CARDIAC CYCLE
Heart healthy person contracts rhythmically at rest with a frequency of 60-80 beats per minute (in young people - up to 90). For highly trained athletes, the lower limit can reach 45 beats per minute.
Cardiac cycle - a period that includes one contraction and subsequent relaxation . A heart rate at rest greater than 90 beats per minute is called tachycardia, and less than 60 - bradycardia.
At a heart rate of 70 beats per minute, the full cycle of cardiac activity lasts 0.8-0.86 s. Normally, the heart rhythm is correct.
Arrhythmia– violation of correctness heart rate. Most types of arrhythmias indicate the development of heart pathology.
Systole- contraction of the heart muscle , diastole - relaxation .
Blood in the cardiovascular system flows in one direction: from the left ventricle, through big circle blood circulation to the right atrium, and from the right atrium to the right ventricle, from the right ventricle along the pulmonary circulation to the left atrium, from the left atrium to the left ventricle.
One-way blood flow depends on the valve apparatus of the heart and the sequential contraction of the heart.
The cardiac cycle has three phases: atrial systole, ventricular systole and general pause.
1. Atrial systole - the beginning of each cycle , duration 0.1 s. During systole, the pressure in the atria increases, which leads to the ejection of blood into the ventricles, which at this moment are relaxed, the leaflets of the atrioventricular valves hang down, and blood passes freely from the atria to the ventricles. After the expulsion of blood from the atria, diastole occurs.
2. Ventricular systole – occurs after the end of atrial systole, lasting 0.3 s. During ventricular systole, the atria are already relaxed. Like the atria, both ventricles - right and left - contract simultaneously. Ventricular systole consists of period of tension and period of exile.
Voltage period- ventricular systole begins with contraction of fibers as a result of the spread of excitation throughout the myocardium. This period is short. IN this moment the pressure in the cavities of the ventricles does not yet increase. It begins to increase sharply when excitability covers all fibers. As a result of an increase in intraventricular pressure, the tendon filaments, which are attached at one end to the leaflet valves and the other to the papillary muscles, are stretched and prevent the atrioventricular valve from everting towards the atrium, the valve closes. At this moment, the semilunar valves (aorta, pulmonary artery) are also still closed, and the ventricular cavity remains closed, the volume of blood in it is constant. Excitation of the myocardial muscle fibers leads to an increase in blood pressure in the ventricles and an increase in tension in them. Appearance heartbeat in the fifth left intercostal space is due to the fact that with an increase in myocardial tension, the left ventricle takes on a rounded shape and produces an impact on the inner surface chest.
Exile period- the blood pressure in the ventricles exceeds the pressure in the aorta and pulmonary artery, the semilunar valves open, their valves are pressed against the inner walls. As a result, blood quickly flows into the aorta and pulmonary trunk, and the volume of the ventricles quickly decreases. With a drop in pressure, the semilunar valves close, impeding the reverse flow of blood from the aorta and pulmonary artery, and the ventricular myocardium begins to relax. A short period begins again, during which the aortic valves are still closed and the atrioventricular valves are not open.
3. Diastole of the atria and ventricles - diastole of the whole heart, duration 0.4 s. Diastole continues until the next atrial systole. Then the cycle of cardiac activity is repeated.
The cardiac cycle lasts 0.8 s. During one heart rate the atria contract for 0.1 s and rest for 0.7 s. The ventricles contract for 0.3 s and rest for 0.5 s.
CYCLE OF THE HEART
Cardiac cycle- a concept reflecting the sequence of processes occurring in one contraction hearts and its subsequent relaxation. Each cycle includes three large stages: systole atria , systoleventricles And diastole . Term systole means muscle contraction. Highlight electrical systole- electrical activity that stimulates myocardium and calls mechanical systole- contraction of the heart muscle and reduction of the heart chambers in volume. Term diastole means muscle relaxation. During the cardiac cycle, blood pressure increases and decreases; accordingly, high pressure at the time 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 asked heart pacemaker.
Periods and phases of the cardiac cycle
Schematic relationship between the phases of the cardiac cycle, ECG, FKG, sphygmograms. Designated ECG waves, numbers of FCG tones and parts of the sphygmogram: a - anacrota, d - dicrota, k - catacrota. The phase numbers correspond to the table. The time scale scale is preserved.
