Inhaled ductus arteriosus: congenital heart disease, left and right shunt

2021-04-29 04:33 PM

Immediately after the baby is born and begins to breathe, the lungs swell, the air-filled alveoli, the resistance of blood flow through the pulmonary artery is also greatly reduced, allowing pulmonary artery pressure to decrease. 

During the fetal period, the lungs collapse, and the elastic pressure of the lungs keeping the alveoli collapsing causes most of the pulmonary blood vessels to collapse.

Therefore, the force of resistance to blood flow through the lungs is very great, causing the fetus to have high pulmonary artery pressure. Also, due to the low resistance of blood flow from the aorta through the major vessels of the placenta, the pressure in the fetal aorta is lower than normal - in fact lower than in the pulmonary artery. This causes almost all of the pulmonary artery blood to flow through a special fetal artery that connects the pulmonary artery with the aorta, called the ductus arteriosus, thereby bypassing the lungs. This mechanism allows for immediate blood circulation through the fetal systemic arteries without the need for blood to travel through the lungs. This lack of blood flow through the lungs is not detrimental to the fetus because the blood is supplied with oxygen to the placenta.

Fig. The ductus arteriosus, in blue, is the changes in venous blood that are oxidized at different points in the circulation. The diagram on the right shows the blood flow back from the aorta into the pulmonary artery and then into the lungs for a second time.

Close the ductus arteriosus after birth

As soon as the baby is born and begins to breathe, the lungs will swell; Not only does the alveoli fill with air, but the resistance of the blood flow through the pulmonary artery is also greatly reduced, enabling the pulmonary artery pressure to decrease. At the same time, aortic pressure is increased because blood flow from the aorta across the placenta stops abruptly. As a result, the pressure in the pulmonary artery decreases, while the pressure in the aorta increases. As a result, the blood flow through the aortic duct stops suddenly at birth, and in fact, the blood begins to flow back through the duct from the aorta into the pulmonary artery. This new condition of backflow causes the ductus to become clogged for a few hours to a few days in most babies, so the blood flowing through the ductus does not continue. The artery is thought to be closed because the oxygen concentration of the aortic blood now flows through it twice as high as the oxygen concentration of the blood flowing from the pulmonary artery into the ductus arteriosus during the fetal period. Oxygen probably contracts muscles in the tube wall. Unfortunately, in 1 out of 5,500 babies, the ductus arteriosus does not close, causing a condition known as the ductus arteriosus.

Circulatory dynamics with ductal arterial existence

In the early months of a newborn’s life, a ductus arteriosus is present usually does not cause serious abnormalities.

However, as the child grows, the difference between the high pressure in the aorta and the low pressure in the pulmonary artery gradually increases, with a corresponding increase in blood flow backwards from the aorta to the pulmonary artery. In addition, high aortic blood pressure often causes the diameter of the partially open artery duct to increase over time, making the condition even worse.

Circulating through the lungs

In an infant with a ductus artery, half to two-thirds of the aortic blood flows back through the tube into the pulmonary artery, then through the lungs, and eventually back to the left ventricle and aorta, passing through the heart's lungs and left side two or more times each time it travels through the circulatory system.

People with these do not show purple manifestations until later in adulthood when the heart fails or the lungs become blocked. Indeed, in the early stages of life, arterial blood is often better supplied with oxygen than usual because the more times it passes through the lungs.

Reduced heart and respiratory reserves

The main effects of the ductus arteriosus in the patient are a decrease in cardiac and respiratory reserve. The left ventricle is pumping cardiac output about twice or more than normal, and the maximum it can pump after an enlarged heart occurs is about four to seven times normal. Therefore, during exercise, blood flow through the rest of the body can never increase to the levels required for strenuous activity. Even with moderate exercise, the person can become weak and may even faint from temporary heart failure.

The high pressure in the pulmonary vessels due to excessive flow through the lungs can also lead to pulmonary obstruction and pulmonary oedema. Due to the heart's overcrowding, and especially the obstructive pulmonary condition that worsens with age, most patients with untreated ductus arteriosus die of heart disease by the age of 20 to 40. year-old.

Heart sound: the sound of a ductus blowing

In infants with ductus arteriosus, abnormal heart sounds sometimes are not heard because the amount of blood flowing back through the tube may not be enough to cause a heart murmur. But as the baby gets older, reaching ages 1 to 3 years, rough blows begin to be heard in the pulmonary artery area of ​​the thorax, as in the F. This sound is much more intense during the mind period Obtained when aortic pressure is high and much less during diastole when aortic pressure is low, so the murmur gradually wanes and disappears with each heartbeat.

Treatment of ductus arteriosus

Simple treatment of ductus arteriosus; one simply plugs the tube or cuts it and then closes the ends. In fact, the procedure was one of the first successful heart surgeries ever performed.

 

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