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Otoacoustic Emissions - An Overview

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Otoacoustic emissions are the sound developed from the cochlea transmitted through the middle ear to the external ear canal. Read the article below.

Medically reviewed by

Dr. Krishan Kumar Rajbhar

Published At November 20, 2023
Reviewed AtNovember 20, 2023

Introduction:

Otoacoustic emissions testing offers another modern evaluation technique of the auditory system exceeding conventional audiometry. It can be performed for patients with hearing loss who cannot handle or finish traditional hearing tests. The testing does not need to record a patient's response to sound. There are different ways to measure otoacoustic emissions per person, with benefits and disadvantages. This activity examines the evaluation of hearing loss using otoacoustic emission and highlights and tests the role of the interprofessional team in treating and treating this condition.

What Are Otoacoustic Emissions?

Otoacoustic emissions (OAE) are sounds yielded from the cochlea transferred through the middle ear to the external ear canal, where they can be studied and recorded. The production of an otoacoustic emission displays inner ear health and is an easy way to diagnose hearing loss. There are two kinds of otoacoustic emission given in the following:

  • Spontaneous otoacoustic emission (SOAE), which appears continuously with no external stimuli.

  • Evoked otoacoustic emission (EOAE), which needs an acoustic stimulus before its measurement.

The creation of sound through the cochlea is because of the cochlear amplifier and is based upon the traveling wave theory, which was developed in the 1940s. Traveling wave theory states that sound stimulates the stapes (the smallest bone in the middle ear), which produces a promulgating fluid wave inside the cochlea (a spiral cavity of the inner ear) and basilar membrane displacement to the apex from the base. The frequency of the stimulus may peak at different sites with the basilar membrane, with even higher frequencies producing maximal vibration at the base of the cochlea, whereas low levels of frequencies may have maximal vibration at the cochlea’s apex.

What Are the Functions of Different Types of Otoacoustic Emissions?

Following are the functions of the otoacoustic emissions:

  • Spontaneous Otoacoustic Emissions: These are the sounds produced from the ear with no acoustic stimulus and can be estimated with microphones attached to the external ear canal. Their frequencies are between 490 Hz to 4,400 Hz. A small percentage, 1 % to 8 %, of people can recognize their spontaneous otoacoustic emissions to be tinnitus.

  • Evoked Otoacoustic Emissions: It can be created using three different acoustic stimuli: stimulus-frequency, transient evoked, and distortion product. Transient evoked and distortion product otoacoustic emissions are the most regularly used techniques for the screening of the newborn’s hearing.

  • Transient-evoked Otoacoustic Emissions: Transient-evoked otoacoustic emissions are created by using toner click-burst stimuli. A click stimulus has a sudden and abrupt onset and short duration, and it also covers a broad frequency range of up to 5 kHz to produce responses from multiple nerve fibers. Since the emission response contains the same frequencies as the stimuli, differentiating between the response emissions can be challenging. Multiple repeated stimuli are needed and adjusted to differentiate the response emission from the initial stimulus. Response emissions are recorded at 2.1 milliseconds to 23.1 millisecond latencies, being consistent with the frequency of the stimulus. Higher frequencies promulgate a lesser distance with the basilar membrane to the base and need a more concise latency. Also, the lower frequencies travel further toward the cochlear apex and need a longer latency.

  • Stimulus-frequency Otoacoustic Emissions: Stimulus frequency is created by a single pure-tone stimulus. Nevertheless, the response emission appears at the same frequency as the stimulus and is complex to distinguish from residual stimulus energy. Thus, there is restricted clinical use for this method.

  • Distortion-product Otoacoustic Emissions: Distortion product otoacoustic emissions are created by using two simultaneous pure tone stimuli known as f1 and f2. It can be adjusted accordingly to estimate frequencies that match the patient’s audiogram and has the potential to detect high-frequency hearing loss.

How Is Otoacoustic Emission Carried Out?

A small earphone, or probe, is placed in the ear. The probe puts sounds into the ear and measures the sounds that resonate. The person does not need to do or say anything during the test. The person conducting the test can see the results on the monitor screen. The test is non-invasive and needs a small probe to be inserted into the ear. A succession of tones or clicking sounds are introduced to the patient. The test is established in a small sound booth, where the patient needs to be still and quiet while testing is taking place. It is approximately performed for half an hour, after which the audiologist shares the test results with the patient. When measuring otoacoustic emissions in infants and young children, the emission amplitudes tend to be higher than those found in adults but are also accompanied by higher background noise levels and some reduction in the low frequencies.

What Is the Clinical Significance of Otoacoustic Emissions?

During analysis, it may also be a concern to differentiate between otoacoustic emissions from background noise. Thus, most otoacoustic emissions require analysis of the reproducible data and the signal-to-noise ratio of the otoacoustic waveform of emission. Since otoacoustic emissions travel via the middle ear, they can also be impacted by any middle ear disease, such as middle ear effusion. Otoacoustic emission may not be measurable in children with adhesive otitis. Thus, otoacoustic emission cannot differentiate between conductive hearing loss and sensorineural loss.

Conclusion:

Otoacoustic emissions are low-level sounds estimated from the ear canals of humans and animals with intact cochlea function. Distortion-product otoacoustic emissions and transient-evoked otoacoustic emissions can be helpful in differentiating sensory (cochlear) from neural (retrocochlear) hearing losses. Poor behavioral hearing thresholds and good emissions mean a retrocochlear site of the lesion. Reduced otoacoustic emission indicates at least cochlear dysfunction. Distortion-product otoacoustic emission is very sensitive to hypoxia and interruption of inner ear blood flow. Being sound waves, otoacoustic emission is described by amplitude, frequency, and phase measures. The development of OAE screening and assessment procedures were catalysts for the generation and implementation of universal newborn screening programs because they provide a quick, non-invasive measurement of cochlear function. Common clinical OAE measures also provide general information about the spectral response of the cochlea. They do not require a behavioral response, although infants and children do need to be relatively still and quiet for clear results.

Dr. krishan kumar Rajbhar
Dr. krishan kumar Rajbhar

Otolaryngology (E.N.T)

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sound in the ear
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