Specific Ventilation in Severe Asthma Evaluated with Noncontrast Tidal Breathing 1H MRI

Purpose: To determine if proton (1H) MRI-derived specific ventilation is responsive to bronchodilator (BD) therapy and associated with clinical biomarkers of type 2 airway inflammation and airways dysfunction in severe asthma. Materials and Methods: In this prospective study, 27 participants with severe asthma (mean age, 52 years +/- 9 [SD]; 17 female, 10 male) and seven healthy controls (mean age, 47 years +/- 16; five female, two male), recruited between 2018 and 2021, underwent same-day spirometry, respiratory oscillometry, and tidal breathing 1H MRI. Participants with severe asthma underwent all assessments before and after BD therapy, and type 2 airway inflammatory biomarkers were determined (blood eosinophil count, sputum eosinophil percentage, sputum eosinophil-free granules, and fraction of exhaled nitric oxide) to generate a cumulative type 2 biomarker score. Specific ventilation was derived from tidal breathing 1H MRI and its response to BD therapy, and relationships with biomarkers of type 2 airway inflammation and airway dysfunction were evaluated. Results: Mean MRI specific ventilation improved with BD inhalation (from 0.07 +/- 0.04 to 0.11 +/- 0.04, P <.001). Post-BD MRI specific ventilation (P =.046) and post-BD change in MRI specific ventilation (P =.006) were greater in participants with asthma with type 2 low biomarkers compared with participants with type 2 high biomarkers of airway inflammation. Post-BD change in MRI specific ventilation was correlated with change in forced expiratory volume in 1 second (r = 0.40, P =.04), resistance at 5 Hz (r = -0.50, P =.01), resistance at 19 Hz (r = -0.42, P =.01), reactance area (r = -0.54, P <.01), and reactance at 5 Hz (r = 0.48, P =.01). Conclusion: Specific ventilation evaluated with tidal breathing 1H MRI was responsive to BD therapy and was associated with clinical biomarkers of airways disease in participants with severe asthma.