Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session R16: Bio: Respiratory System |
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Chair: Luciano Castillo, Texas Tech University Room: D133/134 |
Tuesday, November 22, 2016 1:30PM - 1:43PM |
R16.00001: Experimenatal analysis of the effect of cartilaginous rings on human tracheobronchial flow Jose Montoya Segnini, Humberto Bocanegra Evans, Luciano Castillo We present a set of high-resolution PIV experiments carried out in a refractive index-matched model of a trachea with cartilage rings at Re $\approx$ 2800. Results show a higher vorticity along the walls of the trachea in the model with cartilaginous rings as well as small recirculation areas on the upstream side of the wall cavities created by the rings. Furthermore, the ringed model experiences higher shear stress in the trachea due to the sudden change in the wall position created by the rings. Additionally, small recirculation areas are identified in the cavities between rings. For the smooth model, a stronger separation bubble is observed at the bronchi entrance, generating a stronger shear layer and increasing the wall shear stress on the bottom bronchi wall. The differences observed go against the notion that the main airway, i.e. trachea and main bronchi, may be modeled as smooth. Our results suggest that cartilage rings will have an impact on the wall shear stress and may affect particle deposition, which is of importance in inhaled drug delivery and pollutant deposition in the airway. Additionally, the effects introduced by the rings may change the flow characteristics in further generations. [Preview Abstract] |
Tuesday, November 22, 2016 1:43PM - 1:56PM |
R16.00002: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2016 1:56PM - 2:09PM |
R16.00003: Vortical Structures in CT-based Breathing Lung Models Jiwoong Choi, Changhyun Lee, Eric Hoffman, Ching-Long Lin The 1D-3D coupled computational fluid dynamics (CFD) lung model is applied to study vortical structures in the human airways during normal breathing cycles. During inhalation, small vortical structures form around the turbulent laryngeal jet and Taylor-G\H{o}rtler-like vortices form near the curved walls in the supraglottal region and at airway bifurcations. On exhalation elongated vortical tubes are formed in the left main bronchus, whereas a relatively slower stream is observed in the right main bronchus. These structures result in helical motions in the trachea, producing long lasting high wall shear stress on the wall. The current study elucidates that the correct employment of image-based airway deformation and lung deflation information is crucial for capturing the physiologically consistent regional airflow structures. The pathophysiological implications of these structures in destruction of tracheal wall will be discussed. [Preview Abstract] |
Tuesday, November 22, 2016 2:09PM - 2:22PM |
R16.00004: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2016 2:22PM - 2:35PM |
R16.00005: Relationship between Pulmonary Airflow and Resistance in Patients with Airway Narrowing Using An 1-D Network Resistance and Compliance Model Sanghun Choi, Jiwoong Choi, Eric Hoffman, Ching-Long Lin To predict the proper relationship between airway resistance and regional airflow, we proposed a novel 1-D network model for airway resistance and acinar compliance. First, we extracted 1-D skeletons at inspiration images, and generated 1-D trees of CT unresolved airways with a volume filling method. We used Horsfield order with random heterogeneity to create diameters of the generated 1-D trees. We employed a resistance model that accounts for kinetic energy and viscous dissipation (Model A). The resistance model is further coupled with a regional compliance model estimated from two static images (Model B). For validation, we applied both models to a healthy subject. The results showed that Model A failed to provide airflows consistent with air volume change, whereas Model B provided airflows consistent with air volume change. Since airflows shall be regionally consistent with air volume change in patients with normal airways, Model B was validated. Then, we applied Model B to severe asthmatic subjects. The results showed that regional airflows were significantly deviated from air volume change due to airway narrowing. This implies that airway resistance plays a major role in determining regional airflows of patients with airway narrowing. [Preview Abstract] |
Tuesday, November 22, 2016 2:35PM - 2:48PM |
R16.00006: Effects of lung disease on the three-dimensional structure and air flow pattern in the human airway tree Tristan Van de Moortele, Andras Nemes, Christine Wendt, Filippo Coletti The morphological features of the airway tree directly affect the air flow features during breathing, which determines the gas exchange and inhaled particle transport. Lung disease, Chronic Obstructive Pulmonary Disease (COPD) in this study, affects the structural features of the lungs, which in turn negatively affects the air flow through the airways. Here bronchial tree air volume geometries are segmented from Computed Tomography (CT) scans of healthy and diseased subjects. Geometrical analysis of the airway centerlines and corresponding cross-sectional areas provide insight into the specific effects of COPD on the airway structure. These geometries are also used to 3D print anatomically accurate, patient specific flow models. Three-component, three-dimensional velocity fields within these models are acquired using Magnetic Resonance Imaging (MRI). The three-dimensional flow fields provide insight into the change in flow patterns and features. Additionally, particle trajectories are determined using the velocity fields, to identify the fate of therapeutic and harmful inhaled aerosols. Correlation between disease-specific and patient-specific anatomical features with dysfunctional airflow patterns can be achieved by combining geometrical and flow analysis. [Preview Abstract] |
Tuesday, November 22, 2016 2:48PM - 3:01PM |
