A heart. Abnormal contraction of the heart Diastolic phases of the ventricles

It moves non-stop due to the fact that at the ends of the vascular system (arterial and venous) a pressure difference is formed (0 mm Hg in the main veins and 140 mm in the aorta).

The work of the heart consists of cardiac cycles - continuously replacing each other periods of contraction and relaxation, which are called systole and diastole, respectively.

Duration

As the table shows, the cardiac cycle lasts approximately 0.8 seconds, if we assume that the average contraction rate is from 60 to 80 beats per minute. Atrial systole takes 0.1 s, ventricular systole - 0.3 s, total cardiac diastole - the rest of the time, equal to 0.4 s.

Phase structure

The cycle begins with atrial systole, which takes 0.1 seconds. Their diastole lasts 0.7 seconds. The contraction of the ventricles lasts 0.3 seconds, their relaxation - 0.5 seconds. The general relaxation of the chambers of the heart is called a general pause, and in this case it takes 0.4 seconds. Thus, there are three phases of the cardiac cycle:

atrial systole - 0.1 sec.;
ventricular systole - 0.3 sec.;
diastole of the heart (general pause) - 0.4 sec.

The general pause preceding the beginning of a new cycle is very important for filling the heart with blood.

Before the onset of systole, the myocardium is in a relaxed state, and the chambers of the heart are filled with blood that comes from the veins.

The pressure in all chambers is approximately the same, since the atrioventricular valves are open. Excitation occurs in the sinoatrial node, which leads to atrial contraction, due to the pressure difference at the time of systole, the volume of the ventricles increases by 15%. When the atrial systole ends, the pressure in them decreases.

Systole (contraction) of the atria

Before the onset of systole, blood moves to the atria and they are sequentially filled with it. Part of it remains in these chambers, the rest is sent to the ventricles and enters them through the atrioventricular openings, which are not closed by valves.

At this point, atrial systole begins. The walls of the chambers tense up, their tone grows, the pressure in them rises by 5-8 mm Hg. pillar. The lumen of the veins that carry blood is blocked by annular myocardial bundles. The walls of the ventricles at this time are relaxed, their cavities are expanded, and blood from the atria quickly rushes there without difficulty through the atrioventricular openings. The duration of the phase is 0.1 seconds. The systole is superimposed on the end of the ventricular diastole phase. The muscle layer of the atria is quite thin, because they do not need much force to fill the adjacent chambers with blood.

Systole (contraction) of the ventricles

This is the next, second phase of the cardiac cycle and it begins with the tension of the muscles of the heart. The voltage phase lasts 0.08 seconds and, in turn, is divided into two more phases:

Asynchronous voltage - duration 0.05 sec. The excitation of the walls of the ventricles begins, their tone increases.
Isometric contraction - duration 0.03 sec. The pressure in the chambers increases and reaches significant values.

The free leaflets of the atrioventricular valves floating in the ventricles begin to be pushed into the atria, but they cannot get there because of the tension of the papillary muscles, which stretch the tendon filaments that hold the valves and prevent them from entering the atria. At the moment when the valves close and the communication between the heart chambers stops, the tension phase ends.

As soon as the voltage becomes maximum, the period of ventricular contraction begins, lasting 0.25 seconds. The systole of these chambers occurs just at this time. About 0.13 sec. the phase of rapid expulsion lasts - the ejection of blood into the lumen of the aorta and pulmonary trunk, during which the valves are adjacent to the walls. This is possible due to the increase in pressure (up to 200 mmHg in the left and up to 60 in the right). The rest of the time falls on the phase of slow expulsion: blood is ejected under less pressure and at a lower speed, the atria are relaxed, blood begins to flow into them from the veins. Ventricular systole superimposed on atrial diastole.

General pause time

The diastole of the ventricles begins, and their walls begin to relax. This lasts for 0.45 seconds. The period of relaxation of these chambers is superimposed on the still ongoing atrial diastole, so these phases are combined and called a common pause. What is happening at this time? The ventricle, having contracted, expelled blood from its cavity and relaxed. It formed a rarefied space with a pressure close to zero. Blood tends to get back, but the semilunar valves of the pulmonary artery and aorta, closing, do not allow it to do so. Then she goes through the vessels. The phase that begins with the relaxation of the ventricles and ends with the occlusion of the lumen of the vessels by the semilunar valves is called protodiastolic and lasts 0.04 seconds.

After that, the phase of isometric relaxation begins with a duration of 0.08 seconds. The leaflets of the tricuspid and mitral valves are closed and do not allow blood to flow into the ventricles. But when the pressure in them becomes lower than in the atria, the atrioventricular valves open. During this time, the blood fills the atria and now freely enters the other chambers. This is a fast filling phase with a duration of 0.08 seconds. Within 0.17 sec. the slow filling phase continues, during which blood continues to flow into the atria, and a small part of it flows through the atrioventricular openings into the ventricles. During the diastole of the latter, they receive blood from the atria during their systole. This is the presystolic phase of diastole, which lasts 0.1 sec. Thus the cycle ends and begins again.

Heart sounds

The heart makes characteristic sounds, similar to a knock. Each beat consists of two basic tones. The first is the result of contraction of the ventricles, or to be more precise, the slamming of the valves, which, when the myocardium is strained, block the atrioventricular openings so that the blood cannot return to the atria. A characteristic sound is obtained when their free edges are closed. In addition to valves, the myocardium, the walls of the pulmonary trunk and aorta, and tendon filaments take part in creating a blow.

The second tone is formed during ventricular diastole. This is the result of the work of the semilunar valves, which do not allow blood to get back, blocking its path. A knock is heard when they are connected in the lumen of the vessels with their edges.

In addition to the main tones, there are two more - the third and fourth. The first two can be heard with a phonendoscope, and the other two can only be registered by a special device.

Conclusion

Summing up the phase analysis of cardiac activity, we can say that systolic work takes about the same time (0.43 s) as diastolic work (0.47 s), that is, the heart works half of its life, rests half, and the total cycle time is 0.9 seconds.

When calculating the total timing of the cycle, you need to remember that its phases overlap each other, so this time is not taken into account, and as a result it turns out that the cardiac cycle lasts not 0.9 seconds, but 0.8.

Heart - how does it work?

Some facts about the work of the heart

How does this ideal engine work?

chambers of the heart

These parts of the heart are separated by partitions, between the chambers the blood circulates through the valvular apparatus.

The walls of the atria are quite thin - this is due to the fact that when the muscle tissue of the atria contracts, they have to overcome much less resistance than the ventricles.

The walls of the ventricles are many times thicker - this is due to the fact that it is thanks to the efforts of the muscle tissue of this part of the heart that the pressure in the pulmonary and systemic circulation reaches high values and ensures continuous blood flow.

valve apparatus

2 atrioventricular valves ( as the name suggests, these valves separate the atria from the ventricles)
one pulmonary valve through which blood moves from the heart to the circulatory system of the lung)
one aortic valve this valve separates the aortic cavity from the left ventricular cavity).

The valvular apparatus of the heart is not universal - valves have a different structure, size and purpose.

More about each of them:

Layers of the heart wall

1. The outer mucosal layer is the pericardium. This layer allows the heart to glide while working inside the heart sac. It is thanks to this layer that the heart does not disturb the surrounding organs with its movements.

Some information about the hydrodynamics of the heart

Phases of the contraction of the heart

How is the heart supplied with blood?

What controls the work of the heart?

Further, the excitation covers the muscular tissue of the ventricles - there is a synchronous contraction of the walls of the ventricles. The pressure inside the chambers builds up, causing the atrioventricular valves to close and simultaneously open the aortic and pulmonic valves. In this case, the blood continues its unidirectional movement towards the lung tissue and other organs.

Big Encyclopedia of Oil and Gas

Contraction - atrium

Atrial contraction begins in the region of the mouths of the vena cava, as a result of which the mouths are compressed. Therefore, blood can only move in one direction into the ventricles through the atrioventricular openings. Valves are located in these holes. At the time of diastole and the subsequent systole of the atria, the valve flaps diverge, the valves open and let blood flow from the atria into the ventricles. The left ventricle has a bicuspid mitral valve, while the right ventricle has a tricuspid valve. When the ventricles contract, blood rushes towards the atria and slams the valve flaps. The opening of the valves towards the atria is prevented by tendon threads, with the help of which the edges of the valves are attached to the papillary muscles. The latter are finger-like outgrowths of the inner muscular layer of the ventricular wall. Being part of the myocardium of the ventricles, the papillary muscles contract with them, pulling on the tendon threads, which, like the shrouds of the sails, hold the valve flaps.

When the atria contract, blood is pushed into the ventricles; at the same time, the annular muscles located at the confluence of the hollow and pulmonary veins into the atria contract, as a result of which the blood cannot flow back into the veins. They are also known as atrioventricular (atrioventricular) valves.

The atrial-ventricular valves open when the atria contract, and when the ventricles contract, the valves close tightly, preventing blood from returning back to the atria. At the same time, the papillary muscles contract, stretching the tendon chords, and preventing the valve leaflets from turning towards the atria. At the base of the aorta and pulmonary artery are the semilunar valves, which look like pockets (Fig. 14.14, B) and do not allow blood from these vessels to pass back to the heart.

FKG; 1 - phase of atrial contractions; 2 - phase of asynchronous contraction of the ventricles; 3 - phase of isometric contraction of the ventricles; 4 - phase of exile; 5 - protodiastolic period; 6 - phase of isometric relaxation of the ventricles; 7-phase of rapid filling of the ventricles; 8 - phase of slow filling of the ventricles.

Vibration of the walls of the heart, caused by atrial contraction and additional blood flow into the ventricles, leads to the appearance of a IV heart sound. With normal listening to the heart, I and II tones are clearly audible, they are loud, and III and IV tones are quiet, they are detected only with a graphic recording of heart sounds.

The normal electrocardiogram (ECG) is shown in fig. 1.4. P - a wave corresponds to atrial contraction caused by an electrical impulse that occurs in the sino-atrial node and reaches the atria through the conduction system of the heart; P - - the interval corresponds to the excitation of the atrioventricular node, and Q S-complex - to the contraction of the ventricles; G - tooth corresponds to the recovery phase of the ventricles. If excitation primarily occurs in the sinoatrial node, then such a rhythm is called sinus. Pathological rhythms, the detection of which is very important for the diagnosis of the disease and its treatment, are called arrhythmias; pathologically slow rhythm - sinus bradycardia, pathologically accelerated rhythm - tachycardia.

