Dependence of distortion product emission amplitude on primary-tone stimulus levels during middle-ear pressure...

The measurement of distortion product otoacoustic emissions (DPOAEs) is dependent upon their transmission through the middle ear. The purpose of this study was to measure the combined effects of primary-tone level variation and of middle-ear pressure alterations on DPOAE amplitudes. Twenty ears of normally hearing adults were examined. Four DPOAEs were measured at the frequency 2f1-f2 (614 Hz, 1342 Hz, 2921 Hz, 6341 Hz), with the associated geometric mean (GM) of the primary tones at 1, 2, 4, and 8 kHz. Ambient air pressure was varied in a pressure chamber between 0 kPa and 6 kPa in 2-kPa steps. At each pressure level, L1 or L2 was varied in 5-dB steps between 40 and 60 dB HL with a corresponding fixed level of either L1 or L2 of 40 dB HL. The DPOAE amplitudes showed frequency-dependent changes. The largest mean amplitude reduction with pressure variations could be observed for the DPOAE at 614 Hz, whereas the DPOAEs at 6341 Hz remained practically unaffected. During variation of primary-tone levels, the maximum DPOAE amplitude generally occurred, independent of middle-ear pressure, when L1 was 5 to 15 dB greater L2. The results have implications for clinical measurements in that DPOAEs may be detected in the high-frequency range even under pathologically altered middle-ear pressure, and the optimum difference L1-L2 that produces maximum DPOAE amplitude is relatively unaffected by middle-ear pressure.