Effects of inner ear pathology on the input impedance of the cochlea

The effects of inner ear pathology on the input impedance of the cochlea were studied in animals using a laser-doppler interferometer or a piezoelectric ceramic device of our design. In guinea pigs, vibration amplitudes of the umbo were measured before and after either one of the following three procedures ; rupture of the round window membrane, destruction of the cochlea and increase in inner ear pressure. Rupture of the round window membrane caused increase in umbo vibration up to 10 dB in mid-frequencies. Destruction of the cochlea resulted in 10 dB increase in the vibration at all the frequencies. Pressure loading to the inner ear induced the decrease in the vibration at low frequencies and the increase at mid-frequencies. This suggested that the changes in the inner ear impedance can be detected by the vibration mode of the tympanic membrane. Chaine cochlear input impedance were measured uaing a piezoelectric device. It was designed for future use in human subjects during middle ear surgery. The impedance value was 3.9 Megohm at 1 kHz, which gradually increased at higher frequencies.