The circulation of excitation with a high degree of probability is the cause of such important cardiac arrhythmias as flutter ii fibrillation. Atrial flutter is an autonomous atrial contraction, independent of the action of the pacemaker, caused by the circulation of an excitation wave around some non-excitable obstacle, usually around the superior or inferior vena cava.

On the cardiogram, separate sections are distinguished corresponding to various phases of the work of the heart. So, the P wave occurs when the atria contract (which ensures the filling of the relaxed ventricles with blood), the QRS peak - when the heart ventricles contract, due to which the blood is pushed into the aorta, the T wave - the period when the contraction of the ventricles ends and they go into a relaxed state.

Particularly in its action, the drug stands out - (3-gshperidinopropin - 1 -yl) benzene, which, in addition to a pronounced general inhibitory effect on the heart, causes dissociation of the rhythm of the ventricle and atrium. This dissociation is characterized by the occurrence of only one ventricular contraction for every two atrial contractions. A saturated analogue does not cause such changes.

Undoubtedly, the atrial inflow phase is also active. In this phase, the atria are filled under the action of reverse deformation of elastic structures that have accumulated energy during atrial contraction. Previously, this phase of blood flow was not actually taken into account.

Human physiology: periods and phases of the cardiac cycle

The cardiac cycle is the time during which there is one systole and one diastole of the atria and ventricles. The sequence and duration of the cardiac cycle are important indicators of the normal functioning of the conduction system of the heart and its muscular apparatus. Determining the sequence of phases of the cardiac cycle is possible with simultaneous graphic recording of changing pressure in the cavities of the heart, the initial segments of the aorta and pulmonary trunk, heart sounds - phonocardiograms.

The cardiac cycle includes one systole (contraction) and diastole (relaxation) of the chambers of the heart. Systole and diastole, in turn, are divided into periods, including phases. This division reflects the successive changes that occur in the heart.

According to the norms accepted in physiology, the average duration of one cardiac cycle at a heart rate of 75 beats per minute is 0.8 seconds. The cardiac cycle begins with the contraction of the atria. The pressure in their cavities at this moment is 5 mm Hg. Systole continues for 0.1 s.

The atria begin to contract at the mouths of the vena cava, causing them to contract. For this reason, blood during atrial systole can only move in the direction from the atria to the ventricles.

This is followed by contraction of the ventricles, which takes 0.33 s. It includes periods:

Diastole consists of periods:

isometric relaxation (0.08 s);
filling with blood (0.25 s);
presystolic (0.1 s).

The period of tension, lasting 0.08 s, is divided into 2 phases: asynchronous (0.05 s) and isometric contraction (0.03 s).

In the phase of asynchronous contraction, myocardial fibers are sequentially involved in the process of excitation and contraction. In the isometric contraction phase, all myocardial fibers are tense, as a result, the pressure in the ventricles exceeds the pressure in the atria and the atrioventricular valves close, which corresponds to the 1st heart sound. The tension of the myocardial fibers increases, the pressure in the ventricles rises sharply (up to 80 mm Hg in the left, up to 20 mm Hg in the right) and significantly exceeds the pressure in the initial segments of the aorta and pulmonary trunk. The cusps of their valves open, and blood from the cavity of the ventricles is quickly pumped into these vessels.

This is followed by an exile period lasting 0.25 s. It includes fast (0.12 s) and slow (0.13 s) ejection phases. The pressure in the cavities of the ventricles during this period reaches its maximum values (120 mm Hg in the left ventricle, 25 mm Hg in the right). At the end of the ejection phase, the ventricles begin to relax, their diastole begins (0.47 s). Intraventricular pressure decreases and becomes much lower than the pressure in the initial segments of the aorta and pulmonary trunk, as a result of which blood from these vessels rushes back into the ventricles along the pressure gradient. The semilunar valves close and a second heart sound is recorded. The period from the beginning of relaxation to the slamming of the valves is called proto-diastolic (0.04 seconds).

During isometric relaxation, the valves of the heart are in a closed state, the amount of blood in the ventricles is unchanged, therefore, the length of the cardiomyocytes remains the same. This is where the name of the period comes from. At the end, the pressure in the ventricles becomes lower than the pressure in the atria. This is followed by a period of filling of the ventricles. It is divided into a phase of fast (0.08 s) and slow (0.17 s) filling. With a rapid blood flow due to concussion of the myocardium of both ventricles, a III heart sound is recorded.

At the end of the filling period, atrial systole occurs. Regarding the ventricular cycle, it is the presystolic period. During the contraction of the atria, an additional volume of blood enters the ventricles, causing oscillations of the walls of the ventricles. Recorded IV heart sound.

In a healthy person, only I and II heart sounds are normally heard. In thin people, in children, it is sometimes possible to determine the III tone. In other cases, the presence of III and IV tones indicates a violation of the ability of cardiomyocytes to contract, which occurs for various reasons (myocarditis, cardiomyopathy, myocardial dystrophy, heart failure).

Contraction of the atria and ventricles of the heart

The heart acts as a pump. Atria - containers that receive blood, which continuously flows to the heart; they contain important reflexogenic zones, where volumoreceptors are located (to assess the volume of incoming blood), osmoreceptors (to assess the osmotic pressure of blood), etc.; in addition, they perform an endocrine function (secretion of atrial natriuretic hormone and other atrial peptides into the blood); pumping function is also characteristic.

The ventricles perform mainly a pumping function.

Valves of the heart and large vessels: atrioventricular flap valves (left and right) between the atria and ventricles; semilunar valves of the aorta and pulmonary artery.

The valves prevent backflow of blood. For the same purpose, there are muscular sphincters at the confluence of the hollow and pulmonary veins into the atria.

CARDIAC CYCLE.

Electrical, mechanical, biochemical processes that occur during one complete contraction (systole) and relaxation (diastole) of the heart are called the cycle of cardiac activity. The cycle consists of 3 main phases:

(1) atrial systole (0.1 sec),

(2) ventricular systole (0.3 sec),

(3) total pause or total diastole of the heart (0.4 sec).

General diastole of the heart: the atria are relaxed, the ventricles are relaxed. Pressure = 0. Valves: atrioventricular valves open, semilunar valves closed. There is a filling of the ventricles with blood, the volume of blood in the ventricles increases by 70%.

Atrial systole: blood pressure 5-7 mm Hg. Valves: atrioventricular valves open, semilunar valves closed. There is an additional filling of the ventricles with blood, the volume of blood in the ventricles increases by 30%.

Ventricular systole consists of 2 periods: (1) the tension period and (2) the ejection period.

Ventricular systole:

Direct ventricular systole

1) voltage period

asynchronous reduction phase
isometric contraction phase

2) period of exile

rapid ejection phase
slow ejection phase

Phase of asynchronous contraction: excitation spreads through the ventricular myocardium. Individual muscle fibers begin to contract. The pressure in the ventricles is about 0.

Isometric contraction phase: all ventricular myocardial fibers contract. The pressure in the ventricles increases. The atrioventricular valves close (because the pressure in the ventricles becomes greater than in the precardia). The semilunar valves are still closed (because the pressure in the ventricles is still less than in the aorta and pulmonary artery). The volume of blood in the ventricles does not change (at this time there is neither inflow of blood from the atria, nor outflow of blood into the vessels). Isometric mode of contraction (the length of the muscle fibers does not change, the tension increases).

Exile period: all fibers of the ventricular myocardium continue to contract. The blood pressure in the ventricles becomes greater than the diastolic pressure in the aorta (70 mm Hg) and pulmonary artery (15 mm Hg). The semilunar valves open. Blood flows from the left ventricle to the aorta, from the right ventricle to the pulmonary artery. Isotonic mode of contraction (muscle fibers shorten, their tension does not change). The pressure rises to 120 mm Hg in the aorta and to 30 mm Hg in the pulmonary artery.

DIASTOLIC PHASES OF THE VENTRICULAR.

ventricular diastole

isometric relaxation phase
rapid passive filling phase
slow passive filling phase
rapid active filling phase (due to atrial systole)

Electrical activity in different phases of the cardiac cycle.

Left atrium: P wave => atrial systole (wave a) => additional filling of the ventricles (plays an essential role only with increased physical activity) => atrial diastole => venous blood flow from the lungs to the left. atrium => atrial pressure (wave v) => wave c (P due to the closing of the miter valve - towards the atrium).

Left ventricle: QRS => gastric systole => biliary pressure > atrial P => mitral valve closure. Aortic valve still closed => isovolumetric contraction => gastric P > aortic P (80 mm Hg) => aortic valve opening => blood ejection, decreased V ventricle => inertial blood flow through the valve =>↓ P in the aorta

Ventricular diastole. R in the stomach.<Р в предсерд. =>opening of the miter valve => passive filling of the ventricles even before atrial systole.

EDV = 135 ml (when the aortic valve opens)

CSR = 65 ml (when the mitral valve opens)

The work of the heart consists of three phases: atrial contraction, ventricular contraction, pause. Answer the questions:

In what phases does the heart fill with blood?

In what phase is blood ejected from the ventricles into the arteries?

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Answers and explanations

phenatine
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The heart fills with blood during diastole (the state of the heart muscle during heartbeat, namely, relaxed in the interval between contractions). The phase is called systole, blood from the left ventricle of the heart is ejected into a large circle, into the aorta.

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hayato15goku
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The work of the heart consists of three phases: atrial contraction, ventricular contraction, pause.

1) During the contraction of the ventricles, the atria open and begin to fill with blood.

2) When the atria contract, blood enters the ventricles. And in diastole, the heart relaxes. Systole - blood from the left ventricle of the heart is ejected into a large circle, into the aorta.

Cardiac cycle. Atrial systole and diastole

Cardiac cycle and its analysis

The cardiac cycle is the systole and diastole of the heart, periodically repeating in strict sequence, i.e. a period of time including one contraction and one relaxation of the atria and ventricles.

In the cyclic functioning of the heart, two phases are distinguished: systole (contraction) and diastole (relaxation). During systole, the cavities of the heart are freed from blood, and during diastole they are filled with blood. The period, including one systole and one diastole of the atria and ventricles, followed by a general pause, is called the cycle of cardiac activity.

Atrial systole in animals lasts 0.1-0.16 s, and ventricular systole lasts 0.5-0.56 s. The general pause of the heart (simultaneous atrial and ventricular diastole) lasts 0.4 s. During this period, the heart rests. The entire cardiac cycle lasts for 0.8-0.86 s.

