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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TL;DR: In this paper, the thermophoretic deposition of graphite dust in an HTGR in a straight pipe for various Reynolds numbers and inlet temperatures was investigated, and it was shown that the deposition efficiency increases with increasing inlet temperature.
7 citations
TL;DR: A spontaneous breathing-lung model that integrates branched morphology and deformable alveolar features was constructed using a multilayered fabrication technology to mimic the complex environment of the human lower respiratory tract and can serve as a testing platform to provide a comprehensive understanding of the pharmacokinetics of pulmonary drugs within the lower lungs.
Abstract: Pulmonary administration is a noninvasive drug delivery method that, in contrast to systemic administration, reduces drug dosage and possible side effects. Numerous testing models, such as impingers and impactors, have previously been developed to evaluate the fate of inhaled drugs. However, such models are limited by the lack of information regarding several factors, such as pulmonary morphology and breathing motion, which are required to fully interpret actual inhaled-drug deposition profiles within the human respiratory tract. In this study, a spontaneous breathing-lung model that integrates branched morphology and deformable alveolar features was constructed using a multilayered fabrication technology to mimic the complex environment of the human lower respiratory tract. The developed model could emulate cyclic and spontaneous breathing motions to inhale and exhale aerosols generated by a nebulizer under diseaselike conditions. Results of this research demonstrate that aerosols (4.2 μm) could reach up to the deeper lung regions (generation 19 of the branched lung structure) within the obstructivelike model, whereas lesser penetration (generation 17) was observed when using the restrictivelike model. The proposed breathing-lung model can serve as a testing platform to provide a comprehensive understanding of the pharmacokinetics of pulmonary drugs within the lower lungs.
7 citations
TL;DR: In this article, the authors examined the contribution of gravity settling to the deposition, and the effect of roughness of the pipe wall on the deposition from turbulent flow in a horizontal straight metal pipe.
Abstract: Loss by deposition of aerosol particles in an air sampling pipe causes error in the estimation of aerosol concentration in the atmosphere. For a horizontal pipe, the deposition fraction for laminar flow can be estimated by equations of deposition governed by gravity settling and diffusion. For turbulent flow, there are two methods available—one using the equation by Yoshioka et al, to express deposition velocity, the other being the “extrapolation method” proposed by the present authors. The present paper examines the validity of the two methods, with particular reference to the contribution of gravity settling to the deposition, and the effect of roughness of the pipe wall on the deposition from turbulent flow. The deposition fraction in a horizontal straight metal pipe can be estimated with deviation from experimental values not exceeding a factor of 2, throughout the whole region covered by the study, extending over both laminar and turbulent ranges. Use of a suitable friction factor to account for the...
6 citations