Detection of pulsatile blood flow cycle in frog microvessels by image velocimetry

The detection of pulsatile blood flow velocity through one section of a curved branching frog mesenteric microvessel during a flow cycle, by analysis of a sequence of videomicroscopic images recorded at a frame rate 25 frames s⁻¹, is presented. From these data, 64 sequential digitised frames of 128×128 pixels and 256 grey level were selected. By processing sequential pairs of frames by image velocimetry, the corresponding displacement vector was calculated. Dividing this by the frame rate gave the vector velocity. The same procedure was repeated for all frames, and the corresponding maximum (0.36–0.38 mm s⁻¹), minimum (0.0–0.025 mm s⁻¹) and other velocity values were obtained and plotted. The preliminary data analysis showed that the separation between two velocity maxima was about 20 video frames, which corresponded to one cardiac cycle of time interval 0.8 s.