Methods for measuring blood pressure.

At any point vascular system blood pressure depends on:

and) atmospheric pressure ;

b ) hydrostatic pressure pghdue to the weight of the blood column height hand density R;

at) pressure provided by the pumping function of the heart .

In accordance with the anatomical and physiological structure of cardio-vascular system distinguish: intracardiac, arterial, venous and capillary blood pressure.

Blood pressure - systolic (during the expulsion of blood from the right ventricle) in adults is normally 100 - 140 mm. rt. Art .; diastolic (at the end of diastole) - 70 - 80 mm. rt. Art.

Blood pressure indicators in children increase with age and depend on many endogenous and exogenous factors (Table 3). In newborns, the systolic pressure is 70 mm. rt. Art., then rises to 80 - 90 mm. rt. Art.

Table 3.

Blood pressure in children.

The pressure difference to the internal ( P in) and outer ( R n) the walls of the vessel are called transmural pressure (P t): P t \u003d P in - P n.

It can be assumed that the pressure on the outer wall of the vessel is equal to atmospheric. Transmural pressure is the most important characteristic of the state of the circulatory system, determining the load of the heart, the state of the peripheral vascular bed and a number of other physiological indicators. Transmural pressure, however, does not provide the movement of blood from one point of the vascular system to another. For example, the time-average transmural pressure in a large artery of the arm is about 100 mm Hg. (1.33.10 4 Pa). At the same time, the movement of blood from the ascending aortic arch into this artery is provided difference transmural pressure between these vessels, which is 2-3 mm Hg. (0.03.10 4 Pa).

When the heart contracts, the amount of blood pressure in the aorta fluctuates. The average blood pressure for the period is practically measured. Its value can be estimated by the formula:

R cf »R d+ (P c + P d). (28)

Poiseuille's law explains the drop in blood pressure along a vessel. Since the hydraulic resistance of the blood increases with decreasing radius of the vessel, then, according to formula 12, the blood pressure drops. In large vessels, the pressure drops by only 15%, and in small ones - by 85%. therefore most of the energy of the heart is spent on the flow of blood through the small vessels.

Three measurement methods are currently known blood pressure: invasive (direct), auscultatory and oscillometric .

A needle or cannula, connected by a tube to a pressure gauge, is inserted directly into the artery. The main area of \u200b\u200bapplication is cardiac surgery. Direct manometry is practically the only method for measuring pressure in the cavities of the heart and central vessels. Venous pressure is also reliably measured using a direct method. In clinical and physiological experiments, daily invasive blood pressure monitoring is used. The needle inserted into the artery is flushed with heparinized saline using a microinfusor, and the pressure sensor signal is continuously recorded on a magnetic tape.

Fig. 12. Distribution of pressure (excess over atmospheric) in various parts circulatory system: 1 - in the aorta, 2 - in the large arteries, 3 - in the small arteries, 4 - in the arterioles, 5 - in the capillaries.

The disadvantage of direct blood pressure measurements is the need to introduce measuring devices into the vessel cavity. Without violating the integrity of blood vessels and tissues, blood pressure is measured using invasive (indirect) methods. Most indirect methods are compression - they are based on balancing the pressure inside the vessel external pressure on its wall.

The simplest of these methods is the palpation method for determining systolic blood pressure, proposed Riva Rocci. With this method, a compression cuff is applied to the middle of the upper arm. The air pressure in the cuff is measured with a pressure gauge. When air is pumped into the cuff, the pressure in it rapidly rises to a value above the systolic value. Then the air from the cuff is slowly released, while observing the appearance of a pulse in the radial artery. Having fixed the appearance of the pulse by palpation, the pressure in the cuff is noted at this moment, which corresponds to the systolic pressure.

Of the non-invasive (indirect) methods, auscultatory and oscillometric methods for measuring pressure are most widely used.

A needle or cannula, connected by a tube to a pressure gauge, is inserted directly into the artery.

Auscultatory method of NS Korotkov.

The aucultative method is most widespread and is based on the establishment of systolic and diastolic pressure according to the appearance and disappearance of special sound phenomena in the artery that characterize the turbulence of the blood flow - Korotkov tones.

Oscillometric method.

The method is based on the fact that when blood passes during systole through a squeezed section of an artery, micropulsations of air pressure occur in the cuff, analyzing which it is possible to obtain values \u200b\u200bof systolic, diastolic and average pressure.

Normal blood pressure indicators:

Systolic blood pressure is 100-139 mm. rt. Art.

