CFD analysis of spacer and metered dose inhaler functionality and efficiency
Creators: name: Yousefighalehroudkhani, Morteza
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400308
subject: Medical devices
classificationCode: 401204
subject: Computational methods in fluid flow, heat and mass transfer (incl. computational fluid dynamics)
classificationCode: 401705
subject: Microelectromechanical systems (MEMS)

description: Respiratory drug delivery has been under the research spotlight for the past few decades, mainly due to the high incidence of pulmonary diseases and the fact that this type of delivery offers the highest efficiency for treatment. Despite its invaluable benefits, there are some major drawbacks to respiratory drug delivery- the most important of which being poor delivery efficiency and relatively high drug deposition in undesirable regions, such as the oral cavity. This study focused on improving inhalation therapy devices function using the results and findings obtained from CFD simulations.<br><br>Particle transport and deposition in an idealized oral airway geometry to better optimize the spacer one way-valve shape and design was studied in the second part of this research. A key issue in pulmonary drug delivery is improving the medical delivery device for effective and targeted treatment. Spacers are clear plastic containers attached to inhalers aimed at delivering more drug particles to the respiratory tract. The spacer’s one way-valve plays an important role in controlling and initializing the particles into the oral cavity. Three steady flow rates were used 15, 30 and 60 l/min and a Lagrangian, one-way coupled particle tracking model with near wall turbulence fluctuation correction was used to determine the deposition rates. For all three breathing rates, the velocity field in the mid-sagittal plane showed similar gross fluid dynamics characteristics, such as the separation and recirculation regions that occur after the larynx. The particle deposition rates compared reasonably well with available experiments. Most particles deposited at the larynx, where the airway has a decreasing cross-sectional area. For different particles sizes, most particles introduced at the lower region of the mouth produces higher possibility to pass through upper airway and enter the trachea and lung airways. The particle deposition patterns in the airway were traced back to its initial inlet position at the oral inlet; and this information provides the background for a conceptual and optimized design of the spacer one way valve.<br><br>Pressurized-metered dose inhalers (pMDIs) are the most popular aerosol therapy device for treating lung diseases. Despite its popularity, they are inefficient in delivering drug particles to the lung. Improving its performance involves ongoing investigations in the fields of engineering and medical science. In the last part of this research, the effect of two spray characteristics (injection velocity and spray cone angle) on the drug delivery efficiency was discussed. An idealized oral airway geometry, extending from mouth to the main bronchus, was connected to a pMDI device. Inhalation flow rates of 15, 30 and 60 l/min were used and the drug particle tracking was a one-way coupled Lagrangian model. The results showed that most particles deposited in the pharynx, where the airway has a reduced cross-sectional area. Particle deposition generally decreased with initial spray velocity, and with increased spray cone angle for 30 l/min and 60 l/min flow rates. However for 15 l/min flow rate the deposition increased slightly with an increase in the spray velocity and cone angle. The effect of spray cone angle was greater than the injection velocity on particle deposition. Overall drug delivery to the lungs was best achieved for 30 l/min, which produced on average 5% increase in pulmonary delivery compared to inhalation rates of 15 and 60 l/min.<br><br>Conventional inhalation therapy devices such as inhalers and nebulizers, nevertheless, suffer from low delivery efficiencies wherein only a small fraction of the inhaled drug reaches the lower respiratory tract. This is primarily because these devices are not able to produce a sufficiently fine drug mist that has aerodynamic diameters on the order of a few microns. The last part of this study employs using Computational Fluid Dynamics (CFD) to investigate the transport and deposition of the drug particles produced by a new aerosolization technique driven by surface acoustic waves (SAWs) into an in silico lung model geometrically reconstructed using computed tomography (CT) scanning. The particles generated by the SAW are released in different locations in a spacer chamber attached to a lung model extending from the mouth to the 6th generation of the lung bronchial tree. An Eulerian approach is used to solve the Navier-Stokes equations that govern the airflow within the respiratory tract and a Lagrangian approach is adopted to track the particles, which are assumed to be spherical and inert. Due to the complexity of the lung geometry, the airflow patterns vary as it penetrates deeper into the lung. In particular, we find that larger particles above 10µm are unable to follow the airflow stream immediately after a sharp change in the geometry. As such, these particles tend to deposit at locations where the geometry experiences a significant reduction in cross-section. The findings, nevertheless, show that the injection location can influence the delivery efficiency: injection points close to the spacer centerline result in deeper penetration into the lung. Additionally, we found that the ratio of drug particles entering the right lung is significantly higher than the left lung independent of the injection location.