Night noise guidelines for Europe - WHO/Europe - World Health ...

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CHAPTER 3
EFFECTS OF NIGHT-TIME
NOISE ON SLEEP
Best travel tip: Never ever forget to pack ear plugs.
(Virginia Jealous, Lonely Planet author)
3.1 SHORT-TERM EFFECTS OF TRANSPORTATION
NOISE ON SLEEP WITH SPECIFIC ATTENTION
TO MECHANISMS AND POSSIBLE HEALTH
IMPACT
3.1.1 INTRODUCTION
In this section reactions to single events are presented. In Chapter 2 normal sleep and
sleep disorders are described in medical terms, but here the focus is on the mechanisms
underlying the relation between noise and sleep quality. How does a sound
penetrate the brain and cause a disruption of sleep?
3.1.2 HOW NOISE INFLUENCES NORMAL SLEEP
Noise can induce changes in the EEG or in autonomic variables that are called
arousals or phasic activations. Similar brief episodes of activity also occur without
noise in normal sleep, and, more frequently, in sleep that is otherwise disturbed, for
example by apnoea. Arousal during sleep is not a uniform concept and has been
defined differently by different researchers. Commonly, the occurrence of alpha
rhythms is required for EEG arousal. Depending on the additional requirements and
on the length of time that the slower cortical rhythms are interrupted, arousals have
been called, for instance, micro-arousal, minor arousal, EEG awakening or transient
activation phases. EEG awakening requires an interruption of the sleep patterns of
at least 15 seconds (half the period) when sleep staging is scored by periods of 30
seconds, but need not be experienced consciously. Because normal REM sleep is a
state characterized by cerebral arousal with frequently occurring alpha rhythms,
additional criteria are needed to define arousal from REM. The criteria used are
increased heart rate, EMG, or irregular respiration. However, since the mechanisms
of such autonomic responses appear to be at least partly different from the causal
mechanisms of EEG arousal, such definitions seem to make arousal from sleep a heterogeneous
concept that may not have simple relationships with noise exposure.
EEG arousals lasting at least 30 seconds have been found to occur as often as 4 times
(95% CI: 1–15) per hour during sleep on average, while micro-arousals occurred 21
times (95% CI: 7–56) per hour (Mathur and Douglas, 1995). Since these figures are
from a laboratory study, they almost certainly are higher than the figures that hold
for the natural situation at home. Sleep pressure decreases the density of microarousals
(Sforza, Jouny and Ibanez, 2000). While the number of EEG arousals (dur-
NIGHT NOISE GUIDELINES FOR EUROPE