Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session E15: Focus Session: Respiratory Bio-Fluid Dynamics II |
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Chair: Josue Sznitman, Technion - Israel Institute of Technology Room: 3022/3024 |
Sunday, November 23, 2014 4:45PM - 4:58PM |
E15.00001: Correlations of Flow Structure and Particle Deposition with Structural Alterations in Severe Asthmatic Lungs Sanghun Choi, Shinjiro Miyawaki, Jiwoong Choi, Eric A. Hoffman, Sally Wenzel, Ching-Long Lin Severe asthmatics are characterized by alterations of bifurcation angle, hydraulic diameter, circularity of the airways, and local shift of air-volume functional change. The characteristics altered against healthy human subjects can affect flow structure and particle deposition. A large-eddy-simulation (LES) model for transitional and turbulent flows is utilized to study flow characteristics and particle deposition with representative healthy and severe asthmatic lungs. For the subject-specific boundary condition, local air-volume changes are derived with two computed tomography images at inspiration and expiration. Particle transport simulations are performed on LES-predicted flow fields. In severe asthmatics, the elevated air-volume changes of apical lung regions affect the increased particle distribution toward upper lobes, especially for small particles. The constricted airways are significantly correlated with high wall shear stress, leading to the increased pressure drop and particle deposition. The structural alterations of bifurcation angle, circularity and hydraulic diameter in severe asthmatics are associated with the increase of particle deposition, wall shear stress and wall thickness. [Preview Abstract] |
Sunday, November 23, 2014 4:58PM - 5:11PM |
E15.00002: Perception of Better Nasal Patency Correlates with Increased Mucosal Cooling after Surgery for Nasal Obstruction Guilherme Garcia, Corbin Sullivan, Dennis Frank-Ito, Julia Kimbell, John Rhee Nasal airway obstruction (NAO) is a common health problem with 340,000 patients undergoing surgery annually in the United States. Traditionally, otolaryngologists have focused on airspace cross-sectional areas and nasal resistance to airflow as objective measures of nasal patency, but neither of these variables correlated consistently with patients' symptoms. Given that the sensation of nasal airflow is also associated with mucosal cooling (i.e., heat loss) during inspiration, we investigated the correlation between the sensation of nasal obstruction and mucosal cooling in 10 patients before and after NAO surgery. Three-dimensional models of the nasal anatomy were created based on pre- and post-surgery computed tomography scans. Computational fluid dynamics (CFD) simulations were conducted to quantify nasal resistance and mucosal cooling. Patient-reported symptoms were measured by a visual analog scale and the Nasal Obstruction Symptom Evaluation (NOSE), a disease-specific quality of life questionnaire. Our results revealed that the subjective sensation of nasal obstruction correlated with both nasal resistance and heat loss, but the strongest correlation was between the NOSE score and the nasal surface area where heat flux exceeds 50 W/m2. In conclusion, a significant post-operative increase in mucosal cooling correlates well with patients' perception of better nasal patency after NAO surgery. [Preview Abstract] |
Sunday, November 23, 2014 5:11PM - 5:24PM |
E15.00003: 4DCT-based assessment of regional airflow distribution in healthy human lungs during tidal breathing Jiwoong Choi, Nariman Jahani, Sanghun Choi, Eric Hoffman, Ching-Long Lin Nonlinear dynamics of regional airflow distribution in healthy human lungs are studied with four-dimensional computed tomography (4DCT) quantitative imaging of four subjects. During the scanning session, subjects continuously breathed with tidal volumes controlled by the dual piston system. For each subject, 10 instantaneous volumetric image data sets (5 inspiratory and 5 expiratory phases) were reconstructed. A mass-preserving image registration was then applied to pairs of these image data to construct a breathing lung model. Regional distributions of local flow rate fractions are computed from time-varying local air volumes. The 4DCT registration-based method provides the link between local and global air volumes of the lung, allowing derivation of time-varying regional flow rates during the tidal breathing for computational fluid dynamics analysis. The local flow rate fraction remains greater in the lower lobes than in the upper lobes, being qualitatively consistent with those derived from three static CT (3SCT) images (Yin et al. JCP 2013). However, unlike 3SCT, the 4DCT data exhibit lung hysteresis between inspiration and expiration, providing more sensitive measures of regional ventilation and lung mechanics. [Preview Abstract] |
