Asphyxia

Asphyxia or asphyxiation (from Greek a-, "without" and σφύξις sphyxis, "heartbeat") is a condition of severely deficient supply of oxygen to the body that arises from being unable to breathe normally. An example of asphyxia is choking. Asphyxia causes generalized hypoxia, which primarily affects the tissues and organs.

Oxygen deficiency
The body creates the need to breathe from the excess carbon dioxide in the lungs; the body has no way to detect the absence of oxygen. Many gases, though non-toxic, are classified as simple asphyxiants in their pure 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, thus absence of sufficient oxygen to sustain life, people act normally but with no warning they simply feel dizzy and then 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 single and multiple deaths occurring; the deceased will be observed lying prone in 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.

The use of simple asphyxiant gases, such as the inhalation of pure helium for entertainment purposes, has resulted in death and brain injury from oxygen deficiency.

Other causes are:
 * 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

Smothering
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.

This method is sometimes used by a lion to kill a buffalo, by opening its mouth over the buffalo's mouth and nostrils and securing itself with its canine teeth.

Compressive asphyxia
Compressive asphyxia (also called chest compression) is 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 includes cases in which an individual has been using a car-jack to repair a car from below, only to be 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 cosleeping 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. 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 460 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 the detainees who have been restrained and left prone, for example in police vehicles, and are not able to move into safer positions has been referred to as "positional asphyxia". "Restraint asphyxia" is a term used to describe the death of people who have died 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. Most occur during law enforcement or psychiatric restraint situations. It may be that the "positional asphyxia" deaths of detainees are actually active chest compression deaths caused by the weight of restrainers holding uncooperative detainees 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.

Pressing is a form of torture or execution that works through asphyxia.

Perinatal asphyxia
Perinatal asphyxia is the medical condition resulting from deprivation of oxygen (hypoxia) to a newborn infant long enough to cause apparent harm. It results most commonly from a drop in maternal blood pressure or interference during delivery with blood flow to the infant's brain. This can occur due to inadequate circulation or perfusion, impaired respiratory effort, or inadequate ventilation. Perinatal asphyxia happens in 2 to 10 per 1000 newborns that are born at term.

Nitrogen asphyxiation
Nitrogen asphyxiation is an occasional cause of accidental death and a theoretical method of capital punishment. The painful experience of suffocation is not caused by lack of oxygen, but rather because of a buildup of carbon dioxide in the bloodstream which is exhaled under normal circumstances. 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. Crude simulation of oxygen transport through the lungs and blood stream suggests that the partial pressure of oxygen in arterial blood would be about 50 percent of saturation 1 minute after switching gases and would reach zero within 3 minutes.