Helleman, Jansen, and Dreschler evaluated 233 workers exposed to printing office noises via pure-tone (PT) audiometry as well as transient-evoked and distortion product otoacoustic emissions (TEOAEs and DPOAEs, respectively) over a 17-month period. The overall median age of the employees was 42 years and included 99 percent males. Two primary issues were investigated: (1) A quality criterion of OAEs based on signal-to-noise ratios (SNRs) and (2) the effects of noise exposure with respect to audiograms and OAEs.
Helleman et al reported that TEOAEs showed significant declines from 1000 to 4000 Hz, indeed, at 4000 Hz only approximately half the collected data (55 percent) met the SNR inclusion criteria. The authors note that with respect to TEOAEs and DPOAEs, as the test frequency region increases to 4000 Hz, accepted data responses decrease to approximately 50 percent—exactly in the region of most interest with respect to NIHL. DPOAEs demonstrated poorer responses between 4000 and 8000 Hz, with less changes between 1000 and 2000 Hz. With regard to audiometry, test frequencies included 500, 1000, 2000, 3000, 4000, 6000 and 8000 Hz. Over the 17-month evaluation period, significant deterioration was noted at 6000 and 8000 Hz.
The authors concluded audiometry is indispensable in the presence of a pre-existing hearing loss and/or when OAEs are low or absent. That is, monitoring can only occur when there is room for deterioration. OAEs have limited applicability with regard to monitoring the hearing status of the studied population. However, OAEs might be more sensitive (and perhaps very useful) with regard to detecting noise induced hearing loss (NIHL) at an earlier, "pre-clinical" stage.
For More Information, References, and Recommendations
Helleman HW, Jansen EJM, Dreschler WA. (2010) Otoacoustic Emissions in a Hearing Conservation Program—General Applicability in Longitudinal Monitoring and the Relation to Changes in Pure-Tone Thresholds. International Journal of Audiology. 49(6):410-419.