Tadayoshi Sakurai

Preliminary evaluation of dose-effect relationships for vibration induced white finger in Japan

SummaryHabitual use of many vibrating tools has been found to be connected with the appearance of various disorders affecting the blood vessels, nerves, bones, joints, muscles or connective tissues of the hand and forearm. The vibration exposures required to cause these diseases are not known exactly, either with respect to vibration intensity and the vibration frequency spectrum, or with respect to daily exposure time and total exposure period. The purpose of this study is to investigate available data on the physical conditions in Japan that have caused vibration induced white finger (VWF) and attempt to establish approximate relationships between vibration conditions and prevalence of VWF. The vibration conditions were evaluated using the method of vibration assessment recommended by the International Standardized Organization, which uses the weighted vibration level of the frequency weighted, dominant, single axis component of vibration directed into the hand. A clear correlation between level, prevalence of VWF and exposure period can be found. The results also suggest the relationship between the weighted levels and latent intervals. These dose-effect relationships enable the prediction of the average latent interval for a population group and the range of progression of the disorders—all from a measurement of the vibration entering the hands. In Japanese cases, 4, 8, and 15% of VWF prevalence correspond with 10, 20, and 40% of VWF prevalence in the Draft International Standard ISO/DIS 5349 (1982) within the weighted vibration level range of 2 to 50m · s¨.

Cohort study of vibration-induced white finger among Japanese forest workers over 30 years

SummaryA retrospective longitudinal study was undertaken to evaluate the changes in the prevalence of vibration-induced white finger (VWF) during the period from 1955 to 1988 among a population of Japanese state forestry workers. Since the late 1970s, technical improvements in the engine and the introduction of devices to dampen vibration have reduced the acceleration of chain saw handles from 20 ms−2 rms to less than 3 ms−2 rms. During the study period, the peak prevalence rate was 30.9% in 1973 and 17.2% in 1988. The peak prevalence rate was 54.8%, found in the exposure cohort beginning in 1959–1960 and the peak incidence rate was 5.65 per 100 person year in 1965–1966. Beginning with the 1969–1970 exposure cohort, both the prevalence and the incidence rate decreased significantly. During the study period, prevalence rates were approximately 10, 20, 30 and 35% after 4, 6, 10 and 12 years of exposure, respectively. The latent interval for the development of VWF was 6.2 ± 3.9 years on average, and the duration of VWF was 13.1 ± 7.5 years on average through the 1988 observation period. The 1950 cohort group had a long latent interval and a long prevalent period. On the other hand, the late 1960 cohort group had a short latent interval and a short prevalent period. Of 535 study subjects with VWF during the 20 observation years (prevalence rate: 41.0%), the recovery rate was 38.9% on average from the time of cessation of exposure.

A case-control study on the prognosis of vibration syndrome

SummaryA case-control study was undertaken to evaluate some factors affecting the prognosis of vibration-induced white finger (VWF), 286 workers, who had used a chain saw in forests and had showed some symptoms and signs that were suspected to be vibration syndrome during some of the years from 1956 to 1980, were selected by medical examinations from a total of 612 forestry workers, and were divided into four groups according to the prognosis of the VWF based on a twenty-year follow-up. The study shows an association between the prognosis of VWF and vibration components, particularly vibration levels, severity of the syndromes not only in peripheral circulation but also in peripheral neuropathy before exposure to vibration ceased. There are also significant associations between the prognosis of peripheral neuromuscular symptoms and the factors of aging and duration of exposure. The study suggests that smoking habits and history of heart failure and diabetes had no effect on the prognosis of VWF.