Session H01: Biological Fluid Dynamics: Respiratory Flows

Interchangeable Filter For Virus Filtration and Inactivation

The COVID-19 pandemic has caused a multi-scale impact on people from all walks of life, requiring mandatory use of prevention measures like use of face masks to reduce the probability of exposure to the aerosolized virus. In present study, we propose a novel filter with three unique layers. The outermost layer is a spun-bond PPE coated with water-based, nano-engineered hydrophobic and lipophobic coating to prevent adherence of droplets virus to the mask. The second layer is a non-woven layer. The middle layer is a copper mesh coated with diamond-like carbon coating capable of virus inactivation. The last two layers are non-woven layers, close to the mouth. Pressure resistance across this proposed configuration was simulated and validated experimentally showing a good agreement, with error less than 30% and novel filter shows higher breathability as compared to medicals masks. This experiment is also used for determining the viscous and inertial resistance coefficients, crucial in numerical simulation studies of masks. We use ANSYS FLUENT and model filter as porous media. We test the filter against MS2 bacteriophage virus, comparing the viral log reduction to disposable medical mask. The filter shows 90% efficiency against the aerosolized MS2 virus. The DLC layer is responsible for inactivation of virus stuck in the filter fibers, making the filter reusable in nature. This is tested for inactivation over 2 hours of time. In a non-woven fiber, the particulate removal takes place according to different mechanisms depending on particle size, namely, straining or sieving, inertial impaction, interception, and Brownian diffusion. Different grades of non-woven layers affect the filtering efficiency. Two grades of non-woven layers, namely, 50g/m² and 150g/m² are tested against MS2 virus to quantify the filtration efficiency based on non-woven layers. This helps us shed light on how the proposed filter can prevent and inactivate the nanoscale pathogens.   

Dilute polymer solutions completely suppress aerosolization in dentistry preventing COVID-19 transmission

The aerosol transmissibility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has impacted the delivery of health care and essentially stopped the provision of medical and dental therapies. Dentistry uses rotary, ultrasonic, and laser-based instruments that produce water-based aerosols in the daily, routine treatment of patients. Abundant aerosols are generated, and reach health care workers and other patients. Viruses, including SARS CoV2 virus and coronavirus COVID-19 easily spread by droplets and aerosols. The generation of aerosols in dentistry - an unavoidable part of most dental treatments - creates a high-risk situation. There are several potential ways to reduce or eliminate the virus transmission: (i) cease or postpone dentistry (public and personal health risk), (ii) screen patients immediately prior to dental treatment (but appropriate testing is yet unavailable and troublesome, in general), (iii) block/remove the virus containing aerosol by engineering controls together with stringent personal protective equipment (PPE) use. Here a novel, forth approach is proposed. Viscoelastic response of dilute aqueous solutions of FDA-approved polymers to the inertial forces in dentistry, completely eliminates generation of aerosol particles for both the ultrasonic scaler and dental hand piece.   

Three-dimensional quantification of large central airway collapses during expiration

Expiratory Central Airway Collapse (ECAC), an increasingly recognized disorder particularly among individuals with Chronic Obstructive Pulmonary Disease (COPD), is often combined with other pulmonary obstructions and not understood well. Like many other physiological structures, the central airway consisting of the trachea and the first generation is distensible and subjected to collapses during expiration under diseased conditions. Flow through a collapsible tube is commonly investigated using a straight flexible tube with an imposed driving pressure and transmural pressure (pressure difference between inside and outside of the tube). As a model for large central airways, the current experimental study employs a straight tube, having material properties similar to the large airways and subjected to pressures replicating normal and forced expiration. Observed steady states and self-excited oscillating modes are quantified by reconstructing the tube periphery, both cross-sectionally and along the length of the tube, using stereophotogrammetry. This approach conducted in physiological conditions helps to elucidate the nature of the collapse and subsequently identify the diagnostic procedures.   

