CT and Functional MRI to Evaluate Airway Mucus in Severe Asthma


      Intraluminal contributor(s) to airflow obstruction in severe asthma are patient-specific and must be evaluated to personalize treatment. The occurrence and functional consequence of airway mucus in the presence or absence of airway eosinophils remain undetermined.


      The objective of this study was to understand the functional consequence of airway mucus in the presence or absence of eosinophils and to identify biomarkers of mucus-related airflow obstruction.


      Mucus plugs were quantified on CT scans, and their contribution to ventilation heterogeneity (using MRI ventilation defect percent [VDP]) was evaluated in 27 patients with severe asthma. Patients were dichotomized based on sputum eosinophilia such that the relationship between mucus, eosinophilia, and ventilation heterogeneity could be investigated. Fractional exhaled nitric oxide (F eno) and related cytokines in sputum were measured.


      Mucus plugging was present in 100% of asthma patients with sputum eosinophils and 36% of those without sputum eosinophils ( P = .0006) and was correlated with MRI VDP prebronchodilator ( r = 0.68; P = .0001) and postbronchodilator ( r = 0.72; P < .0001). In a multivariable regression, both mucus and eosinophils contributed to the prediction of postbronchodilator MRI VDP ( R 2 = 0.75; P < .0001). Patients with asthma in whom the mucus score was high had raised F eno ( P = .03) and IL-4 ( P = .02) values. Mucus plugging correlated with F eno ( r = 0.63; P = .005).


      Both airway eosinophils and mucus can contribute to ventilation heterogeneity in patients with severe asthma. Patients in whom mucus is the dominant cause of airway obstruction have evidence of an upregulated IL-4/IL-13 pathway that could be identified according to increased F eno level.

      Key Words


      EB ( eosinophilic bronchitis), Feno ( fractional exhaled nitric oxide), 3He ( helium-3), N2 ( nitrogen), VDP ( ventilation defect percent)
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      Linked Article

      • CT and Functional MRI to Evaluate Airway Mucus in Severe Asthma
        CHESTVol. 156Issue 4
        • In Brief
          With great interest, we read the article by Svenningsen et al in a recent issue of CHEST (June 2019) on CT scanning and functional MRI to evaluate airway mucus in severe asthma.1 We understand their results, but would like to ask the authors two questions. First, the authors included as study subjects “patients with severe asthma.” It takes time to perform MRI; the subjects should be patients who could be in the resting position during the time required for MRI. We would like to ask the authors whether all the patients with “severe asthma” could maintain the resting position during the MRI time.
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      • Response
        CHESTVol. 156Issue 4
        • In Brief
          We thank Drs Okauchi, Yamada, and Satoh for their pertinent questions in response to our multimodality imaging study designed to better understand the functional consequence of intraluminal contributors to airway obstruction in patients with severe asthma.1
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