EFFECT OF NEGATIVE MIDDLE-EAR PRESSURE ON TRANSIENT-EVOKED OTOACOUSTIC EMISSIONS

Objective: The purpose of the study was to illustrate the effect of ne gative middle eaf pressure (MEP) on both the stimulus and response of transient evoked otoacoustic emissions (TEOAEs) and the effect of comp ensating for negative pressure in the middle ear by pneumatically intr oducing pressure into the ear canal. Simulation of negative MEP by int roducing positive pressure into the ear canal also was examined. Desig n: TEOAEs were measured over 6 mo in a subject who frequently had nega tive MEP out to -150 daPa. Compensation was done for MEPs of -105, -13 5, and -165 daPa. Simulation of negative pressure was done for these s ame pressures. The effect of a pressure differential across the eardru m on the stimulus spectrum was measured at 100, 200, and 300 daPa, All measurements were made on the same subject. Results: Small amounts of negative MEP significantly affected both stimulus and response spectr a, The simulated negative MEP approximated actual MEP at MEPs of -105 and -135 daPa. At -165 daPa, a divergence. between the two spectra occ urred below 2.0 kHz. Compensation for negative MEP by pneumatically in troducing pressure into the ear canal essentially returned both spectr a to that seen when the MEP was close to ambient pressure, at least fo r frequencies above 1.5 to 2.0 kHz. At lower frequencies, compensation resulted in increased TEOAE amplitude relative to the amplitude at am bient pressure. Conclusions: Small amounts of negative MEP may affect TEOAE spectra and potentially influence the reliability of the test. F or long-term monitoring of TEOAEs, MEPs either should be near ambient pressure or should be compensated for by an equivalent pressure in the ear canal.