Physiological changes in hemodynamics during physical exercise. Physiological changes in hemodynamics during physical activity During physical activity, blood circulation is reconstructed
Physical activity is accompanied by one of the most natural adaptive reactions for the body, which requires good interaction of all parts of the circulatory system. The fact that skeletal muscles make up up to 40% of body weight, and the intensity of their activity can fluctuate within very wide limits, puts them in a special position compared to other organs. In addition, we must take into account that in nature, both the search for food and, sometimes, life itself depend on the functional capabilities of skeletal muscles. Therefore, in the process of evolution, close relationships between muscle contractions and the cardiovascular system have developed. They are aimed at creating, whenever possible, maximum conditions for blood supply to the muscles, even at the expense of reducing blood flow in other organs and systems. Considering the importance of providing blood to the contractile muscles, in the process of evolution a new level of hemodynamic regulation from the motor parts of the central nervous system was formed. Due to them, conditioned reflex mechanisms for regulating blood circulation are formed, i.e. pre-launch reactions. Their significance is to mobilize the cardiovascular system, due to which, even before the start of muscular activity, heart contractions become more frequent and blood pressure rises.
The sequence of activation of the cardiovascular system during physical labor can be traced during intense exercise. Muscles contract under the influence of impulses traveling along pyramidal tracts, which begin in the precentral torsion. Going down to the muscles, they are next to the motor parts of the central nervous system, also stimulating the respiratory and vasomotor centers of the medulla oblongata. From here, through the sympathetic nervous system, the activity of the heart increases and the blood vessels constrict. At the same time, catecholamines are released from the adrenal glands into the bloodstream, which constrict blood vessels. In functioning muscles, on the contrary, blood vessels dilate sharply. This occurs mainly due to the accumulation of metabolites such as H +, COT, K + 'adenosine and the like. As a result, a redistribution reaction of blood flow occurs: the more the number of muscles contracts, the more blood ejected by the heart flows to them. Due to the fact that the previous IOC is no longer sufficient to meet the increased need for blood, the activity of the heart quickly increases. In this case, the IOC can increase 5-6 times and reach 20-30 l/min. Of this volume, up to 80-85% enters functioning skeletal muscles. If at rest 0.9-1.0 l/min (15-20% of the IOC of 5 l/min) of blood passes through the muscles, then during contraction the muscles can receive up to 20 l/min or more.
At the same time, it is muscle contraction that also affects blood flow. With intense contraction as a result of compression of the vessels, blood access to the muscles decreases, but with relaxation it quickly increases. With less force of contraction, blood access increases during both the contraction and relaxation phases. In addition, contracted muscles squeeze out the blood of the venous section, on the one hand, accompanied by an increase in venous return to the heart, and on the other, the preconditions are created for increased blood access to the muscles during the relaxation phase.
Intensification of heart activity during muscle contraction occurs against the background of a proportional increase in blood flow through the coronary vessels. Autonomic regulation ensures that cerebral blood flow remains at the same level. The blood supply to other organs depends on the load. If the muscle load is intense, then, despite the increase in IOC, blood access to many internal organs may deteriorate. This occurs due to a sharp contraction of the afferent arteries under the influence of sympathetic vasoconstrictor impulses. A developed redistribution reaction can be expressed to such an extent that, for example, due to a decrease in renal blood flow, secretion almost completely stops.
An increase in IOC leads to an increase in Rs. Due to the expansion of muscle vessels, RD may remain the same or even decrease. If the decrease in bpor of the vascular part of the skeletal muscles does not compensate for the narrowing of other vascular zones, then Rd increases.
During physical activity, stimulation of vasomotor neurons is also facilitated by impulses from muscle proprioceptors and vascular chemoreceptors. Along with this, during muscular work, the adrenal system of the adrenal glands takes part in the regulation of blood flow. During work, other hormonal mechanisms for regulating blood flow (vasopressin, thyroxine, renin, atrial natriuretic hormone) are also activated.
During muscular work, the reflexes that control AT at rest are “cancelled.” Despite the increase in AT, reflexes from baroreceptors do not inhibit the activity of the heart. In this case, the influence of other regulatory mechanisms prevails.
In functioning muscles, an increase in AT with vasodilation also leads to changes in the conditions of water exchange. An increase in filtration pressure contributes to the retention of some fluid in the tissues. This causes an increase in hematocrit. An increase in the concentration of red blood cells (sometimes by 0.1012 / l) is one of the appropriate reactions of the body, since this increases the oxygen capacity of the blood.
Introduction
Structure and function of the heart
Movement of blood through vessels
Changes in blood circulation parameters during muscle work
Age-related characteristics of the cardiovascular system’s response to physical activity
Conclusion
Bibliography
Introduction
Anatomy and physiology belong to the biological sciences; they are the main disciplines in the theoretical and practical training of biologists and medical workers. At the same time, every literate person should know, at least in general terms, about the structure and basic functions of his body, his body and its individual organs. This kind of knowledge can be very useful if, in unforeseen circumstances, it is necessary to provide emergency assistance to the victim. Therefore, already in school years, along with biology - the science of all living things, human anatomy and physiology are studied as a representative of the animal world, which occupies a special place in it. Man differs from animals not only in his more advanced structure, but also in the development of thinking, the presence of articulate speech, and intelligence, which are determined by a complex of social conditions of life, social relationships, and socio-historical experience. Work and the social environment have changed the biological characteristics of humans.
Thus, anatomy and physiology are part of biology, just as humans are part of the animal world.
Human anatomy is the science of the forms and structure, origin and development of the human body. Anatomy studies the external forms and proportions of the human body, its parts, individual organs, their design, microscopic and ultramicroscopic structure. Anatomy examines the structure of the human body, its organs and various periods of life, from the prenatal period to old age, and examines the characteristics of the body under the influence of the external environment.
Physiology studies the functions of a living organism, its organs and systems, cells and cellular associations, and their life processes. Physiology studies functional relationships in the human body at different age periods and in conditions of a changing external environment.
Modern anatomy and physiology carefully study the changes and processes occurring in the human body during different age periods.
Revealing the basic patterns of human development in embryogenesis, as well as children in different age periods, anatomy and physiology provide important material for teachers, psychologists, educators and hygienists.
The effectiveness of education and training is closely dependent on the extent to which the anatomical and physiological characteristics of children and adolescents are taken into account. Particular attention is paid to periods of development, which are characterized by the greatest susceptibility to the influence of certain factors, as well as periods of increased sensitivity and reduced resistance of the body.
Structure and functions of the heart
The heart is located on the left side of the chest in the so-called pericardial sac, which separates the heart from other organs. The heart wall consists of three layers - the epicardium, myocardium and endocardium. The epicardium consists of a thin (no more than 0.3-0.4 mm) plate of connective tissue, the endocardium consists of epithelial tissue, and the myocardium consists of cardiac striated muscle tissue.
The heart consists of four separate cavities called chambers: left atrium, right atrium, left ventricle, right ventricle. They are separated by partitions. The right atrium contains the hollow veins, and the left atrium contains the pulmonary veins. The pulmonary artery (pulmonary trunk) and the ascending aorta emerge from the right ventricle and left ventricle, respectively. The right ventricle and left atrium close the pulmonary circulation, the left ventricle and right atrium close the systemic circle. The heart is located in the lower part of the anterior mediastinum, most of its anterior surface is covered by the lungs with the inflowing sections of the vena cava and pulmonary veins, as well as the outflowing aorta and pulmonary trunk. The pericardial cavity contains a small amount of serous fluid.
