CARDIAC CYCLE
The main components of the cardiac cycle are systole (contraction) and diastole (expansion) of the atria and ventricles. To date, there is no consensus on the phases of the cycle and the meaning of the term “diastole”. Some authors call only the process of myocardial relaxation diastole. Most authors include in diastole both a period of muscle relaxation and a period of rest (pause), for the stomach
daughters this is a period of filling. Obviously, one should distinguish between systole, diastole and rest (pause) of the atria and ventricles, since diastole, like systole, is a dynamic process.
The cardiac cycle is divided into three main phases, each of which has periods.
Atrial systole - 0.1 s (additional filling of the ventricles with blood).
Ventricular systole - 0.33 s. The tension period is 0.08 s (the asynchronous contraction phase is 0.05 s and the isometric contraction phase is 0.03 s).
The period of blood expulsion is 0.25 s (fast expulsion phase - 0.12 s and slow expulsion phase - 0.13 s).
General cardiac pause - 0,37 With (the period of relaxation is the diastole of the ventricles and their rest, coinciding with the end of the rest of the atria).
The period of ventricular relaxation is 0.12 s (protodiastole - 0.04 s and the isometric relaxation phase - 0.08 s).
The period of the main filling of the ventricles with blood is 0.25 s (fast filling phase - 0.08 s and slow filling phase - 0.17 s).
The entire cycle of cardiac activity lasts 0.8 s at a contraction frequency of 75 per minute. Ventricular diastole and their pause at this heart rate are 0.47 s (0.8 s - 0.33 s = 0.47 s), the last 0.1 s coincides with atrial systole. The cycle is presented graphically in Fig. 13.2.
Let's consider each phase of the cardiac cycle.
A. Atrial systole provides additional blood supply to the ventricles; it begins after a general pause of the heart. At this point, all the muscles of the atria and ventricles are relaxed. The atrioventricular valves are open, they sag into the ventricles, the sphincters, which are the ring muscles of the atria in the area where the veins flow into the atria and perform the function of valves, are relaxed.
Since the entire working myocardium is relaxed, the pressure in the cavities of the heart is zero. Due to the pressure gradient in the cavities of the heart and arterial system semilunar valves are closed.
Excitation and, consequently, the wave of contraction of the atria begins in the area of the confluence of the vena cava, therefore, simultaneously with the contraction of the working myocardium of the atria, the muscles of the sphincters that perform the function of valves also contract - they close, the pressure in the atria begins to increase, and an additional portion of blood (approximately VS from the course -diastolic volume) enters the ventricles.
During atrial systole, blood from them does not return to the vena cava and pulmonary veins, since the sphincters are closed. By the end of systole, the pressure in the left atrium increases to 10-12 mm Hg, in the right - to 4-8 mm Hg. The same pressure is created in the ventricles towards the end of atrial systole. Thus, during atrial systole, the atrial sphincters are closed and the atrioventricular valves are open. Since in the aorta and pulmonary artery Since the blood pressure is higher during this period, the semilunar valves are naturally still closed. After the end of atrial systole, after 0.007 s (intersystolic interval), ventricular systole, atrial diastole and atrial rest begin. The latter last 0.7 s, while the atria are filled with blood (reservoir function of the atria). The significance of atrial systole also lies in the fact that the resulting pressure provides additional stretching of the ventricular myocardium and subsequent intensification of their contractions during ventricular systole.
B. Ventricular systole consists of two periods - tension and expulsion, each of which is divided into two phases. In the phase of asynchronous (non-simultaneous) contraction excitation of muscle fibers spreads throughout both ventricles. Contraction begins from the areas of the working myocardium closest to the conduction system of the heart (papillary muscles, septum, apex of the ventricles). By the end of this phase, all muscle fibers are involved in contraction, so the pressure in the ventricles begins to increase rapidly, as a result of which the atrioventricular valves close and isometric contraction phase. The papillary muscles, which contract together with the ventricles, stretch the tendon threads and prevent the valves from everting into the atria. In addition, the elasticity and extensibility of the
walking threads soften the impact of blood on the atrioventricular valves, which ensures the durability of their operation. The total surface of the atrioventricular valves is larger than the area of the atrioventricular orifice, so their leaflets are pressed tightly against each other. Thanks to this, the valves close reliably even with changes in the volume of the ventricles and blood does not return back to the atria during ventricular systole. During the isometric contraction phase, ventricular pressure increases rapidly. In the left ventricle it increases to 70-80 mm Hg, in the right - to 15-20 mm Hg. As soon as the pressure in the left ventricle is greater than the diastolic pressure in the aorta (70-80 mm Hg), and in the right ventricle - greater than the diastolic pressure in the pulmonary artery (15-20 mm Hg), the semilunar valves open and the period of exile.
