EXPERIMENTAL STUDIES OF TYMPANOPLASTY

Abstract

To establish a theoretical equation of hearing restored by the tympanopiasty, hearing restored by various types of operation was examined by means of the mesurement of cochlear potential in guinea pig. The results were as follows : 1) Data obtaineb dy the experiment were calculated by classical method of Wullstein cal equation of Schmitt and various inconsistencies were found. 2) The new theoretical equation was established with consideration of two factors, which Schmitt entirely had neglected, i.e. difference in mobility between oval and round windows, and the action of the sound vibrating the whole skull transmitted through bone conduction upon internal ear (the equation of Maruyama & Tsuchida). 3) The equation of Maruyama & Tsuchida is as follows: db=20log 43/43F-0.162d+0.215 F : The ratio of sound pressure transformation when 1 is taken as normal. d: 1-D/100 D: The ratio of sound transmission loss. 4) Application of this theoretical equation showed no inconsistency in the analysis of experimental data.5) The ratio of sound pressure transformation of the artificial ear drum was conveniently expressed by the ratio of effective area. 6) The ratio of sound pressure transformation of the artificial ear drum closely related to the shape of section lining. 7) When a columella was placed out of the center of the membrane, the ratio of the effective area of the membrane was decreased. 8) The thiner was a plastic membrane, the greater was the ratio of effective area; when the abdominal skin of a guinea pig was used, the thickness showed no significant influence upon the ratio. A skin had a greater ratio of effective area than a plastic membrane of the same thickness. 9) The effect of phase shift by the ear drum upon hearing was considered almost negligible when hearing loss was below 30db. 10) The consideration made in the experiment of guinea pig was likewise applied to the case of human tympanoplasty and a new theoretical equation was established. The nomograph of the equation was illustrated