Capillary flow velocity measurements in vivo and in situ by television methods

Abstract

A system for the measurement of red blood cell velocity in televised images of the microcirculation is described. The method measures the time delay between the photometric signals which originate from two “windows” positioned along the centerline of the televised capillary under study. The photometric windows are generated directly within the composite video signal, and are positioned by means of manual analog controls. Spatial and temporal resolution limitations set by the characteristics of broadcast television systems, in conjunction with the characteristic distances over which a configuration of red blood cells does not change substantially in its transit through the capillary, determine an upper limit for velocity measurements of 10 mm/sec. The system was utilized to measure RBC velocities in the capillaries of the rabbit omentum, cat tenuissimus muscle, and the pial microcirculation. These tissues present three limiting cases in terms of optical resolution, correlation length, and velocity patterns. In each case, adequate velocity measurements were routinely obtained.