[Acoustic reflex in workers using hand-held vibration tools. Combined effects of noise and local vibration].

Combined effects of noise and local vibration on the threshold of acoustic reflex (ART) were investigated. ARTs for three different stimuli (ARTWN, ART1k, ART4k) were determined in workers using hand-held vibration tools. The results obtained from these 72 workers (Group A) were compared with the ARTs in 100 control subjects (Group C) who had normal hearing acuity without any history of occupational noise exposure, as previously reported by the authors. The mean age in group A was 46.6 ranging from 26 to 62. The mean period of noise and vibration exposure was 11.4 years in subjects mainly using chain saws and 9.2 years in subjects mainly using bush cleaners (Table 2). ARTWN and ART1k in the exposed group showed significant differences compared to those in the non-exposed group (p less than 0.001), i.e., mean ARTWN was 89.6 dB SPL in Group A and 83.8 in Group C, mean ART1k was 96.1 dB SPL in the former and 92.2 in the latter group (Table 7). No significant difference was observed in mean ART4k between the two group (p greater than 0.1). The difference between ART1k and ARTWN, [ART1k-ARTWN], was significantly reduced in the exposed group (p less than 0.001), i.e., 2.7 dB in Group A and 12.4 in Group C (Table 8). To clarify the effects of aging on [ART1k-ARTWN], the exposed group was classified into three groups according to their HL(4k + 8k)/2. However, no significant correlation was observed between [ART1k-ARTWN] and age in any of these 3 groups (p greater than 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)