Apnea (BrE: apnoea) 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.

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 orthodontist.

 

Note:   The above text is excerpted from the Wikipedia article Apnea, which has been released under the GNU Free Documentation License.