Numerical investigation of transient transport and deposition of microparticles under unsteady inspiratory flow in human upper airways

In this study, we delve into the intricate world of microparticle transport and deposition within the human upper airways, with a specific focus on the dynamic nature of breathing. The significance of this research is far-reaching, as it promises to enrich our understanding of inhalation and exhalation airflow patterns. Such insights are not only pivotal for advancing medical drug delivery methods but also for safeguarding our lungs against the perils of suspended particulate pollutants.

Previous investigations in this field have often simplified matters by assuming a steady airflow, primarily for computational ease and efficiency. However, this study embarks on a different path, recognizing the crucial role played by the transient nature of our breathing. This dimension has, regrettably, been relatively uncharted territory in the realm of scientific inquiry.

The primary aim of this research is to examine the regional and overall deposition fractions of microparticles within a comprehensive model of the upper airways, all while taking into account the ebb and flow of breathing. To accomplish this, a realistic 3-D computational model, based on CT scan images of a healthy human, spans from the vestibule to the end of the trachea (as shown below).

CT scan cross sections of the upper airways

CT scan cross sections of the upper airways

The study employs unsteady simulations of inhaled and exhaled airflow patterns, relying on the Navier-Stokes and continuity equations as its foundation. Furthermore, a Lagrangian trajectory analysis approach is harnessed to explore the transient transport and deposition of particles under the rhythmic conditions of human respiration.

As we investigate the findings and observations of this study, one of the most striking revelations emerges: transient particle deposition fractions within various regions of the human upper airways deviate from those obtained under steady flow assumptions (as shown below for various particle sizes).

Comparison of particle deposition pattern for cyclic breathing with its equivalent steady breathing for various particle sizes

While the overarching trends in steady and unsteady model predictions for local deposition remain similar, discernible disparities emerge in the predicted deposition quantities. Notably, it becomes evident that steady simulations fall short when it comes to accurately predicting critical parameters such as the penetration fraction. This study underscores that the utilization of a detached nasal cavity model, as commonly seen in previous research, may suffice for steady flow simulations but proves inadequate in the realm of transient simulations, where a comprehensive depiction of the entire airway system becomes indispensable.

The implications of this research stretch far and wide. It offers valuable insights into the dynamics of particle deposition within the human respiratory system, particularly in the context of drug delivery and the filtration of harmful pollutants. This study takes a giant stride in unraveling the intricate dance between airflow dynamics and particle behavior within the human upper airways. It forcefully emphasizes the necessity of accounting for the unsteady, transient nature of airflow patterns for accurate predictions. In conclusion, this research drives home the point that complete models of the upper airways are imperative for transient simulations, especially when we seek precision in predicting regional deposition fractions and contemplate the exhalation phase's role in particle deposition.

For more detailed information, please refer to the original paper.