The rate of blood flow in different vessels. Uzdg of the head and neck of the norm in children and adults

The date: 03.03.2020

Circulation is the movement of blood vascular system for gas exchange between the body and external environment, metabolism between organs and tissues and humoral regulation various functions organism.

circulatory system includes and - aorta, arteries, arterioles, capillaries, venules, veins and. Blood moves through the vessels due to the contraction of the heart muscle.

Blood circulation takes place in a closed system consisting of small and large circles:

The systemic circulation provides all organs and tissues with blood and its nutrients.
The small, or pulmonary, circle of blood circulation is designed to enrich the blood with oxygen.

Circulatory circles were first described by the English scientist William Harvey in 1628 in his work Anatomical Studies on the Movement of the Heart and Vessels.

Small circle of blood circulation It begins from the right ventricle, during the contraction of which venous blood enters the pulmonary trunk and, flowing through the lungs, gives off carbon dioxide and is saturated with oxygen. Oxygenated blood from the lungs travels through the pulmonary veins to the left atrium where the small circle ends.

Systemic circulation begins from the left ventricle, during the contraction of which blood enriched with oxygen is pumped into the aorta, arteries, arterioles and capillaries of all organs and tissues, and from there flows through the venules and veins into the right atrium, where the large circle ends.

by the most large vessel great circle blood circulation is the aorta, which exits from the left ventricle of the heart. The aorta forms an arch from which the arteries branch off, carrying blood to the head ( carotid arteries) and to upper limbs(vertebral arteries). The aorta runs down the spine, where it gives off branches that carry blood to the organs. abdominal cavity to the muscles of the trunk and lower extremities.

Arterial blood, rich in oxygen, passes throughout the body, delivering nutrients and oxygen to the cells of organs and tissues necessary for their activity, and in the capillary system it turns into venous blood. Venous blood, saturated with carbon dioxide and cellular metabolic products, returns to the heart and from it enters the lungs for gas exchange. The largest veins of the systemic circulation are the superior and inferior vena cava, which flow into the right atrium.

Rice. Scheme of small and large circles of blood circulation

It should be noted how the circulatory systems of the liver and kidneys are included in the systemic circulation. All blood from the capillaries and veins of the stomach, intestines, pancreas, and spleen enters the portal vein and passes through the liver. in the liver portal vein branches into small veins and capillaries, which then reconnect into a common trunk hepatic vein flowing into the inferior vena cava. All the blood of the abdominal organs before entering the systemic circulation flows through two capillary networks: the capillaries of these organs and the capillaries of the liver. Gate system the liver plays an important role. It provides neutralization toxic substances, which are formed in the large intestine during the breakdown of unabsorbed in small intestine amino acids and are absorbed by the colon mucosa into the blood. The liver, like all other organs, receives and arterial blood through the hepatic artery, which originates from the abdominal artery.

There are also two capillary networks in the kidneys: there is a capillary network in each Malpighian glomerulus, then these capillaries are connected into an arterial vessel, which again breaks up into capillaries braiding the convoluted tubules.

Rice. Scheme of blood circulation

A feature of blood circulation in the liver and kidneys is the slowing down of blood flow, which is determined by the function of these organs.

Table 1. The difference between blood flow in the systemic and pulmonary circulation

Blood flow in the body	Systemic circulation	Small circle of blood circulation
In what part of the heart does the circle begin?	In the left ventricle	In the right ventricle
In what part of the heart does the circle end?	In the right atrium	In the left atrium
Where does gas exchange take place?	In the capillaries located in the organs of the chest and abdominal cavities, the brain, upper and lower extremities	in the capillaries in the alveoli of the lungs
What kind of blood moves through the arteries?	Arterial	Venous
What kind of blood moves through the veins?	Venous	Arterial
Time of blood circulation in a circle
circle function	Supply of organs and tissues with oxygen and transport of carbon dioxide	Saturation of blood with oxygen and removal of carbon dioxide from the body

Blood circulation time the time of a single passage of a blood particle through the large and small circles of the vascular system. More details in the next section of the article.

Patterns of the movement of blood through the vessels

Basic principles of hemodynamics

Hemodynamics is a branch of physiology that studies the patterns and mechanisms of blood movement through the vessels of the human body. When studying it, terminology is used and the laws of hydrodynamics, the science of the movement of fluids, are taken into account.

The speed at which blood moves through the vessels depends on two factors:

from the difference in blood pressure at the beginning and end of the vessel;
from the resistance that the fluid encounters along its path.

The pressure difference contributes to the movement of the fluid: the greater it is, the more intense this movement. Resistance in the vascular system, which reduces the speed of blood flow, depends on a number of factors:

the length of the vessel and its radius (the longer the length and the smaller the radius, the greater the resistance);
blood viscosity (it is 5 times the viscosity of water);
friction of blood particles against the walls of blood vessels and among themselves.

Hemodynamic parameters

The speed of blood flow in the vessels is carried out according to the laws of hemodynamics, common with the laws of hydrodynamics. Blood flow velocity is characterized by three indicators: volumetric blood flow velocity, linear blood flow velocity and blood circulation time.

Volumetric blood flow velocity - the amount of blood flowing through the cross section of all vessels of a given caliber per unit of time.

Linear blood flow velocity - the speed of movement of an individual blood particle along a vessel per unit of time. In the center of the vessel, the linear velocity is maximum, and near the vessel wall it is minimum due to increased friction.

Blood circulation time the time during which blood passes through the large and small circles of blood circulation. Normally, it is 17-25 s. Passing through a small circle takes about 1/5, and passing through a large circle - 4/5 of this time

The driving force of blood flow in the vascular system of each of the circles of blood circulation is the difference in blood pressure ( ΔР) in the initial section of the arterial bed (aorta for the great circle) and the final section of the venous bed (vena cava and right atrium). blood pressure difference ( ΔР) at the beginning of the vessel ( P1) and at the end of it ( R2) is the driving force of blood flow through any vessel of the circulatory system. The force of the blood pressure gradient is used to overcome the resistance to blood flow ( R) in the vascular system and in each individual vessel. The higher the blood pressure gradient in the circulation or in a separate vessel, the greater the volumetric blood flow in them.

The most important indicator of the movement of blood through the vessels is volumetric blood flow velocity, or volumetric blood flow (Q), which is understood as the volume of blood flowing through the total cross section of the vascular bed or the section of an individual vessel per unit time. The volumetric flow rate is expressed in liters per minute (L/min) or milliliters per minute (mL/min). To assess the volumetric blood flow through the aorta or the total cross section of any other level of the vessels of the systemic circulation, the concept is used volumetric systemic circulation. Since the entire volume of blood ejected by the left ventricle during this time flows through the aorta and other vessels of the systemic circulation per unit of time (minute), the concept of systemic volumetric blood flow is synonymous with the concept of (MOC). The IOC of an adult at rest is 4-5 l / min.

Distinguish also volumetric blood flow in the body. In this case, they mean the total blood flow flowing per unit of time through all the afferent arterial or efferent venous vessels of the organ.

Thus, the volume flow Q = (P1 - P2) / R.

