DEPENDENCE OF DISTORTION-PRODUCT EMISSION AMPLITUDE ON PRIMARY-TONE STIMULUS LEVELS DURING MIDDLE-EAR PRESSURE CHANGES

The measurement of distortion product otoacoustic emissions (DPOAEs) i s dependent upon their transmission through the middle ear. The purpos e of this study was to measure the combined effects of primary-tone le vel variation and of middle-ear pressure alterations on DPOAE amplitud es. Twenty ears of normally hearing adults were examined. Four DPOAEs were measured at the frequency 2f(1) - f(2) (614 Hz, 1342 Hz, 2921 Hz, 6341 Hz), with the associated geometric mean (GM) of the primary tone s 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 leve l, L(1) or L(2) was varied in 5-dB steps between 40 and 60 dB HL with a corresponding fixed level of either L(1) or L(2) of 40 dB HL. The DP OAE amplitudes showed frequency-dependent changes. The largest mean am plitude reduction with pressure variations could be observed for the D POAE at 614 Hz, whereas the DPOAEs at 6341 Hz remained practically una ffected. During variation of primary-tone levels, the maximum DPOAE am plitude generally occurred, independent of middle-ear pressure, when L (1) was 5 to 15 dB greater L(2). The results have implications for cli nical measurements in that DPOAEs may be detected in the high-frequenc y range even under pathologically altered middle-ear pressure, and the optimum difference L(1) - L(2) that produces maximum DPOAE amplitude is relatively unaffected by middle-ear pressure.