Ising, H. Braun, C. Acute & Chronic Endocrine Effects of Noise
Acute and chronic endocrine effects of noise: Review of the research conducted at the Institute for Water, Soil and Air Hygiene
Noise & Health Journal, 2000
This is a review of the research into endocrine effects of noise since the early 1980s at the Institute for Water, Soil and Air Hygiene. According to our knowledge, no other group has studied systematically the endocrine effects of acute and chronic noise exposure. Mechanisms of acute noise-induced stress reactions as well as long-term increase of stress hormones in animal and persons under chronic noise exposure were studied. Our theoretical background was Henry’s psychophysiological stress model with the two reaction alternatives : (i) The fight-flight reaction, characterised by an increase in adrenalin and noradrenaline (ii) The defeat reaction with increased cortisol. Extremely intense acute noise exposure near the threshold of pain caused an increased release of cortisol from the suprarenal cortex but acute noise exposure with levels between 90 and 100 dB(A) caused an increase of catecholamines. Nonhabituated noise increased primarily the release of adrenalin from the suprarenal medulla, whereas habituated noise caused a chronic increase of noradrenaline from the sympathetic synapses under long-term noise exposure at work. Environmental noise exposure (Leq > 60 dB(A)) caused catecholamine increase if activities such as conversation, concentration, recreation etc were disturbed through noise. In sleeping persons, traffic noise with only Leq > 30 dB (A) and Lmax > 55 dB(A) caused significant acute increase of cortisol, which developed into chronic increase if the noise exposure was repeated consistently. Parallel to cortisol, chronic noradrenaline increase was also observed. Based upon the empirical results, a noise stress model was developed which is a first step forward in the theoretical understanding of endocrine noise effects.
It is generally accepted that noise has the potential to act as a non specific stressor. The stress concept was introduced into biological sciences by Selye (1956) and since then modified in various ways. We will use one of these modifications as a basis for the study of noise-induced endocrine reactions, the psychophysiological stress model of Henry and Stephens (1977). [Figure – 1] shows a simplified form of this model. A stimulus is perceived by our ears, eyes, nose or other senses and transmitted to the corresponding parts of the brain, where it is analysed.
One of the purposes of this analysis is for the detection of impending danger in the flood of stimuli to which we are exposed. If the stimulus being detected signals danger then immediately one of the two reaction patterns is chosen: If the danger is threatening control over the situation, the organism is prepared for fight or flight. If the danger is overwhelming and inescapable so that the control of the situation appears to be lost, the defeat reaction will automatically follow. Henry and Stephens found that personal coping pattern, early experiences and genetic pre-disposition are important for the decision between the two types of stress reactions.
According to the stress model of Henry and Stephens it is expected that noise stimuli which carry the information of an approaching danger, have the potential to trigger the fight-flight reaction. This is characterised by a secretion of adrenalin and noradenaline from the adrenal medulla. If a person is exposed to an unexpected noise with a very high level and a sudden level increase, the defeat reaction will come into play with increased secretion of cortisol from the adrenal cortex. In this case the sound itself appears as an overwhelming power and imminent danger, and will cause sudden earache if the individual level of pain is exceeded.
Quite often the reaction is to throw oneself onto the ground. An example of this was given by a tank commander in the Yom Kippur war. After the elimination of the SAM rocket sites behind the Egyptian lines across the Suez Canal, he and his men were waiting in the desert for more orders. They spotted an Egyptian fighter plane, tried to gun it down and the plane following it, but then realised that the second plane was Israeli. Afterwards they waited again in silence. Suddenly they experienced an extremely loud noise. All the soldiers flung themselves flat onto the sand. After several seconds they looked up and saw this Israeli plane flying back home. They then realised what had happened: The pilot had flown from behind a mock attack on their tanks! Several incidences similar to this have been reported to us during our studies of low flying fighter plane noise effects.
The following experimental studies are described in order to present an empirical basis for a theoretical understanding of noise-induced stress reactions. Firstly some remarks have to be made about the problem of applicability of the results of animal experiments to human beings. It is well known that Selye derived his stress concept from the results of various rat experiments and that his stress concept has been successfully applied to humans. Therefore the general study of stress reactions, especially those directly transmitted reactions to noise, is possible in the animal model. If however, reasoning is of importance in the human’s response to noise, animal experiments are useless.