Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Gelling or coagulation
Patent
1996-09-12
1998-07-07
Williams, Hezron E.
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Gelling or coagulation
356 39, 422 73, 436 69, G01N 3349
Patent
active
057772150
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus for measuring the coagulation characteristics of test liquids.
An apparatus for measuring the coagulation characteristics of test liquids is disclosed in DE 845 720 and DE-U 76 16 452. In this apparatus a rod is freely suspended at a torsion wire and provided with a stem at its lower end, which stem is immerged into a cup receiving the test liquid for measuring the coagulation characteristics of the test liquid. Usually about 0.36 ml of a test liquid, for example blood, will be in the cup. During the measurement the cup is rotated leftwards and rightwards by 4.75.degree. with a harmonic motion and a period of 10 sec. Conventionally the cup has a diameter of 8 mm and the stem has a diameter of 6 mm. The measurement is based on the fact that the rotation of the cup is not transmitted to the stem as long as there is no link between the stem and the cup. If such a link is formed, for example by networks of fibrin fibres and platelets, the stem more and more follows the rotation of the cup. The forming network tends to counteract a difference in relative angle of rotation between the stem and the cup. Thus, a torque is transmitted from the rotating cup to the stem, and this torque is the higher the more pronounced the network between stem and cup is. On the other hand, the torsion wire acts against an excursion of the stem from its rest position. Hence, a torque equilibrium between the restoring torque of the torsion wire and the torque acting onto the stem is obtained, whereby inertial forces as well as viscous forces can be neglected, because the movements are very slow. The amplitude of the stem movement therefore represents a measure for the strength of the forming network or clot. The amplitude is exactly measured and plotted as a function of time. As outlined above, in the prior art apparatus the stem is freely suspended at the torsion wire through the corresponding rod, whereby the torsion wire exerts the above-mentioned restoring torque. This results in a high sensibility for vibration and translation movements of the measuring device, which distorts the measurements. One has tried to counteract these distorsions by providing the rod with laterally projecting paddles which are lowered into an oil-filled chambered trough. As explained in DE-U-76 16 452, in spite of the provision of the mentioned oil troughs and paddles, the sensitivity to disturbing influences is so high that an optical detection of the angle of rotation of the stem by means of known detection devices is disturbed. The known application describes an expensive inductive differential transformer angle sensor which is made to reduce signal disturbances resulting from movements of the stem which are not caused by the rotation thereof. The known devices consist of a large number of individually manufactured parts, which is expensive, and are again sensitive to shocks, because the respective measuring system is freely suspended. Furthermore, the known devices require an involved operation, because the chambers containing the oil must be filled and the systems must be exactly balanced. The transport of such an apparatus is extremely tedious, in particular because the oil containing chambers must be previously drained and again filled before further operation.
Further devices for measuring coagulation characteristics of blood samples are disclosed in GB 1 353 481 (FIG. 2).
It is the object of the invention to improve an apparatus of the initially defined kind so that it is more stable, less sensitive and easier to manufacture.
According to the invention a mechanical support system is provided which limits the decrease of freedom of the stem to the rotation around the normal or vertical axis.
The inventive apparatus guarantees a nearly frictionless function of the mechanical support system, preferably in form of a ball bearing. Hence, this apparatus allows an exact and correct movement of the stem even at a moment where the blood clot transmits an extremely small force to the stem. This is extremely important
REFERENCES:
patent: 3053078 (1962-09-01), Jewett
patent: 3714815 (1973-02-01), Hartert
Shoupu Chen, Nitish V. Thakor and James W. Wagner, A Microprocessor-Based Two-Channel Thromboelastograph, IEEE Transactions on Biomedical Engineering, vol. BME-33, No. 9, at 887-890 (Sep. 1986).
Calatzis Alexander
Calatzis Andreas
Fritzsche Pablo
Larkin Daniel S.
Williams Hezron E.
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