Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session L18: Biological fluid dynamics: Breathing |
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Chair: Lucy Zhang, Rensselaer Polytechnic Institute Room: Georgia World Congress Center B305 |
Monday, November 19, 2018 4:05PM - 4:18PM |
L18.00001: A numerical analysis of microcirculatory blood flow and oxygen transport to the surrounding tissue Junya Kobayashi, Satoshi Ii, Naoki Takeishi, Shigeo Wada We numerically investigated the behaviors of red blood cells (RBCs) and oxygen supply to surrounding tissue in a simplified microvascular network. The simulation was performed by a computational model, where the fluid mechanics for plasma and cytoplasm flow are coupled with the solid mechanics for cell membrane deformation, and with the oxygen transportation formulated by mixed equations. Our numerical results demonstrated that the distribution of RBCs was almost homogenized as the time passes especially at high hematocrit, resulting in the uniformed oxygen supply to the surrounding tissues. This result suggests that complex microvascular networks such as the brain microcirculation regulates cellular flow and establish uniform oxygen supply. |
Monday, November 19, 2018 4:18PM - 4:31PM |
L18.00002: Particle-Laden Cilia-Driven flow Carlos Abraham Ruvalcaba, Jean-Pierre Delplanque The upper airways of the respiratory system are lined with a mucosal layer which includes: mucus, periciliary fluid, and beating cilia. The coordinated beating of cilia that propels mucus is called the mucociliary escalator. Impairment of the mucociliary escalator can severely impact respiratory health, even more so when harmful particulates deposit in the upper airways. Existing models of the mucociliary escalator dynamics treat particles as massless tracers, quantifying only the bulk fluid transport arising from the driving cilia movement. The dynamics of suspended particles are investigated here using previously established cilia beat patterns in a one-way coupled fluid-structure interaction model. The effects of biophysical airway parameters (beat frequency and synchrony, periciliary height, and cilia arrangement) are investigated. Specific particle sizes and shapes are also considered. The particle dynamics in the periciliary layer are quantified by evaluating particle transport velocity and residence time. Our findings could aid in selection of medical interventions to modulate particle clearance using readily available pharmacological agents. |
Monday, November 19, 2018 4:31PM - 4:44PM |
L18.00003: Effects of uvula morphology on the fluid dynamics in human snoring Junshi Wang, Pan Han, Jinxiang Xi, Reed Gilbow, James Daniero, Haibo Dong The vibrations of uvula play important roles in human snoring. Clinically, it is found that human uvula is commonly in different shapes and sizes, which may significantly affect the air flows in the pharynx and the generation of the snoring sound. In this work, a combined experimental and computational approach was conducted to study the effects of uvula morphology on the fluid dynamics in the human airway. Both anatomically and kinematically accurate human pharynx model was modeled from magnetic resonance images and high-speed photography videos. An immersed-boundary-method-based incompressible flow solver was used to compute the unsteady flows associated with a range of uvula shapes and sizes. Results have shown noticeable changes in vortex formation, pressure oscillation, and wall pressure forces in the human airway. Results from this work are expected to bring more comprehensive understandings on the snoring sound production and provide guidance for future surgical interventions. |
Monday, November 19, 2018 4:44PM - 4:57PM |
L18.00004: Effect of Nebulizer Type and Position on a Ventilator Circuit on Aerosol Deposition in Lung Airway Models Rahul Rajendran, Arindam Banerjee, Ariel Berlinkski Particle transport and deposition are investigated in different idealized and realistic bifurcating airway models using a computational fluid and particle dynamic study. Targeted drug delivery to the pulmonary airways primarily depends on the particle size, breathing pattern and the geometry of the airways. The aerosol characterization of nebulized albuterol delivered at a constant flowrate of 14L/min by two different nebulizers alone and placed in-line at two different positions in an adult ventilator circuit was obtained using the Next Generation Impactor. Simulations are performed using a Lagrangian particle tracking approach to model the transport of the spherical particles with diameters ranging from 0.5 to 5 microns, based on the aerodynamic particle size distribution data obtained for each operating condition. The effectiveness of the clinical treatment for each nebulizer type and position will be discussed based on the total and regional deposition fractions of the particles, and the sites of deposition. The effect of spatial distribution of the injected particles at the inlet and the presence of an endotracheal tube on the aerosol deposition and distribution will be presented. |
Monday, November 19, 2018 4:57PM - 5:10PM |
