Determinants and Reliability of the Ambulatory Arterial Stiffness Index, AASI.

The Ambulatory Arterial Stiffness Index (AASI) was introduced as an easily implemented way to non-invasively assess arterial stiffness from 24-hour ambulatory blood pressure monitoring (ABPM) records. After a brief review of the literature, this investigation considers ABPM records from two clinically healthy populations to compute the AASI and assess its major determinants. The 7-day/24-hour ABPM records collected in one of the two studies served to determine the extent of day-to-day variability in the AASI estimation. In the other study, age, body mass index (BMI), systolic (S) BP MESOR, and pulse pressure (PP) correlated positively with AASI, while the magnitude (extent of predictable daily change) of SBP and the 24-hour amplitude of diastolic (D) BP correlated negatively with AASI. Although AASI computed on separate days correlates well with its value estimated from the entire 7-day record, the day-to-day variation in its estimate is quite large. The relatively large difference in estimated average AASI between the two studies, which included seemingly similar populations, can be accounted for by taking into consideration the small differences in all determinants of the AASI existing between the two samples. Novel findings from this investigation are the effect on AASI of (1) a misaligned circadian BP rhythm, and of (2) a sparser nighttime vs. daytime sampling.