WordNet

a state in which the level of carbon dioxide in the blood is lower than normal; can result from deep or rapid breathing (同)acapnia

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/03/05 20:01:21」(JST)

wiki en

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.

Effects

Even when marked, hypocapnia is normally well tolerated.^[1] 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 increased 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.

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.

Causes

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

Self-induced hypocapnia through hyperventilation is the basis for the dangerous schoolyard fainting game. Deliberate hyperventilation has been used by underwater breath-hold divers for the purpose of extending dive time as it effectively reduces respiratory drive due to low CO₂ levels allowing one to break one's standard limit of breath holding at the risk of shallow water blackout (which is a significant cause of drowning) as while air hunger is reduced the oxygen levels are not increased, in fact hypocapnia reduces the oxygen levels available to the brain due to the elevated affinity of oxygen to hemoglobin (Bohr effect) hence highly increasing the chances of blackout.

References

^ Laffey JG, Kavanagh BP (2002). "Hypocapnia". N. Engl. J. Med. 347 (1): 43–53. doi:10.1056/NEJMra012457. PMID 12097540.

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. 単純性および混合性酸塩基障害 simple and mixed acid base disorders
2. 過換気症候群 hyperventilation syndrome
3. 高齢者の病院でのマネージメント hospital management of older adults
4. 急性肺塞栓症の診断 diagnosis of acute pulmonary embolism
5. 小児における急性肝不全：マネージメント acute liver failure in children management

English Journal

Hypocapnia induced vasoconstriction significantly inhibits the neurovascular coupling in humans.

Szabo K, Lako E, Juhasz T, Rosengarten B, Csiba L, Olah L.SourceDepartment of Neurology, University of Debrecen, Debrecen, Hungary.
Journal of the neurological sciences.J Neurol Sci.2011 Oct 15;309(1-2):58-62. Epub 2011 Aug 10.
BACKGROUND/AIMS: Previous studies proved that vasodilation, caused by hypercapnia or acetazolamide, does not inhibit the visually evoked flow velocity changes in the posterior cerebral arteries. Our aim was to determine whether vasoconstriction induced by hypocapnia affects the neurovascular couplin
PMID 21831399

Hypocapnia induced cerebral ischaemia during therapeutic hypothermia-Potential for harm?

Curley G, Laffey JG.SourceDepartment of Anaesthesia and Intensive Care Medicine, Galway University Hospitals, Galway, Ireland; School of Medicine, Clinical Sciences Institute, National University of Ireland, Galway, Ireland.
Resuscitation.Resuscitation.2011 Sep;82(9):1122-3. Epub 2011 Jun 12.
PMID 21700377

Japanese Journal

人工換気療法 (特集急性脳炎・脳症の概念) -- (急性脳炎・脳症の予防・治療)

濱田哲,石川悠加,石川幸辰 [他]
日本臨床 69(3), 520-524, 2011-03
NAID 40018729437

Effect of hyperventilation on organ tissue blood flow in brain and ventricles of rabbits measured by the colored microsphere method

Momota Yoshihiro,Ishikawa Motoko,Kishimoto Naotaka,Yamabayashi Kazutomo,Kotani Junichiro
Journal of Osaka Dental University 43(1), 57-61, 2009-04
… Hyperventilation (with hypocapnia) was induced by adjusting the ventilation to achieve a PaCO_2 of 25?30mmHg. … Following hypocapnia, normocapnia was attained by loading CO_2 gas without changing the conditions of ventilation to increase PaCO_2 to 40?45mmHg. …
NAID 110007160602