振動工具の健康影響と振動障害検診項目の妥当性に関する研究 ： 奈良県における振動障害検診活動の総括的知見と今後の課題

Abstract

To investigate the validity of cold water immersion test―immersing the affected hand up to the wrist in water at 10℃ for 10 minutes―for evaluating peripheral vascular and nervous functions of workers using vibrating tools, and to study other effects of the tools, more than 6000 medical examination records of forestry workers collected over 10 years were analyzed in Nara Prefecture. The results are as follows : 1) Immersion test could detect cases of VWF (vibration-induced white fingers) only at room temperature 20-23℃. Fingertip skin temperature of workers with VWF was significantly lower than that of workers without it. 2) Vibrotactile threshold has been shown to be negatively associated with skin temperature. After controlling for this association, median vibrotactile threshold was shown to be higher in workers with dysesthesia or with VWF than in controls and workers without VWF. 3) A dose response relationship between estimated VWF incidence rate and duration of chainsaw usage was statistically shown. 4) Almost all audiograms of five-year age groups showed the so-called c⁵dip typical of initial noise-induced permanent threshold shifts. Workers with longer usage of the chainsaw developed significantly greater hearing loss at 4 kHz than those with shorter usage. The association between VWF and hearing loss remained even when confounders on hearing such as age and exposure time to noise were considered. 5) The prevalence of low-back pain was as high as 66%. This was comparable to results derived from occupational medicine studies which reported this to be a major issue. The prevalence of bradycardia was less than 50/min, which is 2 to 3 times higher than that of the normal population. This finding could be due to long-term strenuous work in the forest.