Improving Distortion-Product Otoacoustic Emission Test-Retest Reliability With Forward-Pressure Level Calibration on...

Area of Science:

• Audiology
• Otoacoustic Emissions
• Acoustics

Background:

• Standard in situ calibration using sound pressure level (SPL) for distortion-product otoacoustic emission (DPOAE) testing can introduce significant stimulus level errors (up to 20 dB) due to standing-wave nulls.
• Forward-pressure level (FPL) calibration, derived from wideband acoustic immittance (WAI) measurements, offers a more accurate method by mitigating these standing-wave effects.

Purpose of the Study:

• To compare FPL and SPL calibration methods for DPOAE testing.
• To determine if FPL calibration yields clinically meaningful improvements in test-retest reliability.
• To assess the measurability, validity, and reliability of a prototype WAI and DPOAE system.

Main Methods:

• Nineteen adults with normal hearing (38 ears) participated in two experiments measuring WAI and DPOAEs across various frequencies (0.7-8 kHz).
• Measurements were conducted using the same probe fit for both SPL and FPL calibration methods, with probe removal and refitting between test and retest conditions to assess reliability.
• Experiment 2 utilized a longer sampling time (up to 32 seconds) compared to Experiment 1 (4 seconds).

Main Results:

• A maximum pressure response difference of 22 dB was observed between SPL and FPL calibration.
• DPOAE measurability was high for both methods, with no significant group mean DPOAE level differences in Experiment 1 and only a 2 dB difference at 8 kHz in Experiment 2.
• FPL calibration demonstrated improved test-retest reliability, with lower standard error of measurement and higher intraclass correlation coefficients, particularly at higher frequencies affected by standing-wave nulls.

Conclusions:

• FPL calibration offers clinically meaningful improvements in DPOAE test-retest reliability over SPL calibration, especially above 4 kHz.
• Longer averaging times can extend these reliability benefits to lower frequencies (down to 1 kHz).
• FPL calibration enables reliable detection of smaller DPOAE changes, potentially facilitating earlier intervention through serial monitoring.