Biomedical Engineering Reference
In-Depth Information
Fig. 2.12  Schematic of
venous blood vessel. Valves
are present along the blood
vessels allowing only a one-
way flow and hence prevents
flow reversal
the arteries, while the epicardial vessels stay patent. During the diastolic phase, the
intraventricular pressures decreases and myocardial perfusion occurs.
Coronary arteries are vital to the functions of the heart. Myocardial ischemia
is a condition of the heart whereby oxygenated blood is unable to be supplied ad-
equately. During atherosclerosis, blood flow in coronary arteries is obstructed, and
intense chest pain known as myocardial angina occurs, which results in heart fail-
ure. Prolonged ischemic conditions cause the myocardium to weaken from hypoxia
during myocardial infarction 4 .
The left and right coronary arteries branch out from the left and right aortic sinus
respectively, which is near the aortic root just above the aortic valve. The posterior
descending artery or posterior inter-ventricular artery determines the coronary dom-
inance of the heart.
2.2.6
Physiology of the Vascular Network
The relatively large arteries branch into a network of arterioles that become a sys-
tem of capillaries, which enables maximum transfer of nutrients between the blood
and the vital organs. Capillaries have micro-thin walls that facilitate nutrient trans-
fer and at downstream flows, they merge to become venules, which are further re-
structured into larger vessels to form veins. Veins are notably smaller than arteries
in terms of diameter and strength as they need not withstand high pressures and do
not transfer as much materials. In addition, valves are present along the vessel to
prevent flow reversal (Fig. 2.12 ).
Blood flow characteristics such as velocity and pressure, as well as the total area
of the vascular structure along the structural transition from artery to vein is shown
in Fig. 2.13 . The artery is a multi-layer of muscles and connective tissue that serves
the purpose of transporting blood (Refer to Fig. 2.1 ). The wall of an artery typically
comprises three layers: the intima, media and adventitia. To minimize flow resis-
tance, the internal of the arterial wall is lined with a smooth and thin endothelium.
Damage to the endothelium results in disease of the artery, which will be described
in Sects. 2.3.1 and 2.3.5. Next to the endothelium is the basement membrane, which
allows diffusion of nutrients and waste. At the next level, the elastic layers absorb
energy from the blood to minimize arterial deformation and provide structural rigid-
ity to maintain the flow channel. The elastic properties of the artery declines as it
4 Myocardial infarction is the medical term for a heart attack which is a result of blockage in the
cardiovascular network that prevents blood flow to the heart a long enough time that part of the
heart muscle becomes damaged or dies.
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