Otoacoustic Emission: A Review

Question 1

hair cells are part of what ?

Answer 1

-Part of the cochlear sensory receptor system
They’re located in the organ of Corti
-they get their name from the tufts of stereocilia “hair bundles” that protrude out into the cochlear duct (scala media)

Question 2

what are the 2 types of hair cells ?

Answer 2

OHC and IHC

Question 3

what is the main purposes of the OHC?

Answer 3

-Serve as acoustical pre-amplifiers
-Amplify movement of the basilar membrane during low-intensity sound stimuli

Question 4

how do OHC respond to a stimuli (electromotility)

Answer 4

-Accomplished by ability to change their lengths in response to stimuli (electromotility)
1)Greater change in length = more stereocilia bending, more transduction and greater response
2)Allows for 100-fold increase in hearing sensitivity (40dB)
3)Damage to OHCs results in mild to mod-severe SNHL

Question 5

what do OHC sharpen ?

Answer 5

Sharpens tonotopic organization of basilar membrane (i.e., place coding of frequency, and sharp tuning curves)

Question 6

are OHC efferent or afferent hair cell

Answer 6

their efferent and controls movement and muscle

Question 7

what is the purpose of IHC ?

Answer 7

-Serve as the actual sensory receptors of hearing (95% of fibers of auditory nerve that project to the brain arise from IHCs)
-Transform sound vibrations present in cochlear fluids into electrical signals that can then travel the auditory nerve to the brainstem and auditory cortex

Question 8

where do IHC damage typically happen ?

Answer 8

Damage to IHCs occurs (in conjunction with OHC damage) in severe to profound sensorineural losses

Question 9

How does the cochlea and OAEs correlate ?

Answer 9

-Cochlea actually emits sound under certain conditions
-Theses sounds (OAEs) can be detected by placing a sensitive microphone in the ear canal near the eardrum

Question 10

how can emissions/ potentials be provoked ?

Answer 10

Emissions can be Spontaneous and generated in the absence of an external stimulus (SOAEs) or evoked by a specific sound stimulus (EOAEs)

Question 11

what are the 2 main types of OAEs ?

Answer 11

Transient Evoked Otoacoustic Emissions (TEOAEs)
Distortion Product Otoacoustic Emissions (DPOAEs)

Question 12

what is the 3rd OAE that’s not really common

Answer 12

Stimulus Frequency Otoacoustic Emissions (SFOAEs) - 3rd Type, but not as common

Question 13

what are some characteristics of a spontaneous OAE ?

Answer 13

-The first type to be reported.
-Do not require any type of evoking stimuli.
-Only occur in normal cochleas., won’t happen
in damaged cochleas
-Only occur in 60% of normal ears
-At least one SOAE can be detected in 35-50% of population
-Majority of the people are unaware of SOAEs;
1-9% however perceive a SOAE as an
annoyingtinnitus (Penner, 1990).
-Not clinically useful.
-*not a good diagnostic tool

Question 14

what are some characteristic of Transient Evoked Otoacoustic Emissions (TEOAE)

Answer 14

-Present in all individuals with normal hearing.
-Clicks, as broad band stimuli, result in broad band responses.
-The frequency range is usually from about 500 to 4-5000 Hz; dependent on the frequency response of the transducer.
-Amplitude averages 10-12 dB SPL in young adults.

Question 15

when can TEOAEs be used?

Answer 15

1)Can be used to screen infant hearing (NBHS).
2)Can be used to validate behavioral thresholds.
3)Used to assess cochlear function relative to site of lesion.
L4)imited frequency specificity (response emanates from broad cochlear region due to broad band click stimuli).

Question 16

what is the most common and robust distortion?

Answer 16

The most common and robust distortion product in humans is the cubic DP, noted as 2f1-f2. Two pure tones (f1 & f2) presented simultaneously evoke the DPOAE

Question 17

what is the equation for DPOAE?

Answer 17

2x f1-f2=f3

Question 18

where is the amplitude of DPOAE measured at ?

Answer 18

-The amplitude of the DPOAE is measured at the DP frequency.
-F2 frequency or geometric mean of f1 and f2.

Question 19

DPOAEs is dependent on?

Answer 19

The presence of DPOAEs is dependent on hearing sensitivity in the region of the primaries.

Question 20

when can DPOAEs be used ?

Answer 20

-Can be used to screen infant hearing.
-Can be used to validate behavioral thresholds.
-Used to assess cochlear function relative to site of lesion.
-Ototoxic Monitoring
-Has greater frequency specificity. DPOAEs frequently correspond to the audiometric configuration of a cochlear hearing loss.

Question 21

when are stimulus frequency otoacoustic emissions (SFOAE)

Answer 21

• It’s Measured during the application of a pure-tone stimulus, and are detected by the vectorial difference between the stimulus waveform and the recorded waveform (which consists of the sum of the stimulus and the OAE)

-Newer, less common and not used clinically

Question 22

OAEs are related to?

Answer 22

OAEs are related to the proper function of the outer hair cells (electromotility of OHCs is the generator of response)

Question 23

OAEs disappear after?

