Analysis of skin blood flow signals in the frequency domain applied to the vasodilators histamine and methylnicotinate

Laser Doppler flowmetry was used to obtain the flux, concentration and speed signals of moving red blood cells before and after the application of histamine and methylnicotinate. The effect of topical application of the vasodilators on the frequency spectrum of skin blood flow signal was investigated. The signal was separated into two frequency bands, A (0.02-0.5 Hz) and B (0.5-2.0 Hz), and the effect of the two vasodilators on the total power and on the power in the bands was studied. After the application of the vasodilators, the total power in the flux and the speed signals increased for both histamine and methyinicotinate, but in the concentration signal it increased for histamine while it decreased for methylnicotinate (P>0.05). For both histamine and methylnicotinate, the power in band A decreased and in band B increased (P<0.03). Hence, separating the power of the signal into frequency bands allows more accurate detection of vasodilatation