Laser Doppler flowmetry: multifractal spectra of signals recorded in hand of young healthy subjects before and after local heating

Abstract

Laser Doppler flowmetry (LDF) signals give a peripheral view of the cardiovascular system. We herein propose to analyze the complexity of LDF signals recorded in the palm side of the hand and to compare the results with those obtained in the forearm. Moreover, we also study the possible impact of local heating (40°C) on the width of the multifractal spectra for the hand. For this purpose, LDF signals are recorded simultaneously in the hand and forearm. A local heating of 40°C is performed in the hand palm, leading to an increase of the local skin blood flow via, among others, the production of nitric oxide. LDF data recorded before and during the local heating are processed in order to obtain their multifractal spectra. The latter are computed, without normalization of the signals amplitude, by first estimating the discrete partition function of the data, then by determining their Renyi exponents with a linear regression, and finally by computing their Legendre transform. The results show that, at rest, the average multifractal spectrum of signals recorded in the hand palm is larger and more asymmetric than the one of data from the forearm. Furthermore, without normalization of the signals amplitude, local heating in the hand palm leads to a slightly narrower and more symmetric average multifractal spectrum for this site. This study brings information on the multifractal spectra of LDF signals and is a first step in order to have more knowledge on the potential implication of the endothelium in the complexity of LDF signals in the hand palm.