Application of normalised phase III slope analysis for assessing small and large airways contribution in pulmonary models

Multiple-breath washout testing can by analyzed by calculating indices that represent the acinar and conductive contribution to the phase III alveolar slope seen on the plots of expired concentration against expired volume. The indices have the potential to differentiate between airway alterations in the large (conducting) and small (respiratory) airway zones. This analysis may have clinical significance in not only appropriately diagnosing airway disease, but also in quantifying the efficacy of drug therapies by comparison of pre- and post-therapy gas mixing indices. In the current study a respiratory airway model that produces first-breath phase III results within the physiological range is coupled with a variety of conducting airway models to examine the influence of conducting and respiratory model airway alteration on gas mixing indices using simulations with varying tidal volume, breath duration, breath hold, airway compliance, pre-inspiratory volume, and airway geometry.