This formula expresses the essence of the basic law of hemodynamics, which states that the amount of blood flowing through the total cross section of the vascular system or an individual vessel per unit time is directly proportional to the difference in blood pressure at the beginning and end of the vascular system (or vessel) and inversely proportional to the current resistance blood.

The total (systemic) minute blood flow in a large circle is calculated taking into account the values of the average hydrodynamic blood pressure at the beginning of the aorta P1, and at the mouth of the vena cava P2. Since in this section of the veins the blood pressure is close to 0 , then into the expression for calculation Q or IOC value is substituted R equal to the mean hydrodynamic blood pressure at the beginning of the aorta: Q(IOC) = P/ R.

One of the consequences of the basic law of hemodynamics - the driving force of blood flow in the vascular system - is due to the blood pressure created by the work of the heart. Confirmation of the decisive value of blood pressure for blood flow is the pulsating nature of the blood flow throughout cardiac cycle. During heart systole, when blood pressure reaches its maximum level, blood flow increases, and during diastole, when blood pressure is at its lowest, blood flow decreases.

As blood moves through the vessels from the aorta to the veins, blood pressure decreases and the rate of its decrease is proportional to the resistance to blood flow in the vessels. The pressure in arterioles and capillaries decreases especially rapidly, since they have a large resistance to blood flow, having a small radius, a large total length and numerous branches, creating an additional obstacle to blood flow.

The resistance to blood flow created in the entire vascular bed of the systemic circulation is called total peripheral resistance(OPS). Therefore, in the formula for calculating volumetric blood flow, the symbol R you can replace it with an analogue - OPS:

Q = P/OPS.

From this expression, a number of important consequences are derived that are necessary for understanding the processes of blood circulation in the body, evaluating the measurement results blood pressure and its deviations. The factors affecting the resistance of the vessel, for the fluid flow, are described by Poiseuille's law, according to which

where R- resistance; L is the length of the vessel; η - blood viscosity; Π - number 3.14; r is the radius of the vessel.

From the above expression it follows that since the numbers 8 and Π are permanent, L in an adult person changes little, then the value peripheral resistance blood flow is determined by changing values of the vessel radius r and blood viscosity η ).

It has already been mentioned that the radius of muscle-type vessels can change rapidly and have a significant effect on the amount of resistance to blood flow (hence their name - resistive vessels) and the amount of blood flow through organs and tissues. Since the resistance depends on the magnitude of the radius to the 4th power, even small fluctuations in the radius of the vessels greatly affect the resistance to blood flow and blood flow. So, for example, if the radius of the vessel decreases from 2 to 1 mm, then its resistance will increase by 16 times, and with a constant pressure gradient, the blood flow in this vessel will also decrease by 16 times. Reverse changes in resistance will be observed when the radius of the vessel is doubled. With a constant average hemodynamic pressure, blood flow in one organ can increase, in another - decrease, depending on the contraction or relaxation of the smooth muscles of the afferent arterial vessels and veins of this organ.

The viscosity of the blood depends on the content in the blood of the number of red blood cells (hematocrit), protein, lipoproteins in the blood plasma, as well as on the aggregate state of the blood. Under normal conditions, the viscosity of the blood does not change as quickly as the lumen of the vessels. After blood loss, with erythropenia, hypoproteinemia, blood viscosity decreases. With significant erythrocytosis, leukemia, increased erythrocyte aggregation and hypercoagulability, blood viscosity can increase significantly, which leads to an increase in blood flow resistance, an increase in the load on the myocardium and may be accompanied by a violation of blood flow in the vessels of the microvasculature.

In the established regime of blood circulation, the volume of blood expelled by the left ventricle and flowing through the cross section of the aorta is equal to the volume of blood flowing through the total cross section of the vessels of any other part of the systemic circulation. This volume of blood returns to the right atrium and enters the right ventricle. Blood is expelled from it into the pulmonary circulation and then through pulmonary veins returns to left heart. Since the IOCs of the left and right ventricles are the same, and the systemic and pulmonary circulations are connected in series, the volumetric blood flow velocity in the vascular system remains the same.

However, during changes in blood flow conditions, such as when changing from horizontal to vertical position when gravity causes a temporary accumulation of blood in the veins of the lower torso and legs, on a short time IOC of the left and right ventricles may become different. Soon, intracardiac and extracardiac mechanisms of regulation of the work of the heart equalize the volume of blood flow through the small and large circles of blood circulation.

With a sharp decrease in venous return of blood to the heart, causing a decrease in stroke volume, the arterial pressure blood. With a pronounced decrease in it, blood flow to the brain can decrease. This explains the feeling of dizziness that can occur with a sharp transition of a person from a horizontal to a vertical position.

Volume and linear velocity of blood flow in the vessels

The total volume of blood in the vascular system is an important homeostatic indicator. Its average value is 6-7% for women, 7-8% of body weight for men and is in the range of 4-6 liters; 80-85% of the blood from this volume is in the vessels of the systemic circulation, about 10% - in the vessels of the pulmonary circulation, and about 7% - in the cavities of the heart.

Most of the blood is contained in the veins (about 75%) - this indicates their role in the deposition of blood in both the systemic and pulmonary circulation.

The movement of blood in the vessels is characterized not only by volume, but also by linear velocity of blood flow. It is understood as the distance over which a particle of blood moves per unit of time.

There is a relationship between the volumetric and linear blood flow velocity, which is described by the following expression:

V \u003d Q / Pr 2

where V— linear blood flow velocity, mm/s, cm/s; Q - volumetric blood flow velocity; P- a number equal to 3.14; r is the radius of the vessel. Value Pr 2 reflects the cross-sectional area of the vessel.

Rice. 1. Changes in blood pressure, linear blood flow velocity and cross-sectional area in different parts of the vascular system

Rice. 2. Hydrodynamic characteristics of the vascular bed

From the expression of the dependence of the magnitude of the linear velocity on the volume in the vessels of the circulatory system, it can be seen that the linear velocity of blood flow (Fig. 1.) is proportional to the volumetric blood flow through the vessel (s) and inversely proportional to the cross-sectional area of this vessel (s). For example, in the aorta, which has smallest area cross section in the systemic circulation (3-4 cm 2), the linear velocity of blood largest and is at rest about 20- 30 cm/s. At physical activity it can increase by 4-5 times.

In the direction of the capillaries, the total transverse lumen of the vessels increases and, consequently, the linear velocity of blood flow in the arteries and arterioles decreases. In capillary vessels, the total cross-sectional area of which is greater than in any other part of the vessels of the great circle (500-600 times the cross-section of the aorta), the linear velocity of blood flow becomes minimal (less than 1 mm/s). The slow flow of blood in the capillaries creates best conditions for the flow of metabolic processes between blood and tissues. In veins, the linear velocity of blood flow increases due to a decrease in their total cross-sectional area as they approach the heart. At the mouth of the vena cava, it is 10-20 cm / s, and under loads it increases to 50 cm / s.

