What is a BAER Hearing Test?

A BAER test determines if your dog can hear and how well. The test for dogs is essentially the same test used for young children and newborns.  Unlike the adult test (where you tell the doctor if you can hear the clicks) this test does not need any concious response from the patient.

The (BAER) brainstem auditory evoked response test or brainstem auditory evoked potential (BAEP) test determines what electrical activity is present in the cochlea and auditory pathways of the brain. It works much the same way that an antenna detects radio signals or an EKG detects electrical activity of the heart. The machine used to measure produces a wave on graph paper to determine the level of deafness.  

Peak I is produced by the cochlear nerve and later peaks are produced within the brain. An ear that is totally deaf shows essentially a flat line.The response is so small and hard to detect, it is necessary to average the responses to several clicks so they can be differentiated from background electrical activity that is also present on the scalp (EEG, muscle activity, etc).

The response is collected with a special computer through extremely small electrodes placed in front of each ear, one between the shoulders and one at the top of the head. Most dogs will not show pain from inserting the electrodes.  Usually they dislike the restraint more!

The stimulus click produced by the computer is fed into the ear with a foam insert earphone. Each ear is tested individually.  The test usually takes between 10-15 minutes. Sedation or anesthesia is usually not necessary unless the dog will not be still.  A printout of the test results, showing the actual recorded waveform is provided by the computer. 

A dog can be deaf bi-laterally (1 ear) or both ears, or have any degree of deafness in either ear.

Implants & Hearing Aid Availability in Dogs

Hearing aids have become increasingly sophisticated, however, all aids are merely sound amplifiers. They boost the level of sound so that if there is any hearing left at all, it may be able to detect sound better. In dogs, most congenital deafness in animals is pigment-associated, and the ear is totally deaf, so in that case, no amount of amplification can make a totally deaf ear hear. So in this case, a hearing aid would be useless. 

In Dogs, most hearing problems have been caused by repeated inner ear infections or trauma to the ear (from fights with other dogs or abuse). Other causes of deafness in dogs include drug toxicity, general anesthesia, old age and noise trauma.  Whether a hearing aid would be beneficial would depend on the amount of residual hearing ability still available.

Several investigators have developed hearing aids for use in dogs where residual auditory function remains – particularly Dr. A.E. Marshall at Auburn University in Alabama. He placed used human aids in a collar-mounted container with a plastic tube that led to the ear canal.  He reported that smaller breeds tolerated the presence of a foam plug in the ear better than large breed dogs, but my guess is that a Dog would not be very tolerant at all - choosing to depend on other senses (smell, sight, taste) rather than tolerate something in it's ears. Units are extremely expensive, and since most dogs don't necessarily tolerate them well, they are rarely recommended. (If you're really determined, Dr. Marshall can show your vet how to make his own as the units are not commercially available).

Most deaf dogs and cats give no evidence of being bothered by their deafness, and adapt quite well.  It is the human that is most distressed.

Cochlear mplants have been implanted in deaf humans, with a bundle of stimulating electrodes inserted surgically into one of the coils of the cochlea and there is some question as to whether this surgery may be beneficial to a deaf dog. Because the nerves from the cochlea into the brain usually remain after loss of the hair cells of the cochlea, they may still be capable of responding to stimulation. Deaf Dalmatians aided in the development of these devices but they have not been used to help dogs mainly because the devices cost $20K - $25K before the costs of the surgery itself, and not including the required training needed after surgery. Therefore, it's just not practical for dog at this point. 

BAER Hearing test sites (in the USA)

 

How a Diagnosis is Determined

At the veterinary clinic, the veterinarian will conduct a history and physical examination to measure hearing loss and determine any possible causes. A complete history is taken by the veteruinarian listing any drugs that may have damaged the ear or caused chronic ear disease.  If deafness is noticed at a very young age, that usually means a birth defect is the cause, particularly in predisposed breeds.  Slow onset often means disease of the cerebral cortex of the brain - often caused by cancer or senility (the brain can't register what the ear hears).  Bacterial cultures and hearing tests, as well as testing the sensitivity of the ear canal is also used to make a diagnosis.

The most common methods of determining hearing loss is clapping loudly behind the dog's head or rattling something noisy and getting no response.If Only one ear is affected, it may be more difficult to identiy.  Examination of the ear canal will detect wax accumulation, hair overgrowth, any foreign object blockage, infection, inflammation or injury and ear drum state. If the veterinarian suspects an ear infection, ear swabs and cultures may be done to diagnose the infecting agent and determine the proper mode of treatment. In some instances, a brainstem auditory evoked response (BAER) test will be conducted to measure the brain’s response to auditory stimuli. Radiographs may be used to determine possible causes of deafness. Treatment of Hearing Loss in Dogs Permanent Deafness Congenital deafness and geriatric deafness are not normally treatable. Surgery may attempt to correct hearing if the defect is in the middle or outer ear or involves inner ear inflammation, however most congenital defects involve delicate inner ear mechanics or nervous system defects.

Drug toxicity, heavy metal exposure and exposure to loud noises often cause permanent damage. Hearing Aids Hearing aids and cochlear implants are becoming available for dogs, however they are currently still costly and somewhat impractical. The devices work similar to human devices, but animals do not respond well to the device’s presence on the body and may not tolerate it.

Treatment may involve removing the blocking object, cleaning wax out of the ears, or plucking overgrown ear hair and a thorough ear cleaning. An ear flush and topical ointment to be used for 2-3 weeks with an antibotic may be prescribed, depending on the severity.  Sometimes surgery is required if there are tumors growing in the ear canal blocking sound transmission.

 

 


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