Physicochemical properties of plasma. Physicochemical properties of blood: viscosity, specific gravity, osmotic and oncotic pressure What determines the viscosity of blood physiology

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The functions of blood are largely determined by its physicochemical properties, among which the most important are

• Osmotic pressure, Oncotic pressure, Colloidal stability, Suspension stability, Specific gravity and viscosity.

Osmotic pressure

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The osmotic pressure of blood depends on the concentration in the blood plasma of molecules of substances dissolved in it (electrolytes and non-electrolytes) and is the sum of the osmotic pressures of the ingredients contained in it. In this case, over 60% of the osmotic pressure is created by sodium chloride, and in total, inorganic electrolytes account for up to 96% of the total osmotic pressure. Osmotic pressure is one of the rigid homeostatic constants and in a healthy person averages 7.6 atm with a possible fluctuation range of 7.3-8.0 atm.

• Isotonic solution... If the liquid of the internal environment or an artificially prepared solution has the same osmotic pressure as normal blood plasma, such a liquid medium or solution is called isotonic.
• Hypertonic solution... A fluid with a higher osmotic pressure is called hypertonic.
• Hypotonic solution... A fluid with a lower osmotic pressure is called hypotonic.

Osmotic pressure ensures the transition of the solvent through a semi-permeable membrane from a less concentrated solution to a more concentrated solution, therefore it plays an important role in the distribution of water between the internal environment and the cells of the body. So, if the interstitial fluid is hypertonic, then water will enter it from both sides - from the blood and from the cells, on the contrary, when the extracellular medium is hypotonic, water passes into the cells and blood.

A similar reaction can be observed on the part of blood erythrocytes when the osmotic pressure of the plasma changes: with hypertonicity of the plasma, the erythrocytes, giving off water, shrink, and when the plasma is hypotonic, they swell and even burst. The latter is used in practice to determine osmotic resistanceerythrocytes. Thus, 0.89% NaCl solution is isotonic to blood plasma. Erythrocytes placed in this solution do not change their shape. In sharply hypotonic solutions and, especially, water, erythrocytes swell and burst. The destruction of red blood cells is called hemolysis,and in hypotonic solutions - osmotic hemolysis . If we prepare a series of NaCl solutions with a gradually decreasing concentration of sodium chloride, i.e. hypotonic solutions, and interfere with the suspension of erythrocytes in them, then you can find the concentration of the hypotonic solution at which hemolysis begins and single erythrocytes are destroyed or hemolyzed. This NaCl concentration characterizes minimal osmotic resistance erythrocytes (minimal hemolysis), which in a healthy person is in the range of 0.5-0.4 (% NaCl solution). In more hypotonic solutions, more and more erythrocytes are hemolyzed, and the NaCl concentration at which all erythrocytes will be lysed is called maximum osmotic resistance (maximum hemolysis). In a healthy person, it ranges from 0.34 to 0.30 (% NaCl solution).
The mechanisms of regulation of osmotic homeostasis are described in Chapter 12.

Oncotic pressure

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Oncotic pressure is the osmotic pressure created by proteins in a colloidal solution, therefore it is also called colloid osmotic.Due to the fact that blood plasma proteins poorly pass through the walls of the capillaries into the tissue microenvironment, the oncotic pressure created by them ensures the retention of water in the blood. If the osmotic pressure due to salts and small organic molecules, due to the permeability of the histohematological barriers, is the same in plasma and tissue fluid, then the oncotic pressure in the blood is significantly higher. In addition to the poor permeability of barriers for proteins, their lower concentration in the tissue fluid is associated with the leaching of proteins from the extracellular environment by the lymph flow. Thus, there is a protein concentration gradient between blood and tissue fluid and, accordingly, an oncotic pressure gradient. So, if the oncotic pressure of blood plasma averages 25-30 mm Hg, and in tissue fluid - 4-5 mm Hg, then the pressure gradient is 20-25 mm Hg. Since blood plasma contains the most albumin from proteins, and the albumin molecule is less than other proteins and its molal concentration is therefore almost 6 times higher, the plasma oncotic pressure is created mainly by albumin. A decrease in their content in blood plasma leads to the loss of water in plasma and tissue edema, and an increase leads to water retention in the blood.

Colloidal stability

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Colloidal stability of blood plasma is due to the nature of hydration of protein molecules and the presence on their surface of a double electric layer of ions, which creates a surface or phi potential. Part of the phi potential is electrokineticcue(zeta) potential.The zeta potential is the potential at the boundary between a colloidal particle capable of moving in an electric field and the surrounding liquid, i.e. potential of the sliding surface of a particle in a colloidal solution. The presence of the zeta potential at the sliding boundaries of all dispersed particles forms on them the same charges and electrostatic repulsive forces, which ensures the stability of the colloidal solution and prevents aggregation. The higher the absolute value of this potential, the greater the force of repulsion of protein particles from each other. Thus, the zeta potential is a measure of the stability of a colloidal solution. The value of this potential is significantly higher in plasma albumin than in other proteins. Since there are much more albumin in plasma, colloidal stability of blood plasma is mainly determined by these proteins, which provide colloidal stability of not only other proteins, but also carbohydrates and lipids.

