What Is the Contraction Phase of the Cardiac Cycle

The aortic pressure diagram shows the change in pressure in the aorta throughout the cardiac cycle. The graph has a moderate slope, followed by a notch and then a smaller slope. The chart ends with a gradual decline before starting all over again. Another independent representation of cardiac cycle time is obtained by recording instant ventricular pressure and volume (Figure 11). During ventricular filling, pressure and volume increase non-linearly (phase I). The instantaneous slope of the pressure-volume (P-V) curve during filling (dP/dV) is diastolic stiffness, and its inverse (dV/dP) is conformity. Thus, as the volume of the chamber increases, the ventricle becomes more rigid. In a normal ventricle, surgical adherence is high because the ventricle acts on the flat part of its diastolic P-V curve. During isovolumetric contraction (phase II), the pressure increases and the volume remains constant. During sputum (phase III), the pressure rises and falls until the minimum ventricular size is reached.

The maximum pressure-to-volume ratio (maximum stiffness or elasticity of the active chamber) usually occurs at the end of ejection. This is followed by isovolumetric relaxation (phase IV), and when the left ventricular pressure falls below the left ear pressure, ventricular filling begins. Thus, the end diastole is located in the lower right corner of the loop and the end sysstole in the upper left corner of the loop. Left ventricular P-V diagrams can illustrate the effects of a change in preload, post-load and inotropic state in the intact ventricle (see below). Figure 1. A schematic diagram of the three main phases of filling and emptying four heart chambers of the fish heart. (a) The atrium and ventricle fill due to venous blood pressure. b) The atrium contracts (as indicated by the small arrows), expands further and completes the filling of the ventricle. c) The ventricle contracts and expels fluid into the atheroscopy bulb.

At the same time, the atrium begins to fill up. The cardiac cycle is defined as a sequence of alternating contraction and relaxation of the atria and ventricles to pump blood through the body. It begins at the beginning of one heartbeat and ends at the beginning of another. The process begins as early as the 4th week of pregnancy, when the heart begins to contract for the first time. The first cardiac tone or S1 or the “lub” sound is caused by the closure of the atrioventricular valves. This occurs at the beginning of the ventricular systole. It can be displayed graphically at the point after the first ventricular pressure wave. This coincides with the “a” wave of the ear pressure wave and the “R” wave of the ECG. The second heart tone or S2 or the “dub” sound is caused by the closure of the crescent valves. This occurs at the beginning of the diastole, during the isovolumetric relaxation phase. It coincides with the “incisura” of the aortic pressure curve and the end of the ECG T-wave. The cardiac cycle consists of four main phases of activity: 1) “Relaxation isovole”, 2) Influx, 3) “Contraction isovole”, 4) “Sputum”.

(See wiggers` chart, which labels levels in order 3,4,1,2 from left to right.) If you move from the left along the Wiggers diagram, activities are displayed in four steps during a single cardiac cycle. (See the successive panels entitled “Diastole” then “Systole”). [Citation needed] During the early phase of ventricular diastole, when the ventricular muscle relaxes, the pressure on the blood remaining in the ventricle begins to decrease. When the pressure in the ventricles of the lung shaft and aorta falls below the pressure, the blood returns to the heart, creating the dicrotic notch (small hollow) seen in blood pressure measurements. The crescent-shaped valves close to prevent reflux into the heart. Because the atrioventricular valves remain closed at this site, the blood volume in the ventricle does not change, so the early phase of the ventricular diastole is called the isovole ventricular relaxation phase, also known as the isovolumetric ventricular relaxation phase (see figure below). Ventricular relaxation, or diastole, follows the repolarization of the ventricles and is represented by the T wave of the ECG. It is also divided into two different phases and takes about 430 ms. The atrial diastole is the very first event in the cardiac cycle. It occurs a few milliseconds before the electrical signal from the SA node reaches the earcups.

The atria act as channels that facilitate the passage of blood through the ipsilateral ventricles. They also act as primers to pump residual blood into the ventricles. During the atrial diastole, blood enters the right atrium through the upper and lower vena cava and through the pulmonary veins in the left atrium. At the beginning of this phase, the atrioventricular valves are closed and blood accumulates in the atria. In a normal and healthy heart, there are only two audible heart murmurs: S1 and S2. S1 is the sound produced by the closure of the atrioventricular valves during ventricular contraction and is usually described as “lub” or first heart tone. The second cardiac tone, S2, is the sound of crescent-shaped valves that close during the ventricular diastole and is described as a “dub” (Figure 3). In both cases, when the valves close, the openings inside the atrioventricular septum protected by the valves are reduced, and blood flow through the opening becomes more turbulent until the valves are completely closed. There is a third heart tone, S3, but it is rarely heard in healthy people. It can be the sound of blood flowing through the atria, or blood sliding back and forth into the ventricle, or even tension in the chords tendineae. S3 can be heard in teenagers, some athletes and pregnant women.

If the noise is heard later in life, it may indicate congestive heart failure, which warrants further testing. Some cardiologists refer to the collective sounds S1, S2 and S3 as “Kentucky gallops” because they mimic those produced by a galloping horse. The fourth cardiac tone, S4, results from the contraction of the atria pushing blood into a stiff or hypertrophic ventricle, indicating failure of the left ventricle. S4 occurs before S1 and the collective sounds S4, S1 and S2 are called by some cardiologists a “Tennessee gallop” because they resemble the sound of a galloping horse with a different gait. Some people may have both S3 and S4, and this combined sound is called S7. When the ventricle begins to contract, the pressure exceeds that of the corresponding atrium, which leads to the closure of the atrioventricular valves. At the same time, the pressure is not enough to open the crescent-shaped valves. Therefore, the ventricles are in a state of isovolumetric contraction – since the total volume (final diastolic volume) in the ventricle does not change. Increased excitability in places other than the pacemaker site predisposes the heart to the development of ectopic heartbeat.

These can lead to uncoordinated contraction of the ventricles and different types of ventricular arrhythmias. The relationship between left ventricular volume and intraventricular pressure during systole and diastole is represented by the pressure-volume curves shown in Figure 6.3. The diastolic pressure curve is determined by filling the heart with increasing amounts of blood and then measuring the intraventricular pressure before the onset of contraction. In other words, this curve represents the terminal diastolic pressure for a certain amount of blood volume. The systolic pressure curve represents the measurement of the intraventricular pressure at the end of the contraction for each filling volume. It is important to note that the pressure volume curve for diastoles is initially flat, suggesting that an increase in blood volume only slightly increases ventricular pressure. This applies up to about 150 ml. Above this volume, the pressure increases rapidly, also because the fibrous tissue of the heart and the pericardium that surrounds the heart have reached their stretching limits. In contrast, systolic pressure increases rapidly even at low ventricular volumes and continues to rise steadily before reaching a maximum of about 250 mmHg at a volume of 150 to 170 ml. .

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