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 tactile perception thresholds in users of impact wrenches exposed to intermittent hand transmitted vibration. A further aim was to assess the relation between acute changes in tactile sensation, sensorineural disorders, 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 fingers and hands were graded according to the staging system of the Stockholm workshop scale. Tactile function was tested by measuring aesthesiometric thresholds (two point discrimination and depth sense perception) and vibrotactile perception thresholds at 16, 31.5, and 125 Hz before and after a workshift. Temporary threshold shift was then calculated as the difference between threshold measures before and after the shift. The measurement and assessment of exposure to vibration were made according to the international standard ISO 5349. The vibration dose accumulated over a workshift (m2s-4h) was estimated for each user of impact wrenches. Daily exposure to vibration was also expressed in terms of eight hour energy equivalent frequency weighted acceleration ((ahw)eq(8) in ms-2 rms).

RESULTS

After adjustment for age and alcohol consumption, vibrotactile perception thresholds before exposure were greater in the workers exposed to vibration than in the controls. 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 abnormalities were detected at the physical examination. Owing to the intermittent use of impact wrenches, the estimated mean (ahw)eq(8) for the subjects exposed to vibration was low (1.3 ms-2 rms). A significant temporary threshold shift in vibration perception at all test frequencies was found in the workers exposed to vibration but not in the controls. A significant increase in depth sense perception thresholds was 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 31.5 Hz, was associated with the severity of sensorineural disorders. In the workers exposed to vibration the temporary threshold shift in vibration sense at all test frequencies was positively related to the estimated dose of vibration received over a workshift. No significant relation was found between aesthesiometric threshold changes and vibration dose.

CONCLUSIONS

Intermittent exposure to hand transmitted vibration over a workshift can cause a deterioration of tactile perception in the fingers of users of impact wrenches. Acute tactile dysfunction was related to both the estimated dose of vibration and the severity of sensorineural symptoms. The temporary threshold shift in vibration perception suggested that fast adapting skin mechanoreceptors such as Pacinian and Meissner corpuscles were mainly involved in the acute sensory impairment to the fingertips of the workers exposed to vibration. Changes in tactile perception can occur in workers with daily exposure to vibration that is considered to be associated with a minimal risk of adverse health effects induced by vibration.