Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Patent
1995-03-28
1996-10-15
Noland, Thomas P.
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
73 5426, 73 6442, 73 6165, 73 5402, G01N 1116, G01N 1505
Patent
active
055656200
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of measuring rheological properties of a sample, and a rheometer for carrying out the method.
In medicine, rheology is a little used branch of science. The only exception is the measuring of the blood sedimentation reaction which for many years has been carried out to a large extent in order to check whether a person is sound. The blood sedimentation reaction is connected to the viscosity of the blood.
However, it is known that the viscosity of other body fluids may also be affected by a person's state of health. One knows, for example, that changes in the viscosity of the bile mirrors various states of ill-health in the liver and the biliary passages. Moreover, there is a strong connection between the function of the mucus in the bronchi and the elasticity of the mucus. A further example is that cardiac infarction is associated with an increase of the whole-blood viscosity.
It would thus be of interest if one could study in a simple manner the viscosity of different body fluids, such as blood, saliva, bronchial mucus, bile, semen, vaginal secretion, lachrymal fluid, synovial fluid and peritoneal fluid. However, today no apparatus is available for quick and simple registration of the viscosity of body fluids.
When measuring the blood sedimentation reaction, the sedimentation rate of the red blood corpuscles is determined by filling a test tube with blood and then allowing it to stand for about 1 h, whereupon the height of the plasma column above the blood corpuscles is measured. This measuring process is slow and cannot be used for other body fluids.
In industries, it is known to determine the viscosity of liquids by means of rotary rheometers.
A prior art, Couette-type rotary rheometer comprises two cylinders of slightly different diameters, one arranged in the other. The outer cylinder can be rotated by means of a drive, and the inner is stationary. The liquid sample whose viscosity should be determined is placed in the gap between the cylinders. The viscosity of the liquid sample is determined by measuring the moment by which the liquid affects the inner cylinder as the outer cylinder is rotated and the liquid is shorn between the cylinders.
For a number of reasons, such a rheometer is however not suited for use with body fluids since the volume of the fluid sample must be at least 10 ml to produce accurate viscosity values. Some body fluids, e.g. synovial fluid, has a total volume in the body of this magnitude, and therefore samples cannot be taken that are sufficient for the determination of viscosity.
Furthermore, some body fluids are of very low viscosity, in fact close to that of water. The viscosity of such fluids cannot be measured by means of the prior art rheometer since the effect of the fluid sample on the stationary cylinder is too small to be measured.
Finally, the prior art rheometer is far too expensive to make extensive use in medical attendance realistic.
One object of the invention therefore is to provide a method and a rheometer for measuring rheological properties of a fluid, which makes it possible to determine the viscosity of low viscosity fluids and/or small volumes of fluid samples.
A further object of the invention is to provide a method and a device which can replace the traditional measuring of the blood sedimentation reaction.
These objects are achieved by means of a method and a device having the characteristic features stated in the accompanying claims.
By causing an oscillation system containing the sample to perform free oscillations and by measuring the damping of the oscillation, which is caused by the sample, rheological properties of the sample can be determined. This principle can be generally used independently of the volume and viscosity of the sample. The method according to the invention can thus be used as an alternative to the known method described above.
The theory behind the invention is the following. Now assuming that a hollow cylinder whose inner radius is R and whose inner height is H is suspended by a torsion w
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Aktiebolaget Medicinsk Reologi Lund
Larkin Daniel S.
Noland Thomas P.
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