Otoacoustic Emission: A Review Flashcards
hair cells are part of what ?
-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)
what are the 2 types of hair cells ?
OHC and IHC
what is the main purposes of the OHC?
-Serve as acoustical pre-amplifiers
-Amplify movement of the basilar membrane during low-intensity sound stimuli
how do OHC respond to a stimuli (electromotility)
-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
what do OHC sharpen ?
Sharpens tonotopic organization of basilar membrane (i.e., place coding of frequency, and sharp tuning curves)
are OHC efferent or afferent hair cell
their efferent and controls movement and muscle
what is the purpose of IHC ?
-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
where do IHC damage typically happen ?
Damage to IHCs occurs (in conjunction with OHC damage) in severe to profound sensorineural losses
How does the cochlea and OAEs correlate ?
-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
how can emissions/ potentials be provoked ?
Emissions can be Spontaneous and generated in the absence of an external stimulus (SOAEs) or evoked by a specific sound stimulus (EOAEs)
what are the 2 main types of OAEs ?
Transient Evoked Otoacoustic Emissions (TEOAEs)
Distortion Product Otoacoustic Emissions (DPOAEs)
what is the 3rd OAE that’s not really common
Stimulus Frequency Otoacoustic Emissions (SFOAEs) - 3rd Type, but not as common
what are some characteristics of a spontaneous OAE ?
-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
what are some characteristic of Transient Evoked Otoacoustic Emissions (TEOAE)
-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.
when can TEOAEs be used?
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).
what is the most common and robust distortion?
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
what is the equation for DPOAE?
2x f1-f2=f3
where is the amplitude of DPOAE measured at ?
-The amplitude of the DPOAE is measured at the DP frequency.
-F2 frequency or geometric mean of f1 and f2.
DPOAEs is dependent on?
The presence of DPOAEs is dependent on hearing sensitivity in the region of the primaries.
when can DPOAEs be used ?
-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.
when are stimulus frequency otoacoustic emissions (SFOAE)
- 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
OAEs are related to?
OAEs are related to the proper function of the outer hair cells (electromotility of OHCs is the generator of response)
OAEs disappear after?
OAEs disappear after the inner ear has been damaged, so OAEs are often used in the clinic as a measure of inner ear health
When are emission typically found ?
Emissions are usually found in persons believed to have normal cochlear function accompanied by an uncompromised middle ear.
what happens if the cochlea is damaged and if emissions are obtained with normal amplitude characteristics ?
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
what are non pathologic factors that can influences OAEs
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!!!
how does age affect our OAEs
-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
how can gender affect our OAEs?
-Anatomical differences (length, size) form canal to auditory cortex, body temp
-Affects SOAEs and TEOAEs but not DPOAEs
how can ear difference affect our OAEs
-Research has showed slightly poorer hearing -for the left versus right ear, especially for higher frequencies (TEOAE amplitudes typically higher left ear)
how does genetic affect OAEs
Genetic patterns exist in prevalence of SOAEs, possibly TEOAEs
how does race affect our OAE
not known at the time
can body temp affect oaes?
no but it can affect ABRS
how can the state of arousal and attention affect OAEs
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
how can poor probe placement or seal affect OAEs
Most current equipment alerts clinicians to these problems.
how can Ear Canal Acoustics / Standing Waves
affect our OAEs
-Standing wave interference potential especially for frequencies above 4000 Hz
-Most systems account for this possibility assuming proper probe placement
how can Debris, cerumen, foreign body in the canal affect OAES
Otoscopy, equipment calibration?
how can an uncooperative patient affect our OAEs
Movement or too much noise to obtain properly
how can noise affect OAEs ?
-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
what is the most important non pathological condition to control during OAES
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
how can we minimize noise from affecting our OAES?
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.
what are some middle ear factors that can affect OAES?
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
what characteristics do we see when doing OAEs with negative pressure ?
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.
what characteristics do we see when a tm perforation affects OAES?
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
what might we see when pe tubes affect OAES
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
If OAEs are reliably present and, in particular, within the normal region, what can be concluded ?
-the tubes are open
-there can be little or nor middle ear dysfunction
-Significant cochlear dysfunction is effectively ruled out.
what might we see when otosclerosis affects OAEs?
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
