Peripheral "oscillatory" compliance is associated with aortic augmentationindex

The augmentation index (AIx) and "oscillatory" compliance (C-2) are wave co ntour analysis parameters for the central aorta (P-ao) and radial artery pr essure wave (P-rad)(x) respectively. Both are sensitive to cardiovascular r isk factors such as aging, hypertension, and diabetes and have been propose d as prognostic markers for cardiovascular disease. In this work, we studie d the relation between both. We first calculated P-rad corresponding to a t ypical aortic A-type (AIx >0.15) and C-type wave (AIx <0), taken from the l iterature, by using a generalized aorta-radial pressure transfer function. P-rad corresponding to C-type waves yielded the highest C-2 value. We furth er used simultaneously measured aortic and radial artery pressure in 45 hum an subjects age 34 to 84 years (63 +/- 12 [SD]) at baseline and after admin istration of nitroglycerin to calculate AIx(meas) and C-2, respectively. Tr ansfer function was used to calculate reconstructed aortic pressure and AIx (rec). AIx(rec) underestimates AIx(meas) by 0.03 +/-0.16, but both values c orrelate well (r=0.64; P<0.001). C-2 and AIx were inversely correlated (r=- 0.36; P<0.001 for AIx(meas); r=-0.30; P <0.01 for AIx(rec)). Both AIx(meas) (0.06 +/-0.17 versus 0.20 +/-0.21; P <0.01) and AIx(rec) (0.04 +/-0.12 ver sus 0.16 +/-0.16; P<0.001) were lower after nitroglycerin, whereas C-2 incr eased only nonsignificantly (0.080<plus/minus>0.036 versus 0.071 +/-0.042). C-2 is related to AIx and reflects, at least in part, hemodynamic changes affecting central aortic pressure. Nevertheless, given the model assumption s and computational steps associated with calculating C-2, AIX could be a m ore appropriate parameter to use in the clinical setting because it is dete rmined directly from the pressure wave contour.