in dogs and cats. Br Vet] 1996;152:17-36. 22. Strain GM, Olcott BM, Hokett LD. Electroretinogram and visual-evoked potential measurements in Holstein cows.
Air- and bone-conduction brainstem auditory evoked potentials and flash visual evoked potentials in cats George M. Strain, PhD; Bruce L Tedford, PhD; Martha A. Littlefield-Chabaud, DVM, MS; Lisa T. Trevino
Objective- To document normal values for air- and bone-conducted brainstem auditory evoked potentials (BAEP) and for flash visual evoked potentials (VEP) in cats. Animals-l0 mixed-breed cats (5 males) with nor mal physical, neurologic, otoscopic, and funduscopic examination results. Procedure-BAEP in response to air- and bone-con ducted click stimuli and VEP in response to flash stim uli were recorded to document species normative data. Mean and SD values were calculated for ampli tudes and latencies of 4 peaks in the BAEP in re sponse to air- and bone-conducted stimuli, and for latencies to 5 peaks and the 4 associated peak-to-peak amplitudes in the VEP.
Results-BAEP peak latencies increased and peak amplitudes decreased with decreasing stimulus inten sity. Latencies were shorter for bone-conducted stimuli owing to the shorter transit time to the cochlea through bone, compared with air, but there were no differences for interpeak latencies. The BAEP and VEP recordings were similar to those reported for cats in other reports and were similar to those seen in other species. Clinical Relevance- Normative data will permit performance of noninvasive electrodiagnostic evalua tion of feline auditory and visual systems. (Am J Vet Res 1998;59:135-137)
E
lectrodiagnostic tests of neural function have be come increasingly important as diagnostic tools and research instruments in veterinary medicine. Use ful application of these tests requires the documenta tion of normative response data for the species under consideration. Several studies have involved cat brain stem auditory evoked potentials (BAEP)l-lO and visual evoked potentials (VEP)1l·19 in research applications, but to the authors' knowledge, normative reference data similar to those available for other species have not been published. Further, reports of BAEP in cats have relied only on air-conducted stimuli; however, bone-conducted stimuli are frequently used to distin guish between sensorineural and conductive deafness. 20 •21 The purpose of the study reported here was to document normal values for air- and bone-con ducted BAEP, as well as for flash YEP in cats. Materials and Methods Cats- Ten healthy mixed-breed adult cats (5 males), ranging in body weight from 2.25 to 3.85 (mean, 2.91) kg, Received for publication Mar 28, 1997. Manuscript passed review Jul 15, 1997. From the Departments of Veterinary Physiology, Pharmacology and Toxicology (Strain, Tedford, Trevino) and Veterinary Anatomy and Cell Biology (Littlefield-Chabaud), School of Veterinary Med icine, Louisiana State University, Baton Rouge, LA 70803. Supported by a grant from the Howard Hughes Medical Institute to Louisiana State University in support of undergraduate biomedical education (Trevino) and by a grant from the American Kennel Club.
A]VR, Vol 59, No.2, February 1998
were studied. All cats had normal results of physical and neurologic examinations, and nonnal otoscopic and fundu scopic examination results. Approval of the protocol was re ceived from the university Institutional Animal Care and Use Committee. Recordings-All recordings were obtained without se dation or anesthesia, with the cats positioned in a restraint bag. The BAEP recordings were obtained using subdermal needle electrodes' placed over vertex (positive), rostral to the tragus of the stimulated ear (negative), and at the midpoint of the interorbital line (ground); interelectrode impedances were < 7 kfl. Rarefaction click stimuli were produced by a 100-microsecond square-wave pulse applied to an insert ear phone transducerb Vl-ith an attached 25-cm length of tubing that terminated in an ear plug of compressible foam held just outside the ear canaL Alternating polarity click stimuli were produced by a 100-microsecond square-wave pulse applied to a bone transducer< held firmly against the mastoid process. Stimuli were presented at a rate of 11. 4/s at stimulus inten sities of 95, 75, and 55 dB normal hearing level, where 0 dB normal hearing level is the hearing threshold for young hu man adults, as detennined by the eqUipment manufacturer. Responses of 10 milliseconds duration to 1,000 clicks were averaged twice by a computer-based electrodiagnostic sys tema to ensure repeatability, using a frequency bandpass of 150 to 3,000 Hz. The YEP recordings were obtained using needle electrodes placed over the midpoint of the nuchal crest (positive), the midpoint of the interorbital line (negative), and the vertex (ground); electrode impedances were < 7 kfl. Stimuli consisted of flashes of white light at a rate of 1. Sis, with the flash unite held approximately 20 cm from the eye while the contralateral eye was covered. A single flash intensity of approximately 750,000 candlepower was used. Recordings were obtained in the dark, but extended dark adaptation (> 5 minutes) was not done. Two averages of 100 responses each were recorded, using a bandpass of 1 to 100 Hz; response duration was 250 milli seconds. Mydriatic drugs were not given. Data-Auditory data consisted of measurements of the latency to 4 peaks (1, II, lU, V) of the BAEP and the ampli tude of each peak to the following nadir for air- and bone conducted stimuli at 3 intensities. Peak naming conventions followed those of Sims and Horohov. 5 Visual data consisted of measurements of the latency to 5 peaks (PI, NI, P2, N2, P3) of the YEP and the 4 associated peak-to-peak amplitudes (PI-NI, NI-P2, P2-N2, N2-P3). Peak naming conventions followed those of Strain. 22-25 Mean, SO, and range data are reported for each measure. Analyses of variance were per fonned, using a general linear model with repeated measures, with P :s; 0.05 set as the limit for significance.
Results Typical BAEP in response to air- and bone-con ducted stimuli were compared (Fig 1). Data measure ments were tabulated (Tables 1 and 2). Left-versus-right data differences were not significant, except for the peak I amplitude at 95 dB (air-conducted stimuli only): left ears,2.84 ± 0.761lV (mean ± SD); right ears, 1.94 ± 0.76 IlV. This difference was not considered to be bio logically meaningful, so all results for both ears were combined, giving N = 20 data points. The BAEP peak 135
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