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Why does hyperventilation cause dizziness?

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a dairy product
Nov 1, 2002
Hi folks!

We all know that hyperventilation will push back the breathing reflex mainly because of decreased CO2-levels.
We also know that excessive hyperventilation can cause dizziness.

But I at least don't know the reason for the latter fact. Maybe it has something to do with increased blood alkalinity...?

Could anyone clarify this?
Getting rid of too much CO2 will cause constriction of blood vessesl in the brain and actually supply low levels of O2 to the brain - but there is more to it than that.

There has been some discussion in the past over Blood pH and how it affects O2 carrying capacity. A high pH stengthens the bond between Haemoglobin and Oxygen. Thus not only will blood flow be reduced but also offload less O2 when in the brain.

I think these two factors will explain a lot of the dizziness.

constriction of blood vessels

Thanks Ben!

So why does a low CO2-level cause constriction of blood vessels in the brain? Why would they constrict below normal in this situation? It's not like the brain would be getting too much oxygen otherwise... :confused:

I'm guessing this is just the effect of high CO2 levels (causing blood vessels to constrict elsewhere and dilate in the brain. Or would that be caused by low O2?) being taken to the other extreme... but I can't really think of a reason for it to happen.
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