Apnea is the cessation of breathing. During apnea, there is no movement of the muscles of inhalation, and the volume of the lungs initially remains unchanged. Depending on how blocked the airways are (patency), 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. Voluntarily doing this is called holding one's breath there is the practice like the sport free diving when the breath hold is volunter, the athletes train to increase the breath hold. Apnea may first be diagnosed in childhood, and it is recommended to consult an ENT specialist, allergist or sleep physician to discuss symptoms; malformation and/or malfunctioning of upper airways may be observed by an orthodontis.

Causes

Apnea can be involuntarily—for example, drug-induced (such as by opiate toxicity), mechanically induced (for example, by strangulation or choking), or a consequence of neurological disease or trauma. During sleep in patients who are suffering from sleep apnea, these events can occur up to more than a hundred times per hour every night.

Apnea can also be observed during periods of heightened emotion, such as during crying or accompanied by the Valsalva maneuver when a person laughs. Apnea is a common feature of sobbing while crying, characterised by slow but deep and erratic breathing followed by brief periods of breath holding.

Another example of apnea are breath-holding spells; these are sometimes emotional in cause and are observed in children as a result of frustration, emotional stress and other psychological extremes.

Voluntary apnea can be achieved by closing the vocal cords, simultaneously keeping the mouth closed and blocking the nasal vestibule, or constantly activating expiratory muscles.

Complications

Under normal conditions, humans cannot store much oxygen in the body. Prolonged apnea 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, since the urge to breathe becomes unbearable. The reason for the time limit of voluntary apnea 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.

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