Analysis of Canine Presbycusis using Otoacoustic Emission and
Auditory Brainstem Response Testing Methods
P.M. Scheifele PhD MD(R), M.G. Pinto BS, F.E. Musiek PhD, M. Darre PhD PAS Animal Bioacoustics and Neuroaudiology Laboratory, University of Connecticut
Deafness is a common issue in dogs. Congenital deafness has been reported for approximately 85 breeds (Strain, 2005). Along with congenital deafness, presbycusis is also an important factor in canine hearing ability. Presbycusis is a natural hearing loss that occurs due to fatiguing and wear of the haircells in the inner ear and occurs in old age. It is important to test dogs because dogs with full or partial deafness require special attention. Deaf dogs may be prone to serious injuries. For example, dogs may be more likely to get hit by cars because they are not able to hear vehicles approaching. Deaf dogs are also more likely to startle easy and may bite in self-defense. Canine hearing testing is also valuable for breeders who want to breed healthy dogs with no hearing problems and for service dogs such as Seeing Eye dogs or military dogs that rely on their hearing to assist people on a daily basis.
The common method for veterinarians to determine hearing ability in a dog is behaviorally. A normal hearing dog will respond to any unusual sound introduced into its surroundings with recognizable behavioral signs such as lifting the pinna. The dog will lift the pinna of its ears and may move them toward the source of the sound. This type of testing may yield false results in that dogs can usually sense a person’s body language or may sense vibrations from an object being thrown on the floor rather than actually responding to hearing the sound. Another problem with current behavioral methods of hearing testing is that it is subjective and subject to behavioral bias in its interpretation. It gives little to no objective or quantitative information regarding the severity of hearing loss and no information as to the possible cause of the dog’s deafness.
A technique that is slowly being used more in the animal industry and which has been commonplace since 1967 (Hall, 1992) in human audiology is the use of electrophysiological techniques to determine a patient’s level of hearing. The most widely used electrophysiological test is the Auditory Brainstem Response (ABR). The ABR is an objective test that measures the electrical potential, also known as the auditory evoked potential (AEP), produced in response to sound stimuli by the synchronous discharge of neurons in the auditory nerve and brainstem. Current behavioral hearing tests miss out on the ability to accurately locate the problem in the auditory pathway if there is one. In conjunction with the ABR, an Otoacoustic emission (OAE) is used. An OAE tests cochlear function. An OAE is a sound generated by the energy produced by the outer haircells in the cochlea. There are a few types of OAEs and the one used in this research is the Distortion Product Otoacoustic Emission (DPOAE). The DPOAE specifically transmits two pure tones of similar but different frequencies into the ear canal and a third tone is emitted in response to the first two. Once it is clear that the cochlea is functioning normally, the ABR can be performed with a high degree of certainty that if there are abnormalities in the test result it is safe to infer that the problem exists in the auditory pathway/brainstem and not in the inner ear.
To determine the characteristics of DPOAE and ABR response configurations for canine presbycusis versus normal hearing.
This research involves 18 dogs of various ages, breeds, and gender. The dogs were supplied by various owners. All tests were performed in a dark quiet but not sound proof room. A dark room was used so as to avoid electrical interference and to keep unsedated animals calm. Each dog had an otoscopic exam performed using a handheld Welch Allyn otoscope. Dogs were sedated as necessary by the veterinarian using Acepromazine. Once sedated or acclimated each dog had a Distortion Product Otoacoustic Emission (DPOAE) performed. Upon completion of the DPOAE and confirmation of a normal functioning cochlea, an Auditory Brainstem Response (ABR) test was carried out on a GSI VIASYS Healthcare Audera Unit which was run off of a laptop computer. Rapid pull 13mm VIASYS subdermal needles were inserted subcutaneously into three different locations on the dogs (See Fig. 1). The first being the vertex, the second being either the right or left mastoid, and the third location being medially at the withers for the ground electrode. Disposable 13mm polyurethane foam eartips were inserted into the ear canal of the ear being tested. For the ABR, a modified click stimulus was presented at six different intensities. The six different intensities were 10dB nHL, 20dB nHL, 30dB nHL, 50dB nHL, 70dB nHL, and the highest at 90dB nHL. All six intensities were presented to the left ear and then the right ear. After all intensities were run the waveforms were analyzed, labeled, and slopes were calculated for the wave V latency intensity function. The wave V latency intensity function is seen in animals as well as humans. It is that as intensity decreases, the latency increases and wave amplitude decreases. This experimental protocol was approved by the International Animal Care and Use Committee of UConn as protocol number A06-040.
Figure 2. (a.) Otoacoustic Emissions for a dog with “normal” hearing. (b.) Otoacoustic Emissions for a dog with presbycusis.
Auditory Brainstem Response
Fig 3. A comparison of waveform morphology between the “normal” hearing (a.) and presbycusis dog (b.) at 70dBnHL
Figure 4. Auditory Brainstem Response morphology of a deaf dog.
Figure 5. Wave V latency intensity function for a dog with “normal” hearing (a)(c) and for a dog with presbycusis (b)(d).
Table 1. Slopes of Wave VLatency-Intensity functions for Normal and Presbycusis dogs and means.
To date, eighteen dogs total have been tested. Out of the these eighteen dogs, thirteen showed test results of either having normal hearing or presbycusis, two dogs were completely deaf, and data from three dogs was not included in the results due to excessive noise appearing in the waveforms.
ABR testing thus far for normal hearing dogs show overall early latencies for waves I – V by as much as 0.3 – 0.5 milliseconds when compared to human norms. In addition, wave IV is usually absent. Latencies for dogs with presbycusis were repetitively more coincident with that of adult humans or later by 0.2 milliseconds. The amplitude for dogs with Presbycusis was also shown to be shorter than in a normal hearing dog.
Preliminary results using linear regression models show that slopes of dogs with normal hearing tend to be around 0.010-0.020 with a mean of 0.016 whereas dogs with presbycusis have a slope greater than 0.020 with a mean of 0.025. (See table 1 for slopes) There is no latency-intensity function for deaf dogs because there are no distinguishable wave peaks (See figure 4).
A much greater sample set (n-size) must be taken to establish good normative data for both OAE and ABR tests that can be used consistently among all animal audiologists and veterinarians. Further testing is currently in progress.
Based on this preliminary evidence it appears that normal hearing versus presbycusis in canines can be identified through the use of AEP (ABR) and DPOAE testing. This method is promising for determining hearing loss in dogs and with more research should grow in the veterinary practice.
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