Asphyxia

# Overview
Asphyxia (from Greek a-, "without" and  (sphygmos), "pulse, heartbeat") is a condition of severely deficient supply of oxygen to the body that arises from being unable to breathe normally. Asphyxia causes generalized hypoxia, which primarily affects the tissues and organs most sensitive to hypoxia first, such as the brain, hence resulting in cerebral hypoxia. Asphyxia is usually characterized by air hunger but this is not always the case; the urge to breathe is triggered by rising carbon dioxide levels in the blood rather than diminishing oxygen levels. Sometimes there is not enough carbon dioxide to cause air hunger, and victims become hypoxic without knowing it. In any case, the absence of effective remedial action will very rapidly lead to unconsciousness, brain damage and death. The time to death is dependent on the particular mechanism of asphyxia.

# Classification

## Smothering
Smothering refers to the mechanical obstruction of the flow of air from the environment into the mouth and/or nostrils, for instance by covering the mouth and nose with a hand, pillow, or a plastic bag. Smothering can be either partial or complete, where partial indicates that the person being smothered is able to inhale some air, although less than required. Normally, smothering requires at least partial obstruction of both the nasal cavities and the mouth to lead to asphyxia. Smothering with the hands or chest is used in some combat sports to distract the opponent, and create openings for transitions, as the opponent is forced to react to the smothering. It is also used in BDSM as a type of facesitting.
In some cases, smothering is combined with simultaneous compressive asphyxia. One example is overlay, in which an adult accidentally rolls over an infant during co-sleeping; an accident that often goes unnoticed and is mistakenly thought to be sudden infant death syndrome. Other accidents involving a similar mechanism are cave-ins or when an individual is buried in sand or grain. In homicidal cases, the term burking is often ascribed to a killing method that involves simultaneous smothering and compression of the torso.

## Compressive Asphyxia
Compressive asphyxia (also called chest compression) refers to the mechanical limitation of the expansion of the lungs by compressing the torso, hence interfering with breathing. Compressive asphyxia occurs when the chest or abdomen is compressed posteriorly.
In accidents, the term traumatic asphyxia or crush asphyxia is usually used to describe compressive asphyxia resulting from being crushed or pinned under a large weight or force. An example of traumatic asphyxia include cases where an individual has been using a car-jack to repair a car from below only to be crushed under the weight of the vehicle when the car-jack slips.
In fatal crowd disasters, contrary to popular belief, it is not the blunt trauma from trampling that causes the large part of the deaths, but rather the compressive asphyxia from being crushed against the crowd. In confined spaces, people push and lean against each other; evidence from bent steel railings in several fatal crowd accidents have shown horizontal forces over 4500 N (comparative weight approximately 460kg). In cases where people have stacked up on each other forming a human pile, estimations have been made of around 380kg of compressive weight in the lowest layer.
Chest compression is also featured in various grappling combat sports, where it is sometimes called wringing. Such techniques are either used to tire the opponent, or as complementary or distractive moves in combination with pinning holds, or sometimes even as submission holds.
Examples of chest compression include the knee-on-stomach position, or techniques such as leg scissors (also referred to as body scissors and in budo referred to as do-jime, , "trunk strangle") where you wrap the legs around the opponent's midsection and squeeze them together.
Pressing is a form of torture or execution which works through asphyxia.

# Causes
Asphyxia is used to maim or kill in capital punishment, suicide, torture, and warfare. It is also used non-fatally in martial arts, combat sports, BDSM and during sex as erotic asphyxia.  Because the need to breathe is triggered by the level of carbon dioxide in the blood, some victims may not experience an urgent need to breathe and may remain unaware of the onset of hypoxia.
Various chemical and physiological situations can interfere with the body's ability to absorb and use oxygen or regulate blood oxygen levels:
- Carbon monoxide inhalation, such as from a car exhaust, carbon monoxide has a higher affinity than oxygen to the hemoglobin in the blood's red blood corpuscles bonding with it tenaciously, displacing oxygen and preventing the blood from transporting it around the body.
- Contact with certain chemicals, including pulmonary agents (such as phosgene) and blood agents (such as hydrogen cyanide).
- Self-induced hypocapnia by hyperventilation, as in shallow water or deep water blackout and the choking game.
- A seizure which stops breathing activity.
- Sleep apnea.
- Drug overdose.
- Ondine's curse, central alveolar hypoventilation syndrome, or primary alveolar hypoventilation, a disorder of the autonomic nervous system in which a patient must consciously breathe. Although it is often said that persons with this disease will die if they fall asleep, this is not usuall the case.
- Acute respiratory distress syndrome