Results of a low-altitude flight noise study in Germany: acute extraaural effects.

This paper begins by outlining the aims which our study into the acute effects of low-altitude flight noise set out to achieve. The key question here concerns the relationship between noise parameters (maximum sound level and sound level rise rate) and specific reactions by the individuals affected. The subjects, healthy volunteers, were exposed via earphones to digitally recorded MLAF noise, using sophisticated recording technology. Their reactions were studied on various levels ranging from the subjective experience of negative effects through startle reactions to changes in the cardiovascular and endocrine systems. It emerged that a high sound level rise rate is a physical parameter which leads not only to more physical symptoms being cited by the subjects, but also to more pronounced myokinetic effects of an objectively measurable nature. Studies of circulation physiology were also conducted to throw light on the haemodynamic mechanism of the startle reaction. The findings suggest that increases in cardiac output per minute in a startled subject with a healthy circulation need not necessarily lead to protracted increases in blood pressure. A counter-regulation occurs by means of vasculomotory responses in the muscle. Should this regulatory system be impaired, as may be the case with elderly people, for example, blood pressure increases of up to 45 mm Hg over the initial value may ensure. A sensitization is observed after repeated exposure, with the startle reaction intensifying or else being triggered off by lower sound levels. The sensitization of startle reactions is neuro-physiologically associated with unpleasant or fear-inducing environmental stimuli. Together with the observed increases in plasma hydrocortisone and changes in magnesium metabolism of a type characteristic of stress, this phenomenon of sensitization enables us to establish the hypothetical link between specific acute reactions to MLAF noise and long-term health effects.