A pneumothorax (collapsed lung, dropped lung) is the entry of air into the pleural space (the space between the lungs and chest wall).

When air enters this area, the lung loses contact with the inside of the chest and “drops” down. As this happens, the lung is not able to expand as it usually does. A pneumothorax can be small and require no treatment or be a life-threatening emergency, based on the size of the air sac that is in the pleural space and how much pressure it places on the lung. If the air sac is large or places increased pressure on the lung, it makes it difficult to pull air in and out of the lungs when breathing.

中文翻译：

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气胸

甲气胸（折叠肺，肺下降）是空气的进入胸膜间隙（肺和胸壁之间的空间）。

当空气进入​​该区域时，肺与胸部内部失去接触并“下降”。发生这种情况时，肺部将无法像通常那样扩张。根据胸膜腔中气囊的大小及其对肺部的压力，气胸可以很小，不需要治疗或危及生命。如果气囊很大或对肺部施加压力，则在呼吸时很难将空气吸入肺中或从肺中抽出。