R16.00007: Flow characteristics in the airways of a COPD patient with a saber-sheath trachea Dohyun Jin, Haecheon Choi, Changhyun Lee, Jiwoong Choi, Kwanggi Kim The chronic obstructive pulmonary disease (COPD) is a lung disease characterized by the irreversible airflow limitation caused by the damaged small airways and air sacs. Although COPD is not a disease of the trachea, many patients with COPD have saber-sheath tracheas. The effects of this morphological change in the trachea geometry on airflow are investigated in the present study. An unstructured finite volume method is used for the simulations during tidal breathing in normal and COPD airways, respectively. During inspiration, local large pressure drop is observed in the saber-sheath region of the COPD patient. During expiration, vortical structures are observed at the right main bronchus of the COPD airway, while the flow in the normal airway remains nearly laminar. High wall shear stress exists at convex regions of both airways during inspiration and expiration. However, due to the morphological changes in the COPD airway, relatively higher wall shear stress is observed in the patient airways. [Preview Abstract] |
Tuesday, November 22, 2016 3:01PM - 3:14PM |
R16.00008: The Effects of High Frequency Oscillatory Flow on Particles' Deposition in Upper Human Lung Airways Jeremy Bonifacio, Hamid Rahai, Shahab Taherian The effects of oscillatory inspiration on particles' deposition in upper airways of a human lung during inhalation/exhalation have been numerically investigated and results of flow characteristics, and particles' deposition pattern have been compared with the corresponding results without oscillation. The objective of the investigation was to develop an improved method for drug delivery for Asthma and COPD patients. Previous clinical investigations of using oral airway oscillations have shown enhanced expectoration in cystic fibrosis (CF) patients, when the frequency of oscillation was at 8 Hz with 9:1 inspiratory/expiratory (I:E) ratio. Other investigations on oscillatory ventilation had frequency range of 0.5 Hz to 2.5 Hz. In the present investigations, the frequency of oscillation was changed between 2 Hz to 10 Hz. The particles were injected at the inlet and particle velocity was equal to the inlet air velocity. One-way coupling of air and particles was assumed. Lagrangian phase model was used for transport and depositions of solid 2.5 micron diameter round particles with 1200 kg/m$^{\mathrm{3}}$ density. Preliminary results have shown enhanced PM deposition with oscillatory flow with lower frequency having a higher deposition rate [Preview Abstract] |
Tuesday, November 22, 2016 3:14PM - 3:27PM |
R16.00009: Surfactants and the Mechanics of Respiration. Abdulrahman Jbaily, Andrew J. Szeri Alveoli are small sacs found at the end of terminal bronchioles in human lungs with a mean diameter of 200 $\mu $m. A thin layer of fluid (hypophase) coats the inner face of an alveolus and is in contact with the air in the lungs. The thickness of this layer varies among alveoli, but is in the range of 0.1 to 0.5 $\mu $m for many portions of the alveolar network. The interfacial tension $\sigma $ at the air-hypophase interface tends to favor collapse of the alveolus, and resists its expansion during inhalation. Type II alveolar cells synthesize and secrete a mixture of phospholipids and proteins called pulmonary surfactant. These surfactant molecules adsorb to the interface causing \begin{figure}[htbp] \centerline{\includegraphics[width=0.08in,height=0.17in]{270720161.eps}} \label{fig1} \end{figure} $\sigma $ to decrease. For example, \begin{figure}[htbp] \centerline{\includegraphics[width=0.08in,height=0.17in]{270720162.eps}} \label{fig2} \end{figure} $\sigma $ of water at body temperature is $\approx $70 mN/m and falls to an equilibrium value of $\approx $25 mN/m when surfactants are present. Also, in a dynamic sense, it is known that $\sigma $ is reduced to near 0 during exhalation when the surfactant film compresses. In this work, the authors develop a mechanical and transport model of the alveolus to study the effect of surfactants on various aspects of respiration. The model is composed of three principal parts: (i) air movement into and out of the alveolus; (ii) a balance of linear momentum across the two-layered membrane of the alveolus (hypophase and elastic wall); and (iii) a pulmonary surfactant transport problem in the hypophase. The goal is to evaluate the influence of pulmonary surfactant on respiratory mechanics. [Preview Abstract] |
Tuesday, November 22, 2016 3:27PM - 3:40PM |
R16.00010: Circular flow patterns induced by ciliary activity in reconstituted human bronchial epithelium. Annie Viallat, Kamel Khelloufi, Delphine Gras, Pascal Chanez Mucociliary clearance is the transport at the surface of airways of a complex fluid layer, the mucus, moved by the beats of microscopic cilia present on epithelial ciliated cells. We explored the coupling between the spatial organisation and the activity of cilia and the transport of surface fluids on reconstituted cultures of human bronchial epithelium at air-liquid interface, obtained by human biopsies. We reveal the existence of stable local circular surface flow patterns of mucus or Newtonian fluid at the epithelium surface. We find a power law over more than 3 orders of magnitude showing that the average ciliated cell density controls the size of these flow patterns, and, therefore the distance over which mucus can be transported. We show that these circular flow patterns result from the radial linear increase of the local propelling forces (due to ciliary beats) on each flow domain. This linear increase of local forces is induced by a fine self-regulation of both cilia density and orientation of ciliary beats. Local flow domains grow and merge during ciliogenesis to provide macroscopic mucus transport. This is possible only when the viscoelastic mucus continuously exerts a shear stress on beating cilia, revealing a mechanosensitive function of cilia. [Preview Abstract] |
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