Correlation between trachea internal airway geometry and the auscultation signal response

Human auscultation represents an easy and prompt tool for physicians to diagnose the existence of a pulmonary pathology. The contemporary practice of lung auscultation as an essential part of physical examination can be traced back to the time of Hippocrates (Bohadana et al, 2014). But revolutionary tool called “stethoscope” was only introduced by Rene Laennec in 1816 and gradually refined ever since (Wilks 1883 and Bishop 1980). The process of new physician training in acquiring pulmonary auscultation skills is still time consuming. Moreover, the success rate as revealed by the training examination is also unsatisfactorily elusive. To avoid the subjective nature of pulmonary auscultation, efforts have been carried out to digitally record and analyze lung sounds and further explore the correlation between the acoustic characteristics with the clinical symptoms. 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 model from data collected from a real human patient by Pacific Northwest National Laboratory. We want 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. Once we understand the pattern for a healthy trachea, we alter its internal geometry to simulate a tracheal disease. For this, we investigated a simplified model of stenosis by simply create a small obstruction inside the trachea. Using an A/D board NI USB 6003 with maximum sampling rate of 100 kHz and 16-bit resolution and by processing the signal using “Labview” and Matlab, we established a correlation between the different tracheal shapes and the generated acoustic signal. Using an Ansys Fluent Turbulent CFD simulation, we matched the air flow events inside the trachea with the Power Spectral Density peaks of the tracheal sound.   

Computational investigation of plug instillation into a physiologically representative infant airway tree model

We present 3D multiphase flow simulations of liquid surfactant plug transport through a physically representative model of the human infant lung airway tree. Liquid surfactant instillation into the lung airways is used to treat respiratory distress syndrome (RDS) in preterm infants. The procedure, commonly known as surfactant replacement therapy (SRT), is used in the targeted delivery of surfactant plugs with the goal of achieving a uniform film distribution. SRT's effectiveness is tied to the successful plug propagation through each branching airway network. However, achieving uniform surfactant distribution is quite difficult with SRT having a 35% non-response rate. The challenge resides in overcoming naturally present asymmetries in the lung, which often lead to asymmetric plug propagation. We present computational simulations of plug instillation in a physiologically representative infant airway tree model, investigating effects of plug blockages and rupture on plug splitting and film distribution, with the goal of improving our understanding and the effectiveness of SRT.   

Not Participating

Through evolutionary refinement, insects have developed respiratory systems that have been efficiently handling air inside complex microscale tracheal networks for over 480 million years. They do this exceptionally well, as evidenced by the fact that their metabolic range is the highest in the animal kingdom, about 5 times higher than humans’. This exceptional range has been attributed to their unique respiratory systems, which carry oxygen directly to the cells without using blood as an intermediate carrier. One of the unusual features of insect respiration from a fluid dynamics perspective is that insect tracheal flows are often low-Reynolds-number (~0.1), but high-Knudsen-number (0.0001-1). In this work, we investigate the effects of hydrodynamic slip and fine-scale internal tracheal morphology in intratracheal flows in insects. We hypothesize that the helical taenidial structures found on the inner wall of the tracheal tubes determine the structure of the flow field near the wall and play a vital role in transport. We have closely reproduced the internal morphology of the tracheal tubes of the American cockroach, Periplaneta americana, in our computational geometry. To investigate this hypothesis, we designed a series of simulations using the Lattice Boltzmann method (LBM) at a Reynolds number of 0.1. For simplicity of computational analysis, we use a square microchannel and only add taenidial structure to the bottom wall. In the first set of simulations, we removed the taenidial structures and simulated the flow through the microchannel for both no-slip and slip boundary conditions. In the second set of simulations, we introduce the taenidial structures on the bottom wall and compare the simulation results to those without the taenidia. We find that the taenidia significantly affect the flow structure and characterize their contribution.   

