M.Sc Thesis

M.Sc StudentHeller-Algazi Metar
SubjectComputational Fluid Dynamics as a Framework for Respiratory
Therapy Reasearch
DepartmentDepartment of Biomedical Engineering
Supervisor ASSOCIATE PROF. Josue Sznitman


From respiratory gas exchange to drug delivery, understanding the intricacies of airflow in the lungs is an important step in the development of better patient treatment. Often in vivo experimental and imaging modalities are limited, necessitating the use of alternative research techniques. One attractive approach is computational fluid dynamics (CFD): in silico simulations of airflow and aerosol particle dynamics. Here, we present two distinct topics that utilize CFD for respiratory research: one as an investigative tool to assess high-frequency ventilation in neonates, and one to test a proof-of-concept of a novel aerosol inhalation technique.           

             High-Frequency Ventilation in Neonates: we investigate respiratory flow phenomena in an upper airway model of an intubated neonate undergoing invasive mechanical ventilation, spanning conventional to high-frequency ventilation (HFV) modes. We resolve transient, three-dimensional flow fields and observe a persistent jet flow exiting the endotracheal tube whose strength is directly modulated according to the ventilation protocol. We identify this synthetic jet as the dominating signature of convective flow under intubated ventilation. Concurrently, our in silico wall shear stress analysis reveals a hitherto overlooked possible source of ventilator-induced lung injury as a result of jet impingement on the tracheal carina, suggesting damage to the bronchial epithelium; this type of injury is known as biotrauma. We find HFV advantageous in mitigating the intensity of such impingement, which may contribute to its role as a lung protective method. Our findings may encourage the adoption of less invasive ventilation procedures currently used in neonatal intensive care units.

            Targeted inhalation via Inhaled Volume Tracking method: despite the widespread use of aerosol inhalation as a drug delivery method, targeted delivery to the upper airways remains an ongoing challenge in the quest for improved clinical response in respiratory disease. We examine in silico flow and particle dynamics when using an oral Inhaled Volume Tracking (IVT) manoeuvre. A short pulsed aerosol bolus is injected during slow inhalation flow rates followed by clean air, and a breath-hold is initiated once it reaches the desired depth. We explore the fate of a broad particle size range (1-40 µm) for both upright and supine positions. Our findings illustrate that despite attempts to mitigate dispersion using slower flow rates, the laryngeal jet disperses the aerosol bolus and thus remains a hurdle for efficient targeted delivery. Nevertheless, we show a decrease in extra-thoracic deposition; large aerosols in the range of 10-30 µm potentially outperform existing inhalation methods, showing deposition fractions of up to 80% in an upright orientation. The improved deposition during IVT shows promise for clinical applications and could be leveraged to deliver larger payloads to the upper airways.