Bma Illustrated Medical Dictionary

Echocardiographyis 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

scanningand CT scanning provide infor-

mation about the efficiency of heart

function. Angiographymay 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 machineA machine that

temporarily takes over the function of

the heartand lungsto 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 transplantA procedure in

which the heartand lungsof 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 machineis 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-rateThe 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

HEART–LUNG MACHINE HEART-RATE

H

Heart–lung

machine

Site of

operation

Intravenous

fluid

Endotracheal

tube delivers

anaesthetic

Anaesthetic

machine

Anaesthetist

Technician

SITE OF THE

CONNECTIONS

Heart

Aorta

Tube returns blood

to the circulation

Tube returns

blood to the

circulation

Tubes carry

blood to the

machine

Inferior

vena cava

Superior

vena cava

Tubes carry blood from

the heart to the machine