The linear speed of plasma movement depends not only on the type of vessel, but also on their location in the blood stream. There is a laminar type of blood flow, in which the blood flow can be conditionally divided into layers. In this case, the linear velocity of the movement of blood layers (mainly plasma), close to or adjacent to the vessel wall, is the smallest, and the layers in the center of the flow are the largest. Friction forces arise between the vascular endothelium and the parietal layers of blood, creating shear stresses on the vascular endothelium. These stresses play a role in the production of vasoactive factors by the endothelium, which regulate the lumen of the vessels and the rate of blood flow.

Erythrocytes in vessels (with the exception of capillaries) are located mainly in the central part of the blood flow and move in it at a relatively high speed. Leukocytes, on the contrary, are located mainly in the parietal layers of the blood flow and perform rolling movements at a low speed. This allows them to bind to adhesion receptors at sites of mechanical or inflammatory damage to the endothelium, adhere to the vessel wall, and migrate into tissues to perform protective functions.

With a significant increase in the linear velocity of blood movement in the narrowed part of the vessels, in the places where its branches depart from the vessel, the laminar nature of blood movement can change to turbulent. In this case, the layering of the movement of its particles in the blood stream may be disturbed, and between the wall of the vessel and the blood, big forces friction and shear stresses than in laminar motion. Vortex blood flows develop, the likelihood of damage to the endothelium and the deposition of cholesterol and other substances in the intima of the vessel wall increases. This can lead to mechanical disruption of the structure of the vascular wall and initiation of the development of parietal thrombi.

The time of a complete blood circulation, i.e. the return of a blood particle to the left ventricle after its ejection and passage through the large and small circles of blood circulation, is 20-25 s in mowing, or after about 27 systoles of the ventricles of the heart. Approximately a quarter of this time is spent on moving blood through the vessels of the small circle and three quarters - through the vessels of the systemic circulation.

Normally, systolic pressure in the systemic circulation is on average 120 mm Hg.

· Diastolic pressure - the minimum pressure that occurs during diastole in the systemic circulation averages 80 mm Hg.

Pulse pressure. The difference between systolic and diastolic pressure is called pulse pressure.

Mean arterial pressure (MAP) is roughly estimated by the formula:

SBP = [systolic BP + 2(diastolic BP)]/3

The mean BP in the aorta (90–100 mm Hg) gradually decreases as the arteries branch. In the terminal arteries and arterioles, the pressure drops sharply (up to 35 mm Hg on average), and then slowly decreases to 10 mm Hg. in large veins (Fig. 23-16A).

· Cross-sectional area. The diameter of the aorta of an adult is 2 cm, the cross-sectional area is about 3 cm 2. Toward the periphery, the cross-sectional area of arterial vessels slowly but progressively increases. At the level of arterioles, the cross-sectional area is about 800 cm 2, and at the level of capillaries and veins - 3500 cm 2. The surface area of the vessels decreases significantly when the venous vessels join to form a vena cava with a cross-sectional area of 7 cm 2 .

· The linear velocity of blood flow is inversely proportional to the cross-sectional area of the vascular bed. Therefore, the average speed of blood movement (Fig. 23-16B) is higher in the aorta (30 cm/s), gradually decreases in small arteries and the smallest in capillaries (0.026 cm/s), the total cross section of which is 1000 times greater than in the aorta . The mean flow velocity again increases in the veins and becomes relatively high in the vena cava (14 cm/s), but not as high as in the aorta.

Volumetric blood flow rate (usually expressed in milliliters per minute or liters per minute). The total blood flow in an adult at rest is about 5000 ml / min. This is the amount of blood pumped out by the heart every minute, which is why it is also called cardiac output.

· The rate of blood circulation (blood circulation rate) can be measured in practice: from the moment of injection of the preparation of bile salts into the cubital vein until the sensation of bitterness appears on the tongue (Fig. 23-17A). Normally, the speed of blood circulation is 15 s.

vascular capacity. The size of the vascular segments determines their vascular capacity. Arteries contain about 10% of the total amount of circulating blood, capillaries - about 5%, venules and not large veins- approximately 54% and large veins - 21%. The chambers of the heart hold the remaining 10%. Venules and small veins have a large capacity, making them an efficient reservoir capable of storing large volumes of blood.

Large and small circles of blood circulation

Large and small circles of human circulation

Blood circulation is the movement of blood through the vascular system, which provides gas exchange between the body and the external environment, the metabolism between organs and tissues, and the humoral regulation of various body functions.

The circulatory system includes the heart and blood vessels- aorta, arteries, arterioles, capillaries, venules, veins and lymphatic vessels. Blood moves through the vessels due to the contraction of the heart muscle.

Blood circulation takes place in a closed system consisting of small and large circles:

The systemic circulation provides all organs and tissues with blood and its nutrients.
The small, or pulmonary, circle of blood circulation is designed to enrich the blood with oxygen.

Circulatory circles were first described by the English scientist William Harvey in 1628 in his work Anatomical Studies on the Movement of the Heart and Vessels.

The pulmonary circulation begins from the right ventricle, during the contraction of which venous blood enters the pulmonary trunk and, flowing through the lungs, gives off carbon dioxide and is saturated with oxygen. Oxygen-enriched blood from the lungs through the pulmonary veins enters the left atrium, where the small circle ends.

The systemic circulation begins from the left ventricle, during the contraction of which blood enriched with oxygen is pumped into the aorta, arteries, arterioles and capillaries of all organs and tissues, and from there it flows through the venules and veins into the right atrium, where the large circle ends.

The largest vessel in the systemic circulation is the aorta, which emerges from the left ventricle of the heart. The aorta forms an arc from which arteries branch off, carrying blood to the head (carotid arteries) and to the upper limbs (vertebral arteries). The aorta runs down along the spine, where branches depart from it, carrying blood to the abdominal organs, to the muscles of the trunk and lower extremities.

Rice. Scheme of small and large circles of blood circulation

It should be noted how the circulatory systems of the liver and kidneys are included in the systemic circulation. All blood from the capillaries and veins of the stomach, intestines, pancreas, and spleen enters the portal vein and passes through the liver. In the liver, the portal vein branches into small veins and capillaries, which then reconnect into a common trunk of the hepatic vein, which flows into the inferior vena cava. All the blood of the abdominal organs before entering the systemic circulation flows through two capillary networks: the capillaries of these organs and the capillaries of the liver. The portal system of the liver plays an important role. It ensures the neutralization of toxic substances that are formed in the large intestine during the breakdown of amino acids that are not absorbed in the small intestine and are absorbed by the colon mucosa into the blood. The liver, like all other organs, also receives arterial blood through the hepatic artery, which branches off from the abdominal artery.

Rice. Scheme of blood circulation

A feature of blood circulation in the liver and kidneys is the slowing down of blood flow, which is determined by the function of these organs.

Table 1. The difference between blood flow in the systemic and pulmonary circulation

Systemic circulation

Small circle of blood circulation

In what part of the heart does the circle begin?

In the left ventricle

In the right ventricle

In what part of the heart does the circle end?

In the right atrium

In the left atrium

Where does gas exchange take place?

In the capillaries located in the organs of the chest and abdominal cavities, the brain, upper and lower extremities

in the capillaries in the alveoli of the lungs

What kind of blood moves through the arteries?

