Transcript Pressure Wave Reflection

Pressure Wave Reflection at the Heart
Why arterial stiffness is the major cause of heart failure, stroke and myocardial ischemia.
Pressure Wave Reflection at the Heart
— If there was no wave reflection (ie. the
aorta was an open-ended tube providing
a simple resistance to flow), then:
— the pressure wave in the aortic root
would be the same as the flow wave (see
graph).
Figure 1
Figure 1
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Pressure Wave Reflection at the Heart
— Now if we connect up the network of
arteries with all its bifurcations and
vascular beds, then:
— as this primary wave travels along the
arteries it will generate reflected waves
from each bifurcation and from the
peripheral vascular beds.
— all these small reflect-ed waves return to
the heart, summing to create a reflected
wave as shown, starting even before the
end of systole.
Figure 2
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Pressure Wave Reflection at the Heart
— So the pressure in the aortic root is the
sum of the outgoing and reflected wave
(the green wave).
— note importantly how the reflected wave
boosts the coronary artery perfusion
pressure – the aortic root pressure –
during diastole when over 95% of
perfusion of the sub-endocardium takes
place.
Figure 3
Figure 3
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Pressure Wave Reflection at the Heart
— The speed at which the outgoing and
reflected waves travel is dependent on
the stiffness of the arteries along which
they
are travelling.
— So if a person has stiffer arteries, the
waves will travel out and back quicker,
arriving earlier back at the heart (see
graph).
Figure 4
Figure 4
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Pressure Wave Reflection at the Heart
— Now when the outgoing and reflected
waves are added there is a very different
aortic root pressure waveform.
— there are three important clinical
implications.
Figure 5
Figure 5
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Pressure Wave Reflection at the Heart
Increased Central
Pulse Pressure
PP
— First, the central systolic pressure and
central pulse pressure is increased.
— an increase in the central pulse pressure
that drives cerebral blood flow increases
stroke risk.
— NOTE: this change in central systolic
pressure can occur without any changes
occurring in peripheral cuff systolic
pressure.
Figure 6
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Pressure Wave Reflection at the Heart
Increased LV Load
 LVL
— Second, there is an increase in left
ventricular load (LV load).
— increase in LV load accelerates increase
in LV mass and increases risk of
LV hypertrophy.
— the area under the pressure-time curve
during systole is by definition LV load.
— this increase in LV Load (late systolic
“afterload”) is shown by the black
arrowed region.
Figure 7
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Pressure Wave Reflection at the Heart
Decreased Coronary Artery
Perfusion Pressure in Diastole
— Third, the pressure that is perfusing the
coronary arteries during the critical
diastole period is reduced, increasing
the risk of myocardial ischemias.
— Conclusion: Increasing arterial
stiffness independently increases the
risk of all three major cardiovascular
outcomes.
Figure 8
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