Evaluation of central vestibular syndrome in dogs using brainstem auditory evoked responses recorded with surface electrodes / Avaliação da síndrome vestibular central em cães usando respostas evocadas auditivas do tronco cerebral gravadas com eletrodos de superfície

The present study aimed to analyse the wave morphology, amplitude, latency, and intervals of the brainstem auditory evoked responses (BAERs) in dogs with central vestibular syndrome (CVS) recorded with surface electrodes. Ten dogs with CVS were examined by mono- and binaural stimulation, using the Neuropack electrodiagnostic system, with stimulus intensities of 90 dBSPL. BAERs examinations revealed morphological changes of waves I, II, III, and V and decreased amplitudes of all waves in 7/10 dogs. P values obtained were = 0.014 for wave I amplitude, 0.031 for II, and III and 0.032 for V. Comparing the latencies of waves I, II, III, and V generated by right and left monoaural stimulation in dogs with CVS, we did not observe significant differences (P > 0.05). No statistical differences were observed for BAERs latencies of the waves recorded after binaural and monaural stimulation (left or right). As far as we know, this is the first study of BAERs using surface electrodes, obtained from dogs with CVS.(AU)

Este estudo destina-se à análise da morfologia, da amplitude, da latência e do intervalo das ondas das respostas evocadas auditivas no tronco cerebral (BAERs) em cães com síndrome vestibular central (CVS) registrados com eletrodos de superfície. Dez cães com CVS foram examinados por estimulação mono e binaural usando um sistema de eletrodiagnóstico Neuropack, com intensidade do estímulo de 90 dBSPL. Os exames BAERs relevaram alterações morfológicas das ondas I, II, III e V, bem como baixas amplitudes para todas as ondas no caso dos 7/10 cães. Os valores de P obtidos foram = 0.014 para ampitude da onda I, 0.031 para a II e 0.032 para a V. Compararam-se as latências das ondas I, II, III e V geradas pelo estímulo monoaural direito e esquerdo em cães com CVS e não foram constatadas diferenças significativas (P > 0.05). Igualmente não foram observadas diferenças estatísticas no caso das latências BAERs no que diz respeito às ondas gravadas depois de estímulos binaural e monoaural (esquerdo ou direito). Pelo que é de conhecimento dos autores da presente pesquisa, este é o primeiro estudo sobre BAERs usando eletrodos de superfície obtidos em cães com CVS.(AU)

Evaluation of otoacoustic emissions in clinically normal alert puppies.

OBJECTIVE: To evaluate distortion product otoacoustic emission (DPOAE) measurements in puppies with normal hearing. ANIMALS: 23 clinically normal 7.5-to 10.5-week-old puppies. PROCEDURES: A cross-sectional study was performed. The DPOAE measurements were obtained with a commercially available distortion product otoacoustic measurement system and were performed in a quiet, non-sound-attenuated room. All measurements were obtained from alert puppies and were repeated 1 or 2 times to ensure that the measurements were replicable. Results that were a minimum of 8 dB higher than the noise floor were accepted. Values from the first trial in which emissions were obtained at all test frequencies were used for analysis. RESULTS: Otoacoustic emission measurements were easily obtained, robust, reliable, and consistent with auditory brainstem response and behavioral results. CONCLUSIONS AND CLINICAL RELEVANCE: Hearing screening in alert puppies can be accomplished reliably and rapidly with otoacoustic emissions testing. Results supported the possibility of the use of DPOAE measurement in hearing screening of dogs.

An investigation into the effects of underwater piling noise on salmonids.

Underwater piling was undertaken in 2003 in Southampton Water on the South Coast of England. Monitoring was simultaneously undertaken of the waterborne sound from impact and vibropiling and its effects on brown trout in cages at increasing distances from the piling. Brown trout (Salmo trutta) were used as a model for salmon (Salmo salar), which were the species of interest but were not readily available. No obvious signs of trauma that could be attributed to sound exposure were found in any fish examined, from any of the cages. No increase in activity or startle response was seen to vibropiling. Analysis using the dBh, metric indicated that the noise at the nearest cages during impact piling reached levels at which salmon were expected to react strongly. However, the brown trout showed little reaction. An audiogram of the brown trout was measured by the Auditory Brainstem Response method, which indicated that the hearing of the brown trout was less sensitive than that of the salmon. Further analysis indicated that this accounted for the relative lack of reaction, and demonstrated the importance of using the correct species of fish as a model when assessing the effect of noise.

