In a healthy person at rest, the normal heart rate is 60-90 beats per minute. A heart rate greater than 90 is called tachycardia, less than 60 - bradycardia.
Cardiac cycle consists of three phases: atrial systole, ventricular systole and general pause(simultaneous diastole of the atria and ventricles). Atrial systole is weaker and shorter than ventricular systole and lasts 0.1-0.15 s. Ventricular systole is more powerful and prolonged, equal to 0.3 s. Atrial diastole takes 0.7-0.75 s, ventricular diastole - 0.5-0.55 s. The total cardiac pause lasts 0.4 s. During this period the heart rests. The entire cardiac cycle lasts 0.8-0.85 s. It is estimated that the ventricles work approximately 8 hours a day (I.M. Sechenov). When the heart rate increases, for example, during muscular work, the cardiac cycle shortens due to a reduction in rest, i.e. general pause. The duration of systole of the atria and ventricles remains almost unchanged. Therefore, if at a heart rate of 70 per minute the total pause is 0.4 s, then when the rhythm frequency is doubled, i.e. 140 beats per minute, the total pause of the heart will be correspondingly half as much, i.e. 0.2 s. Conversely, at a heart rate of 35 per minute, the total pause will be twice as long, i.e. 0.8 s.
During a general pause, the muscles of the atria and ventricles relax, the leaflet valves are open, and the semilunar valves are closed. The pressure in the chambers of the heart drops to 0 (zero), resulting in blood from the vena cava and pulmonary veins, where the pressure is 7 mm Hg. Art., flows into the atria and ventricles by gravity, freely (i.e. passively), filling approximately 70% of their volume. Atrial systole, during which the pressure in them increases by 5-8 mm Hg. Art., causes about 30% more blood to be pumped into the ventricles. Thus, the value of the pumping function of the atrial myocardium is relatively small. The atria mainly play the role of a reservoir for incoming blood, easily changing its capacity due to the small thickness of the walls. The volume of this reservoir can be further increased due to additional containers - atrial appendages, which resemble pouches and can, when expanded, accommodate significant volumes of blood.
Immediately after the end of atrial systole, ventricular systole begins, which consists of two phases: the tension phase (0.05 s) and the blood expulsion phase (0.25 s). The tension phase, including periods of asynchronous and isometric contraction, occurs with the leaflet and semilunar valves closed. At this time, the heart muscle tenses around the incompressible - blood. The length of the myocardial muscle fibers does not change, but as their tension increases, the pressure in the ventricles increases. At the moment when the blood pressure in the ventricles exceeds the pressure in the arteries, the semilunar valves open and blood is ejected from the ventricles into the aorta and pulmonary trunk. The second phase of ventricular systole begins - the phase of blood expulsion, including periods of fast and slow expulsion. Systolic pressure in the left ventricle reaches 120 mmHg. Art., in the right - 25-30 mm Hg. Art. A major role in the expulsion of blood from the ventricles belongs to the atrioventricular septum, which during ventricular systole moves forward to the apex of the heart, and during diastole - back to the base of the heart. This displacement of the atrioventricular septum is called the effect of displacement of the atrioventricular septum (the heart works with its own septum).
After the ejection phase, ventricular diastole begins, and the pressure in them decreases. At the moment when the pressure in the aorta and pulmonary trunk becomes higher than in the ventricles, the semilunar valves slam shut. At this time, the atrioventricular valves open under pressure from the blood accumulated in the atria. A period of general pause begins - a phase of rest and filling of the heart with blood. Then the cycle of cardiac activity is repeated.
12. External manifestations of heart activity and indicators of cardiac activity
TO external manifestations cardiac activities include: apical impulse, heart sounds and electrical phenomena in the heart. Indicators of cardiac activity are systolic and cardiac output.
The apex beat is caused by the fact that the heart turns from left to right during ventricular systole and changes its shape: from ellipsoidal it becomes round. The apex of the heart rises and presses on the chest in the area of the fifth intercostal space on the left. This pressure can be seen, especially in thin people, or palpated with the palm(s) of the hand.
Heart sounds are sound phenomena that occur in the beating heart. They can be heard by placing your ear or stethoscope to your chest. There are two heart sounds: the first sound, or systolic, and the second sound, or diastolic. The first tone is lower, dull and long, the second tone is short and higher. In the origin of the first tone, mainly the atrioventricular valves take part (oscillations of the leaflets when the valves close). In addition, the myocardium of the contracting ventricles and vibrations of the stretching tendon threads (chords) take part in the origin of the first tone. The semilunar valves of the aorta and pulmonary trunk take the main part in the occurrence of the second tone at the moment of their closure (slamming).
