Page 11, Hemodynamics, Dr. D. Penney


Let us compare the kinetic energy component as a percent of the total fluid energy, first in an individual at resting cardiac output, then in one with a 3-fold increase in cardiac output. For the aorta (mean pressure), kinetic energy represents only about 0.4% of the total fluid energy. Thus, kinetic energy is insignificant under those conditions. In the vena cavae, on the other hand, kinetic energy represents 12% of the total fluid energy. At this value it is starting to become significant. In the vena cavae at the higher cardiac output, kinetic energy can be as much as 52% of the total fluid energy. Thus it is very significant under these conditions.

In the aorta, again under similar conditions, kinetic energy rises to about 2.6% of total energy, because flow velocity rises sharply while pressure increases only modestly. Thus, kinetic energy remains relatively insignificant in the aorta. Therefore, under most conditions in the arterial system kinetic energy is an insignificant portion of the total fluid energy. This is because even though the arteries have high flow velocities, the pressure is so high that the pressure energy component is dominant. On the other hand, in the venous system, the pressures are so low that even with modest flow velocity the kinetic energy portion of total fluid energy becomes substantial. [SEE MISCONCEPTION 12]



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