Hypocapnia

Hypocapnia, also sometimes known as acapnia, is a state in which the level of carbon dioxidein the bloodis lower than normal. This can result from deep or rapid breathing, known as hyperventilation. Even when severe, hypocapnia is normally well tolerated.

However, hypocapnia causes cerebral vasoconstriction, leading to cerebral hypoxiaand this can cause transient dizziness, visual disturbances, and anxiety. A low partial pressureof carbon dioxide in the blood also causes alkalosis(because CO₂ is acidic in solution), leading to lowered plasma calcium ions and nerve and muscle excitability. This explains the other common symptoms—pins and needles, stiff muscles and tetanyin the extremities, especially hands and feet.

Hypocapnia is sometimes induced in the treatment of certain medical emergencies, such as intracranialhypertension.

Because the body relies on the level of blood CO₂ to trigger the urge to breathe, hypocapnia can supress breathing to the point of blackout (cerebral hypoxia). Self-induced hypocapnia through hyperventilation is the basis for the deadly schoolyard choking game. It is also commonly used by underwater breath-hold diversto extend dive time but at the risk of shallow water blackout, which is a significant cause of drowning.

See also

• Hypercapnia, increased level of carbon dioxide

Reference

• Laffey, J.G. & Kavanagh, B.P. (2002). Hypocapnia. New England Journal of Medicine, 347:43-53.

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Hypocapnia Wikipedia article Hypocapnia.