The work of the atria is less complex than that of the ventricles. Atrial systole provides blood flow to the ventricles and lasts 0.1 s. Then the atria enter the diastole phase, which lasts for 0.7 s. During diastole, the atria fill with blood.

The duration of the various phases of the cardiac cycle depends on the heart rate. With more frequent heart contractions, the duration of each phase, especially diastole, decreases.

Phases of the cardiac cycle

Under the cardiac cycle is understood a period covering one contraction - systole and one relaxation - diastole of the atria and ventricles - a total pause. The total duration of the cardiac cycle at a heart rate of 75 beats/min is 0.8 s.

The contraction of the heart begins with atrial systole, lasting 0.1 s. At the same time, the pressure in the atria rises to 5-8 mm Hg. Art. Atrial systole is replaced by ventricular systole lasting 0.33 s. Ventricular systole is divided into several periods and phases (Fig. 1).

Rice. 1. Phases of the cardiac cycle

The voltage period lasts 0.08 s and consists of two phases:

phase of asynchronous contraction of the myocardium of the ventricles - lasts 0.05 s. During this phase, the excitation process and the contraction process following it spread throughout the ventricular myocardium. The pressure in the ventricles is still close to zero. By the end of the phase, the contraction covers all myocardial fibers, and the pressure in the ventricles begins to increase rapidly.
phase of isometric contraction (0.03 s) - begins with the slamming of the cusps of the atrioventricular valves. When this occurs, I, or systolic, heart sound. The displacement of the valves and blood towards the atria causes a rise in pressure in the atria. The pressure in the ventricles is rapidly increasing: domm Hg. Art. in the left and domm rt. Art. in the right.

The cuspid and semilunar valves are still closed, the volume of blood in the ventricles remains constant. Due to the fact that the liquid is practically incompressible, the length of the myocardial fibers does not change, only their tension increases. The blood pressure in the ventricles rises rapidly. The left ventricle quickly acquires a round shape and hits the inner surface of the chest wall with force. In the fifth intercostal space, 1 cm to the left of the midclavicular line at this moment, the apex beat is determined.

By the end of the tension period, the rapidly increasing pressure in the left and right ventricles becomes higher than the pressure in the aorta and pulmonary artery. Blood from the ventricles rushes into these vessels.

The period of blood ejection from the ventricles lasts 0.25 s and consists of a fast ejection phase (0.12 s) and a slow ejection phase (0.13 s). At the same time, the pressure in the ventricles increases: in the left domm Hg. Art., and in the right up to 25 mm Hg. Art. At the end of the slow ejection phase, the ventricular myocardium begins to relax, and its diastole begins (0.47 s). The pressure in the ventricles drops, blood from the aorta and pulmonary artery rushes back into the cavities of the ventricles and “slams” the semilunar valves, and a II, or diastolic, heart sound occurs.

The time from the onset of relaxation of the ventricles to the “slamming” of the semilunar valves is called the protodiastolic period (0.04 s). As the semilunar valves close, the pressure in the ventricles drops. The flap valves are still closed at this time, the volume of blood remaining in the ventricles, and, consequently, the length of the myocardial fibers do not change, therefore this period is called the period of isometric relaxation (0.08 s). Toward the end of its pressure in the ventricles becomes lower than in the atria, the atrioventricular valves open and blood from the atria enters the ventricles. The period of filling the ventricles with blood begins, which lasts 0.25 s and is divided into phases of fast (0.08 s) and slow (0.17 s) filling.

The fluctuation of the walls of the ventricles due to the rapid flow of blood to them cause the appearance of a III heart sound. By the end of the slow filling phase, atrial systole occurs. The atria pump an additional amount of blood into the ventricles (presystolic period equal to 0.1 s), after which a new cycle of ventricular activity begins.

Vibration of the walls of the heart, caused by atrial contraction and additional blood flow into the ventricles, leads to the appearance of a IV heart sound.

With normal listening to the heart, loud I and II tones are clearly audible, and quiet III and IV tones are detected only with graphic recording of heart sounds.

In humans, the number of heartbeats per minute can vary significantly and depends on various external influences. When performing physical work or sports activity, the heart can contract up to 200 times per minute. In this case, the duration of one cardiac cycle will be 0.3 s. An increase in the number of heartbeats is called tachycardia, while the cardiac cycle decreases. During sleep, the number of heartbeats decreases by up to beats per minute. In this case, the duration of one cycle is 1.5 s. A decrease in the number of heartbeats is called bradycardia, while the cardiac cycle increases.

Structure of the cardiac cycle

Cardiac cycles follow at a rate set by the pacemaker. The duration of a single cardiac cycle depends on the heart rate and, for example, at a frequency of 75 beats / min, it is 0.8 s. The general structure of the cardiac cycle can be represented as a diagram (Fig. 2).

As can be seen from fig. 1, with a cardiac cycle duration of 0.8 s (frequency of contractions 75 beats/min), the atria are in a systole state of 0.1 s and in a diastole state of 0.7 s.

Systole is a phase of the cardiac cycle, including contraction of the myocardium and expulsion of blood from the heart into the vascular system.

Diastole is the phase of the cardiac cycle, including the relaxation of the myocardium and the filling of the cavities of the heart with blood.

Rice. 2. Scheme of the general structure of the cardiac cycle. Dark squares show atrial and ventricular systole, light squares show their diastole.

The ventricles are in systole for about 0.3 s and in diastole for about 0.5 s. At the same time, the atria and ventricles are in diastole for about 0.4 s (total diastole of the heart). Systole and diastole of the ventricles are divided into periods and phases of the cardiac cycle (Table 1).

Table 1. Periods and phases of the cardiac cycle

Ventricular systole 0.33 s

Voltage period - 0.08 s

Asynchronous contraction phase - 0.05 s

Isometric contraction phase - 0.03 s

Ejection period 0.25 s

Rapid ejection phase - 0.12 s

Slow ejection phase - 0.13 s

Ventricular diastole 0.47 s

Relaxation period - 0.12 s

Protodiastolic interval - 0.04 s

Isometric relaxation phase - 0.08 s

Filling period - 0.25 s

Rapid filling phase - 0.08 s

Slow filling phase - 0.17 s

The phase of asynchronous contraction is the initial stage of systole, in which the excitation wave propagates through the ventricular myocardium, but there is no simultaneous contraction of cardiomyocytes and the pressure in the ventricles is from 6-8 domm Hg. Art.

The isometric contraction phase is the stage of systole, during which the atrioventricular valves close and the pressure in the ventricles rapidly rises to DHM. Art. in the right and domm rt. Art. in the left.

The rapid ejection phase is the stage of systole, in which there is an increase in pressure in the ventricles to maximum values of -mm Hg. Art. in the right imm rt. Art. in the left and blood (about 70% of systolic ejection) enters the vascular system.

The slow ejection phase is the stage of systole in which blood (the remaining 30% of systolic ejection) continues to flow into the vascular system at a slower rate. The pressure gradually decreases in the left ventricle sodomy RT. Art., in the right - sdomm rt. Art.

The proto-diastolic period is the transitional period from systole to diastole during which the ventricles begin to relax. The pressure decreases in the left ventricle domm rt. Art., in disposition - up to 5-10 mm Hg. Art. Due to the greater pressure in the aorta and pulmonary artery, the semilunar valves close.

The period of isometric relaxation is the stage of diastole, in which the cavities of the ventricles are isolated by closed atrioventricular and semilunar valves, they relax isometrically, the pressure approaches 0 mm Hg. Art.

The rapid filling phase is the stage of diastole, during which the atrioventricular valves open and blood rushes into the ventricles at high speed.

The slow filling phase is the stage of diastole, in which blood slowly enters the atria through the vena cava and through the open atrioventricular valves into the ventricles. At the end of this phase, the ventricles are 75% filled with blood.

Presystolic period - the stage of diastole, coinciding with atrial systole.

Atrial systole - contraction of the muscles of the atria, in which the pressure in the right atrium rises to 3-8 mm Hg. Art., in the left - up to 8-15 mm Hg. Art. and each of the ventricles receives about 25% of the diastolic blood volume (pml).

Table 2. Characteristics of the phases of the cardiac cycle

The contraction of the myocardium of the atria and ventricles begins after their excitation, and since the pacemaker is located in the right atrium, its action potential initially extends to the myocardium of the right and then the left atria. Consequently, the right atrial myocardium responds with excitation and contraction somewhat earlier than the left atrial myocardium. Under normal conditions, the cardiac cycle begins with atrial systole, which lasts 0.1 s. The non-simultaneity of excitation coverage of the myocardium of the right and left atria is reflected by the formation of the P wave on the ECG (Fig. 3).

Even before atrial systole, the AV valves are open and the atrial and ventricular cavities are already largely filled with blood. The degree of stretching of the thin walls of the atrial myocardium by blood is important for the stimulation of mechanoreceptors and the production of atrial natriuretic peptide.

Rice. 3. Changes in the performance of the heart in different periods and phases of the cardiac cycle

During atrial systole, the pressure in the left atrium can reach mm Hg. Art., and in the right - up to 4-8 mm Hg. Art., the atria additionally fill the ventricles with a volume of blood, which at rest is about 5-15% of the volume that is by this time in the ventricles. The volume of blood entering the ventricles during atrial systole may increase during exercise and amount to 25-40%. The volume of additional filling can increase to 40% or more in people over 50 years of age.

The flow of blood under pressure from the atria contributes to the stretching of the ventricular myocardium and creates conditions for their more effective subsequent contraction. Therefore, the atria play the role of a kind of amplifier of the contractile capabilities of the ventricles. If this atrial function is impaired (for example, with atrial fibrillation), the efficiency of the ventricles decreases, a decrease in their functional reserves develops, and the transition to insufficiency of myocardial contractile function accelerates.

At the time of atrial systole, an a-wave is recorded on the venous pulse curve; in some people, when recording a phonocardiogram, the 4th heart sound may be recorded.

The volume of blood that is in the ventricular cavity after atrial systole (at the end of their diastole) is called end-diastolic. It consists of the volume of blood remaining in the ventricle after the previous systole (end-systolic volume), the volume of blood that filled the ventricular cavity during its diastole to atrial systole, and the additional volume of blood entering the ventricle during atrial systole. The value of the end-diastolic blood volume depends on the size of the heart, the volume of blood flowing from the veins and a number of other factors. In a healthy young person at rest, it can be about a ml (depending on age, sex and body weight, it can range from 90 to 150 ml). This volume of blood slightly increases the pressure in the ventricular cavity, which during atrial systole becomes equal to the pressure in them and can fluctuate in the left ventricle within mm Hg. Art., and in the right - 4-8 mm Hg. Art.

