Biomedical Engineering Reference
In-Depth Information
Fig. 1 Normal blood pressure in the circulatory system. The pulmonary circulation has much
lower pressures and pulsations that extend into the capillaries (Redrawn from Sherwood [ 4 ])
Vasoconstriction is regulated by factors including, paracrine factors, hormones and
neurotransmitters, while vasodilatation is regulated by paracrine factors and acti-
vation of the nervous system. The SMCs also play a role in increasing the diameter
of the vessel during vasodilatation allowing for the decrease of vascular resistance
enabling blood flow and pressure to decrease [ 4 ].
The cyclic pumping function of the heart creates a pulsatile component in the
arteries, thus blood flow and pressure are also pulsatile. The heart cycle includes
periods of systole, heart contraction, and diastole, heart relaxation. During systole,
blood is pumped out of the heart into the arteries. Pulse pressure is a measure of
the change in blood pressure during heart contraction, or systole. When the heart is
at rest (diastole) no new blood is pumped into the arteries, however, blood will
advance to peripheral arterial segments. Large arteries that carry blood away from
the heart provide a reservoir for high pressure allowing pulse pressure to decrease
in the downstream arteries and cause the flow to become more steady or uniform.
There are two major factors that affect pulse pressure, the stroke volume (blood
output of the heart) and the compliance of the arterial trees [ 8 ]. The higher the
stroke volume, the higher the volume of blood that must be accommodated in the
arterial tree which results in either a higher pressure during systole or a higher
pulse pressure. The less compliant the arterial tree the greater the pulse pressure to
pump blood into the arterioles.
2 Vascular Stiffness
Many vascular diseases, such as pulmonary hypertension and coronary heart
disease, are characterized by increased blood flow and pressure in the arteries [ 9 ].
Arteries maintain a homeostatic stress/strain range, stress or strain outside of this
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