Susceptibility of linear and nonlinear otoacoustic emission components to low-dose styrene exposure

OBJECTIVE: To investigate potential susceptibility of active cochlear mechanisms to low-level styrene exposure by comparing TEOAEs in workers and controls. DESIGN: Two advanced analysis techniques were applied to detect sub-clinical changes in linear and nonlinear cochlear mechanisms of OAE generation: the wavelet transform to decompose TEOAEs into time-frequency components and extract signal-to-noise ratio and latency of each component, and the bispectrum to detect and extract nonlinear TEOAE contributions as quadratic frequency couplings (QFCs). STUDY SAMPLE: Two cohorts of workers were examined: subjects exposed exclusively to styrene (N = 9), and subjects exposed to styrene and noise (N = 6). The control group was perfectly matched by age and sex to the exposed group. RESULTS: Exposed subjects showed significantly lowered SNR in TEOAE components at mid-to-high frequencies (above 1.6 kHz) and a shift of QFC distribution towards lower frequencies than controls. No systematic differences were observed in latency. CONCLUSION: Low-level styrene exposure may have induced a modification of cochlear functionality as concerns linear and nonlinear OAE generation mechanisms. The lack of change in latency seems to suggest that the OAE components, where generation region and latency are tightly coupled, may not have been affected by styrene and noise exposure levels considered here.