EFFECT OF CHANGES IN MASS ON MIDDLE-EAR FUNCTION

Vibrating systems such as the middle ear are affected by changes in ma ss. After disease or ear surgery, significant changes in mass may cont ribute positively or negatively to the postoperative hearing threshold . This article describes experiments in 15 human temporal bones of the addition or reduction of mass on the middle ear transfer function. Me asurement of stapes and umbo vibration was performed using a Laser Dop pler Vibrometer before and after the addition of different masses at s everal sites on. the tympanic membrane (TM) and ossicular chain. The i nput was 61 pure tones swept from 147 to 19433 Hz at 80 dB SPL. The ad dition of mass onto the TM produced varying detrimental effects on sou nd transmission, depending on the location and amount of mass. The ins ertion of ventilation tubes, weighing 12 to 17 mg each, produced losse s at 1.5 to 5.0 khz compared with tympanotomy alone. Addition of mass to the umbo and malleus head produced a loss at mid and high frequenci es, whereas addition of mass on the incus long process and stapes also produced a high-frequency decrease in stapes displacement. Reduction of TM mass by removal of the epithelium produced an increase, especial ly at 2.0 to 4.0 kHz.