Cardiac cycle. Atrial systole and diastole
Term systole means muscle contraction. Highlight electrical systole- electrical activity that stimulates the myocardium and causes mechanical systole- contraction of the heart muscle and reduction of the heart chambers in volume. Term diastole means muscle relaxation. During the cardiac cycle, blood pressure increases and decreases; accordingly, high pressure at the time of ventricular systole is called systolic, and low during their diastole - diastolic.
The repetition rate of the cardiac cycle is called the heart rate, it is set by the heart rhythm driver.
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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- 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 a contraction of the muscle mass of the 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 ejects 50-70 ml of blood for each systole (stroke, or systolic, volume). 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 (minute blood volume, MOC). During maximum exercise, the stroke volume of a trained person's heart can exceed 200 ml, the pulse can exceed 200 beats per minute, and blood circulation can reach 40 liters per minute.
Diastole
Diastole- the period of time during which the heart relaxes to receive 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 the center of gravity of the 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
| 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 pressure indicators in the large (120/80 mm Hg) and small (30/15 mm Hg) circulation, cycle duration 0.8 s. Accepted abbreviations: |
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CYCLE OF THE HEART
Cardiac cycle- a concept reflecting the sequence of processes occurring in one contraction hearts and its subsequent relaxation. Each cycle includes three large stages: systole atria , systoleventricles And diastole . Term systole means muscle contraction. Highlight electrical systole- electrical activity that stimulates myocardium and calls mechanical systole- contraction of the heart muscle and reduction of the heart chambers in volume. Term diastole means muscle relaxation. During the cardiac cycle, blood pressure increases and decreases; accordingly, high pressure at the time of ventricular systole is called systolic, and low during their diastole - diastolic.
The repetition rate of the cardiac cycle is called heart rate, it is asked heart pacemaker.
Periods and phases of the cardiac cycle
Schematic relationship between the phases of the cardiac cycle, ECG, FKG, sphygmograms. The ECG waves, numbers of FCG tones and parts of the sphygmogram are indicated: a - anacrota, d - dicrota, j - catacrota. The phase numbers correspond to the table. The time scale scale is preserved.
A summary table of the periods and phases of the cardiac cycle with approximate pressures in the chambers of the heart and the position of the valves is given at the bottom of the page.
Ventricular systole
Ventricular systole- the period of contraction of the ventricles, which allows blood to be pushed into the arterial bed.
Several periods and phases can be distinguished in the contraction of the ventricles:
Asynchronous reduction- 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.
Isovolumetric contraction- almost the entire myocardium of the ventricles is involved, but there is no change in the volume of blood inside them, since the efferent (semilunar - aortic and pulmonary) valves are closed. Term isometric contraction is not entirely accurate, since at this time there is a change in the shape (remodeling) of the ventricles and tension of the chordae.
Quick expulsion- the period from the moment the semilunar valves open until systolic pressure is reached in the ventricular cavity - during this period the maximum amount of blood is ejected.
Slow expulsion- the period when the pressure in the ventricular cavity begins to decrease, but is still higher than the diastolic pressure. At this time, the blood from the ventricles continues to move under the influence of the kinetic energy imparted to it, until the pressure in the cavity of the ventricles and efferent vessels equalizes.
Voltage period- characterized by the beginning of a contraction of the muscle mass of the ventricles without changing the volume of blood inside them.
Exile period- characterized by the expulsion of blood from the ventricles.
In a state of calm, the ventricle of an adult’s heart pumps out 60 ml of blood (stroke volume) for each systole. The cardiac cycle lasts up to 1 s, respectively, the heart makes 60 contractions per minute (heart rate, heart rate). It is easy to calculate that even at rest, the heart pumps 4 liters of blood per minute (cardiac minute volume, MCV). During maximum exercise, the stroke volume of a trained person’s heart can exceed 200 ml, the pulse can exceed 200 beats per minute, and blood circulation can reach 40 liters per minute.
Diastole
Diastole- the period of time during which the heart relaxes to accept blood. In general, it is characterized by a decrease in pressure in the ventricular cavity, closure of the semilunar valves and opening of the atrioventricular valves with the movement of blood into the ventricles.
Protodiastole- the period of the beginning of myocardial relaxation with a drop in pressure lower than in the efferent vessels, which leads to the closure of the semilunar valves.
Isovolumetric relaxation- similar to the phase of isovolumetric contraction, but exactly the opposite. The muscle fibers lengthen, but without changing the volume of the ventricular cavity. The phase ends with the opening of the atrioventricular (mitral and tricuspid) valves.
Fast filling- the ventricles quickly restore their shape in a relaxed state, which significantly reduces the pressure in their cavity and sucks blood from the atria.
Slow filling- the ventricles have almost completely restored their shape, blood flows due to the pressure gradient in the vena cava, where it is 2-3 mm Hg higher. Art.
Ventricular diastole
Filling period
Atrial systole
It is the final phase of diastole. At a normal heart rate, the contribution of atrial contraction is small (about 8%), since during the relatively long diastole the blood already has time to fill the ventricles. However, with an increase in contraction frequency, the duration of diastole generally decreases and the contribution of atrial systole to ventricular filling becomes very significant.
