An experimental study of respiratory aerosol transport in phantom lung bronchioles.
TL;DR: Lower breathing frequency and higher breath hold time could significantly increase the chances of getting infected with COVID-19 in crowded places.
Abstract: The transport and deposition of micrometer-sized particles in the lung is the primary mechanism for the spread of aerosol borne diseases such as corona virus disease-19 (COVID-19). Considering the current situation, modeling the transport and deposition of drops in human lung bronchioles is of utmost importance to determine their consequences on human health. The current study reports experimental observations on deposition in micro-capillaries, representing distal lung bronchioles, over a wide range of Re that imitates the particle dynamics in the entire lung. The experiment investigated deposition in tubes of diameter ranging from 0.3 mm to 2 mm and over a wide range of Reynolds number (10−2 ⩽ Re ⩽ 103). The range of the tube diameter and Re used in this study is motivated by the dimensions of lung airways and typical breathing flow rates. The aerosol fluid was loaded with boron doped carbon quantum dots as fluorophores. An aerosol plume was generated from this mixture fluid using an ultrasonic nebulizer, producing droplets with 6.5 µm as a mean diameter and over a narrow distribution of sizes. The amount of aerosol deposited on the tube walls was measured using a spectrofluorometer. The experimental results show that dimensionless deposition (δ) varies inversely with the bronchiole aspect ratio ( L ¯ ), with the effect of the Reynolds number (Re) being significant only at low L ¯ . δ also increased with increasing dimensionless bronchiole diameter ( D ¯ ), but it is invariant with the particle size based Reynolds number. We show that δ L ¯ ∼ R e − 2 for 10−2 ⩽ Re ⩽ 1, which is typical of a diffusion dominated regime. For Re ⩾ 1, in the impaction dominated regime, δ L ¯ is shown to be independent of Re. We also show a crossover regime where sedimentation becomes important. The experimental results conclude that lower breathing frequency and higher breath hold time could significantly increase the chances of getting infected with COVID-19 in crowded places.
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TL;DR: In this article, the authors investigated the SARS CoV-2 virus particle transport and deposition to the terminal airways in a complex 17-generation lung model and showed that a higher percentage of the virus particles are trapped at the upper airways when sleeping and in a light activity condition.
Abstract: The recent outbreak of the SARS CoV-2 virus has had a significant effect on human respiratory health around the world. The contagious disease infected a large proportion of the world population, resulting in long-term health issues and an excessive mortality rate. The SARS CoV-2 virus can spread as small aerosols and enters the respiratory systems through the oral (nose or mouth) airway. The SARS CoV-2 particle transport to the mouth-throat and upper airways is analyzed by the available literature. Due to the tiny size, the virus can travel to the terminal airways of the respiratory system and form a severe health hazard. There is a gap in the understanding of the SARS CoV-2 particle transport to the terminal airways. The present study investigated the SARS CoV-2 virus particle transport and deposition to the terminal airways in a complex 17-generation lung model. This first-ever study demonstrates how far SARS CoV-2 particles can travel in the respiratory system. ANSYS Fluent solver was used to simulate the virus particle transport during sleep and light and heavy activity conditions. Numerical results demonstrate that a higher percentage of the virus particles are trapped at the upper airways when sleeping and in a light activity condition. More virus particles have lung contact in the right lung than the left lung. A comprehensive lobe specific deposition and deposition concentration study was performed. The results of this study provide a precise knowledge of the SARs CoV-2 particle transport to the lower branches and could help the lung health risk assessment system.
29 citations
TL;DR: In this article, the authors measured the size and number of droplets generated by flushing toilets and urinals in a public restroom and found that the particular designs tested in the study generate a large number of aerosol in the size range 0.3 μ m − 3 μ m, which can reach heights of at least 1.52 m.
Abstract: Aerosolized droplets play a central role in the transmission of various infectious diseases, including Legionnaire's disease, gastroenteritis-causing norovirus, and most recently COVID-19. Respiratory droplets are known to be the most prominent source of transmission for COVID-19; however, alternative routes may exist given the discovery of small numbers of viable viruses in urine and stool samples. Flushing biomatter can lead to the aerosolization of micro-organisms; thus, there is a likelihood that bioaerosols generated in public restrooms may pose a concern for the transmission of COVID-19, especially since these areas are relatively confined, experience heavy foot traffic, and may suffer from inadequate ventilation. To quantify the extent of aerosolization, we measure the size and number of droplets generated by flushing toilets and urinals in a public restroom. The results indicate that the particular designs tested in the study generate a large number of droplets in the size range 0.3 μ m– 3 μ m, which can reach heights of at least 1.52 m. Covering the toilet reduced aerosol levels but did not eliminate them completely, suggesting that aerosolized droplets escaped through small gaps between the cover and the seat. In addition to consistent increases in aerosol levels immediately after flushing, there was a notable rise in ambient aerosol levels due to the accumulation of droplets from multiple flushes conducted during the tests. This highlights the need for incorporating adequate ventilation in the design and operation of public spaces, which can help prevent aerosol accumulation in high occupancy areas and mitigate the risk of airborne disease transmission.
