Rheological properties of blood and other biological fluids. What is blood rheology

Occurring at inflammatory processes in the lungs changes at the cellular and subcellular levels have a significant impact on the rheological properties of blood, and through the disturbed metabolism of biologically active substances (BAS) and hormones - on the regulation of local and systemic blood flow. As is known, the state of the microcirculatory system is largely determined by its intravascular link, which is studied by hemorheology. Such manifestations of hemorheological properties of blood as the viscosity of plasma and whole blood, the patterns of fluidity and deformation of its plasma and cellular components, the process of blood coagulation - all this can clearly respond to many pathological processes in the body, including the process of inflammation.

Development of inflammatory processes in lung tissue accompanied by a change in the rheological properties of blood, increased aggregation of erythrocytes, leading to microcirculation disorders, the occurrence of stasis and microthrombosis. A positive correlation was noted between changes in the rheological properties of blood and the severity of the inflammatory process and the degree of intoxication syndrome.

Assessing blood viscosity in patients with various forms of COPD, most researchers found it to be increased. In some cases, in response to arterial hypoxemia, COPD patients develop polycythemia with an increase in hematocrit up to 70%, which significantly increases blood viscosity, making it possible for some researchers to classify this factor as one of those that increase pulmonary vascular resistance and load on the right heart. The combination of these changes in COPD, especially during an exacerbation of the disease, causes a deterioration in the properties of blood flow and the development of a pathological syndrome of increased viscosity. However, increased blood viscosity in these patients can be observed with normal hematocrit and plasma viscosity.

Of particular importance to rheological state of blood have aggregation properties of erythrocytes. Almost all studies that have studied this indicator in patients with COPD indicate an increased ability to aggregate erythrocytes. Moreover, a close relationship was often observed between an increase in blood viscosity and the ability of erythrocytes to aggregate. In the process of inflammation in COPD patients, the amount of coarsely dispersed positively charged proteins (fibrinogen, C-reactive protein, globulins) sharply increases in the bloodstream, which, combined with a decrease in the number of negatively charged albumins, causes a change in the hemoelectric status of the blood. Adsorbed on the erythrocyte membrane, positively charged particles cause a decrease in its negative charge and suspension stability of blood.

For erythrocyte aggregation Immunoglobulins of all classes, immune complexes and complement components influence, which can play a significant role in patients with bronchial asthma (BA).

red blood cells determine the rheology of blood and another of its properties - deformability, i.e. the ability to undergo significant changes in shape when interacting with each other and with the lumen of the capillaries. A decrease in the deformability of erythrocytes, together with their aggregation, can lead to blocking of individual sections in the microcirculation system. It is believed that this ability of erythrocytes depends on the elasticity of the membrane, the internal viscosity of the contents of the cells, the ratio of the surface of the cells to their volume.

In patients with COPD, including those with BA, almost all researchers found a decrease the ability of erythrocytes to deformation. Hypoxia, acidosis and polyglobulia are considered to be the causes of increased rigidity of erythrocyte membranes. With the development of a chronic inflammatory bronchopulmonary process, functional insufficiency progresses, and then gross morphological changes in erythrocytes occur, which are manifested by a deterioration in their deformation properties. Due to the increase in the rigidity of erythrocytes and the formation of irreversible erythrocyte aggregates, the "critical" radius of microvascular patency increases, which contributes to a sharp violation of tissue metabolism.

Role of aggregation platelets in hemorheology is of interest, first of all, in connection with its irreversibility (unlike erythrocyte) and active participation in the process of gluing platelets of a number of biologically active substances (BAS), which are essential for changes in vascular tone and the formation of bronchospastic syndrome. Platelet aggregates also have a direct capillary-blocking action, forming microthrombi and microemboli.

