Middle ear mechanics of type IV and type V tympanoplasty: I. Model analysis and predictions.

An analysis of type IV and type V tympanoplasty procedures was performed using a quantitative model of the acoustic and mechanical properties of the stapes, cochlea, round window shield, and cavum minor air space. Realistic values for the impedance of these structures were determined from anatomic and functional measurements in normal ears. These model values lead to predicted type IV hearing results that match well with the best surgical results over a broad frequency range (125-4000 Hz). A parametric study of alterations in the model impedances reveals that a good hearing result depends on a mobile stapes, proper aeration of the cavum minor air space, and a sufficiently stiff graft shield. Intersubject variations in the cochlear impedance also can have a significant effect on the postsurgical hearing response.