Noise induced nocturnal cortisol secretion and tolerable overhead flights.

Mainly dependent on level and dynamic increase sound produces over-shooting excitations which activate subcortical processing centers (e.g. the amygdala, functioning as fear conditioning center) besides cortical areas (e. g. arousing annoyance, awakenings) as well. In addition there exist very close central nervous connections between subcortical parts of the auditory system (e.g. amygdala) showing typical plasticity effects (sensitization) and the hypothalmic-pituitary-adrenal (HPA)-axis. Using that causal chain noise induce cortisol excretion even below the awakening threshold. Thus repeated noise events (e.g. overflights during night time) may lead to accumulation of the cortisol level in blood. This can happen because its time-constant of exponential decrease is about 50 to 10 times larger than that one for adrenaline and noradrenaline. This fact and the unusual large permeability of cortisol through the cell membranes opens a wide field of connections between stress-dependent cortisol production and the disturbance of a large number of other endocrine processes, especially as a result of long-term stress activation by environmental influences such as environmental noise. Based upon a physiological model calculating the cortisol accumulation starting at a nightly threshold of physiological over-proportional reactions around Lmax = 53 dB(A) the number of tolerable noise events (over-flights in a nightly time range) can be estimated for given indoor peak sound pressure levels, keeping the cortisol increase within the normal range. Examples of results for 8 hours in the night are for instance number and level combinations (NAL-values) of 13 events with 53 dB(A) indoor peak level or 6 events with 70 dB(A) indoor peak level respectively.