The frequency histogram--a new method for the evaluation of laser Doppler flux motion

A digital filter system (DFS) was implemented to describe the frequency components of laser Doppler signals. The DFS calculates a frequency histogram on the basis of the prevalence of a certain frequency band during the sample period. This approach seems to be more suitable for the detection of low-power small-amplitude flux motion components recorded by laser Doppler as compared to the commonly used fast Fourier algorithm. Fourier analysis provides an amplitude-relevant frequency spectrum which may overlook relevant frequency components with small amplitude due to low power or short duration. DFS allows better detection of such signals as demonstrated by the initial clinical results of this study evaluating flux motion on the feet of 4 healthy controls and 10 patients with peripheral arterial occlusive disease. Three frequency components are easily distinguished corresponding to low (3.6 +/- 1.5 cycles/minute) and high (18.6 +/- 4.5 cycles/min) frequency flux motion and the pulsatile waves due to cardiac action.