Airflow and Particle Deposition in Acinar Models with Interalveolar Septal Walls and Different Alveolar Numbers

Unique features exist in acinar units such as multiple alveoli, interalveolar septal walls, and pores of Kohn. However, the effects of such features on airflow and particle deposition remain not well quantified due to their structural complexity. This study aims to numerically investigate particle dynamics in acinar models with interalveolar septal walls and pores of Kohn. A simplified 4-alveoli model with well-defined geometries and a physiologically realistic 45-alveoli model was developed. A well-validated Lagrangian tracking model was used to simulate particle trajectories in the acinar models with rhythmically expanding and contracting wall motions. Both spatial and temporal dosimetries in the acinar models were analyzed. Results show that collateral ventilation exists among alveoli due to pressure imbalance. The size of interalveolar septal aperture significantly alters the spatial deposition pattern, while it has an insignificant effect on the total deposition rate. Surprisingly, the deposition rate in the 45-alveoli model is lower than that in the 4-alveoli model, indicating a stronger particle dispersion in more complex models. The gravity orientation angle has a decreasing effect on acinar deposition rates with an increasing number of alveoli retained in the model; such an effect is nearly negligible in the 45-alveoli model. Breath-holding increased particle deposition in the acinar region, which was most significant in the alveoli proximal to the duct. Increasing inhalation depth only slightly increases the fraction of deposited particles over particles entering the alveolar model but has a large influence on dispensing particles to the peripheral alveoli. Results of this study indicate that an empirical correlation for acinar deposition can be developed based on alveolar models with reduced complexity; however, what level of geometry complexity would be sufficient is yet to be determined

Unveiling advanced mechanisms of inhalable drug aerosol dynamics using computational fluid dynamics and discrete element method

Capsule-based dry powder inhalers (DPIs) are widely used to treat chronic obstructive pulmonary disease (COPD) by delivering active pharmaceutical ingredients (APIs) via inhalation into human respiratory systems. Previous research has shown that the actuation flow rate, aerodynamic particle size distribution (APSD), and particle shape of lactose carriers are factors that can influence the particle deposition patterns in human respiratory systems. Understanding the dynamics of APIs transport in DPIs and airways can provide significant value for the design optimization of DPIs and particle shapes to enhance the delivery of APIs to the designated lung sites, i.e., small airways. Thus, it is necessary to investigate how to modulate the above-mentioned factors to increase the delivery efficacy to small airways and enhance the therapeutic effect to treat COPD. Compared with in vitro and in vivo methods, computational fluid-particle dynamics (CFPD) models allow researchers to study the transport dynamics of inhalable therapeutic dry powders in both DPI and human respiratory systems. However, existing CFPD models neglect particle-particle interactions, and most existing airway models lack peripheral lung airway and neglect the airway deformation kinematics. Such deficiencies can lead to inaccurate predictions of particle transport and deposition. This study developed a one-way coupled computational fluid dynamics (CFD) and discrete element method (DEM) model to simulate the particle-particle and particle-device interactions, and the transport of API-carrier dry powder mixtures with different shapes of carriers in a DPI flow channel. The influence of actuation flow rate (30 to 90 L/min) and particle shape (aspect ratio equals 1, 5, and 10) on lactose carrier dynamics in a representative DPI, i.e., SpirivaTM HandihalerTM, has been investigated. Subsequently, an elastic truncated whole-lung model has also been developed to predict particle transport and deposition from mouth to alveoli, with disease-specific airway deformation kinematics. Numerical results indicate that 90 L/min actuation flow rate generates the highest delivery efficiency of Handihaler, as approximately 26% API reaches the deep lung region. The elastic truncated whole-lung modeling results show that noticeable differences of predictions between static and elastic lung models can be found, which demonstrates the necessity to model airway deformation kinematics in virtual lung models