Sunday, November 23, 2014 5:24PM - 5:37PM |
E15.00004: Surfactant Delivery into the Lung James Grotberg, Marcel Filoche We have developed a multiscale, compartmentalized model of surfactant and liquid delivery into the lung. Assuming liquid plug propagation, the airway compartment accounts for the plug's volume deposition (coating) on the airway wall, while the bifurcation compartment accounts for plug splitting from the parent airway to the two daughter airways. Generally the split is unequal due to gravity and geometry effects. Both the deposition ratio R$_{\mathrm{D}}$ (deposition volume/airway volume), and the splitting ratio, R$_{\mathrm{S}}$, of the daughters volumes are solved independently from one another. Then they are used in a 3D airway network geometry to achieve the distribution of delivery into the lung. The airway geometry is selected for neonatal as well as adult applications, and can be advanced from symmetric, to stochastically asymmetric, to personalized. R$_{\mathrm{D}}$ depends primarily on the capillary number, Ca, while R$_{\mathrm{S}}$ depends on Ca, the Reynolds number, Re, the Bond number, Bo, the dose volume, V$_{\mathrm{D}}$, and the branch angles. The model predicts the distribution of coating on the airway walls and the remaining plug volume delivered to the alveolar region at the end of the tree. Using this model, we are able to simulate and test various delivery protocols, in order to optimize delivery and improve the respiratory function. [Preview Abstract] |
Sunday, November 23, 2014 5:37PM - 5:50PM |
E15.00005: Nonlinear analysis of the influence of surfactant on the stability of a liquid bilayer inside a tube Yuanyuan Song, David Halpern, James Grotberg The lung's airways are coated internally with a liquid bilayer consisting of a serous layer immediately coating the airway wall and a more viscous mucus layer which is exposed to the gas core. A surface tension instability at the interfaces may lead to the formation of liquid plugs that block the passage of air. This is known as airway closure. Here we consider this thin liquid bilayer coating within a compliant tube in the presence of insoluble surfactant at the mucus-gas interface. Surfactant can reduce the surface tension and induce a stress gradient, both of which are stabilizing. Lubrication theory is used to derive a system of nonlinear evolution equations for the thickness of the layers, the location of the tube wall, and the surfactant concentration. The effects of various parameters, the thickness of the bilayer to the tube radius, the layer thicknesses ratio, the surface tension ratio, and the viscosity ratio between the two layers, and wall compliance parameters, are investigated numerically. For a single layer in a rigid tube, surfactant can increase the closure time by approximately a factor of five. However, for a bilayer, the presence of surfactant slows down the closure time by a significantly larger factor, twenty times or more dependent on system parameters. [Preview Abstract] |
Sunday, November 23, 2014 5:50PM - 6:03PM |
E15.00006: Spatial organization of cilia tufts governs airways mucus transport: Application to severe asthma Mustapha Kamel Khelloufi, Delphine Gras, Pascal Chanez, Annie Viallat We study the coupling between both density and spatial repartition of beating cilia tufts, and the coordinated transport of mucus in an \textit{in-vitro} epithelial model. We use a fully differentiated model epithelium in air liquid interface (ALI) obtained from endo-bronchial biopsies from healthy subjects and patients with asthma. The asthma phenotype is known to persist in the model. Mucus transport is characterized by the trajectories and velocities of microscopic beads incorporated in the mucus layer. When the beating cilia tufts density is higher than $d_{c}=$11/100x100 $\mu$m$^2$ a spherical spiral coordinated mucus transport is observed over the whole ALI chamber (radius$=$6mm). Below $d_{c}$, local mucus coordinated transport is observed on small circular domains on the epithelium surface. We reveal that the radii of these domains scale with the beating cilia tufts density with a power 3.7. Surprisingly, this power law is independent on cilia beat frequency, concentration and rheological properties of mucus for healthy subject and patient with asthma. The rotating or linear mucus transport is related to dispersion of the cilia tufts on the epithelium surface. We show that impaired mucus transport observed in severe asthma model epithelia is due to a drastic lack and dysfunction of cilia tufts. [Preview Abstract] |
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