Inadequacy of Augmentation Index for Monitoring Arterial Stiffness: Comparison with Arterial Compliance and Other Hemodynamic Variables.

Purpose: Augmentation Index (AI) is used clinically for monitoring both wave reflections and arterial stiffness, which when increased is a risk factor of cardiovascular mortality and morbidity. We hypothesize that AI is not solely related to vascular stiffness as described by arterial compliance and other hemodynamic parameters since AI underestimates wave reflections.

Methods: Aortic pressure and flow datasets (n = 42) from mongrel dogs were obtained from our experiments and Mendeley Data under various conditions. Arterial compliances based on the Windkessel model (C), the stroke volume (SV) to pulse pressure (PP) ratio (C = SV/PP), and at inflection pressure point (C) were computed. Other relevant hemodynamic factors are also computed.

Results: AI was poorly associated with arterial stiffness calculated from C (r = 0.299, p = 0.058) or C (r = 0.203, p = 0.203), even when adjusted for heart rates. C and C were monotonically associated. Alterations in inflection pressure (P) did not follow the changes in pulse pressure (PP) (r = 0.475, p = 0.002), and P was quantitatively similar to systolic pressure (r = 0.940, p < 0.001).

Conclusion: AI is neither linearly correlated with arterial stiffness, nor with arterial compliance and several cardiac and arterial parameters have to be considered when AI is calculated.