THE FILTERABILITY OF LEUKOCYTES IN UNDILUTED BLOOD

A filtrometer is described for measuring the flow of fluids through mi crofilters. The flow of Newtonian fluids through the filters can be pr edicted from the diameter, length and number of pores. There are no ph ysical artefacts such as turbulent flow or a significant lag period be fore steady-state flow is achieved. The instrument has been used as a viscometer and has been used to record and analyse the flow of undilut ed blood through 5 mu m polycarbonate filters. The calculated viscosit y of Newtonian fluids agrees well with those measured by a more conven tional viscometer (Ostwald). Flow profiles of blood have been analysed to give both the numbers and the flow properties of a small populatio n of slow leukocytes which equate numerically with the monocytes. They are subdivided into three distinct sub-populations, according to thei r rheological properties, and these are termed SL1, SL2 and PB. The co ncentration of these cells, in blood, are 0.12 +/- 0.02 x 10(6) ml(-1) , 0.11 +/- 0.02 x 10(6) ml(-1), 0.09 +/- 0.02 x 10(6) ml(-1) in young females aged about 25 years. The transit time of these cells, through 5 mu m pores, is 34.8 +/- 1.4 s, 147.5 +/- 2.5 s and > 300 s, respecti vely. Analysis of blood from older men (53-79 years) gives essentially the same results although the concentration of SL1 is slightly higher at 0.19 +/- 0.09 x 106 ml(-1).