Cycle of cardiac activity. Heart cycle Contraction of the ventricles of the heart

The heart is the main organ that performs an important function - maintaining life. The processes that occur in the organ cause the heart muscle to excite, contract and relax, thereby setting the rhythm of blood circulation. Cardiac cycle- the time period between which muscle contraction and relaxation occurs.

In this article we will take a detailed look at the phases of the cardiac cycle, find out what indicators of activity there are, and also try to understand how the human heart works.

If you have any questions while reading the article, you can ask them to the portal specialists. Consultations are provided free of charge 24 hours a day.

The activity of the heart consists of a continuous alternation of contraction (systolic function) and relaxation (diastolic function). The change between systole and diastole is called the cardiac cycle.

In a person at rest, the contraction frequency averages 70 cycles per minute and has a duration of 0.8 seconds. Before contraction, the myocardium is in a relaxed state, and the chambers are filled with blood that comes from the veins. At the same time, all valves are open and the pressure in the ventricles and atria is equal. Myocardial excitation begins in the atrium. The pressure rises and due to the difference, blood is pushed out.

Thus, the heart performs a pumping function, where the atria are a container for receiving blood, and the ventricles “indicate” the direction.

It should be noted that the cycle of cardiac activity is provided by the impulse for muscle work. Therefore, the organ has a unique physiology and independently accumulates electrical stimulation. Now you know how the heart works.

Cycle of cardiac work

Processes occurring during the cardiac cycle include electrical, mechanical and biochemical. Both external factors (sport, stress, emotions, etc.) and physiological characteristics organisms that are subject to change.

The cardiac cycle consists of three phases:

1. Atrial systole has a duration of 0.1 second. During this period, the pressure in the atria increases, in contrast to the state of the ventricles, which are relaxed at this moment. Due to the difference in pressure, blood is pushed out of the ventricles.
2. The second phase consists of atrial relaxation and lasts 0.7 seconds. The ventricles are excited, and this lasts 0.3 seconds. And at this moment the pressure increases, and blood flows into the aorta and artery. Then the ventricle relaxes again for 0.5 seconds.
3. Phase number three is a time period of 0.4 seconds when the atria and ventricles are at rest. This time is called a general pause.

The figure clearly shows the three phases of the cardiac cycle:

At the moment, there is an opinion in the world of medicine that the systolic state of the ventricles contributes not only to the ejection of blood. At the moment of excitation, the ventricles undergo a slight displacement towards the upper region of the heart. This leads to the fact that blood is sucked from the main veins into the atria. At this moment the atria are in a diastolic state, and due to the incoming blood they are stretched. This effect is clearly pronounced in the right stomach.

Heartbeat

The frequency of contractions in an adult is in the range of 60-90 beats per minute. The heart rate of children is slightly higher. For example, in infants the heart beats almost three times faster - 120 times per minute, and children under 12-13 years old have a heartbeat of 100 beats per minute. Of course, these are approximate figures, because... due to different external factors the rhythm can last longer or shorter.

The main organ is enveloped in nerve threads that regulate all three phases of the cycle. Strong emotional experiences, physical activity and much more increase impulses in the muscles that come from the brain. Undoubtedly, physiology, or rather, its changes, plays an important role in the activity of the heart. For example, an increase in carbon dioxide in the blood and a decrease in oxygen gives a powerful boost to the heart and improves its stimulation. If changes in physiology affect the blood vessels, this leads to the opposite effect and the heart rate decreases.

As mentioned above, the work of the heart muscle, and therefore the three phases of the cycle, is influenced by many factors in which the central nervous system is not involved.

Eg, heat the body speeds up the rhythm, and the low one slows it down. Hormones, for example, also have a direct effect, because They enter the organ along with the blood and increase the rhythm of contractions.

The cardiac cycle is one of the most complex processes occurring in the human body, because... there are many factors involved. Some of them have a direct impact, others affect indirectly. But the totality of all processes allows the heart to carry out its work.

The structure of the cardiac cycle is the most important process that supports the functioning of the body. A complex organ with its own generator of electrical impulses, physiology and control of the frequency of contractions – it works all its life. The occurrence of diseases of the organ and its fatigue are influenced by three main factors - lifestyle, genetic characteristics and environmental conditions.

