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Asphyxia or asphyxiation (from Greek α- "without" and σφύξις sphyxis, "heartbeat") is a condition of severely deficient supply of oxygen to the body that arises from abnormal breathing. An example of asphyxia is choking. Asphyxia causes generalized hypoxia, which primarily affects the tissues and organs. There are many circumstances that can induce asphyxia, all of which are characterized by an inability of an individual to acquire sufficient oxygen through breathing for an extended period of time. These circumstances can include but are not limited to: the constriction or obstruction of airways, such as from asthma, laryngospasm, or simple blockage from the presence of foreign materials; from being in environments where oxygen is not readily accessible: such as underwater, in a low oxygen atmosphere, or in a vacuum; environments where sufficiently oxygenated air is present, but cannot be adequately breathed because of air contamination such as excessive smoke. Asphyxia can cause coma or death.
The body creates the need to breathe from the excess carbon dioxide in the blood. The body has chemosensors to detect oxygen levels in the blood, but these don't typically control respiratory rate. Many gases, though non-toxic, are classified as simple asphyxiants in their pure or inpure form or in high concentrations for this very reason.
One form of asphyxiation is from entering a low oxygen atmosphere or an inert atmosphere, such as in a food oil tank that has a covering blanket of nitrogen or argon to shield the oil from atmospheric oxygen. Without sufficient oxygen to sustain life, people will act normally at first but will then abruptly feel dizzy and black out in a matter of seconds as the remaining oxygen in the blood stream is consumed. Oxygen deficient atmospheres are the basis for many occurrences of single and multiple deaths; the deceased will be found lying prone on the bottom of a tank, and then the observer will rush in to rescue them, and succumb to the same effect, hence the need to vent or purge the inert gases from all tanks before entry.
Other causes of oxygen deficiency include:
- 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, and, in the process, displacing oxygen and preventing the blood from transporting oxygen 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 usually the case
- Acute respiratory distress syndrome.
- Exposure to extreme low pressure or vacuum to the pattern (see space exposure)
- Respiratory diseases
Smothering is 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. In a normal situation, 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.
In some cases, when performing certain routines, 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. The term "burking" comes from the method William Burke and William Hare used to kill their victims during the West Port murders. They killed the usually-intoxicated victims by sitting on their chests and suffocating them by putting a hand over their nose and mouth, while using the other hand to push the victim's jaw up. The corpses had no visible injuries, and were supplied to medical schools for money.
Compressive asphyxia (also called chest compression) is mechanically limiting 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 usually refers to compressive asphyxia resulting from being crushed or pinned under a large weight or force. An example of traumatic asphyxia includes cases where an individual has been using a car-jack to repair a car from below, and is crushed under the weight of the vehicle. Pythons, anacondas, and other constrictor snakes kill through compressive asphyxia. In cases of co-sleeping ("overlay"), the weight of an adult or large child may compress an infant's chest, preventing proper expansion of the chest. Risk factors include large or obese adults, parental fatigue or impairment (sedation by drugs or alcohol) of the co-sleeping adult and a small shared sleeping space (for example, both adult and infant sharing a couch).
In fatal crowd disasters, compressive asphyxia from being crushed against the crowd causes the large part of the deaths, rather than blunt trauma from trampling. This is what occurred at the Ibrox disaster in 1971, where 66 Rangers fans died; the 1979 The Who concert disaster where 11 died; the Luzhniki disaster in 1982, when 66 FC Spartak Moscow fans died; and at the Hillsborough disaster in 1989, when 96 Liverpool fans were crushed to death in an overcrowded terrace. 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 (equivalent to a weight of approximately 450 kg, or 1014 lbs). In cases where people have stacked up on each other forming a human pile, estimations have been made of around 380 kg (838 lbs) of compressive weight in the lowest layer.
The cause of death of police prisoners who have been restrained and left prone, for example in police vehicles, and cannot move into safer positions, has been referred to as "positional asphyxia". Restraint asphyxia is death or lost consciousness (to die later in a coma from anoxic brain damage), while being restrained in positions that cause asphyxia by facial compression, neck compression, or chest compression. This mostly occurs during law enforcement or psychiatric restraint situations. It may be that the positional asphyxia deaths of prisoners are actually active chest compression deaths caused by the weight of restrainers holding uncooperative prisoners down in a prone position during the process of being handcuffed and otherwise secured. Thus, the passive deaths following custody restraint presumed to be due to positional asphyxia after being secured by mechanical restraints may actually be examples of active restraint asphyxia occurring during the process of placing restraints.
Chest compression is also featured in various grappling combat sports, where it is sometimes called wringing. Such techniques are used either 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 budō referred to as do-jime, 胴絞, "trunk strangle" or "body triangle") where you wrap the legs around the opponent's midsection and squeeze them together.
Nitrogen asphyxiation is an occasional cause of accidental death and a theoretical method of capital punishment. After just two or three breaths of pure nitrogen, the oxygen concentration in the lungs would be low enough for some oxygen already in the bloodstream to exchange back to the lungs and be eliminated by exhalation.
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- Cross-side to chest compression choke
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