Distortion product otoacoustic mapping measured pre- and post-loud sound exposures.

Objective: Sampling distortion product otoacoustic emissions (DPOAEs) at multiple f/f ratios and f frequency values produces a DPOAE "map." This study examined the efficacy of DPOAE mapping compared with pure tone audiometry and standard DPOAEs for detecting noise effects in subjects exposed to loud sound.

Design: A map significance score was developed as a single measure of map change. Significance scores were evaluated before and after exposure to: loud music (LM), controlled noise (CN), and firing range noise (FR) in three separate sets of subjects. Scores were compared to audiometry and standard DPOAE results in the LM study.

Study Sample: The LM and CN exposure studies involved 22, and 20 healthy young subjects respectively with normal hearing. Eight Marines were studied before and after FR exposure.

Results: After LM exposure, audiometry showed significant changes at 1, 2, 4, and 6 kHz. Standard DPOAE measures were also significantly different at several frequencies. Map significance scores detected changes more effectively and showed the distribution of DPOAE alterations.

Conclusions: Map significance scores detected changes after noise exposure more reliably than audiometry and standard DPOAEs. Additionally, maps showed a diffuse response to sound exposure perhaps explaining why individual DP-grams appear less sensitive.