The main organ (after the brain) is the main link in blood circulation, therefore, it affects all metabolic processes in the body. The heart displays any failure or deviation from the normal state in a split second. Therefore, it is so important for every person to know the basic principles of work (three phases of activity) and physiology. This makes it possible to identify violations in the work of this body.

And calls mechanical systole- contraction of the heart muscle and a decrease in the volume of the heart chambers. Term diastole means muscle relaxation. During the cardiac cycle, blood pressure increases and decreases, respectively high pressure at the moment of ventricular systole is called systolic, and low during their diastole - diastolic.

The repetition rate of the cardiac cycle is called heart rate, it is set by the heart pacemaker.

Periods and phases of the cardiac cycle

A summary table of the periods and phases of the cardiac cycle with approximate pressures in the chambers of the heart and the position of the valves is given at the bottom of the page.

Ventricular systole

Ventricular systole

Ventricular systole- the period of contraction of the ventricles, which allows blood to be pushed into the arterial bed.

Several periods and phases can be distinguished in the contraction of the ventricles:

• Voltage period- characterized by the beginning of a contraction of the muscle mass of the ventricles without changing the volume of blood inside them.
  • Asynchronous reduction- the beginning of excitation of the ventricular myocardium, when only individual fibers are involved. The change in ventricular pressure is sufficient to close the atrioventricular valves at the end of this phase.
  • - almost the entire myocardium of the ventricles is involved, but there is no change in the volume of blood inside them, since the efferent (semilunar - aortic and pulmonary) valves are closed. Term isometric contraction is not entirely accurate, since at this time there is a change in the shape (remodeling) of the ventricles and tension of the chordae.
• Exile period- characterized by the expulsion of blood from the ventricles.
  • Quick expulsion- the period from the moment the semilunar valves open until systolic pressure is reached in the ventricular cavity - during this period the maximum amount of blood is ejected.
  • Slow expulsion- the period when the pressure in the ventricular cavity begins to decrease, but is still higher than the diastolic pressure. At this time, the blood from the ventricles continues to move under the influence of the kinetic energy imparted to it, until the pressure in the cavity of the ventricles and efferent vessels equalizes.

In a state of calm, the ventricle of an adult’s heart pumps out 60 ml of blood (stroke volume) for each systole. The cardiac cycle lasts up to 1 s, respectively, the heart makes 60 contractions per minute (heart rate, heart rate). It is easy to calculate that even at rest, the heart pumps 4 liters of blood per minute (cardiac minute volume, MCV). During maximum exercise, the stroke volume of a trained person’s heart can exceed 200 ml, the pulse can exceed 200 beats per minute, and blood circulation can reach 40 liters per minute.

Diastole

Diastole

Diastole- the period of time during which the heart relaxes to accept blood. In general, it is characterized by a decrease in pressure in the ventricular cavity, closure of the semilunar valves and opening of the atrioventricular valves with the movement of blood into the ventricles.

• Ventricular diastole
  • Protodiastole- the period of the beginning of myocardial relaxation with a drop in pressure lower than in the efferent vessels, which leads to the closure of the semilunar valves.
  • - similar to the phase of isovolumetric contraction, but exactly the opposite. The muscle fibers lengthen, but without changing the volume of the ventricular cavity. The phase ends with the opening of the atrioventricular (mitral and tricuspid) valves.
• Filling period
  • Fast filling- the ventricles quickly restore their shape in a relaxed state, which significantly reduces the pressure in their cavity and sucks blood from the atria.
  • Slow filling- the ventricles have almost completely restored their shape, blood flows due to the pressure gradient in the vena cava, where it is 2-3 mm Hg higher. Art.

Atrial systole

It is the final phase of diastole. At a normal heart rate, the contribution of atrial contraction is small (about 8%), since during the relatively long diastole the blood already has time to fill the ventricles. However, with an increase in contraction frequency, the duration of diastole generally decreases and the contribution of atrial systole to ventricular filling becomes very significant.

