Biomedical Engineering Reference
In-Depth Information
FIGURE 4.14 The coronary arteries that sup-
ply the entire cardiac muscle with blood. These
vessels are principal locations for atherosclerotic
lesions and other cardiac diseases. Depending
on the severity of the damage to these vessels,
blood flow to the cardiac muscle cells can be
severely impaired.
Aorta
Left coronary
artery
Common area for
atherosclerotic
lesions to form
Right coronary
artery
75% of the cardiac tissue. The remaining portions of the cardiac muscle are supplied with
blood from the right coronary artery. The coronary blood vessels branch into smaller ves-
sels that penetrate the muscle mass to supply blood to the entire heart. Because the heart
never rests, it requires about 5% of the total cardiac output, which amounts to approxi-
mately 250 mL/min, to maintain its function. The majority of the venous coronary blood
flow is returned directly to the right side of the heart via the coronary sinus. Also, a small
portion of deoxygenated blood is returned to all chambers of the heart via thebesian veins.
The thebesian veins are similar to open-ended blood vessels, which penetrate the cardiac
mass and open to all four heart chambers.
The flow within the coronary blood vessels is quite interesting, because the majority of
the blood flow occurs during diastole and the flow almost ceases during systole. This is
the reverse of what happens in most other vascular beds. The reason for this reversed
flow is that during systole the cardiac muscle contracts, which causes a compression of the
coronary blood vessels. This compression is so severe that the resistance to blood flow
increases significantly, and the blood flow pressure gradient is not enough to overcome
the resistance to motion. During diastole, the cardiac muscle relaxes and relieves the con-
striction of the coronary blood vessels. Therefore, the resistance to flow reduces and blood
flow continues again. This is especially prevalent in the blood vessels that supply the left
ventricular muscle mass as compared to the right ventricular muscle mass, because the
muscle contraction is much stronger there.
Coronary artery disease is still the most common cause of death in the Western world.
Coronary artery disease lumps together pathologies that lead to a reduction in coronary
blood flow, which can eventually lead to myocardial infarction (see Section 4.6.2 ). In the
United States, the most common cause of coronary artery disease is atherosclerosis.
Atherosclerosis can be initiated by genetic factors or by lifestyle choices (such as eating
foods high in cholesterol). Either way, atherosclerosis initiates through the deposition of
large quantities of cholesterol within the sub-endothelial space. Cholesterol deposits can
be found throughout the body, but many vascular beds can adapt to this reduction in
blood flow. Due to the fact that the coronary arteries are not as adaptable as other vascular
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