Computational Intelligence in Cardiology and Heart Disease Diagnosis - Computational Intelligence in Biomedical Engineering - page 151

pauses in the AV node bundle allowing the atria to empty all their blood
into the ventricles. The impulse then spreads through the ventricular muscles
through the His-Purkinje system causing ventricular contraction. The impulse
must follow this exact route to ensure proper heart function. Although the SA
cells create the impulse that causes the heart to beat, other nerves function to
change the rate at which the SA cells fire. These nerves are part of the auto-
nomic nervous system, which is divided into the sympathetic nervous system
and the parasympathetic nervous system. The sympathetic nerves increase the
heart rate and the force of contraction, whereas the parasympathetic nerves
inhibit or slow the rate of contraction.
4.2.5 The Cardiac Cycle
The heart pumps oxygen-rich blood to body organs and tissues and deoxy-
genated blood back to the lungs to be reoxygenated. This circulation system
is vital to the sustainment of bodily functions and is referred to as the cardiac
cycle . The major blood vessels that carry either oxygen-rich blood or deoxy-
genated blood can be divided into arteries, veins, and capillaries. Arteries
carry oxygenated blood with the exception of the pulmonary artery, whereas
veins carry deoxygenated blood with the exception of the pulmonary vein. At
the top of the heart, two of the major blood vessels emerge, the aorta and the
pulmonary artery (see Figure 4.6). The superior vena cava and inferior vena
cava enter the right-hand side of the heart, whereas the pulmonary vein enters
the left-hand side. It is sometimes easier to visualize the circulation system as
being composed of two separate systems as seen in Figure 4.7.
The first system consisting of the right atrium and right ventricle is respon-
sible for receiving deoxygenated blood from the body and sending it to the
lungs where carbon dioxide can be exchanged for oxygen. Deoxygenated blood
is carried by the body in veins, which cumulate in the superior and inferior
vena cava. The superior vena cava carries the sum of deoxygenated blood from
the upper half of the body, whereas the inferior vena cava carries deoxygenated
blood from the lower half. These two veins join to form a single vena cava, and
this blood vessel empties into the right atrium, which contracts and pushes the
blood into the right ventricle. The time of atrium contraction is known as the
diastole phase , and it is during this phase that the tricuspid valve opens to
allow passage of blood into the ventricle. The term “diastole” is used to refer
to heart relaxation during which the ventricle chambers are filled with blood.
When blood is pumped from the atrium into the ventricle, the ventricular
pressure increases with respect to the atrium pressure. To avoid a backflow of
blood into the atrium, the AV valve (tricuspid in this case) is closed and pre-
vented from opening. When it is full, the right ventricle contracts and pumps
the deoxygenated blood into the pulmonary artery, which leads to the lungs.
The phase of ventricle contraction is known as systole and the tricuspid valve
is also closed to prevent blood flowing into the empty atrium.
The second system responsible for distribution of oxygenated blood to the
body is composed of the left atrium and left ventricle. The newly oxygenated