Auditory threshold shift following meatal pressure change in ossicular disorders.

Auditory threshold shifts for air conduction following meatal pressure changes were examined in 30 normal ears and in 27 ears with ossicular abnormalities. Negative and positive changes in meatal pressure caused threshold elevation at frequencies lower than 1,000 Hz in all normal ears. In the ears with ossicular fixations, air pressures were less effective in attenuating hearing as compared with normal ears. Clearly different results were obtained in the patients with incudostapedial disconnection without stapes fixation. Thresholds were elevated by positive pressure, although marked threshold gains were measured by negative pressure at low frequency tones. Differences in threshold levels between the air pressures of +200 and -200 mm H2O were 26 to 40 dB at 250 Hz. This marked reverse effect in direction of the threshold shifts cannot be explained only by relative compliance changes in the tympanic membrane. Possible mechanisms underlying this phenomenon are discussed.