Answer 23

OAEs disappear after the inner ear has been damaged, so OAEs are often used in the clinic as a measure of inner ear health

Question 24

When are emission typically found ?

Answer 24

Emissions are usually found in persons believed to have normal cochlear function accompanied by an uncompromised middle ear.

Question 25

what happens if the cochlea is damaged and if emissions are obtained with normal amplitude characteristics ?

Answer 25

If the cochlea is damaged and if emissions are obtained with normal amplitude characteristics, those emissions appear to originate in cochlear regions having relatively normal function

Question 26

what are non pathologic factors that can influences OAEs

Answer 26

age
gender
ear differences
diurnal effects (during the day)
genetics
race
body temp
body position
state of arousal and attention
poor probe placement or seal
ear canal acoustics/ standing waves
debris, cerumen, foreign body, in the canal
uncooperative patient
NOISE!!!

Question 28

how does age affect our OAEs

Answer 28

-Amplitude of response is most robust and reproducibility higher in infants than older children and, especially adults (TEOAEs and DPOAEs)
-Factors: Canal volume, resonance properties, compliance system, efferent

Question 29

how can gender affect our OAEs?

Answer 29

-Anatomical differences (length, size) form canal to auditory cortex, body temp
-Affects SOAEs and TEOAEs but not DPOAEs

Question 30

how can ear difference affect our OAEs

Answer 30

-Research has showed slightly poorer hearing -for the left versus right ear, especially for higher frequencies (TEOAE amplitudes typically higher left ear)

Question 31

how does genetic affect OAEs

Answer 31

Genetic patterns exist in prevalence of SOAEs, possibly TEOAEs

Question 32

how does race affect our OAE

Answer 32

not known at the time

Question 33

can body temp affect oaes?

Answer 33

no but it can affect ABRS

Question 34

how can the state of arousal and attention affect OAEs

Answer 34

None except that anesthesia or sedative agents can have slight effect on TEOAEs but not DPOAEs. Nitrous Oxide can affect middle ear status and thus OAE

Question 35

how can poor probe placement or seal affect OAEs

Answer 35

Most current equipment alerts clinicians to these problems.

Question 36

how can Ear Canal Acoustics / Standing Waves
affect our OAEs

Answer 36

-Standing wave interference potential especially for frequencies above 4000 Hz
-Most systems account for this possibility assuming proper probe placement

Question 37

how can Debris, cerumen, foreign body in the canal affect OAES

Answer 37

Otoscopy, equipment calibration?

Question 38

how can an uncooperative patient affect our OAEs

Answer 38

Movement or too much noise to obtain properly

Question 39

how can noise affect OAEs ?

Answer 39

-External ambient (room) noise that can enter the probe mic recording OAE
-Internal noise generated by the patient from breathing, blood flow, muscles
-Noise inherent to recording microphone or equipment

Question 40

what is the most important non pathological condition to control during OAES

Answer 40

By far the most important non-pathologic condition under most control of the tester. In fact, the success and quality of OAE measurement and the accuracy of OAE interpretation is highly dependent on noise

Question 41

how can we minimize noise from affecting our OAES?

Answer 41

1)A deep and secure probe fit in EAC;
2)An adequate number of stimulus repetitions (i.e., signal averages);
3)Appropriate stopping criteria tat require low noise and a clear SNR.
4)Emphasis on or exclusive presentation of signals at frequencies higher than 1k
5)For DPOAE, a protocol that presents signals from higher to lower frequencies.

Question 42

what are some middle ear factors that can affect OAES?

Answer 42

The middle ear influences inward propagation of the OAE stimulus and outward propagation of the OAE response

Must have a near-normal to normal functioning middle ear system to obtain OAE responses

In the absence of a normal functioning middle ear, OAEs cannot be reliably interpreted

Question 43

what characteristics do we see when doing OAEs with negative pressure ?

Answer 43

OAEs are typically recorded except in extreme negative pressure when air-bone gap exceeds about 15 dB.

OAE amplitude is usually below normal limits.

Low frequency OAE components (<2000 Hz are affected first, and more seriously, than high-frequency OAEs.

Question 44

what characteristics do we see when a tm perforation affects OAES?

Answer 44

OAEs are recorded if there is only a small perforation which is not associated w/ active middle ear pathology (e.g., effusion, cholesteatoma)

OAE amplitude may be within normal limits across the frequency range of 500 to 8000 Hz, or within normal limits only for higher frequencies

Question 45

what might we see when pe tubes affect OAES

Answer 45

OAEs may be recorded if there is a patent tube and no active middle ear pathology but the likelihood of OAE presence <50%.

OAE amplitude may be WNL across the frequency range of 500 – 8000 Hz or WNL only for higher frequencies.

For TEOAE w/ click stim. the temporal waveform may show an unusual triphasic pattern

Question 46

If OAEs are reliably present and, in particular, within the normal region, what can be concluded ?

Answer 46

-the tubes are open
-there can be little or nor middle ear dysfunction
-Significant cochlear dysfunction is effectively ruled out.

Question 47

what might we see when otosclerosis affects OAEs?

Answer 47

OAEs typically not detected at any frequency for any degree of hearing loss though much like immittance presentation may vary slightly based upon stage of disease