Following unsuccessful attempts to record visual-evoked potentials (VEPs) in dogs with scalp electrodes, adoption of a new stimulation technique seems to be beneficial. Previously, flashes of white light administered after dark adaptation induced relatively high amplitude electroretinograms (ERGs) covering any VEP activity over the surface of the skull. ERG amplitude, however, can be significantly reduced using flashes of red light after light adaptation (mostly cone stimulation). Simultaneous ERG and VEP recording allows identification of VEPs composed of three significantly different negative peaks (Nl, N2, and N3) measured in dogs anesth2tized with chloralnse and halothane. No more than two of the three peaks were seen in one recording. Only the N1 and N3 waves were consistently recorded in dogs anesthetized with thiopental and thiopental combined with halothane. In 50% of all recordings, N1 was seen alone. The other VEPs consisted of N l and N2, or N l and N3 occurring concurrently. The simultaneous occurrence of N2 and N3 waves, however, was never seen. Among all recordings, N1 was most frequently recorded (85% of measurements), followed by N3 and N2 (38% and 31% of measurements, respectively).Peaks of less than 90 ms are highly reproducible. Anesthesia is necessary to eliminate frequent artifacts obtained in conscious and sedated dogs. Thiopental and/or halothane had no effect on measured latencies compared with chloralose. (Journal of Veterinary Internal Medicine 1988; 2:145-149) THE LARGE VOLUME of literature on visuel-evoked potentials (VEPs) in humans reflects the importance given to this noninvasive electrophysiological tool in the diagnosis of brain dysfunction. ' In animals, direct cortical measurement after implantation of electrodes on the cerebral cortex has been used to record potentials from the visual occipital cortex2-6 and to define the normal VEP.3,7 Recording of evoked cortical potentials (ECPs) with implanted electrodes is not applicable to clinical cases. Nearly atraumatic ECP recordings with scalp electrodes are performed routinely in humans. Until recently, however, VEP recording in animals with scalp electrodes was unsuccessful. The difficulty encountered in attempts to record VEPs in dogs has been attributed to the high amplitude far-field electroretinogram (ERG) conducted over the skull masking the localized lower amplitude VEP activity.8 High amplitude ERGs result when using flashes of white light after dark adaptation, i.e., when the photoreceptors of the retina, rods, and cones are maximally loaded with their respective photopigments. Under this circumstance, retinal stimulation with white light flashes gives rise to a response from most of the reactive cells of the retina. ' Because the retinas of dogs contain more rods than cones in an approximate proportion of 95: 1 , l o a lower amplitude ERG should be obtained by stimulation of the cones only. The lower amplitude of the ERG might allow easier recording of the VEP. The objective of the present study was to design a suita...

The effect of cardiac-cycle phase on the radiographic appearance of the feline heart was investigated. Results show that the size and shape changes in the cardiac silhouette due to the cardiac cycle were present in all three postural positions investigated. Cardiac size and shape changes were present more frequently and in more locations of the cardiac silhouette when patients were in ventral recumbency (DV) versus dorsal recumbency (VD). In most cases, the magnitude of differences was small and detection was facilitated by comparison viewing. It is suggested that these size and shape influences of the cardiac cycle on cardiac appearance should be kept in mind when interpreting feline radiographs for cardiac pathology.

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