HEART-LUNG MACHINE
HEART-RATE
H
Echocardiography
is useful for investi-
gating congenital heart defects and
abnormalities of the valves or heart
wall. An ultrasound technique using the
Doppler effect
allows measurement of
blood flow through valves.
Radionuclide
scanning
and
CT scanning
provide infor-
mation about the efficiency of heart
function.
Angiography
may be used to
show the heart chambers and to assess
the condition of the coronary arteries
and valves. High-quality images of the
heart can be obtained by
MRI.
heart-lung machine
A machine that
temporarily takes over the function of
the
heart
and
lungs
to facilitate opera-
tions such as
open heart surgery
,
heart
transplants
,
and
heart-lung transplants
.
A heart-lung machine consists of a
pump (to replace the heart's function)
and an oxygenator (to replace the lung's
function ). It bypasses the heart and
lungs, and the heart can be stopped.
Use of a heart-lung machine tends to
damage red blood cells and to cause
blood clotting. These problems can be
minimized, however, by the adminis-
tration of
heparin
, an anticoagulant
drug, beforehand.
heart-lung transplant
A procedure in
which the
heart
and
lungs
of a patient
are removed, and replaced with donor
organs. This surgery is used to treat dis-
eases in which the lung damage has
affected the heart, or vice versa. Such
diseases include
cystic fibrosis
,
fibrosing
alveolitis
,
and some severe congenital
heart defects (see
heart disease, congen-
ital
).
A
heart-lung machine
is used to
take over the function of the patient's
heart and lungs during the operation,
which is no more dangerous than a
heart transplant
.
heart-rate
The rate at which the
heart
contracts to pump blood around the
body. Most people have a heart-rate of
between 60 and
100
beats per minute at
rest. This rate tends to be faster in
childhood and to slow slightly with age.
Very fit people may have a resting rate
below 60 beats per minute.
The heart muscle responds automati-
cally to any increase in the amount of
blood returned to it from active muscles
by increasing its output. During extreme
exercise, heart-rate may increase to
200
contractions per minute and the output
to almost 250 ml per beat.
HEART-LUNG MACHINE
Site of
operation
Tubes carry blood from
the heart to the machine
Anaesthetist
Intravenous
fluid
Aorta
Technician
Endotracheal
tube delivers
anaesthetic
Anaesthetic
machine
Superior
vena cava
Tube returns
blood to the
circulation .
Tubes carry
blood to the
machine
Inferior
vena cava
SITE OFTHE
CONNECTIONS
Heart-lung
machine
Tube returns blood
to the circulation
274
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