Diastolic blood pressure is 60-89 mm. rt. Art.

Factors affecting the value of blood pressure:

Stroke blood volume

Minute blood volume

Total peripheral resistance

Circulating blood volume

Venous pressure is the blood pressure in the right atrium.

Factors affecting the VD value:

Circulating blood volume

Venous return

Myocardial contractility

Factors involved in the formation of venous return.

2 groups of factors:

Group 1 is represented by factors that are united by the general term "vis a tegro", acting from behind.

13% of the energy imparted to the blood flow by the heart;

Contraction of skeletal muscles (" muscle heart"," Muscular venous pump ");

The transfer of fluid from tissue to blood in the venous part of the capillaries;

The presence of valves in large veins, prevents the reverse flow of blood;

Constrictor (contractile) reactions of venous vessels to nervous and humoral influences.

Group 2 is represented by factors that are united by the general term "vis a fronte", acting in front:

Suction function chest.
When inhaling, the negative pressure in the pleural cavity increases and this leads to a decrease in central venous pressure (CVP), to an acceleration of blood flow in the veins

Suction function of the heart.
It is carried out by lowering the pressure in the right atrium (CVP) to zero in diastole.

Blood pressure registration curve:

First-order waves are fluctuations in blood pressure due to systole and diastole. If the recording is carried out for a long enough time, then the waves of the 2nd and 3rd order can be registered on the kymograph. 2nd order waves are fluctuations in blood pressure associated with the act of inhalation and exhalation. Inhalation is accompanied by a decrease in blood pressure, and exhalation is accompanied by an increase. The 3rd order waves are caused by changes in blood pressure over about 10-30 minutes - these are slow fluctuations. These waves reflect fluctuations in vascular tone that result from changes in the tone of the vasomotor center.

1. Functional classification of the sections of the vascular bed. Factors that ensure the movement of blood through the vessels of high and low pressure.

Functional classification of vessels.

1. Elastic-tensile (aorta and pulmonary artery), vessels of the "boiler" or "compression chamber". Vessels of an elastic type that receive a portion of blood by stretching the walls. Provide a continuous, pulsating blood flow, form in dynamics systolic and pulse pressure in the large and small circles of blood circulation, determine the nature of the pulse wave.

2. Transient (large, medium arteries and large veins). Vessels of the muscular-elastic type are almost not subject to nervous and humoral influences, do not affect the nature of the blood flow.

3. Resistive (small arteries, arterioles and venules). Muscular vessels make the main contribution to the formation of resistance to blood flow, significantly change their lumen under the influence of nervous and humoral influences.
4. Exchangeable (capillaries). In these vessels, an exchange takes place between blood and tissues.

5. Capacitive (small and medium veins). The vessels in which the bulk of the blood is located. They respond well to nervous and humoral influences. Provide adequate blood return to the heart. Change in pressure in the veins by several mm Hg. increases the amount of blood in the capacitive vessels by 2-3 times.

6. Bypass (arterio-venous anastomoses). They provide the transition of blood from the arterial system to the venous system, bypassing the exchange vessels.

7. Vessels-sphincters (precapillary and postcapillary). Determine the zonal switching on and off of exchange vessels in the bloodstream.

The movement of blood through the arteries is due to the following factors:

1. The work of the heart, providing replenishment of the energy consumption of the circulatory system.

2. The elasticity of the walls of elastic vessels. During the period of systole, the energy of the systolic portion of blood is converted into the energy of deformation of the vascular wall. During diastole, the wall contracts and its potential energy turns into kinetic. This helps to maintain a decreasing blood pressure and smooth out pulsations of arterial blood flow.

3. The difference in pressure at the beginning and end of the vascular bed. It arises as a result of the expenditure of energy to overcome the resistance to blood flow.

The walls of the veins are thinner and more extensible than those of the arteries. The energy of the heart contractions has basically already been spent on overcoming the resistance of the arterial bed. Therefore, the pressure in the veins is low and additional mechanisms are required to facilitate venous return to the heart. Venous blood flow is provided by the following factors:

1. The difference in pressure at the beginning and end of the venous bed.

2. Contractions of skeletal muscles during movement, as a result of which blood is pushed out of the peripheral veins to the right atrium.

3. Suction effect of the chest. On inspiration, the pressure in it becomes negative, which promotes venous blood flow.

4. Suction action of the right atrium during its diastole. The expansion of its cavity leads to the appearance negative pressure in him.

