Extended frequency range hearing thresholds and otoacoustic emissions in acute acoustic trauma.

OBJECTIVE: We sought to evaluate the relative value of pure tone audiometry (PTA), extended high-frequency audiometry (EFA) and transiently evoked otoacoustic emissions (OAE) and distortion products when monitoring acute acoustic trauma (AAT).

STUDY DESIGN: Controlled prospective clinical study.

SETTING: Tertiary referral center.

PATIENTS: Seventy one active duty soldiers in the same age with normal hearing

INTERVENTIONS: Forty one soldiers suffered assault-rifle-induced acute acoustic traumas with hearing loss and tinnitus. Thirty soldiers served as a control group.

MAIN OUTCOME MEASURES: Pure tone threshold changes detected by PTA and EFA, amplitude and reproducibility changes in transiently evoked OAE, distortion products, and tinnitus analysis based on a visual analog scale.

RESULTS: Assault rifle-induced AAT caused unilateral temporary threshold shifts (TTS) in PTA and bilateral TTS in EFA. Two frequency regions with the largest threshold shifts were identified: one between 3 and 6 kHz and another between 11 and 14 kHz. The reproducibility of transiently evoked OAEs revealed changes related to the acoustic trauma in the 3- to 5-kHz frequency window. The amplitudes of the low stimulation level distortion products at 6 kHz were correlated with the audiometric AAT-induced TTS.

CONCLUSION: Acute acoustic trauma-induced audiometric TTS are predominantly confined to 2 specific frequency regions. PTA and EFA are both necessary to identify the full extent of acute acoustic trauma. PTA and EFA revealed that the TTSs were correlated to with distortion product OAE amplitude shifts at 6 kHz and changes in the reproducibility of transiently evoked OAE in the 3- to 5-kHz frequency window. PTA remains the most important measurement to monitor AAT. It may be useful to complement it with EFA, focusing on the 11 to 14 kHz frequency range. If used, OAE should be analyzed in the frequency range of 3 to 6 kHz.