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- 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:
Asynchronous reduction- beginning of excitement 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.
Isovolumetric contraction- 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.
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.
Voltage period- characterized by the beginning of contraction muscle mass ventricles without changing the volume of blood inside them.
Exile period- characterized by the expulsion of blood from the ventricles.
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- 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.
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.
Isovolumetric relaxation- 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.
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.
Ventricular diastole
Filling period
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.
The heart is the main organ human body. His important function is to maintain life. The processes occurring in this organ excite the heart muscle, triggering a process in which contractions and relaxations alternate, which is a vital cycle for maintaining rhythmic blood circulation.
The work of the heart is inherently a change of cyclic periods and continues without stopping. The vitality of the body primarily depends on the quality of the heart.
According to its mechanism of action, the heart can be compared to a pump that pumps blood flows coming from the veins into the arteries. These functions are provided by the special properties of the myocardium, such as excitability, the ability to contract, serve as a conductor, and work in automatic mode.
A feature of myocardial movement is its continuity and cyclicity due to the presence of a pressure difference at the ends of the vascular system (venous and arterial), one of the indicators of which in the main veins is 0 mm Hg, while in the aorta it can reach up to 140 mm.
Cycle duration (systole and diastole)
In order to understand the essence of the cyclic function of the heart, you need to understand what systole is and what diastole is. The first is characterized by the release of the heart from blood fluid, i.e. contraction of the heart muscle is called systole, while diastole is accompanied by filling of the cavities with blood flow.
The process of alternating systole and diastole of the ventricles and atria, as well as what follows general relaxation, is called the cardiac cycle.
Those. The leaflet valves open during systole. When the valve contracts during diastole, blood rushes to the heart.. The pause period also has great importance, because the flap valves are closed during this time to rest.
Table 1. Cycle duration in humans and animals compared
The duration of systole is In humans, the period is essentially the same as diastole, while in animals this period lasts somewhat longer.
The duration of different phases of the heart cycle is determined by the frequency of contractions. Their increase in frequency affects the length of all phases, to a greater extent this applies to diastole, which becomes noticeably shorter. In the resting stage healthy organisms have a frequency of cardiac cycles per minute of up to 70. At the same time, they can have a duration of up to 0.8 s.
Before contractions, the myocardium is relaxed, its chambers are filled with blood fluid coming from the veins. The difference between this period is the complete opening of the valves, and the pressure in the chambers - in the atria and ventricles - remains at the same level. The myocardial excitation impulse originates from the atria.
It then provokes an increase in pressure and, due to the difference, the blood flow is gradually pushed out.
The cyclicity of the heart is distinguished by a unique physiology, because it independently provides itself with an impulse for muscle activity through the accumulation of electrical stimulation.
Phase structure with table
To analyze changes in the heart, you also need to know what phases this process consists of. There are such phases as: contraction, expulsion, relaxation, filling. What are the periods, sequence and place in the heart cycle individual species each of them can be seen in Table 2.
Table 2. Cardiac cycle indicators
| Systole in the atria | 0.1 s | |
|---|---|---|
| Periods | Phases | |
| Ventricular systole0.33 s | voltage - 0.08 s | asynchronous contraction - 0.05 s |
| isometric contraction - 0.03 s | ||
| ejection 0.25 s | fast ejection - 0.12 s | |
| slow ejection - 0.13 s | ||
| Ventricular diastole 0.47 s | relaxation - 0.12 s | Protodiastolic interval - 0.04 s |
| isometric relaxation - 0.08 s | ||
| filling - 0.25 s | fast filling - 0.08 s | |
| slow filling - 0.17 s |
K ardiocycle is divided into several phases with a specific purpose and duration, ensuring the correct direction blood flow in order , precisely established by nature.
Names of cycle phases:
Video: Cardiac cycle
Heart sounds
The activity of the heart is characterized by cyclic sounds produced, they resemble tapping. The components of each blow are two easily distinguishable tones.
