Temporary threshold shift of the vibration perception threshold following a short duration exposure to vibration

The objective of this study is to analyze the evolution of the vibration perception threshold (VPT) following a short duration exposure to vibration. The literature reports experiments with 3 to 10 min exposure to vibration after which a steady state is not necessarily reached. The temporary threshold shift (TTS) of the VPT is extrapolated from data recorded during the recovery period. The assumption of a linear decrease with the logarithm of time gives erroneous results for the TTS extrapolated at the end of the exposure. 81 experiments were conducted on 9 young subjects without any neurological problem, exposed to acceleration amplitudes of 5, 20 and 80 ms-2 at frequencies of 31.5 (conditions 1 to 3), 125 (conditions 4 to 6) and 500 Hz (conditions 7 to 9). The exposure to vibration lasted 32 min and was interrupted shortly at time 2, 4, 8, 16 to record the VPT at 31.5 and 125 Hz. The VPT was also recorded before the exposure and several times during the recovery. The evolution of the VPT appears to follow a first order model characterized by a maximum amplitude TTS, a time constant (tau) and a residual value (r, as a fraction of the TTS). The correlation coefficients between observed and predicted values in the 81 experiments are 0.881 at 31.5 Hz and 0.885 at 125 Hz. The TTS is influenced by the exposure amplitude and frequency and is different at the two test frequencies. It varies also significantly between the subjects and with their initial VPT value. The time constant is about 3 minutes at both test frequencies, while the residual fraction is of the order of 0.14 at 31.5 Hz and 0.07 at 125 Hz. Both parameters appear to be independent of the exposure parameters.