Dynamic Response of Middle-Ear Structures

Abstract

Automatic tracing of vibrations from several locations on the tympanic membrane and from the stapedial footplate, in human anatomical preparations, was performed by use of a capacitive-probe vibration meter. Normally, the vibrations of the tympanic membrane at the umbo and along the junction with the malleus were in synchrony with those of the stapes. The motion of the eardrum as a whole agreed with that postulated by von Békésy. The direct measurements enabled examination of the ossicular-lever transformation of the middle ear under dynamic conditions. In normal cases, undulation of the lever ratio around the 1.3 value was evidenced. Pathological changes caused an artificial increase of the ratio, due to damping features of the ossicular-lever system; the characteristics of an otosclerotic ear served as an conspicuous example. With the CAT 400B, further increase of the sensitivity of measurements (down to 2 Å amplitude) was possible. Some tests were carried out on patients also. Determination of the acoustic input impedance of the ear is discussed and a possibility of simple conversion of the vibration response of the eardrum into the impedance characteristic is presented. A typical input-impedance curve for a human temporal bone preparation with the unloaded stapes is demonstrated.