Investigation of multiphase multicomponent aerosol flow dictating pMDI-spacer interactions

The use of Pressurized metered dose inhalers (pMDIs) for the treatment of asthma and other chronic obstructive pulmonary diseases is frequently associated with breath-actuation synchronization problems and poor pulmonary delivery, particularly amongst the pediatric and geriatric population groups. Spacers, or Valved Holding Chambers (VHCs), are frequently used to address these problems. However, the performance of spacers with different pMDIs is also highly variable and needs to be investigated. The purpose of the current study is to develop a computational fluid dynamics (CFD) model which can characterize multiphase multicomponent aerosol flow issuing from a commercial suspension-based pMDI into a spacer. The CFD model was initially calibrated against published experimental measurements in order to appropriately model the spray characteristics. This model was subsequently used to examine several combinations of inhaler, spacer and USP Throat geometries under different discharge rates of coflow air. The CFD model predictions compared favorably with experimental measurements. In particular, the predictions show, in accordance with experimental determinations, a decrease of drug retained by the spacers with increasing coflow air. The recirculation observed near the obstructions in axial path of the spray within either spacer is considered to be central for increasing spray retention and drug deposition behavior. Fluid flow patterns within the spacers were correlated with drug deposition behavior through a dimensionless variable, the Recirculation index (RCI). Bigger particles were found to be selectively retained within the spacer.