Abstract

Objectives: To investigate prospectively the relation between vibration-induced white finger (VWF) and measures of cumulative (lifetime) exposure to hand-transmitted vibration (HTV).

Methods: Two hundred and forty-nine HTV workers and 138 control men of the same companies participated in a three-year follow up study. The diagnosis of VWF (Raynaud’s phenomenon in the controls) was based on the medical history, the administration of color charts and the results of a cold test. Tool vibration magnitudes were expressed as r.m.s acceleration, frequency weighted according to international standard ISO 5349-1 and also unweighted over the frequency range 6.3 to 1250 Hz. From the vibration magnitudes and exposure durations, alternative measures of cumulative vibration dose were calculated for each HTV worker, according to the expression: dose = Σa_i^mt_i, where a_i is the acceleration magnitude on tool i, ti is the lifetime exposure duration (hours) for tool i, and m = 0, 1, 2 or 4.

Results: The incidence of VWF varied from 5 to 6% in the HTV workers vs 0 to 1.5% for Raynaud’s phenomenon in the controls. After adjusting for potential confounders, measures of cumulative vibration dose derived from total operating hours and high powers of unweighted acceleration (i.e. Σa^m_uwit_i, with m>1) gave better predictions of the occurrence of VWF than dose measures calculated from frequency-weighted acceleration (i.e. Σa^m_wit_i). These findings were observed in the entire sample of HTV workers, in those with no VWF at the initial investigation, and in those with normal cold test results at baseline.

Conclusions: This prospective cohort study suggests that measures of cumulative vibration doses constructed from unweighted r.m.s. acceleration perform better for the prediction of VWF than dose measures calculated according to the recommendations of current standards. These findings should contribute to the improvement of the ISO frequency weighting for evaluating the severity of hand-transmitted vibration.