In the process of progression of COPD and the formation of CHLS, functional insufficiency develops. platelets, which is characterized by an increase in the aggregation and adhesive ability of platelets against the background of a decrease in their disaggregation properties. As a result of irreversible aggregation and adhesion, "viscous metamorphosis" of platelets occurs, various biologically active substrates are released into the microhemocirculatory bed, which serves as a trigger for the process of chronic intravascular microcoagulation of blood, which is characterized by a significant increase in the intensity of formation of fibrin and platelet aggregates. It has been established that disorders in the hemocoagulation system in patients with COPD can cause additional disorders of the pulmonary microcirculation up to recurrent thromboembolism of small pulmonary vessels.

T.A. Zhuravleva revealed a clear relationship between the severity microcirculation disorders and rheological properties of blood from an active inflammatory process in acute pneumonia with the development of hypercoagulation syndrome. Violations of the rheological properties of blood were especially pronounced in the phase of bacterial aggression and gradually disappeared as the inflammatory process was eliminated.

Active inflammation in AD leads to significant violations of the rheological properties of blood and, in particular, to an increase in its viscosity. This is realized by increasing the strength of erythrocyte and platelet aggregates (which is explained by the influence of a high concentration of fibrinogen and its degradation products on the process of aggregation), an increase in hematocrit, and a change in the protein composition of plasma (an increase in the concentration of fibrinogen and other coarse proteins).

Our studies of patients with AD showed that this pathology is characterized by a decrease in the rheological properties of the blood, which are corrected under the influence of trental. When comparing patients with rheological properties in mixed venous (at the entrance to the ICC) and arterial blood (at the exit from the lungs), it was found that in the process of circulation in the lungs, an increase in the properties of blood fluidity occurs. Patients with BA with concomitant systemic arterial hypertension were distinguished by a reduced ability of the lungs to improve the deformability properties of erythrocytes.

In the process of correction rheological disturbances in the treatment of BA with trental, a high degree of correlation was noted between the improvement in respiratory function and a decrease in diffuse and local changes in the pulmonary microcirculation, determined using perfusion scintigraphy.

Inflammatory lung tissue damage in COPD cause violations of its metabolic functions, which not only directly affect the state of microhemodynamics, but also cause pronounced changes in hematological metabolism. In COPD patients, a direct relationship was found between an increase in the permeability of capillary-connective tissue structures and an increase in the concentration of histamine and serotonin in the bloodstream. These patients have disturbances in the metabolism of lipids, glucocorticoids, kinins, prostaglandins, which leads to disruption of the mechanisms of cellular and tissue adaptation, changes in the permeability of microhemovessels and the development of capillary-trophic disorders. Morphologically, these changes are manifested by perivascular edema, pinpoint hemorrhages, and neurodystrophic processes with damage to the perivascular connective tissue and lung parenchyma cells.

As rightly noted by L.K. Surkov and G.V. Egorova, in patients chronic inflammatory diseases of the respiratory system, a violation of hemodynamic and metabolic homeostasis as a result of significant immunocomplex damage to the vessels of the microcirculatory bed of the lungs adversely affects the overall dynamics of the tissue inflammatory response and is one of the mechanisms of chronicity and progression of the pathological process.

Thus, the existence of close relationships between microcirculatory blood flow in tissues and the metabolism of these tissues, as well as the nature of these changes during inflammation in patients with COPD, indicate that not only the inflammatory process in the lungs causes changes in microvascular blood flow, but, in turn, the violation of microcirculation leads to an aggravation of the course of the inflammatory process, those. a vicious circle occurs.

The main characteristic of blood is its viscosity, which is divided into apparent and Caisson (dynamic):

Apparent blood viscosity. It is determined by the ratio of shear force and shear rate, measured in centipoise (cps) and characterizes the non-Newtonian behavior of blood. Depends on the state, mainly erythrocytes and platelets.
Caisson (dynamic) blood viscosity. It is determined under conditions of complete blood dispersion and depends on the protein composition of the plasma. It is measured in centipoise (cps).

