Generalized fractal dimensions of laser Doppler flowmetry signals recorded from glabrous and nonglabrous skin

PURPOSE: The technique of laser Doppler flowmetry (LDF) is commonly used to have a peripheral view of the cardiovascular system. To better understand the microvascular perfusion signals, the authors herein propose to analyze and compare the complexity of LDF data recorded simultaneously in glabrous and nonglabrous skin. Glabrous zones are physiologically different from the others partly due to the presence of a high density of arteriovenous anastomoses. METHODS: For this purpose, a multifractal analysis based on the partition function and generalized fractal dimensions computation is proposed. The LDF data processed are recorded simultaneously on the right and left forearms and on the right and left hand palms of healthy subjects. The signal processing method is first tested on a multifractal binomial measure. The generalized fractal dimensions of the normalized LDF signals are then estimated. Furthermore, for the first time, the authors estimate the generalized fractal dimensions from a range of scales corresponding to factors influencing the microcirculation flow (cardiac, respiratory, myogenic, neurogenic, and endothelial). RESULTS: Different multifractal behaviors are found between normalized LDF signals recorded in the forearms and in the hand palms of healthy subjects. Thus, the variations in the estimated generalized fractal dimensions of LDF signals recorded in the hand palms are higher than those of LDF signals recorded in the forearms. This shows that LDF signals recorded in glabrous zones may be more complex than those recorded in nonglabrous zones. Furthermore, the results show that the complexity in the hand palms could be more important at scales corresponding to the myogenic control mechanism than at the other studied scales. CONCLUSIONS: These findings suggest that the multifractality of the normalized LDF signals is different on glabrous and nonglabrous skin. This difference may rely on the density of arteriovenous anastomoses and differences in nerve supply or biochemical properties. This study provides useful information for an in-depth understanding of LDF data and a more detailed knowledge of the peripheral cardiovascular system.