Cardiac cycle. Cycle of cardiac activity Cardiac cycle and its phase structure
In the vessels, the blood moves due to the pressure gradient in the direction from high to low. The ventricles are the organ that creates this gradient.
The change in states of contraction (systole) and relaxation (diastole) of the parts of the heart, which is repeated cyclically, is called the cardiac cycle. At a frequency (HR) of 75 per 1 min, the duration of the entire cycle is 0.8 s.
It is convenient to consider the cardiac cycle, starting with the total diastole of the atria and ventricles (pause of the heart). In this case, the heart is in this state: the crescent valves are closed, and the atrioventricular valves are open. Blood from the veins enters freely and completely fills the cavities of the atria and ventricles. The blood pressure in them, as well as in the veins lying nearby, is about 0 mm Hg. Art. Approximately 180-200 mji of blood is placed in the right and left halves of the heart of an adult at the end of the total diastole.
Atrial systole. Excitation, originated in the sinus node, first enters the atrial myocardium - atrial systole occurs (0.1 s). At the same time, due to the contraction of the muscle fibers located around the openings of the veins, their lumen is blocked. A kind of closed atrioventricular cavity is formed. With the contraction of the atrial myocardium, the pressure in them rises to 3-8 mm Hg. Art. (0.4-1.1 kPa). As a result, part of the blood from the atria through the open atrioventricular openings passes into the ventricles, bringing the volume of blood in them to 130-140 ml (end-diastolic ventricular volume - EDV). After that, atrial diastole begins (0.7 s).
Systole of the ventricles. At present, the leading system of excitation spreads to ventricular cardiomyocytes and ventricular systole begins, which lasts about 0.33 s. it is divided into two periods. Each of the periods respectively consists of phases.
The first period of tension continues until the crescent valves open. For them to open, the pressure in the ventricles must rise to a higher level than in the corresponding arterial trunks. Diastolic pressure in the aorta is about 70-80 mm Hg. Art. (9.3-10.6 kPa), and in the pulmonary artery - 10-15 mm Hg. Art. (1.3-2.0 kPa). The voltage period lasts about 0.08 s.
It begins with a phase of asynchronous contraction (0.05 s), as evidenced by the non-simultaneous contraction of all ventricular fibers. The first to contract are cardiomyocytes, which are located near the fibers of the conducting system.
The next phase of isometric contraction (0.03 s) is characterized by the involvement of all ventricular fibers in the process of contraction. The beginning of the contraction of the ventricles leads to the fact that with the half-monthly valves closed, the blood rushes to the area of \u200b\u200bno pressure - towards the atria. The atrioventricular valves lying in its path are closed by the blood flow. Their eversion into the atrium is prevented by tendon threads, and the papillary muscles, by contracting, make them even more stable. As a result, closed cavities of the ventricles are temporarily created. And until, due to contraction in the ventricles, the blood pressure rises above the level necessary to open the crescent valves, there is no significant contraction of the fibers. Only their internal tension increases. Thus, in the phase of isometric contraction, all the valves of the heart are closed.
The period of expulsion of blood begins with the opening of the valves of the aorta and pulmonary artery. It lasts 0.25 s and consists of phases of fast (0.12 s) and slow (0.13 s) expulsion of blood. The aortic valves open at a blood pressure of about 80 mm Hg. Art. (10.6 kPa), and pulmonary - 15 mm Hg. in (2.0 kPa). The relatively narrow openings of the arteries can immediately miss the entire volume of blood ejection (70 ml), so the contraction of the myocardium leads to a further increase in blood pressure in the ventricles. In the left, it rises to 120-130 mm Hg. Art. (16.0-17.3 kPa), and in the right - up to 20-25 mm Hg. Art. (2.6-3.3 kPa). The high pressure gradient created between the ventricle and the aorta (pulmonary artery) contributes to the rapid ejection of part of the blood into the vessel.
However, due to the relatively small capacity of the vessel, in which there was still blood, they overflow. Now the pressure is rising already in the vessels. The pressure gradient between the ventricles and vessels gradually decreases, and the rate of blood flow slows down.
