No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Submicron droplet formation in the human lung
Abstract
The exhaled breath of humans contains droplets originating from the lung lining fluid. An analysis of these droplets for non-volatile proteinaceous biomarkers holds potential as a non-invasive diagnosis of lung diseases. To ease the interpretation of the diagnostic results, the source strength of the particles should be known und therefore an understanding of the particle generation process is required. It is assumed that during reopening of a collapsed terminal airway a liquid bridge of the lung lining fluid ruptures and droplets are generated. The objective of our experimental and theoretical study was to clarify the mechanisms of droplet generation for quiet breathing patterns by investigating in detail the number flux and the particle size distribution in the exhaled breath. The process of liquid film rupture is modelled by computational fluid dynamics analysis from which the droplet size distribution is calculated. In addition the number emission flux and the droplet size distribution are systematically measured in the exhaled breath of healthy volunteers. The strong increase of the particle emission flux with tidal volume and the good agreement between measured and calculated droplet number distribution both showing droplets primarily in the submicron range confirm the present hypothesis that reopening of collapsed airway structures associated with the rupture of a surfactant film is the physical mechanism of droplet generation. This was hypothesized previously in the literature.
... Therefore, accurate measurement of the particle size distribution is important. Various measurement techniques have been used, but the particle size distributions reported in the literature vary widely (Fig. 1) [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] . Limitations on the resolution and measurement range of various instruments make it difficult to obtain the entire range of the particle size distribution experimentally. ...
... Various approaches have been used to measure the particle size distributions of respiratory droplets [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] . However, obtaining a comprehensive distribution experimentally is impossible because of differences in measurement methods and conditions. ...
... The droplet size distribution in the present study showed that smaller droplets were generated in larger numbers. Because only shear-induced droplets in the lower airway were considered and the droplets generated were counted rather than the droplets released from oral cavity, the obtained droplet size distributions were significantly different from those obtained experimentally in previous studies [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] . For many of these studies, the droplet size distributions peaked at the microscale. ...
Computational fluid dynamics is widely used to simulate droplet-spreading behavior due to respiratory events. However, droplet generation inside the body, such as the number, mass, and particle size distribution, has not been quantitatively analyzed. The aim of this study was to identify quantitative characteristics of droplet generation during coughing. Airflow simulations were performed by coupling the discrete phase model and Eulerian wall film model to reproduce shear-induced stripping of airway mucosa. An ideal airway model with symmetric bifurcations was constructed, and the wall domain was covered by a mucous liquid film. The results of the transient airflow simulation indicated that the droplets had a wide particle size distribution of 0.1–400 µm, and smaller droplets were generated in larger numbers. In addition, the total mass and number of droplets generated increased with an increasing airflow. The total mass of the droplets also increased with an increasing mucous viscosity, and the largest number and size of droplets were obtained at a viscosity of 8 mPa s. The simulation methods used in this study can be used to quantify the particle size distribution and maximum particle diameter under various conditions.
... Retrospektive, korrelative Analysen bestätigten den Nutzen dieser Maßnahme [20,21]. Nachfolgende Studien zeigten, dass nicht nur größere Tröpfchen, sondern auch kleinere virushaltige Tröpfchenpartikel (Aerosole), die beim Atmen, Sprechen, Singen, Niesen oder Husten ausgeschieden werden, in erheblichem Maße zur Virusausbreitung beitragen [22,23]. ...
... Der wichtigste Übertragungsweg für SARS-CoV-2 ist die respiratorische Aufnahme virushaltiger Partikel unterschiedlicher Größe, die aus dem Respirationstrakt infizierter Personen freigesetzt werden, wenn diese husten, niesen, schreien, singen, sprechen oder atmen [22,23,44]. Diese virushaltigen Partikel "landen" auf den Schleimhäuten von Kontaktpersonen oder werden von diesen eingeatmet, woraus eine Folgeinfektion resultieren kann (besprochen in [45]; [22,23,44]). ...
... Der wichtigste Übertragungsweg für SARS-CoV-2 ist die respiratorische Aufnahme virushaltiger Partikel unterschiedlicher Größe, die aus dem Respirationstrakt infizierter Personen freigesetzt werden, wenn diese husten, niesen, schreien, singen, sprechen oder atmen [22,23,44]. Diese virushaltigen Partikel "landen" auf den Schleimhäuten von Kontaktpersonen oder werden von diesen eingeatmet, woraus eine Folgeinfektion resultieren kann (besprochen in [45]; [22,23,44]). Partikel eines Durchmessers über~100 μm werden häufig als "Tröpfchen" (Droplets) bezeichnet [45]. ...
Zusammenfassung
Die weltweite Ausbreitung des Coronavirus SARS-CoV‑2 hat Gesundheits‑, Wirtschafts- und Gesellschaftssysteme massiv in Mitleidenschaft gezogen. Obwohl mittlerweile effektive Impfstoffe zur Verfügung stehen, ist es wahrscheinlich, dass der Erreger endemisch wird und uns noch über Jahre begleitet. Um andere und sich selbst möglichst effektiv vor einer SARS-CoV-2-Infektion zu schützen, ist ein Verständnis der Übertragungswege von größter Wichtigkeit.
In dieser Übersichtsarbeit erläutern wir Übertragungswege im Hinblick auf den Fremd- und Eigenschutz. Darüber hinaus gehen wir auf die Charakteristika der SARS-CoV-2-Übertragung auf Populationsebene ein. Diese Arbeit soll helfen, folgende Fragen anhand der verfügbaren Literatur zu beantworten: Wann und wie lange ist eine infizierte Person kontagiös (ansteckungsfähig)? Wie wird das Virus ausgeschieden? Wie wird das Virus aufgenommen? Wie verbreitet sich das Virus in der Gesellschaft?
Die Mensch-zu-Mensch-Übertragung von SARS-CoV‑2 wird in starkem Maße durch die biologischen Erregereigenschaften, einschließlich der Infektions‑, Replikations- und Ausscheidungskinetik, bestimmt. SARS-CoV‑2 wird hauptsächlich über humane Aerosole übertragen, die von infizierten Personen ausgeschieden werden, auch wenn Erkrankungssymptome (noch) nicht vorliegen. Hieraus resultiert ein relevanter Anteil prä- bzw. asymptomatischer Transmissionen. In geschlossenen Räumen erfolgen Übertragungen besonders effektiv. Die meisten infizierten Personen rufen eine geringe Zahl von Sekundärfällen hervor, während wenige Fälle (sog. Superspreader) zu vielen Folgeinfektionen führen – auf Populationsebene spricht man hier von einer „Überdispersion“. Die besonderen Merkmale von SARS-CoV‑2 (asymptomatische Aerosolübertragung und Überdispersion) machen die Pandemie schwer kontrollierbar.
... Particle generation related to respiration takes place in the human lung and has been attributed to the so-called airway reopening hypothesis in several previous and recent studies (Edwards et al. 2004;Johnson and Morawska 2009;Almstrand et al. 2010;Haslbeck et al. 2010;Bake et al. 2019;Scheuch 2020). In this hypothesis, the lower very small airways collapse during exhalation and subsequently reopen during inhalation. ...
... As the intensity of scattered light by small particles decreases with particle size, they are increasingly harder to differentiate from background noise by exceeding the trigger threshold. About studies measuring human exhaled aerosol using OPCs (Haslbeck et al. 2010;Schwarz et al. 2010Schwarz et al. , 2015 the following conclusions can be drawn: aerosols with measured particle mean diameters as low as 300 nm likely contain a significant number of particles below the measurement range the size bins below the mode likely contain significantly more particles than detected Thus, studies on the concentration and size distribution of human exhaled aerosols likely underestimate the number of submicron particles in the human breath. ...
In light of the COVID-19 pandemic, the importance of protective measures against infectious aerosols has drastically increased, as the transmission of diseases via airborne particles is impacting many aspects of everyday life. The protective measures against such infections is determinant in the operation of schools and kindergartens, hygiene in hospitals and medical facilities, in offices, administrative and production facilities, hotels and the event industry, amongst others. To test these protective measures, suitable test aerosols and processes are needed. These aerosols ought to be similar to aerosols exhaled by humans as those carry the pathogens and thus need to be removed from the air or inactivated.
The exhaled aerosols of several healthy test subjects were characterized regarding their particle concentration and size distribution. In accordance with previous studies, it was found that exhaled particle concentration varies significantly from subject to subject and most of the particles can be found in the submicron size range. Aerosols technically generated through nebulization were emitted by the generators in particle concentrations several orders of magnitude higher than those exhaled by humans, independent of aerosol generation method and nebulized fluid. The particle size distribution generated by the two nebulizers used however, was quite similar to the measured size distributions of the human aerosols, with most of the particles below 1 µm in size. Consequently, the used aerosol generators are not suitable to mimic single individuals as active aerosol sources, but rather to provide a sufficient amount of aerosol similar to human aerosols in size distribution, which can be used in the testing of air purification technologies.
... It is worth noting that the recirculated air is filtered by absolutely perfect HEPA filters, which means that the air supply diffusers provide 100% fresh air. The size of droplets generated by respiration is in the submicron level [29][30][31][32][33]. In this paper, the size of droplets is set to 1 μm, and the concentration of droplets is 1000/L. ...
... It is worth noting that the recirculated air is filtered by absolutely perfect HEPA filters, which means that the air supply diffusers provide 100% fresh air. The size of droplets generated by respiration is in the submicron level [29][30][31][32][33]. In this paper, the size of droplets is set to 1 µm, and the concentration of droplets is 1000/L. ...
COVID-19 is a respiratory infectious disease that spreads readily between people, and an urgent issue of passengers’ exposure risk assessment in commercial aircraft has been raised because an aircraft cabin as a confined space may carry and transmit the disease worldwide. In this study, the droplets transmission process under different ventilation systems in a twin-aisle wide-body aircraft was studied using CFD simulations and the infection risk of passengers was assessed by the improved Wells–Riley model. Numerical results found that the transmission mechanism of droplets in the aircraft cabin was different depending on the type of ventilation systems and the location of the infectious source. Annular airflow could effectively enhance the ability of droplets transmission, while direct airflow, represented by displacement ventilation, could significantly inhibit droplets transmission. Accordingly, a new type of ventilation system was proposed based on the concept that the overall space is organized by annular airflow and the local area is direct airflow. Compared with sidewall mixing ventilation system, the infection risk of the new ventilation system presented in this study is reduced by 27%.
... While some of the studies in Table 2 were motivated by investigating droplet emission in the context of airborne pathogen contagion (e.g., [89][90][91][92]), the motivation of others is to probe various mechanisms of droplet formation [93][94][95][96][97][98] (see comprehensive discussions and reviews in [86,99,100]), specifically the airway reopening hypothesis of small peripheral airways that normally close following a deep expiration, which was further tested by computerized modeling by Haslbeck et al. [100], who simulated this mechanism of particle formation by rupture of surfactant films involving surface tension. The mechanism was probed by Johnson and Morawska [93] by showing that concentrations of exhaled particles significantly increase with breathing intensities higher than rest tidal volume, but also for fast exhalations but not fast inhalation, while droplet numbers increased up to two orders of magnitude: from ∼230/L in tidal volume (0.7 L) to over 1200/L in a breathing maneuver from fractional residual capacity to total lung capacity (see [95]). ...
