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					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


                                                         — First, the central systolic pressure and
                                     Increased Central
                                       Pulse Pressure
                                                           central pulse pressure is increased.
                                                         — an increase in the central pulse pressure
                                                           that drives cerebral blood flow increases
                                                           stroke risk.
    PP
                                                         — 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


                                                         — Second, there is an increase in left
                                     Increased LV Load     ventricular load (LV load).
            LVL
                                                         — 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


                                                           — Third, the pressure that is perfusing the
                                                             coronary arteries during the critical
                                                             diastole period is reduced, increasing
                                                             the risk of myocardial ischemias.
                           Decreased Coronary Artery       — Conclusion: Increasing arterial
                          Perfusion Pressure in Diastole
                                                             stiffness independently increases the
                                                             risk of all three major cardiovascular
                                                             outcomes.




                          Figure 8


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