External manifestations of cardiac activity

The following groups of manifestations are distinguished:

• Electrical- ECG, Ventriculocardiography
• Sound- auscultation, phonocardiography
• Mechanical:
  • Apex beat - palpation, apexcardiography
  • Pulse wave - palpation, sphygmography, venography
  • Dynamic effects - change in center of gravity chest in the cardiac cycle - dynamocardiography
  • Ballistic effects - body shaking at the moment of blood ejection from the heart - ballistocardiography
  • Changes in size, position and shape - ultrasound, x-ray kymography

see also

Links

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See what “Cardiac cycle” is in other dictionaries:

CARDIAC CYCLE, the sequence of events that occur between every two heartbeats. Blood enters the heart when it is relaxed, filling the ATRIUM and VENTRICLES. Compression of the ventricles pushes blood out of the heart, after which the ventricles... ... Scientific and technical encyclopedic dictionary

- (cyclus cardiacus) a set of electrophysiological, biochemical and biophysical processes occurring in the heart during one contraction; the beginning of S. c. It is generally accepted that the appearance of a P wave or potential on an electrocardiogram... ... Large medical dictionary

Cardiac cycle- (cyclus cardiacus) – correct alternation in time of systole and diastole; a set of electrical, mechanical, biochemical, biophysical mechanisms occurring in the heart during one systole and diastole of the atria and ventricles of the heart... Glossary of terms on the physiology of farm animals

The cardiac cycle is a concept that reflects the sequence of processes occurring during one contraction of the heart and its subsequent relaxation. The rate at which the cardiac cycle repeats is called the heart rate. Each cycle includes three... ... Wikipedia

A sequence between two consecutive heartbeats, usually lasting less than one second. The cardiac cycle includes systole, which is divided into periods of isovolumetric contraction and ejection, and... ... Medical terms

CARDIAC CYCLE- (cardiac cycle) a sequence between two consecutive heart contractions, usually taking less than one second. The cardiac cycle includes systole, which is divided into periods of isovolumetric contraction and... ... Explanatory dictionary of medicine

I Polycardiography (Greek poly many + kardia heart + graphō write, depict) a method of non-invasive study of the phase structure of the cardiac cycle, based on measuring the intervals between elements of synchronously recorded sphygmograms... ... Medical encyclopedia

It is proposed to rename this page. Explanation of the reasons and discussion on the Wikipedia page: Towards renaming/April 16, 2012. Perhaps its current name does not correspond to the norms of the modern Russian language and/or the rules for naming articles... Wikipedia

HEART- HEART. Contents: I. Comparative anatomy........... 162 II. Anatomy and histology........... 167 III. Comparative Physiology......... 183 IV. Physiology................... 188 V. Pathophysiology................ 207 VI. Physiology, pat.... ... Great Medical Encyclopedia

I Heart The heart (Latin cor, Greek cardia) is a hollow fibromuscular organ that, functioning as a pump, ensures the movement of blood in the circulatory system. Anatomy The heart is located in the anterior mediastinum (Mediastinum) in the Pericardium between... ... Medical encyclopedia