What kind of blood moves through the veins?

Time of blood circulation in a circle

Supply of organs and tissues with oxygen and transport of carbon dioxide

Saturation of blood with oxygen and removal of carbon dioxide from the body

The blood circulation time is the time of a single passage of a blood particle through the large and small circles of the vascular system. More details in the next section of the article.

Patterns of the movement of blood through the vessels

Basic principles of hemodynamics

Hemodynamics is a branch of physiology that studies the patterns and mechanisms of blood movement through the vessels of the human body. When studying it, terminology is used and the laws of hydrodynamics, the science of the movement of fluids, are taken into account.

The speed at which blood moves through the vessels depends on two factors:

from the difference in blood pressure at the beginning and end of the vessel;
from the resistance that the fluid encounters along its path.

the length of the vessel and its radius (the longer the length and the smaller the radius, the greater the resistance);
blood viscosity (it is 5 times the viscosity of water);
friction of blood particles against the walls of blood vessels and among themselves.

Hemodynamic parameters

Volumetric blood flow velocity - the amount of blood flowing through the cross section of all vessels of a given caliber per unit of time.

The linear velocity of blood flow is the speed of movement of an individual blood particle along the vessel per unit of time. In the center of the vessel, the linear velocity is maximum, and near the vessel wall it is minimum due to increased friction.

Blood circulation time - the time during which blood passes through the large and small circles of blood circulation. Passing through a small circle takes about 1/5, and passing through a large circle - 4/5 of this time

The driving force of blood flow in the vascular system of each of the circulatory circles is the difference in blood pressure (ΔР) in the initial section of the arterial bed (aorta for a large circle) and the final section of the venous bed (vena cava and right atrium). The difference in blood pressure (ΔP) at the beginning of the vessel (P1) and at the end of it (P2) is the driving force for blood flow through any vessel of the circulatory system. The force of the blood pressure gradient is used to overcome the resistance to blood flow (R) in the vascular system and in each individual vessel. The higher the blood pressure gradient in the circulation or in a separate vessel, the greater the volumetric blood flow in them.

The most important indicator of the movement of blood through the vessels is the volumetric blood flow velocity, or volumetric blood flow (Q), which is understood as the volume of blood flowing through the total cross section of the vascular bed or the section of an individual vessel per unit time. The volumetric flow rate is expressed in liters per minute (L/min) or milliliters per minute (mL/min). To assess the volumetric blood flow through the aorta or the total cross section of any other level of the vessels of the systemic circulation, the concept of volumetric systemic blood flow is used. Since the entire volume of blood ejected by the left ventricle during this time flows through the aorta and other vessels of the systemic circulation per unit of time (minute), the concept of the minute volume of blood flow (MOV) is synonymous with the concept of systemic volumetric blood flow. The IOC of an adult at rest is 4-5 l / min.

Distinguish also volumetric blood flow in the body. In this case, they mean the total blood flow flowing per unit of time through all the afferent arterial or efferent venous vessels of the organ.

Thus, volumetric blood flow Q = (P1 - P2) / R.

The total (systemic) minute blood flow in a large circle is calculated taking into account the values of the average hydrodynamic blood pressure at the beginning of the aorta P1, and at the mouth of the vena cava P2. Since the blood pressure in this section of the veins is close to 0, then the value P equal to the average hydrodynamic arterial blood pressure at the beginning of the aorta is substituted into the expression for calculating Q or IOC: Q (IOC) = P / R.

One of the consequences of the basic law of hemodynamics - the driving force of blood flow in the vascular system - is due to the blood pressure created by the work of the heart. Confirmation of the decisive importance of blood pressure for blood flow is the pulsating nature of blood flow throughout the cardiac cycle. During heart systole, when blood pressure reaches its maximum level, blood flow increases, and during diastole, when blood pressure is at its lowest, blood flow decreases.

The resistance to blood flow created in the entire vascular bed of the systemic circulation is called total peripheral resistance (OPS). Therefore, in the formula for calculating volumetric blood flow, the symbol R can be replaced by its analogue - OPS:

From this expression, a number of important consequences are derived that are necessary for understanding the processes of blood circulation in the body, evaluating the results of measuring blood pressure and its deviations. The factors affecting the resistance of the vessel, for the fluid flow, are described by Poiseuille's law, according to which

From the above expression it follows that since the numbers 8 and Π are constant, L in an adult changes little, then the value of peripheral resistance to blood flow is determined by the changing values of the vessel radius r and blood viscosity η).

It has already been mentioned that the radius of muscle-type vessels can change rapidly and have a significant impact on the amount of resistance to blood flow (hence their name - resistive vessels) and the amount of blood flow through organs and tissues. Since the resistance depends on the magnitude of the radius to the 4th power, even small fluctuations in the radius of the vessels greatly affect the resistance to blood flow and blood flow. So, for example, if the radius of the vessel decreases from 2 to 1 mm, then its resistance will increase by 16 times, and with a constant pressure gradient, the blood flow in this vessel will also decrease by 16 times. Reverse changes in resistance will be observed when the radius of the vessel is doubled. With a constant average hemodynamic pressure, blood flow in one organ can increase, in another - decrease, depending on the contraction or relaxation of the smooth muscles of the afferent arterial vessels and veins of this organ.

In the established regime of blood circulation, the volume of blood expelled by the left ventricle and flowing through the cross section of the aorta is equal to the volume of blood flowing through the total cross section of the vessels of any other part of the systemic circulation. This volume of blood returns to the right atrium and enters the right ventricle. Blood is expelled from it into the pulmonary circulation and then returned through the pulmonary veins to the left heart. Since the IOCs of the left and right ventricles are the same, and the systemic and pulmonary circulations are connected in series, the volumetric blood flow velocity in the vascular system remains the same.

However, during changes in blood flow conditions, such as when moving from a horizontal to a vertical position, when gravity causes a temporary accumulation of blood in the veins of the lower trunk and legs, for a short time, the left and right ventricular cardiac output may become different. Soon, intracardiac and extracardiac mechanisms of regulation of the work of the heart equalize the volume of blood flow through the small and large circles of blood circulation.

With a sharp decrease in venous return of blood to the heart, causing a decrease in stroke volume, arterial blood pressure may decrease. With a pronounced decrease in it, blood flow to the brain can decrease. This explains the feeling of dizziness that can occur with a sharp transition of a person from a horizontal to a vertical position.

Volume and linear velocity of blood flow in the vessels

Most of the blood is contained in the veins (about 75%) - this indicates their role in the deposition of blood in both the systemic and pulmonary circulation.

The movement of blood in the vessels is characterized not only by volume, but also by the linear velocity of blood flow. It is understood as the distance over which a particle of blood moves per unit of time.

There is a relationship between the volumetric and linear blood flow velocity, which is described by the following expression:

where V is the linear velocity of blood flow, mm/s, cm/s; Q - volumetric blood flow velocity; P is a number equal to 3.14; r is the radius of the vessel. The value Pr 2 reflects the cross-sectional area of the vessel.