L18.00005: Assessment of Effects of Selective Airway Luminal Expansion on Inhaled Particle Deposition in Severe Asthmatic Human Lungs - A Numerical Study Jiwoong Choi, Sanghun Choi, Eric A. Hoffman, Patrick O'Shaughnessy, Mario Castro, Renishkumar Delvadia, Ross Walenga, Andrew Babiskin, Ching-Long Lin The aim of the study is to assess the effects of luminal expansion of constricted proximal airways on inhaled particle deposition in severe asthmatic lungs. A recent imaging-based cluster analysis found that one of the two severe asthma clusters was characterized by proximal airway constriction. We performed computational fluid and particle simulations on computed tomography (CT)-based airway models before and after numerically enlarging luminal areas of constricted airways in representative cluster subjects. After constriction reduction, a high-speed air stream, which impinged on the bifurcating wall in the original constricted geometry, disappeared. Consequently, particle deposition density in the region decreased and downstream particle delivery increased. Specifically, after expanding the constricted left lower bronchus of a subject, particle deposition fraction in the left lower lobe decreased by 22-35% for 1-8 µm particles, and hence distal particle advection increased up to 23% for 8 µm. The results imply that the use of imaging-based clustering and enlargement of constricted proximal airway may help improve delivery of orally inhaled drug aerosols to small airways in severe asthmatic lungs. |
Monday, November 19, 2018 5:10PM - 5:23PM |
L18.00006: Effects of coughing on a surfactant-laden liquid plug in distal airways Metin Muradoglu, Francesco Romano, Hideki Fujioka, James Bernard Grotberg We computationally study the effects of coughing on a surfactant-laden liquid plug in distal airways. The airway is assumed to be a rigid axisymmetric tube lined by a thin liquid film and coughing is mimicked by rapidly increasing the upstream pressure while keeping the downstream pressured constant. The evolution equations of the interfacial and bulk surfactant concentrations are solved fully coupled with the incompressible Navier-Stokes equations using a front-tracking method. Extensive simulations are performed for a range of Laplace numbers and non-dimensional pressure drops to investigate the effects of coughing-induced pressure pulses and surfactant on the mechanical stresses that could be injurious to epithelial cells. Simulations are also performed to examine the cough efficiency defined as bulk volume displacement per unit increase in upstream pressure. It is found that the mechanical stresses are substantially amplified by the coughing while they are significantly reduced with the introduction of surfactants. |
Monday, November 19, 2018 5:23PM - 5:36PM |
L18.00007: High Frequency Oscillatory Ventilation in the Neonate: An Experimental study Eliram Nof, Josue Sznitman Convective flow mechanisms during High Frequency Oscillatory Ventilation (HFOV) are investigated experimentally by measuring the time-resolved, three-dimensional (3D) flow fields in a physiologically-relevant, asymmetric, true-scale, multi-generational upper airway model of a premature newborn infant. HFOV is an atypical form of mechanical ventilation credited with reducing ventilator induced lung injury (VILI) in premature infants. The strategy involves ventilating much smaller volumes of air at high frequencies (10-15 Hz), and while common in clinical practice, the optimal settings or a methodology for adapting to specific patients remains ill-defined. The present study employs Tomographic Particle Image Velocimetry to explore for the first time the characteristic convective features of gas dispersion as a function of Reynolds and Womersely numbers, via tidal volume and oscillation frequency. |
Monday, November 19, 2018 5:36PM - 5:49PM |
L18.00008: Evaluation of tracheal stenosis: Comparison between CFD and PIV evaluation in the smooth and cartilaginous trachea model Mellisa Hege, Jose A Montoya Segnini, Ali Doosttalab, Humberto Bocanegra Evans, Joehassin Cordero, Jun Chen, Luciano Castillo Given the inaccessibility of the respiratory system, computational fluid dynamics (CFD) has become an essential tool used to understand the flow characteristics in the complex flow inside the human airways. However, validation of the simulations with experimental work is crucial to have accurate results, especially with CFD models that struggle to predict flow separation. In this study we evaluate a simplified trachea model with stenosis. This condition is characterized by concentric thickening of the soft tissue within the tracheal lumen. Two models are used to evaluate the flow characteristics in an index-matched facility: a model with smooth wall and a model with wall corrugations simulating cartilaginous rings with PDMS were constructed. The flow rate is set comparable to the resting breathing state Reynolds number, ReD=3400. We use particle image velocimetry (PIV) and refractive index matching to measure the flow field. Additionally, we numerically simulate the flow in the same geometry using different CFD models and compare this results to the experimental measurements. This study will help understand the strengths and limitations of CFD models for respiratory fluid dynamics research and provide a baseline for future CFD studies particularly the smooth surface assumption |
Monday, November 19, 2018 5:49PM - 6:02PM |
