An investigation of biological response induced by intermittent noise (trapezoidal noise).

Abstract

Audiometrically normal, male students (aged 18–22, 6–12 persons) were exposed to intermittent and steady-state noise (480 min, pink noise), after which 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. 500 ms and its duration was 6.5 s. Peak levels of intermittent noises were 80 dB (A) and 90 dB (A). Exposure conditions examined were (1) control; (2) peak level of 90 dB (A) with an exposure time of 2 min; (3) peak 90 dB (A), exposure 1 min; (4) peak 90 dB (A), exposure 24 s; (5) peak 90 dB (A), exposure 12 s; (6) Peak 80 dB (A), exposure 2 min; (7) peak 80 dB (A), exposure 1 min; (8) peak 80 dB (A), exposure 24 s; (9) peak 80 dB (A), exposure 12 s; (10) steady-state noise of 90 dB (A); (11) steady-state noise of 80 dB (A). The coefficient of regression of TTS growth induced by exposures 1, 2, 3, 6, 7, or 8 did not have significance, but that by exposure 4, 5, 9, 10, or 11 was significant. When the TTS2 of the noise exposure for 480 min was studied by the on-fraction rule based on these regression equations, the TTS of exposures 4 and 5 (on-fraction 25%, 50%) was found to be same as 29% and 40% of the TTS of exposure 10. There was a significant difference between the 8-h urinary 17 OHCS levels induced by exposures 6 and 7 and those induced by control conditions. However, there was no significant difference between urinary 17 OHCS levels induced by other noise exposures (8, 9, and 11) and that induced by control conditions. The coefficient of regression between the 8-h urinary 17 OHCS levels and the logarithm of the on-fraction was significant.