Suspension properties

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The suspension properties of blood are associated with the colloidal stability of plasma proteins, i.e. maintaining cellular elements in suspension. The value of the suspension properties of blood can be estimated by erythrocyte sedimentation rate(ESR) in a motionless blood volume.

Thus, the higher the content of albumin in comparison with other, less stable colloidal particles, the greater the suspension capacity of the blood, since the albumin is adsorbed on the surface of erythrocytes. On the contrary, with an increase in the level of globulins, fibrinogen, and other large-molecular and unstable proteins in a colloidal solution in the blood, the erythrocyte sedimentation rate increases, i.e. the suspension properties of blood fall. Normal ESR in men is 4-10 mm / h, and in women - 5-12 mm / h.

Blood viscosity

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Viscosity is the ability to resist the flow of liquid when some particles move relative to others due to internal friction. In this regard, the viscosity of blood is a complex effect of the relationship between water and colloidal macromolecules, on the one hand, and plasma and corpuscles, on the other. Therefore, the viscosity of plasma and the viscosity of whole blood are significantly different: the viscosity of plasma is 1.8-2.5 times higher than that of water, and the viscosity of blood is 4-5 times higher than the viscosity of water. The more large-molecular proteins, especially fibrinogen, lipoproteins, are in the blood plasma, the higher the plasma viscosity. With an increase in the number of erythrocytes, especially their ratio with plasma, i.e. hematocrit, blood viscosity increases sharply. An increase in viscosity is also facilitated by a decrease in the suspension properties of blood, when erythrocytes begin to form aggregates. At the same time, there is a positive feedback - an increase in viscosity, in turn, enhances the aggregation of red blood cells - which can lead to a vicious circle. Since blood is a heterogeneous medium and belongs to non-Newtonian fluids, which are characterized by structural viscosity, a decrease in flow pressure, for example, blood pressure, increases blood viscosity, and with an increase in pressure due to the destruction of the structure of the system, the viscosity decreases.

Another feature of blood as a system that, along with Newtonian and structural viscosity, is fareus-Lindquist effect.In a homogeneous Newtonian fluid, according to Poiseuille's law, the viscosity increases with decreasing tube diameter. Blood, which is a heterogeneous non-Newtonian fluid, behaves differently. With a decrease in the radius of the capillaries less than 150 microns, the blood viscosity begins to decrease. The Fareus-Lindqvist effect facilitates the movement of blood in the capillaries of the bloodstream. The mechanism of this effect is associated with the formation of a parietal plasma layer, the viscosity of which is lower than that of whole blood, and the migration of erythrocytes into the axial current. With a decrease in the diameter of the vessels, the thickness of the parietal layer does not change. There are fewer erythrocytes in the blood moving through the narrow vessels in relation to the plasma layer, because some of them are delayed when blood enters narrow vessels, and erythrocytes in their current move faster and their residence time in a narrow vessel decreases.

The viscosity of blood is directly proportional to the value of the total peripheral vascular resistance to blood flow, i.e. affects the functional state of the cardiovascular system.

Specific gravity of blood

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The specific gravity of blood in a healthy middle-aged person ranges from 1.052 to 1.064 and depends on the number of erythrocytes, their hemoglobin content, and plasma composition.
In men, the proportion is higher than in women due to the different content of erythrocytes. The specific gravity of erythrocytes (1.094-1.107) is significantly higher than that of plasma (1.024-1.030), therefore, in all cases of an increase in hematocrit, for example, with thickening of blood due to loss of fluid during sweating under conditions of hard physical work and high ambient temperatures, it is noted an increase in the specific gravity of blood.

Physicochemical properties of blood

Polycythemic hypervolemia

Oligocythemic hypervolemia

Increase in blood volume due to plasma (decrease in hematocrit).

It develops with water retention in the body due to kidney disease, with the introduction of blood substitutes. It can be simulated experimentally by intravenous administration of an isotonic sodium chloride solution to animals.

An increase in blood volume due to an increase in the number of erythrocytes (an increase in hematocrit).

Observed during prolonged intense physical work.

It is also observed with a decrease in atmospheric pressure, as well as with various diseases associated with oxygen starvation (heart disease, emphysema) and is considered as a compensatory phenomenon.

However, with true erythremia (Vakez disease) polycythemic hypervolemia is a consequence of the proliferation of cells of the erythrocyte series of the bone marrow.

Can be observed during muscle work time [++ 736 + C.138-139]. Part of the plasma through the walls of the capillaries leaves the vascular bed into the intercellular space of the working muscles [++ 736 + C.138-139] (muscle, tissue work edema [НД55]). As a result, the volume of circulating blood decreases [++ 736 + C.138-139]. As the formed elements remain in the vascular bed, the hematocrit increases [++ 736 + C.138-139]. This phenomenon is called working hemoconcentration (for more details see [++ 736 + C.138-139]. 11 [++ 736 + C.138-139] .2 [++ 736 + C.138-139] .3) [++ 736 + C. 138-139].

