On the emergence of criticality for inhalation-driven particle deposition in the anatomical upper airway

TL;DR

This study investigates how airflow dynamics in the upper airway lead to critical phenomena in particle deposition, revealing power law behaviors that could influence infection risk modeling.

Contribution

It introduces a novel application of criticality theory to airway airflow, demonstrating power law trends in particle deposition across various geometries and inhalation rates.

Findings

Power law trends observed in particle deposition levels.

Criticality emerges in airflow dynamics during inhalation.

Deposition patterns depend on airway geometry and flow rate.

Abstract

Inhalation directs air through a defined pathway, initiating from nostrils, moving through the main nasal cavity, past the pharynx and trachea, and culminating in the lungs. Inhaled particles, of a range of sizes, are ferried by this incoming air but are filtered and trapped by upper airway structures to protect the delicate lower respiratory system. From an energetics perspective, the airflow physics along this convoluted tract is characterized by turbulence. The system approaches a critical stationary state over the time scales during which particles enter the airway and deposit. This stasis can be conjectured to correspond with the emergence of criticality in the complex flow domain. For such systemic criticality (i.e., sensitivity to perturbations), inhaled particle deposition impacted by the surrounding flow processes can act as signature avalanche-like events. Based on the principles of organized criticality, we have explored the emergence of power law trends in particle deposition levels at the nasopharynx, a key initial infection site for airborne pathogens. These trends are derived from numerical data from five anatomic airway geometries for 15-85 L/min inhalation rates, modeled using high-fidelity Large Eddy Simulations.