In vessels, blood moves due to a pressure gradient in the direction from high to low. The ventricles are the organ that creates this gradient.
The change in states of contraction (systole) and relaxation (diastole) of the heart, which is repeated cyclically, is called the cardiac cycle. At a frequency (heart rate) of 75 per minute, the duration of the entire cycle is 0.8 seconds.
It is convenient to consider the cardiac cycle starting from the total diastole of the atria and ventricles (cardiac pause). In this case, the heart is in this state: the semimonthly valves are closed, and the atrioventricular valves are open. Blood from the veins flows freely and completely fills the cavities of the atria and ventricles. The blood pressure in them, as well as in the veins lying nearby, is about 0 mmHg. Art. At the end of total diastole, approximately 180-200 mji of blood is placed in the right and left halves of the heart of an adult.
Atrial systole. Excitation, originating in the sinus node, first enters the atrial myocardium - atrial systole occurs (0.1 s). In this case, due to the contraction of muscle fibers located around the openings of the veins, their lumen is blocked. A kind of closed atrioventricular cavity is formed. When the atrial myocardium contracts, the pressure in them increases to 3-8 mm Hg. Art. (0.4-1.1 kPa). As a result, part of the blood from the atria passes through the open atrioventricular openings into the ventricles, bringing the blood volume in them to 130-140 ml (ventricular end-diastolic volume - EDV). After this, atrial diastole begins (0.7 s).
Ventricular systole. Currently, the leading excitation system spreads to the ventricular cardiomyocytes and ventricular systole begins, which lasts about 0.33 s. it is divided into two periods. Each period accordingly consists of phases.
The first period of tension continues until the semimonthly valves open. For them to open, the pressure in the ventricles must rise to top level than in the corresponding arterial trunks. Diastolic pressure in the aorta is about 70-80 mmHg. Art. (9.3-10.6 kPa), and in the pulmonary artery - 10-15 mm Hg. Art. (1.3-2.0 kPa). The voltage period lasts about 0.08 s.
It begins with a phase of asynchronous contraction (0.05 s), as evidenced by the non-simultaneous contraction of all ventricular fibers. The first to contract are cardiomyocytes, which are located near the fibers of the conduction system.
The next phase of isometric contraction (0.03 s) is characterized by the involvement of all ventricular fibers in the contraction process. The onset of contraction of the ventricles leads to the fact that when the valves are still closed for half a month, blood rushes to the area of ​​​​no pressure - towards the atria. The atrioventricular valves lying in its path are closed by the blood flow. Their inversion into the atrium is prevented by tendon filaments, and the papillary muscles, by contracting, make them even more stable. As a result, closed ventricular cavities are temporarily created. And until, due to contraction in the ventricles, the blood pressure rises above the level required to open the semimonthly valves, a significant contraction of the fibers does not occur. Only their internal tension increases. Thus, during the isometric contraction phase, all heart valves are closed.
The period of blood expulsion begins with the opening of the aortic and pulmonary valves. It lasts 0.25 s and consists of phases of fast (0.12 s) and slow (0.13 s) expulsion of blood. The aortic valves open when the blood pressure is about 80 mmHg. Art. (10.6 kPa), and pulmonary - 15 mm Hg. in (2.0 kPa). The relatively narrow openings of the arteries can immediately allow the entire volume of blood expulsions (70 ml), so myocardial contraction leads to a further increase in blood pressure in the ventricles. In the left it increases to 120-130 mm Hg. Art. (16.0-17.3 kPa), and in the right - up to 20-25 mm Hg. Art. (2.6-3.3 kPa). The high pressure gradient created between the ventricle and the aorta (pulmonary artery) promotes the rapid release of part of the blood into the vessel.
However, due to the relatively small capacity of the vessel, which still contained blood, they overflow. Now the pressure is growing in the vessels. The pressure gradient between the ventricles and vessels gradually decreases, and the speed of blood flow slows down.
Due to the fact that the diastolic pressure in the pulmonary artery is lower, the opening of the blood ejection valves from the right ventricle begins slightly earlier than from the left. And through a low gradient, blood expulsion ends later. Therefore, the diastolic diastolic of the right ventricle is 10-30 ms longer than that of the left.
Diastole. Finally, when the pressure in the vessels rises to the level of pressure in the cavities of the ventricles, the expulsion of blood stops. Their diastole begins, which lasts about 0.47 s. The time of completion of systolic ejection of blood coincides with the time of cessation of ventricular contraction. Typically, 60-70 ml of blood remains in the ventricles (end-systolic volume - ESV). The cessation of expulsion leads to the fact that the blood contained in the vessels closes the semi-monthly valves with reverse flow. This period is called protodiastolic (0.04 s). After this, the tension subsides, and an isometric period of relaxation begins (0.08 s), after which the ventricles, under the influence of incoming blood, begin to straighten.
Currently, the atria after systole are already completely filled with blood. Atrial diastole lasts about 0.7 s. The atria are filled mainly with blood, which flows passively from the veins. But we can also identify an “active” component, which manifests itself due to the partial coincidence of its diastole from ventricular systolic. When the latter contracts, the plane of the atrioventricular septum shifts towards the apex of the heart; As a result, a priming effect is formed.
When the tension in the ventricular wall decreases, the atrioventricular valves open with blood flow. The blood filling the ventricles gradually straightens them.
The period of filling the ventricles with blood is divided into phases of fast (during atrial diastole) and slow (during atrial systolic) filling. Before the start of a new cycle (atrial systole), the ventricles, like the atria, have time to completely fill with blood. Therefore, due to the flow of blood during atrial systole, the intragastric volume increases by only about 20-30%. But this indicator increases significantly with the intensification of the heart, when the total diastole is reduced and the blood does not have time to fill the ventricles.

