The cardiac cycle, which was fully assembled by Lewis58 but first designed by Wiggers,59 provides important information about the temporal sequence of events (Fig. 22.16). The three basic events related to the left ventricle are VH contraction, LV relaxation and LV filling (Table 22.3). Similar mechanical events occur in the right ventricle. Figure 1. The cardiac cycle begins with the atrial sysstole and progresses to the ventricular systole, atrial diastole and ventricular diastole when the cycle begins again. Correlations with ecg are highlighted. The cardiac cycle includes all physiological events associated with a single heartbeat, including electrical events, mechanical events (pressure and volume), and heart murmurs. The heart has a remarkable ability to absorb an increased volume of blood that enters the heart. In fact, the increase in the final diastolic volume also leads to an increase in cardiac output.
This principle was described by two renowned physiologists and was therefore called the Frank-Starling mechanism of the heart. The underlying principle is that the heart pumps all the blood that returns to it through the veins within physiological limits. LV pressure increases when Ca2+ reaches the contractile proteins after cell depolarization has triggered the actin-myosin interaction.4 This occurs shortly after the ventricular action potential indicated by the electrocardiogram QRS complex (ECG; Fig. 22.16). When the LV pressure exceeds that of the left atrium (usually 8 to 15 mm Hg), the mitral valve closes, creating the mitral component of the first sound, M1. Changes in right ventricular pressure (RV) are usually slightly delayed due to electrical conduction, so closing the tricuspid valve (T1) follows M1. The phase of contraction of VH after mitral occlusion and before aortic opening, when the volume of VL is fixed, is called asisovolumic contraction. As more myofibers are activated, the LV pressure continues to increase until it exceeds the aortic pressure, causing the aortic valve to open (usually a clinically silent event). The opening of the aortic valve is followed by the phase of rapid sputum. The ejection rate is determined by the pressure gradient via the aortic valve, as well as by the elastic properties of the aorta and arterial tree, which undergo systolic expansion. The pressure Lv rises to a peak and then begins to drop.
In the second phase of ventricular diastoles, called late ventricular diastoles, the pressure on the blood in the ventricles decreases even more as the ventricular muscle relaxes. Eventually, he falls under pressure in the earbuds. When this happens, blood flows from the atria into the ventricles, pushing the tricuspid and mitral valves. When the pressure in the ventricles decreases, blood flows from the main veins into the relaxed atria, and from there into the ventricles. Both chambers are located in diastoles, the atrioventricular valves are open, and the crescent-shaped valves remain closed (see figure below). The cardiac cycle is over. Figure 2 illustrates the relationship between the cardiac cycle and the ECG. Stages 1 and 2 together – “isovolumic relaxation” plus influx (equivalent to “rapid influence”, “diastasis” and “atrial systole”) – include the “diastole” ventricular period, including the atrial systole, in which blood returning to the heart flows through the atria into the relaxed ventricles. Stages 3 and 4 together – “isovolumic contraction” plus “sputum” – are the ventricular period “systole”, which is the simultaneous pumping of blood supplies separated from the two ventricles, one to the pulmonary artery and the other to the aorta. Remarkably, towards the end of the “diastole”, the atria begin to contract, and then pump blood into the ventricles; This pressure delivery during ventricular relaxation (ventricular diastole) is called the atrial systemstole, also known as the atrial kick. [Citation needed] In the early stages of ventricular diastole, the atrioventricular and crescent-shaped valves are closed.
During this phase, there is no change in the amount of blood in the ventricle, but there is a sharp drop in intraventricular pressure. This is called isovolumetric relaxation. The cardiac cycle is a highly coordinated and time-bound sequence of electrical, mechanical and valvular events. The cardiac cycle involves complete relaxation and contraction of the atria and ventricles and lasts about 0.8 seconds. Starting with all the cavities of the diastole, blood passively flows from the veins into the atria and passes the atrioventricular valves into the ventricles. The atria begin to contract after depolarization of the atria (atrial systole) and pump blood into the ventricles. The ventricles begin to contract (ventricular systole), which increases the pressure in the ventricles. When the ventricular pressure rises above the pressure in the atria, blood flows to the atria, producing the first heart tone, S1 or Lub. When the pressure in the ventricles increases on two main arteries, the blood pushes to open the two crescent-shaped valves and moves into the pulmonary trunk and aorta in the ventricular ejection phase. After ventricular repolarization, the ventricles begin to relax (ventricular diastoles) and the pressure in the ventricles decreases. When ventricular pressure drops, blood from the main arteries tends to flow back into the atria, creating the dicrotic notch on the ECG and closing the two crescent-shaped valves.
The second heart tone, S2 or dub, occurs when the crescent-shaped valves close. When the pressure drops below that of the atria, blood travels from the atria to the ventricles, opens the atrioventricular valves and marks a complete cardiac cycle. The valves prevent blood from flowing back. Failure of the valves to function properly creates turbulent blood flow in the heart; The resulting heart murmur is often heard with a stethoscope. The sounds associated with heartbeat are due to vibrations in tissues and blood caused by valve closure. Abnormal heart murmurs are called marbles. Isovole contraction: also isovolumetric contraction) Initial phase of ventricular contraction, in which the tension and pressure in the ventricle increase, but no blood is pumped out of the heart or expelled The AV node is connected to a network of fibers that descend along the interventricular septum, and then through the walls of the ventricles. The first segment of this path is called its own beam. The beam of it then branches into the branches of the left and right beam. The branch of the left beam also indicates the left posterior branches that carry pulses to the posterior appearance of the left ventricle. .