... While some of the studies in Table 2 were motivated by investigating droplet emission in the context of airborne pathogen contagion (e.g., [89][90][91][92]), the motivation of others is to probe various mechanisms of droplet formation [93][94][95][96][97][98] (see comprehensive discussions and reviews in [86,99,100]), specifically the airway reopening hypothesis of small peripheral airways that normally close following a deep expiration, which was further tested by computerized modeling by Haslbeck et al. [100], who simulated this mechanism of particle formation by rupture of surfactant films involving surface tension. The mechanism was probed by Johnson and Morawska [93] by showing that concentrations of exhaled particles significantly increase with breathing intensities higher than rest tidal volume, but also for fast exhalations but not fast inhalation, while droplet numbers increased up to two orders of magnitude: from ∼230/L in tidal volume (0.7 L) to over 1200/L in a breathing maneuver from fractional residual capacity to total lung capacity (see [95]). ...
We examine the plausibility of aerial transmission of pathogens (including the SARS-CoV-2 virus) through respiratory droplets that might be carried by exhaled e-cigarette aerosol (ECA). Given the lack of empiric evidence on this phenomenon, we consider available evidence on cigarette smoking and respiratory droplet emission from mouth breathing through a mouthpiece as convenient proxies to infer the capacity of vaping to transport pathogens in respiratory droplets. Since both exhaled droplets and ECA droplets are within the Stokes regime, the ECA flow acts effectively as a visual tracer of the expiratory flow. To infer quantitatively the direct exposure distance, we consider a model that approximates exhaled ECA flow as an axially symmetric intermittent steady starting jet evolving into an unstable puff, an evolution that we corroborate by comparison with photographs and videos of actual vapers. On the grounds of all this theoretical modeling, we estimate for low-intensity vaping (practiced by 80–90% of vapers) the emission of 6–210 (median 39.9, median deviation 67.3) respiratory submicron droplets per puff and a horizontal distance spread of 1–2 m, with intense vaping possibly emitting up to 1000 droplets per puff in the submicron range with a distance spread over 2 m. The optical visibility of the ECA flow has important safety implications, as bystanders become instinctively aware of the scope and distance of possible direct contagion through the vaping jet.
... While some of the studies in Table 3 were motivated by investigating droplet emission in the context of airborne pathogen contagion [79,80,81,82], the motivation of others [83,84,85,86,87,88] is to probe various mechanisms of droplet formation (see comprehensive discussion and reviews in [77,89,90]), specifically the airway reopening hypothesis of small peripheral airways that normally close following a deep expiration, which was further tested by computerized modeling [90] that simulated this mechanism of particle formation by rupture of surfactant films involving surface tension. The mechanism was probed in [83] by showing that concentrations of exhaled particles significantly increase with breathing intensities higher than rest tidal volume, but also for fast exhalations but not fast inhalation, while droplet numbers increased up to two orders of magnitude: from ∼ 230/Lt in tidal volume (0.7 Lt) to over 1200/Lt in a breathing maneuver from fractional residual capacity to total lung capacity [85]. ...
... While some of the studies in Table 3 were motivated by investigating droplet emission in the context of airborne pathogen contagion [79,80,81,82], the motivation of others [83,84,85,86,87,88] is to probe various mechanisms of droplet formation (see comprehensive discussion and reviews in [77,89,90]), specifically the airway reopening hypothesis of small peripheral airways that normally close following a deep expiration, which was further tested by computerized modeling [90] that simulated this mechanism of particle formation by rupture of surfactant films involving surface tension. The mechanism was probed in [83] by showing that concentrations of exhaled particles significantly increase with breathing intensities higher than rest tidal volume, but also for fast exhalations but not fast inhalation, while droplet numbers increased up to two orders of magnitude: from ∼ 230/Lt in tidal volume (0.7 Lt) to over 1200/Lt in a breathing maneuver from fractional residual capacity to total lung capacity [85]. ...
With the proliferation of tobacco and nicotine products, there might be a need for more complex models than current two-product models. We have developed a three-product model able to represent interactions between 3 products in the marketplace. We also investigate if using several implementations of two-product models could provide sufficient information to assess 3 coexisting products. Italy is used as case-study with THPs and e-cigarettes as the products under investigation. We use transitions rates estimated for THPs in Japan and e-cigarettes in the USA to project what could happen if the Italian population were to behave as the Japanese for THP or USA for e-cigarettes. Results suggest that three-product models may be hindered by data availability while two product models could miss potential synergies between products. Both, THP and E-Cigarette scenarios, led to reduction in life-years lost although the Japanese THP scenario reductions were 3 times larger than the USA e-cigarette projections.
... In practically all the listed studies subjects breathed through MP's (mouthpieces) and NC's (noseclips), which as discussed in section 4.2, involves occlusion of nasal air flow that implies a slightly modified mechanics and about 20 % larger tidal volume with respect to normal unencumbered breathing. While some of the studies in Table 3 were motivated by investigating droplet emission in the context of airborne pathogen contagion [89,90,91,92], the motivation of others [93,94,95,96,97,98] is to probe various mechanisms of droplet formation (see comprehensive discussion and reviews in [87,99,100]), specifically the airway reopening hypothesis of small peripheral airways that normally close following a deep expiration, which was further tested by computerized modeling [100] that simulated this mechanism of particle formation by rupture of surfactant films involving surface tension. The mechanism was probed in [93] by showing that concentrations of exhaled particles significantly increase with breathing intensities higher than rest tidal volume, but also for fast exhalations but not fast inhalation, while droplet numbers increased up to two orders of magnitude: from ∼ 230/Lt in tidal volume (0.7 Lt) to over 1200/Lt in a breathing maneuver from fractional residual capacity to total lung capacity [95]. ...
... In practically all the listed studies subjects breathed through MP's (mouthpieces) and NC's (noseclips), which as discussed in section 4.2, involves occlusion of nasal air flow that implies a slightly modified mechanics and about 20 % larger tidal volume with respect to normal unencumbered breathing. While some of the studies in Table 3 were motivated by investigating droplet emission in the context of airborne pathogen contagion [89,90,91,92], the motivation of others [93,94,95,96,97,98] is to probe various mechanisms of droplet formation (see comprehensive discussion and reviews in [87,99,100]), specifically the airway reopening hypothesis of small peripheral airways that normally close following a deep expiration, which was further tested by computerized modeling [100] that simulated this mechanism of particle formation by rupture of surfactant films involving surface tension. The mechanism was probed in [93] by showing that concentrations of exhaled particles significantly increase with breathing intensities higher than rest tidal volume, but also for fast exhalations but not fast inhalation, while droplet numbers increased up to two orders of magnitude: from ∼ 230/Lt in tidal volume (0.7 Lt) to over 1200/Lt in a breathing maneuver from fractional residual capacity to total lung capacity [95]. ...
We examine the plausibility, scope and risks of aerial transmission of pathogens (including the SARS-CoV-2 virus) through respiratory droplets carried by exhaled e–cigarette aerosol (ECA). Observational and laboratory data suggests considering cigarette smoking and mouth breathing through a mouthpiece as convenient proxies to infer the respiratory mechanics and droplets sizes and their rate of emission that should result from vaping. To infer distances for possible direct contagion we model exhaled ECA flow as an intermittent turbulent jet evolving into an unstable puff, estimating for low intensity vaping (practiced by 80-90% of vapers) ECA expirations the emission of 2-230 respiratory submicron droplets per puff a horizontal distance spread of 1-2 meters, with intense vaping possibly carrying hundreds and up to 1000 droplets per puff in the submicron range a distance spread over 2 meters. Bystanders exposed to low intensity expirations from an infectious vaper in indoor spaces (home and restaurant scenarios) face a 1% increase of risk of indirect contagion with respect to a “control case” scenario defined by exclusively rest breathing without vaping. This relative added risk becomes 5 – 17% for high intensity vaping, 40 – 90% and over 260% for speaking or coughing (without vaping). This risk evaluation remains practically unchanged in shared spaces with universal usage of face masks. We estimate that disinfectant properties of glycols in ECA are unlikely to act efficiently on pathogens carried by vaping expirations under realistic conditions.
... For instance, Morawska et al. [59] reported that most airborne particles generated during breathing and speaking were between 0.1 and 1 μm. Asadi et al. [60], Pan et al. [61], Wurie et al. [62], and Haslbeck et al. [63] found that the most airborne particles during normal breathing were less than 1 μm. ...
This study evaluates the efficacy of portable air cleaners (PACs) in a controlled climate chamber that simulates an office environment, assessing their impact on respiratory particle transmission between two thermal manikins (representing an infected and an exposed individual) as well as on the noise level in the chamber. The study explores three types of PAC, namely floor-type (PAC1), table (PAC2) and personalized (PAC3) in various locations and operation modes. The particles were generated using an aerosol generator and introduced into the infected manikin's exhalation; the particle concentration at the exposed manikin's breathing zone (BZ) was measured using an aerodynamic particle sizer. The results showed that the PAC2, operating at a flow rate of 97 m³/h, significantly reduced the intake fraction (IF) by over 90 % within the first hour, proving to be the most effective in minimizing cross-exposure risks while maintaining sound levels within the acceptable limits for office rooms. In contrast, PAC3, with a lower flow rate of 13 m³/h, reduced IF by only 21.6 % after 60 min. The result also showed that settings with higher flow rates (higher than 134 m3/h) resulted in noise levels above the maximum allowable for office spaces for all tested PACs. Additionally, prolonged operation did not further decrease IF significantly after reaching optimal reduction levels within 30–60 min, depending on the PAC type and settings. Further, the study showed that strategic placement away from direct alignment with occupants' BZ is recommended to optimize aerosol removal and noise management.
... [2][3][4][5][6][7][8][9][10] It is generally established that violent respiratory events (sneeze, cough, etc.) are mainly responsible for bioaerosol transmission. 3,4 However, recent studies have shown that even normal activities (breathing, talking, etc.) also generate substantial amount of bioaerosols 11,12 and probably account for more exhaled bioaerosols over a longer time period than intermittent coughs or sneezes. 2,5 In contrast, limited research has been carried out into the mechanisms by which such bioaerosols are formed within the respiratory system. ...
Bioaerosols produced within the respiratory system play an important role in respiratory disease transmission. These include infectious diseases such as common cold, influenza, tuberculosis, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among several others. It is, therefore, of immense interest to understand how bioaerosols are produced within the respiratory system. This has not been extensively investigated. The present study computationally investigates how bioaerosols are produced in a model respiratory tract due to hydrodynamic interactions between breathed air and a thin mucus layer, which lines the inner surface of the tract. It is observed that Kelvin–Helmholtz instability is established in the thin mucus layer due to associated fluid dynamics. This induces interfacial surface waves which fragment forming bioaerosols under certain conditions. A regime map is created—based on pertinent dimensionless parameters—to enable identification of such conditions. Analysis indicates that bioaerosols may be produced even under normal breathing conditions, contrary to expectations, depending on mucus rheology and thickness of the mucus layer. This is possible during medical conditions as well as during some treatment protocols. However, such bioaerosols are observed to be larger ( ∼ O ( 100 ) μm) and are produced in less numbers ( ∼ 100), as compared to those produced under coughing conditions. Treatment protocols and therapeutic strategies may be suitably devised based on these findings.
... These particles had an aerodynamic diameter of up to 100 μm, with typical sizes ranging from 10 nm for small virus particles to 100 μm for large pollen particles. Fungi typically range from 1 to 30 μm, bacteria from 0.25 to 8 μm, and viruses are typically smaller than 0.3 μm (Asadi et al., 2019;Edwards et al., 2004;Karsten et al., 2010;Scheuch, 2020;Schwarz et al., 2010;Schwarz et al., 2015). Even slight contact between bioaerosols and human tissue can affect human health (Kim et al., 2018). ...
