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Asphyxia (from Greek a-, "without" and sphuxis, "pulse, heartbeat") is a condition of severely deficient supply of oxygen to the body that arises from being unable to breathe normally.
In an experiment where dogs were suffocated by placing an air-tight rubber mask over the dogs' heads, it was shown that it took around 8 minutes for the dogs to go into cardiac arrest.
This can be contrasted with another experiment in dogs were suffocated by forcing them to breathe nitrogen, the dogs surviving only an average of 5 minutes.