Poster X6 - Mesh Nebulizer Particle Characteristics and Deposition in a Stochastic Lung Model

Introduction: Approximately 9 million Americans have Chronic Obstructive Pulmonary Disease (COPD) and 18 million more are suspected to have undiagnosed COPD (1). Medication for treating COPD is frequently delivered to patients using nebulizer devices, which are now commonplace and have been in use since the mid-1900s. Surprisingly, there remains a need to better understand how individual nebulizers produce and deposit particles within the lung airways. For most medical treatments, the medicine must reach the deeper lung, such as the pulmonary region. For example, COPD occurs in the pulmonary region, and particles larger than 5 μm will not reach this region (2). Our research focuses on analyzing the particles emitted by nebulizers. We look at the particles produced under various conditions and determine the size distribution, number density of particles, and other parameters that dictate where these particles deposit in the lung. Our experiment uses a standard mesh nebulizer (Auglam, Ultrasound Portable Nebulizer, Model YS35E). This nebulizer pushes resolved medication through a vibrating mesh to generate aerosol particles for delivery into the lung with airflow. The size and number distributions of the particles produced by the nebulizer are analyzed through an experimental airway system and a stochastic lung model to determine where these particles deposit in the lung using the Multiple-Path Particle Dosimetry Model (MPPD).

Materials and

Methods: We have performed a series of experiments generating aerosols from deionized water and saline solutions (0.9% and 7%). 0.9% saline is commonly used in nebulizer applications, whereas 7% saline is only prescribed in specific circumstances with diseases such as cystic fibrosis and bronchiectasis (3). These tests occurred at room temperature with vacuum pulling 4 LPM (liters per minute) through the system.
To produce accurate results for this experiment, we developed an airtight system to pass the aerosol particles through as seen in Figure 1. The nebulizer was connected to the system via tubes, with airflow controlled by a vacuum to mimic respiratory conditions through the model. Generated particles flow through a settling chamber before entering a chamber containing a 3D model of human lungs made of resin. The settling chamber is used to control the particle concentration entering the Wide-Range Particle Spectrometer (1000XP, MSP). The WPS can measure particle size ranging from 0.3-10 μm. The information from the WPS was placed into the MPPD. MPPD takes the information gathered by the WPS and simulates a stochastic lung model to calculate the particle deposition in different airway regions. The data utilized from MPPD were the deposition mass rates for each major airway region.

Results, Conclusions, and Discussions: This experiment focuses on analyzing the particle characteristics and the deposition fractions from the MPPD model. As seen in Figure 2, the number of particles per cubic centimeter were compared to their diameters for each trial. The inlet trials feature data recorded before the nebulized particles flowed through the resin airway model, so there were larger particles recorded for both 0.9% and 7% saline at the inlet. For 7% saline, the particles were larger and the WPS recorded the highest concentrations of particles per diameter size for 7% saline at the inlet. Amongst all the solutions, water produced the highest concentration of the smallest size particles. This was due to the fact it had a much lower viscosity compared to the saline solutions. Generally, particle size decreases as the viscosity of the liquid increases; however, mesh nebulizers function better with low viscosity substances (4).
The MPPD model utilizes the diameter and concentrations recorded by the WPS to provide the deposition fraction of each solution. These fractions are converted into percentages for the head, tracheobronchial (TB), and pulmonary regions for comparison in Figure 3. The 7% saline deposited the most particles in all regions with 22% total, while 0.9% deposited the least with 17% total. This low value indicates most of the aerosol particles are exhaled or continued deeper into the lung than the simulation could process.
From the MPPD model and data analysis, there appears to be a correlation between particle size and deposition. For 7% saline, which has a higher viscosity, the generated particles were larger and deposited in higher percentages in the lung regions. In contrast, the mesh nebulizer produced the highest particle concentrations with solutions of lower viscosity such as 0.9% saline.
Mesh nebulizers are able to produce aerosol particles of small diameter sizes in high concentrations. In the future, the results of this study will be reevaluated experimentally using a 3D-printed porous lung model up to the 2nd generation of branching into the lung along with studying the effects of varying temperatures and airflow rates on particles produced by the nebulizers.

Acknowledgements (Optional): This project was supported by the Engineering Honors Program of Mercer University and Stamps Scholars program.

References:
(1) American Lung Association. Our Impact. https://www.lung.org/about-us/our-impact (accessed 2023-12-10).
(2) COPD - Symptoms and causes. (n.d.). Mayo Clinic. Retrieved May 11, 2024, from https://www.mayoclinic.org/diseases-conditions/copd/symptoms-causes/syc-20353679
(3) Kellett, F., & Robert, N. M. (2011). Nebulised 7% hypertonic saline improves lung function and quality of life in bronchiectasis. Respiratory Medicine, 105(12), 1831–1835. https://doi.org/10.1016/j.rmed.2011.07.019
(4) McCallion, O. N. M., Taylor, K. M. G., Bridges, P. A., Thomas, M., & Taylor, A. J. (1996). Jet nebulisers for Pulmonary Drug Delivery. International Journal of Pharmaceutics, 130(1), 1–11. https://doi.org/10.1016/0378-5173(95)04233-4