asphyxiation

n. suffocation; act of choking; being unable to breathe

Asphyxia (from Greek a-, "without" and σφυγμός (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.
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(n.)
The act of causing asphyxia; a state of asphyxia.
  

noun
being prevented from breathing

Noun
1. the condition of being derprived of oxygen (as by having breathing stopped)
(synonym) suffocation
(hypernym) hypoxia
(derivation) suffocate, stifle, asphyxiate, choke
2. killing by depriving of oxygen
(synonym) suffocation
(hypernym) killing, kill, putting to death
(hyponym) choking, strangling, strangulation, throttling
(derivation) suffocate, stifle, asphyxiate