Neurological effects of exposure to hand-arm vibration
The EU Physical vibration directives prescribe periodical health surveillance of exposed workers. The directive assumes adequate exposure assessments and reliable methods for health control and diagnostics.
The foundation for the directive is foremost based on knowledge concerning the effects on vessels in the hand (i.e white fingers). Corresponding knowledge for effects on peripheral nerves is however limited. Research groups in some European countries, among them Sweden, received 2003 funding from European Commission for a research programme directed towards the risks of exposure to vibration (VIBRISKS, www.humanvibration.com). One objective was to conduct experimental studies on the effects on vibrotactile and thermotactile perception due to vibration exposure with different frequency, duration, magnitude, and intermittency. Among important issues was to determine whether the current frequency weighting procedure is applicable on neurological effects and the importance of vibration free periods. Studies related to the vascular component were conducted by other VIBRISKS partners. An exposure to vibration prior to the determination of vibrotactile and thermotactile thresholds has an influence on the test results. The recommendation is therefore to avoid vibration exposure 2 and 4 hours prior to measurement of thermal and vibrotactile perception thresholds, respectively. The frequency and magnitude of the vibration had a significant acute effect on vibrotactile threshold, but the exposure time does not. Magnitude and duration of the vibration exposure, but not the frequency, affected the thermotactile thresholds significantly. Vibration exposure divided into shorter periods and with the same energy-equivalent frequency weighted acceleration lead to lower temporary vibrotactile threshold shifts. No significant acute effect was found on the thermal perception thresholds between combinations of vibration with different periods of exposure and rest periods.