The Evaluation of Noise-induced Hearing Loss with Distortion Product Otoacoustic Emissions

Background: Distortion product otoacoustic emissions (DPOAEs) is an objective, sensitive test of cochlear function. The aim of this study was the evaluation of noise-induced hearing loss in a group of industrial workers, using this method in conjunction with standard pure-tone audiometry (PTA).

Material/methods: Thirty-four subjects (68 ears) were included in the study. Standard PTA, tympanometry, and DPOAEs were performed. DPOAEs were recorded in the format of the DP-gram, using an ILO Otodynamics analyzer (ILO292 DP Echoport) connected to a portable personal computer. Results were analyzed and compared with the data of 30 normal persons of similar age and sex, examined at the same laboratory, using identical stimulation and recording conditions.

Results: Most subjects had normal hearing thresholds for lower frequencies, but presented with a notched pattern in the 3000 to 6000 Hz region. The DPOAEs of the patients had reduced amplitudes compared with controls, or were even absent, in one or more frequencies. Across the frequency range of 1000 to 6000 Hz, a higher proportion of subjects showed abnormalities in DPOAEs than in the audiogram.

Conclusions: From our data it may be concluded that cochlear dysfunction in noise-induced hearing loss may extend beyond the frequency region suggested by the audiogram, and that DPOAEs is a sensitive test of this damage.