Augmentation Index (AIx)

Aortic Augmentation index (AIx) is frequently used to gauge arterial efficiency through effects of aortic stiffening and peripheral wave reflection. The effect of wave reflection on the aortic systolic pressure peak can be described as augmentation. Accordingly, augmentation is a measure of the additional pressure caused by pulse wave reflection that is seen by the left ventricle. AIx is a noninvasive measure of pulse wave reflection. Augmentation index, non-invasively determined manifestation of increased wave reflection, is a strong, independent risk marker for coronary artery disease (CAD), premature atherosclerosis (endothelial dysfunction) and it is a strong indicator for cardiovascular risk.

The endothelial dysfunction is accompanied with increased vascular resistance (TPR) which can be detected by Arteriograph as elevated Augmentation index. Elevated AIx is associated with an elevated risk of future cardiovascular events. Augmentation index values have been found to strongly correlate with the risk of developing coronary artery disease in asymptomatic individuals with no prior history of coronary artery disease.

The left ventricle ejects a limited amount of blood upon contraction which generates a pressure wave. The Augmentation pressure calculation is based on the difference of the forward pressure wave generated by the left ventricular ejection and a reflected wave created by the impedance mismatch along the peripheral arteries. 

Augmentation index can be calculated by using the following formula

AIx = 100 × ((P2-P1)/ (Pulse Pressure)).