... However, the virus is not emitted individually. It is embedded in saliva droplets covering several orders of magnitude in size, ranging from 200 nm to several hundred microns, depending on the emission mechanism [4][5][6][7][8][9][10]. Big droplets (>10 µm) sediment quickly. ...
Estimating the infection risks of indoor environments comprises the assessment of the behavior of virus-laden aerosols, i.e., their spreading, mixing, removal by air purifiers, etc. A promising experimental approach is based on using non-hazardous surrogate aerosols of a similar size, e.g., salt particles, to mimic virus aerosol behavior. This manuscript addresses the issue of how a successful transfer of such experiments can be accomplished. Corresponding experiments in two very different environments, a large community hall and a seminar room, with the optional use of air purifiers in various constellations, are conducted. While high particle concentrations are advantageous in terms of avoiding the influence of background aerosol concentrations, it is shown that the appropriate consideration of aggregation and settling are vital to theoretically describe the experimentally determined course of particle concentrations. A corresponding model equation for a well-mixed situation is derived, and the required parameters are thoroughly determined in separate experiments independently. It is demonstrated that the clean air delivery rates (CADRs) of air purifiers determined with this approach may differ substantially from common approaches which do not explicitly take aggregation into account.
... However, the virus is not emitted individually. It is embedded in saliva droplets covering several orders of magnitude in size ranging from 200 nm to several hundred microns depending on the emission mechanism [4][5][6][7][8][9][10]. Big droplets (> 10 µm) sediment fast. ...
Estimating the infection risks in indoor environments comprises the assessment of the behavior of virus-laden aerosols, i.e. spreading, mixing, removal by air purifiers etc. A promising experimental approach is based on using non-hazardous surrogate aerosols of similar size, e.g. salt particles, to mimic the virus aerosol behavior. This manuscript addresses the issue how a successful transfer of such experiments can be accomplished. Corresponding experiments in two very different environments, a large community hall and a seminar room, with optional use of air purifiers in various constellations were conducted. While high particle concentrations are advantageous in terms of avoiding influence of background aerosol concentrations, it is shown that appropriate consideration of aggregation and settling are vital to theoretically describe the experimentally determined course of particle concentrations. A corresponding model equation for a well-mixed situation is derived and the required parameters are thoroughly determined in separate experiments independently. It is demonstrated that clean air delivery rates (CADR) of air purifiers determined with this approach may differ substantially from common approaches not explicitly taking into account aggregation.
... One reason may be that the droplets produced in the nasopharynx are relatively larger [19]. Another possibility may be that most of the detected droplets originated from the lower respiratory tract where the viral load is not strongly correlated with the nasopharyngeal viral load [26]. In individuals who were nasally inoculated with influenza A, a low proportion of the subjects had detectable viral RNA in the fine aerosol fractions [27]. ...
Influenza is a highly contagious respiratory illness that commonly causes outbreaks among human communities. Details about the exact nature of the droplets produced by human respiratory activities such as breathing, and their potential to carry and transmit influenza A and B viruses is still not fully understood. The objective of our study was to characterize and quantify influenza viral shedding in exhaled aerosols from natural patient breath, and to determine their viral infectivity among participants in a university cohort in tropical Singapore. Using the Gesundheit-II exhaled breath sampling apparatus, samples of exhaled breath of two aerosol size fractions (“coarse” > 5 µm and “fine” ≤ 5 µm) were collected and analyzed from 31 study participants, i.e., 24 with influenza A (including H1N1 and H3N2 subtypes) and 7 with influenza B (including Victoria and Yamagata lineages). Influenza viral copy number was quantified using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Infectivity of influenza virus in the fine particle fraction was determined by culturing in Madin–Darby canine kidney cells. Exhaled influenza virus RNA generation rates ranged from 9 to 1.67 × 105 and 10 to 1.24 × 104 influenza virus RNA copies per minute for the fine and coarse aerosol fractions, respectively. Compared to the coarse aerosol fractions, influenza A and B viruses were detected more frequently in the fine aerosol fractions that harbored 12-fold higher viral loads. Culturable virus was recovered from the fine aerosol fractions from 9 of the 31 subjects (29%). These findings constitute additional evidence to reiterate the important role of fine aerosols in influenza transmission and provide a baseline range of influenza virus RNA generation rates.
... Computational fluid dynamics (CFD) has significantly contributed to exhaled breath research. For instance, CFD has been used to design breath devices for lung cancer diagnosis [26], to optimize chamber geometries in devices for detecting chronic kidney disease via chemical sensors [27], and to study the generation of submicrometer particles in exhaled breath [28]. However, CFD methods alone do not solve actual individual dispersion or trajectories of particles. ...
Human studies provide valuable information on components or analytes recovered from exhaled breath, but there are limitations due to inter-individual and intra-individual variation. Future development and implementation of breath tests based on aerosol analysis require a clear understanding of how human factors interact with device geometry to influence particle transport and deposition. The computational fluid and particle dynamics (CFPD) algorithm combines (i) the Eulerian approach to fluid dynamics and (ii) the Lagrangian approach to single particle transport and deposition to predict how particles are carried in fluids and deposited on surfaces. In this work, we developed a 3D multiscale CFPD model to provide insight into human factors that could be important to control or measure during sampling. We designed the model to characterize the local transport, spatial distribution, and deposition of polydisperse particles in a single impaction filter of a commercial aerosol collection device. We high-light the use of decoupling numerical strategies to simultaneously quantify the influence of filter geometry, fluid flowrate, and particle size. Our numerical models showed the remarkable effect of flowrate on aerosol dynamics. Specifically, aerosol mass deposition, spatial distribution, and deposition mechanisms inside the filter. This work as well as future studies on the effect of filter geometry and human factors on aerosol collection will guide the development, standardization, and validation of breath sampling protocols for current and emerging breath tests for forensic and clinical applications.
... While the aerosol formation process in the alveolar region (bronchiolar mode: liquid films rupture during inhalation and produce aerosol, which is subsequently transported into the alveoli and leaves the body during the following exhalation process) has been intensively investigated [10][11][12] and is now widely understood and accepted, 8,9,13 the exact generation mechanisms of larger aerosol particles and droplets in the upper airway region still remain unclear and are rather the subject of assumptions. 9,13,14 Studies on aerosol formation in the upper airways do, to the best of the author's knowledge, not exist. ...
Aerosol droplets made from respiratory liquid are of fundamental importance for airborne transmission of several virus-based diseases, such as COVID-19. While the transmission route in the air has been intensively studied in the last two years, only few papers deal with the formation of these droplets. It seems to be accepted that such droplets are generated by upper airway activity such as talking, sneezing or coughing. Especially talking is associated with disease transmission, although the droplet formation mechanisms have not been fully resolved, yet. Thus, we focus on the investigation of the atomization process of respiratory liquid attached to the vocal folds. A new experimental setup has been installed that emulates the vocal folds and their oscillating movement in a simplified manner. A model liquid mimicking the respiratory mucus is dispersed at the vocal folds. The primary atomization of the model liquid into an air stream is observed qualitatively. This new insight shows that, in contrast to the typical assumption that only liquid bridges form between the vocal folds and break up into droplets, rather bubbles are generated, which can break up into much smaller particles than filaments. Further, droplet size distributions downstream of the vocal folds are evaluated. The influence of the oscillation frequency and amplitude as well as air flow rate on the droplet size distributions are analyzed. It is found that an increase in both frequency and amplitude leads to smaller particle sizes, while raising the air flow rate results in a higher proportion of larger particles.
... This makes understanding the deformation and flow of fluid/fluid interfaces under the application of mechanical stresses, i.e., the rheological properties of the interface, a matter of key importance for science and technology [9,10]. For instance, the understanding and control of the rheological response of fluid/fluid interfaces plays a very important role in the control of emulsion stability [11,12], foamability and foam stability (resistance against drainage) [13], lung surfactant performance [4,14], aerosol formation [15], tear film stability [16,17], encapsulation process [18], coffee ring formation [19], tertiary oil recovery [20], or remote sensing [21,22]. ...
Fluid/fluid interfaces are ubiquitous in science and technology, and hence, the understanding of their properties presents a paramount importance for developing a broad range of soft interface dominated materials, but also for the elucidation of different problems with biological and medical relevance. However, the highly dynamic character of fluid/fluid interfaces makes shedding light on fundamental features guiding the performance of the interfaces very complicated. Therefore, the study of fluid/fluid interfaces cannot be limited to an equilibrium perspective, as there exists an undeniable necessity to face the study of the deformation and flow of these systems under the application of mechanical stresses, i.e., their interfacial rheology. This is a multidisciplinary challenge that has been evolving fast in recent years, and there is currently available a broad range of experimental and theoretical methodologies providing accurate information of the response of fluid/fluid interfaces under the application of mechanical stresses, mainly dilational and shear. This review focused on providing an updated perspective on the study of the response of fluid/fluid interfaces to dilational stresses; to open up new avenues that enable the exploitation of interfacial dilational rheology and to shed light on different problems in the interest of science and technology.
... Particles produced when speaking or singing are smaller, with diameters from around 1 μm to 2 μm [6]. Moreover, during normal breathing, small concentrations of particles in the size range from ≤0.2 µm to 0.4 μm are constantly produced [7][8][9]. During respiratory infections, the emission rates can significantly increase [10]. ...
Indoor air cleaners can contribute to reducing infection risks by the filtration of virus-carrying droplets. There are various national standards to test indoor air cleaners that determine the clean air delivery rate (CADR), but typically only as a size-integrated value for particles >0.3 μm. Thus, a test method using potassium chloride (KCl) and paraffin as surrogate particles in the size range of viruses and exhaled droplets was developed. We show that air cleaners with fibrous and electrostatic filters are generally capable of reducing the airborne particle concentrations. However, for electret filters, the performance can strongly degrade over time by being loaded with particles. By comparing filters with different efficiencies in the same air cleaner, we demonstrate that the use of high-efficiency filters can be even at the expense of the cleaning efficacy. We developed a mathematical model to estimate the inhaled dose of viruses and show that the combination of natural venting and an air cleaner can lead to a substantial reduction of the infection risk.
... However, aerosol emitted during normal breathing and speaking are much smaller, with a modal value around 1 micrometer. [34][35][36] Consequently, filtration efficiency of micron and sub-micron aerosols must be considered, since those are large enough to carry respiratory pathogens such as SARS-CoV-2 (single virus diameter Ø 0.06-0.14 µm). ...
The COVID-19 pandemic resulted in shortages of personal protective equipment and medical devices in the initial phase. Agile small and medium-sized enterprises from regional textile industries reacted quickly. They delivered alternative products such as textile-based community masks in collaboration with industrial partners and research institutes from various sectors. The current mask materials and designs were further improved by integrating textiles with antiviral and antimicrobial properties and enhanced protection and comfort by novel textile/membrane combinations, key factors to increase the acceptance and compliance of mask wearing. The innocuity and sustainability of masks, as well as taking into account particular needs of vulnerable persons in our society, are new fields for textile-based innovations. These innovations developed for the next generation of facemasks have a high adaptability to other product segments, which make textiles an attractive material for hygienic applications and beyond.
... While airborne transmission was still critically discussed in the early phase of the pandemic [2] (and before concerning SARS [3]), it is now considered certain that, in contrast to transmission via contaminated surfaces [4], airborne transmission is the primary transmission mechanism of SARS-CoV-2 [5][6][7][8][9][10][11][12][13]. At the same time, the avoidance of this type of transmission-compared to smear and droplet infection-is difficult to realise in terms of the necessary restrictions on public life. ...
