Influence of Middle-ear pressure changes on evoked otoacoustic emissions in guinea pigs

Abstract

Click-evoked otoacoustic emissions (CEOAEs) and distortion product otoacoustic emissions (DPOAEs) were examined before and after increased or decreased middle-ear pressures in 4 guinea pips. A polyethylene tube was inserted through the auditory bulla, and middle-ear pressure was changed by pushing or drawing a syringe connected to the tube. CEOAEs were measured at about 70dBSPL using the ILO88, and DPOAEs were measured at f1=3.3kHz 65dBSPL and f2=4kHz 60dBSPL using home-made instruments. After increased middle-ear pressure, both total echo powers (TEPs) in CEOAEs and DPOAE amplitudes at 2 f1-f2 were decreased inversely in proportion to increased pressure. On the other hand, DPOAE amplitudes disappeared, even after minimum decreased middle ear pressure. TEPs also disappeared, except in one ear, after decreased middle-ear pressure. We conclude that both CEOAEs and DPOAEs can easily be deteriorated after middle-ear pressure changes, especially with negative middle-ear pressure, and that we need to estimate carefully both CEOAEs and DPOAEs in animal experiments.