Ambulatory arterial stiffness index derived from 24-hour ambulatory blood pressure monitoring

We hypothesized that a novel index computed from 24-h systolic and diastolic BPs as recorded during ambulatory monitoring (ambulatory arterial stiffness index, AASI) might reflect arterial stiffness. We used 90207 SpaceLabs monitors and the SphygmoCor device to measure on the same day 24-h BP and arterial stiffness in 348 randomly recruited Chinese. We compared AASI with the central and peripheral augmentation indexes, central pulse pressure, pulse wave velocity and the 24-h pulse pressure. AASI correlated (P<0.0001) with central (r=0.48) and peripheral (r=0.50) systolic augmentation and central pulse pressure (r=0.48). AASI increased with age and mean arterial pressure, but decreased with body height and female gender. Both before and after adjustment for arterial wave reflections, the correlations of AASI with the augmentation indexes were closer than those with the 24-hour pulse pressure in all subjects (P<0.0001) and older adults (≥40y; P<0.05). A further validation study in 96 subjects showed that AASI also significantly correlated with pulse wave velocity (r=0.31, P=0.002). Among normotensive subjects, the 95th percentiles of AASI were 0.55 in our Chinese population and 0.57 in 804 Belgians and 813 Irish enrolled in an International Database on Ambulatory BP Monitoring (J hypertens. 1994;12:s1-s12). In relation to age, the upper boundary of the 95% confidence interval for prediction of the AASI in individual subjects ranged 0.53 at 20 years to 0.72 at 80 years. In conclusion, AASI is a novel index of arterial stiffness, which can be easily measured under ambulatory conditions. Pending further validation in prospective studies, normal values of AASI are probably below 0.50 and 0.70 in young (±20y) and older (±80y) subjects, respectively.