# Dynamic and Quantitative Assessment of Blood Coagulation Status with an Oscillatory Rheometer
## 3 Results
### Extrinsic Coagulation  
The strong activation of the extrinsic coagulation by tissue factor (Thromborel) can be seen in Figure 1. Repeated measurements (\(n\) = 10) of Thromborel-activated blood from the same donor are shown over time (300 s). The data of uncoagulated blood were taken from literature, where an elastic shear modulus of 0.02 Pa (blue dashed line) and a viscous shear modulus of 0.05 Pa (red dashed line) at 1 Hz are given and shown here as a constant dashed line in the diagram [22]. Upon addition of Thromborel coagulation is initiated and the means of viscous and elastic shear modulus increase (Figure 1a). The clotting time (CT) was graphically determined as the intersection between the shear moduli of uncoagulated citrated whole blood (dashed lines) and the linear slope of the shear moduli of citrated blood with the activator Thromborel (see enlarged section in Figure 1b). The identified mean CT by the oscillatory rheometer (25.2 \(\pm\) 1.2) s was comparable to the provided reference measurement determined by the ball coagulometer (25.4 \(\pm\) 3.3) s.  
Apart from simply determining the CT, the oscillatory rheometer is able to provide further information on the coagulation status, which are summarised in Table 1. The linear slope at the beginning of the measurement describes the change of the shear moduli over time, i.e., this parameter provides information about the dynamics of the coagulation process. The linear slopes (m) of the elastic and viscous shear moduli of citrated blood activated with Thromborel were (600.0 \(\times\) 10\({}^{-3}\)\(\pm\) 8.0 \(\times\) 10\({}^{-3}\)) Pa/s and (100.0 \(\times\) 10\({}^{-3}\)\(\pm\) 0.029) Pa/s, respectively. At approximately 60 s the initially steep slopes of elastic and viscous shear moduli level out but still increase at a constant albeit very small rate. To compare the shear moduli or clot firmness respectively of each measurement, the timepoint at 300 s was chosen arbitrarily, where the values of viscous and elastic shear modulus were taken in the plateau phase of the experiment. The elastic component measured (18.5 \(\pm\) 4.5) Pa and the viscous shear modulus (1.7 \(\pm\) 0.4) Pa. The subsequent measurements with citrated blood and various heparin concentrations were compared with these initial data.  
Figure 1: The oscillatory rheometer reliably determines the prothrombin time (PT) of citrated blood activated with Thromborel. (**a**) Mean elastic and viscous shear moduli of citrated blood activated with Thromborel (\(n\) = 10 \(\pm\) SD) are shown over time. The measurement was performed at a shear stress of 0.04 Pa with 1 Hz and a 1\({}^{\circ}\)/40 mm stainless steel cone geometry; (**b**) Enlarged part from diagram (**a**). The dashed red line at 0.02 Pa visualises the elastic shear modulus and the dotted blue line at 0.05 Pa the viscous shear modulus of uncoagulated citrated blood with no coagulation activator. After the addition of the activator Thromborel an increase of G\({}^{\prime}\) and G\({}^{\prime\prime}\) was observed. The black solid line is the clotting time (CT = 25.2 s).