Due to the fact that the diastolic pressure in the pulmonary artery is lower, the opening of the valves for expelling blood from the right ventricle begins somewhat earlier than from the left. And through a low gradient of expulsion of blood ends later. Therefore, the diastolic of the right ventricle is 10-30 ms longer than that of the left.
Diastole. At the end, when the pressure in the vessels rises to the level of pressure in the cavities of the ventricles, the expulsion of blood stops. Their diastole begins, which lasts about 0.47 s. The end time of systolic expulsion of blood coincides with the time of cessation of ventricular contraction. Usually 60-70 ml of blood remains in the ventricles (end-systolic volume - ESC). The cessation of exile leads to the fact that the blood contained in the vessels closes the crescent valves with a reverse current. This period is called protodiastolic (0.04 s). After that, the tension subsides, and an isometric period of relaxation (0.08 s) sets in, after which the ventricles, under the influence of the incoming blood, begin to straighten out.
Currently, the atria after systole are already completely filled with blood. Atrial diastole lasts about 0.7 s. The atria are filled mainly with blood, passively follows from the veins. But it is possible to single out the "active" component, which manifests itself in connection with the partial coincidence of its diastole from the systolic ventricles. With the reduction of the latter, the plane of the atrioventricular septum shifts towards the apex of the heart; as a result, a smoky effect is formed.
When the tension of the wall of the ventricles subsides, the atrioventricular valves open with blood flow. The blood filling the ventricles gradually straightens them.
The period of filling the ventricles with blood is divided into phases of fast (with atrial diastole) and slow (with atrial systolic) filling. Before the start of a new cycle (atrial systole), the ventricles, like the atria, have time to completely fill with blood. Therefore, due to the flow of blood during atrial systole, the intragastric volume increases by approximately only 20-30%. But this figure increases significantly with the intensification of the work of the heart, when the total diastole is reduced and the blood does not have time to fill the ventricles.
Cardiac cycle
This is a period of time during which there is a complete contraction and relaxation of all parts of the heart. Contraction is systole, relaxation is diastole. The duration of the cycle will depend on the heart rate. The normal frequency of contractions ranges from 60 to 100 beats per minute, but the average frequency is 75 beats per minute. To determine the duration of the cycle, we divide 60s by the frequency. (60s / 75s = 0.8s).
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 cuspid 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 8-12mm, it ensures the injection of additional blood into the ventricles and the atrial systole completes the filling of the ventricles with blood. Blood cannot flow back, as the circular muscles contract. The ventricles will contain the final diastolic volume blood. On average, 120-130 ml, but in people engaged in physical activity up to 150-180 ml, which ensures more efficient work, this department goes into a state of diastole. Next comes ventricular systole.
Ventricular systole- the most difficult phase of the cycles, duration 0,#-0,#3 s. secreted in systole stress period, it lasts 0.08 s and period of exile. Each period is divided into 2 phases -
stress period -
1. asynchronous contraction phase - 0.05 s and
2. phases of isometric contraction - 0.03 s. This is the isovalumin contraction phase.
Exile period -
1. fast ejection phase 0.12s and
2. slow phase 0.!3 s.
Ventricular systole begins with a phase of asynchronous contraction. Some cardiomyocytes are excited and are involved in the process of excitation. But the resulting tension in the myocardium of the ventricles provides an increase in pressure in it. This phase ends with the closing of the flap valves and the cavity of the ventricles 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. It has to do with the properties of the liquid. Liquids do not compress. In a closed space, when there is a tension of cardiomyocytes, it is impossible to compress the liquid. The length of cardiomyocytes does not change. Isometric contraction phase. Cut at low length. This phase is called the isovaluminic phase. In this phase, the volume of blood does not change. The space of the ventricles is closed, the pressure rises, in the right up to 5-12 mm Hg. in the left 65-75 mm Hg, while the pressure of the ventricles becomes greater than the diastolic pressure in the aorta and pulmonary trunk and the excess 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 exile phase begins, with the contraction of the ventricles, the 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 25-30 mm. Initially, the fast ejection phase, and then the ejection becomes slower. During the systole of the ventricles, 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 enough blood in the ventricles at the end of systole end systolic volume and this is a kind of reserve, so that if necessary - to increase systolic output. The ventricles complete systole and begin to relax. The pressure in the ventricles begins to fall and the blood that is ejected into the aorta, the pulmonary trunk rushes back into the ventricle, but on its way it meets the pockets of the semilunar valve, which, when filled, close the valve. This period is called proto-diastolic period- 0.04s. When the semilunar valves close, the cuspid valves also close, period of isometric relaxation ventricles. It lasts 0.08s. Here, the voltage drops without changing the length. This causes a pressure drop. Blood accumulated in the ventricles. The blood begins to press on the atrioventricular valves. They open at the beginning of ventricular diastole. There comes a period of blood filling with blood - 0.25 s, while a fast 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 filled with blood by 70-80% and the filling of the ventricles will be completed by the next systole.