For a time interval of 0.12-0.2 s, corresponding to the PQ interval on the ECG, the action potential from the SA node propagates to the apical region of the ventricles, in the myocardium of which the excitation process begins, rapidly spreading in directions from the apex to the base of the heart and from the endocardial surface to the epicardial. Following excitation, contraction of the myocardium or ventricular systole begins, the duration of which also depends on the frequency of heart contractions. At rest, it is about 0.3 s. Ventricular systole consists of periods of tension (0.08 s) and expulsion (0.25 s) of blood.

Systole and diastole of both ventricles occur almost simultaneously, but proceed under different hemodynamic conditions. A further, more detailed description of the events occurring during systole will be considered using the example of the left ventricle. For comparison, some data for the right ventricle are given.

The period of ventricular tension is divided into phases of asynchronous (0.05 s) and isometric (0.03 s) contraction. The short-term phase of asynchronous contraction at the beginning of the systole of the ventricular myocardium is a consequence of the non-simultaneous coverage of excitation and contraction of various parts of the myocardium. Excitation (corresponds to the Q wave on the ECG) and contraction of the myocardium occurs initially in the papillary muscles, the apical part of the interventricular septum and the apex of the ventricles and spreads to the remaining myocardium in about 0.03 s. This coincides in time with the registration of the Q wave on the ECG and the ascending part of the R wave to its top (see Fig. 3).

The apex of the heart contracts before the base, so the apex of the ventricles pulls up toward the base and pushes blood in that direction. The areas of the ventricular myocardium not covered by excitation at this time can slightly stretch, so the volume of the heart remains practically unchanged, the blood pressure in the ventricles still does not change significantly and remains lower than the blood pressure in large vessels above the tricuspid valves. The blood pressure in the aorta and other arterial vessels continues to fall, approaching the value of the minimum, diastolic, pressure. However, the tricuspid vascular valves are still closed.

The atria at this time relax and the blood pressure in them decreases: for the left atrium, on average, from 10 mm Hg. Art. (presystolic) up to 4 mm Hg. Art. By the end of the phase of asynchronous contraction of the left ventricle, the blood pressure in it rises to 9-10 mm Hg. Art. The blood, under pressure from the contracting apical part of the myocardium, picks up the cusps of the AV valves, they close, taking a position close to horizontal. In this position, the valves are held by the tendon filaments of the papillary muscles. The shortening of the size of the heart from its apex to the base, which, due to the invariability of the size of the tendon filaments, could lead to eversion of the valve leaflets into the atria, is compensated by contraction of the papillary muscles of the heart.

At the moment of closing the atrioventricular valves, the 1st systolic heart sound is heard, the asynchronous phase ends and the isometric contraction phase begins, which is also called the isovolumetric (isovolumic) contraction phase. The duration of this phase is about 0.03 s, its implementation coincides with the time interval in which the descending part of the R wave and the beginning of the S wave on the ECG are recorded (see Fig. 3).

From the moment the AV valves close under normal conditions, the cavity of both ventricles becomes airtight. Blood, like any other liquid, is incompressible, so the contraction of myocardial fibers occurs at their constant length or in isometric mode. The volume of the cavities of the ventricles remains constant and myocardial contraction occurs in isovolumic mode. An increase in tension and force of myocardial contraction under such conditions is converted into a rapidly increasing blood pressure in the cavities of the ventricles. Under the influence of blood pressure on the region of the AV septum, a short-term shift occurs towards the atria, is transmitted to the inflowing venous blood and is reflected by the appearance of a c-wave on the venous pulse curve. Within a short period of time - about 0.04 s, the blood pressure in the cavity of the left ventricle reaches a value comparable to its value at that moment in the aorta, which decreased to a minimum level of -mm Hg. Art. The blood pressure in the right ventricle reaches mm Hg. Art.

The excess of blood pressure in the left ventricle over the value of diastolic blood pressure in the aorta is accompanied by the opening of the aortic valves and a change in the period of myocardial tension by a period of blood expulsion. The reason for the opening of the semilunar valves of the vessels is the blood pressure gradient and the pocket-like feature of their structure. The cusps of the valves are pressed against the walls of the vessels by the flow of blood expelled into them by the ventricles.

The period of expulsion of blood lasts about 0.25 s and is divided into phases of fast expulsion (0.12 s) and slow expulsion of blood (0.13 s). During this period, the AV valves remain closed, the semilunar valves remain open. The rapid expulsion of blood at the beginning of the period is due to a number of reasons. About 0.1 s has passed since the start of excitation of cardiomyocytes and the action potential is in the plateau phase. Calcium continues to flow into the cell through open slow calcium channels. Thus, the tension of the myocardial fibers, which was already high at the beginning of the expulsion, continues to increase. The myocardium continues to compress the decreasing volume of blood with greater force, which is accompanied by a further increase in pressure in the ventricular cavity. The blood pressure gradient between the ventricular cavity and the aorta increases and blood begins to be expelled into the aorta at high speed. In the phase of rapid expulsion, more than half of the stroke volume of blood expelled from the ventricle during the entire period of exile (about 70 ml) is ejected into the aorta. By the end of the phase of rapid expulsion of blood, the pressure in the left ventricle and in the aorta reaches its maximum - about 120 mm Hg. Art. in young people at rest, and in the pulmonary trunk and right ventricle - about 30 mm Hg. Art. This pressure is called systolic. The phase of rapid expulsion of blood occurs during the time interval when the end of the S wave and the isoelectric part of the ST interval before the beginning of the T wave are recorded on the ECG (see Fig. 3).

Under the condition of rapid expulsion of even 50% of stroke volume, the rate of blood inflow into the aorta in a short time will be about 300 ml / s (35 ml / 0.12 s). The average rate of outflow of blood from the arterial part of the vascular system is about 90 ml/s (70 ml/0.8 s). Thus, more than 35 ml of blood enters the aorta in 0.12 s, and about 11 ml of blood flows out of it into the arteries during the same time. Obviously, in order to accommodate for a short time the inflowing larger volume of blood compared to the outflowing one, it is necessary to increase the capacity of the vessels that receive this "excessive" volume of blood. Part of the kinetic energy of the contracting myocardium will be spent not only on expelling blood, but also on stretching the elastic fibers of the aortic wall and large arteries to increase their capacity.

At the beginning of the phase of rapid expulsion of blood, stretching of the walls of the vessels is carried out relatively easily, but as more blood is expelled and more and more stretching of the vessels, the resistance to stretching increases. The limit of stretching of elastic fibers is exhausted and rigid collagen fibers of the vessel walls begin to be stretched. The flask of the blood is prevented by the resistance of the peripheral vessels and the blood itself. The myocardium needs to spend a large amount of energy to overcome these resistances. The potential energy of muscle tissue and elastic structures of the myocardium itself accumulated in the isometric tension phase is exhausted and the force of its contraction decreases.

The rate of expulsion of blood begins to decrease and the phase of rapid expulsion is replaced by a phase of slow expulsion of blood, which is also called the phase of reduced expulsion. Its duration is about 0.13 s. The rate of decrease in the volume of the ventricles decreases. The blood pressure in the ventricle and in the aorta at the beginning of this phase decreases almost at the same rate. By this time, slow calcium channels close, and the plateau phase of the action potential ends. Calcium entry into cardiomyocytes decreases and the myocyte membrane enters phase 3 - final repolarization. The systole, the period of expulsion of blood, ends and the diastole of the ventricles begins (corresponding in time to phase 4 of the action potential). The implementation of reduced expulsion occurs in the time interval when the T wave is recorded on the ECG, and the end of systole and the beginning of diastole occur at the end of the T wave.

In the systole of the ventricles of the heart, more than half of the end-diastolic blood volume (about 70 ml) is expelled from them. This volume is called the stroke volume of the blood. The stroke volume of the blood can increase with an increase in myocardial contractility and, conversely, decrease with its insufficient contractility (see below indicators of the pumping function of the heart and myocardial contractility).

The blood pressure in the ventricles at the beginning of diastole becomes lower than the blood pressure in the arterial vessels extending from the heart. The blood in these vessels experiences the action of the forces of the stretched elastic fibers of the walls of the vessels. The lumen of the vessels is restored and a certain amount of blood is forced out of them. Part of the blood at the same time flows to the periphery. The other part of the blood is displaced in the direction of the ventricles of the heart, during its reverse movement it fills the pockets of the tricuspid vascular valves, the edges of which are closed and held in this state by the resulting blood pressure drop.

The time interval (about 0.04 s) from the beginning of diastole to the closing of the vascular valves is called the proto-diastolic interval. At the end of this interval, the 2nd diastolic rut of the heart is recorded and listened to. With synchronous recording of the ECG and phonocardiogram, the beginning of the 2nd tone is recorded at the end of the T wave on the ECG.

The diastole of the ventricular myocardium (about 0.47 s) is also divided into periods of relaxation and filling, which, in turn, are divided into phases. Since the closing of the semilunar vascular valves, the cavities of the ventricles become 0.08 s closed, since the AV valves still remain closed by this time. Relaxation of the myocardium, due mainly to the properties of the elastic structures of its intra- and extracellular matrix, is carried out under isometric conditions. In the cavities of the ventricles of the heart, after systole, less than 50% of the blood of the end-diastolic volume remains. The volume of the cavities of the ventricles does not change during this time, the blood pressure in the ventricles begins to decrease rapidly and tends to 0 mm Hg. Art. Let us recall that by this time blood continued to return to the atria for about 0.3 s, and that the pressure in the atria gradually increased. At the moment when the blood pressure in the atria exceeds the pressure in the ventricles, the AV valves open, the isometric relaxation phase ends, and the period of ventricular filling with blood begins.

The filling period lasts about 0.25 s and is divided into fast and slow filling phases. Immediately after the opening of the AV valves, blood flows rapidly along the pressure gradient from the atria into the ventricular cavity. This is facilitated by some suction effect of the relaxing ventricles, associated with their expansion under the action of elastic forces that have arisen during compression of the myocardium and its connective tissue frame. At the beginning of the rapid filling phase, sound vibrations in the form of the 3rd diastolic heart sound can be recorded on the phonocardiogram, which are caused by the opening of the AV valves and the rapid passage of blood into the ventricles.

As the ventricles fill, the blood pressure difference between the atria and ventricles decreases and after about 0.08 s, the phase of rapid filling is replaced by a phase of slow filling of the ventricles with blood, which lasts about 0.17 s. The filling of the ventricles with blood in this phase is carried out mainly due to the preservation of the residual kinetic energy in the blood moving through the vessels, given to it by the previous contraction of the heart.

