A longitudinal study of peripheral sensory function in vibration-exposed workers

To investigate prospectively the relation between vibration-induced sensory dysfunction and measures of daily exposure to hand-transmitted vibration (HTV). Thermal perception thresholds for warmth and cold (TPT in A degrees C) and vibrotactile perception thresholds (VPT in dB) at 31.5 and 125 Hz were measured at the fingertips of digit II (for the median nerve) and digit V (for the ulnar nerve) of both hands in 27 male controls and 29 naval engine workers exposed to HTV. In the HTV workers, peripheral sensory function was investigated over a follow-up period of 1-3 years. Vibration exposure was expressed in terms of equivalent frequency-weighted acceleration [A (h(eq,T)) in ms(-2) rms], duration of exposure (T in hours), and frequency-weighted acceleration normalised to a period of 8 h [A(8) in ms(-2) rms]. At baseline, the HTV workers showed significantly higher TPT for warmth and lower TPT for cold than the controls, while no differences in the VPTs at both frequencies were observed between the two groups. After adjustment for several confounders, data analysis with the generalised estimating equations method and a transition model showed that the changes over time in the TPTs of the HTV workers were significantly related to all measures of daily vibration exposure [A (h(eq,T)), T, A(8)]. No significant associations were observed for VPTs at either 31.5 or 125 Hz. The findings of this longitudinal study suggest a significant exposure-response relationship between thermal sensory impairment over time and measures of vibration exposure. The measurement of TPT may be a useful testing method to assess vibration-induced neuropathy at an early stage.