5. Abbreviations smooth muscles veins.

The movement of blood through the veins to the heart is also due to the fact that they have protrusions of the walls, which act as valves.

1. Capillary blood flow and its features. Microcirculation and its role in the mechanism of the exchange of fluid and various substances between blood and tissues.

Microcirculation - transport of biological fluids at the tissue level. The set of all vessels that provide microcirculation is called the microcirculatory bed and includes arterioles, precapillaries, capillaries, postcapillaries, venules, arterio-venular anastomoses, lymphatic capillaries.

The blood flow in this part of the blood circulation provides its leading function - the exchange between blood and tissues. That is why the main link in this system - capillaries, are called exchange vessels. Their function is closely related to the vessels from which they begin - arterioles and the vessels into which they pass - venules. There are direct arteriovenous anastomoses connecting them, bypassing the capillaries. If we add lymphocapillaries to this group of vessels, then all this together will make up what is called the microcirculation system. This is the most important link in the circulatory system. It is in it that those disorders occur that are the cause of the bulk of diseases. Capillaries form the basis of this system. Normally, at rest, only 25-35% of capillaries are open, if many of them open at once, then hemorrhage occurs in the capillaries and the body may even die from internal blood loss, since blood accumulates in the capillaries and does not flow to the heart.

Capillaries pass in the intercellular spaces and, therefore, the exchange of substances takes place between blood and intercellular fluid. Factors that contribute to this: the difference in hydrostatic pressure at the beginning and at the end of the capillary (30-40 mm Hg and 10 mm Hg), blood velocity (0.05 m / s), filtration pressure (the difference between hydrostatic pressure in the intercellular fluid - 15 mm Hg) and reabsorption pressure (the difference between the hydrostatic pressure at the venous end of the capillary and oncotic pressure in the intercellular fluid - 15 mm Hg). If these ratios change, then the liquid goes mainly in one direction or another.

Filtration pressure is calculated by the formula FD \u003d GD-OD, or rather FD \u003d (GD cr - GD tk) - (OK cr - OD tk).

Volumetric rate of transcapillary exchange (ml / min) can be represented as:

V \u003d K filter / (GD cr -GD tk) -K osm (OD cr-OD tk), Where To filter– capillary filtration coefficient, reflecting the exchange surface area (the number of functioning capillaries) and the permeability of the capillary wall for liquid , K osm- osmotic coefficient , reflecting the real permeability of the membrane for electrolytes and proteins.

Diffusion is the penetration of substances through a membrane; movement of a solute from a zone with a higher concentration to a zone with a lower concentration.

Osmosis is a form of transport in which a solvent moves from an area with a lower concentration to an area with a higher concentration.

Filtration is a type of transport in which the transfer of a substance occurs through fenestra ("windows" in capillaries, which are holes piercing the cytoplasm with a diameter of 40-60 nm, formed by the thinnest membrane) or through gaps between cells.

Active transport - with the help of small carriers, with the expenditure of energy. Thus, individual amino acids, carbohydrates and other substances are transported. Active transport is often associated with Na + transport. That is, the substance forms a complex with the Na + carrier molecule.

1. The lymphatic system. Lymph functions. Lymphatic formation, its mechanism. Peculiarities of regulation of lymph formation and lymph outflow.

The lymphatic system (Latin systema lymphaticum) is a part of the vascular system in vertebrates that complements the cardiovascular system. It plays an important role in the metabolism and cleansing of cells and tissues of the body. Unlike the circulatory system, the mammalian lymphatic system is open and lacks a central pump. The lymph circulating in it moves slowly and under little pressure.

Lymph consists of lymphoplasm and formed elements (ions K, Na, Ca, Cl, etc.), and there are very few cells in the peripheral lymph, and much more in the central lymph.

Lymph performs or participates in the implementation of the following functions:

1) maintaining the constancy of the composition and volume of the interstitial fluid and the microenvironment of cells;
2) the return of protein from the tissue environment to the blood;
3) participation in the redistribution of fluid in the body;
4) ensuring humoral communication between tissues and organs, the lymphoid system and blood;
5) absorption and transport of food hydrolysis products, especially lipids from the gastrointestinal tract into the blood;
6) providing the mechanisms of immunity by transporting antigens and antibodies, transferring plasma cells, immune lymphocytes and macrophages from the lymphoid organs.

Lymphatic formation.