Both ventricles contract simultaneously, and the wave of their contraction begins at the apex of the heart and spreads upward, pushing blood out of the ventricles into the aorta and pulmonary trunk. During the expulsion period, the length of the muscle fibers and the volume of the ventricles decrease, the atrioventricular valves are closed, since the pressure in the ventricles is high, and in the atria it is zero. During the period of rapid ejection, the pressure in the left ventricle reaches 120-140 mm Hg. (systolic pressure in the aorta and large arteries of the systemic circle), and in the right ventricle - 30-40 mm Hg. During the period of slow ejection, the pressure in the ventricles begins to fall. The state of the heart valves has not yet changed - only the atrioventricular valves are closed, the semilunar valves are open, the atrial sphincters are also open, because the entire atrial myocardium is relaxed, blood fills the atria.
During the period of expulsion of blood from the ventricles, the process of absorption of blood from large veins into the atria takes place. This is due to the fact that the plane of the atrioventricular “septum”, which is formed by the corresponding valves, shifts towards the apex of the heart, while the atria, which are in a relaxed state, stretch, which helps them fill with blood.
Following the ejection phase, ventricular diastole and their pause (rest) begin, with which the atrial pause partially coincides, therefore this period of cardiac activity is proposed to be called a general cardiac pause.
B. General cardiac pause starts with pro-diastole - This is the period from the beginning of relaxation of the ventricular muscles to the closure of the semilunar valves. The pressure in the ventricles becomes slightly lower than in the aorta and pulmonary artery, so the semilunar valves close. During the isometric relaxation phase The semilunar valves are already closed, and the atrioventricular valves are not yet open. As ventricular relaxation continues, ventricular pressure drops, causing the atrioventricular valves to open with the mass of blood accumulated in the atria during diastole. Begins ventricular filling period the expansion of which is ensured by several factors.
1. Relaxation of the ventricles and expansion of their chambers occurs mainly due to part of the energy that is spent during systole to overcome the elastic forces of the heart (potential energy). During the systole of the heart, its elastic connective tissue frame and muscle fibers, which have different directions in different layers, are compressed. The ventricle in this regard can be compared to a rubber bulb, which takes its previous shape after being pressed; the expansion of the ventricles has some suction effect.
2. The left ventricle (the right - to a lesser extent) during the isometric contraction phase instantly becomes round, therefore, as a result of the gravitational forces of both ventricles and the blood in them, the large vessels on which the heart “hangs” quickly stretch. In this case, the atrioventricular “septum” moves slightly downward. When the muscles of the ventricles relax, the atrioventricular “septum” rises again, which also contributes to the expansion of the ventricular chambers and accelerates their filling with blood.
3. In the rapid filling phase, the blood accumulated in the atria immediately falls into the relaxed ventricles and promotes their expansion.
4. Relaxation of the ventricular myocardium is facilitated by blood pressure in the coronary arteries, which at this time begins to flow intensively from the aorta into the thickness of the myocardium (“hydraulic frame of the heart”).
5. Additional stretching of the ventricular muscles is carried out due to the energy of atrial systole (increased pressure in the ventricles during atrial systole).
6. Residual energy of venous blood imparted to it by the heart during systole (this factor acts in the slow filling phase).
Thus, during the general pause of the atria and ventricles, the heart rests, its chambers are filled with blood, the myocardium is intensively supplied with blood, receives oxygen and nutrients. This is very important, since during systole the coronary vessels are compressed by contracting muscles, while there is practically no blood flow in the coronary vessels.
