结论，在准静态状态下，听小骨运动不仅受粘弹性支配，而且当压力变化率降至1 kPa/s以下时，其他影响变得占主导地位。随着运动速度降低，摩擦力增加可能导致滞后现象增加，在缓慢压力变化率下纳入与速度相关的摩擦系数对于生成听小骨运动的真实模型至关重要。