As a result of plasma filtration in the blood capillaries, the liquid enters the intercellular (interstitial) space, where water and electrolytes partly bind to colloidal and fibrous structures, and partly form an aqueous phase. This is how tissue fluid is formed, part of which is reabsorbed back into the blood, and part of it enters the lymphatic capillaries, forming lymph. Thus, lymph is a space of the internal environment of the body, formed from the intercellular fluid. The formation and outflow of lymph from the intercellular space is subject to the forces of hydrostatic and oncotic pressure and occurs rhythmically.

Lymph node (lymph node) - peripheral organ lymphatic systemacting as a biological filter through which lymph flows from organs and parts of the body. The lymph nodes perform the function of lymphocytopoiesis, barrier-filtration, immunological function.

Factors providing the movement of lymph:

When conducting seriously ill, as well as patients with unstable hemodynamics to assess the state of the cardiovascular system and the effectiveness of therapeutic interventions, there is a need for constant registration of hemodynamic parameters.

Direct blood pressure measurements carried out through a catheter or cannula introduced into the lumen of the artery. Direct access is used both for continuous recording of blood pressure and for taking analyzes of the gas composition and acid-base state of the blood. Indications for arterial catheterization are unstable blood pressure and the infusion of vasoactive drugs.

The most common accesses for the introduction of an arterial catheter are radiation and femoral artery... The brachial, axillary or foot arteries are used much less frequently. When choosing access, consider the following factors:
correspondence of the diameter of the artery to the diameter of the cannula;
the catheterization site must be accessible and free from body secretions;
the limb distal to the catheter insertion site must have sufficient collateral blood flow, since there is always the possibility of arterial occlusion.

More often use the radial arterybecause it has a superficial location and is easy to palpate. In addition, its cannulation is associated with the least restriction of patient mobility.
To avoid complications, it is preferable to use arterial cannulas rather than arterial catheters.

Before cannulation of the radial artery conduct the Allen test. To do this, clamp the radial and ulnar arteries. Then the patient is asked to clench and unclench his fist several times until the hand turns pale. The ulnar artery is released and the color of the hand is observed to recover. If it is restored within 5-7 s, the blood flow through the ulnar artery is considered adequate. The time, ranging from 7 to 15 s, indicates a violation of blood circulation in the ulnar artery. If the color of the limb is restored after more than 15 s, the cannulation of the radial artery is abandoned.

Artery cannulation performed under sterile conditions. The system for measuring blood pressure is pre-filled with a solution and the strain gauge is calibrated. To fill and flush the system, physiological solution is used, to which 5000 U of heparin is added.

Monitoring invasive blood pressure provides continuous measurement of this parameter in real time, but when interpreting the information received, a number of limitations and errors are possible. First of all, the shape of the blood pressure curve obtained in the peripheral artery does not always accurately reflect that in the aorta and other great vessels. The shape of the blood pressure curve is influenced by the inotropic function of the left ventricle, resistance in the aorta and peripheral vessels, and the characteristics of the system for monitoring blood pressure. The monitor system itself can cause various artifacts, as a result of which the shape of the blood pressure curve changes. Correct interpretation information obtained through invasive monitoring requires some experience. Here you should point out the need to recognize invalid data. This is important because incorrect analysis and misinterpretation of the data obtained can lead to incorrect medical decisions.

practice report

4. Sensor setup and calibration

Sensor adjustment and calibration is carried out after repair work or if necessary.

Sensor setup includes the following operations:

Setting the sensor output parameters: - setting the units of measurement, setting the characteristics of the output signal;

Reconfiguration of the measurement range;

Setting the averaging time of the output signal (damping);

Calibrate analog output.

Calibrating the analog output includes:

Calibration of "zero" - the operation sets the exact correspondence (using exemplary means) of the initial value of the current output signal of the digital-to-analog converter (DAC) to the nominal value.

During calibration, a parallel shift of the DAC characteristic occurs and its slope does not change;

DAC "slope" calibration - the operation establishes an exact correspondence (with the help of exemplary means) the upper value of the current output signal of the digital-to-analog converter to the nominal value. During calibration, the DAC slope is corrected;

Sensor calibration.

Sensor calibration involves calibrating the lower limit of measurement (LEL) and upper limit of measurement (URL).

The sensor consists of a measuring unit and an analog-to-digital converter (ADC) board. Pressure is supplied to the chamber of the measuring unit, converted into deformation of the sensing element and a change in the electrical signal.

During my practical training, I verified the sensor, the results of the verification are given in the protocol presented below.

