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Erythrocyte Sedimentation Rate (ESR) determination in whole stabilised blood is a widely used diagnostic test indicative of severity of an illness. It is well known that ESR is elevated in many clinical conditions, e.g. malignancies, infection diseases, collagen diseases, ets. It is generally accepted that the mechanism of erythrocytes sedimentation is based on the Stocks law of sedimentation of dense particles in the viscous medium. However, there are a lot of peculiarities in the behavior of individual blood specimens, which show that the behavior of sedimentating blood does not agree with this law. For example, it was noted long ago that if measurements are taken each 10-15 min non-monotonous rate of blood sedimentation can be revealed.

In order to achieve high-temporal resolution of the process of red blood sedimentation we designed an automatic scanning device allowing to register the position of the boundary between red blood cells and plasma each 30 sec with a precision 10 mkm. Information from the scanning device is processed by a PC and is presented as plot of immediate rate of red blood sedimentation vs time (ESR-graph). The results demonstrate non-monotonous character of the rate of red blood sedimentation; reveal macroscopic stages in the whole processes. Amplitude and frequency of oscillations, duration of each stage are characteristic for blood of each particular donor, and they change in the course of patients' medical treatment.

Several unexpected phenomena in sedimentating blood have been observed. First, in most cases upwards movements up to 1 mm of the boundary between red cells and plasma were noted after its initial sedimentation for 2-3 mm (Fig. 1). Second, in many blood samples of patients with different pathologies sets of low frequency (1-10 milliHz) oscillations were developing in blood and continued for many hours. In healthy donors' blood these oscillations were absent or emerging after a prolonged «latency» phase (dozens of minutes and more), and they were highly periodic (Fig. 2). Notable also are sharp variations in ESR-graphs of iscaemic disease patients at the days of geomagnetic storms. These results show that blood is a complex non-linear system with a long-range memory.

The behavior of sedimenting blood reflects, on the one hand, mutual interactions of red cells that associate in a 3D-network constructed of the so called «ruleaux» or «piles of coins» threads. Breaking down or shrinking of several or even one thread should be followed by a cascade of collapsing of several other threads, and this is observed as a downfall event of the interface. Then the system may rest for some time in a quasi-stationary state before the new cycle evolves. On the other hand, white cells, as some of our observations suggest, also play a significant role in the dynamic process. WBC need oxygen for their survival, and RBC are the only oxygen source under the condition of ESR measurements. Most WBC are normally located at the top of the red cell pile, but according to our observations they immerse into the red cell mass from time to time, take a «breath» there and dissociate from erythrocytes. Such events may provoke shrinking of a part of the 3D network of erythrocytes. From this point of view the «negative rate of sedimentation» may be tentatively explained as the network swelling and release from it of a white cells together with some erythrocytes. Highly periodic dynamics developing in the healthy donors' blood shows that interactions of WBC and RBC are well organized. This organization can be distorted to a more or less extent under pathological conditions. We suggest that the process of blood cells sedimentation reveals the active reaction of blood, as of a surviving tissue, upon such stress factors as hypoxia, hypodynamia, action of gravitation, contact with the alien surface of glass. The parameters of this reaction depend upon the metabolic potential of blood, the functional state of all is cellular and plasma elements, and in a complex they reflect the physiological state of the individual. Thus, ESR-graphy may provide significantly more information of patients' state than the usual ESR test. Studies of blood sedimentation dynamics will allow also to get better understanding of the physiological as well as of physical-chemical processes that take place in blood - a surviving tissue outside an organism.

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