Rice. 1. Changes in blood pressure, linear blood flow velocity and cross-sectional area in different parts of the vascular system

Rice. 2. Hydrodynamic characteristics of the vascular bed

From the expression of the dependence of the magnitude of the linear velocity on the volume in the vessels of the circulatory system, it can be seen that the linear velocity of blood flow (Fig. 1.) is proportional to the volumetric blood flow through the vessel (s) and inversely proportional to the cross-sectional area of this vessel (s). For example, in the aorta, which has the smallest cross-sectional area in the systemic circulation (3-4 cm 2), the linear velocity of blood movement is the highest and is at rest approx. cm / s. With physical activity, it can increase by 4-5 times.

In the direction of the capillaries, the total transverse lumen of the vessels increases and, consequently, the linear velocity of blood flow in the arteries and arterioles decreases. In capillary vessels, the total cross-sectional area of which is greater than in any other part of the vessels of the great circle (much larger than the cross-section of the aorta), the linear velocity of blood flow becomes minimal (less than 1 mm/s). Slow blood flow in the capillaries creates the best conditions for the flow of metabolic processes between blood and tissues. In veins, the linear velocity of blood flow increases due to a decrease in their total cross-sectional area as they approach the heart. At the mouth of the vena cava, it is cm / s, and with loads it increases to 50 cm / s.

The linear velocity of plasma and blood cells depends not only on the type of vessel, but also on their location in the blood stream. There is a laminar type of blood flow, in which the blood flow can be conditionally divided into layers. In this case, the linear velocity of the movement of blood layers (mainly plasma), close to or adjacent to the vessel wall, is the smallest, and the layers in the center of the flow are the largest. Friction forces arise between the vascular endothelium and the parietal layers of blood, creating shear stresses on the vascular endothelium. These stresses play a role in the production of vasoactive factors by the endothelium, which regulate the lumen of the vessels and the rate of blood flow.

With a significant increase in the linear velocity of blood movement in the narrowed part of the vessels, in the places where its branches depart from the vessel, the laminar nature of blood movement can change to turbulent. In this case, the layering of the movement of its particles in the blood flow may be disturbed, and between the vessel wall and the blood, greater friction forces and shear stresses may occur than with laminar movement. Vortex blood flows develop, the likelihood of damage to the endothelium and the deposition of cholesterol and other substances in the intima of the vessel wall increases. This can lead to mechanical disruption of the structure of the vascular wall and initiation of the development of parietal thrombi.

The time of a complete blood circulation, i.e. the return of a blood particle to the left ventricle after its ejection and passage through the large and small circles of blood circulation, is in postcos, or after about 27 systoles of the ventricles of the heart. Approximately a quarter of this time is spent on moving blood through the vessels of the small circle and three quarters - through the vessels of the systemic circulation.

Blood flow rate

The speed of blood flow is the speed of movement of blood elements along the bloodstream in a certain unit of time. In practice, experts distinguish between linear velocity and volumetric velocity of blood flow.

One of the main parameters characterizing the functionality of the circulatory system of the body. This indicator depends on the frequency of contractions of the heart muscle, the number and quality composition blood, vessel size, blood pressure, age and genetic characteristics of the organism.

Types of blood flow velocity

Linear velocity is the distance traveled by a blood particle in a vessel in certain period time. It directly depends on the sum of the cross-sectional areas of the vessels that make up a given section of the vascular bed.

Consequently, the aorta is the narrowest part of the circulatory system and it has the highest blood flow velocity, reaching 0.6 m/s. The “widest” place is the capillaries, since their total area is 500 times the area of the aorta, the blood flow velocity in them is 0.5 mm/s. , which provides an excellent exchange of substances between the capillary wall and tissues.

Volumetric blood flow velocity - total blood flowing through the cross section of the vessel for a certain period of time.

This type of speed is determined by:

pressure difference at opposite ends of the vessel, which is formed by arterial and venous pressure;
vascular resistance to blood flow, depending on the diameter of the vessel, its length, blood viscosity.

The importance and severity of the problem

Determining such an important parameter as blood flow velocity is extremely important for studying the hemodynamics of a particular section of the vascular bed or a particular organ. When it changes, we can talk about the presence of pathological narrowing throughout the vessel, obstruction of blood flow (parietal blood clots, atherosclerotic plaques), increased blood viscosity.

Currently non-invasive Objective assessment blood flow through vessels of different caliber is the most urgent task of modern angiology. Success depends on its success early diagnosis such vascular diseases like diabetic microangiopathy, Raynaud's syndrome, various occlusions and stenoses of vessels.

Promising Assistant

The most promising and safest is the determination of blood flow velocity by an ultrasound method based on the Doppler effect.

One of the latest representatives of Doppler ultrasound devices is a Doppler device manufactured by Minimax, which has established itself on the market as a reliable, high-quality and long-term assistant in determining vascular pathology.

How is the velocity of blood flow in the vessels measured?

The measurement of blood flow velocity in the vessels is carried out using various methods. One of the most accurate and reliable results is the measurement made using the method of ultrasonic Doppler flowmetry using the Minimax-Doppler apparatus. The data obtained using the Minimax equipment is the basis for assessing the condition of the subject and is taken into account when determining the diagnosis.

Why is blood velocity measured?

The measurement of blood flow velocity is important for diagnostic medicine. Thanks to the analysis of the data obtained as a result of measurements, it is possible to determine:

the state of the vessels, the index of blood viscosity;
the level of blood supply to the brain and other organs;
resistance to movement in both circles of blood circulation;
the level of microcirculation;
condition of the coronary vessels;
degree of heart failure.

The speed of blood flow in vessels, arteries and capillaries is not constant and the same value: the highest speed is in the aorta, the smallest is inside the microcapillaries.

Why measure the blood flow velocity in the vessels of the nail bed?

The speed of blood flow in the vessels of the nail bed is one of the clear indicators of the quality of blood microcirculation in the human body. The vessels of the nail bed have a small cross section and consist not only of capillaries, but also of microscopic arterioles.

With problems associated with the circulatory system, these capillaries and arterioles are the first to suffer. Of course, it is impossible to judge the state of the entire system only on the basis of a study of blood circulation in the area of the nail bed, but it is worth paying attention if the blood flow in this area is too low or high.

In medicine, to obtain the most reliable information, blood circulation parameters are measured in large areas of blood circulation.

Blood flow rate

Distinguish linear and volumetric velocity blood flow.

Linear blood flow velocity(V LIN.) is the distance that a blood particle travels per unit of time. It depends on the total cross-sectional area of all vessels that form the section of the vascular bed. The narrowest part of the circulatory system is the aorta. Here the highest linear velocity of blood flow is 0.5-0.6 m/sec. In the arteries of medium and small caliber, it decreases to 0.2-0.4 m/sec. The total lumen of the capillary bed is many times greater than that of the aorta. Therefore, the blood flow velocity in the capillaries decreases to 0.5 mm/sec. The slowing down of blood flow in the capillaries is of great physiological importance, since transcapillary exchange takes place in them. In large veins, the linear velocity of blood flow again increases to 0.1-0.2 m/sec. The linear velocity of blood flow in the arteries is measured ultrasonic method. It is based on Doppler effect. A sensor with a source and receiver of ultrasound is placed on the vessel. In a moving medium - blood - the frequency of ultrasonic vibrations changes. The greater the speed of blood flow through the vessel, the lower the frequency of reflected ultrasonic waves. The rate of blood flow in the capillaries is measured under a microscope with divisions in the eyepiece, by observing the movement of a specific red blood cell.

