A comparison between systolic and diastolic pulse contour analysis in the evaluation of arterial stiffness

Several methodologically independent measures of arterial stiffness derived from either the systolic or diastolic segments of the arterial pulse have been proposed. The exact nature of the large and small artery elasticity in dices (C1 and C2, respectively) derived from diastolic pulse contour analys is remains largely unexplored, although C2 has controversially been termed to be "oscillatory" and "reflective." We investigated the relation between C2 and, respectively, a prototype of arterial reflectivity (ie, the augment ation index, AIx) and a covariate of arterial reflectivity (body height). A validated transfer function is used to transform a tonometrically obtained radial pressure wave into an ascending aortic pressure wave, from which AI x is derived using systolic pulse contour analysis. Diastolic pulse contour analysis using a modified Windkessel model is used to derive C1 and C2. On e hundred subjects, who were free from atherothrombotic disease and 19 to 7 7 years of age, with a wide pressure range (97 to 186/52 to 104 mm Hg) were studied. Mean values of C1, C2, AIx, and body height were, respectively, 1 3.8 +/-4.3 mL/mmHgX10, 5.9 +/-3.1 mL/mm HgX 100, 128.5 +/- 24.9%, and 169 /-9 cm. Coefficients of variation were 32.8% for C1, 33.3% for C2, and 6.7% for AIx. C2 was significantly and inversely correlated to AIx (r=-0.707, P <0.001). Both AIx and C2 were correlated to body height (r=-0.487, P<0.001 , and r=0.514, P<0.001). In conclusion, the results of this study provide t he first clinical evidence that validates a probable biophysical equivalent of the C2 element of a third-order, 4-element modified Windkessel model. W e suggest that C2 is, at least in part, a measure of arterial wave reflecta nce. However, although short-term reproducibility of AIx is excellent, C2 s howed markedly increased variability with the devices used.