The cardiac cycle is a complex and very important process. It includes periodic contractions and relaxations, which in medical language are called “systole” and “diastole”. The most important human organ (the heart), which comes second after the brain, resembles a pump in its operation.

Due to excitation, contraction, conduction, and also automaticity, it supplies blood to the arteries, from where it goes through the veins. Due to the different pressures in vascular system this pump works without interruption, so the blood moves without stopping.

What it is

Modern medicine explains in sufficient detail what the cardiac cycle is. It all starts with the systolic work of the atria, which takes 0.1 s. Blood flows to the ventricles while they are in the relaxation stage. As for leaflet valves, they open, and semilunar valves, on the contrary, close.

The situation changes when the atria relax. The ventricles begin to contract, this takes 0.3 s.

When this process just begins, all the valves of the heart remain in a closed position. The physiology of the heart is such that while the muscles of the ventricles contract, pressure is created, which gradually increases. This indicator It also increases where the atria are located.

If we remember the laws of physics, it will become clear why blood tends to move from a cavity in which there is high pressure to a place where it is lower.

Along the way there are valves that do not allow blood to enter the atria, so it fills the cavities of the aorta and arteries. The ventricles stop contracting, and a moment of relaxation occurs at 0.4 s. In the meantime, blood flows into the ventricles without problems.

The purpose of the cardiac cycle is to maintain the functioning of a person's main organ throughout his life.

The strict sequence of phases of the cardiac cycle fits into 0.8 s. The cardiac pause takes 0.4 s. To fully restore heart function, such an interval is quite enough.

Duration of cardiac work

According to medical data, the heart rate ranges from 60 to 80 per minute if a person is in a calm state - both physically and emotionally. After human activity, heart beats become faster depending on the intensity of the load. By the level of arterial pulse you can determine how many heart contractions occur in 1 minute.

The walls of the artery vibrate as they are affected by high blood pressure in the vessels against the background of the systolic work of the heart. As mentioned above, the duration of the cardiac cycle is no more than 0.8 s. The contraction process in the atrium lasts 0.1 s, where the ventricles last 0.3 s, the remaining time (0.4 s) is spent relaxing the heart.

The table shows the exact data of the heart beat cycle.

Phases

Medicine describes 3 main phases that make up the cycle:

1. At first, the atria contract.
2. Ventricular systole.
3. Relaxation (pause) of the atria and ventricles.

An appropriate time is allocated for each phase. The first takes 0.1 s, the second 0.3 s, and the last phase takes 0.4 s.

At each stage, certain actions occur that are necessary for the proper functioning of the heart:

• The first phase involves complete relaxation of the ventricles. As for the leaf valves, they open. The semilunar valves close.
• The second phase begins with the atria relaxing. The semilunar valves open and the leaflet valves close.
• When there is a pause, the semilunar valves, on the contrary, open, and the leaflet valves are in the open position. Some of the venous blood fills the area of ​​the atria, and the rest collects in the ventricle.

The general pause before a new cycle of cardiac activity begins is of great importance, especially when the heart is filled with blood from the veins. At this moment, the pressure in all chambers is almost the same due to the fact that the atrioventricular valves are in an open state.

Excitation is observed in the area of ​​the sinoatrial node, as a result of which the atria contract. When contraction occurs, the volume of the ventricles is increased by 15%. After systole ends, the pressure drops.

Heartbeat

For an adult, the heart rate does not go beyond 90 beats per minute. Children's heart rates increase. Heart infant produces 120 beats per minute, for children under 13 years of age this figure is 100. These are general parameters. Everyone’s values ​​are slightly different - less or more, they are influenced by external factors.

The heart is entwined with nerve threads that control the cardiac cycle and its phases. The impulse coming from the brain to the muscle increases as a result of a serious stressful condition or after physical activity. These can be any other changes in the normal state of a person under the influence of external factors.

The most important role in the work of the heart is played by its physiology, or rather, the changes associated with it. If, for example, the composition of the blood changes, the amount carbon dioxide, there is a decrease in oxygen levels, this leads to a strong shock to the heart. The process of its stimulation intensifies. If changes in physiology affect the blood vessels, then the heart rate, on the contrary, decreases.

