Fractal dimension of mean arterial pressure and heart-rate time series from ambulatory blood pressure monitoring devices

Ambulatory blood pressure monitoring (ABPM) devices provide 24-hour profiles of mean arterial pressure (MAP) and heart rate (HR) by inflating an arm-cuff every 15 minutes during daytime and every 20 minutes during night-time. Aim of this work is to evaluate whether the intrinsic structure of ABPM dynamics can be described during day and night subperiods by calculating the fractal dimension (FD) of MAP and HR. For this aim, first we evaluated the performances a recently proposed FD estimator on short segments of fractional Brownian motions. Then we applied the new FD estimator on 24-hour ABPM recordings of two healthy volunteers. The FD estimator showed good performances on synthesized data, with lower bias compared to Higuchi's method. FD estimates of real data tended to be higher during the day. In particular, FD of daytime MAP (1.84 ±0.06 M±SD) was substantially higher than 1.5, suggesting that anticorrelation mechanisms may influence the diurnal long-term regulation of blood pressure.