The pulmonary valve is typically made up of three leaflets, the anterior, the left, and the right, and it opens during systole to allow blood to be ejected to the lungs. During diastole, it closes to allow the heart to fill with blood and get ready for another systole. If the pulmonary valve doesn’t open all the way, it makes it harder for the heart to pump blood out to the lungs, and this is called pulmonary stenosis. If the pulmonary valve doesn’t close all the way, then blood leaks back into the right ventricle, and this is called pulmonary valve regurgitation or pulmonary insufficiency.
Pulmonary valve stenosis is often congenital, meaning that at birth, the leaflets are irregularly shaped or not fully developed. Pulmonic valve stenosis is often associated with congenital heart conditions like Tetralogy of Fallot, which affects all four chamber of the heart, as well as a genetic condition called Noonan's syndrome. In other cases, pulmonary valve stenosis can be caused by mechanical stress over time, which damages endothelial cells around the valves. This damage causes fibrosis and calcification, which harden the valve and make it more difficult for the valve to open all the way.
Because pulmonary valve stenosis makes it harder for the valve to open when the right ventricle tries to eject blood, the valve resists for a second before finally snapping open, and this causes a characteristic “ejection click.” Because the blood has to flow through a narrow opening, we get increased turbulence, which creates a noise called a murmur. This murmur gets louder as more blood flows past the opening, and then it gets quieter as the amount of blood flowing through the valve decreases because There’s less in the ventricle. This sound is described as a crescendo-decrescendo murmur.
Since it’s more difficult to open this hardened valve and push blood past it, the right ventricle has to generate really high pressures. To achieve those pressures it thickens its muscles, and this is called concentric right ventricular hypertrophy. This happens because new sarcomeres are added in parallel to the existing ones. However, even though you have this bulked up ventricle, the heart still might struggle to get enough blood through the narrowed opening and the lungs. Ultimately, that means that blood gets backed up, and so the person can develop right-sided heart failure. A final, different complication of pulmonic valve stenosis is called microangiopathic hemolytic anemia, and it’s the damage caused to red blood cells as they’re forced through the smaller valve. This splits them into smaller fragments called schistocytes, which leads them to get peed out and to hemoglobinuria, or hemoglobin in the urine.