Where do otoacoustic emissions come from?

• “OAEs are sounds of cochlear origin, which can be recorded by a microphone fitted in the ear canal.” • Most likely tied to OHC amplification • All mammals have OAEs • OHC electromotility from prestin

DPOAEs

Distortion Product OAEs (DPOAEs) – • The ear is stimulated by two pure tones (F1 and F2) • Ears with healthy OHCs generate multiple tones at frequencies mathematically related to F1 & F2 • “Distortion” • 2F1-F2 is most commonly recorded in the ear canal

TEOAEs

Transient Evoked OAEs (TEOAEs) – • The ear is stimulated by a broadband click • Because the stimulus is broadband, it stimulates most of the cochlea from base (high frequencies) to apex (low frequencies) • Waveform measured in the ear canal indicates which frequency-places in the cochlea have normal OHC function Limitation: OAEs are sensitive to ANY abnormality in OHC function Cannot differentiate between mild-profound SNHL

What a DPgram shows

“DPgram” plots DPOAE amplitudes at different test frequencies

Clinical applications of OAEs and rationales for each application

A patient’s DPgram is compared to normative data based on age-adjusted average of listeners with normal hearing If DPOAE at test frequency falls below the normative range for patient’s age, it is “absent” Assuming the ME is functioning, absent DPOAEs indicate impaired OHCs at the F2 test frequency