Table of contents of the topic "Excitability of the cardiac muscle. Cardiac cycle and its phase structure. Heart sounds. Innervation of the heart.":1. Excitability of the heart muscle. Myocardial action potential. Myocardial contraction.
2. Excitation of the myocardium. Myocardial contraction. Coupling of excitation and contraction of the myocardium.
4. Diastolic period of the ventricles of the heart. Relaxation period. Filling period. Cardiac preload. Frank-Starling law.
5. Activity of the heart. Cardiogram. Mechanocardiogram. Electrocardiogram (ECG). ECG electrodes
6. Heart sounds. First (systolic) heart sound. Second (diastolic) heart sound. Phonocardiogram.
7. Sphygmography. Phlebography. Anacrota. Catacrota. Phlebogram.
8. Cardiac output. Regulation of the cardiac cycle. Myogenic mechanisms of regulation of cardiac activity. Frank-Starling effect.
9. Innervation of the heart. Chronotropic effect. Dromotropic effect. Inotropic effect. Batmotropic effect.
10. Parasympathetic effects on the heart. Influence of the vagus nerve on the heart. Vagal effects on the heart.
Work of the heart represents a continuous alternation of periods of contraction ( systole) and relaxation ( diastole). Replacing each other systole And diastole make up cardiac cycle. Since at rest the heart rate is 60-80 cycles per minute, each of them lasts about 0.8 s. In this case, 0.1 s is occupied by atrial systole, 0.3 s by ventricular systole, and the rest of the time by total diastole of the heart.
TO beginning of systole myocardium relaxed, and the heart chambers are filled with blood coming from the veins. At this time, the atrioventricular valves are open and the pressure in the atria and ventricles is almost the same. The generation of excitation in the sinoatrial node leads to atrial systole, during which, due to the pressure difference, the end-diastolic volume of the ventricles increases by approximately 15%. With the end of atrial systole, the pressure in them decreases.
Rice. 9.11. Changes in left ventricular volume and pressure fluctuations in the left atrium, left ventricle and aorta during the cardiac cycle. I - beginning of atrial systole; II - beginning of ventricular systole; III - moment of opening of the semilunar valves; IV - the end of ventricular systole and the moment of closure of the semilunar valves; V - opening of atrioventricular valves. The lowering of the line showing the volume of the ventricles corresponds to the dynamics of their emptying.Since the valves between the main veins and the atria are absent; during atrial systole, the circular muscles surrounding the mouths of the vena cava and pulmonary veins contract, which prevents the outflow of blood from the atria back into the veins. At the same time, atrial systole is accompanied by a slight increase in pressure in the vena cava. Of great importance is ensuring the turbulent nature of the blood flow coming from the atria into the ventricles, which contributes to the closure of the atrioventricular valves. The maximum and average pressure in the left atrium during systole are 8-15 and 5-7 mmHg, respectively. Art., in the right atrium - 3-8 and 2-4 mm Hg. Art. (Fig. 9.11).
With transition stimulation to the atrioventricular node and the conduction system of the ventricles begins the last systole. Its initial stage ( tension period) lasts 0.08 s and consists of two phases. Asynchronous contraction phase(0.05 s) is the process of propagation of excitation and contraction throughout the myocardium. The pressure in the ventricles remains virtually unchanged. In the process of the beginning synchronous contraction of the ventricular myocardium, when the pressure in them increases to a value sufficient to close the atrioventricular valves, but insufficient to open the semilunar valves, the phase of isovolumic, or isometric, contraction begins.
Further increase in pressure leads to the opening of the semilunar valves and the onset of period of exile blood from the heart, the total duration of which is 0.25 s. This period consists of rapid expulsion phases(0.13 s), during which the pressure in the ventricles continues to increase and reaches maximum values, and slow expulsion phases(0.13 s), during which the pressure in the ventricles begins to decrease, and after the end of the contraction it drops sharply. In the main arteries, the pressure decreases much more slowly, which ensures the closure of the semilunar valves and prevents the reverse flow of blood. The period of time from the beginning of ventricular relaxation to the closure of the semilunar valves is called the protodiastolic period.
Term systole means muscle contraction. Highlight electrical systole- electrical activity that stimulates the myocardium and causes mechanical systole- contraction of the heart muscle and reduction of the heart chambers in volume. Term diastole means muscle relaxation. During the cardiac cycle, blood pressure increases and decreases; accordingly, high pressure at the time of ventricular systole is called systolic, and low during their diastole - diastolic.
The repetition rate of the cardiac cycle is called heart rate, it is 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- 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 a contraction of the muscle mass of the 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 ejects 50-70 ml of blood for each systole (stroke, or systolic, volume). 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 (minute blood volume, MOC). During maximum exercise, the stroke volume of a trained person's heart can exceed 200 ml, the pulse can exceed 200 beats per minute, and blood circulation can reach 40 liters per minute.
Diastole
Diastole- the period of time during which the heart relaxes to accept blood. In general, it is characterized by a decrease in pressure in the ventricular cavity, closure of the semilunar valves and opening of the atrioventricular valves with the movement of blood into the ventricles.
- 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 the center of gravity of the 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
| 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 pressure indicators in the large (120/80 mm Hg) and small (30/15 mm Hg) circulation, cycle duration 0.8 s. Accepted abbreviations: |
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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 the 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 the atria, or with 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 remainder of the 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) of the 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.