In order to continue using highly frequented rooms such as classrooms, seminar rooms, offices, etc., any SARS-CoV-2 virus concentration that may be present must be kept low or reduced through suitable ventilation measures. In this work, computational fluid dynamics (CFD) is used to develop a virtual simulation model for calculating and analysing the viral load due to airborne transmission in indoor environments aiming to provide a temporally and spatially-resolved risk assessment with explicit relation to the infectivity of SARS-CoV-2. In this work, the first results of the model and method are presented. In particular, the work focuses on a critical area of the education infrastructure that has suffered severely from the pandemic: classrooms. In two representative classroom scenarios (teaching and examination), the duration of stay for low risk of infection is investigated at different positions in the rooms for the case that one infectious person is present. The results qualitatively agree well with a documented outbreak in an elementary school but also show, in comparisons with other published data, how sensitive the assessment of the infection risk is to the amount of virus emitted on the individual amount of virus required for infection, as well as on the supply air volume. In this regard, the developed simulation model can be used as a useful virtual assessment for a detailed seat-related overview of the risk of infection, which is a significant advantage over established analytical models.
... This suggested that, despite differences in sampling algorithms, the risk of undersampling any maneuver was low. In addition, we saw significant variation between participants, spanning two orders of magnitude, consistent with previous observations (24). ...
Rationale:
Interrupting tuberculosis (TB) transmission requires an improved understanding of how - and when - the causative organism, Mycobacterium tuberculosis (Mtb), is aerosolized. Although cough is commonly assumed to be the dominant source of Mtb aerosols, recent evidence of cough-independent Mtb release implies the contribution of alternative mechanisms.
Objective:
To compare the aerosolization of Mtb bacilli and total particulate matter from TB patients during three separate respiratory manoeuvres: Tidal Breathing (TiBr), Forced Vital Capacity (FVC), and cough.
Methodology:
Bioaerosol sampling and Mtb enumeration by live-cell, fluorescence microscopy were combined with real-time measurement of CO2 concentration and total particle counts from 38 GeneXpert-positive TB patients prior to treatment initiation.
Measurements and main results:
For all manoeuvres, the proportions of particles detected across five size categories were similar with most particles falling between 0.5-5 μm. Although total particle counts were 4.8-fold greater in cough samples than either TiBr or FVC, all three manoeuvres returned similar rates of positivity for Mtb. No correlation was observed between total particle production and Mtb count. Instead, for total Mtb counts, the variability between individuals was greater than the variability between sampling manoeuvres. Finally, when modelled utilizing 24-hour breath and cough frequencies, our data indicate that TiBr might contribute >90% of the daily aerosolised Mtb among symptomatic TB patients.
Conclusions:
Assuming the number of viable Mtb organisms released offers a reliable proxy of patient infectiousness, our observations imply that TiBr and inter-individual variability in Mtb release might be significant contributors to TB transmission among active cases. This article is open access and distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/).
... Aerosol droplets from the respiratory system can be generated by several mechanisms: (i) from thin film ruptures in the small airways during breathing, primarily generating aerosol particles in the size range 0.2-1.0 µm [18,19], (ii) from the vibrations of the vocal chords during vocalization, primarily generating aerosol particles in the size range 1-5 µm [8,9], and (iii) from mouth and lips movements during articulation, primarily generating aerosol droplets in the size range >30 µm [18,20]. In addition, high-velocity airflows in the upper respiratory tubes has been suggested to induce surface instabilities leading to droplet budding from the lining fluid [21]. ...
Background: Covid-19 transmission via exhaled aerosol particles has been considered an important route for the spread of infection, especially during super-spreading events involving loud talking or singing. However, no study has previously linked measurements of viral aerosol emissions to transmission rates.
Methods: During Feb-Mar 2021, covid-19 cases that were close to symptom onset were visited with a mobile laboratory for collection of exhaled aerosol particles during breathing, talking and singing, respectively, and of nasopharyngeal and saliva samples. Aerosol samples were collected using a BioSpot-VIVAS and a NIOSH bc-251 two-stage cyclone, and all samples were analyzed by RT-qPCR for SARS-CoV-2 RNA detection. We compared transmission rates between households with aerosol-positive and aerosol-negative index cases.
Results: SARS-CoV-2 RNA was detected in at least one aerosol sample from 19 of 38 (50%) included cases. The odds ratio of finding positive aerosol samples decreased with each day from symptom onset (OR 0.55, 95CI 0.30-1.0, p=0.049). The highest number of positive aerosol samples were from singing, 16 (42%), followed by talking, 11 (30%), and the least from breathing, 3 (8%). Index cases were identified for 13 households with 31 exposed contacts. Higher transmission rates were observed in households with aerosol-positive index cases, 10/16 infected (63%), compared to households with aerosol-negative index cases, 4/15 infected (27%) (Chi-square test, p=0.045).
Conclusions: Covid-19 cases were more likely to exhale SARS-CoV-2-containing aerosol particles close to symptom onset and during singing or talking as compared to breathing. This study supports that individuals with SARS-CoV-2 in exhaled aerosols are more likely to transmit covid-19.
... All particles were spherical, and the particle density was constant. According to the study by Ref. [51], the density of particle could be considered 1003 kg/m 3 . c. ...
The rapid development of airports and the rapid spread of coronavirus disease 2019 (COVID-19) have brought increased attention to indoor environment quality, airflow organization, key pollutant dispersion, and ventilation modes in airport terminals. However, the characteristics of these parameters, especially carbon dioxide (CO2) and aerosol diffusion, are not fully understood. Therefore, in this study, the airflow patterns; CO2 and aerosol dispersion; and several thermal environment indices, including temperature, wind velocity, and predicted mean vote (PMV), of an airport terminal departure hall with high numbers of occupied passenger were numerically evaluated using the realizable k-ε and passive scalar models. The efficacies of three common ventilation modes, namely, up-supply and up-return, up-supply and down-return with different sides, and up-supply and down-return with the same side, were evaluated based on the CO2 removal efficiency and spreading range of aerosols. The results indicated that under high numbers of occupied passenger conditions, these ventilation modes vary slightly, with respect to create a comfortable and healthy environment. In particular, the up-supply and down-return with different sides mode was the best among the modes considered, when comparing the indices of temperature, wind speed PMV, and CO2 emission efficiency. Conversely, with respect to decreasing the risk of aerosol exposure, the up-supply and down-return with the same side mode was the best. Overall, the results from this study provide fundamental information for predicting CO2 and aerosol exposure levels and will act as a reference for the design and operation of ventilation systems in airport terminal buildings.
... The findings indicate that the deposition and dispersion mechanisms of the expelled microdroplets by patients are incredibly dependent on the droplet size (Chao et al., 2008;. A substantial part of literature consideres the micro-droplet size distribution of expiratory and saliva in sneeze (Buckland and Tyrrell, 1964;Duguid, 1946), cough , talking and breathing (Holmgren et al., 2010;Haslbeck et al., 2010;Almstrand et al., 2010). They confirmed that in various circumstances, the size distribution of micro-droplets is entirely different. ...
During the past two decades, the Electrostatic Rotary Bell Sprayers (ERBSs), because of their superior transfer efficiency (TE) and coating performance, lower environmental destructive effects and cost decrement, attract the attention of many researchers in the coating industry. In this thesis, we developed a 3D comprehensive Eulerian-Lagrangian algorithm in order to investigate the fundamental behaviors of the flow in an electrostatic rotary bell sprayer (ERBS) during the formation of the droplets and depositing on a target. This efficient extended algorithm contains a model for airflow field, spray dynamics, electric field, droplet charge, droplet trajectory tracking and wall film dynamics. The fluid-dynamics is simulated by solving the unsteady 3D compressible Navier-Stokes equations. Unsteady flow is computed by using a Large eddy simulation (LES) turbulence approach, while the motion of the particles is simulated by tracking the droplet size distribution approach. The algorithm is implemented under the framework of the OpenFOAM package.
Creating an initial condition of the particle approach has been proposed that is matched with practical applications. The present work contains a systematic analysis of the recirculation zone length, the toroidal vortex, the overspray phenomena and the flowfield characteristics like mean velocity, pressure, turbulent kinetic energy and velocity fluctuation. Also, the presented results describe exact values for the size, distribution, velocity, and trajectory of the particles in the ERBS. These results are important for coating industries to optimize their working conditions. The effect of operational parameters like bell rotational speed, shaping air and paint flow rate, electrical charge values and droplet size distributions are considered precisely. The results indicate as a main operating parameter the air-paint flow rate with voltage level deeply affecting the spray shape. The effect of the bell rotational speed in comparison with other parameters is dominant. The paint spray distribution obtained in the present work is validated against coating experimental results with suitable accuracy.
Investigation of the various primary and secondary breakup models is one of the main goals of this work to predict the droplet size more precisely. The Reitz-KHRT, Reitz-Diwakar, Pilch-Erdman and the newly modified TAB model are examined in order to predict the secondary breakup process in the ERBS. Here, the implemented wall film function is able to predict the transport in the boundary layer over the target. This study also presents a performance evaluation of the ERBS with a particular focus on droplet charge, electric field, ambient conditions with the implementation of a high-voltage control-ring field pattern effect into the fully turbulent airflow and by including the atomized droplets discrete phase. The results indicate that the new proposal of using a control-ring operation improves the performance and transfer efficiency (TE) of the ERBS, and it also helps to harmonize the direction of the charged paint droplets.
Furthermore, a novel electrostatic spraying system by using high-voltage retractable blades or high-voltage adjustable control ring is also presented in the current study as a recent patent.
Also, some other useful applications of the implemented code are presented. First, the modified spraying part of the code is used, leading to a deeper understanding of the saliva-disease-carrier droplets transmission mechanisms as an atomized droplets during sneezing, coughing, or even exhaling. This is particularly important to ensure safety conditions in the work environment. Second, the implemend electrical field that was added to the code is considered without injecting droplets to accurately simulate the plasma flow by using a multi dielectric-barrier-discharge (DBD) plasma actuator over a 3D-airfoil difference. This shows the versatility of the developed model.
... These exhalatory "viraerosols" (Moreno and Gibbons, 2021) can be released in great numbers not only by coughing, sneezing and normal vocalisation, but also simply by passive tidal breathing (e.g. Almstrand et al., 2010;Bake et al., 2019;Haslbeck et al., 2010;Johnson and Morawska, 2009;Schwarz et al., 2010). Once released into the indoor atmosphere, the potentially infective respiratory pathogens will be carried away from the diseased individual in a buoyant turbulent cloud of gas and particles (Boubouiba, 2021;Jones and Bross, 2015;Lv et al., 2021;Randall et al., 2021). ...
Restaurants present an especial challenge in the prevention of the spread of COVID-19 via exhalatory bioaerosols because customers are unprotected by facemasks while eating, so that ventilation protocols in such establishments become especial important. However, despite the fact that this pandemic airborne disease has been with us for two full years, many restaurants are still not successfully prioritising air renovation as a key tool for reducing infection risk. We demonstrate this in the run-up to the 2021 Christmas celebrations by reporting on CO2 concentration data obtained from a hotel breakfast room and restaurants during the 5-day Spanish holiday period of 4th-8th December. In the case of the breakfast room, poor ventilation resulted in average CO2 levels ranging from 868 to 1237 on five consecutive days, with the highest levels coinciding with highest occupancy numbers. Inside the five restaurants, three of these were well ventilated, maintaining stable average CO2 concentrations below 700ppm. In contrast, two restaurants failed to keep average CO2 levels below 1000ppm, despite sporadic, but ineffective, attempts by one of them to ventilate the establishment. More effort needs to be made to foster in both restaurant managers and the general public an improved awareness of the value of CO2 concentrations as an infection risk proxy and the relevance of ventilation issues to the propagation of respiratory diseases.
