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KMID : 0377619640070050567
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Korean Jungang Medical Journal
1964 Volume.7 No. 5 p.567 ~ p.584
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Pressure-Displacement Relationship of Tympanic Membrane in Dog and Human
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Abstract
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This report describes the relationship between static pressure, applied from auditory canal, and displacement of tympanic membrane in dog and human and the relation-ship between perforation pressure of tympanic membrane and the magnitude of displacement of tympanic membrane was discussed.
Temporal bone was excised and the tympanic membrane was exposed from the middle ear cavity keeping the tympanic membrane and ossicular system intact. Displacement was measured at the umbo, central portions of anterior and/or posterior part of tympanic membrane under low power microscope when pressure was applied up to 100 mm Hg of positive and negative pressure against the tympanic membrane. Displacement measurements were also made on dried specimen of dog and human and perforation pressure were measured on fresh, intact (living and dead) and dried dogs´ specimens. After analysing the results obtained the following facts were concluded.
1. The slope of the pressure-displacement curve of fresh tympanic membrane in dog is hyperbolic in general, that is greater displacement at lower pressure and lesser displacement at higher pressure.
2. Displacement of fresh tympanic membrane under negative pressure is markedly greater than that under positive pressure at the same magnitude of pressure.
3. Pressure-displacement curves of fresh tympanic membranes show a hysteresis phenincomplete reproducibility of curves on repetitive trials.
4. Pressure-displacement curves of dried tympanic membranes show remarkable liiiearity, decreased magnitude of displacement, no displacement difference between the positive and negative pressure and no hysteresis phenomenon.
5. Alinearity and hysteresis of the pressure-displacement curves of fresh tympanic membranes were attributed to a peculiar stress-strain property of the ossicular system.
6. The greater displacement of fresh tympanic membrane under negative pressure than under positive pressure was attributed to a peculiar articulate structure of ossicular system.
7. The pressure-displacement curves of tympanic membrane proper and ossicular system proper were constructed by calculation under some assumptions. These curves show that the pressure-displacement curve of tympanic membrane proper is linear, while that of ossicular system proper is hyperbolic and the displacement ratio of ossicular system proper and tympanic membrane proper is high at the low pressure range and low at the high pressure range.
8. Perforation pressure of dogs´ fresh tympanic membrane, excised and intact, was about 600 mm Hg under positive pressure and about 500 mm Hg under negative pressure. Dried tympanic membranes were perforated at 755 mm Hg under positive pressure and the perforation pressure under negative pressure was approximately the same. The difference of perforation pressure between positive and negative pressure in fresh specimens and the elevated perforation pressure in dried specimens manifest the fact that the perforation pressure of tympanic membrane in the same species is primarily determined by the degree of protection by the ossicular system against the displacement of tympanic membrane.
9. The maximal tension developed in dogs´ tympanic membrane under perforation pressure, 755 mm Hg, was estimated as about 1. 26 x 105 dynes/cm.
10. The possible difference in perforation pressure between a subject whose Eustachian tube is patent and whose Eustachian tube is closed, when pressure was applied from the auditory canal, was discussed and showed the difference is small, if any.
11. The pressure-displacement curve of fresh and dried human tympanic membrane is almost exactly the same in various aspects as that of dogs´ tympanic membrane. Therefore it is safely concluded that the structure and function of the human sound transmitting system are basically the same as that of dog.
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KEYWORD
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