Apnea, apnoea, or apnœa is a technical term for suspension of external breathing.

During apnea there is no movement of the muscles of respiration and the volume of the lungs initially remains unchanged.

Depending on the patency (openness) of the airways there may or may not be a flow of gas between the lungs and the environment; gas exchange within the lungs and cellular respiration is not affected.

Apnea can be voluntarily achieved (i.e., "holding one's breath"), drug-induced (e.g., opiate toxicity), mechanically induced (e.g., strangulation), or it can occur as a consequence of neurological disease or trauma. Mechanism Under normal conditions, humans cannot store much oxygen in the body.

Apnea of more than approximately one minute's duration therefore leads to severe lack of oxygen in the blood circulation.

Permanent brain damage can occur after as little as three minutes and death will inevitably ensue after a few more minutes unless ventilation is restored.

However, under special circumstances such as hypothermia, hyperbaric oxygenation, apneic oxygenation (see below), or extracorporeal membrane oxygenation, much longer periods of apnea may be tolerated without severe consequences. Untrained humans cannot sustain voluntary apnea for more than one or two minutes.

The reason for this is that the rate of breathing and the volume of each breath are tightly regulated to maintain constant values of CO2 tension and pH of the blood.

In apnea, CO2 is not removed through the lungs and accumulates in the blood.

The consequent rise in CO2 tension and drop in pH result in stimulation of the respiratory centre in the brain which eventually cannot be overcome voluntarily..

For more information about the topic Apnea, read the full article at Wikipedia.org, or see the following related articles:

Mechanical ventilation — In medicine, mechanical ventilation is a method to assist or replace spontaneous breathing. Mechanical ventilation can be life-saving and is a ...  > read more

Gas exchange — Gas exchange or respiration takes place at a respiratory surface; a boundary between the external environment and the interior of the body. For ...  > read more

Nasal congestion — Nasal congestion is the blockage of the nasal passages usually due to excessive secretion of mucus that is caused by a virus and typically resolves ...  > read more

Asphyxia — Asphyxia is a condition of severely deficient supply of oxygen to the body that arises from being unable to breathe ...  > read more

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