Otoacoustic emission is the sound generated in the external auditory canal by vibrations of the external hair cells of the cochlea . Her existence was predicted by Thomas Gold in 1948, and she herself was first discovered experimentally by David Kemp in 1978 [1] . Further studies showed that the presence of otoacoustic emission in a person depends on the condition of the inner ear. With sensorineural hearing loss, otoacoustic emission is usually absent (with pathology of the cochlea ) [2] .
There are two types of otoacoustic emission: spontaneous otoacoustic emission - sound vibrations that spontaneously appear in the external auditory canal, and induced otoacoustic emission , which occurs in response to the presentation of a sound stimulus in the auditory canal.
Content
Evoked otoacoustic emission
It got such a name, as it is caused by a sound stimulus presented to the auditory meatus. Two types of evoked otoacoustic emission are known: delayed evoked otoacoustic emission (ZVOAE) and emission at the frequency of the distortion product (ECHP)
ZVOAE
This type of emission occurs in response to a stimulus in the form of a broadband click. Its appearance can be compared with the sound of a tuning fork, after it was clicked on with a finger. The outer hair cells - “tuning forks” begin to oscillate in response to the received acoustic click. Since some time passes for the sound to reach the inner ear and go in the opposite direction, a signal of this type of emission appears in the external auditory canal with a delay relative to the stimulus applied. In the cochlea, hair cells sensitive to a high frequency are located closer to the entrance, while sensitive cells to a low frequency are located deeper. Therefore, the delay of the high-frequency component of the emission is less than the low-frequency component. In the registered emission, first there are high-frequency groups of oscillations, then low-frequency ones. The total duration of the recorded oscillations is 12 - 20 ms from the beginning of the stimulus.
Since the amplitude of the recorded emission is much smaller than the external noise and the noise of the microphone, special statistical methods such as Coherent averaging and others are used to extract it.
The emission amplitude has a nonlinear dependence on the volume of the stimulus. That is, its amplitude grows more slowly than the volume of the stimulus, and at a volume of 90 −100 dB SPL saturation occurs - the amplitude of the emission ceases to increase with a further increase in the volume of the stimulus. This is due to the mechanism of formation of non-linear sensitivity of the ear. This emission property is used in the method of nonlinear averaging, which allows you to get rid of the stimulus artifact when recording emissions.
ECHP
Called by a pair of clear tones with a frequency of f 1 and f 2 supplied to the ear canal. Due to the nonlinear properties of the cochlea, in the auditory meatus, in addition to the tones supplied, their third-order intermodulation distortions (the product of distortion) begin to appear. Usually register the most powerful of them - at a frequency of 2 f 1 - f 2 . The optimal ratio between the frequencies f 2 : f 1 is approximately 1.22. For frequencies above 8 kHz it decreases to approximately 1.15. The most commonly used intensities f 1 - 65 dB SPL , f 2 - 55 dB SPL
Practical Application
The most significant practical application is the Audiological screening of newborns for the early detection of hearing loss [3] . In Russia, testing of hearing of newborns by the method of otoacoustic emission is mandatory [4] [5] . The absence of otoacoustic emission indicates possible problems with hearing, for confirmation or refutation, additional examination is required by methods of recording auditory evoked potentials and consultation with an audiologist . It can also be used in combination with other methods of hearing diagnosis to differentiate cochlear pathology and retrocochlear pathology.
Notes
- ↑ Kemp DT. Stimulated acoustic emissions from within the human auditory system. J Acoust Soc Am. 1978; 64: 1386-1391
- ↑ Tavartkiladze G.A., Gvelesiani T.G. Clinical Audiology. - M .: Svyatigor Press, 2003 .-- 75 p.
- ↑ http://rsmu.ru/fileadmin/rsmu/img/fuv/c_lor/met_rekomendacii.pdf
- ↑ MINISTRY OF HEALTH AND SOCIAL DEVELOPMENT OF THE RUSSIAN FEDERATION LETTER December 30, 2008 N 10329-ВС ABOUT AUDIOLOGICAL SCREENING
- ↑ DB Law on the conduct of audiological screening . Date of treatment January 20, 2013. Archived on June 9, 2013.
See also
- Mass examination of newborns