Effect of negative middle-ear pressure on transient-evoked otoacoustic emissions.

OBJECTIVE: The purpose of the study was to illustrate the effect of negative middle-ear pressure (MEP) on both the stimulus and response of transient-evoked otoacoustic emissions (TEOAEs) and the effect of compensating for negative pressure in the middle ear by pneumatically introducing pressure into the ear canal. Simulation of negative MEP by introducing positive pressure into the ear canal also was examined.
DESIGN: TEOAEs were measured over 6 mo in a subject who frequently had negative MEP out to -150 daPa. Compensation was done for MEPs of -105, -135, and -165 daPa. Simulation of negative pressure was done for these same pressures. The effect of a pressure differential across the eardrum 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 spectra. The simulated negative MEP approximated actual MEP at MEPs of -105 and -135 daPa. At -165 daPa, a divergence between the two spectra occurred below 2.0 kHz. Compensation for negative MEP by pneumatically introducing pressure into the ear canal essentially returned both spectra to that seen when the MEP was close to ambient pressure, at least for frequencies above 1.5 to 2.0 kHz. At lower frequencies, compensation resulted in increased TEOAE amplitude relative to the amplitude at ambient pressure.
CONCLUSIONS: Small amounts of negative MEP may affect TEOAE spectra and potentially influence the reliability of the test. For 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.