Cinamon Udi, Sadé Jacob
Ear Research Laboratory, Department of Bio-Engineering, Tel-Aviv University, Israel.
Otol Neurotol. 2003 Nov;24(6):839-42. doi: 10.1097/00129492-200311000-00002.
The tympanic membrane (TM) and mastoid air cells are measurable pressure buffers of the middle ear (ME).
Pressure homeostasis of the ME is maintained approximately atmospheric by mechanisms that neutralize (buffer) pressure fluctuations, two of which are the TM and mastoid.
Negative pressures were induced by volume changes in an artificial ME model. Those were recorded directly while using a rigid or a flexible TM with "mastoids" of various sizes.
In the rigid TM model, the volume changes correlated linearly with the induced pressures and were confirmed to fit Boyle's law. In the flexible TM model, the pressure/volume correlation was nonlinear up to -50 mmH2O, where the TM was maximally displaced (approximately 25 mm3), became rigid, and constituted 75%, 41%, and 33% of the buffering gained in tandem with the "mastoid" in a model having a "mastoid" of 0, 5, and 10 mL, respectively. Altogether, a large "mastoid" required a greater volume change than a small one to induce the same pressure.
The mastoid air volume "dilutes" pressure changes relatively to its size: the volume change required to alter a given pressure in an average (6 mL) mastoid is six-fold that which is needed in a small (1 mL) mastoid. ME volume reduction by TM retraction buffer negative ME pressures. This maximal ME volume change is constant for a "normal" TM. Therefore, it is the ME with the small mastoid that is most vulnerable to pressure changes and may develop compensatory buffering mechanisms, e.g., additional TM retraction (atelectasis) and/or ME volume reduction by fluid accumulation.
鼓膜（TM）和乳突气房是中耳（ME）可测量的压力缓冲器。
中耳的压力稳态通过中和（缓冲）压力波动的机制维持在接近大气压的水平，其中两种机制是鼓膜和乳突。
通过人工中耳模型中的体积变化诱导负压。在使用具有各种尺寸“乳突”的刚性或柔性鼓膜时直接记录这些负压。
在刚性鼓膜模型中，体积变化与诱导压力呈线性相关，并经证实符合玻意耳定律。在柔性鼓膜模型中，压力/体积相关性在达到-50 mmH₂O之前是非线性的，此时鼓膜最大位移（约25 mm³），变得刚性，并在分别具有0、5和10 mL“乳突”的模型中，与“乳突”串联获得的缓冲中分别占75%、41%和33%。总之，大“乳突”诱导相同压力所需的体积变化比小“乳突 ”大。
乳突气房体积相对于其大小“稀释”压力变化：在平均（6 mL）乳突中改变给定压力所需的体积变化是小（1 mL）乳突所需体积变化的六倍。鼓膜内陷通过缓冲中耳负压来减少中耳体积。对于“正常”鼓膜，这种最大中耳体积变化是恒定的。因此，具有小乳突的中耳最易受压力变化影响，可能会形成代偿性缓冲机制，例如额外的鼓膜内陷（肺不张）和/或通过液体蓄积减少中耳体积。
