Inhalability of micron particles through the nose and mouth

Abstract

Aspiration efficiencies from nose and mouth inhalations are investigated at low and high inhalation rates by using the commercial Computational Fluid Dynamics (CFD) software CFX 11. A realistic human head with detailed facial features was constructed. Facial features were matched to represent the 50th percentile of a human male, aged between 20 and 65 years old, based on anthropometric data. The constant freestream velocity was 0.2 ms(-1), normal to the face, and inhalation rates through the mouth and nose were 15 liters per minute (LPM) for light breathing and 40 LPM for heavy breathing. It was found that the flow field in the near breathing region exhibited vertical direction caused by the presence of the torso where the airstream diverges as it flows around and over the body. The critical area concept was used as a tool to determine the aspiration efficiency of particles. Comparisons between critical areas for the nose and mouth inhalations show similar geometric properties such as the area's shape, and its vertical distance location on the x-z plane located at y = 80 cm upstream. The critical area sizes were found to be slightly larger for the mouth inhalation mainly due to the larger mouth area and also the aligned orientation of the mouth to the upstream flow, whereas the nose is perpendicular to the upstream flow. This study was undertaken to establish the flow field in the near breathing region that will help to characterize the flow and particle field for initial boundary conditions leading to a more holistic modeling approach of respiration through the internal nasal cavity and mouth.

Influence of Mesh Density on Airflow and Particle Deposition in Sinonasal Airway Modeling

“…Some researchers reported velocity profile as the basis for conducting mesh refinement, (6,7,16) others reported airflow, deposition fractions, pressure drop, wall shear stress, or combination of CFD variables. (2,3,13,17,20) A number of other investigators did not specify the variables computed to determine grid independent control volume. (1,(8)(9)(10)(11)14,15) (3) There are no standardized nasal characteristics that investigators conform to when reconstructing nasal geometry for CFD studies.…”

“…There is a lack of consistency in the literature on the number and type of grid elements required to provide numerically accurate CFD solutions for studies involving sinonasal insilico analysis of airflow and particulate matter, (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) even though most investigators performed airflow simulation using the finite volume method software package, FluentÔ (ANSYS, Inc., Canonsburg, PA). Among studies where mesh density analyses were reported, some authors failed to report details regarding how mesh refinement was done to achieve grid-independent numerical solutions.…”

“…Among studies where mesh density analyses were reported, some authors failed to report details regarding how mesh refinement was done to achieve grid-independent numerical solutions. (8)(9)(10)(11)(12)18) In situations where particle transport was simulated (Table 1), the mesh structure utilized varied; some authors utilized unstructured tetrahedral meshes, (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)19,20) whereas other investigators used a hybrid of tetrahedral and prism meshes. (1)(2)(3)(14)(15)(16)(17)(18)21,22) The inclusion of prism boundary layers increases mesh density near airway walls and is generally considered to provide more accurate near-wall particle trajectory calculations.…”

“…(1,(8)(9)(10)(11)14,15) (3) There are no standardized nasal characteristics that investigators conform to when reconstructing nasal geometry for CFD studies. In some articles, CFD analyses were done using unilateral (one side) nasal cavity, (8)(9)(10)(11)21,22) while others performed CFD on bilateral (two sides) nasal cavities without the paranasal sinuses (1)(2)(3)6,(13)(14)(15)(17)(18)(19)(20) or with the paranasal sinuses; as in this study or that of Ge et al (16) The present study uses CFD techniques to systematically perform a two-stage mesh sensitivity analysis in an anatomically accurate 3D sinonasal cavity of a subject who underwent functional endoscopic sinus surgery (FESS) as part of treatment for medically recalcitrant chronic rhinosinusitis (CRS). The motivation for using a post-surgery geometry is two-fold: (1) although FESS is not done on the main nasal cavity, successful post-surgery healing restores the patency of the main nasal cavity to that of a normal subject, as was the case in this subject; (2) since the geometry of the sinonasal cavity is more complex than the main nasal cavity, and very little is known about simulating particle transport in post-surgery sinonasal cavity, there is the need to conduct mesh density analysis that produces an accurate total deposition fraction in the sinonasal cavity for post-surgery nebulized drug delivery.…”

Lagrangian particle modelling of spherical nanoparticle dispersion and deposition in confined flows

“…Studies of particle deposition in confined flows of irregular geometries such as the human upper airways have also been performed. These include the oral cavity (Tian, Longest, Su, Walenga, & Hindle, 2011;Yousefi, Inthavong, & Tu, 2015) , the nasal cavity (Ge, Inthavong, & Tu, 2012;Se, Inthavong, & Tu, 2010;Wang et al, 2009;Zamankhan et al, 2006), and the lower respiratory tract (Xi, Longest, & Martonen, 2008;Zhang & Kleinstreuer, 2003;Zhang & Kleinstreuer, 2011;Piglione, Fontana, & Vanni, 2012).…”