Page 93 - Biomedical Engineering and Design Handbook Volume 1, Fundamentals

70 BIOMECHANICS OF THE HUMAN BODY

FIGURE 3.1 General organization of the circulatory system with averaged
values of normal blood flow to major organs.

2
2
area of 2.5 cm ) is 33 cm/s, while in the capillaries (cross-sectional area of 2500 cm ) it is
about 0.3 mm/s. The blood remains in the capillaries 1 to 3 seconds (Guyton and Hall, 1996;
Saladin, 2001).
At normal conditions, the pulsatile pumping of the heart is inducing an arterial pressure that fluc-
tuates between the systolic pressure of 120 mmHg and the diastolic pressure of 80 mmHg (Fig. 3.2).
The pressure in the systematic capillaries varies between 35 mmHg near the arterioles to 10 mmHg
near the venous end, with a functional average of about 17 mmHg. When blood terminates through
the venae cavae into the right atrium of the heart, its pressure is about 0 mmHg. When the heart ejects
blood into the aorta, a pressure pulse is transmitted through the arterial system. The traveling veloc-
ity of the pressure pulse increases as the vessel’s compliance decreases; in the aorta it is 3 to 5 m/s,
in the large arteries 7 to 10 m/s, and in small arteries 15 to 35 m/s. Figure 3.3 depicts an example of
the variations in the velocity and pressure waves as the pulse wave travels toward peripheral arteries
(Caro et al., 1978; Fung, 1984).