0.1 s before the end of the phase of slow filling of the ventricles with blood, the cardiac cycle ends, a new action potential arises in the pacemaker, the next atrial systole occurs, and the ventricles are filled with end-diastolic blood volumes. This period of time of 0.1 s, which completes the cardiac cycle, is sometimes also called the period of additional filling of the ventricles during atrial systole.

An integral indicator characterizing the mechanical pumping function of the heart is the volume of blood pumped by the heart per minute, or the minute volume of blood (MBC):

where HR is the heart rate per minute; SV - stroke volume of the heart. Normally, at rest, the IOC for a young man is about 5 liters. The regulation of the IOC is carried out by various mechanisms through a change in heart rate and (or) SV.

Influence on heart rate can be provided through a change in the properties of the cells of the pacemaker of the heart. The effect on VR is achieved through the effect on the contractility of myocardial cardiomyocytes and the synchronization of its contraction.

Cardiac cycle - this is the systole and diastole of the heart, periodically repeating in strict sequence, i.e. a period of time including one contraction and one relaxation of the atria and ventricles.

In the cyclic functioning of the heart, two phases are distinguished: systole (contraction) and diastole (relaxation). During systole, the cavities of the heart are freed from blood, and during diastole they are filled. The period, including one systole and one diastole of the atria and ventricles, followed by a general pause, is called cycle of cardiac activity.

Atrial systole in animals lasts 0.1-0.16 s, and ventricular systole - 0.5-0.56 s. The general pause of the heart (simultaneous atrial and ventricular diastole) lasts 0.4 s. During this period, the heart rests. The entire cardiac cycle lasts for 0.8-0.86 s.

The duration of the various phases of the cardiac cycle depends on the heart rate. With more frequent heart contractions, the duration of each phase, especially diastole, decreases.

Phases of the cardiac cycle

Under cardiac cycle understand the period covering one contraction - systole and one relaxation diastole atria and ventricles - a general pause. The total duration of the cardiac cycle at a heart rate of 75 beats/min is 0.8 s.

Rice. 1. Phases of the cardiac cycle

Voltage period lasts 0.08 s and consists of two phases:

the phase of asynchronous contraction of the ventricular myocardium lasts 0.05 s. During this phase, the excitation process and the contraction process following it spread throughout the ventricular myocardium. The pressure in the ventricles is still close to zero. By the end of the phase, the contraction covers all myocardial fibers, and the pressure in the ventricles begins to increase rapidly.
phase of isometric contraction (0.03 s) - begins with the slamming of the cusps of the atrioventricular valves. When this occurs, I, or systolic, heart sound. The displacement of the valves and blood towards the atria causes a rise in pressure in the atria. The pressure in the ventricles increases rapidly: up to 70-80 mm Hg. Art. in the left and up to 15-20 mm Hg. Art. in the right.

Period of exile blood from the ventricles lasts 0.25 s and consists of a fast phase (0.12 s) and a slow ejection phase (0.13 s). At the same time, the pressure in the ventricles increases: in the left to 120-130 mm Hg. Art., and in the right up to 25 mm Hg. Art. At the end of the slow ejection phase, the ventricular myocardium begins to relax, and its diastole begins (0.47 s). The pressure in the ventricles drops, blood from the aorta and pulmonary artery rushes back into the cavities of the ventricles and “slams” the semilunar valves, and a II, or diastolic, heart sound occurs.

The time from the beginning of relaxation of the ventricles to the “slamming” of the semilunar valves is called proto-diastolic period(0.04 s). As the semilunar valves close, the pressure in the ventricles drops. The flap valves are still closed at this time, the volume of blood remaining in the ventricles, and, consequently, the length of the myocardial fibers do not change, therefore this period is called the period isometric relaxation(0.08 s). Toward the end of its pressure in the ventricles becomes lower than in the atria, the atrioventricular valves open and blood from the atria enters the ventricles. Begins filling period of the ventricles, which lasts 0.25 s and is divided into fast (0.08 s) and slow (0.17 s) filling phases.

The fluctuation of the walls of the ventricles due to the rapid flow of blood to them cause the appearance of a III heart sound. By the end of the slow filling phase, atrial systole occurs. The atria pump more blood into the ventricles ( presystolic period equal to 0.1 s), after which a new cycle of ventricular activity begins.

Vibration of the walls of the heart, caused by atrial contraction and additional blood flow into the ventricles, leads to the appearance of a IV heart sound.

With normal listening to the heart, loud I and II tones are clearly audible, and quiet III and IV tones are detected only with graphic recording of heart sounds.

In humans, the number of heartbeats per minute can vary significantly and depends on various external influences. When performing physical work or sports activity, the heart can contract up to 200 times per minute. In this case, the duration of one cardiac cycle will be 0.3 s. An increase in the number of heartbeats is called tachycardia, while the cardiac cycle decreases. During sleep, the number of heartbeats decreases to 60-40 beats per minute. In this case, the duration of one cycle is 1.5 s. A decrease in the number of heartbeats is called bradycardia while the cardiac cycle increases.

Structure of the cardiac cycle

As can be seen from fig. 1, with a cardiac cycle duration of 0.8 s (frequency of contractions 75 beats/min), the atria are in a systole state of 0.1 s and in a diastole state of 0.7 s.

Systole- the phase of the cardiac cycle, including the contraction of the myocardium and the expulsion of blood from the heart into the vascular system.

Diastole- the phase of the cardiac cycle, including the relaxation of the myocardium and the filling of the cavities of the heart with blood.

Rice. 2. Scheme of the general structure of the cardiac cycle. Dark squares show atrial and ventricular systole, light squares show their diastole.

Table 1. Periods and phases of the cardiac cycle

Asynchronous reduction phase - the initial stage of systole, in which the excitation wave propagates through the ventricular myocardium, but there is no simultaneous contraction of cardiomyocytes and the pressure in the ventricles is from 6-8 to 9-10 mm Hg. Art.

Isometric contraction phase - the stage of systole, in which the atrioventricular valves close and the pressure in the ventricles rapidly rises to 10-15 mm Hg. Art. in the right and up to 70-80 mm Hg. Art. in the left.

Rapid ejection phase - the stage of systole, at which there is an increase in pressure in the ventricles to maximum values - 20-25 mm Hg. Art. in the right and 120-130 mm Hg. Art. in the left and blood (about 70% of systolic ejection) enters the vascular system.

Slow ejection phase- the stage of systole, in which blood (the remaining 30% of systolic output) continues to flow into the vascular system at a slower rate. The pressure gradually decreases in the left ventricle from 120-130 to 80-90 mm Hg. Art., in the right - from 20-25 to 15-20 mm Hg. Art.

Proto-diastolic period- the transition period from systole to diastole, in which the ventricles begin to relax. Pressure decreases in the left ventricle to 60-70 mm Hg. Art., in disposition - up to 5-10 mm Hg. Art. Due to the greater pressure in the aorta and pulmonary artery, the semilunar valves close.

Period of isometric relaxation - the stage of diastole, in which the cavities of the ventricles are isolated by closed atrioventricular and semilunar valves, they relax isometrically, the pressure approaches 0 mm Hg. Art.

Rapid filling phase - the stage of diastole, in which the atrioventricular valves open and blood rushes into the ventricles at high speed.

Slow filling phase - the stage of diastole, in which blood slowly enters the atria through the vena cava and through the open atrioventricular valves into the ventricles. At the end of this phase, the ventricles are 75% filled with blood.

Presystolic period - the stage of diastole coinciding with atrial systole.

Atrial systole - contraction of the muscles of the atria, in which the pressure in the right atrium rises to 3-8 mm Hg. Art., in the left - up to 8-15 mm Hg. Art. and about 25% of the diastolic blood volume (15-20 ml) enters each of the ventricles.

Table 2. Characteristics of the phases of the cardiac cycle

Even before atrial systole, the AV valves are open and the atrial and ventricular cavities are already largely filled with blood. Stretch degree thin walls of the atrial myocardium with blood is important for the stimulation of mechanoreceptors and the production of atrial natriuretic peptide.

Rice. 3. Changes in the performance of the heart in different periods and phases of the cardiac cycle

During atrial systole, the pressure in the left atrium can reach 10-12 mm Hg. Art., and in the right - up to 4-8 mm Hg. Art., the atria additionally fill the ventricles with a volume of blood, which at rest is about 5-15% of the volume that is by this time in the ventricles. The volume of blood entering the ventricles during atrial systole may increase during exercise and amount to 25-40%. The volume of additional filling can increase to 40% or more in people over 50 years of age.

The flow of blood under pressure from the atria contributes to the stretching of the ventricular myocardium and creates conditions for their more effective subsequent contraction. Therefore, the atria play the role of a kind of amplifier of the contractile capabilities of the ventricles. With this function of the atria (for example, with atrial fibrillation), the efficiency of the ventricles decreases, a decrease in their functional reserves develops, and the transition to insufficiency of the contractile function of the myocardium is accelerated.

At the time of atrial systole, an a-wave is recorded on the venous pulse curve; in some people, when recording a phonocardiogram, the 4th heart sound may be recorded.

The volume of blood that is in the ventricular cavity after atrial systole (at the end of their diastole) is called end-diastolic. It consists of the volume of blood remaining in the ventricle after the previous systole ( end-systolic volume), the volume of blood that filled the cavity of the ventricle during its diastole to atrial systole, and the additional volume of blood that entered the ventricle during atrial systole. The value of the end-diastolic blood volume depends on the size of the heart, the volume of blood flowing from the veins and a number of other factors. In a healthy young person at rest, it can be about 130-150 ml (depending on age, sex and body weight, it can range from 90 to 150 ml). This volume of blood slightly increases the pressure in the ventricular cavity, which during atrial systole becomes equal to the pressure in them and can fluctuate in the left ventricle within 10-12 mm Hg. Art., and in the right - 4-8 mm Hg. Art.

For a time interval of 0.12-0.2 s, corresponding to the interval PQ on the ECG, the action potential from the SA node extends to the apical region of the ventricles, in the myocardium of which the process of excitation begins, rapidly spreading in directions from the apex to the base of the heart and from the endocardial surface to the epicardial. Following excitation, contraction of the myocardium or ventricular systole begins, the duration of which also depends on the frequency of heart contractions. At rest, it is about 0.3 s. The systole of the ventricles consists of periods voltage(0.08 s) and exile(0.25 s) blood.