The cardiac muscle has a cellular structure and the cellular structure of the myocardium was established back in 1850 by Kelliker, but for a long time it was believed that the myocardium is a network of sensations. And only electron microscopy confirmed that each cardiomyocyte has its own membrane and is separated from each other. Contact area - insert discs. Currently, cardiac muscle cells are divided into cells of the working myocardium - cardiomyocytes of the working myocard of the atria and ventricles of the cells of the conduction system of the heart, in which they secrete
Since childhood, everyone knows that the movement of blood throughout the body provides the heart. In order for the whole process to run smoothly, the cardiac cycle is 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, while it includes a whole list of different phases. The duration of each of them can be determined by graphic registration of PCG, ECG and sphygmogram, but only a specialist knows what happens in each phase of the cardiac cycle.
To understand this and an ordinary person, this article is presented.
General relaxation
Consideration of each phase of the cardiac cycle (the table will be presented at the end of the article) is easiest to start with the time of relaxation of the main muscle of the body. In general, the cardiac cycle is a change of 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 section, provoking the contraction of the atrium first. In this phase of the cardiac cycle (the table will make it possible to compare the time allotted for each stage), due to muscle tension, the venous vessels are closed, and the blood that has come from them is closed in the heart. Further compression of the liquid leads to an increase in pressure in the filled cavities up 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. After that, it is replaced by relaxation for 0.7 seconds and the next phase begins.
The tension of the ventricles takes 0.8 seconds and is divided into several periods. The first is an asynchronous myocardial contraction that takes only 0.05 seconds. It is determined by the alternating contraction of the muscles in the ventricles. The fibers located near the conductive structures begin their voltage first.
The tension continues until the semi-monthly valves are fully open under the influence of growing pressure inside the cavities of the heart. For this, the phase ends with an increase in the pressure of the internal fluid more than the pressure in the aorta and arteries is currently 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 closing of the inlet valves. The duration of the period is 0.3 seconds, and the blood moves into the zone of zero pressure all this time. To prevent closed valves from turning out after the liquid, 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 increase in the muscles, which further contributes to the opening of the crescent 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 present in the arteries, and when it takes on a rounded shape, its impact on the inner surface of the chest determines. This happens a centimeter from the midclavicular line in the fifth intercostal space.
Period of exile
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 for the exit of blood from the cavities and lasts 0.25 seconds. The whole phase can be divided into fast and slow ejection, which take approximately the same time periods. At first, fluid under pressure quickly rushes into the vessels, but due to their poor capacity, the pressure quickly equalizes, and the blood begins to move back. To prevent this, the ventricular systole is constantly increasing, 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 cavity of the heart, the relaxation of the myocardium begins, the second heart sound is diastolic. At this time, the blood begins to fill the ventricles again, as the pressure in them becomes lower.
Relaxation period
The entire time 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 relaxation period and provides a decrease in 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 the filling of the ventricles of the heart, which can be divided into slow and fast. Fast filling is determined by the relaxation of the atria, slow - on the contrary, by tension. As soon as the cavities of the heart are completely filled, the next phase of the cycle begins. Until this happens and myocardial tension provokes blood flow to the heart, a fourth tone appears. With intensive work, the heart muscle performs each cycle faster.
