Page 37 - Libro 2

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Arterial Physiology
Ann Marie Kupinski
OBJECTIVES
KEY TERMS
inertia | kinetic energy | laminar flow | potential energy | pressure | resistance | turbulence | velocity | viscosity
GLOSSARY
inertia the tendency of a body at rest to stay at rest or a body in motion to stay in motion
kinetic energy the energy of work or motion; in the vascular system, it is in part represented by the velocity of blood flow
laminar flow flow of a liquid in which it travels smoothly in parallel layers
Poiseuille’s law the law that states that the volume flow of a liquid flowing through a vessel is
A general understanding of the physiology of the vascular system is important when performing ul- trasounds on the circulatory system. Although anat- omy provides information on the structures being scanned, one must understand function too. There are numerous factors that impact the arterial system. Relationships that govern blood flow result in spectral waveforms that can vary depending on the system be- ing scanned. This chapter will review the basics of normal arterial physiology as well as pathophysiology.
FLUID ENERGY
Blood, like any other fluid, will move from one point to another in response to differences in total energy. The total energy of a system is made up of both po- tential and kinetic energy. Potential energy is also known as stored or resting energy. In the vascular sys- tem, it is represented primarily by the intravascular pressure, which distends the vessels. This pressure is supplied by the contraction of the heart. Kinetic
directly proportional to the pressure of the liquid, and the fourth power of the radius is inversely proportional to the viscosity of the liquid and the length of the vessel
potential energy the stored or resting energy; in the vascular system, it is the intravascular pressure
viscosity the property of a fluid that resists the force tending to cause fluid to flow
energy is the energy of work or motion. The velocity of moving blood represents the kinetic energy com- ponent of the vascular system. Blood will move from an area of high energy (pressure) to an area of lower energy (pressure). The highest pressure in the vas- cular system occurs in the left ventricle of the heart where the pressure is approximately 120 mm Hg. The blood leaves the left ventricle, flowing down an energy (pressure) gradient until it returns to the right atrium. The lowest pressure is found at the right atri- um where pressure is 2 to 6 mm Hg.
There is another component to the energy of the vas- cular system related to differences in the level of body parts. Gravitational potential energy is the potential for doing work related to the force of gravity. If blood is positioned above a reference point (which is usually the right atrium), it has the ability to do work because gravity will act on the blood to move it downward. The gravitational potential energy is reduced in de- pendent parts of the body (below the reference point). Hydrostatic pressure is also pressure within the ves- sels related to the reference point of the right atrium.
List the various hemodynamic forces acting upon the arterial system
Describe the relationship between pressure, flow, and resistance
Identify the factors that control peripheral blood flow
Define physiologic changes associated with arterial disease
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