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The Human Phenotype Ontology (HPO) is downloaded weekly from The file downloaded is considered the "last stable build" available for the ontology. For more about the HPO, view their website at

Term:Expiratory air trapping
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Accession:HP:0032968 term browser browse the term
Definition:Abnormal retention of gas within a lung or part of a lung, as a result of airway obstuction 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.
Comment:The extent of air trapping present on expiratory scans can be measured using a semiquantitative scoring system, which estimates the percentage of lung that appears abnormal on each scan. Such systems have the advantage of being simple, quick, and easy to perform at the time of image interpretation. Furthermore, in one study, a simple 5-point scoring system was found to be associated with better interobserver agreement than a more detailed scoring system.

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  Human phenotype 0
    Phenotypic abnormality 0
      Abnormality of the respiratory system 0
        Abnormal respiratory system morphology 0
          Abnormal pulmonary thoracic imaging finding 0
            Expiratory air trapping 0
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