Spectral analysis of laser Doppler flowmetry signals

A new multi-wavelength laser Doppler flowmeter prototype with different spaced detection optical fibres, built in order to give depth discrimination capabilities to laser Doppler flowmetry technique (LDF), was developed. The Fourier transform and the power spectral density of LDF signals measured by the laser Doppler flowmeter prototype were calculated in order to analyze the frequency oscillations present in human microcirculatory blood flow and to explore the potential of the prototype for blood flood skin depth discrimination. The spectral dependence of the signals was also calculated using the coherence function. Our results show that perfusion signals from the new prototype present marked differences when wavelengths and fibre separations are modified; these results are found both at rest and during perturbations of local blood flow. These findings support our hypothesis that wide probes and higher wavelengths measure blood flux from deeper layers.