PDA flows from aorta to pulmonary artery decreasing afterload. Therefore cardiac output increases
PDA flows from the Aorta ==> Pulmonary arteries, by passing the RV so there is no change in O2 in the RV.
A PDA essentially creates a high-flow heart failure situation in the baby. Since a fraction of the LV output is returned without reaching the body, in order to maintain a normal CO to the body the left ventricle must pump a higher volume. This would also cause higher than normal pulmonary capillary flow.
I think some of the other question are getting at the idea that we don't know the direction of flow for sure. If the flow was aorta-->lungs, the systemic PO2 would be normal and RV PO2 high. But if it's opposite, the opposite would be true.
Since PDAs are maintained by PGE2, that would contribute to a low peripheral vascular resistance.
Why is does a PDA after birth result in "higher than normal left ventricular cardiac output" over increased "right ventricular PO2"? Does the pulm artery --> aorta shunt become reversed after birth, so higher oxygen aorta blood would flow back into the right ventricle? I get that more blood would be pumped to the left ventricle, resulting in RVH/LVH, but don't understand the O2 bit.
This is a very cool concept explained in the Rapid Review pathology book, page 257.
Left-sided to right-sided heart shunts results in volume overload in the right side of the heart, which increases LV volume (preload) due to more blood returning from the right heart to the left heart. An increase in LV preload is equal more cardiac output and more work for the heart. Later in life that will lead to an eccentric type of LVH with decrease cardiac output, pulmonary hypertension and a concentric RVH due to high afterload that the right heart has to pump against.
Low afterload > high CO
This is the actual correct explanation:
PDA causes blood to flow from descending aorta to patent ductus arteriosus into pulmonary circulation ("right-to-left")
The "steal" from the aorta during diastole requires increased cardiac output to compensate to deliver adequate amount of blood to rest of body
Source: https://www.ncbi.nlm.nih.gov/books/NBK430758/
submitted by โd_holles(218)
Here's an excellent image from AMBOSS if people are having difficulty visualizing this: https://imgur.com/a/VmhQRWm