[Studies for diagnostic method for ossicular lesions].

The diagnosis of the ossicular condition, fixation or interruption, is often not achieved by the routine tympanometry. A new tympanometric system has been developed in order to improve the diagnostic value. This produces a sweep-frequency probe tone of 200 to 2000Hz and measures the sound pressure difference and the phase difference between the output and the input. An experimental study was performed using eight fresh human temporal bones. Sound pressure curves and phase angle curves were figurized against the probe tone frequency in three conditions of the ossicular chain: normal, fixation glued by dental cement, and interruption made by mechanical separation. In addition, static compliance was also obtained by the conventional tympanometry. A multivariate analysis was performed to obtain the effective variables which would be a good indicator for the change in transmission characteristics of the ossicular chain. The results showed static compliance was less valuable than other variables of the sound pressure curve and the phase angle curve. Among these variables, four were selected as the most valuable ones from the result of a discriminant analysis. These four variables were clinically applied to differentiate three groups of the ossicular pathology: staps fixation, malleus or incus fixation and incudostapedial disconnection. The internal and external check using the discriminant function were performed in forty ears, in which ossicular lesions were surgically confirmed. This resulted in a high ratio of differentiation. Thus, this system can be of great value in the diagnosis of ossicular abnormalities.