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 blood 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 contraction muscle mass 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
| Period | Phase | t, | AV valves | SL valves | P pancreas, | P LV, | P atrium, | |
|---|---|---|---|---|---|---|---|---|
| 1 | Atrial systole | 0,1 | ABOUT | Z | Start ≈0 | Start ≈0 | Start ≈0 | |
| Voltage period | 2 | Asynchronous reduction | 0,05 | O→Z | Z | 6-8→9-10 | 6-8→9-10 | 6-8 |
| 3 | Isovolumetric contraction | 0,03 | Z | Z→O | 10→16 | 10→81 | 6-8→0 | |
| Exile period | 4 | Quick expulsion | 0,12 | Z | ABOUT | 16→30 | 81→120 | 0→-1 |
| 5 | Slow expulsion | 0,13 | Z | ABOUT | 30→16 | 120→81 | ≈0 | |
| Ventricular diastole | 6 | Protodiastole | 0,04 | Z | O→Z | 16→14 | 81→79 | 0-+1 |
| 7 | Isovolumetric relaxation | 0,08 | Z→O | Z | 14→0 | 79→0 | ≈+1 | |
| Filling period | 8 | Fast filling | 0,09 | ABOUT | Z | ≈0 | ≈0 | ≈0 |
| 9 | Slow filling | 0,16 | ABOUT | Z | ≈0 | ≈0 | ≈0 | |
| This table is calculated for normal indicators pressure in the large (120/80 mm Hg) and small (30/15 mm Hg) circles of blood circulation, cycle duration 0.8 s. Accepted abbreviations: t- duration of the phase, AV valves- position of the atrioventricular (atrioventricular: mitral and tricuspid) valves, SL valves- position of the semilunar valves (located on the ejection tracts: aortic and pulmonary), P RV- pressure in the right ventricle, P LV- pressure in the left ventricle, P atrium- atrial pressures (combined due to slight differences), ABOUT- valve open position, Z- valve closed position. | ||||||||
Links
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See what “Cardiac cycle” is in other dictionaries:
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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
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Since childhood, everyone knows that the movement of blood throughout the body is ensured by the heart. To ensure the entire process runs smoothly, cardiac cycle represents a clear diagram 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 closed 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 at the 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, its impact on the inner surface of the 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 mmHg. | In the left ventricle in mm Hg. | In the atrium in mm Hg. |
||
Atrial contraction | at first zero, at the end 6-8 | ||||
Systole period | Asynchronous voltage | 6-8, end 9-10 | 6-8 constantly |
||
Isometric tension | 10, end 16 | 10, at the end of 81 | 6-8, zero at the end |
||
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. 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.
Works like a pump. Due to the properties of the myocardium (excitability, ability to contract, conductivity, automaticity), it is able to pump blood into the arteries, which enters it from the veins. It moves non-stop due to the fact that at the ends vascular system(arterial and venous) a pressure difference is formed (0 mm Hg in the main veins and 140 mm in the aorta).
The work of the heart consists of cardiac cycles - continuously alternating periods of contraction and relaxation, which are called systole and diastole, respectively.
Duration
As the table shows, the cardiac cycle lasts approximately 0.8 seconds, if we assume that average frequency contractions range from 60 to 80 beats per minute. Atrial systole takes 0.1 s, ventricular systole - 0.3 s, total diastole hearts - all remaining time equal to 0.4 s.
Phase structure
The cycle begins with atrial systole, which lasts 0.1 seconds. Their diastole lasts 0.7 seconds. Ventricular contraction lasts 0.3 seconds, their relaxation lasts 0.5 seconds. General relaxation chambers of the heart is called a general pause, and it takes in this case 0.4 seconds. Thus, there are three phases of the cardiac cycle:
- atrial systole – 0.1 sec.;
- ventricular systole – 0.3 sec.;
- cardiac diastole (general pause) – 0.4 sec.
The general pause preceding the start of a new cycle is very important for filling the heart with blood.
Before the onset of systole, the myocardium is in a relaxed state, and the chambers of the heart are filled with blood that comes from the veins.
The pressure in all chambers is approximately the same, since the atrioventricular valves are open. Excitation occurs in the sinoatrial node, which leads to contraction of the atria; due to the difference in pressure at the time of systole, the volume of the ventricles increases by 15%. When atrial systole ends, the pressure in them decreases.
Atrial systole (contraction)
Before the onset of systole, blood moves to the atria and they are successively filled with it. Part of it remains in these chambers, the rest is sent to the ventricles and enters them through the atrioventricular openings, which are not closed by valves.
At this moment, atrial systole begins. The walls of the chambers tense, their tone increases, the pressure in them increases by 5-8 mm Hg. pillar The lumen of the veins that carry blood is blocked by annular bundles of myocardium. The walls of the ventricles at this time are relaxed, their cavities are expanded, and blood from the atria quickly rushes there through the atrioventricular openings without difficulty. The duration of the phase is 0.1 seconds. Systole overlaps the end of the ventricular diastole phase. Muscle layer The atria are quite thin because they do not require much force to fill adjacent chambers with blood.
Ventricular systole (contraction)
This is the next, second phase of the cardiac cycle and it begins with tension of the heart muscles. The voltage phase lasts 0.08 seconds and in turn is divided into two more phases:
- Asynchronous voltage – duration 0.05 sec. Excitation of the walls of the ventricles begins, their tone increases.
- Isometric contraction – duration 0.03 sec. The pressure increases in the chambers and reaches significant values.