Using the phonocardiography (PCG) method, two more tones were detected: III and IV, which are not audible, but can be recorded in the form of curves. The third tone is caused by vibrations of the walls of the heart due to the rapid flow of blood into the ventricles at the beginning of diastole. It is weaker than tones I and II. IV tone is caused by vibrations of the walls of the heart caused by contraction of the atria and the pumping of blood into the ventricles.
At rest, with each systole, the ventricles of the heart emit 70-80 ml into the aorta and pulmonary trunk, i.e. about half of the blood they contain. This is the systolic, or stroke, volume of the heart. The blood remaining in the ventricles is called reserve volume. There is still a residual volume of blood that is not ejected even with the strongest heart rate. At 70-75 contractions per minute, the ventricles emit 5-6 liters of blood, respectively. This is the minute volume of the heart. So, for example, if the systolic volume is 80 ml of blood, and the heart contracts 70 times per minute, then the minute volume will be.
Since childhood, everyone knows that the movement of blood throughout the body is ensured by the heart. To ensure that the whole process runs smoothly, the cardiac cycle represents a clear pattern of phases replacing each other. Each of them is characterized by its own level of blood pressure and takes a certain amount of time to complete. The entire cycle in a healthy person takes only 0.8 seconds, and includes a whole list of different phases. The duration of each of them can be determined by graphically recording a PCG, ECG and sphygmogram, but only a specialist knows what happens in each phase of the cardiac cycle.
To help the average person understand this, this article is presented.
General relaxation
It is easiest to start considering each phase of the cardiac cycle (the table will be presented at the end of the article) with the time of relaxation of the main muscle of the body. In general, the cardiac cycle is a change in contractions and relaxations of the heart.
So, the work of the heart begins with a pause, when the atrioventricular valves are open and the semi-monthly valves are closed. It is in this state that the heart is completely filled with blood from the veins, which enters it completely freely.
Fluid pressure in the heart and adjacent veins is at zero.
Atrial contraction
After the blood completely fills the heart, excitation begins in its sinus region, first provoking contraction of the atrium. In this phase of the cardiac cycle (the table will make it possible to compare the time allocated for each stage), due to muscle tension, the muscles close. venous vessels, and the blood coming from them turns out to be locked in the heart. Further compression of the liquid leads to an increase in pressure in the filled cavities to a maximum of 8 mm Hg. Art. This provokes the movement of fluid through the holes into the ventricles, where its volume reaches 130-140 ml. Then it is replaced by relaxation for 0.7 seconds and the next phase begins.
Ventricular tension takes 0.8 seconds and is divided into several periods. The first is an asynchronous contraction of the myocardium, which takes only 0.05 seconds. It is determined by the alternating contraction of muscles in the ventricles. The fibers located near the conductive structures are the first to begin their tension.
The tension continues until the semi-monthly valves are completely open under the influence of increasing pressure inside the cavities of the heart. To achieve this, the phase ends with an increase in pressure internal fluid more than this moment pressure in the aorta and arteries is determined - 70-80 and 10-15 mm Hg. Art. respectively.
Isometric systole
The previous phase of the cardiac cycle (the table accurately describes the time of each process) continues with the simultaneous tension of all the muscles of the ventricles, which is accompanied by the closure of the inlet valves. The duration of the period is 0.3 seconds, and all this time the blood moves to the zero pressure zone. To prevent closed valves from turning inside out following the fluid, the structure of the heart provides for the presence of special tendons and papillary muscles. As soon as the cavities are filled with blood and the valves close, tension begins to build in the muscles, which further promotes the opening of the semi-monthly valves and the rapid expulsion of blood. Until this happens, specialists record the first heart sound, also called systolic.
At this time, the pressure inside the heart rises above that in the arteries, and when it takes on a rounded shape, it hits the inner surface chest determines This occurs a centimeter from the midclavicular line in the fifth intercostal space.
Exile period
When the fluid pressure inside the heart exceeds the pressure in the arteries and aorta, the next cycle begins. It is marked by the opening of valves to allow blood to exit the cavities and lasts 0.25 seconds. The entire phase can be divided into fast and slow expulsion, which occupy approximately equal periods of time. At first, fluid under pressure quickly rushes into the vessels, but due to their poor throughput, the pressure quickly equalizes and the blood begins to move back. To prevent this, ventricular systole constantly increases, raising the pressure inside the cavities of the heart for the final release of blood. About 70 ml of liquid is distilled at this stage. Since the pressure in the pulmonary artery is low, the release of blood from the left ventricle begins a little later. When all the fluid leaves the cavities of the heart, the myocardium begins to relax, the second heart sound is diastolic. At this time, blood begins to fill the ventricles again as the pressure in them becomes lower.
