Physiological Reaction – Thresholds to Vibration During Sleep

Abstract

The World Health Organization Night Noise Guidelines for Europe 2009 report that there is sufficient evidence for biological effects of noise on sleep, starting at LAF,max,inside=32 dB. Alterations in sleep structure and electroencephalogram (EEG) awakenings start to occur at LAF,max,inside=35 dB. Changes in cardiovascular activity during sleep also occur as a result of noise exposure, but threshold levels have not been determined. Noise from freight trains in particular has been found to cause more frequent awakenings and stronger cardiac response than passenger trains. In the field, freight trains are often accompanied by low frequency vibration, with amplitudes commonly around 0.4 – 1.5 mm/s (comfort weighted) near railway lines. As with noise, moderate to high level vibration from freight has been shown to contribute towards cortical EEG reactions and changes of heart rate during sleep. However, it is not presently known at what threshold levels physiological effects due to vibration begin to occur. The research group aimed to identify a physiological reaction threshold to vibration during sleep. An initial pilot study was conducted to give a first indication of where such a threshold might lie. A subsequent larger-scale main study further investigated the vibration level response threshold, and also provided knowledge regarding what physiological response occur at 0.4 mm/s, the current lowest limit value enforced for new railway lines in Sweden. Changes in sleep stage and awakenings were observed at 0.4 mm/s, while indications were seen at 0.3 mm/s but not 0.2 mm/s. Changes in heart rate were seen at 0.3 and 0.4 mm/s, but not at 0.2 mm/s. This study found that the physiological effects and threshold levels for these WHO defined effects were 0.3 mm/s for changes in cardiac activity, and 0.4 mm/s for EEG awakenings and changes in sleep structure and fragmentation of sleep.