Frequency-specific electric response audiometry (ERA) and its clinical application in the diagnosis of hearing defects in the dog.

Reference values were established for frequency-specific electric response audiometry (ERA) in dogs on the basis of the results of ERA examinations of 200 animals with normal hearing. Air-conducting acoustic tubes with foam stoppers were used in the determination of the following: the latencies of waves I, III and V; interpeak latencies (IPL) I-III, III-V and I-V; amplitudes I and V; and the amplitude difference I-V. A frequency-specific stimulus (tone pip) was used for frequency-specific examination (1 to 4 kHz) over the entire frequency range indicated. These reference values were then used for the clinical examination of 50 dogs with hearing defects. A frequency-specific ERA was conducted and the results evaluated. These findings made it possible to draw objective conclusions about the degree, type and site of the hearing defects. Frequency-specific electric response audiometry was shown to be an important diagnostic tool for the detection of partial high- and low-frequency hearing loss and for the characterisation of hearing defects of otological, otoneurological and neurological origin.

Behavioral and auditory evoked potential audiograms of a false killer whale (Pseudorca crassidens).

Behavioral and auditory evoked potential (AEP) audiograms of a false killer whale were measured using the same subject and experimental conditions. The objective was to compare and assess the correspondence of auditory thresholds collected by behavioral and electrophysiological techniques. Behavioral audiograms used 3-s pure-tone stimuli from 4 to 45 kHz, and were conducted with a go/no-go modified staircase procedure. AEP audiograms used 20-ms sinusoidally amplitude-modulated tone bursts from 4 to 45 kHz, and the electrophysiological responses were received through gold disc electrodes in rubber suction cups. The behavioral data were reliable and repeatable, with the region of best sensitivity between 16 and 24 kHz and peak sensitivity at 20 kHz. The AEP audiograms produced thresholds that were also consistent over time, with range of best sensitivity from 16 to 22.5 kHz and peak sensitivity at 22.5 kHz. Behavioral thresholds were always lower than AEP thresholds. However, AEP audiograms were completed in a shorter amount of time with minimum participation from the animal. These data indicated that behavioral and AEP techniques can be used successfully and interchangeably to measure cetacean hearing sensitivity.

Click and low-, middle-, and high-frequency toneburst stimulation of the canine cochlea.

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 frequency-following response (FFR). Thresholds were lowest for the CS and the 12- and 16-kHz TS. All individual peak latencies for TS were significantly (P < or = .05) longer than for CS. Peak I latencies were significantly (P < or = .05) shorter for the 12- and 16-kHz TS than for the other TS. Interpeak latencies I-V were significantly (P < or = .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 < or = .05) lower for TS than for CS, except for higher wave V amplitude (P < or = .05) at 2- and 32-kHz TS. Peak I-V amplitude ratios were significantly (P < or = .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.

Normative auditory brainstem response data for hearing threshold and neuro-otological diagnosis in the dog.

There is growing interest in the application of auditory brainstem response (ABR) audiometry for hearing assessment in dogs. The technique is far from standardised, however, resulting in large discrepancies between studies. This study aimed to obtain normative data, under clearly defined conditions, for two breeds of significantly different size; head size being a potential factor determining ABR latency values. The subjects, 20 dalmatians and 20 Jack Russell terriers, were sedated prior to ABR testing, and subcutaneous scalp electrodes used to detect the evoked potential elicited by a click stimulus presented via insert earphones. The mean ABR thresholds for the two breeds, 0 and -5 decibels re normal hearing level (dB nHL), respectively, were very similar to those for humans. The latency values of the main ABR waves and the interval between them were statistically significantly smaller for the smaller breed, but there was no correlation with head size within either breed. The results provide a baseline to assist with confirmation of hearing impairment and neuro-otological diagnosis in the dog.

Investigation of hearing impairment in Cavalier King Charles spaniels using auditory brainstem response audiometry.

