MAGNITUDE CHANGES IN TRANSIENT EVOKED OTOACOUSTIC EMISSIONS AND HIGH-LEVEL 2F(1)-F(2) DISTORTION PRODUCTS IN MAN DURING QUININE ADMINISTRATION

Quinine reversibly affects the outer hair cells (OHC). It is therefore an ideal drug for studying OHC-related phenomena, such as transient evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs). Pure-tone thresholds (PTTs), 1000-4000 Hz, TEOAEs, and DPOAEs were measured monaurally in 5 normal-hearing volunteers during quinine administration. DPOAE was evoked at 75 dB SPL (f(2)/f(1) = 1.22) and analysed at 2f(1)-f(2) with f(2) at 6 frequencies (700-4000 Hz), while TEOAE was obtained at 79 dB SPL(p) and analysed at the f(2) frequencies (1/3 octave). The PTT-shift was flat, 10dB, whereas the TEOAE-power and the global mean of the DPOAEs decreased 4.5 dB and 1.4 dB, respectively. No correlation was found between the intra-individual emission shifts. It is concluded that TEOAE is more sensitive than high-level DPOAE for identifying minor cochlear hearing losses. Support is given to the hypothesis that different sources are involved in generating DPOAEs at different evoking levels.