User guide
BABYS
C
REEN
ECH001XN121-A4 – 07/2022
27
Chapter 4
Otoacoustic emission (TEOAE and DP-gram)
4.1
Presentation
The cochlea, the peripheral organ of hearing, is capable of emitting low-amplitude sounds in response or not to acous-
tic stimulation. These sounds are easily recorded in the external auditory canal using a sensitive miniaturized microphone.
The genesis of these sounds coming from the cochlea, called otoacoustic emission, depends on the proper functioning of
specific cells in the cochlea: the outer hair cells (OHC). In addition, the integrity of the eardrum and the ossicular chain
is also necessary for the transmission of the acoustic stimulation wave and for the propagation of the physiological re-
sponse from the cochlea to the eardrum.
4.1.1
TEOAE
TEOAE :
Transient otoacoustic emissions.
When we speak about otoacoustic emissions, we primarily think about the transient otoacoustic emissions also called
TEOAE which are most used in clinical examination. The OAE are recorded by a small probe placed in the external ear
canal. The detection of transient otoacoustic emissions (TEOAE) is a real asset in the battery of audiometric tests.
The TEOAE are otoacoustic emissions per click, that is to say that we will test the patient ear at frequencies between
2000 Hz and 4000 Hz. The result is represented by a curve that indicates if the otoacoustic emissions are present or not.
This is an objective test because it does not require the cooperation of the patient.
This test is very important, especially in the examination of newborns, because if otoacoustic emissions are present it
means that the newborn hearing does not have a deafness higher than 30-40 dB. This is a routine screening test, more and
more used in the newborns examination.
4.1.2
DP-gram
DP-gram
: Otoacoustic Emission Distorsion Product Phase Shift Graphic
During the recording of the distortions product otoacoustic emission (DPOEA), a bi-tone acoustic stimulation is ap-
plied. This particular stimulation brings two specific regions close to the cochlea into action and leads to the excitation
of a third cochlear region. The OHC's excited in this way, because of their contraction property, will put the basilar
membrane into movement, driving the endolymphatic fluid and finally connecting the ossicles to the eardrum. Put into
vibration, the eardrum will emit a low amplitude sound (1: 10000) which can easily be recorded and identified.
These two stimulating sounds, called primary sounds, have respective frequencies of f1 and f2 and will generate the
emission of a characteristic distortion product for humans at a frequency of 2f1-f2. For instance, with the presentation of
2 primaries f1=1000Hz and f2=1200Hz, the expected distortion product will be 2f1-f2 = 800Hz. The generated distortion
product is lower in frequency and smaller in amplitude than the primaries. It is the amplitude of the distortion product
that will be considered as a criterion for evaluating the cochlear function and more specifically the OHCs of the emitting
region (at a frequency of 800 Hz in this example). Accordingly, a distortion product having an amplitude of more than 7
dB with respect to the background noise will be the signature of the presence and functionality of the OHCs in the emitting
region.