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Review |
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Author |
Makoto FUTATSUKA Dose-effect relationships for hand-arm vibration involve relating a complex physical agent
to the production of a variable and a not fully understood set of disorders. The physical
agent, vibration, may be of variable magnitude, frequency, direction and duration; it is
often intermittent and may contain shocks. The method of holding a tool, its physical
characteristics, the ambient temperature and other factors may affect the severity of
vibration exposure. The first occurrence of white finger is the effect of hand-arm vibration
most usually considered in dose-response relationships. Neither the identification nor the
diagnosis of this disorder is always reliable and it may not be the only significant adverse
effect of exposure to hand-arm vibration. Data from cross-sectional studies show that the
prevalence of white finger generally increases with increases in the vibration magnitude.
The frequency weighting often employed in vibration measurement standard is loosely
based on studies of subjective response to vibration and has a velocity characteristic over
this frequency range. There have been few studies of the influence of vibration exposure
duration on the development of relevant signs and symptoms. In a cohort of persons
exposed to the same vibration, the mean latency increases with increasing duration of
exposure until all persons are affected. It is becoming common for the daily exposure to
vibration to be assessed on a so-called energy basis and expressed as an equivalent 8h
exposure or an equivalent 4h exposure. This time-dependency is convenient because it
enables exposures to be quantified by means of root-mean-square averaging.
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