The measurement of the flow of blood through a device to measure blood viscosity, termed rheocohesion in the art, is a valuable diagnostic procedure. However, problems in obtaining a correct rheocohesion value include: improper venipuncture causing artifacts in the readings so obtained; special equipment is needed to accurately measure the rate of flow of blood through a hypodermic needle inserted directly into the blood vessel of a patient under study while maintaining controlled conditions of standard pressure, temperature and time; whole blood rheocohesion is an indirect measurement, and artifacts such as the hematocrit and total serum protein must be considered.
Direct measurement of whole blood rheocohesion is described in my earlier U.S. Pat. No. 3,999,538 and the apparatus described in my U.S. Pat. No. 4,083,363.
It would be convenient to obtain a single blood sample for numerous blood testing purposes from the patient using conventional syringe and/or vacutainer without specialized equipment of the type referred to above.
I have now found, and hereby disclose, a procedure for measuring the time required for the serum of a patient to coagulate a standardized solution of fibrinogen or serum thrombin time, and of correlating the times so obtained with whole blood rheocohesion. Serum thrombin time values are useful in diagnosis of numerous abnormal conditions, for instance myocardial infarction, stroke, transient ischemic attack, hysterical conversion syndrome, and schizophrenia.
Another significant application for serum thrombin time is in the monitoring of drug treatment for these condition.
Plasma is the clear liquid when whole blood is placed in an anticoagulant and the cellular elements of the blood settle to the bottom. Plasma is routinely obtained in blood banks by physical separation, i.e., centrifuge, to separate the cellular elements by gravity, from the clear, straw-colored liquid. The serum obtained for use in the present invention is withdrawing a blood sample from the patient and placed in a container without an anticoagulant, allowing the blood to clot then centrifuging to separate the cellular elements from the clear liquid. Serum thus obtained is free from anti-coagulants. Without an anticoagulant the blood fibrinogen is converted into fibrin, a three-dimensional gelatin-like network of fibers. As such the fibrin network is separated by the centrifuge, or spun down, with the red cells leaving the clear liquid at the top; the serum thus treated, contains no fibrinogen. Serum, then, is the same as plasma minus fibrinogen.
It is important that no anticoagulant be used in the procedure. The object of this procedure is to omit the patient's fibrinogen and to use the serum to analyze factors that influence purified, standardized fibrinogen, as discussed in more detail below.
In conventional rheology, the term "whole blood viscosity" refers primarily to values obtained by placing anticoagulated blood in rotational viscometers at varying shear rates. Since the results reported in my application are quite different from those of conventional viscometers and since entirely different phenomena are measured, the term rheocohesion is used below in place of viscosity.