The wall of the left ventricle is approximately three times thicker than the wall of the right ventricle, since the left must be strong enough to push blood into the systemic circulation for the entire body (the resistance of blood in the systemic circulation is several times greater, and the blood pressure is several times greater higher than in the pulmonary circulation).
There is a need to maintain blood flow in one direction, otherwise the heart could fill with the same blood that was previously sent into the arteries. Responsible for the flow of blood in one direction are the valves, which at the appropriate moment open and close, allowing blood to pass through or blocking it. The valve between the left atrium and the left ventricle is called the mitral valve or bicuspid valve because it consists of two leaflets. The valve between the right atrium and the right ventricle is called the tricuspid valve - it consists of three petals. The heart also contains the aortic and pulmonary valves. They control the flow of blood from both ventricles.
The following main functions of the heart are distinguished:
Automaticity is the ability of the heart to produce impulses that cause excitement. Normally, the sinus node has the greatest automaticity.
Conductivity is the ability of the myocardium to conduct impulses from the place of their origin to the contractile myocardium.
Excitability is the ability of the heart to become excited under the influence of impulses. During excitation, an electric current occurs, which is recorded by a galvanometer in the form of an ECG. Contractility is the ability of the heart to contract under the influence of impulses and provide pump function.
Refractoriness is the inability of excited myocardial cells to become active again when additional impulses occur. It is divided into absolute (the heart does not respond to any stimulation) and relative (the heart responds to very strong stimulation).
Movement of blood through vessels
Blood circulation occurs along two main paths called circles: the pulmonary and systemic circulation.
In a small circle, blood circulates through the lungs. The movement of blood in this circle begins with the contraction of the right atrium, after which the blood enters the right ventricle of the heart, the contraction of which pushes the blood into the pulmonary trunk. Blood circulation in this direction is regulated by the atrioventricular septum and two valves: the tricuspid valve (between the right atrium and the right ventricle), which prevents blood from returning to the atrium, and the pulmonary valve, which prevents blood from returning from the pulmonary trunk to the right ventricle. The pulmonary trunk branches into a network of pulmonary capillaries, where the blood is saturated with oxygen due to ventilation of the lungs. The blood then returns from the lungs through the pulmonary veins to the left atrium.
The systemic circulation supplies oxygenated blood to organs and tissues. The left atrium contracts simultaneously with the right and pushes blood into the left ventricle. From the left ventricle, blood enters the aorta. The aorta branches into arteries and arterioles that go to various parts of the body and end with a capillary network in organs and tissues. Blood circulation in this direction is regulated by the atrioventricular septum, bicuspid (mitral) valve and aortic valve.
Thus, blood moves through the systemic circulation from the left ventricle to the right atrium, and then through the pulmonary circulation from the right ventricle to the left atrium.
Mechanism of blood circulation
The movement of blood through the vessels is carried out mainly due to the pressure difference between the arterial and venous systems. This statement is completely true for arteries and arterioles; auxiliary mechanisms appear in capillaries and veins, which are discussed below. The pressure difference is created by the rhythmic work of the heart, pumping blood from the veins to the arteries. Since the pressure in the veins is very close to zero, this difference can be taken, for practical purposes, to be equal to the blood pressure.
Cardiac cycle
The right half of the heart and the left work synchronously. For convenience of presentation, the work of the left half of the heart will be considered here.
The cardiac cycle includes general diastole (relaxation), atrial systole (contraction), and ventricular systole. During general diastole, the pressure in the cavities of the heart is close to zero, in the aorta it slowly decreases from systolic to diastolic, normally in humans equal to 120 and 80 mm Hg, respectively. Art. Because the pressure in the aorta is higher than in the ventricle, the aortic valve is closed. The pressure in the large veins (central venous pressure, CVP) is 2-3 mm Hg, that is, slightly higher than in the cavities of the heart, so that blood flows into the atria and, in transit, into the ventricles. The atrioventricular valves are open at this time.
During atrial systole, the circular muscles of the atria compress the entrance from the veins to the atria, which prevents the reverse flow of blood, the pressure in the atria rises to 8-10 mmHg, and the blood moves into the ventricles.
During subsequent ventricular systole, the pressure in the ventricles becomes higher than the pressure in the atria (which begin to relax), which leads to the closure of the atrioventricular valves. The external manifestation of this event is the first heart sound. The pressure in the ventricle then exceeds the aortic pressure, causing the aortic valve to open and expulsion of blood from the ventricle into the arterial system. The relaxed atrium fills with blood at this time. The physiological significance of the atria lies mainly in their role as an intermediate reservoir for blood coming from the venous system during ventricular systole.
At the beginning of general diastole, the pressure in the ventricle drops below the aortic (closing of the aortic valve, II tone), then below the pressure in the atria and veins (opening of the atrioventricular valves), the ventricles begin to fill with blood again.
In a state of calm, the ventricle of an adult’s heart pumps out 75 ml of blood (stroke volume) for each systole. The cardiac cycle lasts up to 1 s, respectively, the heart makes 60 contractions per minute (heart rate, heart rate). It is easy to calculate that even at rest, the heart pumps 4.5-5 liters of blood per minute (cardiac minute volume, MCV). During maximum exercise, the stroke volume of a trained person’s heart can exceed 200 ml, the pulse can exceed 200 beats per minute, and blood circulation can reach 40 liters per minute.
Arterial system
Arteries, which contain almost no smooth muscle, but have a powerful elastic membrane, perform mainly a “buffer” role, smoothing out pressure differences between systole and diastole. The walls of the arteries are elastically extensible, which allows them to accept the additional volume of blood “thrown in” by the heart during systole, and only moderately, by 50-60 mm Hg. raise the pressure. During diastole, when the heart is not pumping anything, it is the elastic stretching of the arterial walls that maintains the pressure, preventing it from falling to zero, and thereby ensuring the continuity of blood flow. It is the stretching of the vessel wall that is perceived as a pulse beat. Arterioles have developed smooth muscles, thanks to which they are able to actively change their lumen and, thus, regulate resistance to blood flow. It is the arterioles that account for the greatest pressure drop, and they determine the ratio of blood flow volume and blood pressure. Accordingly, arterioles are called resistive vessels.
Capillaries
Capillaries are characterized by the fact that their vascular wall is represented by a single layer of cells, so that they are highly permeable to all low molecular weight substances dissolved in the blood plasma. Here the exchange of substances between tissue fluid and blood plasma occurs.
-reabsorption pressure about (20-28) = 8 mmHg. Art. when blood passes through capillaries, blood plasma is completely renewed 40 times with interstitial (tissue) fluid;
-the volume of diffusion alone through the total exchange surface of the body’s capillaries is about 60 l/min or approximately 85,000 l/day;
-pressure at the beginning of the arterial part of the capillary is 37.5 mm Hg. Art.;
-the effective pressure is about (37.5 - 28) = 9.5 mmHg. Art.;
-pressure at the end of the venous part of the capillary, directed outward of the capillary, 20 mm Hg. Art.;
Effective
Venous system
From the organs, blood returns through the postcapillaries into the venules and veins into the right atrium through the superior and inferior vena cava, as well as through the coronary veins. cardiac vascular circulation schoolboy
Venous return occurs through several mechanisms. Firstly, the basic mechanisms due to the pressure difference at the end of the venous part of the capillary, directed outwards of the capillary, are about 20 mm Hg. Art., in the TG - 28 mm Hg), the effective reabsorption pressure directed inside the capillary is about (20 - 28) = minus 8 mm Hg. Art. (- 8 mmHg).