... During the exhalation (when we talk, sing, cough or just breathe), we produce thousands of droplets that may become the carrier for viruses (Shadloo-Jahromi et al. 2020). Porous media have interesting medical applications as, for instance, lungs and surgical masks have a complex structure and transport droplets every day (Dbouk and Drikakis 2020;Leung et al. 2020;Haslbeck et al. 2010). A recent study shows the role of limited micro-droplet formation in children's lungs in lowering COVID-19 transmission rates among the young part of the population (Riediker and Morawska 2020). ...
I use a mechanical model of a soft body to study the dynamics of an individual fluid droplet in a random, non-wettable porous medium. The model of droplet relies on the spring-mass system with pressure. I run hundreds of independent simulations. I average droplets trajectories and calculate the averaged tortuosity of the porous domain. Results show that porous media tortuosity increases with decreasing porosity, similar to single-phase fluid study, but the form of this relationship is different.
Supplementary information:
The online version contains supplementary material available at 10.1007/s11242-021-01705-z.
... Human breathing is accompanied by the formation of small droplets of ALF, which are emitted from the lungs with exhaled air in aerosol form. The droplet formation mechanism is associated with closure and reopening of the airways during breathing [9,10,11]. The exhaled air of a healthy human during normal breathing contains, on average, a few submicron particles per cubic centimeter [12][13][14]. ...
The development of efficient methods for non-invasive collection of alveolar lining fluid (ALF) samples containing pulmonary surfactant (PS) components and the study of the surface activity of the obtained native material is relevant for the diagnosis of inflammatory pneumopathies of the lungs. The paper presents an electrostatic aerosol trapping (ESAT) mobile complex for capturing droplets of ALF contained in an exhaled air. Passing the exhaled air through the corona discharge area results in the aerosol droplets charging and their further transferring by electrostatic force into a water surface, where they accumulate forming an adsorbed layer. Additionally, ALF samples were collected using a bronchoalveolar lavage (BAL). The surface properties of the PS obtained by both methods have been examined using the capillary wave method, which was previously modified by the authors specifically for biomedical applications. Significant difference was found in the results obtained with ESAT and BAL in the group of healthy subjects, which can be explained by different origin of the samples obtained by these techniques. Furthermore, significant difference in surface properties was established in the samples collected from healthy volunteers and patient with disseminated tuberculosis, while we did not find significant differences in the limited inflammatory process. The results presented in the paper demonstrate high potential of the proposed non-invasive technique for clinical usage.
... Another possible mechanism underlying the increased number PEx in smokers might be the effects of smoking on the physical properties of surfactant per se. In computational studies on liquid film burst, an increased surface tension resulted in higher concentrations of droplets [38,39]. Thus, if tobacco smoke increases the surface tension in surfactant, the number PEx might increase in smokers. ...
Small airways are difficult to access. Exhaled droplets, also referred to as particles, provide a sample of small airway lining fluid and may reflect inflammatory responses. We aimed to explore the effect of smoking on the composition and number of exhaled particles in a smoker-enriched study population. We collected and chemically analyzed exhaled particles from 102 subjects (29 never smokers, 36 former smokers and 37 current smokers) aged 39 to 83 years (median 63). A breathing maneuver maximized the number exhaled particles, which were quantified with a particle counter. The contents of surfactant protein A and albumin in exhaled particles was quantified with immunoassays and the contents of the phospholipids dipalmitoyl- and palmitoyl-oleoyl- phosphatidylcholine with mass spectrometry. Subjects also performed spirometry and nitrogen single breath washout. Associations between smoking status and the distribution of contents in exhaled particles and particle number concentration were tested with quantile regression, after adjusting for potential confounders. Current smokers, compared to never smokers, had higher number exhaled particles and more surfactant protein A in the particles. The magnitude of the effects of current smoking varied along the distribution of each PEx-variable. Among subjects with normal lung function, phospholipid levels were elevated in current smokers, in comparison to no effect of smoking on these lipids at abnormal lung function. Smoking increased exhaled number of particles and the contents of lipids and surfactant protein A in the particles. These findings might reflect early inflammatory responses to smoking in small airway lining fluid, also when lung function is within normal limits.
... Ambient weather conditions, such as temperature and humidity, play a multi-faceted role affecting virus transmission. The major form of transmission of SARS-CoV-2 is through droplets and aerosols containing the virus, released during exhalation, talking, singing, or coughing [3,4]. While larger and denser particles sink to the ground, microdroplets are small enough to remain suspended in the air for a long time (hours to days in still air), depending on their size [5]. ...
Weather conditions may have an impact on SARS-CoV-2 virus transmission, as has been shown for seasonal influenza. Virus transmission most likely favors low temperature and low humidity conditions. This systematic review aimed to collect evidence on the impact of temperature and humidity on COVID-19 mortality. This review was registered with PROSPERO (registration no. CRD42020196055). We searched the Pubmed, Embase, and Cochrane COVID-19 databases for observational epidemiological studies. Two independent reviewers screened the title/abstracts and full texts of the studies. Two reviewers also performed data extraction and quality assessment. From 5051 identified studies, 11 were included in the review. Although the results were inconsistent, most studies imply that a decrease in temperature and humidity contributes to an increase in mortality. To establish the association with greater certainty, future studies should consider accurate exposure measurements and important covariates, such as government lockdowns and population density, sufficient lag times, and non-linear associations.
... Lack of knowledge is evident in social distance guides and facial masks [Duguid, 1946], based mainly on literature research [Zhu et al., 2006;Holmgren et al., 2010]. Haslbeck et al. [2010] analyzed the effect of wind speed on the social distance to cough. They found that saliva droplets move at wind speeds of 15 kilometers per hour at 6 meters, and a social distance of 2 meters is not suitable for outdoor environments. ...
COVID-19 is a serious respiratory disease caused by a devastating coronavirus family (2019-nCoV) that has become a global epidemic. It is an infectious virus transmitted by inhalation or contact with the droplet core produced by infected people when they sneeze, cough, and speak. SARS-COV-2 transmission in the air is possible even in a confined space near the infected person. This study examines air conditioners’ effect on the mixed virus and droplets with aerosol disinfectant and gets throughout the elevator to detect the SARS-COV-2, which helps protect passengers’ lives. This study uses fluent 2019R3 software to simulate the virus transmission to model the transient flows numerically. The analysis found that the ventilation system’s turbulent fields can be an effective method of protecting the space from being saturated by the coronavirus.
... 100 The considered respiratory activities include coughing, 20,96,97,[101][102][103][104][105] sneezing, 95,102,103,106 speaking, 20,107-110 and breathing. 18,20,21,97,101,[111][112][113][114] In Table I, we summarize the published data on the size ranges of droplets in droplet swarms in terms of the measuring methods used, the respiratory activities concerned, and the number and health status of the subjects. Table I, the droplet sizes in exhaled droplet swarms span several length scales and can be as large as 2000 lm 102 and as small as 0.01 lm. ...
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.
... Dies entspricht dem Grenzfall τ → ∞ d. h. 1/τ → 0. Als Lösung der Differentialgleichung ergibt sich (5) Die Konzentration an virenbeladenen Tröpfchen steigt also ausgehend von der Startkonzentration C 0 linear mit der Zeit an. Die Steigung ist dabei proportional zur Stärke der Quelle Ṡ 0 und antiproportional zum Raumvolumen V. Für eine weitere Person im Raum, die die virenbeladenen Tröpfchen einatmet und sich somit potenziell infizieren kann, ist insbesondere die eingeatmete Dosis relevant. ...
Luftreiniger werden derzeit häufig als mögliches Hilfsmittel zur Minimierung des Infektionsrisikos im Rahmen der COVID-19-Pandemie diskutiert. Dabei taucht oft die Frage auf, ob Luftreiniger grundsätzlich in der Lage sind, Viren oder virenbeladene Tröpfchen abzuscheiden. Ziel dieses Artikels ist es, die wesentlichen Grundlagen der Wirkungsweise von Luftreinigern und Filtern zu beschreiben, Methoden zur Messung der Reinigungswirkung im Größenbereich von Viren und virenbeladenen Tröpfchen aufzuzeigen sowie typische Szenarien zum Betrieb von Luftreinigern in einem mathematischen Modell zu erfassen. Darauf basierend können die Möglichkeiten und Grenzen von Luftreinigern für reale Anwendungsfälle besser eingeschätzt werden.
... Better understanding of these phenomena under dynamic conditions, crucial for improved treatments, would benefit from a computational modeling approach. The same holds true for better understanding of aerosol formation in breathing or sneezing, where the surfactant film in the lungs plays an important role in the production of submicron droplets [43]. Computational interfacial rheology could aid in predicting the size distribution of these droplets and help in designing mitigation strategies. ...
Fluid-fluid interfaces, laden with polymers, particles or other surface-active moieties, often show a rheologically complex response to deformations, in particular when strong lateral interactions are present between these moieties. The response of the interface can then no longer be described by an isotropic surface tension alone. These “structured” soft-matter interfaces are found in many industrial applications, ranging from foods, cosmetics and pharmaceuticals, to oil recovery. Also many biomedical applications involve such interfaces, including those involving lung surfactants and biofilms. In order to understand, design and optimize processes in which structured interfaces are present, flow predictions of how such multiphase systems deform are of the utmost importance, which is the goal of “computational interfacial rheology”, the main topic of this review. We start by rigorously establishing the stress boundary condition used in the computation of multi-phase flows, and show how this changes when the interface is rheologically complex. Then, constitutive models for the extra stress in interfaces, ranging from 2D generalized Newtonian to hyperelastic and viscoelastic, are reviewed extensively, including common pitfalls when applying these models. This is followed by an overview of different approaches to measure interfacial rheological properties, and a discussion of advanced numerical implementations for deforming interfaces. We conclude with an outlook for this relatively young and exciting field.
... Во время выдоха эластичные стенки бронхиол сокращаются, и слизистая жидкость в просвете образует сплошную пленку, которая может полностью заполнять дыхательные пути. Во время последующего вдоха бронхиолы расширяются, и пленка разрывается, образуя частицы, которые перемещаются в альвеолы и затем выдыхаются [9,10]. Подобный механизм, как полагают, происходит и в гортани во время речи, поскольку голосовые связки многократно смыкаются и открываются при вокализации [11]. ...
For decades, there have been a number of controversial issues regarding the airborne transmission of hospital pathogens. Here we decided to perform a critical review on this topic in light of the current COVID-19 pandemic. We summarise the existing knowledge on biological aerosols including techniques of their generation, propagation of bioaerosol particles in a hospital environment, particle size-, shape- and composition-dependent airborne transmission, and microorganisms inhabitating such particles. It is still unclear which of the particles transfer the pathogens, which of the pathogens are capable of adhering to the particulate matter, and whether such adhesion affects pathogen virulence. Intriguingly, viruses, bacteria and fungi seemingly have distinct patterns of interactions with the bioaerosols. Moreover, particle formation and their colonization may be separated in time, further complicating the puzzle. Apparently, pathogen interactions with the particulate matter are of paramount importance to better understand the role of bioaerosol particles as a potential pathogen reservoir in the hospital environment and to properly assess the influence of environmental pollutants, novel biomedical materials and treatment technologies on airborne transmission of hospital pathogens.
