PP1605 - High-Frequency Hearing in Musicians Compared to Non-Musicians

This study investigated the use of extended high frequency thresholds and distortion product otoacoustic emissions (DPOAEs) in identifying suspected early-stage acoustic trauma in musicians. Subject groups included normal-hearing musicians and non-musicians. Hearing was evaluated using pure-tone audiometry and DPOAEs from 1 – 16 kHz. DPOAE stimuli were calibrated in forward-pressure level to mitigate errors stemming from ear canal acoustics. Compared to non-musicians, musicians exhibited reduced thresholds and DPOAE levels from 6 – 10 kHz. Over this same frequency range, DPOAEs were predictive of audiometric thresholds. Findings suggest diagnostic utility of 6 – 10 kHz for detecting early-stage acoustic trauma.

Summary:

 Rationale. Musicians are at increased risk of developing noise-induced hearing loss (NIHL) due to prolonged exposures to high-level sound. Despite the increased risk, hearing conservation programs are not widely implemented among musicians, including those in training. Moreover, the frequency range over which current regulatory standards target for detecting changes in hearing does not extend beyond 4 – 6 kHz (depending on the agency). Given the broad bandwidth over which musical instruments perform, hazardous exposures to frequencies above 6 kHz are expected. Subjective and objective evaluation of hearing at the extended high frequencies poses numerous challenges; however, improved calibration methods have increased the reliability and accuracy of these methods. Unfortunately, such calibration techniques remain under-utilized. The purpose of this study was to evaluate the use of extended high frequency thresholds and distortion product otoacoustic emissions (DPOAEs) in identifying early-stage acoustic trauma in musicians. In-situ calibration of DPOAE stimulus levels in terms of forward pressure level (FPL) was utilized to mitigate errors stemming from ear canal acoustics.

Design. At the time of writing, forty-nine subjects have participated in the study. Subjects include normal-hearing, young adult musicians (n = 19; recruitment is ongoing with a goal of 30) and non-musicians (n = 30). All subjects completed a music history questionnaire. Musicians had at least 7 years of formal training. Hearing assessment included pure-tone audiometry and DPOAEs over the frequency range from 1 – 16 kHz.  Thresholds were measured using circum-aural earphones. DPOAEs were evoked using simultaneous presentation of two chirps offset in frequency to achieve a primary frequency ratio of 1.22. DPOAE stimuli were calibrated in the ear canal in terms of dB FPL. FPL-based calibrations minimize high-frequency calibration errors stemming from probe placement in the ear canal.

Results. Audiometric thresholds from the musicians closely approximated those from the non-musicians over much of the frequency range. There was no evidence of the classic noise notch in the musician group. Rather, thresholds in musicians were 3 – 5 dB poorer over the frequency range spanning 6 – 11.2 kHz. The largest differences between groups occurred at 10 kHz. DPOAE levels were reduced in the musician group over the frequency range spanning 6 – 10 kHz, mirroring differences noted in the audiograms. The DPOAE level averaged over 6 – 10 kHz was highly correlated with the audiometric threshold average over 6 – 10 kHz.

Conclusions. Musicians did not show evidence of acoustic trauma over the traditional frequency range associated with the classic noise notch. Rather, the elevation in audiometric thresholds and reduction in DPOAE levels observed from 6 – 10 kHz suggests early acoustic trauma occurs more basally in the cochlea. Results suggest the inclusion of hearing sensitivity metrics from 6 – 10 kHz in assays aimed at detecting early changes in hearing resulting from noise exposure, especially in musicians.