The physical and biological constants of thrombelastography

Abstract

The thrombelastograph records continuously the shear modulus of the clot from the very beginning of the clotting reaction. The shear modulus of a normal plasma clot at the end of the clotting process is about 5000 dyn/cm², i.e. about 600–2400 times less than that of rubber. A clot of normal native blood has approximately the same shear modulus as that of recalcified plasma with a normal platelet count.

The adherence of the clot in the measuring device of the apparatus ensures that retraction is negligible. The measured shear modulus includes the retractive force and the shear modulus of the fibrin in varying proportions. In the glass tube, on the other hand, the retraction process and the fibrin shear modulus operate in opposite directions.

The physical property of a blood or plasma clot here discussed is a combination of several effects, such as platelet number and viability, fibrinogen concentration, ionic milieu and the retraction cofactor, which seem to influence the mechanical strength and the elastic tension of the clot. Compared with it, a clot from purified fibrinogen and thrombin is a very weak material. Recently reestablished “normal values” of the constants from the thrombelastograph for normal native blood were: $\mathit{r}=\text{12 min 26 sec}$ ( $\mathit{s}=\pm \text{1 min 34 sec}$ ), $\mathit{k}=\text{5 min 35 sec}$ ( $\mathit{s}=\pm \text{1 min 1 sec}$ ), $\mathit{me}=108$ ( $\mathit{s}=\pm 17.7$ ). The male group had the same values as the female one. According to several authors, citrated or oxalated blood or plasma have widely different values depending on the varying methods of decalcification and recalcification.