Pulsed DPOAEs in serial measurements : Combined analysis paradigm of simultaneously occurring changes in hearing thresholds and DPOAEs.

Background: To date, there is no consensus on how to standardize the assessment of ototoxicity in serial measurements. For the diagnosis of damage to the cochlear amplifier, measurement methods are required that have the highest possible test-retest reliability and validity for detecting persistent damage. Estimated distortion-product thresholds (L_EDPT) based on short-pulse distortion-product otoacoustic emission (DPOAE) level maps use individually optimal DPOAE stimulus levels and allow reliable quantitative estimation of cochlea-related hearing loss.

Materials and methods: Hearing thresholds were estimated objectively using L_EDPT and subjectively using modified Békésy tracking audiometry (L_TA). Recordings were performed seven times within three months at 14 frequencies (f₂ = 1-14 kHz) in 20 ears (PTA_{4 (0.5-4 kHz)} < 20 dB HL). Reconstruction of the DPOAE growth behavior as a function of the stimulus levels L₁, L₂ was performed on the basis of 21 DPOAE amplitudes. A numerical fit of a nonlinear mathematical function to the three-dimensional DPOAE growth function yielded L_EDPT for each stimulus frequency. For the combined analysis, probability distributions of hearing thresholds (L_TA, L_EDPT), DPOAE levels (L_DP), and combinations thereof were determined.

Results: L_TA and L_EDPT each exhibited a test-retest reliability with a median of absolute differences (AD) of 3.2 dB and 3.3 dB, respectively. Combining L_EDPT, L_DP, and L_TA into a single parameter yielded a significantly smaller median AD of 2.0 dB.

Conclusion: It is expected that an analysis paradigm based on a combination of L_EDPT, suprathreshold L_DP, and fine-structure-reduced L_TA would achieve higher test performance (sensitivity and specificity), allowing reliable detection of pathological or regenerative changes in the outer hair cells.