2017 Volume 5 Issue 1 Pages 15-19
Aerosol medicine exhalation through the nose (ETN) is one of promising and comprehensive treatment methods for Eosinophilic Chronic Rhinosinusitis (ECRS) with asthma. In this treatment, the patient inhales aerosol of inhaled corticosteroid (ICS) medicine from mouth using portable inhaler. Then a part of the aerosol still floats and remains in upper airway. When the patient exhales inhaled air through the nose, the aerosol is effectively transported on the walls of middle meatus and olfactory fissure. The mechanism of how ETN improves ECRS with asthma is still controversial even though ETN gets a lot of attention as a treatment method for ECRS with asthma. This study performed Computational Fluid Dynamics (CFD) analysis for the transport phenomena of aerosol medicine during exhalation period in order to evaluate the curative effect of ETN numerically. A 75-years-old male, who had ECRS with asthma and a history of endoscopic sinus surgery was selected as an analysis case in this study. CT data. A 3D anatomically accurate patient-specific model was reconstructed from the data obtained using multidetector CT scanner with medical imaging software package. The entire series was loaded into the software, and then the nasal-pharynx airway was identified in each of the axial images based on predefined threshold of 250 Housfield units relative to the surrounding tissue. The nasal-pharynx airway model was exported into CFD meshing software package to generate discrete volume cells. This study used both a Euler-Lagrange particle transport model for aerosol transport and a Large Eddy Simulation model for complex intranasal turbulent flow, which are able to account for the transient transport of mass and turbulent energy, and consequently, provides highly accurate predictions of the amount of flow separation under adverse pressure gradients. This study assumed that the condition of exhaling flow rate through nose indicial set at 15 l/min and 30 l/min, respectively. As a result of CFD analysis, ETN formed impinging flow toward upper wall of nasopharynx, subsequently complex swirl and circulation flow in the nasopharynx region. In addition, main flow of ETN passed upper region of nasal cavity. Such the tendencies affected on aerosol transport characteristics; a part of aerosol particles moved into ethmoindal sinuses. Total aerosol deposition amount during ETN depended on flow rate of exhalation. This tendency was more remarkable on the upper wall of nasopharynx. On the other hand, deposition rate of aerosol on the ethmoidal sinuses did not appear strong correlation with flow rate of exhalation. These results imply that the phenomena of aerosol transport and deposition during ETN has non-stationary characteristics strongly. In past researches concerning CFD analysis for intranasal aerosol transport, steady-state turbulent flow model had been applied as CFD model. New finding of this study is that unsteady turbulent model, similar to the LES turbulent model adopted in this study, is needed in the further investigation for ETN.