Volumetric blood flow velocity(V OB.) is the amount of blood passing through the cross section of the vessel per unit time. It depends on the pressure difference at the beginning and end of the vessel and the resistance to blood flow. Earlier in the experiment, the volumetric blood flow velocity was measured using a Ludwig blood clock. In the clinic, volumetric blood flow is measured using rheovasography. This method is based on registration of oscillations electrical resistance organs for high-frequency current, with a change in their blood supply in systole and diastole. With an increase in blood supply, the resistance decreases, and with a decrease it increases. In order to diagnose vascular diseases, rheovasography of the extremities, liver, kidneys, chest. Sometimes used plethysmography- this is a registration of fluctuations in the volume of an organ that occurs when their blood supply changes. Volume fluctuations are recorded using water, air and electric plethysmographs. The speed of the blood circulation is the time it takes for a particle of blood to pass through both circles of blood circulation. It is measured by injecting a fluorescein dye into a vein in one arm and timing its appearance in a vein in the other. On average, the speed of the blood circulation is sec.

Blood pressure

As a result of contractions of the ventricles of the heart and the ejection of blood from them, as well as resistance to blood flow, blood pressure is created in the vascular bed. This is the force with which blood presses against the wall of blood vessels. The pressure in the arteries depends on the phase of the cardiac cycle. During systole, it is maximum and is called systolic, during diastole it is minimal and is called diastolic. Systolic pressure in a healthy person of young and middle age in large arteries is mm Hg. Diastolic mm Hg The difference between systolic and diastolic pressure is called pulse pressure. Normally, its value mm Hg. In addition, they define average pressure- this is such a constant (i.e. not pulsating) pressure, the hemodynamic effect of which corresponds to a certain pulsating one. The value of the mean pressure is closer to diastolic, since the duration of diastole is longer than systole.

Blood pressure (BP) can be measured by direct and indirect methods. For measuring direct method a needle or cannula connected by a tube to a pressure gauge is inserted into the artery. Now enter a catheter with a pressure sensor. The signal from the sensor is sent to an electric pressure gauge. In the clinic, direct measurement is made only during surgical operations. Most widely used indirect methods Riva-Rocci and Korotkov. In 1896 Riva Rocci proposed to measure systolic pressure by the amount of pressure that must be created in a rubber cuff to completely clamp the artery. The pressure in it is measured by a manometer. The cessation of blood flow is determined by the disappearance of the pulse on the radial artery. In 1905 Korotkov proposed a method for measuring both systolic and diastolic pressure. It is as follows. The cuff creates pressure at which blood flow in the brachial artery stops completely. Then it gradually decreases and at the same time emerging sounds are heard with a phonendoscope in the cubital fossa. At the moment when the pressure in the cuff becomes slightly lower than systolic, short rhythmic sounds appear. They are called Korotkoff tones. They are caused by the passage of portions of blood under the cuff during systole. As the pressure in the cuff decreases, the intensity of the tones decreases and, at a certain value, they disappear. At this point, the pressure in it approximately corresponds to diastolic. At the moment, to measure blood pressure, devices are used that record fluctuations in the vessel under the cuff when the pressure in it changes. The microprocessor calculates systolic and diastolic pressure.

For objective registration of blood pressure, it is used arterial oscillography- graphic registration of pulsations of large arteries when they are compressed by a cuff. This method allows you to determine the systolic, diastolic, mean pressure and elasticity of the vessel wall. Blood pressure increases with physical and mental work, emotional reactions. During physical work, systolic pressure mainly increases. This is due to the fact that the systolic volume increases. If vasoconstriction occurs, both systolic and diastolic pressures increase. This phenomenon is observed with strong emotions.

With long-term graphic recording of blood pressure, three types of its fluctuations are detected. They are called waves of the 1st, 2nd and 3rd orders. Waves of the first order are pressure fluctuations during systole and diastole. Waves of the second order are called respiratory. When you inhale, blood pressure increases, and when you exhale, it decreases. With cerebral hypoxia, even slower third order waves. They are caused by fluctuations in the tone of the vasomotor center of the medulla oblongata.

In arterioles, capillaries, small and medium sized veins, the pressure is constant. In arterioles, its value is mm Hg, in the arterial end of the capillaries, mm Hg, venous 8-12 mm Hg. Blood pressure in arterioles and capillaries is measured by introducing into them a micropipette connected to a manometer. Blood pressure in the veins is 5-8 mm Hg. In the hollow veins, it is equal to zero, and on inspiration it becomes 3-5 mm Hg. below atmospheric. The pressure in the veins is measured by a direct method called phlebotonometry. An increase in blood pressure is called hypertension, decrease - hypotension. arterial hypertension occurs with aging hypertension, kidney disease, etc. Hypotension is observed in shock, exhaustion, and dysfunction of the vasomotor center.

Blood flow velocity, along with blood pressure, is the main physical quantity characterizing the state of the circulatory system.

Distinguish between linear and volumetric blood flow velocity. Linear blood flow velocity (V-lin) is the distance that a blood particle travels per unit of time. It depends on the total cross-sectional area of all vessels that form the section of the vascular bed. Therefore, in the circulatory system, the widest section is the aorta. Here the highest linear velocity of blood flow is 0.5-0.6 m/s. In the arteries of medium and small caliber, it decreases to 0.2-0.4 m/sec. The total lumen of the capillary bed is 500-600 times less than that of the aorta, so the blood flow velocity in the capillaries decreases to 0.5 mm/sec. The slowing down of blood flow in the capillaries is of great physiological importance, since transcapillary exchange takes place in them. In large veins, the linear velocity of blood flow increases again to 0.1-0.2 m/sec. The linear velocity of blood flow in the arteries is measured by ultrasound. It is based on the Doppler effect. A sensor with a source and receiver of ultrasound will be placed on the vessel. In a moving medium - blood, the frequency of ultrasonic vibrations changes. The greater the speed of blood flow through the vessel, the lower the frequency of reflected ultrasonic waves. The rate of blood flow in the capillaries is measured under a microscope with divisions in the eyepiece, by observing the movement of a specific red blood cell.

Volumetric blood flow velocity (volume) is the amount of blood passing through the cross section of the vessel per unit of time. It depends on the pressure difference at the beginning and end of the vessel and the resistance to blood flow. In the clinic, volumetric blood flow is measured using rheovasography. This method is based on registration of fluctuations in the electrical resistance of organs for high-frequency current, when their blood supply changes in systole and diastole. With an increase in blood supply, the resistance decreases, and with a decrease it increases. In order to diagnose vascular diseases, rheovasography of the extremities, liver, kidneys, and chest is performed. Sometimes plethysmography is used. This is a registration of fluctuations in the volume of an organ that occurs when their blood supply changes. Volume fluctuations are recorded using water, air and electric plethysmographs.

