With a damped-oscillation rheometer, changes in the rheological properties, i.e., logarithmic damping factor (LDF) and period, as obtained from a damped-oscillation curve, were monitored during the coagulation of blood. In our earlier studies, the time of onset of coagulation (Ti) of the blood sample was only determined from the change in LDF. When coagulation of the blood and sedimentation of erythrocytes occurred together, the Ti value could not be determined from the change in LDF. In this paper, a method for determining the Ti value from the change in the period of the damped-oscillation curve was investigated. It was found that the period increased and leveled off as blood coagulation progressed, and the Ti value was determined from the middle point between the minimum and maximum values of the period. In addition, it was suggested that the level of erythrocyte sedimentation could be estimated from the initial decrease in LDF. In blood obtained from diabetic patients, a good correlation between the initial decrease in the LDF and the concentration of fibrinogen was observed. Our study demonstrates that when erythrocyte sedimentation and blood coagulation occur simultaneously, this rheological technique makes it possible to measure the Ti value and erythrocyte sedimentation.
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