Bioresponses in men after repeated exposures to single and simultaneous sinusoidal or stochastic whole body vibrations of varying bandwidths and noise.

This study deals with the changes in temporary hearing threshold (TTS2), upright body posture sway amplitudes in the X and Y direction, heart rate (HR), R-wave amplitude (RWA), systolic (SBP) and diastolic (DBP) blood pressure, pulse pressure (PP) and the index characterizing haemodynamic activity (HDI), when the subjects were exposed to noise alone, to vibrations alone or to simultaneous noise and vibrations. The experiments were carried out in an exposure chamber and the number of exposure combinations was 12. Seven healthy, male students volunteered as subjects, making a total number of 84 experiments. For each person the experiment consisted of a 30-min control period, five consecutive 16-min exposures, between which there was a 4-min measuring interval, and a 15-min recovery period. The noise was broadband (bandwidth 0.2-16.0 kHz) A-weighted (white) noise. The noise categories were: (1) no noise and (2) noise with an intensity of 90 dBA. The categories of low-frequency whole body vibration in the direction of the Z-axis were: (1) vibration within the range 4.4-5.6 Hz, (2) vibration within the range 2.8-5.6 Hz, (3) vibration within the range 2.8-11.2 Hz, (4) vibration within the range 1.4-11.2 Hz and (5) sinusoidal vibration with a frequency of 5 Hz. The (rms) acceleration in all the vibration models was 2.12 m/s2. The results showed that the TTS2 values at 4 and 6 kHz increased as a result of simultaneous exposure to noise and vibration significantly more than as a result of exposure to noise alone. The TTS2 values increased more intensely during the first 16-min exposure. The means of the variances in the amplitudes of body upright posture sway changed not only after exposures to vibration alone, but also after exposure to noise alone. The means of the sway variances in the X and Y directions at 0.1 Hz and within the range 0.06 to 2.00 Hz increased only when the vibration in the noise-vibration combination was sinusoidal. The changes in the heart rate, R-wave amplitude and blood pressure values also depended on the bandwidth of the vibration, the number of consecutive exposures and on whether the subjects were simultaneously exposed to noise in addition to vibration. As a rule, the effects of sinusoidal vibration differed from those due to stochastic vibrations.