INSTRUMENT CALIBRATION PROTOCOL

Date 23.12.2014 No. 123

Device name pressure sensor METRAN Model 150

Serial number 086459708 Shop 4 Position 12

Upper limit of measurement 68

Standards (name of metrological means of verification): METRAN 150-CD

Verification (calibration) results:

External examination: no defects found

Table 3

Measured value (specify unit)	Calculated Output Signal (specify unit)	Actual value of the output signal	Reduced error in%	Signal variation in%
			reverse		reverse

Limit of permissible reduced error 0.5%

The largest error of the output signal 0.025%

Allowable variation 0.5%

Largest variation 0.091%

Conclusion - good

Calibrator D.N. Alekseev

Overhaul was carried out by K.P. Glushchenko

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An important type of human health monitoring is blood pressure measurement. This procedure is carried out by an invasive method in stationary conditions under the close supervision of a qualified medical staff, with an urgent need for just this type of diagnostic study. Blood pressure indicators can also be found at home, independently using auscultatory (with a stethoscope), palpation (palpation with fingers) or oscillometric (tonometer) methods.

Indications

The state of blood pressure is determined by 3 indicators, which are indicated in the table:

The tonometer allows you to regularly monitor blood pressure parameters and monitor its dynamics. If you need to continuously monitor the patient's performance, then an invasive method is used that helps:

Indicate your pressure

Move sliders

• continuously monitor the patient's condition with unstable hemodynamics;
• monitor changes in the work of the heart and blood vessels non-stop;
• constantly analyze the effectiveness of the therapy.

Indications for invasive blood pressure testing:

• artificial hypotension, deliberate hypotension;
• cardiac surgery;
• infusion of vasoactive agents;
• resuscitation period;
• diseases in which it is necessary to obtain constant and accurate blood pressure parameters for productive regulation of hemodynamics;
• a significant likelihood of strong jumps in systolic, diastolic and pulse rates during surgery;
• intensive artificial lung ventilation;
• the need for frequent diagnostics of the acid-base state and blood gas composition in the arteries;
• unstable blood pressure;

Direct measurement of blood pressure is carried out through a catheter inserted into the lumen of the artery.

Constant monitoring of blood pressure will help to timely detect deadly pathologies of the kidneys, heart and blood vessels. The invasive measurement is of particular importance for hypertensive and hypotensive patients who are at an increased risk group. A timely diagnosed disease can reduce potential negative consequences, and in critical situations, save the patient's life.

Very high blood pressure readings can cause:

• heart and kidney failure;
• myocardial infarction;
• stroke;
• ischemic disease.

Too low systolic and diastolic parameters significantly increase the risk of:

• stroke;
• pathological changes in peripheral circulation;
• cardiac arrest;
• cardiogenic shock.

How is it going?

This invasive blood pressure measurement is highly accurate. To perform the procedure, a number of manipulations are carried out:

1. All instruments and devices are sterilized.
2. A catheter or a special needle, a cannula, is inserted into the heart or into the lumen of one of the arteries, to which a manometer is attached with a tube.
3. Through a microinfusor, a means that prevents blood from clotting is fed into the needle - heparinized saline solution.
4. The pressure gauge constantly records all parameters of the magnetic tape.

The installation for determining blood pressure by the invasive method consists of the following elements:

• transducer;
• oscilloscope;
• cannula (or catheter);
• hydraulic system;
• monitor;
• taps;
• fluid-mechanical interface;
• recording device;
• connecting tube.

Where should you measure?

To investigate blood pressure in an invasive way, you can use different arteries:

• Ray. It is used most often because of its superficial location and collateral.
• Femoral. The second most popular artery for catheterization due to its accessibility, despite the significant likelihood of atheroma and pseudoaneurysms.
• Axillary. Carrying out the procedure with its help is characterized by a high risk of cannula injury to the nerves due to the close location of the axillary plexuses.
• Elbow. It goes deep and is sinuous.
• Posterior tibial and dorsalfoot. Monitoring through it is characterized by a significant distortion of the pulse waveform due to the distance from the arterial tree.
• Brachial. Arterial catheterization is characterized by a slight change in the wave configuration, there is a possibility of kinking of the catheter.

Before determining through which artery the diagnosis will be carried out, the doctor takes into account various parameters. The main ones are:

• allen's test is done before penetration into the radial artery;
• the ratio of the cannula and artery diameters is determined;
• the necessary collateral blood flow of the limb is checked, on which the diagnosis is carried out;
• the availability of the artery is taken into account;
• the distance from the places of free penetration of secrets is determined.