The activity of the heart muscle is determined by various factors. The same applies to the phases of cardiac activity. Among these factors is the central nervous system.

For example, increased performance Body temperatures contribute to an accelerated heart rate, while low temperatures, on the contrary, slow down the system. Hormones also affect heart rate. Together with the blood, they flow to the heart, thereby increasing the frequency of beats.

In medicine, the cardiac cycle is considered a rather complex process. It is influenced by numerous factors, some directly, others indirectly. But together, all these factors help the heart function properly.

The structure of heartbeats is no less important for human body. She keeps him alive. An organ such as the heart is complex. It has a generator of electrical impulses, a certain physiology, and controls the frequency of strokes. That is why it works throughout the life of the body.

Only 3 main factors can influence it:

• human life activity;
• hereditary predisposition;
• ecological state of the environment.

Numerous body processes are under the control of the heart, especially metabolic. In a matter of seconds, it can show violations and non-compliance with the established norm. That is why people should know what the cardiac cycle is, what phases it consists of, what their duration is, as well as physiology.

Can be determined possible violations, assessing the work of the heart. And at the first sign of failure, contact a specialist.

Heartbeat phases

As already mentioned, the duration of the cardiac cycle is 0.8 s. The period of tension involves 2 main phases of the cardiac cycle:

1. When asynchronous contractions occur. The period of heart beats, which is accompanied by systolic and diastolic work of the ventricles. As for the pressure in the ventricles, it remains almost the same.
2. Isometric (isovolumic) contractions are the second phase, which begins some time after asynchronous contractions. At this stage, the pressure in the ventricles reaches the level at which the atrioventricular valves close. But this is not enough for the semilunar valves to open.

Pressure levels increase, thus the semilunar valves open. This causes blood to begin leaving the heart. The whole process takes 0.25 s. And it has a phase structure consisting of cycles.

• Quick expulsion. At this stage, the pressure increases and reaches its maximum values.
• Slow expulsion. The period when pressure parameters decrease. Once the contractions are over, the pressure will quickly subside.

After the systolic activity of the ventricles ends, a period of diastolic activity begins. Isometric relaxation. It lasts until the pressure rises to optimal parameters in the atrium.

At the same time, the atrioventricular valves open. The ventricles fill with blood. There is a transition to the rapid filling phase. Blood circulation is carried out due to the fact that different pressure parameters are observed in the atria and ventricles.

In other chambers of the heart, pressure continues to fall. After diastole, a slow filling phase begins, the duration of which is 0.2 s. During this process, the atria and ventricles are continuously filled with blood. By analyzing cardiac activity, you can determine how long the cycle lasts.

Diastolic and systolic work take almost the same time. Therefore, the human heart works for half of its life, and rests for the second half. The total duration time is 0.9 s, but due to the fact that the processes overlap each other, this time is 0.8 s.

The ventricles of the heart form a pressure gradient from high to low. Thanks to it, the blood moves. When the sections contract and relax, a cardiac cycle is formed. Its duration at a contraction frequency of 75 times per minute is 0.8 s. Research and assessment of the process are of diagnostic importance when examining patients with cardiac pathologies. Let's consider this phenomenon in more detail.

Cardiac cycle: diagram. Pause state

It is most convenient to begin considering the phenomenon with the total diastole of the ventricles and atria. The cardiac cycle (heart function) in this case is in a state of pause. In this case, the semimonthly valves of the organ are closed, while the atrioventricular valves, on the contrary, are open. The cardiac cycle (the table will be given at the end of the article) begins with the free flow of venous blood into the cavities of the ventricles and atria. It completely fills these departments. The pressure in the cavities, as well as in the adjacent veins, is at level 0. The cardiac cycle consists of stages in which the movement of blood is carried out due to the relaxation or contraction of the muscles of the organ sections.

Atrial systole

Excitation occurs in the sinus node. First it is sent to the atrial muscle. As a result, systole occurs - contraction. The duration of this stage is 0.1 s. Due to the contraction of muscle fibers located around the venous openings, the lumen of the vessels is blocked. This is how a kind of atrioventricular closed cavity is formed. Against the background of contraction of the atrial muscles, the pressure in these cavities increases to 3-8 mm Hg. Art. Due to this, a certain part of the blood passes from the cavities into the ventricles through the atrioventricular openings. As a result, their volume reaches 130-140 ml. Diastole then enters the cardiac cycle. It lasts 0.7 s.

