Page 92 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

CHAPTER 3

PHYSICAL AND FLOW

PROPERTIES OF BLOOD

David Elad and Shmuel Einav
Tel Aviv University, Tel Aviv, Israel

3.1 PHYSIOLOGY OF THE CIRCULATORY 3.5 BLOOD FLOW IN THE
SYSTEM 69 MICROCIRCULATION 84
3.2 PHYSICAL PROPERTIES OF 3.6 BLOOD FLOW IN THE HEART 86
BLOOD 72 3.7 ANALOG MODELS OF BLOOD FLOW 89
3.3 BLOOD FLOW IN ARTERIES 73 ACKNOWLEDGMENT 91
3.4 BLOOD FLOW IN VEINS 82 REFERENCES 91

3.1 PHYSIOLOGY OF THE CIRCULATORY SYSTEM

The circulatory transport system is responsible for oxygen and nutrient supply to all body tissues
and removal of waste products. The discovery of the circulation of blood in the human body is
related to William Harvey (1578–1657). The circulatory system consists of the heart—the pump
that generates the pressure gradients needed to drive blood to all body tissues, the blood vessels—
the delivery routes, and the blood—the transport medium for the delivered materials. The blood
travels continuously through two separate loops; both originate and terminate at the heart. The
pulmonary circulation carries blood between the heart and the lungs, whereas the systemic circu-
lation carries blood between the heart and all other organs and body tissues (Fig. 3.1). In both
systems blood is transported in the vascular bed because of a pressure gradient through the following
subdivisions: arteries, arterioles, capillaries, venules, and veins. The cardiac cycle is composed of
the diastole, during which the ventricles are filling with blood, and the systole, during which the
ventricles are actively contracting and pumping blood out of the heart (Martini, 1995; Thibodeau
and Patton, 1999).
The total blood volume is unevenly distributed. About 84 percent of the entire blood volume
is in the systemic circulation, with 64 percent in the veins, 13 percent in the arteries, and 7 percent
in the arterioles and capillaries. The heart contains 7 percent of blood volume and the pulmonary
vessels 9 percent. At normal resting activities heart rate of an adult is about 75 beats/min with a
stroke volume of typically 70 mL/beat. The cardiac output, the amount of blood pumped each
minute, is thus 5.25 L/min. It declines with age. During intense exercise, heart rate may increase
to 150 beats/min and stroke volume to 130 mL/beat, providing a cardiac output of about 20 L/min.
Under normal conditions the distribution of blood flow to the various organs is brain, 14 percent;
heart, 4 percent; kidneys, 22 percent; liver, 27 percent; inactive muscles, 15 percent; bones,
5 percent; skin, 6 percent; bronchi, 2 percent. The averaged blood velocity in the aorta (cross-sectional

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