Heart valves

Tricuspid and pulmonary heart valves regulate the blood flow from the tissues to the lungs for oxygenation, the mitral and aortic valves of the left heart control the blood flow to the organs and tissues of the arterial blood. The aortic and pulmonary are the output valves of the left and right ventricles, respectively. The mitral and tricuspid valves of the heart are the output valves of the left and right atriums and simultaneously the inlet valves of the left and right ventricles, respectively. The aortic and pulmonary valves of the heart are open in the phase of contraction of the ventricles (systole) and are closed in the phase of relaxation of the ventricles (diastole). In the phase of isovolumic contraction and relaxation, all four valves are closed. The closed pulmonary and tricuspid valves of the heart can withstand a pressure of 30 mm Hg. Aortic - about 100 mm Hg. St, mitral - up to 150 mm. Gt; Art. Elevated cardiac valve loads on the left determine their greater susceptibility to disease. Hemodynamics can play an important role in the development of valvular pathology

The aortic valve of the heart opens at the beginning of the systolic contraction of the left ventricle and closes before the diastolic relaxation of the ventricle. Systole begins at the time of opening the aortic valve (20-30 ms) and lasts about 1/3 of the time of the cardiac cycle. Blood flow through the valves of the heart rapidly increases and reaches the maximum speed in the first third of the systole after the full opening of the valves. The inhibition of blood flow through the valves of the heart is slower. The inverse pressure gradient inhibits the low-velocity wall flow with the formation of a reverse flow in the sines. During systole, a direct pressure drop, under which the blood moves through the aortic valves of the heart, does not exceed a few mm. Gt; The reverse pressure differential on the valve normally reaches 80 mm Hg. Art. The heart valves close at the end of the braking phase of the flow with the formation of a slight backflow. All the valves of the heart are closed in the phase of isovolumic contraction and relaxation. Aortic valves of the heart change their size and shape during the cycle of contraction of the heart, mainly in the direction of the axis of the aorta. The perimeter of the fibrous ring reaches a minimum at the end of the systole and a maximum at the end of the diastole. Studies on dogs showed a 20% change in the perimeter at aortic pressure 120/80 mm. Gt; Art. During systole in the sinuses, the formation of a vortex motion of the liquid is observed. Vortices contribute to quick and effective closure of the leaflets. The volume of the reverse flow is 5% of the direct flow. In a healthy organism, under the influence of a direct pressure drop, the blood flow velocity rapidly increases to 1.4 ± 0.4 m / s. At children even higher speeds are observed - 1.5 ± 0.3 m / s. At the end of the systole, a short period of reverse blood flow takes place, which is detected by the ultrasonic Doppler method. The source of the reverse flow can serve as the actual reverse flow of blood through the opening of the valve in the closing phase of the valves, and the movement of the already closed valves towards the left ventricle.

The velocity profile in the plane of the fibrous ring is uniform, but with a slight slant toward the septal wall. In addition, the systolic blood flow through the aortic valves of the heart retains a spiral shape formed in the left ventricle. Twisting the blood flow in the aorta (0-10 °) eliminates the formation of stagnant zones, increases the pressure near the walls, contributing to a more efficient blood collection into the waste vessels, prevents injury to the formed elements of the blood due to the continuous flow. Judgments about the direction of rotation of the blood flow in the ascending aorta are ambiguous. Some authors pointed to the rotation of the systolic blood flow through the aortic valves of the heart counterclockwise, when viewed in a stream, others - in the opposite direction, the third - do not mention the spiral nature of the systolic ejection of blood, the fourth - tend to the hypothesis of the origin of a swirling flow in the arch of the aorta . The unstable and, in some cases, the multidirectional nature of the rotation of the blood flow in the ascending aorta and its arc is connected, apparently, with the individual morphofunctional features of the output section of the left ventricle, the aortic structures, the sinuses of Valsalva, and the aortic wall.

Blood flow through the pulmonary valves of the heart is close to aortic, but much less than its size. In a healthy adult body, the velocities reach 0.8 ± 0.2 m / s in the infant - 0.9 ± 0.2 m / s. Behind pulmonary structures, there is also a twist of the flow, which is directed to the phase of acceleration of blood flow counter-clockwise.

The relaxation of the ventricle is followed by inhibition of the blood flow, and the mitral structures are partially closed. With atrial contraction, the velocity in the A-wave is usually less in comparison with the E-wave. Initial studies were aimed at explaining the mechanism of mitral valve closure. J. J. Bellhouse (1972) first suggested that the vortices formed behind the valves during filling of the ventricle contribute to the partial closure of the valves. Experimental studies confirmed that without the formation of large eddies behind the valves, the mitral structures would remain in the open state before the onset of ventricular contraction, and its closure was accompanied by significant regurgitation. J. Reul et al. (1981) found that the reverse pressure drop in the middle of the diastole of the ventricle ensures not only the inhibition of the fluid, but also the initial covering of the valves. Thus, the participation of vortices in the mechanism of closure of the valves refers to the beginning of the diastole. E. L. Yellin et al. (1981) clarified that the mechanism of closure is influenced in totality by chord tension, inhibition of flow and vortices in the ventricle.

The diastolic blood flow, flowing from the left atrium through the mitral structures to the left ventricle, is twisted clockwise when viewed from the stream. Modern studies of the spatial velocity field in the left ventricle by magnetic resonance imaging show vortical movement of the blood both in the phase of covering the valves and in the phase of atrial contraction. The swirl of the flow is ensured by the tangential flow of blood from the pulmonary veins into the cavity of the left atrium, as well as the direction of blood flow by the anterior valve of the mitral valve to the spiral trabeculae of the inner wall of the left ventricle. It is pertinent to ask: what is the meaning of nature in this phenomenon - the twisting of blood in the left ventricle of the heart and the aorta? In a swirling flow, the pressure at the walls of the left ventricle exceeds the pressure on its axis, which contributes to the stretching of its walls during the period of increased intraventricular pressure, the inclusion of the Frank-Starling mechanism in the process, and a more effective systole. The swirling flow intensifies the mixing of blood volumes - saturated with oxygen and depleted. Increase in pressure near the walls of the left ventricle, the maximum value of which falls on the final stage of diastole, creates additional efforts on the valves of the mitral valve and facilitates their rapid closure. After the closure of the mitral valve, the blood continues to rotate. The left ventricle in the systole only changes the direction of the translational motion of the blood, without changing the direction of the rotational movement, therefore, the sign of the twist changes to the opposite, if one continues to look at the flow.

The velocity profile in the tricuspid valve is similar to the mitral valve, but the speed here is less, since the area of the opening of the valve is larger. The tricuspid valve of the heart opens before the mitral valve, and closes later.

[1], [2], [3], [4], [5], [6]