Dynamics of erythrocyte motion in filtration tests and in vivo flow

The characteristics of low haematocrit erythrocyte suspension flow through the 5 micrometer pores of a nuclepore filter, under low pressure drops, are compared to those of red cell flow through the human spleen. (a) For suspension filtration when the haematocrit is less than 1.5% and the pressure drops are less than 1 cmH2O, the characteristic RBC transit time through a 5-micrometer pore filter is about 10 ms, with an overall average velocity of about 1 mm/s, with the fraction of the unplugged filter pores occupied by RBC about 3.5 times the haematocrit of the filtrate. (b) In the human spleen, the mean residence time in the red pulp is about 66 s or longer, with an average velocity of 0.25 micrometer/s or less. During transit through the sinus wall slits (about 1 micrometer by 6 micrometer rectangular openings, about 2 micrometers long, residence time is estimated to be 10 s or longer. Considering the differences in these flow situations (and assuming the human spleen provides the critical in vivo RBC deformability test), it would seem necessary to demonstrate parallelism of the results of the in vitro and in vivo tests.