|Beitragstitel||Experimental ear mechanics: Are fresh cadavaric specimens better than conserved specimens?|
In experimental ear mechanics fresh human specimens are often used although they decay. Conserved specimens would be beneficial for longer use. Therefore, we studied ear mechanics of the same fresh specimens before and after conservation.
Stapes and round window motion was measured with a single point Laser Doppler Vibrometer through a posterior tympanometry. Thirty logarithmically distributed sinusoidal tones between 100 and 10000 Hz were sequentially applied in the external auditory canal with an ER-3A insert phone. Sound pressure level was measured with an ER-7C probe microphone placed in front of the tympanic membrane. For the initial measurement fresh frozen whole heads have been thawed at least 24 hours. Afterwards the entire whole head has been embalmed in a watery solution of salts, the so-called Thiel conservation.
We observed opposite motion between stapes and round window at low frequencies. The deviation from the theoretical 180° phase shift was less than 5° for frequencies below 450 Hz. In direct comparison before and after conservation the deviation ranged between 0.1° to 5.5° (average 3°). The averaged magnitude of the stapes movement after the conservation was 5.9 dB lower than at the initial measurement before the conservation. A slightly lower effect was seen in the averaged magnitude of the round window movement which was lowered by 1.3 dB (frequency range 100- 1000 Hz).
Motion of the stapes and the round window before and after conservation is comparable. The phase shift of 180° between stapes and round window indicates a properly fluid-filled cochlea after conservation, which is a premise for mechanical studies.