In diffuse pleural thickening, the outer
and inner layers of the pleura become
thickened, and excess fluid may accu-
mulate in the cavity between them. This
combination restricts the ability of the
lungs to expand, resulting in shortness
of breath. The condition may develop
even after short exposure to asbestos.
asbestosisSee asbestos-related diseases.
ascariasisInfestation with the round-
worm ASCARIS LUMBRICOIDES, which lives
in the small intestine of its human host.
Ascariasis is common worldwide, espe-
cially in the tropics. The disease is
spread by ingestion of worm eggs, usu-
ally from food grown in soil that has
been contaminated by human faeces.
Light infestation may cause no symp-
toms, but mild nausea, abdominal pain,
and irregular bowel movements may
occur. A worm may be passed via the
rectum or vomited. A large number of
worms may compete with the host for
food, leading to malnutrition and
anaemia, which in children can retard
growth. Treatment is with anthelmintic
drugs, such as levamisole, which usually
produce complete recovery.
ascitesExcess fluid in the peritoneal
cavity, the space between the 2- layered
membrane that lines the inside of the
abdominal wall and which covers the
abdominal organs.
Ascites may occur in any condition
that causes generalized oedema, such
as congestive heart failure, nephrotic
syndrome, and cirrhosisof the liver.
Ascites may occur in cancerif metas-
tases (secondary growths) from a cancer
elsewhere in the body develop in the
peritoneum. The condition also occurs
if tuberculosisaffects the abdomen.
Ascites causes abdominal swelling
and discomfort. It may cause breathing
difficulty due to pressure on the diaph-
ragm. The underlying cause is treated if
possible. Diuretic drugs, particularly
spironolactone, are often used to treat
ascites associated with cirrhosis.
ascorbic acidThe chemical name for
vitamin C.
ASDSee atrial septal defect.
aseptic techniqueCreation of a germ-
free environment to protect a patient
from infection. Aseptic technique is
used during surgery and when caring for
people suffering from diseases, such as
leukaemia, in which the immune system
is suppressed. All people who come in
contact with the patient must scrub their
hands and wear pre-sterilized gowns
and disposable gloves and masks. Sur-
gical instruments are sterilized in an
autoclave. The patient’s skin is cleaned
with antiseptic solutions of iodineor
hexachlorophene. A special ventilation
system in the operating theatre purifies
the air. (See also isolation.)
aspartameAn artificial sweetenerused
in some foods and drugs.
Asperger’s syndromeA rare develop-
mental disorder that is usually first
recognized in childhood because of dif-
ficulties with social interactions, stilted
speech, and very specialized interests.
Intelligence is normal or high. Asperg-
er’s syndrome is considered to be an
autistic spectrum disorder and is also
known as pervasive developmental dis-
order. Special educational support may
be needed, often within mainstream
education. The condition is lifelong.
aspergillosisAn infection caused by
inhalation of spores of aspergillus, a
fungus that grows in decaying vegeta-
tion. Aspergillus is harmless to healthy
people but may proliferate in the lungs
of people with tuberculosis, worsen the
symptoms of asthma, and produce seri-
ous, even fatal, infection in people with
reduced immunity, such as those taking
immunosuppressant drugs.
aspermiaSee azoospermia.
asphyxiaThe medical term for suffoca-
tion. Asphyxia may be caused by the
obstruction of a large airway, usually by
a foreign body (see choking), by insuffi-
cient oxygen in the surrounding air (as
occurs when a closed plastic bag is put
over the head), or by poisoning with a
gas such as carbon monoxide that inter-
feres with the uptake of oxygen into the
blood. First-aid treatment is by artificial
respirationafter clearing the airway of
obstruction. Untreated asphyxia leads
to death within a few minutes.
aspirationThe withdrawal of fluid or
cells from the body by suction. The term
also refers to the act of accidentally
inhaling a foreign body, usually food orASBESTOSIS ASPIRATION
A