Click and Low‐, Middle‐, and High‐Frequency Toneburst Stimulation of the Canine Cochlea

Abstract

A method was developed to deliver tonebursts ranging in frequency from 1 to 32 kHz for frequency-specific assessment of the canine cochlea. Brainstem auditory-evoked responses (early latency responses, 0-10 ms) to a click (CS) and to 1-, 2-, 4-, 8-, 12-, 16-, 24-, and 32-kHz toneburst stimulations (TS) were compared at 80-dB sound pressure level stimulus (SPL) intensity in 10 adult dogs. All stimulations yielded a 5-7 positive wave pattern, with the exception of the 1-kHz TS, which evoked a frequencyfollowing response (FFR). Thresholds were lowest for the CS and the 12-and 16-kHz TS. All individual peak latencies for TS were significantly (P Յ .05) longer than for CS. Peak I latencies were significantly (P Յ .05) shorter for the 12-and 16-kHz TS than for the other TS. Interpeak latencies I-V were significantly (P Յ .05) longer for the 4-to 32-kHz TS than for CS. Differences in interpeak latencies I-III were not significant. Amplitudes of waves I and V were significantly (P Յ .05) lower for TS than for CS, except for higher wave V amplitude (P Յ .05) at 2-and 32-kHz TS. Peak I-V amplitude ratios were significantly (P Յ .05) higher for the 2-, 4-, 16-, 24-, and 32-kHz TS and lower for the 8-and 12-kHz TS, compared to CS. We conclude that reproducible information on frequency specificity of the canine cochlea can be obtained by TS. This report provides a normative database for parameters needed to evaluate frequency-specific hearing loss in dogs.Key words: Brainstem-evoked response audiometry; Dog; Frequency-specificity; Threshold audiogram. Several methods have been employed to test hearing ability in dogs, ranging from behavioral studies to measurement of electrical responses after auditory stimulation, by impedance audiometry (tympanometry, acoustic reflex testing), evoked response audiometry (brainstem [BAER] and middle latency auditory-evoked responses), and cochlear microphony. 1-7During the past 2 decades, BAERs have been used for this purpose with increasing frequency in veterinary medicine. The acoustic signal usually has consisted of a click, which stimulates a large part of the cochlea.8-14 Brainstemevoked response audiometry by a click (CS) is useful for differentiating neurologic from conduction deafness 15,16 and is useful in assessing some brainstem pathologic changes. 17,18 Frequency-specific information is needed to assess the extent of neurologic deafness, such as noise-induced deafness and that caused by ototoxicity and presbycusis, each of which can be partial and frequency-specific. [18][19][20][21][22][23] Considerable research has been conducted on factors that influence wave latency, amplitude, and thresholds in dogs and on the clinical applicability of these factors.9,24-31 Behavioral studies indicate that dogs can hear frequencies up to 45 kHz, 1 considerably higher frequencies than heard by humans, 13 but the tonebursts used in BAER assessment of hearing in dogs have been at frequencies only as high as 8 kHz. 24-26From The aim of this study was to collect reference values for BAER wave...

Effects of Aging on Brainstem Responses to Toneburst Auditory Stimuli: A Cross‐Sectional and Longitudinal Study in Dogs

“…The initial audiograms of these dogs were reported previously. 25 For the longitudinal study, frequency-specific hearing thresholds were determined in this group once yearly or once every other year for 7 years, from a mean age of 5.7 years to a mean age of 12.3 years. Group III consisted of 10 clinically healthy elderly dogs maintained in the kennels of the department from an early age onward.…”

“…In groups II and III, a light plane of anesthesia was induced with medetomidine d (100 mg/kg IV), followed by propofol e (1 mg/kg IV) within 5 minutes and was maintained with these drugs during auditory testing, as described previously. 25 At the end of the procedure, anesthesia was antagonized with atipamezole f (250 mg/kg IV). Rectal temperature was maintained at 36.5-37.5 1C by means of a circulating water heating pad placed under the dog.…”

“…Although different anesthesia protocols were used, the effect of anesthesia on the brainstem auditory-evoked responses (BAER) is generally considered to be negligible and the protocols used in this study have not been reported to affect the BAER. 25 Auditory testing with determination of hearing thresholds by means of BERA was performed as described previously. 25 Briefly, with the dog in sternal recumbency, 3 recording needle electrodes h were inserted SC, 1 at the base of the pinna of each ear and the third as the reference electrode over the occipital protuberance on the midline.…”

“…25 Auditory testing with determination of hearing thresholds by means of BERA was performed as described previously. 25 Briefly, with the dog in sternal recumbency, 3 recording needle electrodes h were inserted SC, 1 at the base of the pinna of each ear and the third as the reference electrode over the occipital protuberance on the midline. The nonstimulated ear was plugged with an adjustable wax plug.…”

“…The technique of BERA using frequency-specific stimulation of the canine cochlea over a wide audiometric range, from 1 to 32 kHz, was described previously and was used for this study. 25 Recently, other techniques for determination of high-frequency hearing loss in dogs have been reported, of which the use of auditory steady-state evoked potentials (AS-SEP) seems to have the most potential. 23,24 Hearing loss in humans affects the individual's psychosocial situation and, if left untreated, contributes to social isolation, depression, and loss of self-esteem.…”