25 citations
TL;DR: In this article, the authors describe respiratory droplets from a physical and mechanical perspective, especially their correlation with the transmission of infectious pathogens, and stress the multidisciplinary nature of their subject and appeals for collaboration among different fields to fight the present pandemic.
Abstract: The outbreak of the coronavirus disease has drawn public attention to the transmission of infectious pathogens, and as major carriers of those pathogens, respiratory droplets play an important role in the process of transmission. This Review describes respiratory droplets from a physical and mechanical perspective, especially their correlation with the transmission of infectious pathogens. It covers the important aspects of (i) the generation and expulsion of droplets during respiratory activities, (ii) the transport and evolution of respiratory droplets in the ambient environment, and (iii) the inhalation and deposition of droplets in the human respiratory tract. State-of-the-art experimental, computational, and theoretical models and results are presented, and the corresponding knowledge gaps are identified. This Review stresses the multidisciplinary nature of its subject and appeals for collaboration among different fields to fight the present pandemic.
23 citations
TL;DR: In this paper, the authors investigated SARS COVID-2 aerosol transport in age-specific airway systems using a highly asymmetric airway model and fluent solver (ANSYS 19.2).
Abstract: The recent outbreak of the COVID-19 causes significant respirational health problems, including high mortality rates worldwide. The deadly corona virus-containing aerosol enters the atmospheric air through sneezing, exhalation, or talking, assembling with the particulate matter, and subsequently transferring to the respiratory system. This recent outbreak illustrates that the severe acute respiratory syndrome (SARS) coronavirus-2 is deadlier for aged people than for other age groups. It is evident that the airway diameter reduces with age, and an accurate understanding of SARS aerosol transport through different elderly people's airways could potentially help the overall respiratory health assessment, which is currently lacking in the literature. This first-ever study investigates SARS COVID-2 aerosol transport in age-specific airway systems. A highly asymmetric age-specific airway model and fluent solver (ANSYS 19.2) are used for the investigation. The computational fluid dynamics measurement predicts higher SARS COVID-2 aerosol concentration in the airway wall for older adults than for younger people. The numerical study reports that the smaller SARS coronavirus-2 aerosol deposition rate in the right lung is higher than that in the left lung, and the opposite scenario occurs for the larger SARS coronavirus-2 aerosol rate. The numerical results show a fluctuating trend of pressure at different generations of the age-specific model. The findings of this study would improve the knowledge of SARS coronavirus-2 aerosol transportation to the upper airways which would thus ameliorate the targeted aerosol drug delivery system.
21 citations
TL;DR: In this paper, the authors explored the disjoining pressure-driven thin-film evaporation mechanism and thereby the virucidal properties of engineered surfaces with varied wettability and texture.
Abstract: Surface engineering is an emerging technology to design antiviral surfaces, especially in the wake of COVID-19 pandemic. However, there is yet no general understanding of the rules and optimized conditions governing the virucidal properties of engineered surfaces. The understanding is crucial for designing antiviral surfaces. Previous studies reported that the drying time of a residual thin-film after the evaporation of a bulk respiratory droplet on a smooth surface correlates with the coronavirus survival time. Recently, we [Chatterjee et al., Phys. Fluids. 33, 021701 (2021)] showed that the evaporation is much faster on porous than impermeable surfaces, making the porous surfaces lesser susceptible to virus survival. The faster evaporation on porous surfaces was attributed to an enhanced disjoining pressure within the thin-film due the presence of horizontally oriented fibers and void spaces. Motivated by this, we explore herein the disjoining pressure-driven thin-film evaporation mechanism and thereby the virucidal properties of engineered surfaces with varied wettability and texture. A generic model is developed which agrees qualitatively well with the previous virus titer measurements on nanostructured surfaces. Thereafter, we design model surfaces and report the optimized conditions for roughness and wettability to achieve the most prominent virucidal effect. We have deciphered that the optimized thin-film lifetime can be gained by tailoring wettability and roughness, irrespective of the nature of texture geometry. The present study expands the applicability of the process and demonstrates ways to design antiviral surfaces, thereby aiding to mitigate the spread of COVID-19.
19 citations
References
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06 Feb 2019
TL;DR: Patients with distressed breathing profiles may be expected to receive a larger aerosol dose than those with normal breathing rates, due to the main trends identified in the statistical DOE predicted aerosol delivery across adult patient breathing profiles, in terms of tidal volume, breath rate, and I:E ratio.