Factors that most affect blood viscosity include:

temperature and ,
hematocrit,
the amount of high molecular weight proteins in plasma,
the degree of erythrocyte aggregation and its reversibility,
shear characteristics.

Liquid limit of blood. It shows what minimum force must be applied to move one layer of blood relative to another (measured in days / cm 2).

Aggregation factor. It indicates the strength of the adhesion of blood cells, that is, the strength of aggregates and (measured in days / cm 2).

All of the above parameters of blood viscosity are determined using a coaxial-cylindrical viscometer with a free-floating internal cylinder of the V.N. Zakharchenko, which makes it possible to make a model and plot a blood flow curve in a wide range of shear stresses.

Indirect indicators of blood viscosity is the value of hematocrit, the number of erythrocytes, the level of fibrinogen and globulin protein fractions, the level of total lipids and their spectrum in plasma, as well as the content of sugar in the blood. With certain diseases, for example, with varicose veins in men, as a rule, these indicators are enough to assess the viscosity and set indications for the appointment.

The degree of erythrocyte aggregation- is determined using a calorimeter - nephelometer and is expressed in units of optical density (or in percent).

Degree of platelet aggregation- (induced ADP) is determined using an aggregometer of the Elvi-840 type (England), expressed in units of optical density (or in percent).

Course of lectures on resuscitation and intensive therapy Vladimir Vladimirovich Spas

Rheological properties of blood.

For the viscosity properties of blood, the protein composition of the plasma is important. Thus, albumins reduce the viscosity and ability of cells to aggregate, while globulins act in the opposite way. Fibrinogen is especially active in increasing the viscosity and tendency of cells to aggregate, the level of which changes under any stressful conditions. Hyperlipidemia and hypercholesterolemia also contribute to the violation of the rheological properties of the blood.

Hematocrit is one of the important indicators associated with blood viscosity. The higher the hematocrit, the greater the viscosity of the blood and the worse its rheological properties. Hemorrhage, hemodilution and, conversely, plasma loss and dehydration significantly affect the rheological properties of blood. Therefore, for example, controlled hemodilution is an important means of preventing rheological disorders during surgical interventions. With hypothermia, blood viscosity increases 1.5 times compared to that at 37 C, but if the hematocrit is reduced from 40% to 20%, then with such a temperature difference, the viscosity will not change. Hypercapnia increases blood viscosity, so it is less in venous blood than in arterial blood. With a decrease in blood pH by 0.5 (with high hematocrit), blood viscosity increases threefold.

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Volume and physico-chemical properties of blood Blood volume - the total amount of blood in the body of an adult is on average 6 - 8% of body weight, which corresponds to 5-6 liters. An increase in the total blood volume is called hypervolemia, a decrease is called hypovolemia. Relative

Rheology is a field of mechanics that studies the features of the flow and deformation of real continuous media, one of the representatives of which are non-Newtonian fluids with structural viscosity. A typical non-Newtonian fluid is blood. Blood rheology, or hemorheology, studies the mechanical patterns and especially changes in the physico-colloid properties of blood during circulation at different speeds and in different parts of the vascular bed. The movement of blood in the body is determined by the contractility of the heart, the functional state of the bloodstream, and the properties of the blood itself. At relatively low linear flow velocities, blood particles are displaced parallel to each other and to the axis of the vessel. In this case, the blood flow has a layered character, and such a flow is called laminar.

If the linear velocity increases and exceeds a certain value, which is different for each vessel, then the laminar flow turns into a chaotic, vortex, which is called "turbulent". The rate of blood movement at which laminar flow becomes turbulent is determined using the Reynolds number, which for blood vessels is approximately 1160. Data on Reynolds numbers indicate that turbulence is possible only at the beginning of the aorta and at the branches of large vessels. The movement of blood through most vessels is laminar. In addition to the linear and volumetric blood flow velocity, the movement of blood through the vessel is characterized by two more important parameters, the so-called "shear stress" and "shear rate". Shear stress means the force acting on a unit surface of the vessel in the direction tangential to the surface and is measured in dynes/cm2, or in Pascals. The shear rate is measured in reciprocal seconds (s-1) and means the magnitude of the velocity gradient between parallel moving layers of fluid per unit distance between them.

