Importance of wavelet analysis in laser Doppler flowmetry time series.

Spectral analysis of microvascular laser Doppler flowmetry time series is performed to resolve their complex dynamics. The method of analysis should be carefully chosen such that as much information as possible of the signal is obtained. Conventional Fourier transform and short-time Fourier transform are compared with wavelet analysis to resolve several oscillatory components on a wide frequency interval. Wavelet transform with the Morlet mother wavelet is shown to have an advantage of adjustable window length as it detects each frequency with a window of a corresponding length. In this way good localization in time and frequency is provided. Low and high frequencies can be resolved and their variations traced in time. This is of crucial importance in analysis of oscillations in LDF signals and studies of their physiological origin as well as their changes in health and disease.