Changes in hearing, cardiovascular functions, haemodynamics, upright body sway, urinary catecholamines and their correlates after prolonged successive exposures to complex environmental conditions

Summary

This study deals with changes in temporary threshold shifts of hearing (TTS₂), cardiovascular functions (HR, SBP, DBP, PP, RWA), haemodynamic activity (HDI), upright body sway (VUBSA), ratios of urinary catecholamines (10A/DA, 10NA/DA, A/NA, NA/A) and correlations between these changes in complex exposure situations. The study was carried out in a special exposure chamber on 60 healthy male students. It was based on a factorial experimental design with a total of 12 exposure combinations. Each individual experiment took 6 h with a pause of 1 h at noon. There were 12 sequential exposure periods lasting 16 min each. A pause of 4 min followed each exposure period. The subjects were exposed to noise and whole body vibration at two different dry bulb temperatures. Noise classes were: (1) no noise, and (2) stable broad-band noise of 90 dBA. Vibration classes were: (1) no vibration, (2) a sinusoidal 5 Hz vibration, and (3) a stochastic vibration with a frequency range of 2.8 to 11.2 Hz along the Z-axis and with an acceleration of 2.12 m/s². Temperature classes were: (1) 20°C and (2) 35°C. Changes in body functions were registered during the pauses. Urine samples were gathered for the morning and afternoon sessions and for the preceding and the following night of the test. The changes were dependent on the combinations of noise, vibration and temperature to which the subjects were exposed. The TTS₂ values at 4 kHz were associated with the HDI-values when subjects were exposed simultaneously to noise and stochastic vibration at 35°C. The TTS₂ values at 6 kHz were associated most strongly with the HDI values after exposure to a combination of noise, stochastic or sinusoidal vibration and a temperature of 20°C. The TTS₂ values at 4 and 6 kHz correlated positively with the NA/A ratio when subjects were exposed to noise at 35°C. The association between TTS₂ values and the 10A/NA ratio and especially the A/NA ratio was very strong when subjects had been simultaneously exposed to noise and sinusoidal or stochastic vibration at 35°C. Furthermore, the highest positive correlation coefficients were found between TTS₂ values at 4 kHz and VUBSA values in the X-direction when subjects had been exposed to noise or simultaneously to noise and sinusoidal vibration at 20°C. With vibration exposure at 35°C, noise led to an increase in the 10NA/DA and NA/A ratios, but with vibration exposure at 20°C, noise decreased the 10NA/DA and NA/A ratios. The exposure was reflected as a rise in the NA/A ratio during the night following the experiment. The variance analytical model as a whole explained 58 to 62% in the morning and 55 to 60% in the afternoon (TTS₂ values at 4 kHz), 50 to 62% and 45 to 50% (TTS₂ values at 6 kHz), 9 to 12% and 9 to 19% (HR values), 16 to 31% and 23 to 36% (SBP values), 3 to 7% and 2 to 6% (DBP values), 7 to 12% and 9 to 13% (PP values), 5 to 8% and 1 to 3% (RWA values), 10 to 18% and 12 to 23% (HDI values), 6 to 7% and 7% (VUBSA values in X direction), 1% and 1 to 8% (VUBSA values in the Y direction), 18% and 20% (10A/DA), 17% and 20% (10NA/DA), 28% and 24% (A/NA), and 27% and 21% (NA/A) of the variation in the values of the variables involved.