Let's consider a specific case (task) [++ 736 + C.138-139].

How will the hematocrit change during physical work, if the blood volume at rest is 5.5 liters [++ 736 + C.138-139], the plasma volume is 2.9 liters, which changes by 500 ml?

The blood volume at rest is 5.5 liters [++ 736 + C.138-139]. Of these, 2.9 liters are plasma and 2.6 liters are blood corpuscles, which corresponds to a hematocrit of 47% (2.6 / 5.5) [++ 736 + C.138-139]. If during operation 500 ml of plasma leaves the vessels, the circulating blood volume is reduced to 5 liters [++ 736 + C.138-139]. Since the volume of blood cells does not change in this case, the hematocrit increases - up to 52% (2.6 / 5.0) [++ 736 + C.138-139].

More Pokrovsky I volume pp. 280-284.

The physico-chemical properties of blood include:

Density (absolute and relative)

Viscosity (absolute and relative)

Osmotic pressure, including oncotic (colloid-osmotic) pressure

Temperature

Hydrogen ion concentration (pH)

Suspension stability of blood, characterized by ESR

Blood color

Blood color determined by hemoglobin content, bright red color of arterial blood - oxyhemoglobin , dark red with a bluish tinge, the color of venous blood - reduced hemoglobin.

Density - bulk density

Relative blood density is 1.058 - 1.062 and depends mainly on the content of erythrocytes.

The relative density of blood plasma is mainly determined by the concentration of proteins and is 1.029-1.032.

Density of water (absolute) \u003d 1000 kg m -3.

Blood viscosity

More Remizov ++ 636 + С.148

Viscosity is internal friction.

Water viscosity (at 20 ° C) 0.001 Pa × s or 1 mPa × s.

The viscosity of human blood (at 37 ° C) is normally 4-5 mPa s, with pathology it fluctuates 1.7 ¸ 22.9 mPa s.

Relative blood viscosity 4.5-5.0 times the viscosity of water. Plasma viscosity does not exceed 1.8-2.2.

The ratio of blood viscosity and water viscosity at the same temperature is called relative blood viscosity.

Changes in the viscosity of blood as a non-Newtonian fluid

Blood - non-Newtonian fluid - abnormal viscosity, i.e. the blood flow is variable.

Viscosity of blood in vessels

The slower the blood speed, the higher the blood viscosity. This is due to reversible aggregation of erythrocytes (the formation of coin bars), adhesion of erythrocytes to the walls of blood vessels.

The Fareus-Lindqvist phenomenon

In vessels with a diameter of less than 500 microns, the viscosity decreases sharply and approaches the viscosity of plasma. This is due to the orientation of erythrocytes along the axis of the vessel and the formation of a “cell-free marginal zone”.

Blood viscosity and hematocrit

The viscosity of blood depends mainly on the content of erythrocytes and to a lesser extent on plasma proteins.

An increase in Ht is accompanied by a more rapid increase in blood viscosity than with a linear relationship

The viscosity of venous blood is somewhat higher than that of arterial [B56].

The viscosity of the blood increases with the emptying of the blood depot, which contains a greater number of red blood cells.

Venous blood has a slightly higher viscosity than arterial blood. With hard physical work, blood viscosity increases.

Some infectious diseases increase viscosity, while others, such as typhoid fever and tuberculosis, decrease it.

Blood viscosity affects the erythrocyte sedimentation rate (ESR).

Methods for determining blood viscosity

The set of methods for measuring viscosity is called viscometry, and the devices used for such purposes - viscometers.

The most common viscometry methods are:

falling ball

capillary

rotary.

Capillary method is based on the Poiseuille formula and consists in measuring the time of flow of a liquid of a known mass through a capillary under the action of gravity at a certain pressure drop.

The falling ball method is used in viscometers based on Stokes' law.

There is no harmonious theory of the deformation mechanism of erythrocytes. Apparently, this mechanism is based on the general principles of sol-gel transition. It is assumed that the deformation of erythrocytes is an energy-dependent process. Perhaps hemoglobin A takes an active part in it. It is known that the content of hemoglobin A in the erythrocyte decreases in some hereditary blood diseases (sickle-cell anemia), after operations under artificial circulation. At the same time, the shape of erythrocytes and their plasticity change. An increased blood viscosity is observed, which does not correspond to a low Ht.

Plasma viscosity. Plasma as a whole can be classified as "Newtonian" liquids. Its viscosity is relatively stable in various parts of the circulatory system and is mainly determined by the concentration of globulins. Among the latter, fibrinogen is of primary importance. It is known that the removal of fibrinogen reduces the plasma viscosity by 20%, so the viscosity of the resulting serum approaches the viscosity of water.

