The phases of cardiac activity
Heart rhythmically reduced. Reducing heart is pumping blood from the atria to the ventricles and the ventricles of the blood vessels, but also creates a difference in blood pressure in the arterial and venous system, through which the blood moves. The phase of contraction of the heart is referred to as systole, and relaxation – both diastole.
The cycle consists of a cardiac systole and diastole and atrial systole and diastole of the ventricles. The cycle starts with the reduction of the right atrium, and immediately begins to decline, and the left atrium. Atrial systole begins with 0.1 to ventricular systole. During atrial systole the blood can not get out of the right atrium into the vena cava, as it reduces the atrium closes the opening of the veins. The ventricles are relaxed at this time, so the venous blood through the open tricuspid valve enters the right ventricle and the arterial blood from the left atrium, he entered into it from the lungs through the open butterfly valve is pushed into the left ventricle. At this time, the blood from the aorta and pulmonary arteries can not get into the heart, as semilunar valves closed blood pressure in these blood vessels.
Then begins the atrial diastole and as relaxing the walls of blood from their veins fills the cavity.
Immediately after the end of atrial systole the ventricles begin to contract. First, declining only part of the muscle fibers of the ventricles, and the other part is stretched. This changes the shape of the ventricles, and the pressure in them remains the same. This phase asynchronous contraction or ventricular shape changes, which lasts about 0.05 seconds. After the complete reduction of the muscle fibers of the ventricles pressure in their cavities growing very quickly. This causes the slamming of the tricuspid and bicuspid valves and closing holes in the atrium. Semilunar valves remain closed because the pressure in the ventricles still lower than in the aorta and pulmonary artery. This phase, in which the wall of the ventricular muscle strains, but their value is not changed until the pressure therein exceeds the pressure in the aorta and pulmonary artery, called the isometric contraction phase. It takes about 0.03 seconds.
During an isometric contraction of the ventricles pressure in the atria during diastole them goes to zero or even become negative, ie. E. Less than atmospheric, so atrioventricular valves are closed and semilunar valves slam reverse flow of blood from the arteries.
The two-phase asynchronous and isometric contractions together constitute a voltage between the ventricles. In human aortic semilunar valves disclosed when left ventricular pressure reaches 65-75 mmHg. Art., and crescent-shaped pulmonary valve open, the pressure in the right ventricle reaches – 12 mm Hg. Art. In this phase begins ejection or systolic ejection of blood in which the blood pressure in the ventricles rises steeply during 0.10-0.12 s (rapid ejection) and then, as the ventricles decrease in blood pressure increase and stops it at the end of systole begins to fall within a 0.10-0.15 (slow expulsion).
After opening semilunar valves ventricles, changing its volume and using some of the stress for the expulsion of blood in the blood vessels (auksotonicheskoe reduction). During the isometric contraction of the blood pressure in the ventricles becomes higher than in the aorta and pulmonary artery, which causes opening of semilunar valves and REM, and then slow ejection of blood from the ventricles into the blood vessels. After this phase comes the sudden relaxation of the ventricular diastole them. Aortic pressure becomes higher than in the left ventricle and therefore semilunar valves close. The time interval between the beginning of ventricular diastole and closing the semilunar valves called protodiastolic period, which lasts 0.04 seconds.
In the period of diastole the ventricles for about 0.08 to relax in private atrioventricular and semilunar valves until the pressure in them will not fall lower than in the atria, already filled with blood. This phase of isometric relaxation. Ventricular diastole accompanied by a drop in pressure them to zero.
A sharp drop in pressure in the ventricle and increased pressure in the atria at the beginning of their three-sided open reduction and butterfly valves. Starts REM ventricular filling with blood, which lasts 0.08 seconds, and then due to a gradual increase in pressure in the ventricles filled with blood when there is a delay ventricular filling, the phase of slow filling within 0.16 sec, which coincides with late diastolic phase.
The man ventricular systole lasts about 0.3 seconds, ventricular diastole – 0.53 seconds, atrial systole – 0.11 seconds, atrial diastole – 0.69 seconds. The entire cardiac cycle continues in humans with an average of 0.8. Time total diastole the atria and ventricles are sometimes called a pause. In the heart of man and the higher animals under physiological conditions, there is no pause in addition to diastole, what distinguishes the activity of the heart of man and the higher animals from the cold-activity of the heart.
The horse with frequent cardiac duration of one cardiac cycle is 0.7 s, of which atrial systole lasts 0.1 seconds, ventricular – 0.25, and total cardiac systole – 0.35. Since atrial relaxed during ventricular systole, the atrial relaxation continues with 0.6 or 90% of the duration of the cardiac cycle, and relaxation of the ventricles – 0.45, or 60-65%.
This restores the length of relaxation of the heart muscle.
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