Relaxation period
The entire duration of diastole takes 0.47 seconds, and when the blood begins to move in the opposite direction, it closes under its own pressure. This period is called protodiastolic.
Its time is only 0.04 seconds, and after it the next period of the cardiac cycle immediately begins - isometric diastole. It lasts 2 times longer than the previous period of relaxation and reduces fluid pressure in the ventricles more than in the atria. Thus, the valves between them open and allow blood to pass from one cavity to another. This is mainly venous blood that enters the heart passively.
Filling
The appearance of the third marks the beginning of filling of the ventricles of the heart, which can be divided into slow and fast. Fast filling is determined by relaxation of the atria, slow filling, on the contrary, by tension. Once the chambers of the heart are completely filled, the next phase of the cycle begins. Until this happens and myocardial tension provokes blood flow into the heart, a fourth sound appears. At intensive work the heart muscle performs each cycle faster.
Abbreviated Contents
The table displays the phases of the cardiac cycle for healthy people in a calm state, therefore it is customary to consider them standard. Of course, minor deviations are often attributed to individual characteristics or slight anxiety before the procedure, so you should be afraid of differences when recording heart cycles only if they significantly exceed the norm or, conversely, decrease.
So, what happens in each phase of the cardiac cycle was described in detail above, now it is proposed to look at the overall picture in an abbreviated form:
Duration in seconds | Pressure in the right ventricle in mm Hg. | In the left ventricle in mm Hg. | In the atrium in mm Hg. |
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Atrial contraction | at first zero, at the end 6-8 | ||||
Systole period | Asynchronous voltage | 6-8, end 9-10 | 6-8 constantly |
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Isometric tension | 10, end 16 | 10, at the end of 81 | 6-8, zero at the end |
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The cycle of exile | first 16, then 30 | first 81, then 120 | |||
Slow | first 30, then 16 | first 120, then 81 | |||
Ventricular relaxation | Protodiastolic period | 16, then 14 | 81, then 79 | ||
Isometric relaxation | 14, then zero | 79, zero at the end | |||
Filling cycle | |||||
Slow |
Periods of contraction
When a person feels the pulse or listens to the heartbeat, only 1 and 2 tones are heard, the rest can only be seen with graphical recording.
The periods of the cardiac cycle can be divided according to other criteria. Thus, experts distinguish refractory periods - absolute, effective and relative, vulnerable period and supernormal phase.
The periods differ in that during the first mentioned the heart muscle is not able to contract on its own, regardless of the external stimulus. The next period already allows the heart to start working with a slight electrical impulse. Next, the heart is activated by a strong stimulus. On the ECG you can see the last two refractory periods as indicated by the electrical systole of the ventricles.
The vulnerable period of the cycle corresponds to muscle relaxation at the completion of all the above phases. In comparison with refractory ones, it is considered short. The last period represents increased excitability of the heart and is detected only in the presence of cardiac depression.
An experienced specialist in deciphering cardiograms always knows to which period a particular heartbeat wave should be attributed, and will correctly determine whether a person has a disease, or whether existing deviations from the norm should be considered as minor features of the body.
Conclusion
Even after a routine heart test, you should not try to decipher the results yourself. This article is offered for review solely so that patients can understand the peculiarities of their heart’s functioning and can better understand what exactly is going wrong in their body. Only experienced doctor is able to simultaneously take into account all the nuances of each case in order to collect them into a single picture and determine the diagnosis. In addition, not all deviations from the norm presented above can be considered a disease.
It is also important to know that the exact conclusion of any specialist cannot be based only on the results of one study. If there is any suspicion, the doctor should prescribe additional examinations.
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 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 open, 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 the heart 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.
Cardiac cycle
This is a period of time during which complete contraction and relaxation of all parts of the heart occurs. Contraction is systole, relaxation is diastole. The length of the cycle will depend on your heart rate. Normally, the contraction frequency ranges from 60 to 100 beats per minute, but average frequency is 75 beats per minute. To determine the cycle duration, divide 60 s by frequency (60 s / 75 s = 0.8 s).
Atrial systole – 0.1 s
Ventricular systole – 0.3 s
Total pause 0.4 s
State of the heart at the end of the general pause. The leaflet valves are open, the semilunar valves are closed, and blood flows from the atria to the ventricles. By the end of the general pause, the ventricles are 70-80% filled with blood. The cardiac cycle begins with
atrial systole, the atria contract to complete the filling of the ventricles with blood. It is the contraction of the atrial myocardium and the increase in blood pressure in the atria - in the right up to 4-6, and in the left up to 8-12 mm that ensures the pumping of additional blood into the ventricles and atrial systole completes the filling of the ventricles with blood. Blood cannot flow back because the circular muscles contract. The ventricles will contain the final diastolic volume blood. On average 120-130 ml, but for people exercising physical activity up to 150-180 ml, which provides more effective work, this department enters the diastole state. Next comes ventricular systole.
