njit-etd2003-081 - New Jersey Institute of Technology

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2.2 Blood Pressure
The force that blood exerts against the walls of a vessel is called blood pressure.
Normally, some amount of blood is present in every blood vessel of the body, including
all arteries, arterioles, capillaries, venules and veins.
Blood volume is greatest in the veins. Venous blood pressure, however, is quite
low because the vein walls are thin and compliant. Skeletal movement, mechanical
movement from respiration and one-way valves, facilitates return of deoxygenated blood
to the heart.
Less than fifteen percent of the blood volume is present in the arteries. Mean
arterial pressure, however, is approximately 100 mm Hg. Mean arterial pressure (MAP)
[6] depends upon total peripheral resistance (TPR) and cardiac output (CO).
Specifically:
The resistance of a particular arteriole depends upon the associated organ's
requirements. Under different conditions, an arteriole radius will be varied by control
mechanisms to accommodate the need of the associated organ. If the overall radius of all
arterioles decreases, then the TPR is increased, which may cause arterial blood pressure
to increase, depending upon the CO value.
When blood flows into arteries and arterioles, stretching occurs due to the
pressure that blood exerts on the arterial walls. The maximum pressure, which is
reached when the ventricles eject blood, is called the systolic pressure. The minimum
arterial pressure occurs just before ventricular ejection begins and is called diastolic
pressure [5].