Physiological responses induced by 555-min exposure to intermittent noise.

Normal medical college students were exposed to noise for 555 min, while the Temporary Threshold Shift (TTS) and changes in the circulatory system were measured. The exposure noise employed was the so-called pink noise of a trapezoidal form. There were two time patterns, A(I) with 1 s of rise-decay time and 1 s of peak level, and A(II) with 500 ms of rise-decay time and 3.5 s of peak level. Thirteen exposure conditions were examined. The noise exposure time of all experiments was 555 min. The following results were obtained. 1. TTS Growth. Significant TTs increases were obtained following exposure to intermittent noise of 85 dB(A), intermittent noise of 80 dB(A), and steady state noise of various intensities. The TTS growth observed with steady state noise at 80 dB(A) was significantly greater than that of intermittent noise exposure at 85 dB(A). Moreover, TTS growth observed with steady noise at 82 dB(A) was significantly greater than that with intermittent noise exposure of 85 dB(A). However, the levels of TTS growth observed with steady state noise of 75 dB(A) and steady state noise at 77 dB(A) were almost equal to those of 6 s trapezoidal noise at 80 dB(A) (the "on fraction" being 33%), and 8 s trapezoidal noise at 80 dB(d) (the "on fraction' being 50%). In the above-mentioned experiments, significant increases of TTS growth were observed with various cycle times of trapezoidal noise with peak levels of 85 dB(A) and 80 dB(A), and with four exposure noise conditions of steady state. Under exposure conditions of 75 dB(A), trapezoidal noise with a 6 s cycle time (the "on fraction" being 33%) did not show a significant increase in TTS growth. 2. Changes in the Circulatory System. There were no significant differences in systolic and diastolic pressure or pulse rate among the three exposure conditions. The findings on ECG were as follows. Under intermittent noise exposure, decrease in the height of the T wave was observed in all examinees with a depression of the ST segments also being observed in two cases. On exposure to steady state noise, however, slight decrease in the height of the T wave was induced in only two cases, and under control conditions in only one case.