Increased ventilation heterogeneity in asthma can be attributed to proximal bronchioles

In recent years, tests of ventilation heterogeneity such as the multiple breath washout (MBW) have gained popularity as potentially sensitive measures of disease in the small airways [1]. The premise of a non-invasive test such as the MBW, is that morphological alterations at differing lung depths can be sampled at the mouth via their effect on ventilation heterogeneity. MBW phase-III slope derived indices of ventilation heterogeneity include the conductive slope index (Scond), a purely convection-dependent contribution generated in the conducting zone of the lungs, and the acinar slope index (Sacin), brought about by diffusion-convection mechanisms operating near acinar entrances in the respiratory zone [2, 3]. Footnotes This manuscript has recently been accepted for publication in the European Respiratory Journal . It is published here in its accepted form prior to copyediting and typesetting by our production team. After these production processes are complete and the authors have approved the resulting proofs, the article will move to the latest issue of the ERJ online. Please open or download the PDF to view this article. Conflict of interest: Dr. Foy has nothing to disclose. Conflict of interest: Dr. Kay has nothing to disclose. Conflict of interest: Dr. Siddiqui has nothing to disclose. Conflict of interest: Dr. Brightling reports grants and personal fees from GSK AZ/MedImmune, Novartis, Chiesi, Pfizer, Vectura, Theravance, BI, Roche/Genetech, outside the submitted work. Conflict of interest: Dr. Paiva has nothing to disclose. Conflict of interest: Dr. Verbanck has nothing to disclose.