Hypocapnia
Encyclopedia
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
.
, 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.
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.
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
in the false assumption that it will extend dive time but at the risk of shallow water blackout
, which is a significant cause of drowning.
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
in the blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
. Hypocapnia usually results from deep or rapid breathing, known as hyperventilation
Hyperventilation
Hyperventilation or overbreathing is the state of breathing faster or deeper than normal, causing excessive expulsion of circulating carbon dioxide. It can result from a psychological state such as a panic attack, from a physiological condition such as metabolic acidosis, can be brought about by...
.
Hypocapnia is the opposite of hypercapnia
Hypercapnia
Hypercapnia or hypercapnea , also known as hypercarbia, is a condition where there is too much carbon dioxide in the blood...
.
Effects
Even when severe, hypocapnia is normally well tolerated. However, hypocapnia causes cerebral vasoconstrictionVasoconstriction
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries, small arterioles and veins. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in...
, leading to cerebral hypoxia
Cerebral hypoxia
Cerebral hypoxia refers to a reduced supply of oxygen to the brain. Cerebral anoxia refers to a complete lack of oxygen to the brain. There are four separate categories of cerebral hypoxia; in order of severity they are; diffuse cerebral hypoxia , focal cerebral ischemia, cerebral infarction, and...
and this can cause transient dizziness, visual disturbances, and anxiety. A low partial pressure
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
of carbon dioxide in the blood also causes alkalosis
Alkalosis
Alkalosis refers to a condition reducing hydrogen ion concentration of arterial blood plasma . Generally, alkalosis is said to occur when pH of the blood exceeds 7.45. The opposite condition is acidosis .-Causes:...
(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
Paresthesia
Paresthesia , spelled "paraesthesia" in British English, is a sensation of tingling, burning, pricking, or numbness of a person's skin with no apparent long-term physical effect. It is more generally known as the feeling of "pins and needles" or of a limb "falling asleep"...
, muscle cramps and tetany
Tetany (medical sign)
Tetany is a medical sign consisting of the involuntary contraction of muscles, which may be caused by disease or other conditions that increase the action potential frequency...
in the extremities, especially hands and feet.
Because the brain stem
Brain stem
In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...
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 emergenciesMedical emergency
A medical emergency is an injury or illness that is acute and poses an immediate risk to a person's life or long term health. These emergencies may require assistance from another person, who should ideally be suitably qualified to do so, although some of these emergencies can be dealt with by the...
such as intracranial hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
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
Free-diving
Freediving is any of various aquatic activities that share the practice of breath-hold underwater diving. Examples include breathhold spear fishing, freedive photography, apnea competitions and, to a degree, snorkeling...
in the false assumption that it will extend dive time but at the risk of shallow water blackout
Shallow water blackout
A shallow water blackout is a loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive in water typically shallower than five metres , when the swimmer does not necessarily experience an urgent need to breathe and has no other obvious medical condition that might have...
, which is a significant cause of drowning.
See also
- HypercapniaHypercapniaHypercapnia or hypercapnea , also known as hypercarbia, is a condition where there is too much carbon dioxide in the blood...
, increased level of carbon dioxide - Hyperventilation syndromeHyperventilation syndromeHyperventilation syndrome is a respiratory disorder, psychologically or physiologically based, involving breathing too deeply or too rapidly...
, which is often associated with hypocapnia - Shallow water blackoutShallow water blackoutA shallow water blackout is a loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive in water typically shallower than five metres , when the swimmer does not necessarily experience an urgent need to breathe and has no other obvious medical condition that might have...
, where hyperventilation and the subsequent hypocapnia is a cause