Role of flow dispersion in the computation of microvascular flows by the dual-slit method

Microvascular blood flow is commonly calculated from a "centerline" velocity derived from the dual-slit method. This is done by relating the computed centerline velocity to an average velocity through an empirically derived conversion factor. To determine the physical basis of the conversion factor, we utilized a Fourier transform and indicator dilution theory to model the parameters governing the conversion factor. We assumed Poiseuille flow from slit 1 to 2 and that the signals from the two slits were sinusoidal functions. Under these conditions, the conversion factor was found to depend primarily on a dimensionless time which is the product of the frequency of the sinusoidal signals and their time delay. Theory shows that if this dimensionless time is in the range of 3 to 7, the conversion factor lies within 1.5 to 1.7. Analysis of original dual-slit samples showed the conversion factor, obtained from the data of five arterioles and three venules, to be 1.58 +/- 0.03, and independent of the microvessel diameter.