Study of airflow past endotracheal tubes – effect ventilator flow cycles on transport of mucus

Tracheal airflow in intubated patients presents a range of interesting flow patterns via flow through convoluted geometries. Interaction of the resulting flow structures with the variable, high-viscosity mucus secretions leads mucus pooling which in turn leads to bacterial colonization and secondary infections in patients. The stagnation of mucus is a function of a range of parameters including, but not limited to, the shape and size of the endotracheal tube (ETT) cuff, the inflation pressure of the cuff, and ventilator flow cycles. The present study predicts mucus behavior in intubated patients, via a flow analysis of an intubated upper trachea model. Large-eddy simulations incorporating the respiratory cycle and mucus distribution are carried out and the role of the ventilator flow parameters in mucus leakage is determined. The results will be employed in the development of a predictive, empirical model for mucus leakage which will improve the current experiential selection of the ETT, enable reduced patient monitoring promoting reduced secondary infections in patients, and reduced exposure for clinicians.   

Surfactant, viscoelasticity, elastoviscoplasticity and two-layer lining in an airway closure model

The human lung airways are lined by the airway surface liquid (ASL). The ASL is either a layer of mucus or a two-layer liquid film consisting of the serous (outer) and the mucus (inner) layer. Owing to the Plateau-Rayleigh instability, the ASL can lead to airway closure, i.e. the occlusion of the airway due to the formation of a liquid plug. This is typical of distal airways, namely the bronchioles from the 7th generation onwards. In our simulations we focus on the fluid dynamics phenomena occurring during an airway closure, hence we assume the bronchiles walls as rigid. We isolate several elements of complexity to well comprehend their standalone effect on the airway closure. Indeed, we consider the airway closure with: (i) surfactant in a single-layer film, (ii) viscoelasticity and (iii) elastoviscoplasticity of a single-layer liquid, and (iv) two-layer Newtonian film. Apart from the primary instability leading to aiway closure, we focus on the post-coalescence wall stresses and secondary instabilities due to viscoelastic effects. Our future long-term goal is to carry out omni-comprehensive simulations that include the weakly viscoelasticy of the serous layer, the pronuouced  elastoviscoplasticity of the mucus layer and the surfactant dynamics.   

Mathematical Modelling for Virus Transport in a Viscous Fluid Medium

The  worldwide  spread  of  coronavirus  is  a  major  concern  for  health  worriers  and  scientists.   Primary investigation reveals that humans got affected by coronavirus through acute respiratory transmission like the Influenza virus.  This becomes severe for patients who require an oxygen supplementation device. It was noticeable that the viruses transmit from person to person through solid surfaces, air medium, and fluid medium.   Therefore, it is essential to analyze the behavior of virus transmission in the fluid medium.   This will help healthcare workers to arrest the vulnerable and to restrict the spread of the Coronavirus virus.  Accordingly, a mathematical model is developed to simulate the nature of virus transport through the fluids driven by the peristaltic mechanism. The present study considers four types of viruses (Corona Virus, Influenza AB virus, Swine Influenza), traveling through the fluid medium.  The effects of various parameters like gravity, virtual mass, basset force, and drag forces on virus trajectories, velocity field vectors are analyzed and discussed the significance of the physical parameters. A comparative analysis for all types of viruses is also presented.   

Design of new-generation scalable filters with tortuous pathways inspired from animal noses

We have explored new-generation filter pathways, taking inspiration from the topologically complex nasal cavities found in high-olfactory animals (e.g., dogs, pigs). Inhaled particulates are more efficiently screened as the air recirculates through the tortuous nasal passages in these animals, thereby augmenting their olfaction. The proposed bio-inspired filters would use regular airflow paths with continuous tortuosity, inducing a reduced resistance inside conduits and a high likelihood of particle-trapping by altering their trajectories with tortuous paths and local flow instability. We have tested the iterative designs for pressure drop and particle filtering efficiency over a wide range of airflow rates (3–73 L/min) using manometers and optical technique, a subset of which corresponds to the range for steady to forceful breathing (15–55 L/min). We have also cross-validated the observed screening efficiency through theory and LES-based numerical simulations. The proposed filters exhibit a lower pressure drop than commercial mask filters (e.g., N95, surgical) by a factor of 2 under similar filtering thresholds.