Impedance Audiometry in Rabbits

Abstract

The two principal components of impedance audiometry, the tympanogram and acoustic reflexes, were measured in eight rabbits (12 ears). A probe tone frequency of 221 Hz yielded both tympanograms and acoustic reflex threasholds roughly comparable to analogous data in humans at a same probe tone frequency. Rabbit showed a notable “M” pattern tympanogram. Ipsilateral acoustic reflex thresholds were determined for 500 Hz, 1 KHz, 2KHz and 4 KHz signals. The reflex threshold improved systemically as the signal frequency was raised from 500 to 2KHz. Ipsilateral acoustic reflex threshold for 2KHz pure tone signal was 77.7 ± 8.0 (1 SD) dB SPL. Our previous data for reflex threshold that was measured by the change in cochlear microphonics following contraction of the tympanic muscles showed 74.8 ± 7.5 (1SD) dB SPL in 2 KHz pure tone signal. So both impedance audiometry and electrocohleography had analogous data for acoustic reflex threshold at 2 KHz. Impedance audiometry then serves as a sensitive, easily administered technique for monitoring the middle ear function on experimental animal.