Stability ratio of red blood cells: its dependence on temperature and its relationship to the erythrocyte sedimentation rate.

The theory of the coagulation of particles in laminar shear flow was applied in a study of the aggregation of red blood cells. The theory predicts that in a system of initially dispersed particles the total particle concentration would decay (because of aggregation) logarithmically with time with the decay rate, depending on the adhesiveness of the particles. The applicability of this theory was tested at 4 different shear rates (G = 5-0 s", 12-6 a", 15-7 s" and 23-3 s") for normal red blood cells in plasma. At every shear rate it was found that an equilibrium condition was approached after 10-20 min, suggesting that the equation is valid only during the first 10-20 min of the aggregation process. Having established the time period over which the theory is valid, values for the stability ratio of red blood cells were computed. The stability ratio, which is essentially a measure of the adhesiveness of the cell*, is defined as the ratio of the number of effective collisions (collisions resulting in adhesion) to the total number of collisions. A very simple shearing technique was used. The suspension of red blood cells was placed in a small weighing bottle and the shearing force was provided by a small magnetic stirring rod, whose rotational frequency could be controlled. The mixing chamber was clamped in a small water bath, which in turn rested on a heated magnetic stirrer. Samples for microscopic viewing and counting were prepared by transferring a very small volume of the suspension onto a microscope slide and preserving it by placing an identical slide on top. The stability ratio (a) was found to have a negative linear relationship with shear rate (regression line a — 0-02640 — 0-00084 G, r = 0-94) and extrapolation to a = 0 suggests that a minimum shear rate of ~ 32 s" is required to prevent re-aggregation of the red blood cells. For 10 healthy men and women the stability ratio, calculated at a shear rate of I2-6 s~, was found to be 0-0129 ±0-0009 (S.E.M.). The stability ratio was also found to be temperature-dependent. It increased linearly with temperature from 4 °C to 41 °C and then decreased at higher temperatures, becoming zero at a temperature of 52 °C. Results obtained from a group of patients with high erythrocyte sedimentation rate (e.s.r.) were combined with those from normal, healthy subjects and a positive linear relationship between a and e.s.r. was obtained. This finding suggests that the stability ratio might be a valuable measurement in comparing red blood cells in disease with normal red blood cells.