The augmentation index (AI) is a measure of wave reflection but also depends on the wave shapes of the forward and reflected pressure waves. The shape of the forward wave is determined by the interaction between the heart and the vasculature and thus is, in part, determined by cardiac function. The reflection magnitude, (RM, the ratio of the backward and forward wave), may be less dependent on cardiac function. We therefore investigated quantitatively how cardiac function affects AI and RM.

A mathematical model of the arterial system allowed calculation of pressures using flow waves with a range of shapes from convex to concave, with the form factor (peak flow / stroke volume; convex flow has a low form factor) ranging from 5.5 to 9.6. Arterial stiffness was varied from 0.5 to 3 times control and AI and RM were calculated from central aortic pressure and flow.

The form factor of the flow had a larger effect on the AI than on the RM, and at all form factors arterial stiffness had a larger effect on the AI than on the RM.

We conclude that the flow wave shape, and thus cardiac function, has a considerable effect on the AI.