Capillary pore rheology of erythrocytes: IV. Effect of pore diameter and haematocrit

Abstract

In preceding work (Lingard, P. S., 1974, Microvasc. Res. 8, 53–63; Lingard, P. S., 1977, Microvasc. Res. 13, 29–58), erythrocyte suspensions were found to exhibit nonlinear hydrodynamic resistance behaviour in the narrow capillary pores of a new rheometer, which embodies a Nuclepore filter. For pores of diameter 4–7 μm, constant, relatively high resistances were found at low velocities, giving way to falling resistances with increasing velocity beyond a well-defined transition point The resistances are consistent with virtual occlusion of the lumen by the cells, and the resistance changes with changing clearance due to distortion of the cells. This paper shows that resistance within a population of donors is greater in narrower pores and increases with suspension concentration. Representative parameters (viz., lubricating film width, pressure drop per cell) depend strongly on the pore diameter. Resistance-concentration relations are not linear and differ from expectation of hydrodynamic theory. The differences are explained by a shunting mechanism, based on a hypothesis of random cell distribution among the pores. This reduces resistance measured in multipore filters compared with baseline data for long-bore tubes, reinforcing earlier conclusions that cells are tight-fitting in capillary pores and that resistance changes by elastic deformation of the cells.