[Development of a cochlear input-impedance measuring device and its application in the temporal bones of dogs]

Cochlear input impedance was measured in 6 temporal bones taken from 3 dogs by use of a newly developed ceramic device. The device was composed of two ceramic bimorph elements, one for activation of the stapes and the other to pick-up vibration of the former element in the form of an electric output, which varies in accordance with the magnitude of cochlear impedance. Average impedance in the dogs was 2.3 Mohm at 2 kHz, 6.3 Mohm at 4 kHz and 17.8 Mohm at 6 kHz. Effect of closure of the round window was also investigated by placing dental cement on the window. In 3 ears, the impedance increased mainly below 4 kHz, while in the remaining 3 ears no such change occurred. This was probably because the closure was complete in the former but not in the latter.