Can Augmentation Index Quantify Impact of Pulse Wave Reflection in Isolated Systolic Hypertension?

Systolic and diastolic blood pressures are determined, in part, by pressure pulse‐waves generated by the heart that are reflected back from multiple sites in the periphery. The magnitude and timing of the reflected pulse‐wave is significantly altered in isolated systolic hypertension (ISH), and results in significant changes in pulse pressure morphology. Conventional belief states that the recorded aortic pressure above a distinctive inflection point in the systolic pulse contour is a result of 'augmentation' due to the early arrival of reflected pulse‐wave. Accordingly, the ratio of augmented pressure to pulse pressure, Augmentation Index (AI), has been introduced to quantify the contribution of reflection. To test AI estimation, we utilized a 121‐element arterial system model which predicts realistic pressure and flow in the vessel segments, followed by analysis of experimental data, to demonstrate that the notion of augmentation index widely misinterprets the contribution of reflected waves in cases of a very compliant system or ISH. In the first case, forward and reflected pulses can add destructively and thus decrease pulse pressure, rather than augment it, resulting in negative augmentation. In the second case, the arterial system degenerates into a classical 2‐element Windkessel, and pulse wave reflection ceases to affect arterial pressure pulses, resulting in 37% overestimation of augmentation.