Ambulatory Arterial Stiffness Index and circadian blood pressure variability

The manner in which the circulation accommodates each heartbeat may underlie blood pressure (BP) variability. We used the Ambulatory Arterial Stiffness Index (AASI), which reflects this ventricular-vascular interaction, in untreated individuals with prehypertension and Stage 1 hypertension to evaluate two different measures of BP variability using the brachial pulse pressure (PP) obtained over 24 hours. We enrolled 64 untreated adults with systolic BP between 130-159 mm Hg and diastolic values of <100 mm Hg who underwent 24-hour ambulatory BP monitoring with calculation of 24-hour AASIs. Variability in brachial PP was determined using the standard deviation of the measurements over 24 hours and the average real variability. The 24-hour AASI correlated with both measures of 24-hour PP variability (P <.001 for both). Subdividing the 24-hour stiffness index into daytime and nighttime components showed modest differences in their relationship to PP variability, with the daytime being significantly different from 24-hour AASI and the standard deviation of the brachial PP consistently having a higher correlation to the AASI when compared with the average real variability. These observations may be useful to understand differences in variability measures of BP measurements, such as PP, to measures like the AASI as reported in longitudinal studies.