I am thinking the mechanism from hyperventilation into brain damage:
- [CO2] decreases in plasma
- cerebral vasoconstriction
which then decreases the oxygen supply i.e. [O2] in the brain. The vessels get thinner. Those vessels are not surrounded by muscles so no Laplace law. There should be extensive diffusion. I do not understand how the vasoconstriction lead to decreased [O2] in cerebellum (probably in other parts of the brain too as complications; but primary complication in cerebellum first).
My intuition is that the smaller volume in the vessels can hold less oxygen particles inside (simplifying thinking by ideal gas Law pV = nRT; volume V down so the amount of substance n down too). Since there is continuous diffusion from vessels into brain tissue, the pressure p in the vessels and brain keeps constant. It is important to regulate this for homeostasis.
Concentration is directly proportional to the amount of substance. So vasoconstriction (decreased volume) leads to
- decreased oxygen and
- also carbon dioxide supply to the brain.
I think it would be better to say that vasoconstriction leads to decreased circulation of essential molecules. Hypoxia is a decreased oxygen supply so Decreased oxygen supply is NOT causing hypoxia. Carbon dioxide play some role in brain when in little quantities; at least, it is similarly required by the buffer system.
I think it is most correct to say that
Vasoconstriction leads to decreased local circulation of brain and eventually hypoxia.
I think this kind of logical mistake has been done in many books about the subject earlier. Claiming that A is causing A.
How can cerebral vasoconstriction lead to decreased O2 supply?