Download Otoacoustic Emissions

Otoacoustic Emissions
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Low-level sounds produced by the
cochlea and recordable in the external
ear canal.
Spontaneous
Click-evoked
Distortion Product
Stimulus Frequency
History
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First described by Kemp (1977 & 1978),
But predicted by Gold (1948!)
Supported by almost simultaneous
discovery of OHC motility
Movement into Clinical Use:
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Screening for hearing loss
Role in Audiologic Battery
Anatomy and Physiology
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Generators = Outer Hair Cells
“Pre-neural”
Low-level event//High level stimuli
produce their own distortions
Reduction/Loss of emission in NITTS
SOAEs correlated to number of rows of
OHCs
Energy Path:
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“Reverse Traveling Wave” is debated
Through Middle Ear: Filtering and
attenuation
Into ear canal
Note: requirement of healthy middle
ear and clear outer ear.
Neonatal Hearing Screening
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Transient and Distortion-Product OAEs
Rationale: quick, relatively inexpensive,
possibly catching losses in a broader
frequency range than ABR
NIH (1994) recommended two-stage
protocol combining OAEs and ABR
Audiologic Battery
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Assessment of cochlear health in site-of
lesion testing
Objective info on peripheral auditory
functioning
Correlation to audiogram
Assessment of Auditory Efferents
through Contralateral Suppression
Recording
OAEs
Spectrum of Sound in Ear Canal
Stimulus Tones
Background Noise
Emission
Frequency
OAE as Measure of Cochlear
Health
Tone Decay:
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Loss of audibility for a tone that is on
continuously.
Greater decay is indicative of
retrocochlear problem.
There are different methods:
Some Tone Decay Tests
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Carhart: begin at 0 SL, up in 5 dB
steps until tone is heard for a full
minute
Olson-Noffsinger: begin at 20 SL, up
until heard for full minute.
Tone Decay Results:
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Type I: no decay: norm, conduct or
cochlear
Type II: heard for longer times as level
is increased: cochlear
Type III: No growth with increasing
level: retrocochlear
TONE DECAY SUCCESS?
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Sensitivity = 75%
Specificity = 91%
Auditory Brainstem Response:
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Response within 10 ms of stimulus
waves labeled with Roman numerals
Peaks I, III, and V most useful
Latencies are the key measure
Disorders will produce delays
ABR SUCCESS?
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Sensitivity = 97%
Specificity = 88%