Noise-induced hearing loss in relation to vibration-induced white finger in chain-saw workers.

From the viewpoint of the etiologies of noise-induced permanent threshold shift (NIPTS) and vibration-induced white finger (VWF), the association between VWF and hearing loss was examined among 499 chain-saw workers who underwent a compulsory health examination for vibration syndrome. They were classified by age, duration of noise and vibration exposure, and the severity of VWF. The severity of VWF was evaluated according to the following criteria: no prior history; VWF history, but symptoms had disappeared; VWF present but appearing rarely; frequent appearance of VWF (more than 20 times per winter season). In three age groups (ie, 40-49, 50-59, 60-69 years) with 5-9 years of exposure, the chainsaw workers with VWF had a significantly greater hearing loss at higher frequencies than those without VWF. However, in the 10- to 14-year exposure groups, a significant difference was not found between the VWF and non-VWF groups, except that the 50- to 59-year age groups showed a significant difference in mean age. It was suggested that interindividual differences in susceptibility to noise and vibration may be the reason for the synergistic effects of noise and vibration.