Effect of CO2 on Cerebral Vascular Tone

[E.S.Prakash]

---------- Forwarded message ----------
From: Waye Young <waye...@hotmail.com>
Date: Sat, Nov 6, 2010 at 6:56 PM
Subject: Hyperventilation and Cerebral Vasoconstriction

I read that CO2 is a potent vasodilator of cerebral vessels. In hyperventilation, there is a decrease of pCO2 which causes vasoconstriction leading to dizziness and progressively to a loss of consciousness.

 

How does CO2 affect cerebral vascular tone? I’m unclear which ion gates it affects.

 

The other effect of hyperventilation is hypocalcemia (which gives you the tingling sensation) and it’s mediated by Na-H as well as Na-Ca gates (I think ?).

How can there be hypocalcemia and vasoconstriction?

 

Any help is appreciated.

 

Regards,

Confused - Waye Young

Year 2 Student

[E.S.Prakash]

Waye Young,

1. "How does CO2 affect cerebral vascular tone - which ion channels does it gate?

It appears that the effect of CO2 on cerebral vascular tone is tied to its effects on the pH of brain extracellular fluid [Lassen, 1974]. Hypercapnia induces cerebral vasodilation, and hypocapnia induces cerebral vasoconstriction. Thus it appears that the cerebral blood flow is regulated to guard against deviations in brain pH from normal. There is evidence that cerebral vasodilation secondary to hypercapnia is mediated by a rise in nitric oxide in the cerebral circulation. [See Ladecola, 1992; http://www.pnas.org/content/89/9/3913.short]

2. "The other effect of hyperventilation is hypocalcemia"

The hypocalcemia that accompanies hyperventilation is secondary to an increase in pH of blood (alkalosis). One response to a rise in plasma pH is dissociation of protons from plasma proteins; the plasma proteins bind more ionized calcium and this results in a decrease in ionized calcium levels in plasma. Hypocalcemia is associated with an increase in excitability of neurons as well as skeletal muscle - this results in manifestations such as tingling, carpal and pedal spasm. 

3. "How can there be hypocalcemia and vasoconstriction"

Vasoconstriction in the cerebral circulation that occurs as a result of hyperventilation is secondary to hypocapnic alkalosis; the hypocalcemia is also secondary to the alkalosis. 

Best

Prakash

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