Fractal characteristics of blood pressure and heart rate from ambulatory blood pressure monitored over 24 hours

Since devices for measuring ambulatory blood pressure (BP) noninvasively have very low sampling rates, BP fluctuations are generally quantified by simple indices of variability. Aim of this study is to describe the characteristics of a more sophisticated feature of BP variability, the fractal dimension (FD), as assessed by ambulatory BP devices in healthy volunteers. 24-hour ambulatory BP was recorded in 47 normotensive volunteers; 4-hour segments of systolic BP (SBP), diastolic BP (DBP) and heart rate (HR) were selected at daytime and nighttime. Mean (M), standard deviation (SD) and FD were calculated in each segment. While M and SD decreased from day to night, as expected, SBP FD tended to increase at night, where it was significantly greater than DBP FD. The HR FD was always significantly lower than the FD of SBP or DBP. Results suggest that FD of ambulatory BP may provide novel information on the cardiovascular control.