Ventricular systole– the most difficult phase of the cycles, duration 0.№-0.№3 s. In systole they secrete tension period, it lasts 0.08 s and period of exile. Each period is divided into 2 phases -
voltage period –
1. phase of asynchronous contraction – 0.05 s and
2. phases of isometric contraction – 0.03 s. This is the phase of isovalumic contraction.
Exile period –
1. rapid ejection phase 0.12s and
2. slow phase 0.!3 s.
Ventricular systole begins with a phase of asynchronous contraction. Some cardiomyocytes become excited and are involved in the excitation process. But the resulting tension in the ventricular myocardium ensures an increase in pressure in it. This phase ends with the closure of the leaflet valves and the ventricular cavity is closed. The ventricles are filled with blood and their cavity is closed, and the cardiomyocytes continue to develop a state of tension. The length of the cardiomyocyte cannot change. This is due to the properties of the liquid. Liquids do not compress. In a confined space, when cardiomyocytes are tense, it is impossible to compress the liquid. The length of cardiomyocytes does not change. Isometric contraction phase. Shortening at low length. This phase is called the isovalumic phase. During this phase, blood volume does not change. The ventricular space is closed, the pressure increases, in the right up to 5-12 mm Hg. in the left 65-75 mmHg, while the ventricular pressure will become greater than the diastolic pressure in the aorta and pulmonary trunk and the excess of the pressure in the ventricles over the blood pressure in the vessels leads to the opening of the semilunar valves. The semilunar valves open and blood begins to flow into the aorta and pulmonary trunk.
The expulsion phase begins, when the ventricles contract, blood is pushed into the aorta, into the pulmonary trunk, the length of cardiomyocytes changes, the pressure increases and at the height of systole in the left ventricle 115-125 mm, in the right ventricle 25-30 mm. At first there is a rapid expulsion phase, and then the expulsion becomes slower. During ventricular systole, 60–70 ml of blood is pushed out and this amount of blood is the systolic volume. Systolic blood volume = 120-130 ml, i.e. There is still a sufficient volume of blood in the ventricles at the end of systole - end systolic volume and this is a kind of reserve so that, if necessary, the systolic output can be increased. The ventricles complete systole and relaxation begins in them. The pressure in the ventricles begins to fall and the blood that is thrown into the aorta, the pulmonary trunk rushes back into the ventricle, but on its way it encounters the pockets of the semilunar valve, which close the valve when filled. This period was called protodiastolic period– 0.04s. When the semilunar valves are closed, the leaflet valves are also closed, the period of isometric relaxation ventricles. It lasts 0.08s. Here the voltage drops without changing the length. This causes a decrease in pressure. Blood has accumulated in the ventricles. Blood begins to put pressure on the atrioventricular valves. They open at the beginning of ventricular diastole. The period of filling the blood with blood begins - 0.25 s, while a rapid filling phase is distinguished - 0.08 and a slow filling phase - 0.17 s. Blood flows freely from the atria into the ventricle. This is a passive process. The ventricles will be 70-80% filled with blood and the filling of the ventricles will be completed by the next systole.