The normal plasma viscosity is about 2 rel. units This is approximately 1/15 of the internal resistance that develops with whole blood in the venous microcirculation. However, plasma has a very significant effect on peripheral blood flow. In the capillaries, the viscosity of the blood is halved compared to the proximal and distal vessels of a larger diameter (phenomenon §). This "prolapse" of viscosity is associated with the axial orientation of erythrocytes in a narrow capillary. In this case, the plasma is pushed back to the periphery, to the vessel wall. It serves as a "lubricant" that allows the chain of blood cells to slide with minimal friction.

This mechanism functions only when the plasma protein composition is normal. An increase in the level of fibrinogen or any other globulin leads to obstruction of capillary blood flow, sometimes of a critical nature. So, myeloma, Waldenstrom's macroglobulinemia and some collagenoses are accompanied by excessive production of immunoglobulins. In this case, the viscosity of the plasma increases relative to the normal level by 2-3 times. Symptoms of severe microcirculation disorders begin to predominate in the clinical picture: decreased vision and hearing, drowsiness, weakness, headache, paresthesia, bleeding of the mucous membranes.

Pathogenesis of hemorheological disorders. In the practice of intensive care, hemorheological disorders arise under the influence of a complex of factors. The action of the latter in a critical situation is universal.

Biochemical factor. On the first day after surgery or injury, the fibrinogen level is usually doubled. The peak of this increase falls on the 3-5th day, and the normalization of the fibrinogen content occurs only by the end of the 2nd postoperative week. In addition, fibrinogen degradation products, activated platelet procoagulants, catecholamines, prostaglandins, and LPO products appear in the bloodstream in excess amounts. They all act as inducers of red blood cell aggregation. A peculiar biochemical situation is formed - "rheotoxemia".

Hematological factor. Surgical intervention or trauma is also accompanied by certain changes in the cellular composition of the blood, which are called hematological stress syndrome. Young granulocytes, monocytes and platelets of increased activity enter the bloodstream.

Hemodynamic factor. The increased aggregation tendency of blood cells under stress is superimposed on local hemodynamic disturbances. It has been shown that with uncomplicated abdominal interventions, the volumetric blood flow velocity through the popliteal and iliac veins decreases by 50%. This is due to the fact that immobilization of the patient and muscle relaxants block the physiological mechanism of the "muscle pump" during the operation. In addition, under the influence of mechanical ventilation, anesthetics or blood loss, systemic pressure decreases. In such a situation, the kinetic energy of systole may not be enough to overcome the adhesion of blood cells to each other and to the vascular endothelium. The natural mechanism of hydrodynamic disaggregation of blood cells is disrupted, and microcirculatory stasis occurs.

Hemorheological disorders and venous thrombosis. Slowing down the speed of movement in the venous section of the blood circulation provokes the aggregation of erythrocytes. However, the inertia of movement may be large enough and the blood cells will experience an increased deformation load. Under its influence, ATP is released from erythrocytes - a powerful inducer of platelet aggregation. The low shear rate also stimulates the adhesion of young granulocytes to the venule wall (Farheus-Vejiens phenomenon). Irreversible aggregates are formed, which can make up the cell nucleus of a venous thrombus.

Further development of the situation will depend on the activity of fibrinolysis. As a rule, an unstable balance occurs between the processes of formation and resorption of a thrombus. For this reason, most cases of deep vein thrombosis of the lower extremities in hospital practice are latent and resolve spontaneously, without consequences. The use of antiplatelet agents and anticoagulants is a highly effective way to prevent venous thrombosis.

Methods for studying the rheological properties of blood. The “non-Newtonian” character of blood and the associated shear rate factor must be taken into account when measuring viscosity in clinical laboratory practice. Capillary viscometry is based on gravity flow of blood through a graduated vessel and is therefore physiologically incorrect. The real conditions of blood flow are simulated on a rotational viscometer.

The basic elements of such a device include the stator and the rotor congruent to it. The gap between them serves as a working chamber and is filled with a blood sample. The movement of the fluid is initiated by the rotation of the rotor. It, in turn, is arbitrarily set in the form of a certain shear rate. The measured quantity is the shear stress, which occurs as a mechanical or electrical moment required to maintain the selected speed. The blood viscosity is then calculated using Newton's formula. The unit of measurement of blood viscosity in the CGS system is Poise (1 Poise \u003d 10 dynes x s / cm 2 \u003d 0.1 Pa x s \u003d 100 rel. Units).

It is considered mandatory to measure blood viscosity in the range of low (100 s -1) shear rates. The low shear rate range reproduces blood flow conditions in the venous microcirculation. The determined viscosity is called structural. It mainly reflects the tendency of erythrocytes to aggregate. High shear rates (200-400 s -1) are achieved in vivo in the aorta, great vessels and capillaries. At the same time, as rheoscopic observations show, erythrocytes occupy a predominantly axial position. They stretch in the direction of movement, their membrane begins to rotate relative to the cellular contents. Due to hydrodynamic forces, an almost complete disaggregation of blood cells is achieved. The viscosity, determined at high shear rates, depends primarily on the plasticity of the red blood cells and the shape of the cells. It is called dynamic.

