Simultaneous effects of sinusoidal whole body vibration and broadband noise on TTS2's and R-wave amplitudes in men at two different dry bulb temperatures.

The aim of this study was to investigate the temporary hearing threshold shift (TTS2) and R-wave amplitudes in eleven healthy males when they were exposed to paired sinusoidal whole body (Z-axis) vibration (5 Hz--2.12 m/s2) and stable broadband A-weighted white noise at dry bulb temperatures of 20 degrees C and 30 degrees C. The intensity of noise in the exposure combinations was 75, 85 and 95 dB(A). The total number of tests was 66, and they were carried out in an exposure chamber. The subjects were dressed in standard clothing, and carried out simple tasks using a choice reaction time device during the test. According to the results, the means of the TTS2 values were usually higher at the dry bulb temperature of 30 degrees C than at 20 degrees C. Hearing threshold shifts were the greatest at frequencies of 4 and 6 kHz, and the smallest at 8 kHz. The more intense the noise in the paired combination of noise and vibration, the clearer the tendency for an increase in the ambient temperature to accelerate the increase in the hearing threshold. The effect of the ambient temperature on the temporary hearing threshold shifts also appeared to be slightly stronger during successive exposure cycles. Changes in the values for the R-wave amplitudes seemed to be connected with those in the hearing threshold. The decrease in the R-wave amplitude was connected to the increase in the TTS2 values, especially when the subjects were simultaneously exposed to a 95 dB(A) noise and whole body vibration at the dry bulb temperature of 30 degrees C. This implies that an increase in the ambient temperature intensifies cardiovascular disturbances in the body, which accelerate the development of functional disturbance in the inner ear.