The period of tension of the ventricles is divided into phases asynchronous(0.05 s) and isometric(0.03 s) contractions. The short-term phase of asynchronous contraction at the beginning of the systole of the ventricular myocardium is a consequence of the non-simultaneous coverage of excitation and contraction of various parts of the myocardium. Excitation (corresponds to the tooth Q on the ECG) and myocardial contraction occurs initially in the region of the papillary muscles, the apical part of the interventricular septum and the apex of the ventricles and spreads to the remaining myocardium in about 0.03 s. This coincides in time with the registration on the ECG wave Q and ascending part of the tooth R to its top (see Fig. 3).

At the time of closing of the atrioventricular valves, 1st systolic tone heart, the phase of asynchronous contraction ends and the phase of isometric contraction begins, which is also called the phase of isovolumetric (isovolumic) contraction. The duration of this phase is about 0.03 s, its implementation coincides with the time interval in which the descending part of the tooth is recorded. R and the beginning of the tooth S on the ECG (see Fig. 3).

From the moment the AV valves close under normal conditions, the cavity of both ventricles becomes airtight. Blood, like any other liquid, is incompressible, so the contraction of myocardial fibers occurs at their constant length or in isometric mode. The volume of the cavities of the ventricles remains constant and myocardial contraction occurs in isovolumic mode. An increase in tension and force of myocardial contraction under such conditions is converted into a rapidly increasing blood pressure in the cavities of the ventricles. Under the influence of blood pressure on the region of the AV-septum, a short-term shift occurs towards the atria, is transmitted to the inflowing venous blood and is reflected by the appearance of a c-wave on the venous pulse curve. Within a short period of time - about 0.04 s, the blood pressure in the cavity of the left ventricle reaches a value comparable to its value at that moment in the aorta, which decreased to a minimum level - 70-80 mm Hg. Art. The blood pressure in the right ventricle reaches 15-20 mm Hg. Art.

Period of exile blood lasts about 0.25 s and is divided into phases rapid exile(0.12 s) and slow exile blood (0.13 s). During this period, the AV valves remain closed, the semilunar valves remain open. The rapid expulsion of blood at the beginning of the period is due to a number of reasons. About 0.1 s has passed since the start of excitation of cardiomyocytes and the action potential is in the plateau phase. Calcium continues to flow into the cell through open slow calcium channels. Thus, the tension of the myocardial fibers, which was already high at the beginning of the expulsion, continues to increase. The myocardium continues to compress the decreasing volume of blood with greater force, which is accompanied by a further increase in pressure in the ventricular cavity. The blood pressure gradient between the ventricular cavity and the aorta increases and blood begins to be expelled into the aorta at high speed. In the phase of rapid expulsion, more than half of the stroke volume of blood expelled from the ventricle during the entire period of exile (about 70 ml) is ejected into the aorta. By the end of the phase of rapid blood expulsion, the pressure in the left ventricle and in the aorta reaches its maximum - about 120 mm Hg. Art. in young people at rest, and in the pulmonary trunk and right ventricle - about 30 mm Hg. Art. This pressure is called systolic. The phase of rapid expulsion of blood is carried out in the period of time when the end of the wave is recorded on the ECG S and isoelectric part of the interval ST before the beginning of the tooth T(See Fig. 3).

The rate of expulsion of blood begins to decrease and the phase of rapid expulsion is replaced by the phase of slow expulsion of blood, which is also called reduced ejection phase. Its duration is about 0.13 s. The rate of decrease in the volume of the ventricles decreases. The blood pressure in the ventricle and in the aorta at the beginning of this phase decreases almost at the same rate. By this time, slow calcium channels close, and the plateau phase of the action potential ends. Calcium entry into cardiomyocytes decreases and the myocyte membrane enters phase 3 - final repolarization. The systole, the period of expulsion of blood, ends and the diastole of the ventricles begins (corresponding in time to phase 4 of the action potential). The implementation of reduced expulsion occurs in the period of time when a wave is recorded on the ECG T, and the end of systole and the beginning of diastole occur at the end of the tooth T.

In the systole of the ventricles of the heart, more than half of the end-diastolic blood volume (about 70 ml) is expelled from them. This volume is called stroke volume of blood. The stroke volume of blood can increase with an increase in myocardial contractility and, conversely, decrease with its insufficient contractility (see below indicators of the pumping function of the heart and myocardial contractility).

The time interval (about 0.04 s) from the onset of diastole to the closing of the vascular valves is called proto-diastolic interval. At the end of this interval, the 2nd diastolic rut of the heart is recorded and listened to. With synchronous recording of the ECG and phonocardiogram, the beginning of the 2nd tone is recorded at the end of the T wave on the ECG.

0.1 s before the end of the phase of slow filling of the ventricles with blood, the cardiac cycle ends, a new action potential arises in the pacemaker, the next atrial systole occurs, and the ventricles are filled with end-diastolic blood volumes. This period of time of 0.1 s, which completes the cardiac cycle, is sometimes also called periodadditionalfilling ventricles during atrial systole.

An integral indicator characterizing the mechanical is the volume of blood pumped by the heart per minute, or the minute volume of blood (MOV):

IOC = heart rate. uo,

where HR is the heart rate per minute; SV — stroke volume of the heart. Normally, at rest, the IOC for a young man is about 5 liters. The regulation of the IOC is carried out by various mechanisms through a change in heart rate and (or) SV.

(Latin cor, Greek cardia) - a hollow fibromuscular organ located in the middle of the chest between two lungs and lying on the diaphragm. In relation to the midline of the body, the heart is located asymmetrically - about 2/3 to the left of it and about 1/3 to the right.

Heart size a person is approximately equal to the size of his fist, weighs on average 220-260 grams (up to 500 g).

How the heart works
The heart pumps blood throughout the body, supplying the cells with oxygen and nutrients. The heart can be considered a real crossroads of highways, a regulator of the "movement" of blood, since veins and arteries converge in it, and it continuously acts as a pump - in one contraction it pushes 60-75 ml of blood (up to 130 ml) into the vessels. The normal pulse at rest is 60-80 beats per minute, and in women the heart beats 6-8 beats per minute more often than in men. With heavy physical exertion, the pulse can accelerate to 200 or more beats per minute. During the day, the heart contracts about 100,000 times, pumping from 6000 to 7500 liters of blood or 30-37 full baths with a capacity of 200 liters.
The pulse is formed when blood is pushed out of the left ventricle into the aorta and spreads in the form of a wave through the arteries at a speed of 11 m / s, that is, 40 km / h.

The force developed by the heart during contraction, N	70-90
Work of the heart:
at one contraction, J (kgf m)	1 (0,102)
during the day, kJ (kgf m)	86,4 (8810)
Average power developed by the heart, W (hp)	2,2 (0,003)
The volume of blood ejected by the heart in one contraction, cm 3	60-80
The volume of blood ejected by the heart, l:
in 1 min
at 70 beats per minute	4,2-5,6
in cross country skiing	25-35
at work of medium intensity	18
for 1 hour	252-336
per day	6050-8100
per year, mln.	2,2-3,0

Blood moves in the heart in a figure of eight : from the veins flows into the right atrium, then the right ventricle pushes it into the lungs, where it is saturated with oxygen and returns through the pulmonary veins to the left atrium. Then, into the left ventricle and out of it through the aorta and the arterial vessels branching off from it, it spreads throughout the body.
Having given up oxygen, the blood is collected in the vena cava, and through them - into the right atrium and right ventricle. From there, through the pulmonary artery, the blood enters the lungs, where it is again enriched with oxygen.

It is not entirely clear how the brain manages to maintain the synchronism of the activity of the heart and 40 thousand kilometers (up to 100 thousand km) of the vascular systems- lymphatic, venous, arterial. Imagine: under load, your body needs to dramatically increase blood flow, oxygen consumption, etc. The heart should work in an instant!

The heart is made up of a type of striated muscle - myocardium, covered on the outside with a serous two-layer membrane: the layer adjacent to the muscle is epicardium; and the outer layer, which attaches the heart to neighboring structures, but allows it to contract, - pericardium.

Anatomy of the conduction system of the heart
The muscular septum divides the heart longitudinally into left and right halves. The valves divide each half into two chambers: an upper (atrium) and a lower (ventricle). So the heart is like four-chamber muscle pump , consists of four chambers, divided in pairs fibrous valves, which allow blood to flow in only one direction . A number of blood vessels enter and leave these chambers, through which the blood circulates.
Four heart chambers lined with a layer of elastic tissue - endocardium, - form two atrium and two ventricle. The left atrium communicates with the left ventricle through mitral valve and the right atrium communicates with the right ventricle via tricuspid valve.
Two vena cava flow into the right atrium, and four pulmonary veins into the left atrium. The pulmonary artery departs from the right ventricle, and the aorta from the left ventricle. The flow of blood to the heart is constant and unhindered, while the output of blood from the ventricles to the arteries is regulated semilunar valves, which open only when the blood in the ventricle reaches a certain pressure.

The heart works in two types of movements: systolic, or contraction motion, and diastolic, or movement of relaxation. The contraction, regulated by the autonomic nervous system, is not amenable to voluntary control, since the pumping and circulation of blood in the body must be continuous.

(cyclus cardiacus) - usually called a stroke - a set of electrophysiological, biochemical and biophysical processes occurring in the heart during one contraction.
The heart cycle consists of three phases:
1. Atrial systole and ventricular diastole. When the atria contract, the mitral and tricuspid valves open and blood enters the ventricles.
2. Ventricular systole. The ventricles contract, causing an increase in blood pressure. The semilunar valves of the aorta and pulmonary artery open and the stomachs empty through the arteries.
3. General diastole. After emptying, the ventricles relax and the heart remains in the resting phase until the blood filling the atrium pushes against the atrioventricular valves.

Contracting, the heart muscle pushes blood first through the atria and then through the ventricles.
The right atrium of the heart receives oxygen-poor blood from two main veins: superior vena cava and inferior vena cava, as well as from the smaller coronary sinus, which collects blood from the walls of the heart itself. When the right atrium contracts, blood enters the right ventricle through the tricuspid valve. When the right ventricle is sufficiently filled with blood, it contracts and ejects blood through the pulmonary arteries into the pulmonary circulation.
The oxygenated blood in the lungs travels through the pulmonary veins to the left atrium. After filling with blood, the left atrium contracts and pushes blood through the mitral valve into the left ventricle.
After filling with blood, the left ventricle contracts and ejects blood with great force into the aorta. From the aorta, blood enters the vessels of the systemic circulation, carrying oxygen to all cells of the body.

