Effect of acute inner ear pressure changes on low-level distortion product otoacoustic emissions in the guinea pig

Objective-To determine a relation between acute inner ear pressure changes and cochlear function as measured by low-level 2f1-f2 distortion product otoacoustic emissions (DPOAEs). Material and Methods-During and after a change in inner ear pressure induced by injection or aspiration of perilymph, the 2f1-f2 DPOAE at 4.5 kHz generated by low-level primaries was recorded in the guinea pig. Results-Large changes in overall inner ear pressure produced only small changes in the 2f1-f2 amplitude and phase. During injection of 0.5 μl of artificial perilymph into the scala tympani over a 10-s period, the mean inner ear pressure increased by 500 Pa, with an accompanying mean increase in the 2f1-f2 amplitude of 0.7 dB. During aspiration of 0.5 μl of perilymph over a 10-s period, the mean inner ear pressure decreased by 700 Pa, with an accompanying mean decrease in the 2f1-f2 amplitude of 0.9 dB. Changes in DPOAE amplitude followed inner ear pressure changes with a delay of 1-2 s. The magnitude and sign of the amplitude changes can (partly) be explained by a change in oval window stiffness. No explanation was found for the measured delay. Conclusion-Clinically, these experiments can be of value in gaining insight into the pathophysiological mechanisms of pathological pressure changes as seen in Ménière's disease and perilymphatic fistulae.