Assessment of heat pain perception in relation to vibration exposure.

The effect of vibration on thin unmyelinated sensory fibers was studied by perception threshold measurement of heat pain. The investigation was a cross-sectional study of 98 vibration-exposed and 53 non-vibration-exposed workers. Pain perception was determined by using the "Marstock" method. The perception threshold of contact heat induced pain was assessed by the method of limits. Quantified personal energy-equivalent vibration exposure was assessed for all subjects on a group basis. The cumulated lifetime equivalent frequency-weighted vibration exposure was estimated based on measurements according to ISO 5349. The mean heat perception threshold was 46.2 degrees C (SD 2.6 degrees C) for the right hand and 46.0 degrees C (SD 2.7 degrees C) for the left. The results showed no mean difference (left = 0.1 degree C, right = 0.6 degree C) in heat pain perception between vibration-exposed and non-exposed subjects. There was a high correlation between the right and left hand measurements (r = 0.81). The risk (rate ratio) for impairment was 1.02 (95% CI 0.81-1.30) for the right hand and 1.00 (95% CI 0.79-1.26) for the left. The results of the study did not indicate any impairment as assessed by an increased perception threshold for heat pain. The lack of an increased heat pain threshold among the vibration-exposed workers in our study cannot exclude a possible lesional somatosensory influence from the exposure, as the lesional effect may also be a lowering of the threshold. The multiple and unrelated percepts of thermal sensations imply that it is not legitimate to draw conclusions about the total status of the small calibre afferents when testing only the heat pain perception.