The pulse waveform affected by arterial stiffness
Normal curve: 120/80
O2 is used during systolic phase = time heart (ventricular) muscle contracts to pump
Oxygen rich blood perfuses ventricular muscle during diastolic phase = rest phase
With normal arterial stiffness, the process is potentiated, and blood perfusion through the ventricular muscle is enhanced
Increased arterial stiffness
The reflected wave is more or less the same size as the forward wave or smaller (AI ≤ 100% )
The pulse curve is extended to accommodate the increase in pressure
Pump time is extended, and rest time is shortened – more O2 is used and less replenishment
The heart muscle is being exhausted
Arterial stiffness increased more
Reflected wave is larger than forward wave (AI ≥ 100%)
Pulse curve is extended PLUS load on ventricular muscle is increased
The ventricular muscle enlarges, and heart attack could follow
For increased BP and increased AI, variable exercise is required or
vasodilating medication
Stiffening of the large arteries increases the speed of the pulse waves.
The reflected wave reaches the aorta earlier and at first delays the next ejection period, thereby extending the time the myocardium uses oxygen.
In the same time the perfusion of the myocardium is impeded due to less kinetic energy stored in the aortic walls.
As arteries stiffen more, the reflected wave increases and becomes larger than the forward wave.
The afterload on the myocardium increases.
The combined effect of extended pump time, decreased oxygen rich blood perfusion and myocardial load, eventually leads to enlargement of the heart and heart failure or CV event.
Reflected wave affecting the central pulse pressure waveform¹⁰
Analysis of central pulse pressure waveform (Modified from JMA Journal: Volume 4, Issue 2 )
Arterial stiffness is expressed as central or peripheral Augmentation index (AI)
Central Augmentation Index (AIx)
Central and brachial augmentation indexes are calculated in different ways: Central AIx is defined for a central pressure waveform as the ratio of Augmentation Pressure (CAP) to Pulse Pressure (PP): AIx = CAP / cPP (Wilkinson et al., 2000).
Peripheral augmentation index (pAI)
Peripheral augmentation index (pAI) on the other hand is defined (as a %) as the ratio of late systolic pressure (P2) to early systolic pressure (PI): pAI = P2 / PI (Wilkinson et al., 2000).