Auditory brainstem response audiometry was used to investigate nine Cavalier King Charles spaniels with a history of hearing impairment. Successful recordings were made in all cases. In eight of the dogs, the hearing impairment was between 40 and 85 decibels re normal hearing level. In addition to confirming the degree of impairment in each ear, information was obtained concerning the site of the lesion. The auditory brainstem technique may have an important role to play in assessing treatment outcome. Other applications include screening animals used in breeding programmes as well as working dogs requiring good binaural hearing.

Conductive hearing loss in bighorn sheep.

In January 1993 we simulated a conductive hearing loss in three Mexican bighorn sheep (Ovis canadensis mexicana) by placing bone wax or saline solution in their ear canals. Our objective was to test whether lesions of the external auditory canal caused by psoroptic mites (Psoroptes ovis) may lead to conductive hearing loss in bighorn sheep. We assessed the effects of these manipulations using the auditory brainstem response test. Placing saline solution in the external auditory canal, which loads the tympanic membrane, had a more dramatic effect on the auditory brainstem response than did bone wax. We propose that decreased hearing sensitivity or alterations in resonance characteristics of the external auditory canal, due to psoroptic scabies lesions, may make bighorn sheep more susceptible to predation.

A method of assessing auditory and brainstem function in horses.

Brainstem auditory evoked potential (BAEP) waveforms were recorded as a means of objectively evaluating auditory and brainstem function in horses. BAEP recordings were readily and repeatably recorded from horses, under minimal restraint, using signal averaging equipment. Clearly identified BAEP waveforms were obtained with compression clicks of 30-100 dB (HHL) at 10 Hz applied in the external auditory meatus of one ear and masking white noise (10 dB lower) in the other ear. Vertex positive (upwards) waveforms I through V were obtained with an active, subdermal electrode over the ipsilateral and contralateral zygomatic processes of the temporal bones and the reference electrode over the vertex. Recording sweep duration was 10 ms, amplifier sensitivity 10 microV/division, display gain x 10 and low and high amplifier filters set at 200 Hz to 2 kHz. Such recordings can be useful in evaluation of all clinical cases suspected of showing degrees of deafness, vestibular disease or brainstem disease, and in monitoring the progress of such cases.

Auditory brainstem responses in the normal beagle.

The latencies of the peaks in brainstem responses and the threshold response were determined in 18 healthy beagles. In the first series of measurements the dogs were sedated and the stimulus was delivered via an in-the-ear transducer. The latencies, the threshold levels, and the influence of the stimulus repetition rate on the latencies were measured. Using a miniature electric microphone in the outer ear canal near the tympanic membrane, it was found that at a level setting corresponding to 0 dB human level (HL) the major peak in damped oscillation during condensation reached a sound pressure level (SPL) of about 27 dB and the secondary rarefaction peak reached 24 dB SPL. In the second series of measurements the dogs were not sedated and the stimulus was delivered via a headphone. The wave forms, the mean latencies for peaks I to V as a function of the stimulus level, and the threshold of each wave are presented from both series. In the first series the latency values at 80 dB HL (107 dB SPL) were 1.21, 1.97, 2.67, 3.12 and 3.61 ms for peaks I, II, III, IV and V, respectively. The thresholds for peaks I to V were 47.5 +/- 9.5, 47.5 +/- 11.5, 41.3 +/- 13.0, 63.3 +/- 17.4 and 28.0 +/- 9.7 dB HL, respectively. The difference in peak latency between the first and the second series was 0.065 ms. This difference corresponded to the difference in length of the acoustic pathways.(ABSTRACT TRUNCATED AT 250 WORDS)

An inner ear anomaly in golden hamsters.

A new mutation of the inner ear was discovered in golden hamsters raised in our laboratories. Although scanning electron microscopy showed a normal arrangement of individual stereocilia on the first row of outer hair cells, the entire bundle of stereocilia were irregular in orientation and scattered in several directions. Seventy per cent to 85% of the stereociliary bundles were found to be abnormal throughout the cochlea, with no apparent difference between the right and left sides. Transmission electron microscopy showed that the cuticles of the first row of the outer hair cells were dislocated, but no dislocation due to this mutation was apparent in the lower portions. This mutation of the inner ear was already present in the basal turn four days after birth. The kinocilium was located outside of the stereocilia in the first row of outer hair cells, but sensory hairs were scattered in every direction, as in the adult animals. A comparison of auditory brainstem response tests revealed no difference between the abnormal and normal hamsters.

