TRANSIENTLY EVOKED OTOACOUSTIC EMISSIONS IN DOGS

Dogs with normal behavioral responses to sound were lightly anesthetized, and ear canals were examined otoscopically. Tympanograms, acoustic reflexes, and brain stem auditory evoked responses were recorded from test ears to further establish normal auditory function. The dogs were anesthetized with pentobarbital and placed in a sound-attenuating booth in lateral recumbency on a padded surface. Transiently evoked otoacoustic emissions (TEOAE) were recorded unilaterally in response to click stimuli delivered into a closed ear canal at a rate of 50/sec at sound levels of approximately 75 to 95 dB sound pressure level (SPL) in approximately 5-dB steps. Stimulus and recording conditions in the booth remained stable throughout recording sessions. Emissions were recorded from each dog on two separate occasions approximately 1 week apart. Paired TEOAE time-waveforms were analyzed for response amplitude and whole-response reproducibility. Fast Fourier transforms were performed on the time-waveforms, and primary energy peaks were identified in 1-kHz-wide frequency bands. Transiently evoked OAE were successfully recorded from all dogs for most stimuli. Mean (+/- SD) emission amplitudes were 2.9 +/- 4.0, 4.1 +/- 5.2, 8.3 +/- 5.0, 10.5 +/- 4.5, and 14.1 +/- 4.3 dB SPL for stimulus levels of approximately 75, 80, 85, 90, and 95 dB SPL, respectively. Mean whole-response reproducibility ranged from a low of 50% at a stimulus level of 75 dB SPL to a high of 90. 1% at 90 dB SPL. The mean peak energy across stimulus levels ranged from 1.8 to 2.1 kHz, and reproducibility by frequency was consistently the highest at 2 kHz. Analysis of the stimulus revealed a stability that ranged from 94.2 to 97.5% while the noise floor ranged from 32.6 to 33.6 dB SPL. None of the response variables were different (P > 0.05) between recording sessions. Stimulus levels had a significant (P less-than-or-equal-to 0.05) effect on response amplitudes and the number of rejected signals. Stimulus levels that differed by approximately 5 dB SPL did not produce TEOAE with different amplitudes (P > 0.05), whereas response amplitudes differed (P less-than-or-equal-to 0.05) ff evoked by stimulus levels that differed by approximately 10 dB SPL. The TEOAE was shown to be a quick non-invasive method for assessing peripheral auditory function in dogs. Records of evoked emissions add yet another dimension to the clinical assessment of auditory function in dogs. Because TEOAE provide specific information about receptor function, they can be used to distinguish between sensory and neural dysfunction in pathologic conditions resulting in hearing loss.