Veterinary Hearing Assessment Device is an electronic device designed to test hearing in animals to reveal, diagnose, and monitor hearing loss (HL). The most widely used in veterinary hearing assessment metod is recording Auditory Brainstem Response (ABR) which is the gold standard for evaluating hearing impairment in animals.
Auditory Brainstem Response (ABR), also called Brainstem Auditory Evoked Potentials (BAEP) is an auditory evoked potential (AEP) recorded in response to auditory (sound) stimuli from electrodes (in animals, typically subdermal needle) placed on the scalp. ABR is a very faint signal, measured in the nanovolts and microvolts, and thus, it requires averaging of multiple responses to multiple stimuli.
ABR is recorded in the time domain as a series of six to seven vertex-positive waves, called ABR waves, labeled with Roman numerals from I to VII, of which ABR waves I through V have clinical significance and are are evaluated.
ABR waves occur in the first 10 milliseconds after onset of an auditory stimulus, and the time of their appearance, called latency, varies depending on the stimulus level (intensity), as well as the type and severity of hearing loss.
The auditory pathway structures that generate ABR are believed to be as follows:
- Waves I through III are generated by the auditory branch (Audiory Nerve) of cranial nerve VIII and lower. More specifically, wave I originates from the dendrites of the auditory nerve fibers, wave II from the cochlear nucleus (CN), wave III reflects activity in the superior olivary complex.
- Wave IV and V are associated with the lateral lemniscus in the upper brainstem.
ABR allows quickly and accurately assess hearing, diagnose hearing loss, differentiate the site of lesion (with air-conducted and bone-conducted stimuli), monitor hearing to prevent hearing loss, e.g. caused by ototoxicity or noise exposure, as well as identify frequency-specific hearing sensitivity using tone-burst stimuli.
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