Since childhood, everyone knows that the movement of blood throughout the body provides the heart. To ensure that the whole process runs smoothly, the cardiac cycle is a clear diagram of the phases that are interchanged. Each of them is characterized by its level of blood pressure and takes a certain amount of time to execute. The whole cycle in a healthy person takes only 0.8 seconds, while including a whole list of different phases. The duration of each of them can be determined by graphical registration of FKG, ECG and sphygmograms, but only a specialist knows what happens in each phase of the cardiac cycle.
To understand this and the average person, this article is presented.
General relaxation
An examination of each phase of the cardiac cycle (the table will be presented at the end of the article) is easiest to start with the relaxation time of the main muscle of the body. In general, the cardiac cycle is a change in contractions and relaxation of the heart.
So, the work of the heart begins with a pause, when the atrioventricular valves are open and the half-month-old 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 level.
Atrial contraction
After the blood completely fills the heart, excitation begins in its sinus region, provoking atrial contractions first. In this phase of the cardiac cycle (the table will make it possible to compare the time allotted for each stage), venous vessels are closed due to muscle tension, and the blood received from them is 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 in the ventricles, where its volume reaches 130-140 ml. After this, systole is replaced by relaxation for 0.7 seconds and the next phase begins.
Ventricular systole
Ventricular tension takes 0.8 seconds and is divided into several periods. The first is an asynchronous myocardial contraction, which takes only 0.05 seconds. It is determined by alternating muscle contraction in the ventricles. The first to begin their tension are fibers located near conductive structures.
The tension continues until the half-month valves are fully open under the influence of increasing 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 heart 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 the blood all this time moves into the zone of zero pressure. So that the closed valves do not turn out after 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 are closed, tension begins to build up in the muscles, which contributes to the further opening of half-month-long valves and the rapid expulsion of blood. Until this happens, experts record the first heart tone, also called systolic.
At this time, the pressure inside the heart rises above the pressure in the arteries, and when the
left ventricle takes a rounded shape, its impact on the inner surface of the chest determines the
apical impulse. This happens in 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 for the exit of blood from the cavities and lasts 0.25 seconds. The entire phase can be divided into fast and slow exile, which take approximately the same periods of time. At first, liquid under pressure quickly rushes into the vessels, but due to their poor flow rate, the pressure quickly equalizes, and the blood begins to move back. To prevent this ventricular systole is constantly increasing, raising the pressure inside the heart cavities 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 bit later. When all the fluid leaves the cavity of the heart, myocardial relaxation begins, the second heart tone - diastolic. At this time, the blood again begins to fill the ventricles, as the pressure in them becomes lower.
Relaxation period
All the time of diastole takes 0.47 seconds, and when the blood begins to move in the opposite direction, it closes the lunar valves under its own pressure . This period is called protodiastolic.
Its time is only 0.04 seconds, and after it immediately begins the next period of the cardiac cycle - 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. Mostly it is venous blood that passes passively into the heart.
Filling
The appearance of the third heart tone 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 in the heart, a fourth tone appears. With intense work, the heart muscle performs each cycle faster.
Abbreviated content
The table displays the phases of the heart cycle for healthy people in a calm state, therefore it is customary to consider them as reference. 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 work 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 general picture in abbreviated form:
Period | Phase | Duration in seconds | Right ventricular pressure in mmHg | In the left ventricle in mmHg | In the atrium in mmHg |
| Atrial contraction | 0.1 | zero first, at the end of 6-8 | same | same |
Systole period | Asynchronous voltage | 0.05 | 6-8, at the end of 9-10 | same | 6-8 constantly |
Isometric voltage | 0,03 | 10, at the end of 16 | 10, at the end of 81 | 6-8, zero at the end |
Exile cycle | Fast | 0.12 | first 16, then 30 | 81 first, then 120 | 0 → -1 |
Slow | 0.13 | 30 first, then 16 | first 120, then 81 | zero |
Ventricular relaxation | Protodiastolic period | 0.04 | 16, then 14 | 81, then 79 | 0- + 1 |
Isometric relaxation | 0.08 | 14, then zero | 79, at the end zero | ≈ + 1 |
Filling cycle | Fast | 0.08 | zero | zero | zero |
Slow | 0.17 | zero | zero | zero |
Reduction periods
When a person probes a pulse or listens to a heartbeat, only 1 and 2 tones are heard, the rest can be seen only with graphic registration.
The periods of the cardiac cycle can be divided according to other criteria. So, experts distinguish refractory periods - an absolute, effective and relative, vulnerable period and supernormal phase.
The periods differ in that during the first time the heart muscle is not able to contract independently, regardless of the 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 irritant. On the ECG, you can see the last two refractory periods in the form of an equal to the ventricular electrical systole.
The vulnerable period of the cycle corresponds to muscle relaxation at the completion of all the above phases. Compared to refractory ones, it is considered short. The last period is an increased excitability of the heart and is detected only in the presence of heart depression.
An experienced specialist in decoding cardiograms always knows which period a particular wave of heartbeat should be attributed to and will correctly determine whether a person has a disease or existing abnormalities should be considered as insignificant features of the body.
Conclusion
Even after a routine study of the heart, you should not try to decipher the available results yourself. This article is offered for review solely so that patients can understand the features of their heart and can better understand what exactly is happening in their body. Only an experienced doctor is able to take into account at the same time all the nuances of each case in order to assemble them into a single picture and determine the diagnosis. In addition, not all deviations from the above norms 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 schedule additional examinations.