Fig. 1.

Illustration of augmentation index calculation in stiff (upper panel) and normal vessels (lower panel). The left panel illustrates tonometrically measured radial artery wave form obtained from a patient prior to CABG surgery (upper panel) and a healthy volunteer (lower panel). The right panels show derived aortic waveforms. The augmentation index is calculated as the quotient of the difference between systolic blood pressure and the pressure measured at the inflection point of the waveform over the pulse pressure. In normal vessels (lower panel) the augmented pressure resulting from reflected waves is small in magnitude and occurs during diastole. In contrast, in stiff vessels (upper panel), the augmented pressure is amplified and occurs during systole, resulting in increased pulsatile load in the cardiovascular system.