Abbreviated content
The table displays the phases of the cardiac cycle for healthy people in a calm state, therefore it is customary to consider them as reference ones. Of course, minor deviations are often attributed to individual characteristics or slight excitement before the procedure, therefore, one should be afraid of differences when registering heart cycles only if their norm is significantly exceeded or, conversely, lowered.
So what happens in each phase of the cardiac cycle has been described in detail above, now it is proposed to look at the big 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. |
||
Atrial contraction | zero at first, 6-8 at the end | ||||
systole period | Asynchronous voltage | 6-8, at the end of 9-10 | 6-8 constantly |
||
Isometric tension | 10, at the end of 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 | |||
Relaxation of the ventricles | Proto-diastolic period | 16 then 14 | 81 then 79 | ||
Isometric relaxation | 14 then zero | 79, zero at the end | |||
Filling cycle | |||||
Slow |
Reduction periods
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 graphic registration.
The periods of the cardiac cycle can be divided according to other criteria. So, experts distinguish refractory periods - absolute, effective and relative, vulnerable period and supernormal phase.
The periods differ in that during the first mentioned period, the heart muscle is not able to contract on its own, regardless of an external stimulus. The next period already allows the start of the heart with a slight electrical impulse. Further, the heart is activated already with a strong stimulus. On the ECG, you can see the last two refractory periods as indicated by equal to the electrical systole of the ventricles.
The vulnerable period of the cycle corresponds to the relaxation of the muscles at the end of the work of all the above phases. Compared to refractory, it is considered short. The last period is an increased excitability of the heart and is found only in the presence of depression of the heart.
An experienced specialist in deciphering cardiograms always knows to which period this or that wave of the heartbeat should be attributed, and will correctly determine whether a person has a disease, or existing deviations from the norm should be considered as minor features of the body.
Conclusion
Even after a routine study of the work of the heart, you should not try to decipher the results on your own. This article is offered for review solely so that patients can understand the peculiarities of the work of their heart and be able to better understand what exactly is going wrong in their body. Only an experienced doctor is able to take into account all the nuances of each case at the same time in order to collect them into a single picture and determine the diagnosis. In addition, not all deviations from the above norm 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. In case of any suspicion, the doctor should prescribe additional examinations.
The human body functions due to the presence of the circulatory system and cellular nutrition. The heart as the main organ of the circulatory system is able to provide uninterrupted supply of tissues with energy substrates and oxygen. This is achieved due to the cardiac cycle, the sequence of phases of the work of the body, associated with a constant alternation of rest and load.
This concept should be considered from several points of view. Firstly, from the morphological point of view, that is, from the point of view of a basic description of the phases of the work of the heart as an alternation of systole with diastole. Secondly, with hemodynamic, associated with the decoding of capacitive and barometric characteristics in the cavities of the heart at each stage of systole and diastole. Within the framework of these points of view, the concept of the cardiac cycle and its constituent processes will be considered below.
Characteristics of the work of the heart
The uninterrupted work of the heart from the moment of its laying in embryogenesis until the death of the organism is ensured by the alternation of systole with diastole. This means that the body does not work constantly. Most of the time, the heart even rests, which allows it to provide for the needs of the body throughout life. The work of some structures of the body occurs at the time of rest of others, which is necessary to ensure the constancy of blood circulation. In this context, it is appropriate to consider the cycle of heart contractions from a morphological point of view.
Fundamentals of morphophysiology of the heart
The heart in mammals and humans consists of two atria that flow into the ventricular cavities (VP) through the atrioventricular (AV) orifices with valves (AVK). Systole and diastole alternate, and the cycle ends with a general cardiac pause. As soon as blood is ejected from the VP into the aorta and pulmonary artery, the pressure in them drops. A retrograde current develops from these vessels back into the ventricles, which is quickly stopped by the opening of the valves. But at this time, the atrial hydrostatic pressure is higher than the ventricular pressure, and the AVKs are forced to open. As a result, on the pressure difference, at the moment when the systole of the ventricles has passed, but the atria have not come, ventricular filling occurs.
