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'''Apnea, apnoea, or apnœa''' (from the Greek, meaning ''to breathe'') is a term for suspension of external [[breathing]]. During an obstructive apnea event, the upper airway closes, usually at the pharynx, as the muscles of the throat and tongue relax. There is strong respiratory effort, but inspiration is blocked and very little or no airwayair can enter the lungs. During a central apnea (CSA) there is no respiratory effort from expansion of the chest and diaphram diaphragm [[respiration]] and the volume of the lungs initially remains unchanged. See For more details, see also [[Obstructive sleep apnea (OSA)]] and [[Central sleep apnea (CSA)]], and [[Hypopnea]].