Cardiac cycle and its phases. Ventricular systole

Its duration is about 0.33 s. Ventricular systole is divided into 2 periods. Each of them has certain phases. 1 period of tension continues until the semi-monthly valves open. For this to happen, the pressure in the ventricles must become higher. It should be greater than in the corresponding arterial trunks. In the aorta, diastolic pressure is at the level of 70-80 mmHg. Art., in the pulmonary artery it is about 10-15 mm Hg. Art. The duration of the voltage period is about 0.8 s. The beginning of this period is associated with the phase of asynchronous contraction. Its duration is 0.05 s. This onset is evidenced by multi-simultaneous contraction of fibers in the ventricles. Cardiomyocytes are the first to react. They are located near the fibers of the conductive structure.

Isometric contraction

This phase lasts about 0.3 s. All ventricular fibers contract simultaneously. The beginning of the process leads to the fact that, with the semi-monthly valves still closed, the blood flow is directed to the zone of zero pressure. Thus, the atria are involved in the cardiac cycle and its phases. The atrioventricular valves lying in the path of blood close. Tendon threads prevent them from everting into the atrium cavity. Papillary muscles give even greater stability to the valves. As a result, the ventricular cavities close for a certain period. And until the moment when, due to contraction, the pressure in them increases above the level that is necessary to open the semi-monthly valves, a significant reduction in the fibers will not occur. Only internal tension increases. During isometric contraction, all heart valves are thus closed.

Expulsion of blood

This is the next period that enters the cardiac cycle. It begins with the opening of the pulmonary artery and aortic valves. Its duration is 0.25 s. This period consists of two phases: slow (about 0.13 s) and fast (about 0.12 s) expulsion of blood. Aortic valves open at a pressure level of 80, and pulmonary valves open at about 15 mm Hg. Art. The entire volume of expelled blood can pass through the relatively narrow openings of the arteries at once. This is approximately 70 ml. In this regard, with subsequent contraction of the myocardium, a further increase in blood pressure in the ventricles occurs. So, in the left it increases to 120-130, and in the right - 20-25 mm Hg. Art. The rapid release of part of the blood into the vessel is accompanied by the formation of an increased gradient between the aorta (artery of the lung) and the ventricle. Due to the insignificant throughput, the vessels begin to overflow. Now the pressure begins to rise in them. There is a gradual decrease in the gradient between the vessels and the ventricles. As a result, blood flow slows down. The pressure in the pulmonary artery is low. In this regard, the expulsion of blood from the left ventricle begins somewhat later than from the right.

Diastole

When vascular pressure rises to the levels of the ventricular cavities, the expulsion of blood stops. From this moment, diastole begins - relaxation. This period lasts about 0.47 s. The moment of cessation of ventricular contraction coincides with the end of blood expulsion. As a rule, the end-systolic volume in the ventricles is 60-70 ml. The completion of expulsion provokes the closure of the semi-monthly valves by the reverse flow of blood contained in the vessels. This period is called prodiastolic. It lasts about 0.04 s. From this moment, tension subsides and isometric relaxation begins. It lasts 0.08 s. After it, the ventricles straighten under the influence of the blood filling them. The duration of atrial diastole is about 0.7 s. Filling of the cavities is carried out mainly by venous, passively entering blood. However, it is possible to highlight the "active" element. When the ventricles contract, the plane of the atrioventricular septum shifts towards the apex of the heart.

Ventricular filling

This period is divided into two phases. Slow corresponds to atrial systole, fast - diastole. Before a new cardiac cycle begins, the ventricles, as well as the atria, have time to completely fill with blood. In this regard, when a new volume arrives during systole, the total intraventricular quantity will increase only by 20-30%. However, this level increases significantly against the background of increased intensity of heart activity during the diastolic period, when blood does not have time to fill the ventricles.

Table

The above describes in detail how the cardiac cycle occurs. The table below summarizes all the stages briefly.

All the best and don’t get sick!