Assessment of ventilation heterogeneity in severe asthma using phase-resolved functional lung magnetic resonance imaging.

Abstract

Ventilation heterogeneity is a hallmark of asthma. This study examines the feasibility of phase-resolved functional lung magnetic resonance imaging (PREFUL MRI) in the evaluation of ventilation heterogeneity in severe asthma, its response to bronchodilator, and correlation with spirometry. Twenty-three patients with severe asthma and seven healthy volunteers completed PREFUL MRI and spirometry pre and post-bronchodilator. Ventilation heterogeneity was assessed using ventilation defect percentages (VDP) for regional ventilation (RVent) and flow-volume loop cross-correlation (FVL), interquartile distance (IQD), and inhomogeneity index (IHI). Patients exhibited a significantly higher pre-bronchodilator VDP_RVent (19.9 ± 14.0 vs. 1.9 ± 1.9%, p < 0.001), VDP_FVL (21.6 ± 15.9 vs. 1.7 ± 2.1%, p < 0.001), IQD (0.60 ± 0.25 vs. 0.30 ± 0.06, p < 0.001), and IHI (0.34 ± 0.12 vs. 0.18 ± 0.04, p < 0.001) compared to healthy volunteers. Post-bronchodilator, VDP_RVent (14.7 ± 12.5 vs. 19.9 ± 14.0%, p = 0.02), IQD (0.51 ± 0.20 vs. 0.60 ± 0.25, p = 0.02), and IHI (0.30 ± 0.11 vs. 0.34 ± 0.12, p = 0.02) decreased significantly in patients but remained significantly higher than in healthy volunteers. Significant correlations were observed between pre-bronchodilator FEV1 and VDP_RVent (ρ = -0.61, p < 0.001), VDP_FVL (ρ = -0.73, p < 0.001), IQD (ρ = -0.57, p = <0.001), and IHI (ρ = -0.60, p < 0.001). PREFUL MRI derived markers of ventilation heterogeneity are worse in patients with asthma, improve post-bronchodilator, and correlate with the severity of airflow obstruction. These findings support the role of PREFUL MRI in assessing ventilation heterogeneity in asthma.