Udi Cinamon1, Jacob Sadé. 1. Ear Research Laboratory, Department of Bio-Engineering, Tel-Aviv University, Israel. udicin@hotmail.co.il
Abstract
HYPOTHESIS: The tympanic membrane (TM) and mastoid air cells are measurable pressure buffers of the middle ear (ME). BACKGROUND: Pressure homeostasis of the ME is maintained approximately atmospheric by mechanisms that neutralize (buffer) pressure fluctuations, two of which are the TM and mastoid. MATERIALS AND METHOD: 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. RESULTS: 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. CONCLUSIONS: 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.
HYPOTHESIS: The tympanic membrane (TM) and mastoid air cells are measurable pressure buffers of the middle ear (ME). BACKGROUND: Pressure homeostasis of the ME is maintained approximately atmospheric by mechanisms that neutralize (buffer) pressure fluctuations, two of which are the TM and mastoid. MATERIALS AND METHOD: 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. RESULTS: 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. CONCLUSIONS: 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.
Authors: Ahmet Kutluhan; Behcet Tarlak; Huseyin Cetin; Elif Ersoy Callioglu; Kazim Bozdemir; Mustafa Kemal Demir Journal: Int J Clin Exp Med Date: 2015-04-15
Authors: Toby W A Gould; John P Birchall; Ali S Mallick; Tamara Alliston; Lawrence R Lustig; Kevin M Shakesheff; Cheryl V Rahman Journal: Laryngoscope Date: 2013-05-13 Impact factor: 3.325