The heart muscle has cellular structure and the cellular structure of the myocardium was established back in 1850 by Kölliker, but long time It was believed that the myocardium is a network of sensations. But only electron microscopy confirmed that each cardiomyocyte has its own membrane and is separated from each other. The contact area is insertion disks. Currently, cardiac muscle cells are divided into cells of the working myocardium - cardiomyocytes of the working myocardium of the atria and ventricles, cells of the conduction system of the heart, in which they are distinguished
The work of the heart is accompanied by changes in pressure in the cavities of the heart and in the vascular system, the appearance of heart sounds, the appearance of pulse fluctuations, etc. The cardiac cycle is a period spanning one systole and one diastole. At a heart rate of 75 per minute, the total duration of the cardiac cycle will be 0.8 s; at a heart rate of 60 per minute, the cardiac cycle will take 1 s. If the cycle takes 0.8 s, then of this ventricular systole accounts for 0.33 s, and ventricular diastole accounts for 0.47 s. Ventricular systole includes following periods and phases:
1) tension period. This period consists of a phase of asynchronous contraction of the ventricles. During this phase, the pressure in the ventricles is still close to zero, and only at the end of the phase does a rapid increase in pressure in the ventricles begin. The next phase of the tension period is the phase of isometric contraction, i.e. this means that the length of the muscles remains unchanged (iso – equal). This phase begins with the slamming of the atrioventricular valves. At this time, the 1st (systolic) heart sound occurs. The pressure in the ventricles increases quickly: up to 70-80 in the left and up to 15-20 mm Hg. in the right. During this phase, the leaflet and semilunar valves are still closed and the volume of blood in the ventricles remains constant. It is no coincidence that some authors, instead of the phases of asynchronous contraction and isometric tension, distinguish the so-called phase of isovolumetric (iso - equal to volume - volume) contraction. There is every reason to agree with this classification. Firstly, the statement about the presence of asynchronous contraction of the working ventricular myocardium, which works as a functional syncytium and has a high speed of propagation of excitation, is very doubtful. Secondly, asynchronous contraction of cardiomyocytes occurs during ventricular flutter and fibrillation. Thirdly, during the phase of isometric contraction, the length of the muscles decreases (and this no longer corresponds to the name of the phase), but the volume of blood in the ventricles at this moment does not change, because both the atrioventricular and semilunar valves are closed. This is essentially a phase of isovolumetric contraction or tension.
2) period of exile. The expulsion period consists of a fast expulsion phase and a slow expulsion phase. During this period, the pressure in the left ventricle increases to 120-130 mm Hg, in the right - up to 25 mm Hg. During this period, the semilunar valves open and blood is released into the aorta and pulmonary artery. Stroke volume of blood, i.e. the volume ejected per systole is about 70 ml, and the end-diastolic volume of blood is approximately 120-130 ml. About 60-70 ml of blood remains in the ventricles after systole. This is the so-called end-systolic, or reserve, blood volume. The ratio of stroke volume to end-diastolic volume (for example, 70:120 = 0.57) is called the ejection fraction. It is usually expressed as a percentage, so 0.57 must be multiplied by 100 and in this case we get 57%, i.e. ejection fraction = 57%. Normally, it is 55-65%. A decrease in the ejection fraction is an important indicator of weakened contractility of the left ventricle.
Ventricular diastole has the following periods and phases: 1) protodiastolic period, 2) period of isometric relaxation and 3) filling period, which in turn is divided into a) fast filling phase and b) slow filling phase. The protodiastolic period takes place from the beginning of ventricular relaxation to the closure of the semilunar valves. After these valves close, the pressure in the ventricles drops, but the leaflet valves are still closed at this time, i.e. the ventricular cavities have no communication with either the atria or the aorta and pulmonary artery. At this time, the volume of blood in the ventricles does not change and therefore this period is called the period of isometric relaxation (or more correctly it should be called the period of isovolumetric relaxation, since the volume of blood in the ventricles does not change). During the period of rapid filling, the atrioventricular valves are open and blood from the atria quickly enters the ventricles (it is generally accepted that blood at this moment enters the ventricles by gravity.). The main volume of blood from the atria into the ventricles enters precisely during the rapid filling phase, and only about 8% of the blood enters the ventricles during the slow filling phase. Atrial systole occurs at the end of the slow filling phase and due to atrial systole, the remaining blood is squeezed out of the atria. This period is called presystolic (meaning presystole of the ventricles), and then a new cycle of the heart begins.
Thus, the heart cycle consists of systole and diastole. Ventricular systole consists of: 1) a period of tension, which is divided into a phase of asynchronous contraction and a phase of isometric (isovolumetric) contraction, 2) a period of ejection, which is divided into a phase of fast ejection and a phase of slow ejection. Before the onset of diastole, there is a proto-diastolic period.
Ventricular diastole consists of: 1) a period of isometric (isovolumetric) relaxation, 2) a period of filling with blood, which is divided into a fast filling phase and a slow filling phase, 3) a presystolic period.
Phase analysis of the heart is carried out using polycardiography. This method is based on synchronous recording of ECG, FCG (phonocardiogram) and sphygmogram (SG) carotid artery. The duration of the cycle is determined by the R–R teeth. The duration of systole is determined by the interval from the beginning of the Q wave on the ECG to the beginning of the 2nd tone on the FCG, the duration of the ejection period is determined by the interval from the beginning of anacrotism to incisura on the SG, the duration of the ejection period is determined by the difference between the duration of systole and the ejection period - the period of tension, by the interval between the beginning of the Q wave ECG and the beginning of the 1st tone of the FCG - the period of asynchronous contraction, according to the difference between the duration of the period of tension and the phase of asynchronous contraction - the phase of isometric contraction.
