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Abstract
Microvascular perfusion is commonly used to study the peripheral cardiovascular system. Microvascular blood flow can be continuously and non-invasively monitored with laser speckle contrast imaging (LSCI) or with laser Doppler flowmetry (LDF). These two optical-based techniques give perfusion values in arbitrary units. Our goal is to better understand the perfusion time series given by each technique. For this purpose, we propose a nonlinear complexity analysis of LSCI and LDF time series recorded simultaneously in nine healthy subjects. This is performed through the computation of their multiscale compression entropy. The results obtained with LSCI time series computed from different regions of interest (ROI) sizes are examined. Our findings show that, for LSCI and LDF time series, compression entropy values are less than one for all of the scales analyzed. This suggests that, for all scales, there are repetitive structures within the data fluctuations. Moreover, at the largest scales studied, LDF signals seem to have structures that are different from those Entropy 2014, 16 5778 of Gaussian white noise. By opposition, this is not observed for LSCI time series computed from small ROI sizes
Highlights
Analysis of the microvascular perfusion presents a particular challenge in cardiovascular studies because, for pathologies, such as diabetes or hypertension, microcirculation is affected long before organ dysfunctions become clinically manifest
For laser Doppler flowmetry (LDF) signals, our results show that the pattern of the multiscale compression entropy changes when the window size w changes
For scale factors larger than three, compression entropy values of LDF signals become larger than the ones of laser speckle contrast imaging (LSCI) time series, whatever the regions of interest (ROI) sizes and the sliding window size w
Summary
Analysis of the microvascular perfusion presents a particular challenge in cardiovascular studies because, for pathologies, such as diabetes or hypertension, microcirculation is affected long before organ dysfunctions become clinically manifest (see, e.g., [1,2,3]). A continuous monitoring of microvascular perfusion has become of clinical interest. For this purpose, several optical-based techniques have been developed [5]. Laser Doppler flowmetry (LDF) [6] and laser speckle contrast imaging (LSCI) [7] are commercially-available modalities that have the advantage of leading to real-time perfusion data [8]. In LDF, the tissue under study (skin, for example) is illuminated with a low-power laser light through a probe containing optical fiber light guides. LDF relies on the Doppler frequency shift that appears when light is scattered by moving blood cells of the microcirculation.
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