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 Syncope in anemia  

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What is the cause for, or mechanism of syncopy in a patient with severe anemia?

How is the state of anemia a state of 'hyperdynamic circulation'?

Waiting patiently for your valuable replies.


My 2 cents...

It can be considered a state of hyperdynamic circulation because, if I recall correctly, anemic blood does not raise BP on its own (compensatory mechanisms do this, though), overall blood flow increases and systemic vascular resistance is maintained; blood becomes «more fluid». Even though O2 is delivered to brain faster this way, it's no doubt a smaller amount... and when it becomes insufficient because it must be directed to organs like the heart, sudden loss of consciousness occurs.


1. anemia leads to tissue hypoxia causing peripheral vasodilation ------> Inc Venous return---> inc cardiac out put

mechanism of syncope is same as said by renegade (the mechanism of hyperdynamic circulation is also same as renegade, i just used the words differntly to make them look simpler)


Thank you both for the replies.smiling face

Renegade, I'm not sure what you mean by 'anemic blood does not raise B.P. on its own'.

What I gather from your explanation is that there's more blood in the capacitance vessels and less in the systemic circulation (?), which leads to cerebral hypoperfusion, hence syncope.

Or Mani...if the cardiac output is increased, why should less blood go to the brain? Because of peripheral vasodialation? I thought in matters of blood distribution, the brain was given top priority (eg. in shock).confused


Whole body needs O2... when there's tissue hypoxia (less O2 carried, which happens in anemia), it must be directed to where it is needed the most. Brain and heart have great blood supply, but when O2 is scarce (less hemoglobin to carry O2) heart takes priority... and people faint. Some react differently... Anemia may instead cause heart ischemia (angina) in other people shocked, possibly because brain and other organs take priority (considering a healthy heart).

As you can see, the hyperdynamic state is NOT responsible for syncope.
«Anemic blood does not raise B.P. on its own» means that it's not because a certain amount of blood has less red cells (or decreased [hemoglobin] or hematocrit) that it's likely to increase blood pressure: only after hypoxia generates the compensatory mechanisms that activate the sympathetic system is blood pressure to rise. nod


Vasodilation resulting from hypoxia actually causes fall in blood pressure that is countered by increased cardiac out put resulting from increased venous return. so there is no rise in BP.
Even though the total cardiac out put is increased, the O2 carried is low due to low hemoglobin. When even increased cardiac out put becomes insuffcient to meet the brains demand for O2, syncopy result. Hypoxic insult also occurs to other organs as well in the same way like u can get angina in anemia


Fine discussion. Thank you both.smiling face

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