L18.00009: Transport of fine particles in a standardized human nasal cavity John Eaton, Daniel Borup, Lindsey E. Engel, Christopher J. Elkins Understanding particle transport through human nasal cavities is a critical step towards accurate prediction of deposition of inhaled hazardous particulates or medicinal sprays. Magnetic Resonance Imaging (MRI) was used to obtain 3D, 3-component velocity and 3D particle concentration data in a model of the Carleton-Civic Standardized Nasal Cavity, which provides a balance between generality and patient-specific features. The 3D mean velocity field was obtained for clean flow at two anatomically relevant Reynolds numbers. The velocity data show that the flow is likely transitional, weakly dependent on flow rate, and contains important secondary flow features resulting from the convoluted nasal passage geometry. A newly developed MRI diagnostic for 3D particle concentration was used to obtain the mean volume fraction field for two particle-laden streaks injected just upstream of the nostril. The full-field concentration data can be used to quantify the mixing between the two streaks, which shows that the fastest mixing occurs in the nasal vestibule (nostril). However, certain portions of the upper nose (e.g., the olfactory region) are only reached by particles injected near the nostril tip, which could have useful implications in the medical arena. |
Monday, November 19, 2018 6:02PM - 6:15PM |
L18.00010: Topical drug delivery: how CFD can revolutionize the usage protocol for nasal sprays Saikat Basu, Charles S Ebert Jr., Julia S Kimbell Topical delivery is meant to provide high concentrations of drugs to nasal mucosal surfaces, with sprays being the most frequently prescribed treatment. However, these potent drugs are often ineffective, in part owing to deficient transport. Patients are typically instructed in the use of spray devices by the physicians and the package inserts; a protocol we refer to as "current use (CU)". We have quantified the CU drug delivery, through Fluent-based CFD simulations in anatomically realistic respiratory models. These numbers are compared against our innovation of "line-of-sight (LoS)" protocol, developed by re-orienting the spray axis towards specific anatomic landmarks. Analysis on five airway models indicates an average seven-fold increase in drug transport to nasal targets, while using LoS. To verify robustness of this discovery, we considered release zones close to the LoS and the CU points, and still spray release around LoS resulted in better drug transmission compared to that around CU. The improvement was statistically significant with p-values less than 0.05, both for t-tests and Wilcoxon signed-rank tests. Experiments in 3D-printed replicates have validated the CFD results. Our findings will help advance therapeutics for sinonasal ailments. |
Monday, November 19, 2018 6:15PM - 6:28PM |
L18.00011: Toward a Smart Stethoscope: Correlation between trachea internal airway geometry and the auscultation signal response Mohamed Amine Abassi, Xiaofeng Liu, Jose R Moerto, Kee Moon, Chantal Darquenne, Andrew Kuprat, Sean Colby, Brian Garibaldi Stethoscope for human auscultation represents an easy and prompt tool for physicians to diagnose rapidly the existence of a pulmonary disease. However, the physics that stands behind the generation of acoustic signals and the internal geometry of the trachea or lung airways has not been clearly defined. In our project, we started to tackle the problem using a microphone, and instead of carrying out experiments on human beings, we chose to use a 3D-printed trachea model based on geometry data collected from a real human patient. Our main purpose is to understand how the geometry of the trachea wall interacts with the air flow and thus, impacts the acoustic signal generated and acquired by the microphone. To carry out our experimental measurements, we use an artificial air pump to simulate the respiratory process in the 3D-printed trachea mounted in an anechoic chamber. The acoustic signal is conditioned and low-pass filtered at 3000 Hz, then processed using a Labview based data acquisition sysyem. The signal is then analyzed using spectral analysis methods as implemented in Liu and Katz (2013, J of Fluid Mech., 728, 417:57) to establish the correlation between the tracheal acoustic signal and its internal geometry. |
Monday, November 19, 2018 6:28PM - 6:41PM |
L18.00012: Scaled experiments for improving diagnosis of pathological lower airway obstruction Ken Kiger, Chang Liu, Daniel Hariprasad, Bora Sul, Anders Wallqvist, Jaques Reifman Many lung diseases, such as asthma and chronic obstructive pulmonary disease, are characterized by obstructed airflow, particularly, in the lower airway branches in the lung. Our current work aims to provide a better understanding of the connection between lower-airway obstruction and modifications to the velocity profiles within the trachea as a potential means of pathology diagnosis. To investigate this matter, a transparent patient-specific lung model, resolved down to the 5th daughter branches and scaled up to 1.8 times the human size, was constructed. 5 independently controlled piston pumps are used to prescribe the flowrate to the different lung lobes, simulating constant inhalation and exhalation processes with both healthy and diseased/obstructed lobar flow fractions. Quantification of the complex 3D flow in the lower trachea is achieved by conducting stereo PIV measurements performed in the coronal midplane and several transverse planes at different elevations. Results obtained under two different Reynolds numbers (1461 and 3506 respective, based upon the bulk flowrate and the tracheal diameter) will be presented, documenting the system performance and examining the detectability of under-performing lobes within the tracheal flow profile. |
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