Long-term effect of hand-arm vibration on thermotactile perception thresholds

Background: Occupational exposure to hand-transmitted vibration (HTV) is known to cause neurological symptoms such as numbness, reduced manual dexterity, grip strength and sensory perception. The purpose of this longitudinal study was to compare thermotactile perception thresholds for cold (TPTC) and warmth (TPTW) among vibration exposed manual workers and unexposed white collar workers during a follow-up period of 16 years to elucidate if long-term vibration exposure is related to a change in TPT over time. Methods: The study group consisted of male workers at a production workshop at which some of them were exposed to HTV. They were investigated in 1992 and followed-up in 2008. All participants were physically examined and performed TPT bilaterally at the middle and distal phalanges of the second finger. Two different vibration exposure dosages were calculated for each individual, i.e. the individual cumulative lifetime dose (mh/s2) or a lifetime 8-h equivalent daily exposure (m/s(2)). Results: A significant mean threshold difference was found for all subjects of about 4-5 degrees C and 1-2 degrees C in TPTW and TPTC, respectively, between follow-up and baseline. No significant mean difference in TPTC between vibration exposed and non-exposed workers at each occasion could be stated to exist. For TPTW a small but significant difference was found for the right index finger only. Age was strongly related to thermotactile perception threshold. The 8-h equivalent exposure level (A (8)) dropped from about 1.3 m/s2 in 1992 to about 0.7 m/s(2) in 2008. Conclusions: A lifetime 8-h equivalent daily exposure to hand-transmitted vibration less than 1.3 m/s(2) does not have a significant effect on thermotactile perception. Age, however, has a significant impact on the change of temperature perception thresholds why this covariate has to be considered when using TPT as a tool for health screening.