As a standard for research on a rotational viscometer and the corresponding norm, indicators according to the method of N.P. Alexandrova et al. (1986) (Table 23.2).

Table 23.2.

The rate of blood viscosity in rotational viscometry

Shear rate, s -1
Blood viscosity, cPoise

For a more detailed presentation of the rheological properties of blood, several more specific tests are performed. The deformation capacity of erythrocytes is assessed by the speed of passage of diluted blood through a microporous polymer membrane (d \u003d 2-8 μm). The aggregation activity of red blood cells is studied using nephelometry by changing the optical density of the medium after adding aggregation inducers (ADP, serotonin, thrombin or adrenaline) to it.

Diagnostics of hemorheological disorders ... Disorders in the hemorheological system, as a rule, are latent. Their clinical manifestations are nonspecific and subtle. Therefore, the diagnosis is determined mainly by laboratory data. Its leading criterion is the value of blood viscosity.

The main direction of shifts in the hemorheological system in critically ill patients is the transition from increased blood viscosity to a lower one. This dynamic, however, is accompanied by a paradoxical deterioration in blood flow.

Syndrome of high blood viscosity. It is nonspecific and widespread in the clinic of internal diseases: with atherosclerosis, angina pectoris, chronic obstructive bronchitis, gastric ulcer, obesity, diabetes mellitus, obliterating endarteritis, etc. At the same time, a moderate increase in blood viscosity up to 35 cP is noted at y \u003d 0, 6 s -1 and 4.5 cPis at y \u003d 150 s -1. Microcirculatory disorders are usually mild. They progress only as the underlying disease develops. High viscosity syndrome in patients admitted to the intensive care unit should be considered a background condition.

Low blood viscosity syndrome. As the critical state unfolds, blood viscosity decreases due to hemodilution. Viscometry indicators are 20-25 cP at y \u003d 0.6 s -1 and 3-3.5 cps at y \u003d 150 s -1. Similar values \u200b\u200bcan be predicted for Ht, which usually does not exceed 30-35%. In the terminal state, the decrease in blood viscosity reaches the stage of "very low" values. Severe hemodilution develops. Ht decreases to 22-25%, the dynamic blood viscosity - up to 2.5-2.8 cP and the structural viscosity of blood - up to 15-18 c Poise

The low blood viscosity in a patient in critical condition creates a deceptive impression of hemorheological well-being. Despite hemodilution, microcirculation significantly deteriorates in low blood viscosity syndrome. The aggregation activity of red blood cells increases 2-3 times, the passage of erythrocyte suspension through nucleopore filters slows down 2-3 times. After reduction of Ht by hemoconcentration in vitro, blood hyperviscosity is detected in such cases.

Against the background of low or very low blood viscosity, massive aggregation of erythrocytes can develop, which completely blocks the microvasculature. This phenomenon, described by M.N. Knisely in 1947 as a "sludge" -phenomenon, testifies to the development of a terminal and, apparently, irreversible phase of a critical state.

The clinical picture of the syndrome of low blood viscosity is made up of severe microcirculatory disorders. Note that their manifestations are nonspecific. They can be caused by other, non-rheological mechanisms.

Clinical manifestations of low blood viscosity syndrome:

Tissue hypoxia (in the absence of hypoxemia);

Increased OPSS;

Deep vein thrombosis of the extremities, recurrent pulmonary thromboembolism;

Adinamia, sopor;

Deposition of blood in the liver, spleen, subcutaneous vessels.

Prevention and Treatment. Patients entering the operating room or intensive care unit need to optimize the rheological properties of the blood. This prevents the formation of venous thrombi, reduces the likelihood of ischemic and infectious complications, and facilitates the course of the underlying disease. The most effective methods of rheological therapy are blood dilution and suppression of the aggregation activity of its formed elements.

Hemodilution. The erythrocyte is the main carrier of structural and dynamic resistance to blood flow. Therefore, hemodilution is the most effective rheological agent. Its beneficial effect has been known for a long time. For centuries, phlebotomy has been one of the most common treatments for disease. The appearance of low molecular weight dextrans was the next stage in the development of the method.

Hemodilution increases peripheral blood flow, but at the same time decreases the oxygen capacity of the blood. Under the influence of two oppositely directed factors, ultimately, DO 2 is added to the tissues. It may increase due to dilution of blood or, on the contrary, significantly decrease under the influence of anemia.

The lowest Ht, which corresponds to the safe level of DО 2, is called optimal. Its exact value is still a matter of debate. The quantitative ratios of Ht and DO 2 are well known. However, it is not possible to assess the contribution of individual factors: the tolerance of anemia, the tension of tissue metabolism, hemodynamic reserve, etc. In the general opinion, the goal of therapeutic hemodilution is Ht 30-35%. However, the experience of treating massive blood loss without blood transfusion shows that an even greater decrease in Ht to 25 and even 20% is quite safe from the point of view of tissue oxygen supply.

