Holographic observation of the tympanic membrane vibration after stapes fixation

Sclerosis of auditory ossicle was experimentally induced by fixation of the stapes, and its effect on the tympanic membrane vibration was examined using fresh 10 canine temporal bones by means of holographic interferometry. By changing the sound pressure (from 90 to 110dB) and the frequency (from 250Hz to 8kHz) in steps, vibration of the membrane was induced in a free field. At each frequency, the vibration of the membrane was photographed by the time averaged method using He-Ne laser. A small hole was created in the tympanic bulla and the stapes was fixed with an adhesive (Alon Alpha), followed by closure of the hole. Before stapes fixation, the posterior part of the membrane showed a simple vibration pattern, forming cocentric interference circles at frequencies from 250Hz to 2kHz. At 3kHz, segmental vibration began to be noted, and complex segmental vibration was seen at frequencies 4.5 and 6kHz. The vibration after stapes fixation became simpler at frequencies over 3kHz, accompanied by decrease in the number of segmental vibrations. Vibration amplitude in the posterior part of the membrane decreased from 250Hz to 3kHz, while it increased at frequencies over 4kHz. In the anterior part of the membrane, the amplitude decreased at frequencies under 2kHz, remained unchanged at 3kHz and increased at frequencies over 4kHz after stapes fixation. In the tip of the manubrium mallei, the amplitude decreased at frequencies under 3kHz and increased at frequencies over 4kHz. Thus, a shift of peak vibration to high sound region was observed after stapes fixation at every part of tympanic membrane.(ABSTRACT TRUNCATED AT 250 WORDS)