Effects of Wavelets Analysis on Power Spectral Distributions in Laser Doppler Flowmetry Time Series

Abstract

The evaluation of endothelium function impairments are of great clinical interest in many vascular diseases and laser Doppler flowmetry (LDF) is the gold standard technique for its evaluation. LDF signals show low-frequency oscillations related to heartbeat, respiratory, myogenic and endothelial activities. Although wavelets analysis (WLT) of LDF has been shown as a better technique than Fourier (FFT) and Short Time Fourier Transform (STFT) in the resolution of these oscillatory components, the overall spectral power modifications have not yet been described. Aim of the paper is to study the effects of WLT analysis on power spectral distributions in LDF. We studied 20 min LDF recordings of 20 obese subjects by PeriFlux LDF system. Signals were detrended by moving average algorithms and transformed by FFT, STFT and WLT for spectral analysis. The spectral power has been calculated in bands I (0.6-2 Hz), II (0.145-06), III (0.052-0.145), IV (0.021-0.052), V (0.0095-0.021) and VI (0.005-0.0095) in percent values of the total spectral power. Results of the ANOVA tests between spectral powers in the six bands by the three different spectral analysis’ methods showed that WLT exhibited the highest F-value, reflecting significant difference (p<0.001) between II vs III and IV, III vs V and VI, IV vs V and VI bands. Moreover, while WLT values in I band are significantly lower of those of FFT and STFT, WLT values, both in IV and III band, are significantly higher than those of FFT and STFT (p<0.001). Therefore, the overall effects of WLT analysis on power spectral distributions in LDF time series in the studied population seem to limit the spectral power in the I band moving the power to the III and IV bands with the interesting effect to minimize heart rate variability spectral power enhancing myogenic and neurogenic sympathetic activity spectral power in LDF signals.