Blood viscosity is defined as the ratio of shear stress to shear rate, and is measured in mPas. The viscosity of whole blood depends on the shear rate in the range of 0.1 - 120 s-1. At a shear rate >100 s-1, the changes in viscosity are not so pronounced, and after reaching a shear rate of 200 s-1, the blood viscosity practically does not change. The value of viscosity measured at high shear rate (more than 120 - 200 s-1) is called asymptotic viscosity. The principal factors affecting blood viscosity are hematocrit, plasma properties, aggregation and deformability of cellular elements. Considering the vast majority of erythrocytes compared to leukocytes and platelets, the viscous properties of blood are determined mainly by red cells.

The main factor that determines blood viscosity is the volumetric concentration of red blood cells (their content and average volume), called hematocrit. Hematocrit, determined from a blood sample by centrifugation, is approximately 0.4 - 0.5 l / l. Plasma is a Newtonian fluid, its viscosity depends on temperature and is determined by the composition of blood proteins. Most of all, plasma viscosity is affected by fibrinogen (plasma viscosity is 20% higher than serum viscosity) and globulins (especially Y-globulins). According to some researchers, a more important factor leading to a change in plasma viscosity is not the absolute amount of proteins, but their ratios: albumin / globulins, albumin / fibrinogen. The viscosity of blood increases with its aggregation, which determines the non-Newtonian behavior of whole blood, this property is due to the aggregation ability of red blood cells. Physiological aggregation of erythrocytes is a reversible process. In a healthy organism, a dynamic process of "aggregation - disaggregation" continuously occurs, and disaggregation dominates over aggregation.

The property of erythrocytes to form aggregates depends on hemodynamic, plasma, electrostatic, mechanical, and other factors. Currently, there are several theories explaining the mechanism of erythrocyte aggregation. The most famous today is the theory of the bridge mechanism, according to which bridges from fibrinogen or other large molecular proteins, in particular Y-globulins, are adsorbed on the surface of the erythrocyte, which, with a decrease in shear forces, contribute to the aggregation of erythrocytes. The net aggregation force is the difference between the bridge force, the electrostatic repulsion force of the negatively charged red blood cells, and the shear force causing disaggregation. The mechanism of fixation on erythrocytes of negatively charged macromolecules: fibrinogen, Y-globulins is not yet fully understood. There is a point of view that the adhesion of molecules occurs due to weak hydrogen bonds and dispersed van der Waals forces.

There is an explanation for the aggregation of erythrocytes through depletion - the absence of high molecular weight proteins near the erythrocytes, resulting in an "interaction pressure" similar in nature to the osmotic pressure of a macromolecular solution, which leads to the convergence of suspended particles. In addition, there is a theory that erythrocyte aggregation is caused by erythrocyte factors themselves, which lead to a decrease in the zeta potential of erythrocytes and a change in their shape and metabolism. Thus, due to the relationship between the aggregation ability of erythrocytes and blood viscosity, a comprehensive analysis of these indicators is necessary to assess the rheological properties of blood. One of the most accessible and widely used methods for measuring erythrocyte aggregation is the assessment of the erythrocyte sedimentation rate. However, in its traditional version, this test is uninformative, since it does not take into account the rheological characteristics of the blood.

