Temporary threshold shift of vibratory sensation induced by a vibrating handle and its gripping force

Nerve Function Impairment After Acute Vibration Exposure

OBJECTIVE

This study was to investigate the acute effects of hand-arm vibrations on the nerve functions of the hands, and the impact of the grip force applied to the vibrating tool during exposure.

METHODS

Grip strength and perception of vibration, touch, and temperature were evaluated using quantitative sensory testing (QST) before and after vibration exposure in 21 occupationally unexposed individuals. The procedure was performed twice, with a higher grip force being applied during exposure on the second occasion.

RESULTS

Vibration perception was significantly impaired after both exposures. Grip strength, perception of touch, and temperature were only significantly affected after the high grip force exposure.

CONCLUSIONS

Exposure to hand-arm vibrations has acute effects on hand nerve function that are sensitive to the grip force applied during exposure.

Work ability in vibration-exposed workers

Background

Hand–arm vibration exposure may cause hand–arm vibration syndrome (HAVS) including sensorineural disturbances.

Aims

To investigate which factors had the strongest impact on work ability in vibration-exposed workers.

Methods

A cross-sectional study in which vibration-exposed workers referred to a department of occupational and environmental medicine were compared with a randomized sample of unexposed subjects from the general population of the city of Gothenburg. All participants underwent a structured interview, answered several questionnaires and had a physical examination including measurements of hand and finger muscle strength and vibrotactile and thermal perception thresholds.

Results

The vibration-exposed group (47 subjects) showed significantly reduced sensitivity to cold and warmth in digit 2 bilaterally (P < 0.01) and in digit 5 in the left hand (P < 0.05) and to warmth in digit 5 in the right hand (P < 0.01), compared with the 18 referents. Similarly, tactilometry showed significantly raised vibration perception thresholds among the workers (P < 0.05). A strong relationship was found for the following multiple regression model: estimated work ability = 11.4 − 0.1 × age − 2.3 × current stress level − 2.5 × current pain in hands/arms (multiple r = 0.68; P < 0.001).

Conclusions

Vibration-exposed workers showed raised vibrotactile and thermal perception thresholds, compared with unexposed referents. Multiple regression analysis indicated that stress disorders and muscle pain in hands/arms must also be considered when evaluating work ability among subjects with HAVS.

Acute vibration reduces Aβ nerve fiber sensitivity and alters gene expression in the ventral tail nerves of rats

Long-term occupational exposure to hand-arm vibration can result in a permanent reduction in tactile sensitivity in exposed fingers and hands. Little is known about how vibration causes this reduction in sensitivity, and currently no testing procedures have been developed to monitor changes in sensory perception during ongoing exposures. We used a rat-tail model of hand-arm vibration syndrome (HAVS) to determine whether changes in sensory nerve function could be detected after acute exposure to vibration. Nerve function was assessed using the current perception threshold (CPT) method. We also determined whether changes in nerve function were associated with changes in gene transcription. Our results demonstrate that the CPT method can be used to assess sensory nerve function repeatedly in rats and can detect transient decreases in the sensitivity of Abeta nerve fibers caused by acute exposure to vibration. This decrease in Abeta fiber sensitivity was associated with a reduction in expression of nitric oxide synthase-1, and a modest increase in calcitonin gene-related peptide transcript levels in tail nerves 24 h after vibration exposure. These transient changes in sensory perception and transcript levels induced by acute vibration exposure may be indicators of more prolonged changes in peripheral nerve physiology.

Dependency of temporary threshold shift of vibratory sensation in fingertip on 1/3 octave-band hand-arm vibration exposure period

OBJECTIVES

To investigate the dependency of temporary threshold shift of vibratoty sensation (TTS(v)) in fingertip on hand-arm vibration exposure period.

METHODS

Six healthy students were instructed to grip a vibrating or nonvibrating handle in the experimental room. The gripping force was 40 N. The vibratory sensation threshold at 125 Hz was measured before and after the exposure in the exposed middle fingertip. The exposure vibration was vertical and the 1/3 octave-band vibration with had a central frequency of 200 Hz and an intensity of 39.2 m/s(2). The exposure periods were 8, 15, 30, 60, 120, 240 and 600 s. TTS(v,t) was evaluated as the difference in vibratory sensation threshold between immediately before and t seconds after the exposure.

RESULTS

TTS(v) recovered exponentially as in several previous studies and its use enabled us to estimate the time constant and TTS(v,0). TTS(v,0) with vibration exposure was significantly larger than that without it. The regression analysis of the relationship between vibration exposure period (T) and TTS(v,0) (T) for each subject confirmed the good fit of the equation TTS(v,0)(T)=B(0)+B(1) (*)Log(10)(T), where B(0) and B(1) are the calculated constants (adjusted R(2)=0.56-0.87). The time constants did not show such a clear dose effect relationship of exposure period as TTS(v,0).

CONCLUSION

The dependency of TTS(v,0) on vibration exposure period was asymptotically proportional to the logarithm of gripping period. To more quantitatively confirm the relationship of the time constants for recovering time course of TTS(v), it may be necessary to improve the measurement method for TTS(v).