Effect of leukocytes and platelets on blood flow through a parallel array of microchannels: micro- and macroflow relation and rheological measures of leukocyte and platelet activities.

The effect of leukocytes and platelets on the flow of blood through a parallel array of identical microchannels (equivalent diameter 6 microns, equivalent length 20 microns, number 2600) was examined by microscopy and total flow rate under constant suction (20 cm H2O). Fresh heparinized whole blood was used for the measurement with dilution by autologous plasma to give leukocyte counts 1200-1300/microliters or platelet counts 45,000-50,000/microliters. Despite the uniform flow conditions, cells treated with 1-10 nM FMLP or 0.1-1 microM ADP produced large temporal and spatial (channel to channel) variations in the flow by their transient blocking of the channels. The irregular flow was further accentuated by concomitant aggregation of erythrocytes. However, no fluctuations were observed in the total flow rate of blood, which decreased exponentially with time or with blood volume that had passed through the channels and approached a constant value despite a continual increase in erythrocyte aggregation. Furthermore, the flow curve pattern, i.e., an exponential approach to a steady state, appeared to be independent of both the structural details of the microchannels and the degree of blocking within the microchannels. This suggests that the total flow rate shows a statistical mechanical behavior, i.e., a relaxation process of a macrosystem composed of identical microscopic components that fluctuate independently of each other. Phenomenological parameters (rate constants of blocking and reopening of the microchannels) which can describe the observed flow curves depended on the stimulant does and also differed between different subjects, and hence appear to be useful as measures of leukocyte and platelet activities related to their rheology.