OAE

Otoacoustic Emissions 

  • Pre-neural potentials generated by the cochlea that can be recorded in the ear canal 

  • Sounds from the cochlea are transmitted back through the middle ear to the external ear canal 

    • Anytime you see an absent OAE you need tymps/middle ear evaluation, want to know how middle ear transfers 

  • Generated in a healthy cochlea either randomly or in response to an acoustic stimuli 

  • They reflect the active, non-linear processes within the cochlea, aka reflect the outer hair cells 

  • OAEs demonstrate outer hair cell function 

  • OAEs not a hearing test, bc it requires no response from participant 

  • In a newborn hearing test present OAEs and good auditory brainstem response that’s a good to go baby 

OAE Measures 

  • Do not need an airtight seal 

  • The test is objective and noninvasive 

  • What does a person have to do when being tested for OAEs?

    • Person should sit still with probe in ear canal 

  • What happens with the probe in ear canal? 

    • Microphone within the probe records the low level emissions and sends them to a computer for signal averaging 

  • What are the other factors that can interfere with the probe records? 

    • Breathing, heart beat, other internal sounds and movements that involve electricity 

Types of OAEs 

  • Distortion product OAEs (DPOAEs) 

    • Generated by two pure-tone freq f1 and f2

    • f2>f1 which creates an interaction within the cochlea producing a third tone 

    • Largest DPOAE is 2f1-f2 (2 times f1-f1)

    • Clinically L1/L2 is 65/55 dB SPL is routinely used 

    • Usually test from 1000-8000 Hz

      • Why would you test from 1000-8000 Hz? 

      • Bc emissions measured below 1000 Hz may be a problem bc of background and internal noise 

    • What type of people have absent DPOAEs?

      • People with sensorineural hearing loss >55 dB HL, they will have absent or very low OAEs and people with conductive hearing loss

    • What type of people have present DPOAEs?

      • People with pure/neural/retrocochlear hearing loss 

  • Transient evoked OAEs (TEOAEs) 

    • Generated by a click stimulus with acoustic energy of a broad band of freq b/w 2000Hz-5000Hz 

      • Send a click then get a bunch of responses (OAE) back 

    • Produces a wide freq range of OAEs 

    • Emissions occurs about 4 msec after the stimulus and last about 10 msec 

    • Presentation level for TEOAEs is about 80-84 dB SPL

      • Why is it the 80-84 range? 

      • 80-84 range bc of how big or small your ear canal is 

    • Narrower freq response compared to DPOAEs but may be a faster measures than DPOAEs 

      • Why is TEOAEs a narrower freq response than DPOAEs? 

        • Bc input stimulus is fixed you get a narrower range of freq back out

    • What kind of person would have absent TEOAEs?

      • People with sensorineural hearing loss >30 dB HL and also conductive loss

    • What kind of person would have present TEOAEs? 

      • People with pure neural/retrocochlear hearing loss 

General Evoked OAE interpretation 

  • Can only speak to this in regards to outer hair function at specific freq

  • Does not tell you degree of hearing loss

  • TEOAEs are better at 1000Hz or below 

  • DPOAEs are better at 2000Hz or above 

Clinical application of OAEs 

  • Newborn screening 

    • Looking for functional measures in newborns 

  • Pediatric assessment 

    • Kids aren’t cooperative 

  • Difficult to test individuals 

    • People with developmental disabilities

  • Functional hearing losses 

    • Fakers 

  • Monitor outer hair cell function 

    • From ototoxic medication like cancer 

  • Intraoperative monitoring 

    • During surgeries to make sure they aren’t near the 8th cranial nerve