The pulmonary valve regulates the flow of blood from the heart to the lungs. Diseases can significantly affect its performance.
What is the pulmonary valve?
The term pulmonic comes from the Latin term pulmo for the lungs. Accordingly, the pulmonic valve is the one that regulates the flow of deoxygenated blood to the lungs. It is located at the junction between the right ventricle and the pulmonary artery (truncus pulmonalis). There are a total of 4 heart valves, 2 leaflet valves between the atria (atrium) and the ventricles and two pocket valves between the ventricles and the vessels leading away from the heart. The pulmonary valve has 3 crescent-shaped pockets, one right, one left, and one anterior, arranged to allow blood flow only toward the lungs; in the other direction, they close the opening to the heart. The deoxygenated blood that meets the pulmonary valve in the right ventricle gets there via the two vena cavae and the right atrium. On its way into the ventricle, it passes through the leaflet valve, which is located at the junction. The passage of blood through the heart valves is controlled by the changing pressures during the heart rhythm.
Anatomy and structure
The three leaflets of the pulmonic valve arise from the inner layer of the pulmonary truncus at the junction with the right ventricle, called the tunica intima. They have a crescent (semilunar) shape with an inward bulge that initially collects the returning blood. At each of the free tips are nodular thickenings with a surrounding cuticle, which come into contact with each other during closure. Unlike the leaflet valves, the pocket valves do not have muscles controlling their opening and closing. Their opening and closing mechanism is regulated solely by the direction of blood flow and pressure conditions. Although the pulmonic valve is structurally identical to the aortic valve, it has a smaller and thinner design due to the lower pressure in the right ventricle and less mechanical stress. All 4 heart valves are embedded in a coarse connective tissue layer called the cardiac skeleton. This forms what is known as the valvular plane, which is displaced by the change in shape of the heart during respiration, thereby supporting the heart’s suction-pressure mechanism.
Function and tasks
The main function of the pulmonary valve is to regulate the direction of flow of deoxygenated blood on its way to the lungs. It ensures that blood from the right ventricle enters the pulmonary artery but does not return. The driving force for the opening and closing mechanism is pressure. If the pressure in the right ventricle exceeds that in the vessel, the valve opens and blood is expelled toward the lungs. If the pressure ratios are reversed, the 3 pockets are automatically closed by the returning blood. This mechanism is rhythmic and occurs in 2 phases called diastole and systole, which occur in parallel in the right and left hemispheres of the heart. Initially, all valves are closed and the heart muscles are relaxed. On the right side of the heart, deoxygenated blood from the systemic circulation flows into the right atrium until the pressure there is greater than in the right ventricle. The leaflet valve opens and, following the pressure gradient, the blood flows into the right ventricle. When the ventricle has reached a certain filling volume, the leaflet valves are closed, and the pulmonary valve is still closed. This is followed by the tightening phase of the myocardium of the right ventricle. The contraction increases the pressure on the blood there. If this exceeds that in the pulmonary artery, the pulmonary valve is opened and the blood is expelled toward the lungs. The cycle ends when the three pockets are closed again by the returning blood.
Diseases
Dysfunction affecting blood flow can basically result from 2 types of impairment. Either by a narrowing of the flow orifice, called stenosis, or by inadequate closure of the three pockets, called insufficiency. The causes of these valvular defects can vary. In rarer cases, pulmonary valve insufficiency can result from pathological changes in the valve tissue, for example, as a result of inflammation of the inner layer of the heart (endocarditis).The more common cause is increased blood pressure caused by the back pressure that occurs in certain lung diseases. The pulmonary artery becomes dilated due to the increased pressure in the vessel and the distance between the pockets increases. They can no longer completely close the lumen of the vessel. This mechanism causes blood to flow back into the right ventricle with each cycle, reducing ejection volume. The heart tries to compensate for this deficit by increasing muscle activity. If sufficient compensation is no longer possible, right heart failure develops. Similar mechanisms occur in pulmonary stenosis, although the causative mechanism is different. This narrowing of the pulmonary valve, which reduces the amount of blood volume pumped into the pulmonary artery during the expulsion phase, is usually congenital. Here, too, the heart attempts to compensate for the lack of ejection volume by increased pumping, with the same consequences as in insufficiency. Depending on the magnitude of the impairment, typical symptoms of varying intensity may occur. The reduced output of the heart means that not enough blood reaches the lungs and is enriched with oxygen. Blue discoloration (cyanosis) develops in certain areas of the skin, shortness of breath at rest or on exertion, and performance is reduced. Pulmonary insufficiency can have additional complications that arise due to the reduced flow rate. Blood clots can form on the valve, leading to pulmonary embolism if detached. Pulmonary atresia is a congenital malformation in which the valve either does not open or is not present. This condition can have serious consequences and may require surgery immediately after birth to restore the body’s circulatory supply.
