Application of image analysis for evaluation of red blood cell dynamics in capillaries.

We have devised a method to display and directly evaluate red blood cell (rbc) dynamics in capillaries using the same dual camera intravital video microscopy system employed to determine rbc oxygen saturation (Ellis et al., 1990). Capillary images are recorded on videotape and an interactive graphics system is used for analysis. Data are sampled once a frame for 60 sec using a window (one pixel wide (0.93 micron) and 100 pixels high) positioned along the axis of a capillary. The resulting data are displayed as sequential space-time images 100 pixels high by 300 pixels wide (10 sec). The space-time images thus created represent the dynamics of the rbc's in a single comprehensive static image in which the rbc's appear as dark, diagonal bands separated by light bands representing plasma gaps. From these images one can obtain information on velocity of individual rbc's (micron/sec), lineal density of rbc's (rbc/mm), and rbc supply rate (rbc/sec). This information can be used to delineate the temporal and spatial heterogeneity of hemodynamics in capillary networks. These data can then be combined with coincident data on red blood cell oxygenation to provide a complete picture of oxygen transport in capillaries or it can be used alone as a tool for the evaluation of basic in vivo and in vitro rheological questions.