Vibration analysis of the tympanic membrane with ossicular chain abnormalities by holography

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1) Dislocation of the incudostapedial joint and fixation of the joint and the stapes were prepared using the temporal bones of dogs, and an analysis was performed by the holography interference method using a He-Ne laser.2) Dislocation of the incudostapedial joint : in a comparison with the normal vibration of the tympanic membrane, there were no changes in the pattern of the vibrations in the frequency range from 250 Hz to 2 KHz; changes occurred at 3 KHz or higher. The vibration amplitude of the tympanic membrane increased at 2 KHz or loss, but decreased at 3 KHz or higher. When joint between the incus and stapes was broken, the malleus and incus were displaced toward the exterior, i.e., the tympanic membrane was displaced toward the exterior from the normal position. under this condition, it appeared that the stiffness of the tympanic membrane decreased, and the resonance frequency shifted to the low frequency range. The resonance frequency also shifts to the low frequency range due to an increase in the volume of the tympanic cavity, this can be disregarded compared with the effect in stiffness.3) Fixation of the incudostapedial joint and the stapes : In the frequency range 250 Hz to 2 KHz, the same tendency was seen, but there was a change at over 3 KHz, and there was a decrease in the number of segmentations. the vibration amplitude of the tympanic membrane increased at 5 KHz or higher and decreased at 4 KHz or less. With fixation of the ossicular chain and the stapes, there was no displacement of the ossicular chain or the tympanic membrane as in the case of dislocation, but only the stiffners increased in the middle ear vibration system. Therefore, the resonance frequency shifted to the high frequency range.