Dose-Response Relationship for Hand-Arm Vibration Syndrome

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 effect 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.