Air trapping, also called gas trapping, is an abnormal retention of air in the

lungs The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side ...

where it is difficult to exhale completely. It is observed in

obstructive lung disease Obstructive lung disease is a category of respiratory disease characterized by airway obstruction. Many obstructive diseases of the lung result from narrowing (obstruction) of the smaller bronchi and larger bronchioles, often because of excessiv ...

s such as

asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...

, bronchiolitis obliterans syndrome and

chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...

s such as emphysema and

chronic bronchitis Bronchitis is inflammation of the bronchi (large and medium-sized airways) in the lungs that causes coughing. Bronchitis usually begins as an infection in the nose, ears, throat, or sinuses. The infection then makes its way down to the bronchi. ...

. Air trapping is not a diagnosis but is a presentation of an illness, and can be a guide to the appropriate differential. __TOC__

Imaging

high resolution CT High-resolution computed tomography (HRCT) is a type of computed tomography (CT) with specific techniques to enhance image resolution. It is used in the diagnosis of various health problems, though most commonly for lung disease, by assessing t ...

air trapping has a typical imaging appearance, although often evaluation with both maximum inhalation and exhalation, or inspiratory and expiratory views, are needed for a more specific diagnosis. One of its typical imaging patterns is mosaic attenuation. 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 Atelectasis is the collapse or closure of a lung resulting in reduced or absent gas exchange. It is usually unilateral, affecting part or all of one lung. It is a condition where the alveoli are deflated down to little or no volume, as distinct ...

. This helps distinguish it from mosaic attenuation due to patchy fibrosis, as occurs with

nonspecific interstitial pneumonia Non-specific interstitial pneumonia (NSIP) is a form of idiopathic interstitial pneumonia. Symptoms Symptoms include cough, difficulty breathing, and fatigue. Causes It has been suggested that idiopathic nonspecific interstitial pneumonia ha ...

, and in early usual interstitial pneumonitis (the hallmark imaging diagnosis of

interstitial lung disease Interstitial lung disease (ILD), or diffuse parenchymal lung disease (DPLD), is a group of respiratory diseases affecting the interstitium (the tissue and space around the alveoli (air sacs)) of the lungs. It concerns alveolar epithelium, pu ...

) in which there is no change with inspiration and expiration.

Measurement and function

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. 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 Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle. The average total lung capacity of an adult human male is about 6 litres of air. Tidal breathing is normal, resting breathin ...

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.Johny A. Verschakelen; W. De Weber
"5.2.2 Air Trapping"
''Computed Tomography of the Lung: A Pattern Approach'', Springer, 2007, p. 51

References

{{DEFAULTSORT:Air Trapping Respiratory diseases