Influence of altered middle ear pressure on cochlear microphonics

Abstract

Patients with otitis media with effusion often have impaired hearing loss caused by bone conduction. Among several possible causes for this hearing loss, the influence of middle ear pressure upon hearing was examined. Cochlear microphonics (CM) of guinea pigs were recorded under positive or negative pressure created simultaneously in the middle ear and in the external ear canal. CM was recorded from each turn (basal, second, third and apical). Whereas under negative pressure CM decreased suddenly but soon became stable, under positive pressure CM normalized gradually after the initial drop. Thus, in the stable state, CM amplitude was low under negative pressure but was slightly subnormal under positive pressure. One possible explanation is that perilymphatic efflux appears to cause such recovery of CM under positive pressure. It is postulated that perilymphatic inflow does not seem to occur under negative pressure, since CM and perilymphatic pressure were stable.

Key Words:

• CM
• guinea pig
• cochlear turns
• perilymphatic pressure