label: Expiratory air trapping
label_lc: expiratory air trapping
description: "Abnormal retention of gas within a lung or part of a lung, as a result of airway obstruction of abnormalities in lung compliance. In the classic presentation, the lung will appear normal at inspiration, but on exhalation, the diseased portions of the lung which have lost connective tissue recoil will remain lucent while the healthy portions of the lung will become more dense due to atelectasis. This helps distinguish it from mosaic attenuation due to patchy fibrosis, as occurs with nonspecific interstitial pneumonia, and in early usual interstitial pneumonitis (the hallmark imaging diagnosis of interstitial lung disease) in which there is no change with inspiration and expiration."