Bolus filtration of leukocytes: A method to study the pressure dependence of leukocyte filter pore passage time distributions

Abstract

Bolus infusion of human leukocytes (Polys and/or Monos) during continuous, constant pressure filtration of 5 μm pore (Nuclepore^®) filters was performed in order to calculate cell passage time distributions. The ratio cell to pore number was kept small (about 0.4) to prevent clogging of the filters and to simplify the analyses of the flow recordings that were made continuously with an ultrasonic transit time flow probe.

In a first step the flow curves were simply inverted to show the changes in resistance during and after cell filtration. The resistance change in the filters due to the passage of the leukocyte bolus was similar, both in shape and magnitude, to that seen earlier in isolated organs perfused with a leukocyte bolus. Thus, there was an initial peak in the resistance followed by a slow decline towards a plateau value 5–20% above the baseline. In addition, the results showed that permanent plugging of the filters was inversely related to the driving pressure (25, 50 or 100 mm H₂O), which also correlates well with the results from organ perfusion experiments. The percentage of cells that became permanently trapped in the pores differed between Polys and Monos only at the lowest pressure (35% Monos and 25% Polys).

The dynamics of the bolus' approach to and contact with the filter was investigated using glutaraldehyde fixated (rigid) Polys, and then used to de-convolute the flow recordings from the normal cells in order to obtain their passage time distributions. In these analyses, it appeared that the normal leukocytes could be divided into a number of sub-populations with passage times ranging from 0 to infinity. When pressure was changed there was a shift of cells between these sub-populations with the sub-population with infinite passage time being greatest at the lowest pressure. This finding indicates that the importance of the viscous element of the leukocytes, which has been regarded to be the most significant determinator of leukocyte rheology, must be re-evaluated. The present results suggest that cell properties such as adhesiveness and elasticity influence leukocyte rheology to a greater extent than has hitherto been recognized.