Secondly, for the veins of skeletal muscles, it is important that when the muscle contracts, the pressure “from the outside” exceeds the pressure in the vein, so that the blood is “squeezed out” from the veins of the contracting muscle. The presence of venous valves determines the direction of blood movement in this case - from the arterial end to the venous end. This mechanism is especially important for the veins of the lower extremities, since here the blood rises through the veins, overcoming gravity. Thirdly, the suction role of the chest. During inspiration, the pressure in the chest drops below atmospheric pressure (which we take to be zero), which provides an additional mechanism for blood return. The size of the lumen of the veins, and accordingly their volume, significantly exceeds those of the arteries. In addition, the smooth muscles of the veins ensure a change in their volume within a very wide range, adapting their capacity to the changing volume of circulating blood, therefore the physiological role of the veins is defined as “capacitive vessels”.
Changes in blood circulation parameters during muscle work
Research related to the analysis of the activity of organs and systems of the body that directly provide muscle work is relevant. The most useful information for these purposes can be obtained by studying the response of the cardiovascular system and, in particular, such hemodynamic parameters as systolic volume.
Minute volume of blood circulation was calculated using the classic Fick formula:
Qm = VCO2 / VADCO2
where Qm is the minute volume of blood circulation in l/min; VCO2 is the amount of carbon dioxide released in ml/min (STPD); VADCO2 - venous-arterial difference in CO2 in ml/l.
With regular exercise or any kind of sport, the number of red blood cells and hemoglobin in the blood increases, ensuring an increase in the oxygen capacity of the blood; The number of leukocytes and their activity increases, which increases the body's resistance to colds and infectious diseases.
Human physical activity, physical exercise, and sports have a significant impact on the development and condition of the cardiovascular system. Perhaps no organ needs training so much and does not lend itself to it as easily as the heart. Working under heavy load during sports exercises, the heart inevitably trains. The boundaries of its capabilities expand, it adapts to pumping much more blood than the heart of an untrained person can do. In the process of regular exercise and sports, as a rule, there is an increase in the mass of the heart muscle and the size of the heart. Thus, the weight of the heart in an untrained person is on average about 300 g, in a trained person - 500 g.
Indicators of heart performance are pulse rate, blood pressure, systolic and minute blood volume.
Systolic volume at rest in an untrained person is 50-70 ml, in a trained person 70-80 ml; with intense muscular work, respectively - 100-130 ml and 200 ml more.
Physical work helps to dilate blood vessels and reduce the tone of their walls; mental work, as well as nervous and emotional stress, leads to a narrowing of blood vessels, increased tone of their walls and even spasms. This reaction is especially characteristic of the vessels of the heart and brain.
Prolonged intense mental work, frequent neuro-emotional stress, unbalanced with active movements and physical activity, can lead to a deterioration in the nutrition of these most important organs, to a persistent increase in blood pressure, which, as a rule, is the main sign of hypertension.
The disease is also indicated by a decrease in blood pressure at rest (hypotension), which may be a consequence of weakened activity of the heart muscle.
As a result of special exercise and sports, blood pressure undergoes positive changes. Due to the denser network of blood vessels and their high elasticity in athletes, as a rule, the maximum pressure at rest is slightly lower than normal. The maximum heart rate in trained people during physical activity can be at the level of 200-240 beats/min, while the systolic pressure remains at the level of 200 mm Hg for quite a long time. Art. An untrained heart simply cannot achieve such a contraction frequency, and high systolic and diastolic pressure, even during short-term intense activity, can cause pre-pathological and even pathological conditions.
Systolic blood volume is the amount of blood ejected by the left ventricle of the heart with each contraction. Minute blood volume is the amount of blood ejected by the ventricle within one minute. The greatest systolic volume is observed at a heart rate from 130 to 180 beats/min. At heart rates above 180 beats/min, systolic volume begins to decrease significantly. Therefore, the best opportunities for training the heart occur during physical activity, when the heart rate is in the range from 130 to 180 beats/min.
Age-related characteristics of the cardiovascular system’s response to physical activity
The child's body's response to physical activity changes as the body grows and develops. Children and adolescents respond to dynamic physical activity by increasing their heart rate and maximum blood pressure. The younger the child’s age, the more they react to even slight physical activity.
Children and adolescents who engage in physical education and labor under strictly regulated loads train the cardiovascular system, increasing its functional and reserve capabilities. They increase their performance and endurance compared to their untrained peers. In response to physical activity, the volume of blood pumped by the heart per minute (minute blood volume) increases. In trained children, this occurs due to an increase in systolic volume rather than heart rate. During maximum physical activity in trained adolescents, unlike untrained ones, the minute volume of blood is sufficient to supply all organs with oxygen.
In schoolchildren-athletes, after dosed physical activity (20 squats in 30 seconds), the heart rate increases by 60-70% (in untrained ones by 100%), the maximum blood pressure increases by 25-30%, the minimum decreases by 20-25% (in the untrained, by 40% and 5-10%, respectively). In adolescents with hidden insufficiency of the cardiovascular system, these indicators are even worse: maximum blood pressure decreases, minimum blood pressure increases, time to recuperate lasts more than 3 minutes, shortness of breath and dizziness appear. If the same signs appear in athletes, this is evidence of overtraining of the body due to incorrectly standardized physical activity.
During static physical activity (prolonged sitting, standing, etc.), both maximum and minimum blood pressure increases in trained and untrained children and adolescents. This reaction occurs even to a light static load (30% of the compression force of a hand-held dynamometer) and is recorded within 5 minutes. after stopping the load. At the beginning of the school year, these figures are lower than at the end. Prolonged static load can cause arteriole spasm in schoolchildren (the overall blood pressure rises) and can contribute to the occurrence of organic changes in the heart muscles and valves.
One of the measures to prevent cardiovascular diseases is to increase the physical activity of schoolchildren during the educational process within the age limits of permissible physical activity.
Conclusion
Modern science about the human body is developing very quickly. It has been enriched with the latest research methods. Thanks to physics, chemistry, electronics, cybernetics, technology and other sciences, very complex and advanced instruments and equipment are used to study the structure, activity of the body and its treatment. For example, to study the functioning of the human brain, a complex device is used that records very weak electrical currents in the brain. For this purpose, hundreds of small electrodes connected to this device are applied to the outside of a person’s head. Everyone needs to know their body. The sciences of the human body make it possible to understand its structure and functions, maintain and improve health, increase labor productivity and significantly extend life.
The need for knowledge of physiology I.P. Pavlov expressed it in the following words: “...In order to use the treasures of nature, in order to enjoy these treasures, a person must be healthy, strong and smart... Physiology teaches us - and the further, the more fully and perfectly, how to properly , i.e. useful and pleasant, work, relax, eat, etc. But this is not enough. She will teach us how to think, feel and desire correctly.” Physiology and hygiene have proven that all sorts of excesses, mental and physical overstrain, and systematic overwork are harmful to the body. The extremely harmful effects on the body of drinking alcoholic beverages and smoking tobacco have been established. Anatomy, physiology and hygiene help you consciously choose the healthiest lifestyle.
Bibliography
1.Anatomy, physiology, human psychology: Ill. times words / Ed. A.S. Batueva. - St. Petersburg: Lan, 1998. - 268 p.
