CARDIAC OUTPUT
CARDIOPULMONARY RESUSCITATION
C
attack) or heart surgery but sometimes
occurring when there is no previous heart
trouble. The person experiences symp-
toms, such as breathlessness and chest
pain, that are typical of heart disease, and
may be reluctant to exercise or work for
fear of an attack. Medical investigation
reveals no physical cause.
Psychothera-
py
may be of benefit.
cardiac output
The measured volume of
blood pumped by the heart each minute,
used to assess how efficiently the heart is
working. At rest, a healthy adult's heart
pumps 2.5-4.5 litres of blood per minute;
during exercise this figure may be as
much as 30 litres per minute. A low out-
put during exercise indicates damage to
the heart muscle or major blood loss.
cardiac stress test
One of a group of
tests used to assess the function of the
heart in people who experience chest
pain, breathlessness, or palpitations dur-
ing exercise. The test establishes whether
the patient has
coronary artery disease.
An
ECG
machine records the patterns
of the heart's electrical activity while the
heart is stressed. This is usually achieved
by the patient exercising on a treadmill
or cycling. Specific changes in the elec-
trical pattern as exercise levels increase
indicate
angina.
Cardiac stress testing
may be used in conjunction with
radio-
nuclide scanning
to identify damaged
areas of heart muscle.
cardiology
The study of the function of
the heart and the investigation, diagno-
sis, and medical treatment of disorders
of the heart and blood vessels.
cardiomegaly
Enlargement of the
heart.
Cardiomegaly may take the form of
hypertrophy
(thickening) of the heart
muscle or of dilatation (increase in
volume) of
1
or more of the heart cham-
bers. Hypertrophy occurs in conditions
in which the heart has to work harder
than normal to pump blood around the
body. These include
hypertension
,
pul-
monary hypertension,
and one type of
cardiomyopathy.
Dilatation of a heart
chamber may be due to heart valve
incompetence (failure of a valve to
close properly after a contraction) such
as occurs in
aortic insufficiency.
Symptoms may not occur until the
heart has enlarged to the point where it
cannot cope with additional stress. Its
reduced pumping efficiency leads to
heart failure,
with symptoms of breath-
lessness and ankle swelling. Cardiomegaly
is diagnosed by physical examination,
chest X-ray,
and
ECG.
Treatment is
directed at the underlying cause.
cardiomyopathy
Any disease of the
heart muscle that weakens the force of
cardiac contractions, thereby reducing the
efficiency of blood circulation. Cardio-
myopathies may have an infectious,
metabolic, nutritional, toxic, autoimmune,
or degenerative cause. However, in many
cases the cause is unknown.
There are 3 main types. In hypertrophic
cardiomyopathy, which is usually inher-
ited, the heart muscle is abnormally
thickened. In dilated cardiomyopathy,
metabolism
of the heart muscle cells is
abnormal and the walls of the heart
tend to balloon out under pressure.
Restrictive cardiomyopathy is caused by
scarring of the endocardium (the inner
lining of the heart) or by
amyloidosis
.
Symptoms of cardiomyopathy include
fatigue, chest pain, and palpitations.
The condition may lead to
heart failure
,
symptoms of which include breathing
difficulty and
oedema.
A
chest X-ray
may
show enlargement of the heart, and
echocardiography
may show thickened
heart muscle. A
biopsy
of heart muscle
may reveal muscle cell abnormalities.
Symptoms may be treated with
diuretic
drugs
to control heart failure and
anti-
arrhythmic drugs
to correct abnormal
heart rhythm. In many cases, heart mus-
cle function deteriorates, and the only
remaining option is a
heart transplant
.
cardiopulmonary bypass
The method
by which the circulation of blood around
the body is maintained while the heart is
stopped during heart surgery. A
heart-
lung machine
is used to maintain the
supply of oxygenated blood to the body.
cardiopulmonary resuscitation
The
administration of life-saving measures
to a person who has suffered a
cardiac
arrest.
A person in cardiac arrest is not
breathing and has no detectable pulse or
heartbeat. First, mouth-to-mouth resus-
citation (see
artificial respiration
) is given;
if this fails to restart breathing, repeated
chest compressions, using the heel of
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