The free leaflets of the atrioventricular valves floating in the ventricles begin to be pushed into the atria, but they cannot get there due to the tension of the papillary muscles, which stretch the tendon threads that hold the valves and prevent them from entering the atria. At the moment when the valves close and communication between the heart chambers stops, the tension phase ends.
As soon as the voltage reaches its maximum, a period of ventricular contraction begins, lasting 0.25 seconds. The systole of these chambers occurs precisely at this time. About 0.13 sec. the rapid expulsion phase lasts - the release of blood into the lumen of the aorta and pulmonary trunk, during which the valves adhere to the walls. This is possible due to an increase in pressure (up to 200 mmHg in the left and up to 60 in the right). The rest of the time falls on the slow ejection phase: blood is ejected under less pressure and at a lower speed, the atria are relaxed, and blood begins to flow into them from the veins. Ventricular systole is superimposed on atrial diastole.
General pause time
Ventricular diastole begins, and their walls begin to relax. This lasts for 0.45 seconds. The period of relaxation of these chambers is superimposed on the still ongoing atrial diastole, therefore these phases are combined and called a general pause. What happens during this time? The ventricle contracted, expelled blood from its cavity and relaxed. A rarefied space with pressure close to zero formed in it. The blood strives to get back, but the semilunar valves of the pulmonary artery and aorta, closing, prevent it from doing this. Then it is sent through the vessels. The phase that begins with relaxation of the ventricles and ends with the closure of the lumen of the vessels by the semilunar valves is called protodiastolic and lasts 0.04 seconds.
After this, an isometric relaxation phase begins, lasting 0.08 seconds. The valves of the tricuspid and mitral valves are closed and do not allow blood to flow into the ventricles. But when the pressure in them becomes lower than in the atria, the atrioventricular valves open. During this time, blood fills the atria and now freely flows into other chambers. This is a fast filling phase lasting 0.08 seconds. Within 0.17 sec. the slow filling phase continues, during which blood continues to flow into the atria, and a small part of it flows through the atrioventricular openings into the ventricles. During the diastole of the latter, blood enters them from the atria during their systole. This is the presystolic phase of diastole, which lasts 0.1 seconds. Thus the cycle ends and begins again.
Heart sounds
The heart makes characteristic sounds similar to a knock. Each beat consists of two main tones. The first is the result of contraction of the ventricles, or, more precisely, the slamming of valves, which, when the myocardium is tense, block the atrioventricular openings so that blood cannot return to the atria. A characteristic sound is produced when their free edges close. In addition to the valves, the myocardium, the walls of the pulmonary trunk and aorta, and tendon threads take part in creating the shock.
The second sound is formed during ventricular diastole. This is the result of the semilunar valves, which prevent blood from flowing back, blocking its path. A knock is heard when they connect in the lumen of the vessels with their edges.
In addition to the main tones, there are two more - the third and fourth. The first two can be heard using a phonendoscope, while the other two can only be recorded by a special device.
Heartbeats are important diagnostic value. Based on their changes, it is determined that disturbances have occurred in the functioning of the heart. In case of illness, the beats can bifurcate, be quieter or louder, and be accompanied by additional tones and other sounds (squeaks, clicks, noises).
Conclusion
To summarize the phase analysis of cardiac activity, we can say that systolic work takes approximately the same amount of time (0.43 s) as diastolic work (0.47 s), that is, the heart works for half its life, rests for half, and the total cycle time is 0.9 seconds.
When calculating the overall timing of the cycle, you need to remember that its phases overlap each other, so this time is not taken into account, and as a result it turns out that the cardiac cycle lasts not 0.9 seconds, but 0.8.
Contraction of the heart is accompanied by changes in pressure in its cavities and arterial vessels, the appearance of heart sounds, the appearance of pulse waves, etc. With simultaneous graphical recording of these phenomena, the duration of the phases of the cardiac cycle can be determined.
The cardiac cycle is understood as a period covering one contraction - systole, and one relaxation - diastole of the atria and ventricles. An example of synchronous registration of a number of processes during cardiac activity is presented in Fig. 7.8. The curves were recorded at a heart rate of 75 per minute. In this case, the total duration of the cardiac cycle is 0.8 s. Heart contraction begins with atrial systole, lasting 0.1 s. The pressure in the atria rises to 5-8 mm Hg. Art. Atrial systole is replaced by ventricular systole for a long
Rice. 7.8. Schematic curves of changes in pressure in the right (A) and left (B) parts of the heart, heart sounds (C), ventricular volume (D) and electrocardiogram (E).