Currently, to achieve hemodilution, mainly three methods are used.

Hemodilution in the hypervolemic mode implies such a transfusion of fluid, which leads to a significant increase in the BCC. In some cases, a short-term infusion of 1-1.5 liters of plasma substitutes precedes induction of anesthesia and surgical intervention, in other cases requiring longer hemodilution, Ht reduction is achieved with a constant fluid load at the rate of 50-60 ml / kg of the patient's body weight per day. A decrease in the viscosity of whole blood is a major consequence of hypervolemia. Plasma viscosity, plasticity of erythrocytes and their tendency to aggregation do not change. The disadvantages of this method include the risk of volume overload of the heart.

Hemodilution in normovolemia mode was originally proposed as an alternative to heterologous transfusions in surgery. The essence of the method consists in preoperative sampling of 400-800 ml of blood into standard containers with a stabilizing solution. Controlled blood loss, as a rule, is replenished at once with the help of plasma substitutes at a rate of 1: 2. With some modification of the method, it is possible to harvest 2-3 liters of autologous blood without any side hemodynamic and hematological consequences. The collected blood is then returned during or after surgery.

Normovolemic hemodilution is not only a safe, but low-cost method of self-donation, which has a pronounced rheological effect. Along with the decrease in Ht and the viscosity of whole blood after exfusion, a persistent decrease in plasma viscosity and the aggregation capacity of erythrocytes is noted. The flow of fluid between the interstitial and intravascular space is activated, along with it, the exchange of lymphocytes and the flow of immunoglobulins from the tissues increase. All this ultimately leads to a reduction in postoperative complications. This method can be widely used for elective surgical interventions.

Endogenous hemodilution develops with pharmacological vasoplegia. The decrease in Ht in these cases is due to the fact that protein-depleted and less viscous fluid enters the vascular bed from the surrounding tissues. Epidural block, halogenated anesthetics, ganglion blockers and nitrates have a similar effect. The rheological effect accompanies the main therapeutic action of these agents. The degree of reduction in blood viscosity is not predicted. It is determined by the current state of volemia and hydration.

Anticoagulants. Heparin is obtained by extraction from biological tissues (cattle lungs). The final product is a mixture of polysaccharide fragments with different molecular weights, but with similar biological activity.

The largest fragments of heparin in a complex with antithrombin III inactivate thrombin, while fragments of heparin with a molecular weight of 7000 affect mainly the activated factor X.

The introduction in the early postoperative period of high molecular weight heparin in a dose of 2500-5000 IU under the skin 4-6 times a day has become a widespread practice. Such an appointment reduces the risk of thrombosis and thromboembolism by 1.5-2 times. Small doses of heparin do not lengthen the activated partial thromboplastin time (APTT) and, as a rule, do not cause hemorrhagic complications. Heparin therapy, along with hemodilution (intentional or collateral), is the main and most effective method of preventing hemorheological disorders in surgical patients.

Low molecular weight fractions of heparin have a lower affinity for platelet von Willebrand factor. Because of this, they, in comparison with high molecular weight heparin, even less often cause thrombocytopenia and bleeding. The first experience with the use of low molecular weight heparin (clexane, fraxiparin) in clinical practice has given promising results. Heparin preparations turned out to be equipotential to traditional heparin therapy, and according to some reports, even exceeded its preventive and therapeutic effect. In addition to safety, low molecular weight fractions of heparin are also distinguished by economical administration (1 time per day) and the absence of the need for APTT monitoring. Dose selection is usually carried out without regard to body weight.

Plasmapheresis. The traditional rheological indication for plasmapheresis is primary hyperviscosity syndrome, which is caused by excessive production of abnormal proteins (paraproteins). Their removal leads to a rapid reverse development of the disease. The effect, however, is short-lived. The procedure is symptomatic.

Currently, plasmapheresis is actively used for preoperative preparation of patients with obliterating diseases of the lower extremities, thyrotoxicosis, gastric ulcer, and purulent-septic complications in urology. This leads to an improvement in the rheological properties of blood, activation of microcirculation, and a significant reduction in the number of postoperative complications. Replace up to 1/2 of the VCP volume.

The decrease in the level of globulins and plasma viscosity after one plasmapheresis procedure can be significant, but short-term. The main beneficial effect of the procedure, which extends over the entire postoperative period, is the so-called phenomenon of resuspension. Washing of erythrocytes in a protein-free environment is accompanied by a stable improvement in the plasticity of erythrocytes and a decrease in their aggregation tendency.

Photomodification of blood and blood substitutes. During 2-3 procedures of intravenous blood irradiation with a helium-neon laser (wavelength 623 nm) of low power (2.5 mW), a distinct and long-term rheological effect is observed. According to the data of precision nephelometry, under the influence of laser therapy, the number of hyperergic reactions of platelets decreases, the kinetics of their aggregation in vitro is normalized. The viscosity of the blood remains unchanged. UV rays (with a wavelength of 254-280 nm) in the extracorporeal circuit also have a similar effect.