Abstract: The use of concurrent aerosol delivery during high-flow nasal therapy (HFNT) may be exploited to facilitate delivery of a variety of prescribed medications for inhalation. The study assessed the effect of tidal volume, breath rate, and inspiratory:expiratory (I:E) ratio on the quantity of aerosol captured at the level of the trachea during simulated HFNT. Testing was completed according to a factorial statistical design of experiments (DOE) approach. Tracheal dose was characterized with a vibrating mesh nebulizer (Aerogen Solo, Aerogen Ltd) using simulated adult, small child, and infant HFNT models. Furthermore, aerosol delivery was evaluated across a range of adult patient profiles with clinically representative test setups. Aerosol delivery increased with a large tidal volume, a rapid breath rate, and a long inspiratory time. Tidal volume, breath rate, and I:E ratio each had a significant effect on tracheal dose across simulated adult, small child, and infant breathing. The main trends that were identified in the statistical DOE predicted aerosol delivery across adult patient breathing profiles, in terms of tidal volume, breath rate, and I:E ratio. Therefore, patients with distressed breathing profiles may be expected to receive a larger aerosol dose than those with normal breathing rates. Aerogen Limited.
16 citations
TL;DR: This work uses a Monte Carlo based algorithm to predict the virus infection rate for different population densities using the most recent epidemic data and test the spread of the coronavirus using three different lockdown models and eight various combinations of constraints, which allow them to examine the efficiency of each model and constraint.
Abstract: By the end of July 2020, the COVID-19 pandemic had infected more than seventeen million people and had spread to almost all countries worldwide. In response, many countries all over the world have used different methods to reduce the infection rate, such as including case isolation, the closure of schools and universities, banning public events, and mostly forcing social distancing, including local and national lockdowns. We use a Monte-Carlo (MC) based algorithm to predict the virus infection rate for different population densities using the most recent epidemic data in our work. We test the spread of the Coronavirus using three different lockdown models, and eight various combinations of constraints, which allow us to examine the efficiency of each model and constraint. In this paper, we have tested three different time-cyclic patterns of no-restrictions/lockdown patterns. This model's main prediction is that a cyclic schedule of no-restrictions/lockdown that contains at least ten days of lockdown for each time cycle can help control the virus infection. In particular, this model reduces the infection rate when accompanied by social distancing and complete isolation of symptomatic patients.
15 citations
TL;DR: It was found that the chaotic acinar flow irreversibility played a significant role in the aerosol transport in higher generations and deposition in the intra-acinar region of the human lung.
Abstract: The determination of the particle dynamics in the human acinar airways having millions of alveoli is critical in preventing potential health problems and delivering therapeutic particles effectively to target locations. Despite its complex geometrical structure and complicate wall movements, the advanced calculation simulations can provide valuable results to accurately predict the aerosol deposition in this region. The objective of this study was to numerically investigate the aerosol particle transport and deposition in the intra-acinar region of a human lung for different breathing scenarios (i.e., light, normal, and heavy activities) during multiple breaths. Idealized intra-acinar models utilized in this study consisted of a respiratory bronchial model, an alveolar duct model, and an alveolar sac model. The particles with 5 μm in diameter released from the inlet of the model were tracked until they deposited or escaped from the computational domain. The results showed that due to the rhythmic alveolar wall movement, the flow field was divided into two regions: one is the low-speed alveolar flow and the other is the channel flow. It was found that the chaotic acinar flow irreversibility played a significant role in the aerosol transport in higher generations. During the succeeding breaths, more particles deposited or escaped to the relating acinar generation and reached the more distal regions of the lung. The number of particles remaining in the suspension at the end of the third cycle ranged from 0.016% to 3%. When the mouth flow rate increased, the number of particles remaining in the suspension reduced, resulting in higher deposition efficiency. The total deposition efficiencies for each flow rate were 24%, 47%, and 77%, respectively. The particle simulation results also showed that more breathing cycle was required for full aerosol particle deposition or escape from the model. In addition to the alveolar wall motion, the type of breathing condition and breathing cycle had a significant effect on the accurate prediction of the aerosol deposition in the intra-acinar region of the human lung.
13 citations
TL;DR: In the supine posture, deposition appears to lack sensitivity for assessing the effect of lung morphology and/or ventilation distribution alteration induced by mild-to-moderate lung disease on the fate of inhaled aerosols, however, other parameters such as aerosol bolus dispersion and mode shift may be more sensitive parameters for evaluating models of lungs with moderate disease.
13 citations
TL;DR: In this paper, the size-dependent lateral displacement of particles between 0.2 μm and 2 μm in straight microchannels and size-based lateral displacement caused by centrifugal forces in a curved channel is investigated.
Abstract: The measurement of airborne particles is important for environmental and exposure monitoring. Microfluidic technologies present potential advantages for aerosol monitoring but have been applied very little to the handling of airborne particles. In this paper, we examine the flow focusing and cross-streamline diffusion of aerosols in straight microchannels, and the size-based lateral displacement of aerosols caused by centrifugal forces in a curved channel. We present calculations, simulations, and experimental results verifying the models: measurements of the focusing and diffusion of 0.2 μm and 0.75 μm particles in straight channels and of the size-dependent lateral displacement of particles between 0.2 μm and 2 μm in curved channels are demonstrated and shown to match well with the simulations. We observe lateral dispersion of the particles: particles closer to the top and bottom wall of the channel experience less lateral displacement than particles near the center due to the flow velocity distribution...
13 citations