Experimental Study of Vibrations of Gerbil Tympanic Membrane with Closed Middle Ear Cavity

The purpose of the present work is to investigate the spatial vibration pattern of the gerbil tympanic membrane (TM) as a function of frequency. In vivo vibration measurements were done at several locations on the pars flaccida and pars tensa, and along the manubrium, on surgically exposed gerbil TMs with closed middle ear cavities. A laser Doppler vibrometer was used to measure motions in response to audio frequency sine sweeps in the ear canal. Data are presented for two different pars flaccida conditions: naturally flat and retracted into the middle ear cavity. Resonance of the flat pars flaccida causes a minimum and a shallow maximum in the displacement magnitude of the manubrium and pars tensa at low frequencies. Compared with a flat pars flaccida, a retracted pars flaccida has much lower displacement magnitudes at low frequencies and does not affect the responses of the other points. All manubrial and pars tensa points show a broad resonance in the range of 1.6 to 2 kHz. Above this resonance, the displacement magnitudes of manubrial points, including the umbo, roll off with substantial irregularities. The manubrial points show an increasing displacement magnitude from the lateral process toward the umbo. Above 5 kHz, phase differences between points along the manubrium start to become more evident, which may indicate flexing of the tip of the manubrium or a change in the vibration mode of the malleus. At low frequencies, points on the posterior side of the pars tensa tend to show larger displacements than those on the anterior side. The simple low-frequency vibration pattern of the pars tensa becomes more complex at higher frequencies, with the breakup occurring at between 1.8 and 2.8 kHz. These observations will be important for the development and validation of middle ear finite-element models for the gerbil.

本研究的目的是探究沙鼠鼓膜（TM）的空间振动模式随频率的变化情况。在活体上，对松弛部和紧张部的多个位置以及锤骨柄进行了振动测量，测量对象是中耳腔封闭且经手术暴露的沙鼠鼓膜。使用激光多普勒测振仪测量耳道内音频正弦扫描时的运动。给出了两种不同松弛部状态的数据：自然平坦状态和回缩到中耳腔的状态。平坦的松弛部在低频时的共振会导致锤骨柄和紧张部的位移幅值出现一个最小值和一个较浅的最大值。与平坦的松弛部相比，回缩的松弛部在低频时位移幅值要低得多，并且不会影响其他点的响应。所有锤骨柄和紧张部的点在1.6到2 kHz范围内都显示出宽频共振。在此共振频率之上，包括脐点在内的锤骨柄各点的位移幅值大幅下降且不规则。锤骨柄各点从外侧突向脐点位移幅值逐渐增大。在5 kHz以上，锤骨柄上各点之间的相位差开始变得更加明显，这可能表明锤骨柄尖端弯曲或锤骨振动模式发生变化。在低频时，紧张部后侧的点往往比前侧的点位移更大。紧张部的简单低频振动模式在高频时变得更加复杂，在1.8到2.8 kHz之间出现分解。这些观察结果对于沙鼠中耳有限元模型的建立和验证具有重要意义。