Air trapping

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Air trapping, also called gas trapping, is an abnormal retention of air in the lungs where it is difficult to exhale completely.[1] It is observed in obstructive lung diseases such as asthma, bronchiolitis obliterans syndrome and chronic obstructive pulmonary diseases such as emphysema and chronic bronchitis.

Air trapping is not a diagnosis but is a presentation of an illness and can be used to find an appropriate diagnosis.

Measurement and Function[edit]

Exhaled volumes are measured by a pulmonary function test or simple spirometry, leading to an elevated residual volume and a measurement of forced expiratory volume. Air trapping is often incidentally diagnosed on computed tomography (CT) scanning. On expiratory films, retained hyperlucent gas will be visualised in cases of air trapping.[2]

Air trapping represents poorly aerated lung, but on its own is clinically benign. It is a common problem for smokers who dive. On diving the lung volume collapses and pushes air into the poorly aerated regions. On arising from a deep depth, these air-trapped areas of lung expand. This places great pressure on the lung tissue which can rupture.[3]


  1. ^ U. Joseph Schoepf; " Expiratory Hyperinflation - Air Trapping", Multidetector-Row CT of the Thorax Birkhäuser, 2005, p.101
  2. ^ Javier Luca ya; A. L. Baert; Janet L. Strife; "4.6.5 Air Trapping", Pediatric Chest Imaging: Chest Imaging in Infants and Children, Springer, 2007, p. 92
  3. ^ Johny A. Verschakelen; W. De Weber; "5.2.2 Air Trapping", Computed Tomography of the Lung: A Pattern Approach, Springer, 2007, p. 51