Characterization of regulatory differences in ambulatory blood pressure monitoring data by means of fractal analysis

Non-invasive wearable 24-hour ambulatory blood pressure monitoring (ABPM) devices are widely used in clinical practice and allow measuring of systolic and diastolic blood pressure (BP) time series in freely moving subjects. Complex system such as hemodynamics is demonstrated to be a self-similar hierarchy. The aim of the study is to determine the clinical potential of fractal analysis of ABPM data, in particular the fractal dimension (FD) as a quantitative measure of the chaotic component of the hemodynamics. The FD estimator and linear regression modeling (LRBPP, Linear Regression of BP Parameters) were applied on ABPM data of 57 healthy volunteers, 47 hypertensive patients and 25 patients with acute hypotensive episodes caused by various diseases. The fractal analysis of ABPM data of normotensive, hypertensive and hypotensive patients showed that all ABPM time series demonstrate antipersistence and a tendency to return to the average BP level. It was shown, if FD value of the patient's systolic blood pressure is greater or less than FDn = 1.8 (characteristic of normal hemodynamics, H2-class by LRBPP), then it is associated with pathology and worsening of the patient's hemodynamic status, regardless of the disease. A decrease in the complexity of ABPM BP series (a decrease in FD values corresponding to hypotensive D1-class on LRBPP) indicates to weakened/absent regulatory influence of the BP level; an increase in FD to FDu = 2.0 indicates on the correlated or quasi-periodic behavior of the ABPM BP series caused by extreme regulatory impact (hypertensive H3-class). Thus, the FD value of ABPM data can be a hemodynamic marker of the regulatory differences due to process of adaptation, self-organization, and relationship of regulatory structures of different levels. FD value and an individual hemodynamic class determined by LRBPP can use as an integral indicator of ABPM data for assess the physiological/pathological state of the patient's blood circulation.