Excitement of the heart takes place in the conduction system of the heart muscular nodular tissue, more precisely, muscle cells specialized in the excitation of the heart muscle. This fabric is made up of sinoatrial node(S-A node, sinus node, Kees-Flak node) and atrioventricular node(A-V-node, atrioventricular node) located in the right atrium (on the border of the atria and ventricles). In the first of these nodes, electrical impulses arise, causing the heart to contract (70-80 beats per minute). Then the impulses pass through the atria and excite the second node, which can independently make the heart beat (40-60 beats per minute). Through bundle of His and Purkinje fibers excitation spreads to both ventricles, causing them to contract. After that, the heart rests until the next impulse, from which a new cycle begins.

The impulses set the heart rate (required frequency), uniformity and synchronism of atrial and ventricular contractions in accordance with the activity and needs of the body, time of day and many other factors affecting a person.

Cardiac pause - the period between auscultatory recorded heart sounds (Latin auscultare listen, listen); distinguish between small S. p., corresponding to ventricular systole, and large S. p., corresponding to ventricular diastole.

Heart valves act as gates, allowing blood to pass from one chamber of the heart to another and from the chambers of the heart to their associated blood vessels. The heart has the following valves: tricuspid, pulmonary (pulmonary trunk), bicuspid (aka mitral) and aortic.

Tricuspid valve located between the right atrium and the right ventricle. When this valve opens, blood flows from the right atrium to the right ventricle. The tricuspid valve prevents blood from flowing back into the atrium by closing during ventricular contraction. The very name of this valve suggests that it consists of three valves.

Pulmonary valve . When the tricuspid valve is closed, blood in the right ventricle finds an outlet only into the pulmonary trunk. The pulmonary trunk divides into the left and right pulmonary arteries, which lead respectively to the left and right lung. The entrance to the pulmonary trunk is closed by the pulmonary valve. The pulmonary valve consists of three leaflets that are open when the right ventricle contracts and closed when it relaxes. The pulmonary valve allows blood to flow from the right ventricle into the pulmonary arteries, but prevents blood from flowing back from the pulmonary arteries into the right ventricle.

Bivalve or mitral valve regulates blood flow from the left atrium to the left ventricle. Like the tricuspid valve, the bicuspid valve closes when the left ventricle contracts. The mitral valve consists of two leaflets.

aortic valve consists of three valves and closes the entrance to the aorta. This valve allows blood to flow from the left ventricle when it contracts and prevents backflow of blood from the aorta into the left ventricle when the latter relaxes.

Nutrition and respiration of the heart itself is provided by the coronary (coronary) vessels
Left coronary artery starts from the left posterior sinus of Vilsalva, goes down to the anterior longitudinal groove, leaving the pulmonary artery to its right, and the left atrium and the ear surrounded by adipose tissue, which usually covers it, to the left. It is a wide, but short trunk, usually no more than 10-11 mm long.
The left coronary artery is divided into two, three, in rare cases, four arteries, of which the anterior descending (LAD) and circumflex branch (OB), or arteries, are of the greatest importance for pathology.
The anterior descending artery is a direct continuation of the left coronary artery. Along the anterior longitudinal cardiac sulcus, it goes to the region of the apex of the heart, usually reaches it, sometimes bends over it and passes to the back surface of the heart.
Several smaller lateral branches depart from the descending artery at an acute angle, which are directed along the anterior surface of the left ventricle and can reach the blunt edge; in addition, numerous septal branches depart from it, perforating the myocardium and branching in the anterior 2/3 of the interventricular septum. Lateral branches feed the anterior wall of the left ventricle and give branches to the anterior papillary muscle of the left ventricle. The superior septal artery gives a branch to the anterior wall of the right ventricle and sometimes to the anterior papillary muscle of the right ventricle.
Throughout the entire length of the anterior descending branch lies on the myocardium, sometimes plunging into it with the formation of muscle bridges 1-2 cm long. For the rest of its length, its anterior surface is covered with fatty tissue of the epicardium.
The circumflex branch of the left coronary artery usually departs from the latter at the very beginning (the first 0.5-2 cm) at an angle close to a right one, passes in the transverse groove, reaches the blunt edge of the heart, goes around it, passes to the posterior wall of the left ventricle, sometimes reaches the posterior interventricular sulcus and in the form of the posterior descending artery goes to the apex. Numerous branches depart from it to the anterior and posterior papillary muscles, the anterior and posterior walls of the left ventricle. One of the arteries that feed the sinoauricular node also departs from it.

Right coronary artery begins in the anterior sinus of Vilsalva. First, it is located deep in the adipose tissue to the right of the pulmonary artery, goes around the heart along the right atrioventricular sulcus, passes to the posterior wall, reaches the posterior longitudinal sulcus, then, in the form of a posterior descending branch, descends to the apex of the heart.
The artery gives 1-2 branches to the anterior wall of the right ventricle, partly to the anterior septum, both papillary muscles of the right ventricle, the posterior wall of the right ventricle and the posterior interventricular septum; the second branch also departs from it to the sinoauricular node.

There are three main types of myocardial blood supply : middle, left and right.
This subdivision is based mainly on variations in the blood supply to the posterior or diaphragmatic surface of the heart, since the blood supply to the anterior and lateral regions is fairly stable and not subject to significant deviations.
At middle type all three main coronary arteries are well developed and fairly evenly developed. The blood supply to the entire left ventricle, including both papillary muscles, and the anterior 1/2 and 2/3 of the interventricular septum is carried out through the system of the left coronary artery. The right ventricle, including both right papillary muscles and the posterior 1/2-1/3 septum, receives blood from the right coronary artery. This appears to be the most common type of blood supply to the heart.
At left type blood supply to the entire left ventricle and, in addition, to the entire septum and partly the posterior wall of the right ventricle is carried out due to the developed circumflex branch of the left coronary artery, which reaches the posterior longitudinal groove and ends here in the form of the posterior descending artery, giving part of the branches to the posterior surface of the right ventricle .
Right type observed with a weak development of the circumflex branch, which either ends without reaching the obtuse edge, or passes into the coronary artery of the obtuse edge, not spreading to the posterior surface of the left ventricle. In such cases, the right coronary artery, after leaving the posterior descending artery, usually gives a few more branches to the posterior wall of the left ventricle. In this case, the entire right ventricle, the posterior wall of the left ventricle, the posterior left papillary muscle and partly the apex of the heart receive blood from the right coronary arteriole.

Myocardial blood supply is carried out directly :
a) capillaries lying between the muscle fibers braiding them and receiving blood from the system of coronary arteries through arterioles;
b) a rich network of myocardial sinusoids;
c) Viessant-Tebesia vessels.

With an increase in pressure in the coronary arteries and an increase in the work of the heart, the blood flow in the coronary arteries increases. The lack of oxygen also leads to a sharp increase in coronary blood flow. The sympathetic and parasympathetic nerves seem to have little effect on the coronary arteries, exerting their main action directly on the heart muscle.

Outflow occurs through the veins, which are collected in the coronary sinus
Venous blood in the coronary system is collected in large vessels, usually located near the coronary arteries. Some of them merge, forming a large venous canal - the coronary sinus, which runs along the back surface of the heart in the groove between the atria and ventricles and opens into the right atrium.

Intercoronary anastomoses play an important role in coronary circulation, especially in pathological conditions. There are more anastomoses in the hearts of people suffering from ischemic disease, so the closure of one of the coronary arteries is not always accompanied by necrosis in the myocardium.
In normal hearts, anastomoses are found only in 10-20% of cases, and they are of small diameter. However, their number and magnitude increase not only in coronary atherosclerosis, but also in valvular heart disease. Age and gender by themselves have no effect on the presence and degree of development of anastomoses.

The heart has its own stem cells
06/01/2006. Computerra #46
Previously, experts believed that self-restoration of the heart is impossible, since the developed cells of this organ do not divide. However, in 2003, according to New Scientist, researchers from the laboratory of Piero Anversa from the Medical College in Valhalla (New York, USA) found stem cells in the heart tissues of mice. Until now, scientists have not been able to say for sure whether these cells are permanently present in the heart or whether they migrate from other tissues, such as the bone marrow.
Anversa's colleague, Annaroza Leri, took up the search for an answer to this question. She tried to find in the heart the so-called "niches" for stem cells. "Niches" where stem and mature cells are grouped, found between cardiac muscle cells . Having made this discovery, Leri and her collaborators conducted a series of experiments. Scientists removed a small amount of heart stem cells from people who had undergone heart surgery, grew them in the laboratory and transplanted them into damaged hearts of mice and rats.
Lehry calls the results of the experiments promising and believes that the use of stem cells from the heart in the treatment of heart disease can be much more effective than the use of stem cells derived from bone marrow. Now the main task of researchers is to find out how cardiac stem cells work, what regulates their activity and how this mechanism can be imitated.

A group of physicists from Boston University, led by Yosef Ashkenazy (Yosef Ashkenazy) studied in detail the patterns of heart rhythm.
Widely used electrocardiogram helps to analyze only the general characteristics of the heartbeat, but does not take into account the rhythmic pattern of heart beats - that is, the exact sequence of its beats and pauses.
Ashkenazi and his colleagues have developed a computer algorithm that allows them to penetrate deeper into the secrets of the heart. The calculations showed that the time the intervals between heartbeats are rarely the same . That is, the heartbeat is more like a virtuoso drum part than the even ticking of a clock.
According to scientists, a healthy heart works like a good drummer. In general, the musician keeps the rhythm, but from time to time deliberately allows small failures. Since he strikes the drum rather quickly, accelerations or delays are almost indistinguishable to the ear, but give the part a special charm. So it is with the heart - it constantly "improvises". Curiously, some the randomness of the rhythmic pattern is characteristic of a healthy heart . In people who are in a pre-infarction state, the rhythm of the heartbeat becomes mechanically accurate.
Ashkenazi drew conclusions about the work of the heart by analyzing tape recordings of the "music" of the heart. Then he examined the heart rate of 18 healthy and 12 sick people - mostly suffering from blood clots in the vessels of the heart - and was finally convinced of the correctness of his calculations.
Ashkenazi claims that his work will allow diagnosing not only already developed heart diseases, but also a predisposition to them.
Article published in Physical Review Letters.

