An engineering view of middle ear surgery

Abstract

As evidenced in the preceeding papers, the function of the normal middle ear is now reasonably well defined. This provides the mathematical basis for an estimate of the acoustical effects of middle ear surgeries. By using a model based on a combination of Bauer's [J. Acoust. Soc. Am. 42, 1095–1097 (1967)] equivalent circuit to account for head diffraction, Zuercher's (J. Acoust. Soc. Am. Suppl. 1 62, S56(A) [1977]) approximations for acoustic tubes to model the pinna, concha, and earcanal, and Shaw's [J. Acoust. Soc. Am. Suppl. 1 62, S12(A) (1977)] equivalent circuit to model the normal middle ear, we obtained excellent agreement with available data on the normal sound-field-to-oval-window transformation in humans. By altering appropriate sections of the model, we calculated the expected effects of Type IV tympanoplasty, fenestration, etc., on the sound pressure delivered to the oval window. Our results are in general agreement with the observations of Goode et al. [Ann. Oto. Rhyn. Laryngol. 86, 441–450 (1977)]. New experimental results, and their implications, will be discussed. The estimated quality of sound transmission resulting from some common middle-ear alterations will be demonstrated with tape-recorded examples obtained from electrical analogs.