As described in the Sleep Disturbances section, polysomnography is regarded as the gold standard for sleep measurements. It comprises several measurements such as the electrophysiological measurement of brain activity, muscle and eye movement, as well as oxygen level and heart rate. This sleep measurement approach allows, for instance, for the detection of the transition from deeper sleep stages to lighter sleep stages or wake at any time during sleep. Moreover, polysomnographic analyses have the considerable advantage that they are not subject to biases due to, for example, personal attitudes and knowledge, as it is the case for self-rated sleep assessments.
Figure 1: Schematic representation of the electrode positioning for the measurement of polysomnography (source: DLR)
Figure 2: Preparing subjects for polysomnographic recordings (source: DLR)
A combination of polysomnography with continuously recorded sound pressure levels at the subjects home allows an exact calculation of the effect of the noise of single aircraft noise events on sleep, in particular, awakening reactions due to it. Such controlled experimental studies provide a so-called event-related evaluation at any time during the night. Through this, it is possible to develop an optimal statistical model, focusing on all relevant acoustic parameters such as maximum levels, level rise speed, event duration and the background noise level when the aircraft noise event occurs, but also non-acoustic situational factors, such as the elapsed sleep duration, the stage of rather deep or relatively light sleep before the noise event occurs, the time spent in the sleep stage before the noise event as well as personal parameters (e.g. age). All this data is condensed in exposure-response models and curves derived from these models. Exposure-response curves deliver the probability of awakeness for every noise event depending on its maximum sound pressure level and control of the influence of the other acoustical and non-acoustical factors mentioned above.
This methodology is very costly and time-consuming. Moreover, it requires that only subjects are examined without any inherent sleep disorders and without any diseases which have side effects on sleep. Otherwise, any sleep effects following an aircraft noise event and total sleep quality parameters cannot be interpreted unambiguously. Consequently, the examination of subjects only on the two- to lower three-digit number range can be performed, and only very few research groups worldwide investigate the effects of noise on sleep employing polysomnography and provide exposure-response functions. When the ANIMA standard prediction model for sleep disturbances due to nocturnal aircraft noise was developed, only two field studies were available using this polysomnographic measurement approach. Both studies were operated by the German Aerospace Center (DLR):
- The STRAIN (STudy on human Response on AIrcraft Noise) study that was conducted between 1999 and 2003 and examined the influence of nocturnal aircraft noise on sleep utilising field studies (64 residents in 9 successive nights each) around Cologne/Bonn Airport with a 24 h operating scheme;
- The NORAH study (NOise Related Annoyance, cognition and Health) was carried out between 2011 and 2015 around Frankfurt airport before and after the beginning of the operation of the fourth runway in October 2011 and the associated night flight ban between 23 h and 05 h.