CSIRO Division of Applied Physics, Lindfield NSW 2070, Australia
The information produced by the erythrocyte sedimentation rate (ESR) test is non-specific and the physics of the underlying processes is inadequately understood. However, the test is, and will continue to be, widely used because of its simplicity. The ESR reflects the balance between the concentrations of erythrocytes and of plasma proteins and this balance, in turn, controls the rate of erythrocyte aggregation and sedimentation. The ESR has some indicative value because inflammatory diseases generally increase the concentration of plasma proteins, but, a better physical understanding would render it more informative.
The separate effects on the ESR of the concentrations of erythrocytes, albumin, globulins and fibrinogen have recently been measured (Hung et al., 1994) but erythrocyte shape and deformability also play a role (Reinhart et al., 1989, 1990). Reinhart and Singh (1991) have obtained surprising ESR results for mixtures of normal RBC and cells hardened by (a) glutaraldehyde fixing and (b) heating at 47.5oC. Heat-hardened RBC cause an expected drop in the ESR, whereas the ESR increases to a maximum for 40% volume fractions of glutaraldehyde-fixed cells and thereafter drops quickly. This has been attributed to "stickiness" between normal and glutaraldehyde-fixed cells whereas the latter are too inflexible to aggregate (Reinhart, 1991). We have studied this simple model of aggregation in mixtures of normal and glutaraldehyde-fixed RBC by Monte Carlo computer simulation. Different "sticking" coefficients (probabilities of adherence after random collisions) are assigned to spheres A and B which represent the two types of cell with coefficients A.B > A.A > B.B. The range in, and average size of aggregates have been determined as a function of volume fraction and compared with experimental data.
*Oscar Franklin (Uppsala) and Iwona Chrzaszcz (UTS) were vacation scholars at DAP.
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