Objectives: To follow changes in transient evoked and distortion product otoacoustic emissions (TEOAEs, DPOAEs) as they relate to pure-tone audiometry (PTaud) thresholds during the first 2 years of occupational noise exposure.
Design: Prospective controlled.
Methods: Pure-tone audiometry thresholds, TEOAE and DPOAE amplitudes, and contralateral medial olivocochlear reflex strength were repeatedly evaluated during 2 years and compared between and within a cohort of 135 ship engine room recruits and a control group of 100 subjects with no noise exposure.
Results: Pure-tone audiometry thresholds for 2,000, 3,000 and 4,000 Hz in both ears were significantly elevated in the study group after 2 years of noise exposure. Significantly lower TEOAE amplitudes were found at 2,000 Hz in the right ear and 2,000 and 4,000 Hz in the left ear. Longitudinal intrasubject analysis of the study group revealed significant reductions of TEOAE amplitudes at 2,000 to 4,000 Hz in both ears and reduced DPOAE amplitudes for 5,957 Hz in the right ear and 3,809, 4,736, and 5,957 Hz in the left ear in the second follow-up evaluation. Baseline medial olivocochlear reflex strength showed no correlation to PTaud thresholds after 2 years of noise exposure. Poor to moderate negative linear correlations (r = -0.07 to -0.37) were found between the DPOAE-averaged amplitudes at 2,979 to 5,957 Hz and PTaud threshold means at 3,000 to 6,000 Hz. Abnormal TEOAE parameters after the first year of noise exposure had high sensitivity (86-88%) and low specificity (33-35%) for the prediction of noise-induced hearing loss (NIHL) after 2 years.
Conclusion: The DP-gram is not significantly correlated with PTaud and cannot be used as an objective measure of pure-tone thresholds in early NIHL. Medial olivocochlear reflex strength before the beginning of chronic exposure to occupational noise has no relation to individual vulnerability to NIHL. Although TEOAEs changes after 1 year showed high sensitivity in predicting NIHL after 2 years of exposure, they cannot be recommended as an efficient screening tool due to high false-positive rates.