This period is also called a general cardiac pause, which lasts until the pressure in the cavities of the ventricles (RV) and the atria (AP) of the corresponding side equalizes. As soon as this has happened, atrial systole begins to push the remaining portion of blood into the pancreas. After it, when the rest of the blood is squeezed out into the ventricular cavities, the pressure in the right ventricle drops. This causes a passive inflow of blood: venous discharge from the pulmonary veins is carried out into the left atrium, and from the hollow ones into the right atrium.
Systemic view of the cardiac cycle
The cycle of cardiac activity begins with ventricular systole - expulsion of blood from their cavities along with simultaneous atrial diastole and the beginning of their passive filling on the pressure difference in the afferent vessels, where at this moment it is higher than in the atria. After ventricular systole, a general cardiac pause occurs - the continuation of passive atrial filling with negative pressure in the ventricles.
Due to the higher hemodynamic pressure in the RA and the low hemodynamic pressure in the RV, along with the continuation of passive atrial filling, the AV valves open. The result is passive ventricular filling. As soon as the pressure in the atrial and ventricular cavities equalizes, passive current becomes impossible, and atrial replenishment stops, which causes them to contract in order to pump an additional portion into the ventricular cavities.
From the atrial systole, the pressure in the ventricular cavities increases significantly, ventricular systole is provoked - the muscle contraction of its myocardium. The result is an increase in pressure in the cavities and the closure of atrioventricular connective tissue valves. Due to the reset at the mouth of the aorta and the pulmonary trunk, pressure is formed on the corresponding valves, which are forced to open in the direction of the blood flow. This completes the cardiac cycle: the heart again begins passive filling of the atria in their diastole and then at the moment of a general cardiac pause.
Cardiac pauses
There are many episodes of rest in the work of the heart: diastole in the atria and ventricles, as well as a general pause. Their duration can be calculated, although it depends very much on the heart rate. At 75 beats / min, the cardiac cycle time will be 0.8 seconds. This period included atrial systole (0.1 s) and ventricular contraction - 0.3 seconds. This means that the atria rest for approximately 0.7 s and the ventricles for 0.5. During the rest, a general pause (0.5 s) is also included.
About 0.5 seconds the heart passively fills, and 0.3 seconds it contracts. Atria, the relaxation time is 3 times longer than in the ventricles, although they pump similar volumes of blood. However, they mostly enter the ventricles by passive current along the pressure gradient. Blood by gravity at the moment of low pressure in the cardiac cavities enters the cavities, where it accumulates for subsequent contraction and expulsion into the efferent vessels.
The meaning of periods of relaxation of the heart
In the cavity of the heart, blood enters through the holes: into the atria - through the mouths of the hollow and pulmonary veins, and into the ventricles - through the AVK. Their capacity is limited, and the actual filling takes longer than its expulsion through the circulation. And the phases of the cardiac cycle are exactly what are needed for sufficient filling of the heart. The smaller these pauses, the less the atria will be filled, the less blood will be sent to the ventricles and, accordingly, through the circles of blood circulation.
With an increase in the actual frequency of contractions, which is achieved by shortening the relaxation period, the filling of the cavities decreases. This mechanism still remains effective for the rapid mobilization of the functional reserves of the body, but an increase in the frequency of contractions gives an increase in the minute volume of blood circulation only up to a certain limit. Upon reaching a high frequency of contractions, the filling of the cavities due to the extremely short diastole will drop significantly, as will the level of blood pressure.
Tachyarrhythmias
The mechanism described above is the basis for reducing physical endurance in a patient with tachyarrhythmias. And if sinus tachycardia, if necessary, allows you to increase pressure and mobilize the resources of the body, then atrial fibrillation, supraventricular and ventricular tachycardia, ventricular fibrillation, and ventricular tachysystole in WPW syndrome lead to a drop in pressure.
The manifestation of the patient's complaints and the severity of his condition starts from discomfort and shortness of breath to loss of consciousness and clinical death. The phases of the cardiac cycle, discussed above in terms of the importance of pauses and their shortening in tachyarrhythmias, are the only simple explanation why arrhythmias should be treated if they have a negative hemodynamic contribution.