2.Brin V.B. Human physiology in diagrams and tables. - Rostov n/d: Phoenix, 1999. - 216 p.3. Maryutina T.M., Ermolaev O.Yu.
.Psychophysiology. - M.: Publishing house Mosk. state University, 1998. - 306 p.4. Fundamentals of psychophysiology / Ed. Yu.I. Alexandrova. - M.: INFRA-M, 1997. - 408 p.5. Sapim M.R., Sivoglazov R.I.
.Human anatomy and physiology with age-related characteristics of the child’s body. - M.: Academy, 2000. - 365 p.6. Human physiology / N.A. Agadzhanyan, L.Z. Tel, V.I. Tsirkin, S.A. Chesnokova. - St. Petersburg: Sotis, 1998. - 385 p.
.Small medical encyclopedia. - M.: Medical encyclopedia. 1991-96 2. First aid. - M.: Great Russian Encyclopedia. 1994
.Lishchuk V.A. Mathematical theory of blood circulation. - 1991.
.I.P. Pavlov “Lectures on the physiology of blood circulation 1912-1913.” "Educational book plus", 2002
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The chapter examines blood circulation at different levels of physical activity, lack and excess of oxygen, low and high ambient temperatures, and changes in gravity.
PHYSICAL ACTIVITY
The work can be dynamic, when resistance is overcome at a certain distance, and static - with isometric muscle contraction.
Dynamic operation
Physical stress causes immediate reactions in various functional systems, including muscular, cardiovascular and respiratory. The severity of these reactions is determined by the body’s adaptation to physical activity and the severity of the work performed.
Heart rate. Based on the nature of changes in heart rate, two forms of work can be distinguished: light, non-tiring work - with the achievement of a stationary state - and hard, fatigue-causing work (Fig. 6-1).
Even after completion of work, heart rate changes depending on the stress that took place. After light work, heart rate returns to its original level within 3-5 minutes; After hard work, the recovery period is much longer - with extremely heavy loads it reaches several hours.
During hard work, blood flow and metabolism in the working muscle increases more than 20 times. The degree of changes in cardio- and hemodynamic indicators during muscle activity depends on its power and the physical fitness (adaptability) of the body (Table 6-1).
Rice. 6-1.Changes in heart rate in individuals with average performance during light and heavy dynamic work of constant intensity
In individuals trained for physical activity, myocardial hypertrophy occurs, capillary density and contractile characteristics of the myocardium increase.
The heart increases in size due to hypertrophy of cardiomyocytes. The weight of the heart in highly qualified athletes increases to 500 g (Fig. 6-2), the concentration of myoglobin in the myocardium increases, and the cavities of the heart increase.
The density of capillaries per unit area in a trained heart increases significantly. Coronary blood flow and metabolic processes increase in accordance with the work of the heart.
Myocardial contractility (the maximum rate of increase in pressure and ejection fraction) significantly increases in athletes due to the positive inotropic effect of sympathetic nerves.
Table 6-1.Changes in physiological parameters during dynamic work of different power in people not involved in sports (top line) and in trained athletes (bottom line)
Nature of work | Light | Average | Submaximal | Maximum |
Operating power, W | 50-100 | 100-150 | 150-250 |
|
100-150 | 150-200 | 200-350 | 350-500 and> |
|
Heart rate, beats/min | 120-140 | 140-160 | 160-170 | 170-190 |
90-120 | 120-140 | 140-180 | 180-210 |
|
Systolic blood volume, l/min | 80-100 | 100-120 | 120-130 | 130-150 |
80-100 | 100-140 | 140-170 | 170-200 |
|
Minute blood volume, l/min | 10-12 | 12-15 | 15-20 | 20-25 |
8-10 | 10-15 | 15-30 | 30-40 |
|
Average blood pressure, mm Hg. | 85-95 | 95-100 | 100-130 | 130-150 |
85-95 | 95-100 | 100-150 | 150-170 |
|
Oxygen consumption, l/min | 1,0-1,5 | 1,5-2,0 | 2,0-2,5 | 2,5-3,0 |
0,8-1,0 | 1,0-2,5 | 2,5-4,5 | 4,5-6,5 |
|
Blood lactate, mg per 100 ml | 20-30 | 30-40 | 40-60 | 60-100 |
10-20 | 20-50 | 50-150 | 150-300 |
During physical activity, cardiac output increases due to an increase in heart rate and stroke volume, and changes in these values are purely individual. In healthy young people (with the exception of highly trained athletes), cardiac output rarely exceeds 25 L/min.
Regional blood flow. During physical activity, regional blood flow changes significantly (Table 6-2). Increased blood flow in working muscles is associated not only with an increase in cardiac output and blood pressure, but also with a redistribution of blood volume. With maximum dynamic work, blood flow in the muscles increases by 18-20 times, in the coronary vessels of the heart by 4-5 times, but decreases in the kidneys and abdominal organs.
In athletes, the end-diastolic volume of the heart naturally increases (3-4 times more than the stroke volume). For an ordinary person, this figure is only 2 times higher.
Rice. 6-2.Normal heart and athlete's heart. An increase in heart size is associated with elongation and thickening of individual myocardial cells. In the adult heart there is approximately one capillary for every muscle cell.
Table 6-2.Cardiac output and organ blood flow in humans at rest and during physical activity of varying intensity
O absorption 2 , ml/(min*m 2) |
||||
Peace | Light | Average | Maximum |
|
140 | 400 | 1200 | 2000 |
|
Region | Blood flow, ml/min |
|||
Skeletal muscles | 1200 | 4500 | 12 500 | 22 000 |
Heart | 1000 |
|||
Brain | ||||
Pregnant | 1400 | 1100 | ||
Renal | 1100 | |||
Leather | 1500 | 1900 | ||
Other organs | ||||
Cardiac output | 5800 | 9500 | 17 500 | 25 000 |
During muscle activity, myocardial excitability increases, the bioelectrical activity of the heart changes, which is accompanied by a shortening of the PQ, QT intervals of the electrocardiogram. The greater the power of work and the lower the level of physical fitness of the body, the more the electrocardiogram indicators change.
When the heart rate increases to 200 per minute, the duration of diastole decreases to 0.10-0.11 s, i.e. more than 5 times relative to this value at rest. Ventricular filling occurs within 0.05-0.08 s.
Arterial pressure in humans, it increases significantly during muscle activity. When running, which causes heart rate to increase to 170-180 per minute, the following increases:
Systolic pressure averaged from 130 to 250 mm Hg;
Average pressure - from 99 to 167 mm Hg;
Diastolic - from 78 to 100 mm Hg.
With intense and prolonged muscle activity, the stiffness of the main arteries increases due to the strengthening of the elastic frame and increasing the tone of smooth muscle fibers. In arteries of the muscular type, moderate hypertrophy of muscle fibers can be observed.
The pressure in the central veins during muscle activity, as well as the central blood volume, increases. This is due to an increase in venous blood return with an increase in the tone of the vein walls. Working muscles act as an additional pump, which is referred to as a “muscle pump,” providing increased (adequate) blood flow to the right heart.
The total peripheral vascular resistance during dynamic work can decrease by 3-4 times compared to the initial, non-working state.
Oxygen consumption increases by an amount that depends on the load and the efficiency of the effort expended.
During light work, a steady state is reached when oxygen consumption and utilization are equivalent, but this occurs only after 3-5 minutes, during which the blood flow and metabolism in the muscle adapt to the new requirements. Until a steady state is reached, the muscle depends on little oxygen reserve,
which is provided by O 2 bound to myoglobin and from the ability to extract oxygen from the blood.
