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otoacoustic emissions n.
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Otoacoustic Emissions

Otoacoustic Emissions

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Otoacoustic Emissions

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  1. Otoacoustic Emissions • Low-level sounds produced by the cochlea and recordable in the external ear canal. • Spontaneous • Click-evoked • Distortion Product • Stimulus Frequency

  2. History • First described by Kemp (1977 & 1978), • But predicted by Gold (1948!) • Supported by almost simultaneous discovery of OHC motility • Movement into Clinical Use: • Screening for hearing loss • Role in Audiologic Battery

  3. Anatomy and Physiology • 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

  4. Energy Path: • “Reverse Traveling Wave” is debated • Through Middle Ear: Filtering and attenuation • Into ear canal Note: requirement of healthy middle ear and clear outer ear.

  5. Neonatal Hearing Screening • 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

  6. Audiologic Battery • 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

  7. Recording OAEs

  8. Spectrum of Sound in Ear Canal Stimulus Tones Emission Frequency Background Noise

  9. OAE as Measure of Cochlear Health

  10. Tone Decay: • Loss of audibility for a tone that is on continuously. • Greater decay is indicative of retrocochlear problem. • There are different methods:

  11. Some Tone Decay Tests • 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.

  12. Tone Decay Results: • 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

  13. TONE DECAY SUCCESS? • Sensitivity = 75% • Specificity = 91%

  14. Auditory Brainstem Response: • 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

  15. ABR SUCCESS? • Sensitivity = 97% • Specificity = 88%