One of them arises from contractions in the ventricles, the impulse of which arises from the slamming of the valves that close the atrioventricular openings during myocardial tension, preventing the penetration of blood flow back into the atria.
The sound at this time appears directly when the free edges are closed. The same blow is produced with the participation of the myocardium, the walls of the pulmonary trunk and aorta, and tendon threads.
The next tone occurs during diastole from the movement of the ventricles, being at the same time a consequence of the activity of the semilunar valves, which prevent the blood flow from penetrating back, acting as a barrier. The knocking becomes heard at the moment of connection in the lumen of the edges of the vessels.
In addition to the two most noticeable tones in the heart cycle, there are two more, called the third and fourth. If a phonendoscope is enough to hear the first two, then the rest can only be recorded with a special device.
Listening to heartbeats is extremely important for diagnosing its condition and possible changes, allowing one to judge the development of pathologies. Some ailments of this organ are characterized by a violation of cyclicity, bifurcation of beats, changes in their volume, accompanied by additional tones or other sounds, including squeaks, clicks, and noises.
Video: Auscultation of the heart. Basic tones
Cardiac cycle- a unique physiological reaction of the body created by nature, necessary to maintain its vital functions. This cycle has certain patterns, which include periods of muscle contraction and relaxation.
Based on the results of the phase analysis of the activity of the heart, we can conclude that its two main cycles are intervals of activity and rest, i.e. between systole and diastole are essentially approximately the same.
An important indicator of the health of the human body, determined by the activity of the heart, is the nature of its sounds; in particular, noises, clicks, etc. should cause caution.
In order to avoid the development of pathologies in the heart, timely diagnosis is necessary. medical institution, where a specialist will be able to assess changes in the cardiac cycle based on its objective and accurate indicators.
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 total diastole 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, from the cavities certain part blood passes 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 respond. 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. It only increases internal tension. During isometric contraction, all heart valves are thus closed.
Expulsion of blood
This next period, which is part of 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 an increased gradient formed between the aorta ( pulmonary arteries) and 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!
To move blood through the vessels, it is necessary to create a pressure difference, since the blood flow is carried out from high level to low. This is possible due to the contraction (systole) of the ventricles. During the period of diastole (relaxation), they are filled with blood; the more it enters, the stronger the muscle fibers work, pushing the contents into large vessels.
For diseases of the myocardium, endocrine and nervous pathology the synchrony and duration of parts of the cardiac cycle are disrupted.
Alternate contraction and relaxation of cardiomyocytes ensures synchronous functioning of the entire heart. The cardiac cycle consists of: 
- pauses– general relaxation (diastole) of all parts of the myocardium, atrioventricular valves are opened, blood passes into the cavities of the heart;
- atrial systole– movement of blood into the ventricles;
- ventricular contractions– release of the great vessels.
Atrial
The impulse for myocardial contraction occurs in the sinus node. After the vascular openings are blocked, the atrial cavity becomes closed. At the moment the entire muscle layer is covered by excitation, the fibers are compressed and blood is pushed into the ventricles. The valve flaps open under pressure. The atria then relax.
Normally, the atrial contribution to the total filling of the ventricles is insignificant, since they are already 80% filled during the pause period. But with an increase in the frequency of contractions (flickering, fluttering, fibrillation, supraventricular form of tachycardia), their role in filling increases significantly.
Zheludochkov
The first period of contractions is called myocardial tension. It lasts until the valve flaps of large vessels leaving the ventricles open. Consists of 2 parts: non-simultaneous contraction (asynchronous) and isometric. The latter means the involvement of all myocardial cells in the work. The blood flow closes the atrial valves, and the ventricle is completely closed on all sides.
The second stage (expulsion) begins with the opening of the valve flaps of the pulmonary trunk and aorta. It also has two periods - fast and slow. Upon completion cardiac output the pressure already increases in the vascular network, and when it becomes equal to the heart pressure, systole stops and diastole begins.
Difference between systole and diastole
For the heart muscle, relaxation is no less important than contraction. By apt definition, diastole makes systole. This period is just as active. During this time, actin and myosin filaments diverge in the cardiac muscle, which, according to the Frank-Starling law, determines the force of cardiac output - the greater the stretch, the greater the contraction.
