Environmental Engineering Reference
In-Depth Information
•
delayed sleep onset;
•
increased awakenings from sleep;
•
sleep loss;
•
premature awakening at the end of the sleep;
•
reduced reported quality of sleep.
It can also cause changes in the natural pattern of electrophysiologically defined sleep
stages that humans display, reasonably consistently, each night. Noise can also evoke
minor perturbations or brief arousals of the electroencephalogram recordings, which
would not be consciously registered. Many of these brief arousals are associated with
autonomic nervous system (ANS) activation, such as a temporary increase in heart rate
(Muzet and Ehrhart, 1980; Whitehead et al, 1998). However, it is still unresolved how
much such unwanted activation of the ANS contributes to pathological changes, as
in cardiovascular disease.
Carter et al (1994a, b) carried out a laboratory study on a vulnerable group -
nine heart-diseased subjects (cardiac arrhythmias). They found that road and air
traffic noise (65-72dB(A)) increased arousals fivefold, while neither the rhythm
defect nor the urinary catecholamine (a consequence of increased 'stress hormones')
levels were significantly affected. There are further consequences with sleep distur-
bance. Sleep is the major time for rest and restitution of the brain and body, and
when sleep is disturbed, one does not function optimally both mentally or physically
during the following day, as the natural restorative processes have been impaired.
Carter (1996, 1998) has suggested that chronic noise-induced sleep disturbance
could lead to several health disorders. They suggest a mechanism in which disturb-
ance impairs the functions of sleep, which are largely unknown but are related to brain
restoration, immune responses and other physiological systems. As sleep serves as a time
of respite for the cardiovascular system, constant disturbance to sleep and the func-
tions of sleep may have implications on long-term cardiovascular health (Carter, 1998).
The slow-wave sleep that is affected by environmental noise is thought to be important
to the immune system (Brown and Czeisler, 1992), and Carter (1996) states that the
immune response of many people could be impaired by noise.
Many early studies on the assessment of noise-induced sleep disturbance were con-
ducted in laboratories, as opposed to field studies where subjects are studied in their
own homes. However, during the late 1980s, large discrepancies were becoming evi-
dent between laboratory and field studies, with far greater levels of sleep disturbance
reported in the laboratory (Pearson et al, 1990, 1995).
During the early 1990s, a large field study (Ollerhead et al, 1992) was con-
ducted in the UK to inform government decisions on night operations. The effects
of night-time aircraft noise on the sleep of 400 residents living at eight sites adjacent
to the four main airports in the UK was assessed. The main findings were that for
aircraft noise below 80dB(A) L
max
outdoors (= 55dB(A) L
max
indoors) there was
little disturbance, while for higher noise levels there was a chance of about 1 in 75 of
being aroused from sleep (Horne et al, 1994). However, aircraft noise was found to
be a relatively minor cause of sleep disturbance (about 5 per cent of reported awak-
enings), with domestic and other non-aircraft factors causing greater disturbance. In
addition to the main technique of actimetry (measurement of limb movement),
used for assessing sleep disturbance, the sleep of a sample (46) of the residents was
