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 (?) in FEV1 or VDP (n=58, 38% COPD), G2 = ?FEV1 and ?VDP (n=23, 39% COPD), G3 = ?FEV1 only (n=20, 45% COPD), G4 = ?VDP only (n=35, 69% COPD).

Results: In G1, 86% and 41% had normal FEV1 or VDP respectively post-BD. In G2, ?FEV1 was correlated to ?VDP, but not to ?AOS. Discordance of ?FEV1 and ?VDP was observed in 40% patients (G3 and G4). Of those with ?FEV1 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, ?FEV1 did not correlate to other ?metrics. In G4, 57% had normal FEV1 and 2% had normal VDP post-BD. ?VDP was correlated to ?AX and ?X5 but not to ?FEV1 or ?FVC. 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 ?FEV1 may reflect changes in larger conductive airways not assessed by VDP. G4 have more advanced disease where ?VDP reflects ?lung compliance possibly due to dilation of the small airways.