Large Conducting Airway Luminal Area is Not Different after Initiating Cystic Fibrosis Transmembrane Conductance Regulatory Modulator Therapy

Background: Cystic fibrosis (CF) is a genetic disorder in which patients have dysfunctional cystic fibrosis transmembrane regulatory (CFTR) proteins in the lungs that disrupt ion regulation resulting in a thick, viscous mucus layer on the airway epithelium. Consequential poor mucociliary clearance leads to repeated infections and chronic inflammation contributing to bronchiectasis which is associated with increased airway luminal area. CFTR modulator therapy can improve and even restore the function and expression of a mutated CFTR gene which has been shown to improve sweat chloride levels and pulmonary symptoms rapidly. However, the effect of CFTR modulator therapy on large conducting airway luminal area is unclear. We compared large conducting airway luminal area in patients with CF before and after initiating CFTR modulator therapy. We hypothesized that airway luminal area would normalize (decrease) after initiating CFTR modulator therapy. Methods: Twenty-three patients with CF (32±15 years, 11 female) with computed tomography (CT) imaging of their lungs before and after initiating CFTR modulator therapy were included in analyses. In each patient we measured seven large conducting airways (trachea, left and right main bronchus, bronchus intermediate, left and right upper lobe, and left lower lobe) before and after CFTR modulator therapy initiation. To control the potential effect of height, airway luminal area (mm2) was divided by patient height (cm). Paired t-tests compared differences between luminal area before after initiating CFTR modulator therapy. Results: Patients were taking CFTR modulator therapy for a median of 1.1 years (range: 22–2111 days) at the time of their CT imaging after initiating CFTR modulator therapy. Large conducting airway luminal area was not different before and after initiating CFTR modulator therapy in all seven airways: trachea (1.50±0.35 vs. 1.56±0.34 mm2/cm, p=0.14), right main bronchus (1.05±0.21 vs. 1.09±0.19 mm2/cm, p=0.11), bronchus intermediate (0.68±0.16 vs. 0.68±0.16 mm2/cm, p=0.54), right upper lobe (0.42±0.10 vs. 0.45±0.09 mm2/cm, p=0.27), left main bronchus (0.81±0.19 vs. 0.83±0.18 mm2/cm, p=0.21), left upper lobe (0.51±0.13 vs. 0.52±0.13 mm2/cm, p=0.45), and left lower lobe (0.44±0.11 vs. 0.46±0.10 mm2/cm, p=0.42). Conclusion: There was no change in large conducting airway luminal area after initiating CFTR modulator therapy suggesting CFTR modulator therapy may not reverse CF-associated airway luminal area changes. However, longitudinal analysis and investigation into the small airways are necessary for a comprehensive understanding of the effect of CFTR modulator therapy on airway luminal area changes. Funding: NIH (HL139854 to MJJ, HL131151 to SEB) and NSERC (PDF-577750-2023 to AHR). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.