With heavy muscular work, even if it is performed with constant effort, a stationary state does not occur; like heart rate, oxygen consumption constantly increases, reaching a maximum.
Oxygen debt. As work begins, the energy requirement increases immediately, but it takes some time for blood flow and aerobic metabolism to adjust; Thus, an oxygen debt arises:
During light work, the oxygen debt remains constant after reaching a steady state;
With hard work, it increases until the very end of the work;
At the end of work, especially in the first minutes, the rate of oxygen consumption remains above the resting level - the “payment” of the oxygen debt occurs.
A measure of physical stress. As the intensity of dynamic work increases, heart rate increases and the rate of oxygen consumption increases; The greater the load on the body, the greater the increase compared to the resting level. Thus, heart rate and oxygen consumption serve as a measure of physical exertion.
Ultimately, the body’s adaptation to high physical activity leads to an increase in the power and functional reserves of the cardiovascular system, since it is this system that limits the duration and intensity of the dynamic load.
HYPODYNAMIA
Freeing a person from physical labor leads to physical detraining of the body, in particular to a change in blood circulation. In such a situation, one would expect an increase in efficiency and a decrease in the intensity of the functions of the cardiovascular system. However, this does not happen - the efficiency, power and efficiency of blood circulation are reduced.
In the systemic circulation, a decrease in systolic, mean and pulse blood pressure is more often observed. In the pulmonary circulation, when hypokinesia is combined with a decrease in hydrostatic blood pressure (bed rest, weightlessness)
Most) blood flow to the lungs increases, pressure in the pulmonary artery increases.
Under resting conditions with hypokinesia:
Heart rate naturally increases;
Cardiac output and blood volume decrease;
With prolonged bed rest, the size of the heart, the volume of its cavities, and the mass of the myocardium noticeably decrease.
The transition from hypokinesia to the normal activity mode causes:
Marked increase in heart rate;
Increased minute volume of blood flow - IOC;
Decrease in total peripheral resistance.
When transitioning to intense muscular work, the functional reserves of the cardiovascular system decrease:
In response to muscle load, even of low intensity, heart rate quickly increases;
Shifts in blood circulation are achieved through the inclusion of less economical components;
At the same time, IOC increases mainly due to an increase in heart rate.
Under conditions of hypokinesia, the phase structure of the cardiac cycle changes:
The phase of blood expulsion and mechanical systole is reduced;
The duration of the tension phase, isometric contraction and relaxation of the myocardium increases;
The initial rate of increase in intraventricular pressure decreases.
Myocardial hypodynamia. All of the above indicates the development of the phase syndrome of myocardial “hypodynamia”. This syndrome is usually observed in a healthy person against the background of reduced blood return to the heart during mild physical activity.
ECG changes.With hypokinesia, electrocardiogram parameters change, which are expressed in positional changes, relative slowing of conduction, reduction of P and T waves, changes in the ratio of T values in different leads, periodic displacement of the S-T segment, changes in the repolarization process. Hypokinetic changes in the electrocardiogram, regardless of the pattern and severity, are always reversible.
Changes in the vascular system. With hypokinesia, a stable adaptation of the vascular system and regional blood flow to these conditions develops (Table 6-3).
Table 6-3.Basic indicators of the cardiovascular system in humans under conditions of hypokinesia
Changes in blood circulation regulation. With hypokinesia, signs of the predominance of sympathetic influences over parasympathetic ones change the system of regulation of cardiac activity:
High activity of the hormonal component of the sympathoadrenal system indicates the high stress potential of hypokinesia;
Increased excretion of catecholamines in the urine and their low content in tissues is realized by a violation of the hormonal regulation of the activity of cell membranes, in particular, cardiomyocytes.
Thus, the decrease in the functional capabilities of the cardiovascular system during hypokinesia is determined by the duration of the latter and the degree of limitation of mobility.
BLOOD CIRCULATION IN OXYGEN INSUFFICIENCY
As altitude increases, atmospheric pressure drops and the partial pressure of oxygen (PO 2) decreases in proportion to the decrease in atmospheric pressure. The body's response (primarily the respiratory, circulatory and blood organs) to oxygen deficiency depends on its severity and duration.
Short-term reactions in high altitude conditions require only a few hours, primary adaptation requires several days and even months, and the stage of stable adaptation of migrants takes years to acquire. The most effective adaptive reactions are manifested in the indigenous population of high mountain regions due to long-term natural adaptation.
Initial adaptation period
Human movement (migration) from flat terrain to mountains is accompanied by a pronounced change in the hemodynamics of the systemic and pulmonary circulation.
Tachycardia develops and minute volume of blood flow (MVV) increases. The heart rate at an altitude of 6000 m for new arrivals under resting conditions reaches 120 per minute. Physical activity causes more pronounced tachycardia and an increase in IOC than at sea level.
Stroke volume changes slightly (both an increase and a decrease can be observed), but the linear velocity of blood flow increases.
Systemic blood pressure increases slightly in the first days of staying at altitudes. The rise in systolic blood pressure is caused mainly by an increase in IOC, and in diastolic blood pressure - by an increase in peripheral vascular resistance.
BCC increases due to the mobilization of blood from the depot.
Excitation of the sympathetic nervous system is realized not only by tachycardia, but also by paradoxical dilatation of the veins of the systemic circulation, which leads to a decrease in venous pressure at altitudes of 3200 and 3600 m.
A redistribution of regional blood flow occurs.
Blood supply to the brain increases due to a reduction in blood flow in the vessels of the skin, skeletal muscles and digestive tract. The brain is one of the first to react
for oxygen deficiency. This is explained by the special sensitivity of the cerebral cortex to hypoxia due to the use of a significant amount of O 2 for metabolic needs (a brain weighing 1400 g consumes about 20% of the oxygen consumed by the body).
In the first days of high-altitude adaptation, blood flow in the myocardium decreases.
The volume of blood in the lungs increases markedly. Primary high-altitude arterial hypertension- increase in blood pressure in the vessels of the lungs. The basis of the disease is an increase in the tone of small arteries and arterioles in response to hypoxia; usually pulmonary hypertension begins to develop at an altitude of 1600-2000 m above sea level, its value is directly proportional to the altitude and persists throughout the entire period of stay in the mountains.
An increase in pulmonary blood pressure occurs immediately upon rising to altitude, reaching its maximum within 24 hours. On the 10th and 30th days, pulmonary blood pressure gradually decreases, but does not reach the initial level.
The physiological role of pulmonary hypertension is to increase the volumetric perfusion of the pulmonary capillaries due to the inclusion of structural and functional reserves of the respiratory organs in gas exchange.
Inhalation of pure oxygen or a gas mixture enriched with oxygen at high altitude leads to a decrease in blood pressure in the pulmonary circulation.
Pulmonary hypertension, together with an increase in IOC and central blood volume, places increased demands on the right ventricle of the heart. At high altitudes, if adaptive reactions are disrupted, mountain sickness or acute pulmonary edema may develop.
Height threshold effects
The effect of oxygen deficiency, depending on the height and degree of extremeness of the terrain, can be divided into four zones (Fig. 6-3), delimited from each other by effective thresholds (Ruf S., Strughold H., 1957).
Neutral zone. Up to an altitude of 2000 m, the ability for physical and mental activity suffers little or does not change at all.
