Experimental Studies on the Effects of the Tympanic Membrane Perforation on Middle Ear Transmission / 听力学及言语疾病杂志

ABSTRACT

Objective The goal of the present study was to determine the effects of different location perfora-tions on the middle ear transfer functions by measuring the velocity and pattern of the tympanic membrane vibration in guinea pigs with intact and perforated TM .Methods A laser Doppler vibrometer was used to measure the sound transmission properties on the movement of the tympanic membrane on 6 fresh temporal bones of guinea pigs in the frequency range of 0 .5~8 kHz at 90 dB SPL .The velocity was measured at three points on the manubrium before and after a different location perforation was made with a 20-gauge needle(1 .1 mm diameter) .The locations of the perforations were in anterior -inferior quadrants of left ears and in posterior -inferior quadrants of right ears .And the velocity was measured from 6 poins with the intact tympanic membrane .Results The highest velocities were re-corded at the site of inferior umbo throughout the frequency range .The manubrium vibration velocity losses were noted in the perforated ears below 1 .5 kHz ,the velocity losses were smaller above 1 .5 kHz ,and the maximum ve-locity loss was about 7 dB at 500 Hz with the posterior -inferior quadrant perforation .Although there was a trend for anterior-inferior perforations to show a slighter loss than posterior -inferior perforations in velocity below 1 .5 kHz ,no statistical differences in velocity loss were found between different perforations .The average ratio of short process velocity to umbo velocity at all frequencies was approximately 0 .5 ,and the ratios were found no systematic differences before and after perforation at almost all frequencies from different perforations .Conclusion The manu-brium vibration velocity losses from TM perforation are frequency -dependent and the largest losses occur at the lowest sound frequencies .Different sites of small perforation have not any important effects on middle ear sound transmission .