Capillary pore rheology of erythrocytes: V. The glass capillary array—Effect of velocity and haematocrit in long bore tubes

Abstract

In earlier reports (P. S. Lingard, 1974, Microvasc. Res. 8 , 53–63; 1977, Microvasc. Res. 13 , 29–58; 1977, Microvasc. Res. 13 , 59–77), the resistance-velocity and resistance-concentration behaviour of human erythrocyte suspensions was described for Nuclepore filters. A potential disadvantage of Nuclepore filter geometry was the shortness (only 10–15 μm) of the capillary pores. This paper describes the hydrodynamic resistance-velocity and-concentration behaviour for erythrocyte suspensions in Glass Capillary Arrays (GCAs) of length-to-radius ratio 200 and diameter 5 μm. Two-limbed linear relations between pressure drop and velocity are found as for Nuclepore filters, showing a region of constant resistance at velocities below a critical value followed by a region in which resistance decreases in proportion to the inverse of velocity. This finding eliminates hypothetical entrance effects as possible explanations for the nonlinear velocity behaviour described before. Although less than with the Nuclepore filter, resistance levels are consistent with tight-fitting conditions for the cells (lubricant film thickness 0.15 μm). The falling resistance with velocity is again consistent with changing clearance due to distortion of the cells. Haematocrit-dependent relative resistance behaviour is again found, weaker at concentrations below 60% than seen before, but strengthening markedly between 50 and 80% as before. Possible evidence of “seize-up” at high concentrations is now reported and evidence for the absence of virtual shunting (considered for Nuclepore filters) is noted at low concentrations.