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Arterial Pulse Pressure
As the left ventricle ejects blood into the aorta,
the aortic pressure increases. The greater the stroke volume, the greater
the change in aortic pressure during ejection. The maximal change in aortic
pressure during systole (from the time the aortic valve opens until the peak
aortic pressure is attained (see Cardiac Cycle)
represents the aortic pulse pressure, which is defined as the systolic pressure
minus the diastolic pressure. For example, if the systolic pressure is 130 mmHg
and the diastolic pressure is 85 mmHg, then the pulse pressure is 45 mmHg.
Pulse
Pressure = Systolic Pressure ─ Diastolic Pressure
 The rise in aortic pressure from its diastolic to
systolic value is determined by the compliance of the
aorta as well as the ventricular stroke volume. In the arterial system, the aorta has the highest compliance,
due in part to a relatively greater proportion of elastin fibers versus smooth muscle and
collagen. This serves the important function of dampening the pulsatile output of the left
ventricle, thereby reducing the pulse pressure (systolic minus diastolic arterial
pressure). If the aorta were a rigid tube, the pulse pressure would be very
high. Because the aorta is compliant, as blood is ejected into the aorta, the
walls of the aorta expand to accommodate the increase in blood volume. As the
aorta expands, the increase in pressure is determined by the compliance
of the aorta at that particular range of volumes. The more
compliant the aorta, the smaller the pressure change during ventricular ejection (i.e.,
smaller pulse pressure) (see figure). Therefore, aortic compliance is a major determinant,
along with stroke volume, of the pulse pressure.
Summary:
A highly compliant aorta (i.e., less stiff)
has a smaller pulse
pressure for a given stroke volume into the aorta.
A larger stroke volume (not shown in
the figure) produces
a larger pulse pressure at any given compliance.
Aortic compliance decreases with age
due to structural changes, thereby producing age-dependent increases in pulse pressure.
For a given stroke volume, compliance determines pulse
pressure and not mean aortic pressure.
However, because vessels display dynamic compliance, increasing the rate of ventricular ejection (as occurs with increased ventricular
inotropy) will increase the pulse pressure compared to the same volume ejected at a lower
rate.
RK Revised
03/29/2007
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Cardiovascular Physiology Concepts
