Missing airways, ventilation defects and conductive airway physiology in asthma.

<bold>Aim:</bold> In asthma patients, excessive luminal narrowing or mucus plugs potentially generate a perturbation in bronchial asymmetry. Based on realistic models of asthma patients’ bronchial trees we hypothesized that in asthma, CT-derived total airway count (TAC) and hyperpolarized gas magnetic resonance imaging (MRI) derived ventilation defect percent (VDP) should be primarily related to the multiple breath washout (MBW) measure of conductive ventilation heterogeneity, irrespective of degree of acinar ventilation heterogeneity. <bold>Methods:</bold> We investigated associations between MBW derived indices of conductive and acinar ventilation heterogeneity (Sacin*, Scond*) and TAC and VDP, both post-bronchodilation. <bold>Results:</bold> Twenty-one asthma patients (52±12[SD]yrs) of widely varying degrees of asthma severity (GINA1-3 n=4, GINA4 n=3, GINA5 n=14), with mean[±SD] FEV₁: 83 [+20]%pred, Sacin*: 188 [+146]%pred, Scond*: 197 [+106]%pred. Besides univariate relationships of TAC and VDP with Scond* (Figure 1), principal components analysis revealed a strong relationship between imaging-derived TAC and MBW-derived Scond*, but not Sacin*. In addition, VDP was also independently associated with Scond*. <fig><object-id>erj;64/suppl_68/PA3383/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig> <bold>Discussion:</bold> This imaging structure-function study is consistent with prior patient-specific modeling of ventilation distribution in asthma linking the asymmetry of bronchial airway ramification to the MBW measure of convective ventilation heterogeneity.