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 2f(1)-f(2) 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 2f(1)-f(2) 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 2f(1)-f(2) amplitude and phase. During injection of 0.5 microl of artificial perilymph into the scala tympani over a 10-s period, the mean inner ear pressure increased by approximately 500 Pa, with an accompanying mean increase in the 2f(1)-f(2) amplitude of 0.7 dB. During aspiration of 0.5 microl of perilymph over a 10-s period, the mean inner ear pressure decreased by approximately 700 Pa, with an accompanying mean decrease in the 2f(1)-f(2) 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 Meniere's disease and perilymphatic fistulae.