In the congenital heart defect known as patent ductus arteriosus, the ductus art
ID: 84581 • Letter: I
Question
In the congenital heart defect known as patent ductus arteriosus, the ductus arteriosus, which connects the aorta and the pulmonary arteries during fetal development, fails to close at birth. This will likely lead to all of the following EXCEPT:
A. equal, or increased, oxygen concentration in the blood that reaches the systemic tissues.
B. increased oxygen concentration in the blood that reaches the lungs.
C. increased work load imposed on the left ventricle.
D. increased work load imposed on the right ventricle.
I don't understand why the correct answer is A (meaning A is untrue). If the aorta is disconnected from the pulmonary arteries, which transfers DEOXYGENATED blood, wouldn't that lead to more oxygen in the systemic tissues, not less?
Explanation / Answer
The reason why less oxygenated blood will reach and not more is because some of the oxygenated blood will be pulled to the lower pressure pulmonary arteries from the aorta. So the blood that is more oxygenated than normal rate will be carried by the pulmonary circulation. The reason behind this is that due to failure of closing the ductus arteriosus there is mixing of highly oxygenated blood (from aorta) and deoxygenated blood when the blood is pumping towards the lungs. This causes heart to pump harder.