The mechanism of the disaggregation action of laser and ultraviolet radiation is not entirely clear. It is believed that photomodification of blood first causes the formation of free radicals. In response, antioxidant defense mechanisms are triggered, which block the synthesis of natural inducers of platelet aggregation (primarily prostaglandins).

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Physicochemical properties of blood

Blood color. It is determined by the presence in erythrocytes of a special protein - hemoglobin. Arterial blood is characterized by a bright red color, which depends on the content of hemoglobin saturated with oxygen (oxyhemoglobin). Venous blood has a dark red color with a bluish tinge, which is explained by the presence of not only oxidized, but also reduced hemoglobin in it. The more active the organ is and the more oxygen is given to the tissues by hemoglobin, the darker the venous blood looks.

Relative density of blood. It fluctuates from 1.058 to 1.062 and depends mainly on the content of erythrocytes. The relative density of blood plasma is mainly determined by the concentration of proteins and is 1.029-1.032.

Viscosity of blood. It is determined in relation to the viscosity of water and corresponds to 4.5-5.0. The viscosity of blood depends mainly on the content of erythrocytes and to a lesser extent on plasma proteins. The viscosity of venous blood is slightly higher than that of arterial, which is due to the entry of CO2 into erythrocytes, due to which their size slightly increases. The viscosity of the blood increases with the emptying of the blood depot, which contains a larger number of red blood cells. Plasma viscosity does not exceed 1.8-2.2. With an abundant protein diet, the viscosity of the plasma, and, consequently, of the blood, can increase.

Osmotic blood pressure. Osmotic pressure is the force that makes the solvent (for blood, water) pass through a semipermeable membrane from a less concentrated solution to a more concentrated solution. Osmotic blood pressure is calculated by the cryoscopic method by determining the depression (freezing point), which for blood is 0.56-0.58 ° C. Depression of a molar solution (a solution in which 1 gram-molecule of a substance is dissolved in 1 liter of water) corresponds to 1.86 ° C. Substituting the values \u200b\u200binto the Clapeyron equation, it is easy to calculate that the osmotic pressure of the blood is approximately 7.6 atm.

The osmotic pressure of blood depends mainly on the low molecular weight compounds dissolved in it, mainly salts. About 60% of this pressure is generated by NaCl. Osmotic pressure in blood, lymph, tissue fluid, tissues is approximately the same and is constant. Even in cases when a significant amount of water or salt enters the blood, the osmotic pressure does not undergo significant changes. With an excessive intake of water into the blood, water is rapidly excreted by the kidneys and passes into tissues and cells, which restores the original value of osmotic pressure. If the concentration of salts in the blood increases, then water from the tissue fluid passes into the vascular bed, and the kidneys begin to intensively remove salts. The products of digestion of proteins, fats and carbohydrates absorbed into the blood and lymph, as well as low molecular weight products of cellular metabolism, can change the osmotic pressure within small limits.

Maintaining a constant osmotic pressure plays an extremely important role in the vital activity of cells.

Oncotic pressure. It is part of the osmotic and depends on the content of large molecular compounds (proteins) in the solution. Although the concentration of proteins in plasma is quite high, the total number of molecules, due to their high molecular weight, is relatively small, due to which the oncotic pressure does not exceed 30 mm Hg. Oncotic pressure is more dependent on albumin (80% of oncotic pressure is created by albumin), which is associated with their relatively low molecular weight and a large number of molecules in the plasma.

Oncotic pressure plays an important role in the regulation of water exchange. The greater its value, the more water is retained in the vascular bed and the less it passes into the tissues and vice versa. Oncotic pressure affects the formation of tissue fluid, lymph, urine and water absorption in the intestine. Therefore, blood-substituting solutions must contain colloidal substances that can retain water.

With a decrease in the concentration of protein in the plasma, edema develops, since water is no longer retained in the vascular bed and passes into the tissues.

Blood temperature. It largely depends on the metabolic rate of the organ from which the blood flows, and fluctuates between 37-40 ° C. When the blood moves, not only does some equalization of temperature in various vessels occur, but conditions are also created for the return or preservation of heat in the body.

Suspension stability of blood (erythrocyte sedimentation rate - ESR). Blood is a suspension, or suspension, since its formed elements are suspended in plasma. A suspension of erythrocytes in plasma is supported by the hydrophilic nature of their surface, as well as by the fact that erythrocytes (like other corpuscular elements) carry a negative charge, due to which they repel each other. If the negative charge of the formed elements decreases, which may be due to the adsorption of such positively charged proteins as fibrinogen, β-globulins, paraproteins, etc., then the electrostatic "separation" between erythrocytes decreases. In this case, the erythrocytes, sticking together, form the so-called coin columns. At the same time, positively charged proteins act as inter-erythrocyte bridges. Such "coin columns", getting stuck in the capillaries, interfere with the normal blood supply to tissues and organs.