Knowing the physicochemical properties of exhaled droplets and aerosol particles is a prerequisite for a detailed mechanistic understanding and effective prevention of the airborne transmission of infectious human diseases. This review provides a critical consideration and synthesis of scientific knowledge on the number concentrations, size distributions, composition, mixing state, and related properties of respiratory particles emitted upon breathing, speaking, singing, coughing, and sneezing. A parametrization of respiratory particle size distributions is derived and presented based on five log-normal modes related to different origins in the respiratory tract, which can be used to trace and localize the sources of infectious particles. This approach may support the medical treatment as well as the risk assessment for aerosol and droplet transmission of infectious diseases. It was applied to analyze which respiratory activities may drive the spread of specific pathogens, such as Mycobacterium tuberculosis, influenza viruses, and severe acute respiratory syndrome coronaviruses 2 (SARS-CoV-2). The results confirm the high relevance of vocalization for the transmission of SARS-CoV-2, as well as the usefulness of physical distancing, face masks, room ventilation, and air filtration as preventative measures against coronavirus disease 2019 and other airborne infectious diseases.
Water contains enormous amounts of energy yet to be fully utilized. Although humans have been able to extract energy from liquid water, gaseous moisture is often regarded as an underutilized...
Understanding infection transmission between individuals, as well as evaluating the efficacy of protective measures, are key issues in pandemics driven by human respiratory particles. The key is a quantitative understanding of the size and concentration of particles exhaled and their variability across the size range for a representative population of all ages, genders, and different activities. Here we present data from 132 healthy volunteers aged 5 to 80 years, measured over the entire particle size range for each individual. Conventional particle spectrometry was combined with in-line holography under well-controlled conditions for common activities such as breathing, speaking, singing,and shouting. We find age to be the most important parameter for the concentration of small exhale particles <5 µm (PM5), which doubles over a 7-year period in adolescents and over a 30-year period in adults. Gender, body mass index, smoking or exercise habits have no discernible effect. We provide evidence that particles with a diameter of <5 µm originate from the lower respiratory tract, 5–15 µm from the larynx/pharynx, and >15 µm from the oral cavity. PM5 concentration can vary by one order of magnitude within a person, while inter-person variability can span two orders of magnitude, largely explained by difference in age. We found no discernible inter-person variability for particles larger than 5 µm. Our results show that cumulative volume of PM5 is 2–8 times higher in adults than in children. In contrast, number and volume concentration of larger particles, which are produced predominantly in the upper respiratory tract, is largely independent of age. Finally, we examined different types of airborne-transmissible respiratory diseases and provided insights into possible modes of infection transmission with and without several types/fits of face masks.
Aerosols, generated and expelled during common human physiological activities or medical procedures, become a vital carrier for the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). During non-contact intraocular pressure measurements, aerosols can be produced from the tear film on eyes and potentially convey the SARS-CoV-2 in tears, creating a high risk for eye care practitioners and patients. Herein we numerically investigate deformation and fragmentation of the tear films with various thicknesses and surface tensions that are impinged by an air jet. Evolution of the tear films manifests several types of breakup mechanisms, including both the bag breakup and ligament breakup of tear film on the eyeball, the ligament breakup of tear film on the eyelid margin, and the sheet breakup near the eyelid margin. The sheet near the eyelid margin is critical for generating large droplets, and can be formed only if the jet velocity is high enough and the film is sufficiently thick. A criterion based on Weber number and capillary number is proposed for the breakup of tear film into droplets, in which three regions are used to classify the film evolution. Our results indicate that eyes with excessive tears have a greater probability of generating aerosols than eyes under normal conditions. We recommend that enhanced protections should be adopted upon measurement for the patients with watery eyes, and the time interval between two adjacent measurements for the same individual should be also prolonged during the COVID-19 pandemic.
A study of the aerodynamic characteristics of aerosol expiration is important for understanding the size distribution of droplet concentration in COVID-19 disease transmission. This study measured the initial concentration and size distribution of droplets released during four breathing processes: nose breathing, mouth breathing, reading alphabets and counting numbers. Influencing factors on droplet generation were studied by statistical analyses. Significant differences in droplet concentration among the four breathing activities in pairs were found ( p < 0.001), except for reading alphabets and numbers ( p = 1). The droplet concentration during nose breathing ( p < 0.05), but not mouth breathing ( p = 0.136), of male subjects, was found significantly higher than that of female subjects. The droplet concentration generated by speaking during letters reading with special phonemes, for example, /i:/, was significantly ( p < 0.05) higher than reading letters without phonemes. The discharged droplet sizes from four breathing activities were dominated by small droplets ( d p < 1.037 μm of over 50% and d p < 2.642 μm of over 80%). Basically, no particles larger than 8 μm were detected by the aerodynamic particle sizer. The inference indicates a possible aerosol transmission of disease during non-symptomatic aerosol-producing activities such as breathing or speaking and may elucidate the disease transmission pathway of COVID-19.
Computational fluid dynamics is widely used to simulate droplet-spreading behavior due to respiratory events. However, droplet generation inside the body, such as the number, mass, and particle size distribution, has not been quantitatively analyzed. The aim of this study was to identify quantitative characteristics of droplet generation during coughing. Airflow simulations were performed by coupling the discrete phase model and Eulerian wall film model to reproduce shear-induced stripping of airway mucosa. An ideal airway model with symmetric bifurcations was constructed, and the wall domain was covered by a mucous liquid film. The results of the transient airflow simulation indicated that the droplets had a wide particle size distribution of 0.1–400 µm, and smaller droplets were generated in larger numbers. In addition, the total mass and number of droplets generated increased with an increasing airflow. The total mass of the droplets also increased with an increasing mucous viscosity, and the largest number and size of droplets were obtained at a viscosity of 8 mPa·s. The simulation methods used in this study can be used to quantify the particle size distribution and maximum particle diameter under various conditions.
Not only coughing and sneezing, but even normal breathing can produce aerosols, because rupture of liquid plugs forms microdroplets during pulmonary airway reopening. Aerosols are important carriers of various viruses, such as influenza, SARS, MERS, and COVID-19. To control airborne disease transmission, it is important to understand aerosol formation, which is related to the pressure drop, liquid plug, and film. In addition, the detrimental pressure and shear stress at the airway wall produced in the process of airway reopening have also attracted a lot of attention. In this paper, we proposed a multiphase lattice Boltzmann method to numerically simulate pulmonary airway reopening, in which the gas-liquid transition is directly driven by the equation of state. After validating the numerical model, two rupture cases with and without aerosol formation were compared and analyzed. We found that injury of the epithelium in the case with aerosol formation was almost the same as that without aerosol formation, even though the pressure drop in the airway increased by about 50%. Further investigation showed that the aerosol size and maximum differences of the wall pressure and shear stress increased with pressure drop in the pulmonary airway. A similar trend was observed when the thickness of the liquid plug became larger, while an opposite trend occurred when the thickness of the liquid film increased. The model can be extended to study generation and transmission of bioaerosols carrying the influenza or coronavirus.
Capillary instability of a two-layer liquid film lining a rigid tube is studied computationally as a model for liquid plug formation and closure of human airways. The two-layer liquid consists of a serous layer, also called the periciliary liquid layer, at the inner side and a mucus layer at the outer side. Together, they form the airway surface liquid lining the airway wall and surrounding an air core. Liquid plug formation occurs due to Plateau–Rayleigh instability when the liquid film thickness exceeds a critical value. Numerical simulations are performed for the entire closure process, including the pre- and post-coalescence phases. The mechanical stresses and their gradients on the airway wall are investigated for physiologically relevant ranges of the mucus-to-serous thickness ratio, the viscosity ratio, and the air–mucus and serous–mucus surface tensions encompassing healthy and pathological conditions of a typical adult human lung. The growth rate of the two-layer model is found to be higher in comparison with a one-layer equivalent configuration. This leads to a much sooner closure in the two-layer model than that in the corresponding one-layer model. Moreover, it is found that the serous layer generally provides an effective protection to the pulmonary epithelium against high shear stress excursions and their gradients. A linear stability analysis is also performed, and the results are found to be in good qualitative agreement with the simulations. Finally, a secondary coalescence that may occur during the post-closure phase is investigated.
This paper focuses on simultaneous, time- and space-resolved measurements of particle size distributions in three different closed indoor environments (small office room, elementary-school classroom, and seminar room) applying mobile air filters in four scenarios (decay curves, filtration while people are present, a temporal strong point source, impact of filter orientation & cross-flow ventilation). The experiments reveal, that mobile indoor air filters, equipped with high-performance filter media (HEPA - quality), remove particles in the investigated rooms in relevant submicron size classes (x < 1 μm) efficiently and uniformly over time.
For the description of the local decrease in particle concentration a simple mathematical model based on a transient continuous stirred tank reactor was applied. The local decay curves obtained in the different room-types were compared to simulated ones assuming ideal mixing of the indoor air. The real-room scenarios show a slower particle decay than the predicted ones assuming ideal mixing of the indoor air. The experiments reported in this contribution demonstrate, that indoor air filters, operated with a filtration rate of 3.5 h⁻¹ and positioned correctly, are capable to lower the particle concentration in all relevant size classes in real-world closed indoor environments slowly over time (e.g. a reduction in particle concentration of 50% after 30 min in a classroom w/o particle sources). In the investigated set-ups, at filtration rates above 9 h⁻¹, the filters’ performance is close to cross-flow window-ventilation. The experiments reveal, that mobile air filters cannot avoid close distance transmission of submicron aerosols from one person to another. Therefore, they do not replace any of the well-known methods to avoid aerosol-driven infection (like wearing an efficient face mask correctly, limiting the number of people and time of stay in closed indoor environments, frequent ventilation). Mobile air filter devices may represent an additional component in an entire prevention strategy, especially when rooms cannot be ventilated regularly, efficiently or the constellation of people changes frequently (e.g. waiting areas).
Ongoing uncertainty over the relative importance of aerosol transmission of COVID-19 is in part rooted in the history of medical science and our understanding of how epidemic diseases can spread through human populations. Ancient Greek medical theory held that such illnesses are transmitted by airborne pathogenic emanations containing particulate matter (“miasmata”). Notable Roman and medieval scholars such as Varro, Ibn al-Khatib and Fracastoro developed these ideas, combining them with early germ theory and the concept of contagion. A widely held but vaguely defined belief in toxic miasmatic mists as a dominant causative agent in disease propagation was overtaken by the science of 19th century microbiology and epidemiology, especially in the study of cholera, which was proven to be mainly transmitted by contaminated water. Airborne disease transmission came to be viewed as burdened by a dubious historical reputation and difficult to demonstrate convincingly. A breakthrough came with the classic mid-20th century work of Wells, Riley and Mills who proved how expiratory aerosols (their “droplet nuclei”) could transport still-infectious tuberculosis bacteria through ventilation systems. The topic of aerosol transmission of pathogenic respiratory diseases assumed a new dimension with the mid-late 20th century “Great Acceleration” of an increasingly hypermobile human population repeatedly infected by different strains of zoonotic viruses, and has taken centre stage this century in response to outbreaks of new respiratory infections that include coronaviruses. From a geoscience perspective, the consequences of pandemic-status diseases such as COVID-19, produced by viral pathogens utilising aerosols to infect a human population currently approaching 8 billion, are far-reaching and unprecedented. The obvious and sudden impacts on for example waste plastic production, water and air quality and atmospheric chemistry are accelerating human awareness of current environmental challenges. As such, the “anthropause” lockdown enforced by COVID-19 may come to be seen as a harbinger of change great enough to be preserved in the Anthropocene stratal record.
