bronchodilators. An asthma attack that
has not responded to treatment with a
bronchodilator needs immediate assess-
ment and treatment in hospital.
asthma, cardiacBreathing difficulty in
which bronchospasmand wheezing are
caused by accumulation of fluid in the
lungs (pulmonary oedema). This is usu-
ally due to reduced pumping efficiency
of the left side of the heart (see heart
failure) and is not true asthma. Treat-
ment is with diuretic drugs.
astigmatismA condition in which the
front surface of the corneadoes not
conform to the normal “spherical” curve,
although the eye is perfectly healthy.
Because the cornea is unevenly curved,
it refracts (bends) the light rays that
strike it to differing degrees. The lensis
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 astigmatism causes blurring of
lines at a particular angle and requires
correction, which be achieved by spe-
cial “cylindrical” glasses that can be
framed at a precise angle, contact lens-
es that can give an even spherical
surface for focusing, or laser surgery.
astringentA substance that causes tis-
sue to dry and shrink by reducing its
ability to absorb water. Astringents are
widely used in antiperspirantsand to
promote healing of broken or inflamed
skin. They are also used in some eye or
ear preparations. Astringents may cause
burning or stinging when applied.
astrocytomaA type of cancerous brain
tumour. Astrocytomas are the most com-
mon type of glioma, a tumour arising
from the glial (supporting) cells in the
nervous system. They most commonly
develop in the cerebrum (the main
mass of the brain). Astrocytomas are
classified in 4 grades (I–IV) according to
their rate of growth and malignancy.
The most severe type is called glioblas-
toma multiforme. Symptoms are similar
to those of other types of brain tumour.
Diagnostic tests include CT scanningor
MRI. Treatment is with surgery and, in
some cases, radiotherapyin addition.
asylumAn outdated term for an institu-
tion providing care for the mentally ill.asymptomaticA medical term mean-
ing without symptoms. For example,
hypertensionis often asymptomatic and
is usually discovered during a routine
blood pressure test.
asystoleA term meaning absence of the
heartbeat (see cardiac arrest).
ataxiaIncoordination and clumsiness
that affects balance and gait, limb or
eye movements, and/or speech. Ataxia
may be caused by damage to the cere-
bellum or to nerve pathways in the
brainstem and spinal cord. Possible
causes include injury to the brain or
spinal cord. In adults, ataxia may be
caused by alcohol intoxication, a stroke
or a brain tumouraffecting the cerebel-
lum or the brainstem, a disease of the
balance organ in the ear, or multiple
sclerosisor other types of nerve degener-
ation. In children, causes include acute
infection, brain tumours, and the inher-
ited condition Friedreich’s ataxia.
Symptoms of ataxia depend on the
site of damage, although a lurching,
unsteady gait is common to most
forms. In addition, damage to certain
parts of the brain may cause nystagmus
and slurred speech. CT scanningor MRI
may be used to determine the cause of
ataxia. Treatment of the condition
depends on the cause.
atelectasisCollapse of part or all of a
lungcaused by obstruction of one or
more air passages in the lung. Obstruc-
tion may be caused by accumulation of
mucus, by an accidentally inhaled for-
eign body, by a tumour in the lung, or
by enlarged lymph nodes exerting pres-
sure on the airway.
The main symptom is shortness of
breath. There may also be a cough and
chest pain. The condition can be diag-
nosed by chest X-ray. Treatment is
aimed at removing the cause of the
blockage and may include physiother-
apyor bronchoscopy. If the obstruction
can be removed, the lung should rein-
flate normally.
atenololA beta-blocker drugcommonly
used to treat hypertension, angina, and
certain types of arrhythmia.
atheromaFatty deposits on the inner
lining of an artery that occur in athero-
sclerosisand restrict blood flow.ASTHMA, CARDIAC ATHEROMAA