Full compensation zone. At altitudes between 2000 and 4000 m, even at rest, heart rate, cardiac output and MOP increase. The increase in these indicators during work at such heights occurs to a greater extent
degrees than at sea level, so that both physical and mental performance are significantly reduced.
Zone of incomplete compensation (danger zone). At altitudes from 4000 to 7000 m, an unadapted person develops various disorders. Upon reaching the threshold of violations (safety limit) at an altitude of 4000 m, physical performance drops significantly, and the ability to react and make decisions weakens. Muscle twitching occurs, blood pressure decreases, and consciousness gradually becomes clouded. These changes are reversible.
Rice. 6-3.The influence of oxygen deficiency when ascending to altitude: the numbers on the left are the partial pressure of O 2 in the alveolar air at the corresponding altitude; the numbers on the right are the oxygen content in gas mixtures, which gives the same effect at sea level
Critical zone. Starting from 7000 m and above, the alveolar air becomes below the critical threshold - 30-35 mm Hg. (4.0-4.7 kPa). Potentially fatal central nervous system disorders occur, accompanied by unconsciousness and convulsions. These disturbances can be reversible if there is a rapid increase in inspired air. In the critical zone, the duration of oxygen deficiency is critical. If hypoxia continues for too long,
disturbances occur in the regulatory parts of the central nervous system and death occurs.
Long stay in the highlands
When a person spends a long time in high altitude conditions at altitudes up to 5000 m, further adaptive changes in the cardiovascular system occur.
Heart rate, stroke volume and IOC stabilize and decrease to initial values and even lower.
Severe hypertrophy of the right chambers of the heart develops.
The density of blood capillaries in all organs and tissues increases.
BCC remains increased by 25-45% due to an increase in plasma volume and erythrocyte mass. At high altitudes, erythropoiesis increases, so the hemoglobin concentration and the number of red blood cells increase.
Natural adaptation of highlanders
The dynamics of the main hemodynamic parameters in highland aborigines (highlanders) at an altitude of up to 5000 m remains the same as in lowland residents at sea level. The main difference between “natural” and “acquired” adaptation to high-altitude hypoxia is the degree of tissue vascularization, microcirculation activity and tissue respiration. In permanent residents of the highlands, these parameters are more pronounced. Despite the reduced regional blood flow in the brain and heart of highland aborigines, the minute oxygen consumption of these organs remains the same as that of lowlanders at sea level.
BLOOD CIRCULATION WITH EXCESS OF OXYGEN
Long-term exposure to hyperoxia leads to the development of toxic effects of oxygen and a decrease in the reliability of adaptive reactions of the cardiovascular system. Excess oxygen in tissues also leads to increased lipid peroxidation (LPO) and depletion of endogenous antioxidant reserves (in particular, fat-soluble vitamins) and the antioxidant enzyme system. In this regard, the processes of catabolism and cell deenergization intensify.
Heart rate decreases, arrhythmias may develop.
For short-term hyperoxia (1-3 kg X sec/cm -2) electrocardiographic characteristics do not go beyond the physiological norm, but with many hours of exposure to hyperoxia, the P wave disappears in some subjects, which indicates the appearance of atrioventricular rhythm.
Blood flow in the brain, heart, liver and other organs and tissues is reduced by 12-20%. In the lungs, blood flow can decrease, increase, and return to its original level.
Systemic blood pressure changes slightly. Diastolic pressure usually increases. Cardiac output significantly decreases, and total peripheral resistance increases. The speed of blood flow and bcc when breathing a hyperoxic mixture decreases significantly.
Pressure in the right ventricle of the heart and pulmonary artery during hyperoxia often decreases.
Bradycardia during hyperoxia is caused primarily by increased vagal influences on the heart, as well as the direct effect of oxygen on the myocardium.
The density of functioning capillaries in tissues decreases.
Vasoconstriction during hyperoxia is determined either by the direct effect of oxygen on vascular smooth muscle, or indirectly through a change in the concentration of vasoactive substances.
Thus, if the human body responds to acute and chronic hypoxia with a complex and fairly effective set of adaptive reactions that form long-term adaptation mechanisms, then the body does not have effective means of defense against the effects of acute and chronic hyperoxia.
BLOOD CIRCULATION AT LOW EXTERNAL TEMPERATURES
There are at least four external factors that have a serious impact on human blood circulation in the Far North:
Sharp seasonal, inter- and intra-day changes in atmospheric pressure;
Cold exposure;
A sharp change in photoperiodicity (polar day and polar night);
Fluctuations in the Earth's magnetic field.
The complex of climatic and ecological factors at high latitudes places stringent demands on the cardiovascular system. Adaptation to high latitude conditions is divided into three stages:
Adaptive tension (up to 3-6 months);
Stabilization of functions (up to 3 years);
Adaptability (up to 3-15 years).
Primary northern arterial pulmonary hypertension - the most characteristic adaptive reaction. An increase in blood pressure in the pulmonary circulation occurs at sea level under conditions of normal barometric pressure and O 2 content in the air. The basis of such hypertension is the increased resistance of small arteries and arterioles of the lungs. Northern pulmonary hypertension is widespread among the migrant and indigenous population of the polar regions and occurs in adaptive and maladaptive forms.
The adaptive form is asymptomatic, equalizes ventilation-perfusion relationships and optimizes the oxygen regime of the body. Systolic pressure in the pulmonary artery with hypertension rises to 40 mm Hg, total pulmonary resistance increases slightly.
Maladaptive form. Latent respiratory failure develops - “polar dyspnea”, and performance decreases. Systolic pressure in the pulmonary artery reaches 65 mm Hg, and total pulmonary resistance exceeds 200 dynes Hsek X cm -5 .
In this case, the trunk of the pulmonary artery expands, pronounced hypertrophy of the right ventricle of the heart develops, and at the same time the stroke and minute volumes of the heart decrease.
BLOOD CIRCULATION WHEN EXPOSED TO HIGH TEMPERATURES
Adaptation is distinguished in arid and humid zones.
Arid zones are characterized by high temperatures and low relative humidity. Temperature conditions in these zones during the hot season and during the daytime are such that heat entering the body through insolation and contact with hot air can be 10 times higher than heat generation in the body at rest. Similar heat stress in the absence
effective heat transfer mechanisms quickly leads to overheating of the body.
The thermal states of the body under conditions of high external temperatures are classified as normothermia, compensated hyperthermia and uncompensated hyperthermia.
Hyperthermia- a borderline state of the body, from which a transition to normothermia or death (heat death) is possible. The critical body temperature at which heat death occurs in humans corresponds to +42-43? C.
The effect of high air temperature on a person not adapted to heat causes the following changes.
Dilation of peripheral blood vessels is the main response to heat in arid zones. Vasodilation, in turn, should be accompanied by an increase in BCC; if this does not happen, then a drop in systemic blood pressure occurs.
The circulating blood volume (CBV) increases in the first stages of thermal exposure. With hyperthermia (due to evaporative heat transfer), the blood volume decreases, which entails a decrease in central venous pressure.
Total peripheral vascular resistance. Initially (first phase), even with a slight increase in body temperature, systolic and diastolic blood pressure decreases.
The main reason for the decrease in diastolic pressure is a decrease in total peripheral vascular resistance. During heat stress, when body temperature rises to +38? C, the total peripheral vascular resistance decreases by 40-55%. This is due to dilatation of peripheral vessels, primarily the skin. A further increase in body temperature (second phase), on the contrary, may be accompanied by an increase in total peripheral vascular resistance and diastolic pressure with a pronounced decrease in systolic pressure.
