An investigation of biological response induced by intermittent noises (trapezoidal noise) (author's transl)

Abstract

Audiometrically normal, male students (ages 18 to 22, 6-12 persons) were exposed to intermittent and steady-state noise (480 minutes, pink noise), after which the Temporary Threshold Shift (TTS) and urinary 17 OHCS levels were measured.The rise-decay time of an exposed noise (trapezoidal noise, cf, Fig. 1) was ca 500ms and the duration was 6.5 seconds. Peak levels of the intermittent noises were 80dB (A) and 90dB (A).Experimental ConditionsExposure 1: ControlExposure 2: Peak level 90dB (A); duty cycle 2 minutes.Exposure 3: Peak level 90dB (A); duty cycle 1 minute.Exposure 4: Peak level 90dB (A); duty cycle 24 seconds.Exposure 5: Peak level 90dB (A); duty cycle 12 seconds.Exposure 6: Peak level 80dB (A); duty cycle 2 minutes.Exposure 7: Peak level 80dB (A); duty cycle 1 minute.Exposure 8: Peak level 80dB (A); duty cycle 24 seconds.Exposure 9: Peak level 80dB (A); duty cycle 12 seconds.Exposure 10: Steady state noise; sound level 90dB (A).Exposure 11: Steady state noise; sound level 80dB (A).Results(1) TTS growthThe coefficients of regression of TTS growth by exposures 1, 2, 3, 6, 7 and 8 were not significant. The coefficient of regression of TTS growth induced by exposures 4, 5, 9, 10 and 11 were significant.The TTS2 of noise exposure for 480 minutes, calculated according to regression equations, were determined by the on fraction rule. This gave a TTS for exposures 4 and 5 (on fraction 25%, 50%) that equaled 29% and 40% respectively of the TTS of exposure 10.(2) Urinary 17 OHCS levelsThere was a significant difference between the 8 hours-urinary 17 OHCS levels induced by exposures 6 and 7 and that induced by the control. No significant difference appeared between the urinary 17 OHCS levels induced by other noise exposures (exposures 8, 9 and 11) and that induced by the control.The coefficient of regression between the 8-hour-urinary 17 OHCS levels to the logarithm of the on fraction was significant.