Pressure Transmission Properties from the Externa Ear Canal to the Inner Ear: An Experimental Study Using Guinea Pigs

Abstract

The inner ear pressure (P_ie) in response to pressure changes in the external ear canal was measured in guinea pigs while alternatively opening and closing the perforation of the otic bulla. When the bulla was opened, only a transient degree of applied pressure was transmitted to the inner ear and the amplitude of the P_IE was smaller than that of the corresponding P_IE when the bulla was closed. This was because the applied pressure was exclusively transmitted to the inner ear via the ossicular chain. When the otic bulla was closed, the pressure was transmitted not only via the ossicular chain but also via the round window (RW) through the middle ear cavity. When the bulla was closed, the amplitude of P_IE was larger by a positive pressure load than by the corresponding negative one. The amplitude of P_IE showed a linear relationship to ear canal pressure of at least within the ± 200 mmH₂O range, as long as pressure was slowly applied to the ear canal. When the loading pressure was abruptly changed, a bouncing response, possibly reflecting elasticity of the RW, was evoked, which diminished or disappeared when the round window was artificially ruptured.

Key Words:

• pressure loading test
• bouncing response
• perilymphatic fistula