Changes in CMDP and DPOAE during acute increased inner ear pressure in the guinea pig

During and after an increase of inner ear pressure, induced by injection of artificial perilymph, the 2f ₁ − f ₂ and f ₂ − f ₁ distortion products (DPs) in cochlear microphonics (CM) and otoacoustic emissions (OAE) were recorded in the guinea pig. An inner pressure increase of ∼600 Pa gave only small changes in CMDP and DPOAE. Along with a decrease in f ₁ amplitude, a small decrease in amplitude of the 2f ₁ − f ₂ and a small increase in the f ₂ − f ₁ were measured in CM. This matches a shift from a symmetrical position of the operating point for hair cell transduction, leading to an increase in even-order distortion and a decrease in odd-order distortion. Similar, a decrease in 2f ₁ − f ₂ DPOAE was expected. This might be the case at the generation sites but this effect was then more than compensated for by a better middle ear transfer, accounting for the increase of 0.4 dB of the 2f ₁ − f ₂ DPOAE amplitude. In conclusion, changes of overall inner ear fluid pressure have minor effects on cochlear function. This is a relevant finding for further understanding of diseases with changed inner ear fluid volumes, as Ménière’s.