[Animal experiment studies using a low-frequency, phase-delayed masker in inner ear diagnosis].

Endolymphatic hydrops is usually diagnosed on the basis of clinical symptoms although objective parameters for this disease can be difficult to differentiate from other disorders of the inner ear. Low-frequency acoustic biasing using a highly intensive phase-shifted low-frequency masker was studied according to its ability to determine disorders of cochlear micromechanics in diseases caused in animal models. Ossicular disruption, experimentally induced early endolymphatic hydrops and gentamycin-induced inner ear damage could be objectively determined histologically and electrophysiologically. Statistical analysis proved that the low-frequency acoustic biasing technique allowed electrophysiologic differentiation of the groups studied that was independent from known clinical parameters. To substantiate the group differences by variance analysis, an intensity of at least 100 dB SPL was required for the 52 Hz masker, and the difference in relation to the test-tone intensity had to be 10 or 20 dB SPL. The early stages of experimentally-induced endolymphatic hydrops could be identified by means of a low-distinct modulation span of the compound action potential amplitude (< 50 uV) and a reduced positive summating potential amplitude with a phase-shifted maximum value compared to the control groups. During the test phases the cochlear microphonic potentials showed only slight suppression of their amplitudes and no modulation effect when compared to the control groups. The modulation behavior of the responses could be correlated with the histologic and supposed micromechanic states of the basilar membrane and organ of Corti, thus allowing validation of the measuring technique.