Numerical and Experimental Analysis of Drug Inhalation in Realistic Human Upper Airway Model

The demand for a more efficient and targeted method for intranasal drug delivery has led to sophisticated device design, delivery methods, and aerosol properties. Due to the complex nasal geometry and measurement limitations, numerical modeling is an appropriate approach to simulate the airflow, aerosol dispersion, and deposition for the initial assessment of novel methodologies for better drug delivery. In this study, a CT-based, 3D-printed model of a realistic nasal airway was reconstructed, and airflow pressure, velocity, turbulent kinetic energy (TKE), and aerosol deposition patterns were simultaneously investigated. Different inhalation flowrates (5, 10, 15, 30, and 45 L/min) and aerosol sizes (1, 1.5, 2.5, 3, 6, 15, and 30 µm) were simulated using laminar and SST viscous models, with the results compared and verified by experimental data. The results revealed that from the vestibule to the nasopharynx, the pressure drop was negligible for flow rates of 5, 10, and 15 L/min, while for flow rates of 30 and 40 L/min, a considerable pressure drop was observed by approximately 14 and 10%, respectively. However, from the nasopharynx and trachea, this reduction was approximately 70%. The aerosol deposition fraction alongside the nasal cavities and upper airway showed a significant difference in pattern, dependent on particle size. More than 90% of the initiated particles were deposited in the anterior region, while just under 20% of the injected ultrafine particles were deposited in this area. The turbulent and laminar models showed slightly different values for the deposition fraction and efficiency of drug delivery for ultrafine particles (about 5%); however, the deposition pattern for ultrafine particles was very different.

Detailed computational analysis of flow dynamics in an extended respiratory airway model

BACKGROUND

Understanding respiratory physiology can aid clinicians in diagnosing the cause of respiratory symptoms or shed light on drug delivery inhaler device optimisation. However, the sheer complexity of the human lung prohibits a full-scale study.

METHODS

In this study, a realistic respiratory airway model including large-to-small conducting airways was built. This airway model consists of subject-specific upper and lower airways, extending from nasal and oral openings to terminal bronchioles (up to the 15th generation). Based on the subject-specific airway model, topological information was extracted and a digital reference model that exhibits strong asymmetry and multi-fractal properties was provided. Inhalation flow rates 18 L/min and 50 L/min were adopted to understand inspiratory conditions subjecting to resting and light exercise inhalation modes. Regional airflow in terms of axial velocity and secondary flow vortices along the lung airway model was extracted.

FINDINGS

Obvious secondary flow currents were seen in the larynx-trachea segment and left main bronchus, while for the terminal conducting airway in the right lower lobe, the airflow tends to be much smoother with no secondary flow currents.

INTERPRETATION

This paper provides insights on respiratory physiology, especially in the lower lung airways, and will be potentially useful for diagnosis of lower airway diseases.