CHANGES OVER A WORKSHIFT IN AESTHESIOMETRIC AND VIBROTACTILE PERCEPTION THRESHOLDS OF WORKERS EXPOSED TO INTERMITTENT HAND TRANSMITTED VIBRATION FROM IMPACT WRENCHES

Objectives-To investigate the changes over a workshift in fingertip ta ctile perception thresholds in users of impact wrenches exposed to int ermittent hand transmitted vibration. A further aim was to assess the relation between acute changes in tactile sensation, sensorineural dis orders, and vibration dose. Methods-The study populations consisted of 30 workers exposed to vibration (16 men and 14 women) and 25 control manual workers (10 men and 15 women). Sensorineural disorders in the f ingers and hands were graded according to the staging system of the St ockholm workshop scale. Tactile function was tested by measuring aesth esiometric thresholds (two point discrimination and depth sense percep tion) and vibrotactile perception thresholds at 16, 31.5, and 125 Hz b efore and after a workshift. Temporary threshold shift was then calcul ated as the difference between threshold measures before and after the shift. The measurement and assessment of exposure to vibration were m ade according to the international standard ISO 5349. The vibration do se accumulated over a workshift (m(2)s(-4)h) was estimated for each us er of impact wrenches. Daily exposure to vibration was also expressed in terms of eight hour energy equivalent frequency weighted accelerati on ((alpha hw)(eq(8)) in ms(-2) rms). Results-After adjustment for age and alcohol consumption, vibrotactile perception thresholds before ex posure were greater in the workers exposed to vibration than in the co ntrols. No differences in aesthesiometric thresholds before the shift were found between the study groups. Sensorineural disorders were mild in the workers exposed to vibration and minor neurological abnormalit ies were detected at the physical examination. Owing to the intermitte nt use of impact wrenches, the estimated mean (alpha(hw))(eq(8)) for t he subjects exposed to vibration was low (1.3 ms(-2) rms). A significa nt temporary threshold shift in vibration perception at all test frequ encies was found in the workers exposed to vibration but not in the co ntrols. A significant increase in depth sense perception thresholds wa s found in the men exposed to vibration. The temporary threshold shift in vibration perception at 125 Hz, and to a lesser extent at 16 and 3 1.5 Hz, was associated with the severity of sensorineural disorders, I n the workers exposed to vibration the temporary threshold shift in vi bration sense at all test frequencies was positively related to the es timated dose of vibration received over a workshift. No significant re lation was found between aesthesiometric threshold changes and vibrati on dose. Conclusions-Intermittent exposure to hand transmitted vibrati on over a workshift can cause a deterioration of tactile perception in the fingers of users of impact wrenches. Acute tactile dysfunction wa s related to both the estimated dose of vibration and the severity of sensorineural symptoms. The temporary threshold shift in vibration per ception suggested that fast adapting skin mechanoreceptors such as Pac inian and Meissner corpuscles were mainly involved in the acute sensor y impairment to the fingertips of the workers exposed to vibration. Ch anges in tactile perception can occur in workers with daily exposure t o vibration that is considered to be associated with a minimal risk of adverse health effects induced by vibration.