Bronchodilator Response Discordance in Patients with Asthma And/or COPD Using Xe-MRI and Spirometry

Introduction: The magnitude of bronchodilator (BD) response from Xe-MRI and FEV1 may be discordant due to differences in airways disease pathophysiology. Here we assessed BD responders and non responders using Xe-MRI and spirometry. Methods: 136 Patients from primary care with asthma and/or COPD taking part in the NOVELTY study [NCT02760329] were assessed pre and post-BD with Xe-MRI, spirometry and airwave oscillometry (AOS). From Xe-MRI, ventilation defect percent (VDP) assesses the proportion of non-ventilated lung. 4 groups were categorised; G1 = No clinically significant change (Δ) in FEV1 or VDP (n=58, 38% COPD), G2 = ΔFEV1 and ΔVDP (n=23, 39% COPD), G3 = ΔFEV1 only (n=20, 45% COPD), G4 = ΔVDP only (n=35, 69% COPD). Results: In G1, 86% and 41% had normal FEV1 or VDP respectively post-BD. In G2, ΔFEV1 was correlated to ΔVDP, but not to ΔAOS. Discordance of ΔFEV1 and ΔVDP was observed in 40% patients (G3 and G4). Of those with ΔFEV1 only (G3), 85% had normal post-BD FEV1 and 40% normal VDP. In G1 and G3 a visual change in ventilation was observed for some despite a static VDP. In G3, ΔFEV1 did not correlate to other Δmetrics. In G4, 57% had normal FEV1 and 2% had normal VDP post-BD. ΔVDP was correlated to ΔAX and ΔX5 but not to ΔFEV1 or ΔFVC. G4 had significantly (p<0.001) worse post-BD Xe-MRI acinar dimensions, FEV1, VDP, R5-R20, AX and X5 than G3. 7 patients with COPD had a significant worsening in VDP post-BD. Conclusions: FEV1 and VDP are complementary methods of assessing BD response. In G3 ΔFEV1 may reflect changes in larger conductive airways not assessed by VDP. G4 have more advanced disease where ΔVDP reflects Δlung compliance possibly due to dilation of the small airways.