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Hypocapnia or hypocapnea also known as hypocarbia, sometimes incorrectly called acapnia, is a state of reduced carbon dioxide in the blood. Hypocapnia usually results from deep or rapid breathing, known as hyperventilation.

Hypocapnia is the opposite of hypercapnia.

Even when severe, hypocapnia is normally well tolerated. However, hypocapnia causes cerebral vasoconstriction, leading to cerebral hypoxia and this can cause transient dizziness, visual disturbances, and anxiety. A low partial pressure of 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 of hyperventilation —pins and needles, muscle cramps and tetany in the extremities, especially hands and feet.

Hypocapnia is sometimes induced in the treatment of the medical emergencies, such as intracranial hypertension and hyperkalaemia.

Because the brain stem regulates breathing by monitoring the level of blood CO2, hypocapnia can suppress breathing to the point of blackout from cerebral hypoxia. Self-induced hypocapnia through hyperventilation is the basis for the deadly schoolyard fainting game. Deliberate hyperventilation has been unwisely used by underwater breath-hold divers to extend dive time but at the risk of shallow water blackout, which is a significant cause of drowning.

ee also

* Hypercapnia, increased level of carbon dioxide
* Hyperventilation syndrome, which is often associated with hypocapnia



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Look at other dictionaries:

  • hypocapnia — Abnormally decreased arterial carbon dioxide tension. SYN: hypocarbia. [hypo + G. kapnos, smoke, vapor] * * * hy·po·cap·nia kap nē ə n a deficiency of carbon dioxide in the blood hy·po·cap·nic nik adj …   Medical dictionary

  • hypocapnia — hy·po·cap·nia …   English syllables

  • hypocapnia — n.; see acapnia …   The new mediacal dictionary

  • hypocapnia — noun a state in which the level of carbon dioxide in the blood is lower than normal; can result from deep or rapid breathing • Syn: ↑acapnia • Ant: ↑hypercapnia • Derivationally related forms: ↑acapnial (for: ↑acapnia), ↑ …   Useful english dictionary

  • Акапния (Acapnia), Гипокапния (Hypocapnia) — отсутствие или значительное уменьшение содержания углекислоты в крови. Данное состояние может развиться вследствие глубокого дыхания или при низкой физической активности человека. Источник: Медицинский словарь …   Медицинские термины

  • Гипокапния (Hypocapnia) — см. Акапния. Источник: Медицинский словарь …   Медицинские термины

  • гипокапния — (hypocapnia; гипо + греч. kapnos дым; син. акапния нрк) пониженное содержание двуокиси углерода в артериальной крови, напр. в результате гипервентиляции …   Большой медицинский словарь

  • acapnia — hypocapnia; n. a condition in which there is an abnormally low concentration of carbon dioxide in the blood. This may be caused by breathing that is exceptionally deep in relation to the physical activity of the individual …   The new mediacal dictionary

  • Гипокапния — (hypocapnia, от греч. hypo мало + kapnos дым) – сос тояние организма, вызванное пониженным содержанием угле кислоты в артериальной крови, что снижает возбудимость дыха тельного центра …   Словарь терминов по физиологии сельскохозяйственных животных

  • Deep water blackout — Latent hypoxia hits on ascent A deep water blackout is a loss of consciousness caused by cerebral hypoxia on ascending from a deep freedive or breath hold dive, typically of ten metres or more when the swimmer does not necessarily experience an… …   Wikipedia

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