Blood is a special liquid tissue of the body, in which the shaped elements are freely suspended in a liquid medium. Blood as a tissue has the following features: 1) all its constituent parts are formed outside the vascular bed; 2) the intercellular substance of the tissue is liquid; 3) the main part of the blood is in constant motion. The main functions of blood are transport, protective and regulatory. All three functions of the blood are interconnected and inseparable from each other. The liquid part of the blood - plasma - has a connection with all organs and tissues and reflects the biochemical and biophysical processes occurring in them. The amount of blood in a person under normal conditions is from 1/13 to 1/20 of the total mass (3-5 liters). The color of blood depends on the content of oxyhemoglobin in it: arterial blood is bright red (rich in oxyhemoglobin), and venous blood is dark red (poor in oxyhemoglobin). The viscosity of blood is on average 5 times higher than the viscosity of water. The surface tension is less than the tension of water. In the composition of the blood, 80% is water, 1% is inorganic substances (sodium, chlorine, calcium), 19% is organic substances. Blood plasma contains 90% water, its specific gravity is 1030, lower than that of blood (1056-1060). Blood as a colloidal system has colloidal osmotic pressure, i.e., it is able to retain a certain amount of water. This pressure is determined by the dispersion of proteins, salt concentration and other impurities. Normal colloid osmotic pressure is about 30 mm. water. Art. (2940 Pa). The formed elements of blood are erythrocytes, leukocytes and platelets. On average, 45% of the blood is formed elements, and 55% is plasma. The formed elements of the blood are a heteromorphic system consisting of elements differently differentiated in structural and functional terms. Combine their common histogenesis and coexistence in the peripheral blood.

blood plasma- the liquid part of the blood, in which the formed elements are suspended. The percentage of plasma in the blood is 52-60%. Microscopically, it is a homogeneous, transparent, somewhat yellowish liquid that collects in the upper part of the vessel with blood after sedimentation of formed elements. Histologically, plasma is the intercellular substance of the liquid tissue of the blood.

Blood plasma consists of water, in which substances are dissolved - proteins (7-8% of the plasma mass) and other organic and mineral compounds. The main plasma proteins are albumins - 4-5%, globulins - 3% and fibrinogen - 0.2-0.4%. Nutrients (in particular, glucose and lipids), hormones, vitamins, enzymes, and intermediate and end products of metabolism are also dissolved in the blood plasma. On average, 1 liter of human plasma contains 900-910 g of water, 65-85 g of protein and 20 g of low molecular weight compounds. Plasma density ranges from 1.025 to 1.029, pH - 7.34-7.43.

Rheological properties of blood.

Blood is a suspension of cells and particles suspended in plasma colloids. This is a typically non-Newtonian fluid, the viscosity of which, unlike the Newtonian, varies hundreds of times in different parts of the circulatory system, depending on the change in blood flow velocity. For the viscosity properties of blood, the protein composition of the plasma is important. Thus, albumins reduce the viscosity and ability of cells to aggregate, while globulins act in the opposite way. Fibrinogen is especially active in increasing the viscosity and tendency of cells to aggregate, the level of which changes under any stressful conditions. Hyperlipidemia and hypercholesterolemia also contribute to the violation of the rheological properties of the blood. Hematocrit- one of the important indicators associated with blood viscosity. The higher the hematocrit, the greater the viscosity of the blood and the worse its rheological properties. Hemorrhage, hemodilution and, conversely, plasma loss and dehydration significantly affect the rheological properties of blood. Therefore, for example, controlled hemodilution is an important means of preventing rheological disorders during surgical interventions. With hypothermia, blood viscosity increases 1.5 times compared to that at 37 degrees C, but if the hematocrit is reduced from 40% to 20%, then with such a temperature difference, the viscosity will not change. Hypercapnia increases blood viscosity, so it is less in venous blood than in arterial blood. With a decrease in blood pH by 0.5 (with high hematocrit), blood viscosity increases threefold.

DISORDERS OF BLOOD RHEOLOGICAL PROPERTIES.