The speed of the blood circulation is the time it takes for a particle of blood to pass through both circles of blood circulation. It is measured by injecting a fluorescein dye into a vein in one arm to determine when it appears in a vein in the other. On average, the speed of the blood circulation is 20-25 seconds.

dopplerography is a method for studying blood flow in large and medium-sized human vessels based on the application of the Doppler effect. In patients, the method is used to clarify the nature and degree of circulatory disorders in any not very small vessels. This survey used during pregnancy - to assess the work of the placenta and uterine arteries.

To obtain information about the speed and nature of blood flow, pressure, the direction of blood movement in the vessel and the degree of its patency, the same ultrasound is used as in the case of a "normal" ultrasound. It only emits it and receives back a special sensor based on the Doppler effect. Given physical phenomenon is that the frequency of the ultrasound reflected from moving objects (blood cells) varies greatly compared to the frequency of the ultrasound emitted by the transducer. The device registers not the oscillation frequency itself, but the difference between the initial and reflected frequencies. Moreover, signal processing not only allows you to calculate this speed, but also to see the direction of blood flow (from the sensor or to it), to assess the anatomy and patency of the vessel.

Indications for research doppler ultrasound (USDG)

USDG of vessels lower extremities it is prescribed if there are such complaints: altered veins on the legs are visible. The legs (feet and shins) swell in the evening, the color of one or two legs has changed, it hurts to walk, after standing, it becomes easier to feel “goosebumps” legs quickly freeze, the wounds on the legs do not heal well.

fetal doppler carried out in such cases: the mother suffers diabetes, hypertension, anemia, the size of the child does not correspond to his age, the mother has a negative Rh, the child is positive, several fetuses develop, the umbilical cord wraps around the baby's neck. Such an ultrasound scan during pregnancy (that is, Doppler ultrasound) allows you to find out from the 23rd week whether the baby is suffering from a lack of oxygen.

Dopplerography is a method of studying not only the above-mentioned vessels, but also the vessels of the thoracic and abdominal sections of the aorta and their branches, the head, neck, arteries and veins of the upper limb.

color doppler mapping(CDI) is one of the subtypes of ultrasound based on the Doppler effect. It also "works" with the assessment of blood flow in the vessels. At the core this study- combination of conventional black-and-white ultrasound and Doppler assessment of blood flow. In the CFM mode, the doctor sees a black-and-white image on the monitor, in a certain (investigated) part of which the data on the speed of structures movement are displayed in color. So, shades of red will encode the speed of blood flow directed to the sensor (the lighter, the lower the speed), shades blue color is the velocity of blood flow directed from the sensor. A scale is displayed next to it, on which it is indicated which particular speed corresponds to one or another shade. That is, not veins are indicated in blue, and arteries are not indicated in red. color doppler mapping visualize and analyze: direction, nature, speed of blood flow; permeability, resistance, vessel diameter.

Diagnoses: the degree of thickening of the vascular wall parietal thrombi or atherosclerotic plaques (can distinguish them) pathological tortuosity of the vessel vessel aneurysm. This study helps not only to detect specific vascular pathology. Based on the data obtained as a result, it is possible to distinguish a benign process from a malignant one, to determine the tendency of the tumor to grow, to distinguish some formations.

Doppler mapping, carried out in relation to the vessels of the abdominal cavity, helps in the diagnosis of those pains in the abdominal cavity that occur due to insufficient blood supply to the intestine (this pathology cannot be determined by another method).

Rheovasography or RVG – modern method functional diagnostics, which determines the intensity and volume of blood flow in the arterial vessels of the extremities.

The principle of the method of this study is to measure the resistance of a skin area when passing through it electric current minimum force (absolutely harmless), voltage and a certain frequency using special sensors. Depending on the intensity of blood supply to tissues, their resistance changes. The worse the blood flow, the higher the resistance of the skin and tissues. Changes in the resistance parameter are displayed on a paper tape in the form of a curved line, along which the doctor of functional diagnostics determines the nature of the blood flow in the body area under study.

The main indication for such a functional study is the diagnosis of blood vessels in such diseases:

Atherosclerosis of the arteries of the legs is a pathology in which atherosclerotic plaques form on their walls, which reduce the lumen of the vessels and worsen the blood supply to the lower extremities.
Thrombophlebitis - inflammation of the veins of the legs, in which blood clots form in them.
Endarteritis - inflammation inner wall arteries of the arms or legs.
Varicose veins veins - a pathology in which superficial and deep veins legs with a violation of the normal outflow of blood through them.

Rheovasography is uncomplicated and not lengthy procedure. The person during its implementation is located on the back, on the couch. A functional diagnostics doctor attaches (usually with suction cups) sensors to the skin of the examined area of the arms or legs. The procedure itself takes about 10-15 minutes. Before it is carried out, it is necessary to follow a few simple preparatory recommendations:

Preliminary rest for complete relaxation of the muscles and normalization of blood flow in them (15-20 minutes before the start of the examination).
For a few days (at least 24 hours), it is necessary to stop taking drugs that affect the level of blood pressure and the condition of the vessels.
It is necessary to exclude the intake of alcohol for several days before the examination.
Smokers should refrain from smoking for several hours.
On the day of rheovasography, it is advisable to try to avoid pronounced physical or emotional stress.

Blood flow rate

Distinguish between linear and volumetric blood flow velocity. The linear velocity of blood flow (V-lin) is the distance that a blood particle travels per unit of time. It depends on the total cross-sectional area of all vessels that form the section of the vascular bed. Therefore, in the circulatory system, the narrowest section is the aorta. Here the highest linear velocity of blood flow is 0.5-0.6 m/s. In the arteries of medium and small caliber, it decreases to 0.2-0.4 m/sec. The total lumen of the capillary bed is 500-600 times greater than that of the aorta, so the blood flow velocity in the capillaries decreases to 0.5 mm/sec. The slowing down of blood flow in the capillaries is of great physiological importance, since transcapillary exchange takes place in them. In large veins, the linear velocity of blood flow increases again to 0.1-0.2 m/sec. The linear velocity of blood flow in the arteries is measured by ultrasound. It is based on the Doppler effect. A sensor with a source and receiver of ultrasound will be placed on the vessel. In a moving medium - blood, the frequency of ultrasonic vibrations changes. The greater the speed of blood flow through the vessel, the lower the frequency of reflected ultrasonic waves. The rate of blood flow in the capillaries is measured under a microscope with divisions in the eyepiece, by observing the movement of a specific red blood cell. Volumetric blood flow velocity (vol.) is the amount of blood passing through the cross section of the vessel per unit of time. It depends on the pressure difference at the beginning and end of the vessel and the resistance to blood flow.

Earlier in the experiment, the volumetric blood flow velocity was measured using a Ludwig blood clock. In the clinic, volumetric blood flow is assessed using rheovasography. This method is based on registration of fluctuations in the electrical resistance of organs for high-frequency current, when their blood supply changes in systole and diastole. With an increase in blood supply, the resistance decreases, and with a decrease it increases. In order to diagnose vascular diseases, rheovasography of the extremities, liver, kidneys, and chest is performed. Sometimes plethysmography is used. This is a registration of fluctuations in the volume of an organ that occurs when their blood supply changes. Volume fluctuations are recorded using water, air and electric plethysmographs. The speed of the blood circulation is the time it takes for a particle of blood to pass through both circles of blood circulation. It is measured by injecting a fluorescein dye into a vein of one arm and determining the time of its appearance in a vein of the other. On average, the speed of the blood circulation is 20-25 seconds.