Auditory-evoked responses of dogs with different hearing abilities.

Sixteen dogs were separated into three groups, based on clinical impressions of their abilities to hear and historical information pertaining to their hearing loss: group I (n = 7) had normal hearing, group II (n = 4) had reduced hearing and group III (n = 5) were deaf. Monaural clicks of alternating polarities were used to elicit brainstem auditory-evoked responses. The responses of the normal group and of the reduced hearing group consistently had four major peaks (I, II, III-IV, V) with latencies similar to those previously reported in dogs with normal hearing. No difference (p greater than or equal to 0.05) was found in mean latencies of the four major waveforms when comparing the normal group with the reduced hearing group. Significant reductions in mean amplitudes of waves I (p less than 0.01) and II (p less than 0.025) were found in the reduced hearing group. No recognizable waves could be recorded from the deaf group, indicating a lack of peripheral auditory function.

Auditory brain stem response testing in anesthetized horses.

Auditory brain stem response testing, using insert earphones, was performed in 10 healthy horses given general anesthesia. The procedure involved clicks of alternating polarity delivered at a rate of 25 clicks/s. Wave forms, including five peaks, were commonly identified. Latencies were measured in milliseconds for waves I through V for all intensities. Latencies of all waves decreased as stimulus intensity increased. For waves I through V, a least-squares regression line was determined for each horse, using all responses between 87-dB sound pressure level (SPL) and 136-dB SPL, inclusive. Slopes were significantly (P less than 0.05) less than zero for waves I through IV, but not for wave V. Peak latencies of each wave averaged at 87-dB SPL for waves I through V were 1.73, 2.6, 3.82, 4.80, and 5.71 ms, respectively; latencies of these five waves at 136-dB SPL were 1.36, 2.2, 3.06, 3.92, and 4.71 ms, respectively. The decrease in latency among the five waves ranged from 0.13 to 0.004 ms/dB. When peak values were below 87-dB SPL, waves became essentially unrecognizable.

Electrodiagnostic evaluation of deafness in two English setter littermates.

Two English Setter littermates (male and female) were evaluated for hearing difficulties at 4, 16, and 24 months of age. Auditory function was evaluated by behavioral response to pure-tone sounds, tympanometry, brain stem auditory evoked response, and acoustic reflex testing. Hereditary sensorineural deafness was diagnosed in both dogs. The extent of the hearing deficit, as characterized by these tests, was slightly different between the dogs, as well as between the ears in 1 dog.

Disseminated protothecosis causing acute blindness and deafness in a dog.

A 3-year-old Collie bitch was euthanatized two weeks after the onset of blindness and deafness. The hearing deficit had been localized by clinical signs, brain stem auditory evoked responses, and impedance audiometry. Protothecosis was diagnosed by cytologic and histologic examinations. The organism was identified as Prototheca zopfii . Organisms and granulomatous lesions were found in kidney, heart, liver, skeletal muscle, thyroid gland, colon, bronchial lymph node, brain, and cochlea.

Brainstem auditory evoked response in the diagnosis of inner ear injury in the horse.

Brainstem auditory evoked response (BAER) testing was done to evaluate inner ear/VIIIth cranial nerve (CN8) function in the horse. The BAER test consisted of stimulating the auditory system with clicks and recording far-field responses of the brainstem auditory components via cutaneous electrodes and a signal averaging system. The normal response was shown to be a series of waves occurring within the first 10 msec after the stimulus click. Functional loss of the auditory receptor organ (cochlea) or CN8 results in loss of the entire response on the side of the injury. Because of the anatomic relationships of the peripheral auditory and vestibular systems, trauma to one will injure the other. Therefore, auditory testing (BAER tests) may be used to advantage in the diagnosis of peripheral vestibular disease. The BAER test was used in a horse that had signs suggestive of vestibular dysfunction or a brain lesion. The test helped to demonstrate a unilateral inner ear/CN8 lesion and to discount the probability of a more central lesion.