Features of atrial systole
Atrial (atrial) systole lasts about 0.1 s: the atrial muscles contract simultaneously in accordance with the rhythm generated by the sinus node. Its importance lies in pumping approximately 15% of the blood into the cavity of the ventricles. That is, if the left ventricle is about 80 ml, then about 68 ml of this portion passively filled the ventricle in atrial diastole. And only 12 ml is pumped by atrial systole, which allows you to increase the pressure level in order to close the valves during ventricular systole.
Atrial fibrillation
In conditions of atrial fibrillation, their myocardium is constantly in a state of chaotic contraction, which does not allow the formation of a whole atrial systole. Because of this, arrhythmia makes a negative hemodynamic contribution - it impoverishes blood flow to the ventricular cavities by about 15-20%. Their filling is carried out by gravity during a general cardiac pause and during the period of ventricular systole. That is why some part of the portion of the blood always lingers in the atria and is constantly shaken up, greatly increasing the risk of thrombosis in the circulatory system.
The retention of blood in the cavities of the heart, and in this case in the atria, leads to their gradual stretching and makes it impossible to maintain the rhythm with a successful cardioversion. Then the arrhythmia will become constant, which accelerates the development of cardiac insufficiency with stagnation and hemodynamic disturbances in the circles of blood circulation by 20-30%.
Phases of ventricular systole
With a cardiac cycle duration of 0.8 s, the ventricular systole will be 0.3 - 0.33 seconds with two periods - tension (0.08 s) and expulsion (0.25 s). The myocardium begins to contract, but its efforts are not enough to squeeze blood out of the ventricular cavity. But the pressure created already allows the atrial valves to close. The ejection phase occurs at the moment when systolic pressure in the ventricular cavities allows a portion of blood to be expelled.
The tension phase in the cardiac cycle is divided into asynchronous and isometric contractions. The first lasts about 0.05 s. and is the beginning of an integral contraction. An asynchronous (random) contraction of myocytes develops, which does not lead to an increase in pressure in the ventricular cavity. Then, after excitation covers the entire mass of the myocardium, the phase of isometric contraction is formed. Its importance lies in a significant increase in pressure in the cavity of the ventricles, which allows you to close the atrioventricular valves and prepare to push blood into the pulmonary trunk and aorta. Its duration in the cardiac cycle is 0.03 seconds.
Period of exile phase of ventricular systole
Ventricular systole proceeds to the expulsion of blood into the cavity of the efferent vessels. Its duration is a quarter of a second, and it consists of a fast and a slow phase. First, the pressure in the ventricular cavities rises to maximum systolic, and muscle contraction pushes out of their cavity a portion of about 70% of the actual volume. The second phase is slow ejection (0.13 s): the heart pumps the remaining 30% of the systolic volume into the efferent vessels, however, this occurs already with a decrease in pressure, which precedes ventricular diastole and a general cardiac pause.
Phases of ventricular diastole
Ventricular diastole (0.47 s) includes a period of relaxation (0.12 seconds) and filling (0.25 seconds). The first is divided into protodiastolic and myocardial isometric relaxation phase. The filling period in the cardiac cycle consists of two phases - fast (0.08 sec) and slow (0.17 sec).
During the proto-diastolic period (0.04 s.), the transitional stage between ventricular systole and diastole, the pressure in the ventricular cavities drops, which causes the aortic and pulmonary valves to close. In the second phase, a period of zero pressure begins in the ventricular cavities with simultaneously closed valves.
During the period of rapid filling, the atrioventricular valves instantly open, and blood flows along the pressure gradient into the ventricular cavities from the atria. At the same time, the cavities of the latter are constantly supplemented by inflow through the bringing veins, which is why, with a smaller volume of the cavities of the atria, they still pump similar portions of blood, like the ventricles. After that, due to the peak value of pressure in the ventricular cavities, the inflow slows down, a slow phase begins. It will end with atrial contraction, which occurs in ventricular diastole.