Blood pressure

as a result of contractions of the ventricles of the heart and the ejection of blood from them, as well as resistance to blood flow in the vascular bed, blood pressure is created. This is the force with which blood presses against the wall of blood vessels. The pressure in the arteries depends on the phase of the cardiac cycle. During systole, it is maximum and is called systolic, during the period of diastole it is minimal and is called diastolic. Systolic pressure in a healthy person of young and middle age in large arteries is 100 - 130 mm Hg. Diastolic 60-80 mm Hg The difference between systolic and diastolic pressure is called pulse pressure. Normally, its value is 30-40 mm Hg. In addition, the average pressure is determined. This is such a constant, i.e. non-pulsating pressure, the hemodynamic effect of which corresponds to a certain pulsating one. The value of the mean pressure is closer to diastolic, since the duration of diastole is longer than systole. Blood pressure (BP) can be measured by direct and indirect methods; for direct measurement, a needle or cannula is inserted into the artery, connected by a tube to a manometer. Now enter a catheter with a pressure sensor. The signal from the sensor is sent to an electric pressure gauge. In the clinic, direct measurement is performed only during surgical operations. The most widely used indirect methods are Riva-Rocci and Korotkov. In 1896, Riva-Rocci proposed to measure systolic pressure by the amount of pressure that must be created in a rubber cuff to completely occlude an artery. The pressure in it is measured by a manometer. The cessation of blood flow is determined by the disappearance of the pulse on the radial artery. In 1905, Korotkoe proposed a method for measuring both systolic and diastolic pressure. It is as follows. The cuff creates pressure at which blood flow in the brachial artery stops completely. Then it gradually decreases and at the same time emerging sounds are heard with a phonendoscope in the cubital fossa. At the moment when the pressure in the cuff becomes slightly lower than systolic, short rhythmic sounds appear. They are called Korotkoff tones. They are caused by the passage of portions of blood under the cuff during systele. As the pressure in the cuff decreases, the intensity of the tones decreases and, at a certain value, they disappear. At this point, the pressure in it approximately corresponds to diastolic. At the moment, to measure blood pressure, devices are used that record fluctuations in the vessel under the cuff when the pressure in it changes. The microprocessor calculates systolic and diastolic pressure. For this, arterial oscillography is used. This is a graphic recording of the pulsations of large arteries when they are compressed by a cuff. This method allows you to determine the systolic, diastolic, mean pressure and elasticity of the vessel wall. Blood pressure increases with physical and mental work, emotional reactions. During physical work, systolic pressure mainly increases. This is due to the fact that the systolic volume increases. If vasoconstriction occurs, both systolic and diastolic pressures increase. This phenomenon is observed with strong emotions. With long-term graphic recording of blood pressure, three types of its fluctuations are detected. They are called waves of the 1st, 2nd and 3rd orders. Waves of the first order are pressure fluctuations during systole and diastole. Waves of the second order are called respiratory. When you inhale, blood pressure increases, and when you exhale, it decreases. With cerebral hypoxia, even slower waves of the third order arise. They are caused by fluctuations in the tone of the vasomotor center of the medulla oblongata.

In arternoles, capillaries, small and medium sized veins, the pressure is constant. In the arternoles, its value is 40-60 mm Hg, in the arterial end of the capillaries 20-30 mm Hg, in the venous end 8-12 mm Hg. Blood pressure in arternoles and capillaries is measured by introducing into them a micropipette connected to a manometer. The blood pressure in the veins is 5 mm Hg. In the hollow veins, it is 0, and on inspiration it becomes 3-5 mm Hg, below atmospheric. The pressure in the veins is measured by a direct method called phlebometry. An increase in blood pressure is called hypertension, a decrease is called hypotension. Arterial hypertension occurs with aging, hypertension, kidney disease, etc. Hypotension is observed in shock, exhaustion, and dysfunction of the vasomotor center.

Volumetric blood flow velocity called the amount of blood that flows in 1 minute through the entire circulatory system. This value corresponds to the IOC and is measured in milliliters per 1 min. Both general and local volumetric blood flow velocities are not constant and change significantly during physical exertion.

The volumetric velocity of blood through the vessels depends on the pressure difference at the beginning and end of the vessel, the resistance to blood flow, and also on the viscosity of the blood.

In accordance with the laws of hydrodynamics, the volumetric flow rate of the liquid is expressed by the equation: Q=P1 - P2/R, where Q is the volume of the liquid, P1 - P2 is the pressure difference at the beginning and end of the pipe, R is the resistance to the flow of the liquid.

To calculate the volumetric velocity of blood, it must be taken into account that the viscosity of blood is approximately 5 times higher than the viscosity of water. As a result, the resistance to blood flow in the vessels increases dramatically. In addition, the amount of resistance depends on the length and radius of the pipe.

These parameters are taken into account in the Poiseuille equation: R=8lη/πr4, where η is the viscosity of the liquid, l is the length, r is the radius of the pipe. This equation takes into account the peculiarities of fluid movement through rigid pipes, but not through elastic vessels.

From the magnitude of the volumetric blood flow and the cross-sectional area of the heart, it is possible to calculate the linear velocity.

Linear blood flow velocity called the speed of movement of blood particles along the vessels. This value, measured in centimeters per 1 s, is directly proportional to the volumetric blood flow velocity and inversely proportional to the cross-sectional area of the bloodstream. The linear velocity is not the same: it is greater in the center of the vessel and less near its walls, higher in the aorta and large arteries, and lower in the veins. The most low speed blood flow in capillaries, the total cross-sectional area of which is 600-800 times greater than the cross-sectional area of the aorta. The average linear velocity of blood flow can be judged by the time of a complete blood circulation. At rest, it is 21-23 s, with hard work it decreases to 8-10 s.

The linear speed of blood movement is equal to the ratio of the volumetric velocity to the cross-sectional area of the vessel: V=Q/S.

The blood flow velocity is maximum in the aorta and is 40 - 50 cm/s. In the capillaries, blood flow slows down sharply. The magnitude of this fall is proportional to the increase in the total lumen of the bloodstream. The lumen of the capillaries is approximately 600-800 times larger than the lumen of the aorta. Therefore, the calculated velocity of blood flow in the capillaries should be about 0.06 cm/s. Direct measurements give an even smaller figure - 0.05 cm/s. In large arteries and veins, the blood flow velocity is 15 - 20 cm/s.

The volume of blood flowing in 1 minute through the vessels in any part of the closed system is the same: the blood flow to the heart is equal to its outflow. Therefore, the low linear velocity of blood flow should be compensated by an increase in the total lumen of the vessels. Preservation of a constant volumetric blood flow velocity with a small total lumen of the vessels occurs due to the high linear velocity.