Blood Sedimentation: A Study in Haemo-Mechanics

Erythrocyte sedimentation is widely used as a clinical index in certain diseases. It is a mechanical test, but its mechanics is not understood. In the present paper, sedimentation tests were carried out with constant volumes of cells at constant temperature, and the relevant physical quantities were measured at the same time. It was hoped that some insight into the operative mechanical laws might be obtained. An equation for the maximum sedimentation velocity, in the conditions described, is proposed, from which the velocities can be forecast in terms of an independent set of measurements. The most important variable is shown to be the 'agglutination power' of the plasma, it being possible to express the maximum velocity, $V_{t}$, in the approximate formula, 0.759$V_{t}$ = $N^{7.7}$, where $N$ is the 'agglutination number' as defined. It is shown that the effect of variations in the specific gravity of plasma and of red cells is negligible, in the experiments performed: and that while the plasma viscosity plays a relatively minor part in the sedimentation mechanics, it also acts as an index of agglutination. It follows that a clinical test, consisting of the measurement of the plasma kinematic viscosity, is possible.