HEART SOUNDS
HEART TRANSPLANT
The heart-rate is also regulated by the
autonomic nervous system
.
The parts of
this system concerned with heart action
are a nucleus of nerve cells, called the
cardiac centre, in the
brainstem
,
and
2
sets of nerves (the parasympathetic and
sympathetic).
At rest, the parasympathetic nerves -
particularly the
vagus nerve
- act on the
sinoatrial node to maintain a slow
heart-rate. During or in anticipation of
muscular activity, this inhibition less-
ens and the heart-rate speeds up.
Sympathetic nerves release
noradrenaline
,
which further increases the heart-rate
and force of contraction. Sympathetic
activity can be triggered by fear or
anger, low blood pressure, or a reduc-
tion of oxygen in the blood.
Release of
adrenaline
and noradren-
aline by the adrenal glands also acts to
increase heart-rate.
The rate and rhythm of the heart can
be measured by feeling the
pulse
or by
listening with a
stethoscope
;
a more
accurate record is provided by an
ECG
.
A resting heart-rate above 100 beats
per minute is termed a
tachycardia
, and a
rate below 60 beats per minute a
brady-
cardia
.
(See also
arrhythmia, cardiac
.)
heart sounds
The sounds made by the
heart
during each
heartbeat
.
In each
heart cycle, there are
2
main heart
sounds
that
can
clearly
be
heard
through a
stethoscope
.
The first is like a
"lubb". It results from closure of the
tri-
cuspid
and
mitral valves
at the exits of
the atria, which occurs when the ventri-
cles begin contracting to pump blood
out of the heart. The second sound is a
higher-pitched "dupp" caused by clo-
sure of the pulmonary and aortic valves
at the exits of the ventricles when the
ventricles finish contracting.
Abnormal heart sounds may be a sign
of various disorders. For example, high-
pitched sounds or "clicks" are due to
the abrupt halting of valve opening,
which can occur in people with certain
heart valve
defects. Heart
murmurs
are
abnormal sounds caused by turbulent
blood flow. These may be due to heart
valve defects or congenital heart disease.
heart surgery
Any operation that is
performed on the
heart
.
Open heart
surgery
allows the treatment of most
types of heart defect present at birth
(see
heart disease, congenital
) and vari-
ous
disorders
of the
heart valves
.
Coronary artery bypass
is performed to
treat obstruction of the coronary arter-
ies. Narrowing of the coronary arteries
can be treated by balloon
angioplasty.
Angioplasty balloons have also been
used to open up narrowed heart valves
in cases where the patient is unsuitable
for open heart surgery (see
valvulo-
plasty). Heart transplant
surgery can
offer hope to people with progressive,
incurable heart disease.
heart
transplant
Replacement of a
patient's damaged or diseased
heart
with a healthy heart taken from a donor
at the time of death. Typically, trans-
plant patients have advanced
coronary
artery disease
or
cardiomyopathy
. During
the operation, the function of the heart
is taken over by a heart-lung machine.
HEART TRANSPLANT
SITE OF
INCISION
Back walls of atria
are left in place _
Diseased area
to be replaced
Aorta
Pulmonary
artery
Most of the diseased heart is removed,
but the back walls of the atria (upper
chambers) are left in place. The ventricles
(upper chambers) are then attached to
the remaining areas of the recipient's
heart. Once the immediate post-opera-
tive period is over, the outlook is good.
Patients face the long-term problems
associated with other forms of
transplant
surgery.
(See also
heart-lung transplant.)
275
previous page 273 BMA Illustrated Medical Dictionary read online next page 275 BMA Illustrated Medical Dictionary read online Home Toggle text on/off