Apart from the electroencephalogram (EEG), the electrooculogram(EOG), the Electromyogram (EMG) (see Sleep) and the the computer-assisted performance tests, the study STRAIN will also use a whole set of further measurement variables which may be relevant to an examination of the effects of nocturnal aircraft noise on humans.
Clinical-Chemical Parameters (Stress Hormones):
Stress, and concomitantly noise, cause changes in psysiological processes in the body. When the stressor, e.g. the noise event, is felt, the processing of the stimulus by he brain can lead to immediate reactions caused by the activation of the sympathetic nervous system. One of the most important of those reactions is the secretion of stress hormones like adrenalin and noradrenalin. These hormones then initiate further physiological reactions (changes in heartbeat frequency, blood vessel extension, metabolic increase etc.). Situations of stress can also lead to a temporally delayed activation of the adrenal cortex by the automatic nervous system. Cortisol is the most important hormone of the gluocorticoids produced here. Among other things, it has effects on the immune system and the electrolyte metabolism - the regulation of water and salt. These are general reactions to stress, which can be triggered by noise events. The stress hormones mentioned are processed and will in the long run be discharged as waste matter and/or still intact molecules over the kidney into the urine.
Therefore, the nocturnal urine will be collected in the study and the quantities of adrenalin, noradrenalin, cortisol and elecrolytes in the urine will be analyzed in the laboratory. In the evaluation, we have to take into consideration e.g. the different concentrations of salt caused by food intake in the evening or the circadian rhythm (natural daily fluctuations) of the cortisol concentration. Since blood can't be taken during the time in which the noise events acutely effect the volunteers, only the cumulated excretions of the whole night will be registered. A single-event correlation is not possible.
The heartbeat is directed by electrical impulses. These impulses are conducted via the conductive system, which originates in the wall of the right atrium (sinus node), through the complete cardiac muscle into the cardiac ventricles. The ECG registers and records these impulses. Under the acute noise influence and a specific noise level, an increased heartbeat frequency caused by an activation of the sympathetic nervous system can be observed.
Finger Puls Amplitude
With every heartbeat, blood is pumped via the left heart into the greater cardiovascular system. With the opening of the cardiac valve, the initial extension of the main artery continues as a so-called pulse wave through the complete arterial vascular system of the cardiovascular system. After a time period corresponding to its propagation speed, the pulse wave reaches the extremities, where it can be measured e.g. at the middle finger as the so-called finger pulse amplitude (FPA).Technically speaking, the measurement of the FPA is a so-called photoplethysmography. This procedure can selectively record the pulsing blood and forms the basic condition for the pulse oxymetry, which is a standard in today's sleep facilities and by the use of which we have been able to non-invasively measure the arterial oxygen tension since 1975.The amplitude of the finger pulse is essentially determined by five parameters: Blood pressure amplitude, mean arterial pressure, venous discharge, elastic vascular tension and contraction of the muscular arterial wall.Additionally to a rise in blood pressure amplitude and of the arterial medium pressure, the application of noise of a specific volume leads to an increase of tension in the smooth musculature of the arterial wall, the flexibility of which is reduced by this. For this reason, we can observe a decrease of the FPA in an acute noise situation.
Measurement of Respiratory Movements with Strain Gauges
Using the recording of respiratory movements by strain gauges, we can make an observation about respiratory depth as well as respiratory frequency. The influence of acute noise events of a specific volume often leads to accelerated and deepened respiration.The elastic strain gauges contain a so-called piezo-crystal, which produces an electrical tension proportional to the deformations caused by respiratory movements.
The actometer consists of several piezo-crystals serving as acceleration recorders. By use of the actometer, the activity-rest-cycles can be recorded over longer periods of time. It is worn at the wrist of the non-dominant arm (left arm with right-handed persons, right arm with left-handed persons).The special feature of this method is the low effort in handling and evaluation. Many studies on the influence of nocturnal aircraft noise only use actometry. This way, a high number of subjects taking part in the study is possible while keeping the expenditure small. However, the informative capability of this method is very limited and not very valid compared to polysomnography, by the use of which we can assess the microstructure of sleep. The subjects of our aircraft noise study will wear the device continually. By day, it has a controlling function, as sleeping by day is not permitted. The night data will be used for a comparison of the informative capability of actometry and polysomnography.
Body Position Measurement
In the clinic, the body position measurement gives valuable information for the diagnosis of specific clinical sleep disorders like the sleep apnea syndrome. In our aircraft noise study, it records position changes induced by aircraft noise. The question here is which amount and volume of aircraft noise is necessary to induce a significant increase in body position changes compared to the body position changes occuring physiologically in normal sleep.The basic principle of the sensors is usually the gravity-dependent position adjustment of a mobile indicator in a casing attached to the surface of the body and the conversion of the position adjustment into a direct-current signal.
The thermistor is attached above the upper lip in front of the openings of mouth and nose. The sensor registers the changes in temperature of air when the subjects breathes in or out. This is a qualitative procedure. It is especially important for the diagnosis of respiratory disorders connected to sleep: With the obstructive sleep-apnea-syndrome (OSAS), the tongue bottom draws back, which leads to a blocking of the upper respiratory pathways. Futile respiratory movements without measurable respiratory gas flow at the mouth and nose can be registered.In our aircraft noise study, we will use the thermistor to exclude an OSAS and as an alternative medium in the case of a failure of the strain gauges.