RESUMO
Introduction: Domestic pigs (or only pigs) have a cochlear anatomy and endocochlear potential similar to humans, making them a potential animal model for experimentation in auditory sciences. However, how does their cochlea work? We aimed to describe the amplitude and signal-to-noise ratio (SNR) of transient evoked otoacoustic emissions (TEOAE) and distortion product otoacoustic emissions (DPOAE) to answer this question. Methods: Procedures were approved by the Institution's Animal Use Ethics Committee (1989/2023). Large white pigs received intramuscular pre-anesthetic of ketamine and xylazine. Anesthesia was then induced with intravenous propofol and maintained by constant isoflurane inhalation. Pigs have a complex pinna anatomy. Therefore, surgical procedures were necessary to remove the convolutions that make it difficult to access the external auditory canal (EAC). Surgery was performed in three steps: shaving of the head and neck area; dissection of the skin and subcutaneous tissues and disarticulation of the pinna’s convolutions. All procedures were performed on the right ear. Finally, otoscopy was performed and no bleeding was observed within the canal. The probe of the Titan® was carefully inserted into the exposed EAC and a Tympanometry, TEOAE, and DPOAE were performed. TEOAEs were performed with a nonlinear click at ambient pressure. Responses were recorded in a 4 to 12.5 ms window and presented for frequency bands of 1 to 4 kHz. DPOAEs were performed with a ratio ƒ2/ƒ1 = 1.22, where ƒ2 ranged from 1 to 6 kHz, and stimuli intensity was set with L1 and L2 of 65 and 55 dB SPL, respectively. Recordings ran for three minutes so that noise and emissions could stabilize. Only the ear with a Type A tympanometric peak was included for statistical analysis. Results: Twelve three-month-old pigs (6 males and 6 females), weighing approximately 20 kg, were included. The t-test showed no statistical difference between sexes, regardless of the frequency tested. Therefore, descriptive statistics are presented considering the mean ± SD of both sexes combined. TEOAE (Amplitude in dB SPL): 1 kHz (15.3 ± 3.6); 1.5 kHz (17.8 ± 3.9); 2 kHz (15.1 ± 5.7); 3 kHz (10.7 ± 4) and 4 kHz (1.9 ± 5.6). TEOAE (SNR in dB SPL): 1 kHz (31.1 ± 5.1); 1.5 kHz (31.1 ± 4); 2 kHz (29.4 ± 6.2); 3 kHz (24.3 ± 4.3) and 4 kHz (17.3 ± 5.7). DPOAE (Amplitude in dB SPL): 1 kHz (10.1 ± 5.2); 1.5 kHz (15.5 ± 5.7); 2 kHz (17.9 ± 5.2); 3 kHz (15.1 ± 4.9); 4 kHz (10.7 ± 5.3) and 6 kHz (4.4 ± 7.3). DPOAE (SNR in dB SPL): 1 kHz (28.8 ± 6.3); 1.5 kHz (38.5 ± 6.5); 2 kHz (41.9 ± 5.5); 3 kHz (43.5 ± 5.2); 4 kHz (41.8 ± 5.5) and 6 kHz (39.3 ± 6.7). Conclusion: The amplitude of evoked otoacoustic emissions in pigs increases up to mid-frequencies and then decreases toward higher frequencies, especially for transient emissions. The SNR is robust, regardless of the frequency tested. These findings suggest that pigs present good cochlear conditions for experimentation in the field of auditory sciences.