I
DEFENCE MECHANISMS
and mottling and severe pain in and
around the larger joints. Symptoms of
nervous system impairment (such as
leg weakness or visual disturbances)
are particularly serious, as is a painful,
tight feeling across the chest.
TREATMENT
Divers with decompression sickness are
immediately placed inside a recom-
pression chamber. Pressure w ithin the
chamber is raised, causing the bubbles
w ithin the tissues to redissolve. Subse-
quently, the pressure in the chamber is
slowly reduced, allowing the excess gas
to escape safely via the lungs.
OUTLOOK
If treated promptly by recompression,
most divers with the “bends” make a
full recovery. In serious, untreated cases,
however, there may be long-term com-
plications
such
as
partial
paralysis.
Repeated episodes may lead to degen-
erative disorders of the bones or joints.
decompression, spinal canal
Surgery
to
relieve
pressure
on
the
spinal cord or a nerve root emerging
from it (see
microdiscectomy
) .
Pressure
may have various causes, including a
disc prolapse
(“slipped” disc); a tumour
or abscess of the spinal cord;
or a
tumour, abscess, or fracture of the ver-
tebrae. Any of these
conditions
can
cause
weakness
or
paralysis
of the
limbs and loss of bladder control.
To treat major disc prolapses and
tumours, a
laminectomy
(removal of the
bony arches of one or more vertebrae)
to expose the affected part of the cord
or nerve roots may be performed.
Recovery after treatment depends on
the severity and duration of the pres-
sure,
the success of the surgery in
relieving
the pressure,
and whether
any damage is sustained by the nerves
during the operation.
decongestant drugs
Drugs used to relieve
nasal congestion,
commonly in people who have upper
respiratory tract infections
.
The drugs are
thought to work by narrowing the blood
vessels in the membranes lining the nose.
This action reduces swelling, inflamma-
tion, and the amount of mucus that is
produced by the nasal lining. Common
decongestants include ephedrine, oxy-
metazoline,
and
phenylephrine.
Small
amounts of these drugs are found in
many over-the-counter cold remedies.
There is little objective evidence that
decongestants effectively relieve respi-
ratory disorders. Taken by mouth, they
may cause tremor and palpitations, and,
taken for longer than five days, they be-
come ineffective; if they are stopped at
this stage, symptoms may be worse than
at the start of treatment. Therefore, they
should not be used continuously for more
than five days without medical advice.
Decongestants may be unsuitable for peo-
ple with certain medical conditions and
must be avoided in people taking MAOIs.
decubitus
The position of reclining or lying down,
as in a decubitus ulcer (see
bedsore).
decubitus ulcer
See
bedsore
.
decussation
A point at w hich two or more struc-
tures in the body cross over each other
to the opposite side. An example is the
point at w hich nerve fibres intercross
in the
central nervous system
.
deep vein thrombosis
See
thrombosis, deep vein.
defaecation
The expulsion of waste material as
fae-
ces
from the body through the anus.
defence mechanisms
Techniques used by the m ind to lessen
unpleasant
or
unwelcome
emotions,
impulses, experiences, or events, and to
avoid external or internal conflict.
TYPES
The principal defence mechanism is
repression, w hich is the suppression of
unacceptable thoughts. Other types of
defence mechanism include displace-
ment, rationalization, projection, reaction
formation, and isolation.
In displacement, dangerous thoughts
or feelings are redirected at a harmless
object; for example, someone who is
angry at another person may kick the
furniture instead of hitting that person.
Rationalization involves reinterpreting
thoughts or actions in a more accept-
able way; for example, a person may
criticize someone else but claim “It’s
for your own good” . In projection, a
person attributes his or her own faults
to someone else, for example by think-
ing “that person hates me” when in
fact he or she hates that person. In reac-
tion formation, an unacceptable feeling
is hidden by actions that suggest the
opposite; for example, someone may
disguise hatred for another person by
showing great concern for that person.
THE ACTION OF DECONGESTANTS
Decongestants work by narrowing blood vessels in the membranes that line the
nose. This action reduces swelling, inflammation, and the amount of mucus
produced by the nasal lining.
infection or irritation, increased amounts of
fluid pass into the lining, which swells and
produces more mucus.
vessels in the nasal lining, which reduces
swelling, mucus production, and nasal
congestion.
D
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