Central venous pressure increases with increasing body temperature, but thermal exposure can also cause the opposite effect - a transient decrease in central blood volume and a persistent decrease in pressure in the right atrium. The variability of central venous pressure is due to differences in the activity of the heart and the blood circulation.
Minute volume of blood circulation (MCV) increases. The stroke volume of the heart remains normal or decreases slightly, which is observed more often. The work of the right and left ventricles of the heart when exposed to high external temperatures (especially with hyperthermia) increases significantly.
High external temperature, which practically excludes all ways of heat transfer in a person, except for the evaporation of sweat, requires a significant increase in skin blood flow. The increase in blood flow in the skin is ensured mainly by an increase in the IOC and, to a lesser extent, by its regional redistribution: under heat load under resting conditions, a person’s blood flow in the celiac region, kidneys and skeletal muscles decreases, which “frees” up to 1 liter of blood/min; the rest of the increased cutaneous blood flow (up to 6-7 liters of blood/min) is provided by cardiac output.
Intense sweating ultimately leads to dehydration of the body, thickening of the blood and a decrease in blood volume. This entails additional stress on the heart.
Adaptation of migrants in arid zones. Newly arrived migrants in the arid zones of Central Asia experience hyperthermia 3-4 times more often when performing heavy physical work than native residents. By the end of the first month of stay in these conditions, the indicators of heat exchange and hemodynamics in migrants improve and approach those of local residents. By the end of the summer season, there is a relative stabilization of the functions of the cardiovascular system. Starting from the second year, the hemodynamic parameters of migrants are almost no different from those of local residents.
Aborigines of arid zones. Aboriginal people of arid zones experience seasonal fluctuations in hemodynamic parameters, but to a lesser extent than migrants. The skin of indigenous people is richly vascularized and has developed venous plexuses, in which blood moves 5-20 times slower than in the main veins.
The mucous membrane of the upper respiratory tract is also richly vascularized.
Human adaptation in the humid zones
Human adaptation in humid zones (tropics), where - in addition to elevated temperatures - the relative humidity of the air is high, proceeds similarly to arid zones. The tropics are characterized by significant tension in water and electrolyte balance. For permanent residents of the humid tropics, the difference between the temperature of the “core” and “shell” of the body, hands and feet is greater than for migrants from Europe, which contributes to better removal of heat from the body. In addition, the natives of the humid tropics have more advanced mechanisms for releasing heat through sweat than visitors. Aboriginal people, in response to temperatures exceeding +27°C, begin to sweat faster and more intensely than migrants from other climatic and geographical regions. For example, among Australian aborigines, the amount of sweat evaporated from the surface of the body is twice that of Europeans under identical conditions.
BLOOD CIRCULATION UNDER CHANGED GRAVITY
The gravitational factor has a constant effect on blood circulation, especially in areas of low pressure, forming the hydrostatic component of blood pressure. Due to the low pressure in the pulmonary circulation, blood flow in the lungs largely depends on hydrostatic pressure, i.e. gravitational effect of blood.
The model of gravitational distribution of pulmonary blood flow is presented in Fig.
6-4. In an upright adult, the apices of the lungs are located approximately 15 cm above the base of the pulmonary artery, so the hydrostatic pressure in the upper parts of the lungs is approximately equal to arterial pressure. In this regard, the capillaries of these sections are perfused slightly or not at all. In the lower parts of the lungs, on the contrary, hydrostatic pressure combines with arterial pressure, which leads to additional stretching of the vessels and their congestion.
These features of pulmonary hemodynamics are accompanied by significant unevenness of blood flow in different parts of the lungs. This unevenness significantly depends on body position and is reflected in regional saturation indicatorsA model that connects the uneven distribution of pulmonary blood flow in a vertical position of the human body with the amount of pressure acting on the capillaries: in zone 1 (apex), the alveolar pressure (P A) exceeds the pressure in the arterioles (P a), and blood flow is limited. In zone 2, where P a > P A , the blood flow is greater than in zone 1. In zone 3, the blood flow is increased and is determined by the difference in pressure in the arterioles (P a) and pressure in the venules (Pu). In the center of the lung diagram are the pulmonary capillaries; vertical tubes on the sides of the lung - pressure gauges
blood oxygen. However, despite these features, in a healthy person, the oxygen saturation of the blood of the pulmonary veins is 96-98%.
With the development of aviation, rocket technology and man's entry into space, changes in systemic hemodynamics under conditions of gravitational overload and weightlessness are becoming of great importance. Changes in hemodynamics are determined by the type of gravitational loads: longitudinal (positive and negative) and transverse.
QUESTIONS FOR SELF-CONTROL
1. What types of work can be distinguished by changes in heart rate?
2. What changes in the myocardium and regional circulation are observed during physical activity?
3. By what mechanisms is blood circulation regulated during physical activity?
4. How does oxygen consumption change during physical activity?
5. What changes occur in the circulatory system during hypokinesia?
6. Name the types of hypoxia depending on the duration of action.
7. What changes in the circulatory system are observed during adaptation to high altitudes?
The most obvious manifestation of circulatory failure is during physical activity. Therefore, let us briefly dwell on the reaction of the circulatory system when performing physical activity. In addition, physical work is one of the most natural adaptive behavioral reactions for the body, which requires good interaction of all parts of the circulatory system. The fact that skeletal muscles make up up to 40% (!) of body weight, and the intensity of their work can fluctuate within very wide limits, puts them in a special position compared to all other organs. In addition, evolution “had to take into account” that in natural conditions a lot depends on the functional capabilities of skeletal muscles, from the search for food to the preservation of life itself. Therefore, the body has formed the closest relationships between muscle contractions and one of the most important systems that “serve” them - the cardiovascular system. These relationships are aimed at creating the best possible conditions for blood supply to the muscles, even at the expense of reducing blood flow in other organs and systems of the body. The importance of muscles for the body and the need to provide blood for their contractions has led to the formation of an additional mechanism for the regulation of hemodynamics from the motor parts of the central nervous system. This creates the opportunity for the formation of conditioned reflexes regulating blood circulation, called pre-start reactions. Their significance lies in the mobilization of the cardiovascular system for upcoming muscular activity. This mobilization is mediated by a sympathetic effect on the heart and blood vessels, due to which, even before the onset of muscle activity, heart contractions become more frequent and blood pressure increases. This should also include a similar reaction to emotions, which in their natural nature, as a rule, are also accompanied by muscle activity.
The sequence of involvement of formations of the cardiovascular system during physical work can be schematically traced when performing intense exercise. Muscle contractions occur under the influence of impulses traveling along the pyramidal tracts, starting in the precentral gyrus. Descending to the muscles, they, along with the motor parts of the central nervous system, excite the respiratory and vasomotor centers of the medulla oblongata and spinal cord. From here, through the sympathetic nervous system, the work of the heart increases, which is necessary to increase the IOC. To supply working muscles, the blood vessels in them sharply dilate. This occurs mainly due to the metabolites that accumulate in them, such as H +, CO 2, K +, adenosine, etc. As a result, a pronounced redistribution reaction of blood flow is observed: the more muscles contract and the higher the intensity of contractions, the more blood ejected by the left ventricle of the heart flows to them. Under these conditions, the previous IOC is no longer sufficient and the work of the heart must increase sharply. When performing intense muscle activity, both SV and heart rate increase. As a result, the IOC can increase 5-6 times (up to 20-30 l/min). Moreover, up to 80-85% of this volume goes to functioning skeletal muscles. As a result, if at rest 900-1200 ml/min passes through the muscles from 5 l/min (15-20% of the IOC), then with a release of 25-30 l/min the muscles can receive up to 20 l/min or more. The redistribution reaction of blood flow involves sympathetic vasoconstrictor influences coming from the same pressor region of the medulla oblongata. At the same time, during muscular work, catecholamines are released from the adrenal glands into the bloodstream, increasing cardiac activity and constricting the blood vessels of non-working muscles and internal organs.
