Fractal scaling of laser Doppler flowmetry time series in patients with essential hypertension

Abstract

The full diagnostic potential of the fractal complexity measure, α, of detrended fluctuation analysis (DFA) has not been realized yet. To reveal the impaired mechanisms in the blood flow regulation in patients with essential hypertension (EHT), we studied the laser Doppler flowmetry (LDF) time series by applying DFA. Forearm microvascular blood flow was measured by LDF during supine rest. After a 15min baseline recording, microvascular response to thermal hyperemia was measured over 30min. We found three distinct scaling regions; corresponding to the integration of local mechanisms, cardiac effect on local blood flow, and the coupling of extrinsic factors (cardiac and respiratory) to local blood flow by myogenic mechanism. In the control group, local scaling exponent, αL=0.96±0.08, did not change but cardiac scaling exponent, αC=1.53±0.05, for baseline signal was increased to αCT=1.73±0.10 and cardio-respiratory scaling exponent, αCR=0.73±0.19, was decreased to αCRT=0.24±0.06 during vasodilatation in response to local heating. However, we found significantly different scaling exponents, αLT<1, αCT≥αC<1.5 and αCR≈αCRT>0.5 in patients with EHT. Our findings suggest that the local regulatory and the cushioning peripheral vascular functions are impaired in patients with EHT, and vascular/microvascular pathology can be evaluated by applying DFA to LDF signal.