Determination of in vitro simulated blood cell velocity by laser-Doppler with state space methods.

In this paper a signal processing method based on an important tool of numerical analysis, the singular value decomposition (SVD), is used. This method is applied to the unprocessed output of a Laser-Doppler fluxmeter to obtain parameters that are more sensitive to blood velocity than to hematocrit. The SVD-based method utilizes the exponential shape of the frequency spectrum of the laser light scattered from the moving red blood cells and demonstrates an inverse relationship between the damping constant beta associated with the exponential shape and the blood velocity. This method was applied to samples of rat blood of several known hematocrit values that were rotated at different velocities on a turntable. The method extracted one dominant singular value from the spectra, indicating that the spectra can be modeled as a single exponential dominated by scatterings with a single moving red blood cell. A 68% change in inverse velocity resulted in a 50% change in the damping constant (hematocrit 29.5% vol). On the other hand, a 37% change in hematocrit resulted in a far smaller change in the damping constant beta of only 17%. Analysis of the extracted parameters shows that the damping constants are far more influenced by blood velocity than by blood hematocrit.