The muscle contraction itself also influences the blood flow (Fig.). With intense contraction, due to compression of blood vessels, the flow of blood into the muscles decreases, but with relaxation, it increases sharply. In contrast, a small contraction force helps to increase their blood supply both during the contraction and relaxation phases. In addition, contracting muscles squeeze blood out of the venous section, which, on the one hand, ensures an increase in venous return to the heart, and on the other, creates the prerequisites for increasing the flow of blood into the muscles during the relaxation phase.
When performing physical activity, the intensification of heart function occurs with a proportional increase in blood flow through the coronary vessels. Autonomic regulation ensures that the same cerebral blood flow is maintained. At the same time, the blood supply to other organs depends on the intensity of the load performed. If muscle work is intense, then despite the increase in IOC, blood flow to many internal organs may decrease. This occurs as a result of a sharp narrowing of the afferent arteries under the influence of sympathetic vasoconstrictor impulses. The developing redistribution reaction can be so pronounced that, for example, in the kidneys, due to decreased blood flow, the process of urine formation almost completely stops.
An increase in IOC leads to a sharp increase in systolic pressure. Diastolic pressure may remain the same or even decrease due to the dilation of muscle vessels. If the decrease in the resistance of the vascular part of the skeletal muscles does not compensate for the narrowing of other vascular zones, then the diastolic pressure also increases.
During physical activity, impulses from muscle proprioceptors and vascular chemoreceptors also contribute to the excitation of vasomotor neurons. Along with this, during muscular work (especially during prolonged work), in addition to the adrenal system of the adrenal glands, other hormonal mechanisms (vasopressin, renin, atrial natriuretic hormone) are included in the regulation of blood flow. Moreover, during the period of muscular work, reflexes that control blood pressure at rest do not appear and, despite the increase in blood pressure, reflexes from baroreceptors do not inhibit the work of the heart.
In addition, in working muscles, an increase in blood pressure with vasodilation leads to a change in the conditions of water exchange. An increase in filtration pressure contributes to the retention of some fluid in the tissues. This is also one of the appropriate reactions of the body, since this increases the oxygen capacity of the blood: due to blood thickening, the concentration of red blood cells increases (sometimes up to 0.5 million/μl).
The above-mentioned features of the hemodynamics of working muscles determine that if the body has a compensated (hidden) form of circulatory failure, then when performing physical activity it manifests itself.
Restoring blood flow when pressure in the vascular bed increases. With short-term deviations in the parameters of systemic blood pressure and blood volume, their stabilization occurs mainly through reflex reactions of blood vessels. An increase in pressure in arterial vessels irritates the baroreceptors of reflexogenic zones, primarily the aorta and carotid sinus. Afferent impulses through the bulbar section of the vasomotor center inhibit its pressor section and excite the depressor section. At the same time, the tonic effect on resistive vessels decreases, and they expand. The dilation of venous vessels leads to an increase in their capacity and a decrease in the volume of blood returning to the heart. At the same time, the strength and frequency of heart contractions decreases. As a result of the complex of these changes, the pressure decreases.
If the irritation of baroreceptors continues for a relatively long time, then the above efferents (heart, blood vessels) are influenced by the BCC. Thus, with the expansion of resistive vessels in the capillaries, the effective filtration pressure increases. And this leads to the fact that the release of fluid from the blood into the tissue begins to greatly prevail over its return to the bloodstream. The simultaneous increase in urine formation and the removal of water from the body further reduces total blood pressure and cardiac output.
Restoration of blood flow when pressure in the vascular bed decreases. When blood pressure falls, the frequency of impulses from baroreceptors decreases, which leads to an effect opposite to that described above. An increase in pressure will occur as a result of a reflex spasm of blood vessels and an increase in heart contractions. At the same time, with spasm of peripheral vessels, the effective filtration pressure decreases and the reabsorption of water from the intercellular fluid increases. The latter will lead to an increase in blood volume, which in turn will contribute to an increase in blood pressure. In addition, just one increase in blood volume, in itself, will ensure an increase in venous return to the heart, an increase in cardiac output and an increase in blood pressure.
If these mechanisms are not enough, then to normalize hemodynamic parameters, a new level of regulatory influences is activated, which is based on hormonal influences. Excitation of the sympathetic nerves leads to increased secretion of catecholamines by the adrenal medulla. In some extreme situations, their level in the blood can increase 10-20 times. These hormones stimulate the heart and constrict the blood vessels of most organs. With the help of these hormones, the effect of the sympathetic nerves on the cardiovascular system is lengthened and enhanced.
Hormones also participate in active changes in the volume of circulating plasma. The main ones are: cardiac natriuretic hormone, vasopressin and the renin-angiotensin-aldosterone system (RAAS). The latter is activated when renal blood flow is disrupted. A decrease in blood supply to the kidneys is observed as a result of a drop in systemic pressure or spasm of the renal vessels. The resulting angiotensin II has a dual effect. On the one hand, it constricts arterial vessels and increases systemic pressure, on the other hand, it stimulates the release of aldosterone in the adrenal glands, which retains Na + and water in the blood through the kidneys. The renin-angiotensin-aldosterone system plays an important role in normalizing blood flow with a pathological decrease in blood pressure and volume. But on the other hand, an increase in the activity of this system with some kidney damage can lead to hypertension.
Restoring blood flow when blood volume changes. The order of connection of regulatory mechanisms similar to that described above is also observed when blood volume changes. They are launched from the venous section of the cardiovascular system - from the capacitive bed. Irritation of receptors located in the vena cava and atria is transmitted to two parts of the central nervous system:
- to the circulatory center of the medulla oblongata,
- to the osmoregulation center of the hypothalamus.
As a result of excitation of the depressor department, on the one hand, the blood vessels dilate, and on the other, cardiac activity is inhibited. Through the hypothalamus, the release of the hormone vasopressin from the pituitary gland is stimulated, which constricts blood vessels and enhances the reabsorption of water in the kidneys, exhibiting its antidiuretic effect.
The amount of vasopressin released is directly dependent on the impulse from the atrial receptors. With prolonged flow of large volumes of blood into the atria through the osmoregulatory center of the hypothalamus, the release of vasopressin is inhibited. This reflex effect appears after 10-20 minutes and can continue, gradually increasing, for several days. As a result, the excretion of water by the kidneys increases. In addition, with prolonged stimulation of baroreceptors, natriuretic hormone is released from the atria. It travels to the kidneys, where it reduces Na + reabsorption. Retention of Na + in the urine promotes the excretion of water and a decrease in blood volume. On the contrary, with a decrease in venous return and a decrease in blood volume, the production of vasopressin increases. Hormonally caused retention of fluid in the body or its excretion makes it easier for other mechanisms to maintain hemodynamics in case of sudden disturbances in the ratio of blood volume and capacitive bed.