Details
The heart acts as a pump. atrium- containers that receive blood, which continuously flows to the heart; they contain important reflexogenic zones, where volumoreceptors are located (to assess the volume of incoming blood), osmoreceptors (to assess the osmotic pressure of blood), etc.; in addition, they perform an endocrine function (secretion of atrial natriuretic hormone and other atrial peptides into the blood); pumping function is also characteristic.
Ventricles perform mainly a pumping function.
valves heart and large vessels: atrioventricular flap valves (left and right) between the atria and ventricles; semilunar valves of the aorta and pulmonary artery.
The valves prevent backflow of blood. For the same purpose, there are muscular sphincters at the confluence of the hollow and pulmonary veins into the atria.
CARDIAC CYCLE.
Electrical, mechanical, biochemical processes that occur during one complete contraction (systole) and relaxation (diastole) of the heart are called the cycle of cardiac activity. The cycle consists of 3 main phases:
(1) atrial systole (0.1 sec),
(2) ventricular systole (0.3 sec),
(3) total pause or total diastole of the heart (0.4 sec).
General diastole of the heart: the atria are relaxed, the ventricles are relaxed. Pressure = 0. Valves: atrioventricular valves open, semilunar valves closed. There is a filling of the ventricles with blood, the volume of blood in the ventricles increases by 70%.
Atrial systole: blood pressure 5-7 mm Hg. Valves: atrioventricular valves open, semilunar valves closed. There is an additional filling of the ventricles with blood, the volume of blood in the ventricles increases by 30%.
Ventricular systole consists of 2 periods: (1) the tension period and (2) the ejection period.
Ventricular systole:
Direct ventricular systole
1)stress period
- asynchronous reduction phase
- isometric contraction phase
2)period of exile
- rapid ejection phase
- slow ejection phase
Asynchronous reduction phase: excitation spreads through the myocardium of the ventricles. Individual muscle fibers begin to contract. The pressure in the ventricles is about 0.
Isometric contraction phase: all fibers of the ventricular myocardium are reduced. The pressure in the ventricles increases. The atrioventricular valves close (because the pressure in the ventricles becomes greater than in the precardia). The semilunar valves are still closed (because the pressure in the ventricles is still less than in the aorta and pulmonary artery). The volume of blood in the ventricles does not change (at this time there is neither inflow of blood from the atria, nor outflow of blood into the vessels). Isometric mode of contraction (the length of the muscle fibers does not change, the tension increases).
Period of exile: all ventricular myocardial fibers continue to contract. The blood pressure in the ventricles becomes greater than the diastolic pressure in the aorta (70 mm Hg) and pulmonary artery (15 mm Hg). The semilunar valves open. Blood flows from the left ventricle to the aorta, from the right ventricle to the pulmonary artery. Isotonic mode of contraction (muscle fibers shorten, their tension does not change). The pressure rises to 120 mm Hg in the aorta and to 30 mm Hg in the pulmonary artery.
DIASTOLIC PHASES OF THE VENTRICULAR.
ventricular diastole
- isometric relaxation phase
- rapid passive filling phase
- slow passive filling phase
- rapid active filling phase (due to atrial systole)
Electrical activity in different phases of the cardiac cycle.
Left atrium: P wave => atrial systole (wave a) => additional filling of the ventricles (plays an essential role only with increased physical activity) => atrial diastole => venous blood flow from the lungs to the left. atrium => atrial pressure (wave v) => wave c (P due to the closing of the miter valve - towards the atrium).
Left ventricle: QRS => gastric systole => biliary pressure > atrial P => mitral valve closure. Aortic valve still closed => isovolumetric contraction => gastric P > aortic P (80 mm Hg) => aortic valve opening => blood ejection, decreased V ventricle => inertial blood flow through the valve =>↓ P in the aorta
and stomach.
Ventricular diastole. R in the stomach.<Р в предсерд. =>opening of the miter valve => passive filling of the ventricles even before atrial systole.
EDV = 135 ml (when the aortic valve opens)
CSR = 65 ml (when the mitral valve opens)
UO = BDO - KSO = 70 ml
EF \u003d UO / KDO \u003d normal 40-50%
