Otoacoustic Emissions (OAE)/ KEMP Echoes 

What is an Electrophysiological Test?

A machine-generated test to test the electrophysiological activity happening in the cochlea, cochlear nerve, brain stem, or cerebral cortex on providing auditory stimuli. Electrophysiological tests are objective tests to determine the extent of hearing loss and the location of hearing loss (for example, the hearing loss in the cochlea of the cochlear nerve).

Q. Why should we assess Hearing Loss?

Earlier detection can help in the rehabilitation process. Earlier detection helps in speech development. Hearing and speech are interdependent. There are different techniques for testing hearing loss. The techniques for adults and older children are not suitable for young children. These techniques are non-reliable for young children, have inherent challenges, and many times, children are unable to respond desirable to sound stimuli. The techniques, along with children, are also inappropriate for adults with learning disabilities.

Also read: Deaf Child Hearing Assessment

Otoacoustic Emissions (OAE)/ KEMP Echoes

Primarily used as screening tests in newborns and infants. It is also known as KEMP Echoes. Cochlea has outer, inner, sustincular, deter cells, and other supporting cells. OAE reflects the function of the outer hair cells. OAE presence denotes good functioning of outer hair cells.

Thus, the presence of OAE signifies higher chances of outer hair cells functioning and thus healthy cochlea.

However, absence of OAE need not denote or confirm the non-functioning of outer hair cells.

OAE cannot determine the degree of hearing loss, such as severe or moderate hearing loss.

OAE presence denotes that the peripheral hearing is satisfactory. There can be false positives when it comes to the functioning of the cochlea in rare cases. The presence of OAE doesn't exclude hearing disorders. 

Principle: Identifying the function of outer hair cells of the cochlea that are efferent. 

Inner hair cells—Afferent function: Inner hair cells conduct the impulses to the 8th nerve, which then goes to the brain. 

Outer hair cells—efferent function: It controls the degree of impulse the inner hair cells send to the 8th nerve. Processing of sound signals.

Active Processing

The outer hair cell, stimulated by sound, amplifies the sound. The amplified sound goes to inner hair cells and further goes afferent to the brain.

Passive Processing 

Loud sound directly stimulates inner hair cells. Loud sound causes movement of the basilar membrane. The basilar membrane directly stimulates inner hair cells attached to the membrane.

Loss of outer hair cells resulting from the problem of cochlea won't allow proper functioning of the outer cells. Thus, inner cells will have to depend on loud sounds for impulse transmission to the brain. Using an ultra-sensitive probe (yellow probe) with a monitor to the outer auditory canal will inform about the presence of emissions. The presence of emissions denotes cochlea is healthy. However, the absence of emissions need not confirm unhealthy cochlea. Further investigation is necessary.

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Types of Otoacoustic Emissions (OAE)

Spontaneous OAE: Emissions are present in the absence of acoustic stimulus.

Evoked OAE: Transient evoked OAE: Emissions happening on the sound stimulus in the form of clicks. 

Distortion product OAE: Emissions happening on providing two sound frequencies.

Prerequisites

• No sedation is required.
• The child needs to sleep to avoid inaccurate results.
• There should be no middle ear or EAC pathology.
• Ear wax in EAC may lead to false or inaccurate results.
• It can be done by otoscopic examination. There should be optimum positioning of the probe.
• Quiscent child
• A silent testing environment is needed.
• It is a simple test.
• Training is easy.
• It is a screening investigation of choice due to the ease of conducting tests.
• It is a portable device.
• If OAE are absent, refer for further testing.

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Inference

Spontaneous Otoacoustic Emissions

The presence of spontaneous (without auditory stimulus) OAE denotes healthy cochlea. Absence of spontaneous OAE requires further cochlea investigation.

Transient Otoacoustic Emissions (OAE)

Emissions on the sound stimulus in the form of clicks at 80-85 dB sound pressure level (SPL) for 2-3 milliseconds are given.

Advantage: Fast and reliable

Disadvantage: Poor result at high frequency. Inappropriate results in a noisy environment.

Distortion Product Otoacoustic Emissions (OAE)

Advantage: Good at high frequency. Useful to identify early cochlear damage.

Every child must be screened for OAE to detect early hearing issues.

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