If the blood is placed in a test tube, after having added to it substances that prevent clotting, then after a while you can see that the blood is divided into two layers: the upper one consists of plasma, and the lower one is formed elements, mainly erythrocytes. Based on these properties, Farreus proposed to study the suspension stability of erythrocytes by determining the rate of their sedimentation in the blood, the coagulability of which was eliminated by the preliminary addition of sodium citrate. This indicator has received the name "erythrocyte sedimentation rate (ESR)".

The ESR value depends on age and gender. In newborns, ESR is 1-2 mm / h, in children over 1 year old and in men - 6-12 mm / h, in women - 8-15 mm / h, in the elderly of both sexes - 15-20 mm / h. The greatest influence on the value of ESR is exerted by the content of fibrinogen: with an increase in its concentration over 4 g / l, the ESR increases. ESR increases dramatically during pregnancy, when the plasma fibrinogen content increases significantly. An increase in ESR is observed in inflammatory, infectious and oncological diseases, as well as with a significant decrease in the number of erythrocytes (anemia). A decrease in ESR in adults and children over 1 year old is an unfavorable sign.

The ESR value depends more on the properties of plasma than erythrocytes. So, if the erythrocytes of a man with normal ESR are placed in the plasma of a pregnant woman, then the erythrocytes of a man settle at the same rate as in women during pregnancy.

Stabilized with an anticoagulant, the blood in the tube separates into a sediment - shaped elements(erythrocytes, leukocytes, platelets) and plasma... Plasma is a clear yellowish liquid. When blood clots outside the body (blood coagulation), a blood clot is formed, which includes the formed elements and fibrin and serum. Serum differs from plasma, first of all, in the absence of fibrinogen.

Plasma, composition of blood plasma, the value of plasma proteins.

Blood plasma is 90 - 92% water, 7 - 8% of plasma is proteins (albumin - 4.5%, globulins - 2 - 3%, fibrinogen - up to 0.5%), the rest of the dry residue falls on nutrients, minerals and vitamins. The total mineral content is approximately 0.9%. Macro- and microelements are conventionally distinguished. The limit is the concentration of the substance 1mg%. Macronutrients(sodium, potassium, calcium, magnesium, phosphorus) primarily provide osmotic blood pressure and are necessary for vital processes: sodium and potassium - for excitation processes, calcium - blood coagulation, muscle contractions, secretion; trace elements(copper, iron, cobalt, iodine) are considered as components of biologically active substances, activators of enzymatic systems, stimulants of hematopoiesis, metabolism.

4. Physicochemical properties of plasma. Oncotic and osmotic blood pressure.

Oncotic and osmotic pressure is the force with which the molecules of organic and inorganic matter attract a water molecule to them to create a water shell. Osmotic pressure is created by substances of inorganic nature, oncotic - organic.

With a total osmotic pressure of plasma of 7.6 atm, oncotic pressure is 0.03-0.04 atm (25-30 mm Hg). Large-molecular proteins do not penetrate into the interstitial space from the vascular bed and are a factor determining the reverse flow of water from the intercellular space in the venular part of the microvasculature. Osmotic and oncotic pressure determine the volumetric distribution of water between the cell and the extracellular space. Water moves through the membrane towards a higher osmotic pressure. By the magnitude of the osmotic pressure (the main role in maintaining which is 80% NaCl, 15% glucose and 5% urea) relative to plasma, all solutions can be divided into:

1. Isotonic - equal in osmotic pressure (0.9% NaCl solution).

2. Hypotonic - with a lower osmotic pressure in relation to plasma.

3. Hypertensive - with a plasma osmotic pressure exceeding. All injection solutions must be isotonic to the cell, otherwise they can cause either the loss of water by the cell (hypertonic solutions), or the ingress of water into the cell, followed by its swelling and rupture of the membrane (hypotonic solutions).

The acid-base state of the blood. Buffer systems. Alkalosis and acidosis

Acid-base state of blooddepends on the concentration of hydrogen ions in the medium, which is expressed in pH units. The concentration of hydrogen ions (pH \u003d -lg [H +] at the level of 7.37 - 7.43 for arterial blood is a rigid constant in the body. The pH of venous blood due to the higher concentration of carbon dioxide and organic acids is lower and decreases to 7.30 - 7.35, intracellular pH is equal to 7.26 - 7.30 An increase in the concentration of hydrogen ions (decrease in pH) is defined as acidosis, and the decrease in the proton concentration is denoted as alkalosis... Maintaining the constancy of blood pH is ensured by physicochemical buffer systems and the functioning of the physiological systems of the body - excretory and respiration.

Any buffer system consists of an equilibrium ratio of protons (H +), a conjugated base (A -), and an undissociated weak acid: In accordance with the law of mass action, an increase in the content of protons is accompanied by an increase in the concentration of undissociated acid, and alkalization of the medium leads to an increase in the dissociation of the acid with the formation of protons , and the dissociation (equilibrium) constant K does not change.