Measuring and monitoring noise-induced hearing loss with otoacoustic emissions and pure-tone audiometry

This thesis discusses the use of otoacoustic emissions (OAEs) in comparison to pure-tone audiometry (PTA) for monitoring noise-induced hearing loss (NIHL). A longitudinal study on 233 workers in a newspaper printing office showed that OAEs could not be measured reliably in those subjects with a history of noise exposure and with concomitant hearing loss. Although there was an overall worsening in hearing (increase in PTA, decrease in OAE), almost all individual changes were too small to be labelled as significant. Furthermore, there was no congruency between individual changes in PTA and OAEs. A similar pattern was seen in a review on longitudinal changes in both PTA and OAEs in occupational settings. There was a large heterogeneity between the included studies, but it was clear that changes in OAEs and PTA lacked in agreement. A short-term, controlled experiment was conducted with 2 hours exposure of dance music. Both PTA and OAEs were capable of detecting small, group-averaged changes but there was no congruency between individual changes. Despite many differences between the longitudinal study, the studies included in the review and the short-term experiment, it was clear that individual significant shifts in OAEs could not reliably detect individual significant shifts in PTA. For young, normal hearing subjects, OAEs required a smaller change to be labelled to be significant than for elderly, noise-exposed subjects. This makes OAEs more suitable to monitor hearing and the early stages of NIHL. In conclusion, OAEs in occupational settings should not be recommended as a replacement for PTA but can be considered as an addition to the current practice depending on the specific goals and population under investigation