The COVID-19 pandemic has suddenly gained urgency in Germany for implementation of new structures in healthcare sector to take care of seriously ill COVID-19 patients. The shortage of skilled healthcare workers, which has already been discussed before the pandemic situation, has become more tangible than ever. Society relies on a properly working healthcare system, especially in a pandemic like the one we now witness. After the comparatively mild course of the first COVID-19 wave in Germany, the interest in long overdue changes decreased. The second wave of the pandemic occurred in Germany as well. Also, in the meantime of the first and the second wave, numerous findings were collected and presented, where changes could have an effect. To motivate going forward, the text describes John P. Kotter's model of change management, eight steps to describe necessary changes in organizations and leadership in the German healthcare system.
When an infected person coughs, many virus-laden droplets will be exhaled out of the mouth. Droplets from deep lungs are especially infectious because the alveoli are the major sites of coronavirus replication. However, their exhalation fraction, size distribution, and exiting speeds are unclear. This study investigated the behavior and fate of respiratory droplets (0.1–4 μm) during coughs in a single-path respiratory tract model extending from terminal alveoli to mouth opening. An experimentally measured cough waveform was used to control the alveolar wall motions and the flow boundary conditions at lung branches from G2 to G18. The mouth opening was modeled after the image of a coughing subject captured using a high-speed camera. A well-tested k-ω turbulence model and Lagrangian particle tracking algorithm were applied to simulate cough flow evolutions and droplet dynamics under four cough depths, i.e., tidal volume ratio (TVR) = 0.13, 0.20. 0.32, and 0.42. The results show that 2-μm droplets have the highest exhalation fraction, regardless of cough depths. A nonlinear relationship exists between the droplet exhalation fraction and cough depth due to a complex deposition mechanism confounded by multiscale airway passages, multiregime flows, and drastic transient flow effects. The highest exhalation fraction is 1.6% at the normal cough depth (TVR = 0.32), with a mean exiting speed of 20 m/s. The finding that most exhaled droplets from deep lungs are 2 μm highlights the need for more effective facemasks in blocking 2-μm droplets and smaller both in infectious source control and self-protection from airborne virus-laden droplets.
Zusammenfassung
Die SARS-CoV-2-Pandemie stellte in einem bundesweiten Lockdown die Versorgung von Patienten mit Dysphagie in Pflegeheimen vor große Schwierigkeiten. Mittels eines zweiteiligen Fragebogens wurden landesweit Pflegefachkräfte hinsichtlich der Versorgung von Patienten mit Dysphagie befragt. In diesem Artikel werden die Ergebnisse des ersten Fragenkomplexes vorgestellt. Es wurden Bedingungen hinsichtlich der Diagnostik sowie die Therapie von schluckgestörten Klienten in stationären Pflegeeinrichtungen untersucht.
Droplets exhaled during normal breathing and not associated with coughing may pose hazardous agents to infective diseases dissemination. The objective is to explore the physical mechanism, which may lead to droplets formation.
We hypothesize that liquid menisci occlusions, which may form inside small airways, travel along the airway, may lose mass and finally disintegrate into small droplets. This hypothesis was numerically investigated applying physiologically plausible values of the phenomenological coefficients and geometrical conformations.
We show that three important dimensionless parameters control the motion and disintegration of menisci: the dimensionless mucus layer thickness, the dimensionless menisci initial thickness (all scaled by the airway radius), and the capillary number. Menisci traveling within airways may either remain at equilibrium or diminish or increase in size. Menisci that diminish in size may collapse into the mucus layer; form a large droplet that contains most of the menisci mass before disintegration; or form a larger number of small droplets (we show the forming of three or four droplets in a single occluded airway).
A critical capillary number for menisci at equilibrium could be defined. It was shown that menisci tend to diminish in size as the capillary number increases above the critical value, and a number of small droplets may be formed during normal breathing.
Aerosol production during normal breathing is often attributed to turbulence in the respiratory tract. That mechanism is not consistent with a high degree of asymmetry between aerosol production during inhalation and exhalation. The objective was to investigate production symmetry during breathing.
The aerosol size distribution in exhaled breath was examined for different breathing patterns including normal breathing, varied breath-holding periods, and contrasting inhalation and exhalation rates. The aerosol droplet size distribution measured in the exhaled breath was examined in real time using an aerodynamic particle sizer.
The dependence of the particle concentration decay rate on diameter during breath holding was consistent with gravitational settling in the alveolar spaces. Also, deep exhalation resulted in a four- to sixfold increase in concentration, and rapid inhalation produced a further two- to threefold increase in concentration. In contrast, rapid exhalation had little effect on the measured concentration. A positive correlation of the breath aerosol concentration with subject age was observed. The results were consistent with the breath aerosol being produced through fluid film rupture in the respiratory bronchioles in the early stages of inhalation and the resulting aerosol being drawn into the alveoli and held before exhalation. The observed asymmetry of production in the breathing cycle with very little aerosol being produced by exhalation is inconsistent with the widely assumed turbulence-induced aerosolization mechanism.
Alveolar surfactant is well known for its ability to reduce minimal surface tension at the alveolar air-liquid interface to values below 5 mN/m. In addition, it has been suggested that an analogous conductive airway surfactant is also present in the airways. To elucidate the composition, possible origin, and surface activity of conductive airway phospholipids (PL), we compared in adult porcine lungs the PL classes and phosphatidylcholine (PC) molecular species of nonpurified tracheal aspirate samples with those of bronchoalveolar lavage fluid (BAL), tracheobronchial epithelium, and lung parenchyma. We also analyzed PL and PC composition, protein content, and surface activity of surfactant isolated from tracheal aspirates (SurfTrachAsp), BAL (SurfBAL), and the 27,000 x g pellet of BAL (SurfP27000) by density-gradient centrifugation. Although PL composition revealed contributions of the airways to tracheal aspirates, the composition of PC molecular species of tracheal aspirates was similar to that of BAL and lung parenchyma, but differed considerably from that of airway epithelium. SurfTrachAsp had the same PL and PC composition as SurfBAL and SurfP27000, indicating that this fraction of tracheal aspirates may have originated from the alveoli. Nevertheless, minimal and maximal surface tensions were higher in SurfTrachAsp than in SurfBAL and SurfP27000. Analysis of surfactant proteins A, B, and C (SP-A, SP-B, and SP-C) revealed that SP-A was decreased and SP-B and SP-C were absent, whereas total protein was increased in SurfTrachAsp. We conclude that as compared with alveolar surfactant, PL of SurfTrachAsp show the same composition, but that surface-tension function is impaired and the concentration of surfactant proteins is decreased in SurfTrachAsp.
Humans commonly exhale aerosols comprised of small droplets of airway-lining fluid during normal breathing. These “exhaled bioaerosols” may carry airborne pathogens and thereby magnify the spread of certain infectious diseases, such as influenza, tuberculosis, and severe acute respiratory syndrome. We hypothesize that, by altering lung airway surface properties through an inhaled nontoxic aerosol, we might substantially diminish the number of exhaled bioaerosol droplets and thereby provide a simple means to potentially mitigate the spread of airborne infectious disease independently of the identity of the airborne pathogen or the nature of any specific therapy. We find that some normal human subjects expire many more bioaerosol particles than other individuals during quiet breathing and therefore bear the burden of production of exhaled bioaerosols. Administering nebulized isotonic saline to these “high-producer” individuals diminishes the number of exhaled bioaerosol particles expired by 72.10 ± 8.19% for up to 6 h. In vitro and in vivo experiments with saline and surfactants suggest that the mechanism of action of the nebulized saline relates to modification of the physical properties of the airway-lining fluid, notably surface tension.
• drug delivery
• lung
• infectious disease
• influenza
A new method for modeling surface tension effects on fluid motion has been developed. Interfaces between fluids of different properties, or "colors", are represented as transition regions of finite thickness, across which the color variable varies continuously. At each point in the transition region, a force density is defined which is proportional to the curvature of the surface of constant color at that point. It is normalized so that the conventional description of surface tension on an interface is recovered when the ratio of local transition region thickness to local radius of curvature approaches zero. The continuum method eliminates the need for interface reconstruction, simplifies the calculation of surface tension, enables accurate modeling of two- and three-dimensional fluid flows driven by surface forces, and does not impose any modeling restrictions on the number, complexity, or dynamic evolution of fluid interfaces having surface tension. Computational results for two-dimensional flows are given to illustrate the properties of the method.
Several methods have been previously used to approximate free boundaries in finite-difference numerical simulations. A simple, but powerful, method is described that is based on the concept of a fractional volume of fluid (VOF). This method is shown to be more flexible and efficient than other methods for treating complicated free boundary configurations. To illustrate the method, a description is given for an incompressible hydrodynamics code, SOLA-VOF, that uses the VOF technique to track free fluid surfaces.
Values for the critical thickness of rupture (or ‘black spot formation’) of aqueous and non-aqueous (aniline and nitrobenzene) foam films were computed by the Vrij (1966) and Radoev–Scheludko–Manev (1983) theories. The ‘critical thickness versus film radius’ dependences were derived, using different formulae for the rate of film thinning. The theoretical values were compared to the available – from the literature, as well as the investigations conducted here – experimental data for the critical thickness determined in the thinnest domains of the investigated microscopic horizontal foam films. It has been established that in all cases the agreement between theory and experiment is largely enhanced when the formula of Manev et al. (1997) is employed to describe the rate of film thinning, instead of the classical Stefan–Reynolds equation.
The thinning and the critical thickness (of rupture or “black spots” formation) of foam films from aqueous solutions of mixed nonionic surfactants are studied under varied experimental conditions, as a function of film radius (0.05–0.15mm), surfactant concentration (0.01–1.0CMC) and ionic strength (0.001–0.1M NaCl). The experimental values of the drainage coefficient (α), determined from the film thickness versus time dependences, were used to calculate the theoretical values of the film critical thickness.The real velocity of film thinning is a major factor in the process of reaching the state of kinetic instability when approaching the critical thickness (Scheludko's criterion). The classical equation used to describe the film thinning rate, proposed and named by Scheludko (1955) “Reynolds Law”, is applicable for small film radii (r
In a variety of physico-chemical reactions, the actual process takes place in a reactive zone, called the “active surface”. We define the active surface of the lung as the set of airway segments that are closed but connected to the trachea through an open pathway, which is the interface between closed and open regions in a collapsed lung. To study the active surface and the time interval between consecutive openings, we measured the sound pressure of crackles, associated with the opening of collapsed airway segments in isolated dog lungs, inflating from the collapsed state in 120 s. We analyzed the sequence of crackle amplitudes, inter-crackle intervals, and low frequency energy from acoustic data. The series of spike amplitudes spans two orders of magnitude and the inter-crackle intervals spans over five orders of magnitude. The distribution of spike amplitudes follows a power law for nearly two decades, while the distribution of time intervals between consecutive crackles shows two regimes of power law behavior, where the first region represents crackles coming from avalanches of openings whereas the second region is due to the time intervals between separate avalanches. Using the time interval between measured crackles, we estimated the time evolution of the active surface during lung inflation. In addition, we show that recruitment and instabilities along the pressure–volume curve are associated with airway opening and recruitment. We find a good agreement between the theory of the dynamics of lung inflation and the experimental data which combined with numerical results may prove useful in the clinical diagnosis of lung diseases.