The main phenomenon of blood rheological disorders is erythrocyte aggregation, coinciding with an increase in viscosity. The slower the blood flow, the more likely this phenomenon is to develop. The so-called false aggregates ("coin columns") are of a physiological nature and decompose into healthy cells when conditions change. True aggregates that arise in pathology do not disintegrate, giving rise to the phenomenon of sludge (translated from English as "sucks"). Cells in aggregates are covered with a protein film that glues them into irregularly shaped clumps. The main factor causing aggregation and sludge is a violation of hemodynamics - a slowdown in blood flow that occurs in all critical conditions - traumatic shock, hemorrhage, clinical death, cardiogenic shock, etc. Very often, hemodynamic disorders are combined with hyperglobulinemia in such severe conditions as peritonitis, acute intestinal obstruction, acute pancreatitis, prolonged compression syndrome, burns. They increase the aggregation of the state of fat, amniotic and air embolism, damage to erythrocytes during cardiopulmonary bypass, hemolysis, septic shock, etc., that is, all critical conditions. It can be said that the main cause of blood flow disturbance in the capillary is a change in the rheological properties of the blood, which in turn depend mainly on the blood flow velocity. Therefore, blood flow disorders in all critical conditions go through 4 stages. Stage 1- spasm of resistance vessels and changes in the rheological properties of blood. Stress factors (hypoxia, fear, pain, trauma, etc.) lead to hypercatecholaminemia, which causes primary spasm of arterioles to centralize blood flow in case of blood loss or a decrease in cardiac output of any etiology (myocardial infarction, hypovolemia in peritonitis, acute intestinal obstruction, burns, etc.) .d.). Narrowing of arterioles reduces the rate of blood flow in the capillary, which changes the rheological properties of the blood and leads to aggregation of sludge cells. This begins the 2nd stage of microcirculation disorders, at which the following phenomena occur: a) tissue ischemia occurs, which leads to an increase in the concentration of acid metabolites, active polypeptides. However, the sludge phenomenon is characterized by the fact that the flows are stratified and the plasma flowing from the capillary can carry acidic metabolites and aggressive metabolites into the general circulation. Thus, the functional ability of the organ where microcirculation was disturbed is sharply reduced. b) fibrin settles on erythrocyte aggregates, as a result of which conditions arise for the development of DIC. c) aggregates of erythrocytes, enveloped by plasma substances, accumulate in the capillary and are switched off from the bloodstream - blood sequestration occurs. Sequestration differs from deposition in that in the "depot" the physico-chemical properties are not violated and the blood ejected from the depot is included in the bloodstream, completely physiologically suitable. Sequestered blood, on the other hand, must pass through a lung filter before it can again meet physiological parameters. If the blood is sequestered in a large number of capillaries, then its volume decreases accordingly. Therefore, hypovolemia occurs in any critical condition, even in those that are not accompanied by primary blood or plasma loss. II stage rheological disorders - a generalized lesion of the microcirculation system. Before other organs, the liver, kidneys, and pituitary gland suffer. The brain and myocardium are the last to suffer. After blood sequestration has already reduced the minute volume of blood, hypovolemia, with the help of additional arteriolospasm aimed at centralizing blood flow, includes new microcirculation systems in the pathological process - the volume of sequestered blood increases, as a result of which BCC falls. Stage III- total damage to blood circulation, metabolic disorders, disruption of metabolic systems. Summing up the above, it is possible to distinguish 4 stages for any violation of blood flow: violation of the rheological properties of blood, blood sequestration, hypovolemia, generalized damage to microcirculation and metabolism. Moreover, in the thanatogenesis of the terminal state, it does not matter what was primary: a decrease in BCC due to blood loss or a decrease in cardiac output due to right ventricular failure (acute myocardial infarction). in the event of the above vicious circle, the result of hemodynamic disturbances is in principle the same. The simplest criteria for microcirculation disorders can be: a decrease in diuresis to 0.5 ml / min or less, the difference between the skin and rectal temperatures is more than 4 degrees. C, the presence of metabolic acidosis and a decrease in the arterio-venous oxygen difference are a sign that the latter is not absorbed by the tissues.

Conclusion

The cardiac muscle, like any other muscle, has a number of physiological properties: excitability, conductivity, contractility, refractoriness and automaticity.

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