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/s². 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)=B₀+B₁ ^*Log₁₀(T), where B₀ and B₁ are the calculated constants (adjusted R²=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.