MEASUREMENT OF UMBO VIBRATION IN HUMAN-SUBJECTS - METHOD AND POSSIBLECLINICAL-APPLICATIONS

A commercial laser doppler vibrometer (LDV) was used to evaluate umbo displacement at sound pressure levels of 60, 70, and 80 dB SPL at the tympanic membrane (TM) of six subjects. Thirty-five pure-tone test fre quencies, five per octave, were tested from 140 to 19,433 Hz. A comput er program (Tymptest) produced and controlled the tones as well as imp roved the signal-to-noise ratio of the LDV. The test took about an hou r to perform and provided reproducible results in all subjects. In add ition, measurement of umbo displacement using the same system was made in 15 fresh human temporal bones for comparison. Results in the human s revealed a relatively flat umbo displacement from 140 to 1000 Hz, wi th a gradually sloping roll-off of -8.25 dB per octave from 1000 to 70 00 Hz. From 8000 to 14,000 Hz the roll-off increased to -12.5 dB per o ctave. At the mean resonant frequency of the middle ear, 1000 Hz, and an 80 dB SPL input, umbo displacement was 0.045 micron. The human temp oral bones showed similar results. Possible future clinical applicatio ns of this measurement include the identification of ears with acousti cally inefficient TMs (tin ears). By identifying and studying such ear s we should be able to develop methods to improve their function and p roduce hearing threshold increases of 15 dB or more at key speech freq uencies. In addition, analysis of umbo and TM vibration in reconstruct ed middle ears should help us achieve better postoperative hearing res ults.