Changes of the vibratory sensation threshold in workers using vibrating tools.

Vibratory sensation thresholds of ten fingertips of each person were measured by each of the three frequencies in groups using three kinds of vibrating tools and the control groups. The subject groups were using leg-drill (n=37), chipping-hammer (n=25) and chain-saw (n=19). The control groups were engaged in desk work or outdoor work in a bureau of forest management (n=24), a local forest office (n=30) and a gas company (n=22) (Table 1). The tested frequencies were 63 Hz, 125 Hz and 250 Hz. The room temperature was kept at 20 degrees C. 1) The threshold values were found in such order as V greater than IV greater than III greater than I and II-finger in the subject groups, whereas I and V greater than II, III and IV-finger in the control groups. No significant difference between left and right hands was found in any group, both the subject and the control. 2) The threshold values were significantly higher in the chipping-hammer group and the chain-saw group than in the control (p less than 0.05 at 63 Hz, p less than 0.01 at 125 Hz and 250 Hz). They were higher in the leg-drill group than in the control but it was statistically not significant. 3) Regression analysis was performed about age and experience-years of the subject groups which were thought to have an effect upon the threshold change. But the effect of both factors to the threshold values were small in all subject groups. 4) The patterns of threshold values made up by each of the three frequencies were different among the three subject groups. The chipping-hammer group had the higher vibratory sensation threshold shift in the order of 250 Hz, 125 Hz and 63 Hz, the leg-drill group had almost equal threshold shift among the three frequencies, and the chain-saw group had the intermediate tendency between the other two groups. 5) Frequencies of 125 Hz and 250 Hz were more advantageous than that of 63 Hz in order to discriminate between the subject group and the control. Both 125 Hz and 250 Hz vibratory sensation threshold should be measured to find early disorders of vibration disease if possible, because the relation between thresholds of 125 Hz and 250 Hz was not so linear. 6) The observed significant differences of threshold values among the control groups were thought to be caused by different climatic circumstances.