The ability to relax depends on the fitness of the heart muscle; in athletes, due to prolonged diastole, the frequency of contractions is reduced, and blood flow is reduced. coronary vessels at this time it increases. There are two phases during the relaxation period:
- protodiastolic(the reverse movement of blood closes the valve valves of blood vessels);
- isometric- straightening of the ventricles.
This is followed by filling, and then atrial systole begins. Upon completion, the ventricular cavities are ready for subsequent contraction.
Time of systole, diastole, pause
If the heart rate is normal, then the approximate duration of the entire cycle is 800 milliseconds. Of these, individual stages account for (ms):
- atrial contraction 100, relaxation 700;
- ventricular systole 330 – asynchronous tension 50, isometric 30, ejection 250;
- Ventricular diastole 470 – relaxation 120, filling 350.
Expert opinion
Alena Ariko
Expert in Cardiology
That is, for most of life (470 to 330) the heart is in a state active rest. In response to stress impact the frequency of contractions increases precisely due to a decrease in relaxation time. An accelerated pulse is considered one of the risk factors for diseases of the circulatory system, since the myocardium does not have time to recover and accumulate energy for the next beat, which leads to a weakening of the heart.
What determine the phases of systole and diastole?
To the factors that determine the distensibility and subsequent contractility of the myocardium, relate:
- wall elasticity;
- thickness of the heart muscle, its structure (scar changes, inflammation, dystrophy due to malnutrition);
- cavity size;
- structure and patency of valves, aorta, pulmonary artery;
- activity of the sinus node and the speed of propagation of the excitation wave;
- condition of the pericardial sac;
- blood viscosity.
Watch the video about the cardiac cycle:
Reasons for violation of indicators
Violation of myocardial contractility and weakening of systole cause ischemic and dystrophic processes -,. Due to narrowing of the valve openings or difficulty in ejecting blood from the ventricles, the amount of residual blood in their cavities increases, and a reduced volume enters the vascular network.
Such changes are characteristic of congenital and hypertrophic cardiomyopathy, narrowing of the great vessels.
Violation of the formation of an impulse or its movement through the conduction system changes the sequence of myocardial excitation, the synchrony of systole and diastole of parts of the heart, and reduces cardiac output. Arrhythmias change the duration of the phases of the cardiac cycle, the efficiency of ventricular contractions and the possibility of their complete relaxation.
To diseases that are accompanied by diastolic and then systolic dysfunction, also include:
- systemic autoimmune pathologies;
- violations endocrine regulation– diseases thyroid gland, pituitary gland, adrenal glands;
- – an imbalance between parts of the autonomic nervous system.
Cardiac cycle on ECG and ultrasound
An ECG allows one to study the synchronicity of heart function and changes in individual phases of the cardiac cycle. On it you can see the following periods:
- wave P – atrial systole, the rest of the time their diastole continues;
- the ventricular complex 0.16 seconds after P reflects the process of ventricular systole;
- occurs a little earlier than systole ends and relaxation begins (ventricular diastole).
Ultrasound with Doppler ultrasound helps to visualize and measure the parameters of the heart. This diagnostic method provides information about the rate of blood flow into the ventricles, its expulsion, the movement of the valve leaflets, and the magnitude of cardiac output.
Example of speckle-tracking EchoCG. LV along the long axis from the apical position (APLAX), the posterior and anteroseptal segments of the LV are marked Systole means the period of contraction, and diastole means the period of relaxation of the heart. They successively and cyclically replace each other. In turn, each part of the cardiac cycle is divided into phases. In terms of time, most of it occurs in diastole; the usefulness of muscle fiber contractions depends on it.
With pathology of the myocardium, valves, and conduction system, systolic and diastolic functions are impaired. Changes in the functioning of the heart can also occur under the influence of disturbances in hormonal or nervous regulation.
Read also
Systolic and diastolic pressure, or rather, the difference between them, will tell your doctor a lot. Indicators may differ significantly. For example, a small difference, like a big one, will certainly interest the doctor. It will not be ignored if the systolic is higher/lower, the diastolic is low with a normal systolic, etc.