I-IV - FCG tones; I - phase of atrial contractions; 2 - phase of asynchronous contraction of the ventricles; 3 - phase of isometric contraction of the ventricles; 4 - expulsion phase; 5 - protodiastolic period; 6 - phase of isometric ventricular relaxation;
- - phase of rapid filling of the ventricles;
- - phase of slow ventricular filling.
The voltage period lasts 0.08 s and consists of two phases.
The phase of asynchronous contraction of the ventricular myocardium lasts 0.05 s. The starting point for the beginning of this phase is the Q wave of the ECG, indicating the beginning of ventricular excitation. During this phase, the excitation process and the subsequent contraction process spread throughout the ventricular myocardium. The pressure in the ventricles is still close to zero. By the end of the phase, the contraction covers all myocardial fibers, and the pressure in the ventricles begins to increase rapidly.
The isometric contraction phase (0.03 s) begins with the slamming of the atrioventricular (atrioventricular) valves. In this case, I, or systolic, heart sound occurs. The displacement of the valves and blood towards the atria causes an increase in pressure in the atria. A small peak is visible on the atrial pressure recording curve. The pressure in the ventricles increases quickly: up to 70-80 mm Hg. Art. in the left and up to 15-20 mm Hg. Art. in the right.
The leaflet and semilunar valves (“entry” and “exit” of the ventricles) are still closed, the volume of blood in the ventricles remains constant. Due to the fact that the fluid is practically incompressible, the length of the myocardial fibers does not change, only their tension increases. Blood pressure in the ventricles increases rapidly. The left ventricle quickly takes on a round shape and hits the inner surface with force chest wall. In the fifth intercostal space, 1 cm to the left of the midclavicular line, the apical impulse is detected at this moment.
Towards the end of the period of tension, the rapidly increasing pressure in the left and right ventricles becomes higher than the pressure in the aorta and pulmonary artery. Blood from the ventricles rushes into these vessels.
The period of blood expulsion from the ventricles lasts 0.25 s and consists of a fast phase (0.12 s) and a slow ejection phase (0.13 s). At the same time, the pressure in the ventricles increases: in the left one up to 120-130 mm Hg. Art., and in the right up to 25 mm Hg. Art. At the end of the slow ejection phase, the ventricular myocardium begins to relax and diastole begins (0.47 s). The pressure in the ventricles drops, blood from the aorta and pulmonary artery rushes back into the ventricular cavities and slams the semilunar valves, and a second, or diastolic, heart sound occurs.
The time from the beginning of ventricular relaxation to the closure of the semilunar valves is called the protodiastolic period (0.04 s). After the semilunar valves close, the pressure in the ventricles drops. The leaflet valves are still closed at this time, the volume of blood remaining in the ventricles, and therefore the length of the myocardial fibers, does not change, therefore this period is called the period of isometric relaxation (0.08 s). Towards the end, the pressure in the ventricles becomes lower than in the atria, the atrioventricular valves open and blood from the atria enters the ventricles. The period of filling the ventricles with blood begins, which lasts 0.25 s and is divided into phases of fast (0.08 s) and slow (0.17 s) filling.
Vibrations of the walls of the ventricles due to the rapid flow of blood to them cause the appearance of the third heart sound. Towards the end of the slow filling phase, atrial systole occurs. The atria pump additional blood into the ventricles (presystolic period equal to 0.1 s), after which a new cycle of ventricular activity begins.
Vibration of the walls of the heart, caused by contraction of the atria and additional flow of blood into the ventricles, leads to the appearance of the IV heart sound.
During normal listening of the heart, loud I and II tones are clearly audible, and quiet III and IV tones are detected only with graphical recording of heart sounds.
The sequence of individual phases of the ventricular activity cycle can be presented as follows: 
For phase analysis of the cardiac cycle in humans, cardiac catheterization is usually not performed, but a number of non-invasive methods are used. In particular, the polycardiography method, based on the synchronous recording of an ECG, phonocardiogram (PCG) and sphygmogram (SG), has become widespread. carotid artery(Fig. 7.9). On the synchronous recording of these curves R-R interval
Rice. 7.9. Criteria for dividing the heart cycle into phases. Explanation in the text.
The ECG determines the duration of the cycle (1), the duration of systole is determined by the interval from the beginning of the Q wave on the ECG to the beginning of the second tone on the FCG (2), the duration of the expulsion period is determined by the interval from the beginning of anacrotic to incisura on the SG (3), and the difference between the duration systole and the ejection period - the period of tension (4), according to the interval between the beginning of the Q wave of the ECG and the beginning of the first sound of the PCG - the period of asynchronous contraction (5), according to the difference between the duration of the period of tension and the phase of asynchronous contraction - the phase of isometric contraction (6).
