Intra- and intersubject variability of acoustically evoked otoacoustic emissions. II. Distorsion product otoacoustic emissions.

Background: Distorsion product otoacoustic emissions (DPOAEs) are evoked by simultaneously stimulating the cochlea with two tones. The DPOAE with the highest amplitude (at the frequency 2f(1)-f(2)) is usually used for routine audiological evaluation. Any interpretation of DPOAEs in a clinical settin g must consider their intra- and intersubject variability. Methods: DPOAE m easurements were performed in 36 normally hearing adults in three weekly te st sessions. Each ear was tested twice per session, and the results were st atistically analyzed. Results: All test candidates had measurable DPOAEs. S tatistically significant differences in absolute DPOAE amplitudes were neit her found between two measurements at the same day, nor at weekly intervals , nor between right and left ear of the same candidate. Absolute DPOAE ampl itudes in women were significantly higher in the 2-6 kHz range whereas they presented with significantly lower amplitudes below 2 kHz when compared to men. Conclusions: The present results indicate that monitoring of the inne r ear status can be reliably performed using DPOAE measurements. Change in DPOAE amplitudes effectively indicate changes in the cochlear function with high sensitivity. Compared to TEOAE measurements, DPOAEs offer a higher fr equency resolution in a broader frequency band and thus more detailed infor mation about the cochlear condition.