I
in the blood. This causes
cyanosis
(a
bluish discoloration) of the face, partic-
ularly of the lips. Left untreated, such
attacks can be fatal.
TREATMENT
There is no cure for asthma, but attacks
can be prevented to a large extent if a
particular allergen can be identified and
consequently avoided.
Treatment involves inhaled
broncho-
dilator drugs
(sometimes
known
as
relievers) to widen the airways, thereby
relieving symptoms. When symptoms
occur frequently, or are severe, inhaled
corticosteroids
are also prescribed. These
drugs (also known as preventers) are
used continuously to prevent attacks by
reducing inflammation in the airways.
Other drug treatments include
sodium
cromoglicate
and nedocromil sodium,
both of which are useful in the preven-
tion of exercise-induced asthma. The
use of a
leukotriene receptor antagonist
in
combination with a corticosteroid drug
may enable the required dose of cortico-
steroid to be reduced.
Theophylline
or
the inhaled
anticholinergic drug
ipratro-
pium bromide may also be used as
bronchodilators. An asthma attack that
has not responded to treatment with a
bronchodilator needs immediate assess-
ment and treatment in hospital.
asthma, cardiac
Breathing difficulty in which
broncho-
spasm
(narrowing of the airways) and
wheezing occur as a result of fluid
accumulation in the lungs
(pulmonary
oedema).
Cardiac asthma is usually due
to reduced pumping efficiency of the
left side of the heart (see
heart failure)
and is not true asthma. Treatment is
with
diuretic drugs
or other drugs for
heart failure.
astigmatism
A condition in which the front surface
of the
cornea
does not conform to the
normal “spherical” curve, even though
the eye is perfectly healthy. Because the
cornea is unevenly curved, it refracts
(bends) the light rays that strike it to
differing degrees. The
lens
is then unable
to bring all the rays into focus on the
light-sensitive
retina.
A minor degree of
astigmatism is normal and does not
require correction. More severe astigma-
tism causes blurring of lines at a certain
angle and does require correction.
TREATMENT
Correction may be achieved by using
special “cylindrical” glasses that can be
ATELECTASIS
framed at a precise angle; contact lenses
that can give an even spherical surface
for focusing; or by undergoing
laser
treatment
on the cornea.
astringents
COMMON DRUGS
• Aluminium acetate •Potassium
permanganate •Silver nitrate •Zinc sulphate
Substances that causes tissue to dry and
shrink by reducing its ability to absorb
water. Astringents are widely used in
antiperspirants
and to promote healing
of broken or inflamed skin. They are
also used in some eye or ear prepara-
tions. Astringents may cause burning or
stinging when applied.
astrocytoma
A type of cancerous
brain tumour.
Astro-
cytomas are the most common type of
glioma,
a tumour that arises from the
glial (supporting) cells within the ner-
vous system.
Astrocytomas most commonly devel-
op in the cerebrum (the main mass of
the brain) and are classified in four
grades (I to IV) according to their rate
of growth and malignancy A grade I
astrocytoma is a slow-growing tumour
that may spread widely throughout the
brain but may be present for many
years before causing symptoms. The
most severe and fast-growing type is
called
glioblastoma multiforme
(a grade
IV astrocytoma).
Symptoms are similar to those of
other types of brain tumour. Diagnostic
tests include
CT scanning
or
MRI.
Treat-
ment is with surgery as well as, in some
cases,
radiotherapy.
asylum
An outdated term for an institution that
provides care for the mentally ill.
asymptomatic
A medical term meaning without
symp-
toms
(indications of illness noticed only
by the patient). For example,
hyperten-
sion
(high blood pressure)
is often
asymptomatic and is usually discovered
during a routine blood pressure test and
diabetes mellitus
is often diagnosed from
a routine blood or urine test.
Most disorders have no symptoms in
their early stages. In the case of
cancer
,
much effort has been made to devise
screening tests for the detection of
tumours at their early, asymptomatic,
stage. (See also
sign.)
asystole
A term meaning absence of the heart-
beat (see
cardiac arrest).
ataxia
Incoordination and clumsiness that may
affect balance and gait (see
walking),
limb and eye movements, and/or speech.
CAUSES
Ataxia may be the result of damage to
the
cerebellum
(the part of the brain
concerned with coordination)
or to
nerve pathways in the
brainstem
(a stalk
of nerve tissue linking the brain to the
spinal cord
) and/or spinal cord.
Possible causes include injury to the
brain or spinal cord. In adults, ataxia
may be caused by
alcohol intoxication
; a
stroke
or
brain tumour
affecting the cere-
bellum or brainstem; a disease of the
balance organ in the ear; or
multiple
sclerosis
or other types of nerve degener-
ation. In children, causes include acute
infection, brain tumours, and the inher-
ited condition
Friedreich’s ataxia.
SYMPTOMS
Symptoms of ataxia depend on the site
of damage within the nervous system,
although a lurching, unsteady gait is
common to most forms. In addition,
damage to certain parts of the brain
may cause
nystagmus
(jerky eye move-
ments) and slurred speech.
DIAGNOSIS AND TREATMENT
CT scanning
or
MRI
(techniques that
produce cross-sectional or three-dimen-
sional images of body structures) may
be used to determine the cause of ataxia.
Treatment of the condition depends on
the cause.
atelectasis
Collapse of part or all of a
lung
caused
by obstruction of the bronchus (the
main air passage through the lung) or
the bronchioles (smaller air passages).
When obstruction occurs, air already in
the lung cannot be breathed out and is
therefore absorbed into the blood, lead-
ing to the collapse of all or part of the
lung. After collapsing, the lung loses its
elasticity and cannot take in air; conse-
quently, the blood passing through it
can no longer absorb oxygen or dispose
of carbon dioxide.
In an adult, atelectasis is not normally
life-threatening because unaffected parts
of the lung and/or the other lung can
compensate for the loss of function in
the collapsed area. However, when a
newborn
baby’s
lung
collapses,
the
baby’s life is at risk.
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