DEFIBRILLATION
In the mechanism of isolation, unpleas-
ant memories (for example, of being
assaulted) are retained but the feelings
that go with them are hidden, so that a
person may recall such an event appar-
ently without emotion.
defibrillation
Administration of one or more brief
electric shocks to the heart, usually via
two metal plates, or paddles, placed on
the chest over the heart. It is performed
to return the heart’s rhythm to normal
in some types of
arrhythmia
(irregular
or rapid heartbeat), such as
atrial fibrilla-
tion
or
ventricular fibrillation
.
Defibrillation can be carried out as
an emergency procedure to treat ven-
tricular fibrillation, w hich is a cause
of
cardiac arrest
and most commonly
occurs after a heart attack (see
myocar-
dial infarction
) .
It can also be used as
a planned treatment, in w hich case it
is performed under a brief general
anaesthesia
.
Breathing may be m ain-
tained
by
artificial
means
for
the
duration of the procedure.
deficiency anaemia
A type of anaemia. See
anaemia, iron-
deficiency
;
pernicious anaemia
.
defluoridation
The removal of excess fluoride from
drinking water, often using domestic
water filters, to prevent
fluorosis
(mot-
tling of tooth enamel) in consumers.
(See also
fluoridation
;
fluoride
. )
defoliant poisoning
The toxic effects of plant poisons that
cause leaves to drop off. Defoliants are
poisonous if they are swallowed. Widely
used defoliant poisons include sodium
chlorate
,
potassium chlorate, phenoxy
herbicides, and
paraquat
.
deformity
Any malformation or distortion of part
of the body. Deformities may be con-
genital (present from birth), or they
may be acquired as a result of injury,
disorder, or disuse.
Most congenital deformities are rela-
tively rare. Among the more common
are club-foot
(
talipes
)
and
cleft lip and
palate
.
Injuries that can cause deformity
include burns, torn muscles, and bro-
ken bones. Disorders that may cause
deformity include certain nerve prob-
lems, some deficiencies, such as
rickets
,
and
Paget’s disease
of the bone. Disuse
of a part of the body can lead to defor-
mity through stiffening and
contracture
of unused muscles or tendons.
Many deformities can be corrected
by means of orthopaedic techniques,
plastic surgery
,
or specific exercises.
degeneration
Physical and/or chemical changes in
cells,
tissues,
or
organs that reduce
their efficiency. Degeneration is a fea-
ture of aging and may also be due to
disease processes. Other known causes
include injury, reduced blood supply,
poisoning (by alcohol, for example), or
a diet deficient in a specific vitamin.
(See also
degenerative disorders
. )
degenerative disorders
A term covering a wide range of condi-
tions
in w hich
there
is progressive
impairment in the structure and func-
tion of a body system, organ, or tissue.
The number
of specialized
cells
or
structures in the organ affected is usu-
ally reduced, and cells are replaced by
connective tissue
or scar tissue. In many
cases, the cause of the disease is poorly
understood, but degenerative disorders
are the subjects of intensive research.
Degenerative nervous system disor-
ders include
Alzheimer’s disease
,
motor
neuron disease, Huntington’s disease
,
and
Parkinson’s disease
.
Degenerative disor-
ders of the eye include Leber’s
optic
atrophy
and senile
macular degeneration
.
Degenerative
disorders of the joints
include
osteoarthritis
.
Muscle degenera-
tion occurs in
muscular dystrophies
.
Some degree of hardening of the arter-
ies seems to be a feature of normal aging,
but
in
certain
people
degenerative
changes in the muscle coat of the arteries
are unusually severe, and calcium deposits
may be seen on
X-rays
(as in Monckeberg’s
sclerosis, a type of
arteriosclerosis
) .
In most cases, there is little that can
be done to slow the progress of the dis-
ease, but it is often possible to relieve
symptoms with drug treatment
(for
example, in Parkinson’s disease).
Degos syndrome
A rare disorder that affects the linings
of small and medium-sized arteries
throughout the body, particularly in the
skin,
intestine, and nervous system,
causing the vessels to become blocked.
The cause is unknown.
The disease typically produces m ulti-
ple
small
skin
lesions
that
initially
appear as red, raised spots and then
form
depressed, white scars. Lesions
may then form in arteries supplying
other parts of the body, such as the
intestine and the nervous system. This
development may cause severe or even
life-threatening problems, such as
stroke
from lesions that have formed in the
brain and perforation of the intestine by
lesions that penetrate through the intes-
tine wall (see
peritonitis
) .
dehiscence
The splitting open of a partly healed
wound. The term is most commonly
used to refer to the splitting open of a
surgical incision that has been closed
with sutures or clips.
dehydration
A condition in w hich a person’s
water
content is at a dangerously low level.
Water accounts for about 60 per cent of
a man’s body weight and about 5
0
per
cent of a woman’s. The total content of
water (and mineral salts and other sub-
stances that are dissolved in the body’s
fluids) must be kept within fairly nar-
row
limits
to
enable
the
healthy
functioning of cells and tissues.
CAUSES
Dehydration occurs due to inadequate
intake of fluids or excessive fluid loss.
The latter may occur as a result of
severe or prolonged vomiting or diar-
rhoea, or in people who have poorly
controlled
diabetes mellitus
,
diabetes insip-
idus
,
and certain types of
kidney failure
.
Children are particularly susceptible to
dehydration due to diarrhoea.
SYMPTOMS
The symptoms of severe dehydration
are extreme thirst; dry lips and tongue;
an increase in heart rate and breath-
ing rate; dizziness; confusion; lethargy;
and eventual
coma
.
The skin looks dry
and loses its elasticity. Any urine passed
is small in quantity and dark-coloured.
If there is also salt depletion (for exam-
ple, due to heavy sweating), there may
be headaches, cramps, and pallor.
TREATMENT
Drinking bottled mineral water helps
to maintain the intake of salts. In cases
of persistent vomiting and diarrhoea,
rehydration therapy
is required; salt and
glucose rehydration mixtures are avail-
able from chemists.
In severe cases of dehydration, fluids
may be given intravenously, and the
water/salt balance is carefully m oni-
tored by means of blood tests and is
adjusted as necessary.
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