Distortion product otoacoustic emissions. The influence of the middle ear transmission.

Distortion product otoacoustic emissions (DPOEs) were recorded in 8 normal hearing subjects (16 ears, mean age 37) in order to evaluate the sensitivity of the DPOE amplitudes as a function of pneumatic changes (-400 to +200 daPa) in the external ear canal. The responses were collected using time averaging and subsequent FFT-analysis of the collected data. Distortion products were measured at the following geometric mean frequencies: 1,000, 2,000, 4,000, 6,000 and 8,000 Hz. The results show that the amplitudes of the distortion products depend on an optimal transmission through the middle ear, and that measurements of DPOEs should always be preceded by determination of the middle ear pressure. The present findings are in good agreement with investigations based on evoked otoacoustic emissions published by other researchers.