Run Bunny Run
Everyone knows that lying on the couch is more harmful than walking and exercising. And why? The scientists of the Institute of Clinical Cardiology figured it out. They put the rabbits in cramped cages (almost the size of the body) and kept them motionless for 70 days. Then they looked at their hearts under an electron microscope. We saw a terrible picture. Many myofibrils- the fibers, due to which the muscle contracts, have atrophied. The connections between cells that help them work together have been disrupted. The changes affected the nerve endings that control the muscles. The walls of the capillaries carrying blood to them began to grow inward, reducing the lumen of the vessels. Here's your sofa!

Why people love Petrosyan and K
Dr. Michael Miller of the University of Maryland and his colleagues conducted a series of experiments by showing volunteers two films: a happy one and a sad one. And at the same time, they tested the work of their hearts and blood vessels. After the tragic film, 14 out of 20 volunteers have blood flow in their vessels decreased by an average of 35% . And after the funny, on the contrary, increased by 22% in 19 out of 20 subjects.
Changes in blood vessels in laughing volunteers were similar to those that occur during aerobic exercise. But at the same time, they did not have any pain in the muscles, nor fatigue and overexertion, which often accompanies great physical exertion. Scientists have concluded that laughter reduces the risk of cardiovascular disease.

Broken heart syndrome
Such a new diagnosis appeared in cardiology. It was first described 12 years ago by Japanese doctors. Now it is recognized in other countries. The syndrome occurs, as a rule, in women over forty who have experienced a love failure. The cardiogram and ultrasound show the same disorders in them as in a heart attack, although the coronary vessels are in order. But levels of the stress hormone adrenaline , for example, they are 2-3 times higher than in heart patients. And in comparison with healthy people, it is exceeded by 7-10, and in some cases even 30 times!
It is the hormones, according to doctors, that "hit" the heart, forcing it to respond with the classic symptoms of a heart attack: pain behind the sternum, fluid in the lungs, acute heart failure. Fortunately, patients with the new syndrome recover fairly quickly if they are treated correctly.

Chocolate is good for the heart
06/01/2004. Membrana
Eating small portions of chocolate every day has a beneficial effect on the functioning of blood vessels in the body, which, in turn, is very good for heart health.
This conclusion was reached by a group of doctors from the University of California in San Francisco (University of California, San Francisco). Indeed, such an effect not any chocolate, but only one in the course of which a large amount of flavonoids contained in cocoa was preserved .
A team led by Mary Engler studied 21 randomly selected people for two weeks. All of them during the experiment ate chocolate, the same in appearance. But some of the tiles were rich in flavonoids, while the other, on the contrary, almost did not contain these substances. Naturally, the volunteer testers did not know which version of the tile they were given. Scientists conducted an ultrasound examination of the brachial artery - the volume of blood flow in it and the ability of the vessel walls to expand and contract. It turned out that for those who consumed chocolate with flavonoids, these parameters improved by about 13% in two weeks.
New work (30.09.2004) by Dr. Charalambos Vlachopoulos from the University of Athens adds points to the popular dessert. Dark chocolate (but not milk) improves blood flow and reduces the risk of blood clots that can clog blood vessels, says an Athenian researcher. The results of the study showed an improvement in the functioning of the endothelium - a thin layer of cells on the inside of the vessels. In addition, a survey of volunteers showed that chocolate protects the body from the damaging effects of so-called free radicals.

The eyes are the mirror of the heart
06/09/2006. Light portal
Associate Professor Tin Wong, University Center for Eye Research (Melbourne, Australia) received the Commonwealth Health and Medical Research Award.
He was awarded such a high award for the development of eye diagnostics, which will help in the detection of a number of heart and other serious diseases.
Professor Wong's group has done extensive work on more than 20,000 patients over the course of five years. Scientists have developed and brought to clinical practice a technique that helps to measure the degree of narrowing of the small blood vessels of the eye, which give a signal of the onset of the development of various diseases.

What is the cardiac cycle?

The atria begin to contract at the mouths of the vena cava, causing them to contract. For this reason, blood during atrial systole can only move in the direction from the atria to the ventricles.

This is followed by contraction of the ventricles, which takes 0.33 s. It includes periods:

voltage;
exile.

Diastole consists of periods:

isometric relaxation (0.08 s);
filling with blood (0.25 s);
presystolic (0.1 s).

Systole

The period of tension, lasting 0.08 s, is divided into 2 phases: asynchronous (0.05 s) and isometric contraction (0.03 s).

This is followed by an exile period lasting 0.25 s. It includes fast (0.12 s) and slow (0.13 s) ejection phases. The pressure in the cavities of the ventricles during this period reaches its maximum values (120 mm Hg in the left ventricle, 25 mm Hg in the right). At the end of the ejection phase, the ventricles begin to relax, their diastole begins (0.47 s). Intraventricular pressure decreases and becomes much lower than the pressure in the initial segments of the aorta and pulmonary trunk, as a result of which blood from these vessels rushes back into the ventricles along the pressure gradient. The semilunar valves close and a second heart sound is recorded. The period from the beginning of relaxation to the slamming of the valves is called proto-diastolic (0.04 seconds).

Diastole

At the end of the filling period, atrial systole occurs. Regarding the ventricular cycle, it is the presystolic period. During the contraction of the atria, an additional volume of blood enters the ventricles, causing oscillations of the walls of the ventricles. Recorded IV heart sound.

Option 1.

1. What function does the circulatory system not perform? a) support and movement b) transport c) respiratory d) regulatory.

2. In what blood vessels does gas exchange take place? a) in the veins b) in the arteries c) in the capillaries.

3. In which vessels does blood flow the slowest? a) in the arteries b) in the veins c) in the capillaries.

4. Where does the pulmonary circulation begin? a) in the right ventricle b) in the left ventricle c) in the right atrium d) in the left atrium.

5. Department of the heart with the thickest muscular wall a) right atrium b) left atrium c) left ventricle d) right ventricle.

6. In what state are the valves of the heart during atrial contraction? a) all are open b) all are closed c) the semilunar ones are open and the valves are closed d) the semilunar ones are closed and the valves are open.

7. Departments of the heart in which relaxation occurs when blood is pushed out of the heart: a) left atrium b) right atrium c) left ventricle d) right ventricle.

8. In which blood vessel does venous blood flow? a) in the veins of the lesser circle b) in the veins of the greater circle c) in the aorta d) in the arteries of the greater circle.

9. What kind of blood is called arterial? a) poor in oxygen b) rich in oxygen c) the one that flows through the arteries.

10. How does the strength and frequency of heart contractions change during exercise? a) slows down and weakens b) increases and slows down c) increases and becomes more frequent d) weakens and becomes more frequent.

Option 2.

1.What is blood circulation? a) the supply of oxygen to the human body b) the continuous flow of blood through a closed system of blood vessels c) the transfer of erythrocytes from the lungs to the tissues d) the rhythmic vibrations of the walls of blood vessels.

2. What kind of blood is called venous? a) poor in oxygen b) rich in oxygen c) the one that flows through the veins.

3.What is a pulse? a) rhythmic oscillations of the walls of the arteries b) blood pressure on the walls of blood vessels c) contraction of the atria d) contraction of the ventricles.

4. What are the names of the vessels in which there are valves? a) capillaries b) lymphatic c) arteries d) veins.

5. Where does the systemic circulation begin? a) in the right ventricle b) in the left ventricle c) in the right atrium d) in the left atrium.

6. Where does the pulmonary circulation end? a) in the right atrium b) in the right ventricle c) in the left atrium d) in the left ventricle.

7. In which blood vessel does arterial blood flow? a) in the arteries of the lesser circle b) in the veins of the lesser circle c) in the veins of the greater circle d) in the pulmonary artery.

8.0 parts of the heart in which contraction occurs when blood is pushed out of the heart. a) right atrium b) left atrium c) left ventricle d) right ventricle.

9. In what state are the valves of the heart when it relaxes? a) all are open b) all are closed c) the semilunar ones are open and the valves are closed d) the semilunar ones are closed and the valves are open.

10. How does the strength and frequency of heart contractions change under the influence of adrenaline? a) slows down and weakens b) increases and slows down c) increases and becomes more frequent d) weakens and becomes more frequent.

Option 3.

1. Vessels in which venous blood becomes arterial? a) in the veins b) in the arteries c) in the capillaries.

2. Which blood vessels have the lowest blood pressure? a) in the arteries b) in the capillaries c) in the veins.

3. Which blood vessels have the highest blood pressure? a) in the arteries b) in the capillaries c) in the veins.

4. Where does the big circle end? a) left atrium b) right atrium c) left ventricle d) right ventricle.

5.Where are the capillaries of the small circle? a) in the digestive system b) in the kidneys c) in the lungs d) in the heart.

6. In which veins does arterial blood flow? a) in the pulmonary veins b) in the vena cava c) in the veins of the extremities d) in the portal vein of the liver.

7. What chamber of the heart receives blood from the pulmonary circulation? a) left atrium b) right atrium c) left ventricle d) right ventricle.

8. What valves are located between the atria and ventricles of the heart? a) semilunar b) valvular c) venous.

9. What is the state of the heart valves during ventricular contraction? a) all are open b) all are closed c) the semilunar ones are open and the valves are closed d) the semilunar ones are closed and the valves are open.

10. How does the strength and frequency of heart contractions change when exposed to acetylcholine? a) slows down and weakens b) increases and slows down c) increases and becomes more frequent d) weakens and becomes more frequent.

Option 4.

1. Where does the systemic circulation begin: a) right atrium b) left atrium c) left ventricle d) right ventricle?

2. Where does the systemic circulation end: a) right ventricle b) right atrium c) left atrium d) left ventricle?

3. Where does the pulmonary circulation begin: a) right atrium b) left atrium c) left ventricle d) right ventricle?

4. Where does the pulmonary circulation end: a) left atrium b) right atrium c) left ventricle d) right ventricle?

5. Where does gas exchange take place in the small circle: a) brain b) lungs c) skin d) heart?

6. What features are arteries characterized by: a) thick walls b) the presence of valves c) high pressure d) branching into capillaries?

7. What kind of blood moves through the pulmonary vein: a) arterial b) venous c) mixed?

8. What muscles are part of the heart muscle: a) smooth b) striated c) striated cardiac?

9. Which chamber of the heart receives blood from the systemic circulation? a) right atrium b) left atrium c) left ventricle d) right ventricle.

10. What valves are located at the base of the major arteries of the heart? a) semilunar b) valvular c) venous.

Answers: 1 var: a; in; in; a; in; G; a, b; b; b; in. 2 var: b; a a; G; b; in; b; c, d; G; in. 3 var: in; in; a; b; in; a; a; b; in; a. 4 var: in; b; G; a; b; a, c; a; in; a; a.