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 deadly 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 his 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.
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