Evaluation of noise susceptibility: effects of noise exposure on acoustic reflex.

The threshold of acoustic reflex (AR) was measured in workers exposed to occupational noise. White noise (WN), and pure tones of 1 and 4 kHz were selected as activating stimuli for AR. The results were compared with the thresholds of AR (ART) in the normal group (Group C) reported by the authors previously. To examine in relation between noise exposure and ART, the exposed group was classified into two groups by their hearing levels (HL) at 4 and 8 kHz; i.e. Group D (HL(4k + 8k)/2 less than 25 dB) and Group E (HL(4k + 8k)/2 greater than or equal to 25 dB). A significant (P less than 0.001) elevation of ARTWN was observed not only in Group E (8.8 dB) but also in D (7.5 dB) with normal hearing acuity. A significant (P less than 0.001) lowering of ART1k was observed in Group E only. The difference between ART1k and ARTWN, [ART1k-ARTWN], was reduced significantly (P less than 0.001) in the exposed groups; i.e. 12.4 dB in Group C, 3.7 dB in Group D and 0.6 dB in Group E. These results suggested that the value of [ART1k-ARTWN] may be used as a sensitive and objective indicator for detecting and evaluating the early stages of noise-induced hearing impairment and individual susceptibility to noise.