Fiber optical spatial filter anemometry--intravital measurement of red blood flow velocity (RBCV) in the microcirculation.

The fiberoptical spatial filter anemometry (SFA) is a common technique based on an optical grid to measure the velocity of corpuscular components in a multiphase flow, e.g. in the microvessels. The technical innovation is the analysis of flow velocities using an optical grid sensor and frequency analysis by Fast Fourier Transformation (FFT). This study describes a non-invasive, on-line technique to measure RBCV in the microcirculation. The sensor's validity was proven by in vitro measurements using a rotation disk of an exactly defined velocity with a correlation coefficient of 0.99967. For validation of RBCV measurements in the microcirculation in vivo, the setup was adapted to an intravital microscope. RBCV was measured in arterioles, capillaries, and postcapillary venules ranging from 8-140 microm diameter. As reference method for velocity measurements a computer assisted imaging system was used to measure the RBC-velocity in the identical vessels by frame to frame analysis. Both methods revealed a high significant correlation using transillumination technique for capillaries (r=0.986, p<0.001) and venules (r=0.952, p<0.001) as well as epiillumination technique (capillaries r=0.939, venules r=0.975, p<0.001).