Detrended fluctuation analysis of laser Doppler flowmetry time series: the effect of extrinsic and intrinsic factors on the fractal scaling of microvascular blood flow.

The relative contribution of extrinsic (central) and intrinsic (local) oscillatory mechanisms to the fractal scaling of blood flow in forearm cutaneous microcirculation is unclear. The aim of this study was to investigate the contributions of these mechanisms to the fractal properties of the blood flow signal by using their frequency spectrum in the analyses. To evoke local oscillatory components, acetylcholine (ACh) was iontophoresed into the forearm and cutaneous perfusion was measured by a laser Doppler flowmeter (LDF) at rest. Depending on the involved factors in ACh-induced vasodilatation, central, cardiac and respiratory, signals have also increasingly appeared in LDF. The detrended fluctuation analysis (DFA) of filtered LDF time series demonstrated that the LDF was fractal with three distinct scaling regions. Furthermore, the findings of the present study indicated that these regions are related to the frequency bands of well-known control systems of blood flow and were called cardiac, cardio-respiratory and local regions. The mean scaling exponent increased with vasodilatation in the cardiac region but decreased and even changed its sign in the cardio-respiratory region. Inhibition of a local vasodilator mechanism not only decreased the scaling exponent of the local region but also eliminated the effect of respiratory coupling on fractal scaling. These findings suggest that the scaling exponents might have a diagnostic value for detecting pathological dynamics in vascular beds.