Forced oscillation technique and MRI predictions of airway reactance in moderate-severe asthma

Introduction: In silico airway models of asthma have incorporated airway abnormalities related to MRI ventilation defects to predict airway impedance (1) but this work did not include a direct comparison with experimental forced oscillation technique (FOT) measurements of airway reactance (X rs ), which is sensitive to peripheral airway narrowing. Objective: We investigated the relationship between FOT measurements in moderate-severe asthmatics with simulated measurements of airway impedance derived using an asymmetric branching airway tree model that was modified for individual patients using their MRI ventilation defect map. We hypothesized that X rs measured using FOT would be strongly related to airway tree model predictions. Methods: Participants underwent pulmonary function tests and hyperpolarized 3 He MRI to generate ventilation defect percent (VDP). MRI ventilation maps were co-registered to the airway tree model and small airways proximal to ventilation defects were constricted; model predictions of X rs at 5Hz were generated for each participant as previously described (1). On the same visit as MRI, X rs was measured using FOT and compared with model-predicted values. Results: We evaluated 35 moderate-severe asthmatics (15M/20F, 47±12 years, R AW =178±84% pred , FEV 1 =69±25% pred , FEV 1 /FVC=65±15%, VDP=10±9%). FOT-measured X rs was significantly correlated with VDP (ρ=-0.46, p=0.003) and model-predicted X rs (ρ=0.45, p=0.003). Conclusion: Ventilation MRI and airway tree models may be used to better understand reactance measurements in asthma. Our results provide strong support for the clinical use of FOT and MRI in asthmatics. REFERENCES: 1. Leary, D., et al. Physiol Rep, 2016. 4(7).