The present study examines the effects of auditory stress on the plasma levels of pituitary hormones and cortisol. Each of twelve healthy male subjects participated in two experimental series; during one of them they were exposed to 85 dB(A) industrial noise from 9:00 to 21:00 h. Blood samples were taken by an indwelling venous catheter for 24 h at intervals of 20 min from 8:00 to 8:00 h. The plasma levels of ACTH, growth hormone, prolactin, oxytocin, vasopressin and cortisol were determined. In all subjects except one noise stress affected the profiles of the pituitary hormones but the responses were interindividually different. The oxytocin level was significantly elevated (p less than .01), ACTH also responded but less clearly, whereas the other hormones reacted only in individual cases. During the subsequent night sleep only PRL concentrations were elevated above the baseline plateau in several subjects. It was concluded that in humans the pituitary responses to noise stress are highly individual.
This study examines the influence of daytime noise load on the spontaneous EEG activity during wakefulness and sleep. Twelve healthy male subjects participated in two experimental series, each consisting of three consecutive nights and the two days in between. EEG, EOG, EMG, ECG and respiration were continuously recorded. During one series from 9:00 to 21:00 h the subjects were exposed to 85 dB(A) industrial noise. Direct effects of the noise exposure were a slight blockade of the alpha and theta activity; towards the evening, when self-estimated tiredness was high, increased alpha and beta power were found (p less than .01). Aftereffects on subsequent undisturbed night sleep were a reduction in REM sleep (p less than .001), shortened sleep cycles (p less than .01) and an increase in slow wave sleep during the 2nd sleep cycle (p less than .05). These results are interpreted as signs of strained wakefulness and intensified fatigue, as disturbance of sleep processes and as an intensified need for recovery.
The effects of daytime noise on recovery processes during subsequent undisturbed night sleep were studied in six healthy men (21-27 years), exposed to 80 dB (A) pink noise 8 h per day for 2 days. Sleep EEG, ECG, and respiration were recorded in the laboratory for five consecutive nights: two baseline nights, two nights following noise stimulation, and again one baseline night. Additionally questionnaire data were collected, reflecting a subjective impairment of the recovery function of sleep after noise exposure. EEG sleep data of the first post-noise night showed an increase in slow wave sleep with a simultaneous decrease in stage 2 sleep. During the second post-noise night these changes were less prominent. Three subjects additionally showed an instability in the sleep course coinciding with elevated heart and respiration rates. However, altogether the autonomic parameters were not clearly affected by the noise exposure. The findings support the assumption that strong daytime noise may interfere with subsequent sleep processes.
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