1.2 Augmentation Index is Not a Valid Measure of Wave Reflection when it is Negative and this Distorts the Presumed Relationship Between Aging and Wave Reflection

Background The relationship between aging and wave reflection has been disputed [1, 2]. Augmentation index (AI x ) increases with increasing age, however the validity of AI x as a measure of wave reflection, particularly when AI x is negative is unknown. Methods Measurements of carotid pressure and flow velocity were made in the carotid artery of 65 healthy normotensive individuals (age 21–78yr; 43 male). AI x , wave reflection index (WRI) and P b /P f were calculated. Results AI x was positively correlated with age (beta (95% CI) = 0.46 (0.19, 0.73); p = 0.001). In contrast log WRI and P b /P f showed negative associations with age (beta (95% CI) = −0.009 (−0.016, −0.002) p = 0.01 and −0.001 (−0.001, −0.000); p = 0.001 respectively). AI x did not correlate with WRI or P b /P f , although AI x and WRI correlated weakly when AI x was restricted to positive values (rho = 0.35; p = 0.03). In contrast log WRI and P b /P f were closely correlated (r = 0.66; p < 0.001). Wave intensity analysis showed that negative augmentation was due to a forward decompression wave in mid systole and was consequently an unreliable indicator of reflected compression waves. Conclusions Augmentation index is not a valid measure of wave reflection when it is negative; this is common in younger individuals and distorts the relationship between aging and wave reflection. In healthy normotensive individuals wave reflection in the common carotid artery decreases with increasing age