A new expiratory droplet investigation system (EDIS) was used to conduct the most comprehensive program of study to date, of the dilution corrected droplet size distributions produced during different respiratory activities.Distinct physiological processes were responsible for specific size distribution modes. The majority of particles for all activities were produced in one or more modes, with diameters below 0.8 μm at average concentrations up to 0.75 cm−3. These particles occurred at varying concentrations, during all respiratory activities, including normal breathing. A second mode at 1.8 μm was produced during all activities, but at lower concentrations of up to 0.14 cm−3.Speech produced additional particles in modes near 3.5 and 5 μm. These two modes became most pronounced during sustained vocalization, producing average concentrations of 0.04 and 0.16 cm−3, respectively, suggesting that the aerosolization of secretions lubricating the vocal chords is a major source of droplets in terms of number.For the entire size range examined of 0.3–20 μm, average particle number concentrations produced during exhalation ranged from 0.1 cm−3 for breathing to 1.1 cm−3 for sustained vocalization.Non-equilibrium droplet evaporation was not detectable for particles between 0.5 and 20 μm, implying that evaporation to the equilibrium droplet size occurred within 0.8 s.
An axisymmetric numerical method to simulate the dynamics of insoluble surfactant on a moving liquid–fluid interface is presented. The motion of the interface is captured using a volume-of-fluid method. Surface tension, which can be a linear or nonlinear function of surfactant concentration (equation of state), is included as a continuum surface force. The surfactant evolution is governed by a convection–diffusion equation with a source term that accounts for stretching of the interface. In the numerical method, the masses of the flow components and the surfactant mass are exactly conserved. A number of test cases are presented to validate the algorithm. Simulations of a drop in extensional flow, and its subsequent retraction and breakup upon cessation of the external flow, are performed. Even when the initial surfactant distribution is dilute, we observe that increases in surfactant concentration locally (i.e. at the drop tips) can result in a local deviation from the dilute limit. We show that this can lead to differences in effective surface tension, the Marangoni forces and the associated drop dynamics between results using the linear and nonlinear equations of state.
Measurements were made of the number concentrations of particles in exhaled breath under various conditions of exercise. A laser light scattering particle spectrometer was used to count particles exhaled by test subjects wearing respirators in a challenge environment of clean, dry air. Precautions were taken to ensure that particles were not generated by the the respirators and that no extraneous water or other particles were produced in the humid exhaled air. The number of particles detected in exhaled air varied over a range from less than 0.1 to about 4 particles per cm3 depending upon the test subject and his activity. Subjects at rest exhaled the lowest concentration of particles, whereas exercises producing a faster respiration rate caused increased exhalation of particles. Exhaled particle concentrations can limit the usefulness of nondiscriminating, ambient challenge aerosols for the fit testing of highly protective respirators.
Although some investigators have reported that crackles are present only in persons with lung disease, others say they also occur in normal persons. In order to clarify this difference of opinion, we determined the prevalence of crackles in 56 women without significant lung disease. The subjects ranged from 19 to 33 yr of age (mean, 21.3). They all had a FVC greater than 80% predicted and a FEV1/FVC ratio greater than 75%. None had a history of acute or chronic lung disease. During slow inspirations from residual volume, midinspiratory fine crackles were heard at the anterior bases in 35 of 56 subjects by a physician using an acoustic stethoscope, whereas a bioengineer using an 800 Hertz high pass filtered stethoscope heard crackles in 53 subjects. Crackles during tidal breathing were heard in 2 subjects. It is postulated that the crackles noted after expiration to residual volume are nonpathologic, and occur when basilar airways, which close at the end of a forced expiration, suddenly open during inspiration. Examination of the quality, timing, and anatomic distribution of the crackles in apparently normal subjects suggests that they can often be distinguished from those resulting from diseases such as bronchitis, interstitial fibrosis, and congestive heart failure.
An alveolar capsule oscillation technique was used to determine 1) the lobe pressure and volume at which airways close and reopen, 2) the effect of expiration rate on closing volume and pressure, 3) the phase in the breathing cycle at which airway closure occurs, and 4) the site of airway closure. Experiments were conducted in excised dog lobes; closure was detected by an abrupt increase in the input impedance of surfacemounted alveolar capsules. Mean transpulmonary pressure (Ptp) at closure was slightly less than zero (Ptp = -2.3 cmH2O); the corresponding mean reopening pressure was Ptp = 14 cmH2O. The expiration rate varied between 1 and 20% of total lobe capacity per second and had no consistent effect on the closing volume and pressure. When lung volume was cycled up to frequencies of 0.2 Hz, closure generally occurred on expiration rather than inspiration. These observations support the conclusion that mechanical collapse, rather than meniscus formation, is the most likely mechanism producing airway closure in normal excised dog lungs. Analysis of measured acoustic impedances and reopening pressures suggests that closure occurs in the most peripheral airways. Reopening during inspiration was often observed to consist of a series of stepwise decreases in capsule impedance, indicating a sequence of opening events.
Droplets carried in exhaled breath may carry microorganisms capable of transmitting disease over both short and long distances. The size distribution of such droplets will influence the type of organisms that may be carried as well as strategies for controlling airborne infection. The aim of this study was to characterize the size distribution of droplets exhaled by healthy individuals. Exhaled droplets from human subjects performing four respiratory actions (mouth breathing, nose breathing, coughing, talking) were measured by both an optical particle counter (OPC) and an analytical transmission electron microscope (AEM). The OPC indicated a preponderance of particles less than 1 mu, although larger particles were also found. Measurements with the AEM confirmed the existence of larger sized droplets in the exhaled breath. In general, coughing produced the largest droplet concentrations and nose breathing the least, although considerable intersubject variability was observed.
Bulk shear viscosities were measured with a cone and plate microviscometer as a function of concentration, shear rate, and temperature for lavaged calf lung surfactant (LS), Exosurf, Infasurf, Survanta, and synthetic lipid mixtures dispersed in normal saline. Viscosity increased with phospholipid concentration for all surfactants, but its magnitude and shear dependence varied widely among the different preparations. Saline dispersions of Exosurf and synthetic phospholipids had low viscosities of only a few centipoise (cp) and exhibited minimal shear dependence. LS, Infasurf, Survanta, and lipid mixtures containing palmitic acid and tripalmitin had larger non-Newtonian viscosities that increased as shear rate decreased. At 35 mg of phospholipid/ml and 37 degrees C, viscosity values were 52.3 cp (Survanta), 31.1 cp (LS), and 25 cp (Infasurf) at a shear rate of 77 s(-1) and 16.9 cp (Survanta), 10.1 cp (LS), and 6.6 cp (Infasurf) at 770 s(-1). At 25 mg of phospholipid/ml and 37 degrees C, viscosity values at 77 s(-1) were 28.8 cp (Survanta), 4.7 cp (LS), and 12.5 cp (Infasurf). At fixed shear rate, viscosity was substantially decreased at 23 degrees C compared with 37 degrees C for LS and Infasurf but was increased for Survanta. Calcium (5 mM) greatly reduced the viscosity of both Survanta and Infasurf at 37 degrees C. Studies on synthetic mixtures indicated that phospholipid/apoprotein interactions were important in the rheology of lung-derived surfactants and that palmitic acid and tripalmitin contributed to the increased viscosity of Survanta. The viscous behavior of clinical exogenous surfactants potentially influences their delivery and distribution in lungs and varies significantly with composition, concentration, temperature, ionic environment, and physical formulation.
We describe how surface-tension-driven instabilities of the lung's liquid lining may lead to pulmonary airway closure via the formation of liquid bridges that occlude the airway lumen. Using simple theoretical models, we demonstrate that this process may occur via a purely fluid-mechanical "film collapse" or through a coupled, fluid-elastic "compliant collapse" mechanism. Both mechanisms can lead to airway closure in times comparable with the breathing cycle, suggesting that surface tension is the primary mechanical effect responsible for the closure observed in peripheral regions of the human lungs. We conclude by discussing the influence of additional effects not included in the simple models, such as gravity, the presence of pulmonary surfactant, respiratory flow and wall motion, the airways' geometry, and the mechanical structure of the airway walls.
Critical thickness of thin liquid films: Comparison of theory and experiment. Colloids and Surfaces A: Physicochemical and Engineering Aspects Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities
- E D Manev
- J K Angarska
- L Morawska
- G R Johnson
- Z D Ristovski
- M Hargreaves
- K Mengersen
- S Corbett
Manev, E. D., & Angarska, J. K. (2005). Critical thickness of thin liquid films: Comparison of theory and experiment. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 263, 250. Morawska, L., Johnson, G. R., Ristovski, Z. D., Hargreaves, M., Mengersen, K. Corbett, S., et al. (2009). Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities. Journal of Aerosol Science, 40, 256.
Surfactant and lung mechanics Pulmonary surfactant: From molecular biology to clinical practice
- J Goerke
Goerke, J. (1992). Surfactant and lung mechanics. In B. Robertson, L. M.G. van Golde, & J. J. Batenburg (Eds.), Pulmonary surfactant: From molecular biology to clinical practice. Amsterdam, London, New York, Tokyo: Elsevier.
Crackles and instabilities during lung inflation Conductive airway surfactant: Surface-tension function, biochemical composition, and possible alveolar origin A continuum method for modeling surface tension Culture medium optimization and scale-up for microbial fermentations
- M Alencar
- A Majumdar
- Z Hantos
- S V Buldyrev
- H E Stanley
- B Suki
- W Bernhard
- H P Haagsman
- T Tschernig
- C F Poets
- A D Postle
- M E Van Eijk
Alencar, M., Majumdar, A., Hantos, Z., Buldyrev, S. V., Stanley, H. E., & Suki, B. (2005). Crackles and instabilities during lung inflation. Physica A, 357, 35. Bernhard, W., Haagsman, H. P., Tschernig, T., Poets, C. F., Postle, A. D. van Eijk, M. E., et al. (1997). Conductive airway surfactant: Surface-tension function, biochemical composition, and possible alveolar origin. American Journal of Respiratory Cell and Molecular Biology, 17, 41. Brackbill, J. U., Kothe, D. B., & Zemach, C. (1992). A continuum method for modeling surface tension. Journal of Computational Physics, 100, 335. Connors, N. C. (2002). Culture medium optimization and scale-up for microbial fermentations. In V. A. Vinci, & S. R. Parekh (Eds.), Handbook of industrial cell culture: Mammalian, microbial, and plant cells (pp. 171–196). Totowa, NJ: Humana Press.
Particle concentration in exhaled breath The human lung as aerosol generator
- C I Fairchild
- J F Stamper
- J Gebhart
- J Anselm
- J Heyder
- W Stahlhofen
Fairchild, C. I., & Stamper, J. F. (1987). Particle concentration in exhaled breath. American Industrial Hygiene Association Journal, 48, 948. Gebhart, J., Anselm, J., Heyder, J., & Stahlhofen, W. (1988). The human lung as aerosol generator. Journal of Aerosol Medicine, 1, 196.
The size distribution of droplets in the exhaled breath of healthy human subjects Drainage and critical thickness of foam films from aqueous solutions of mixed non-ionic surfactants The prevalence and character of crackles (rales) in young women without significant lung disease
- R S Papineni
- F S Rosenthal
- V Simulescu
- J K Angarska
- E D Manev
Papineni, R. S., & Rosenthal, F. S. (1997). The size distribution of droplets in the exhaled breath of healthy human subjects. Journal of Aerosol Medicine, 10, 105. Simulescu, V., Angarska, J. K., & Manev, E. D. (2008). Drainage and critical thickness of foam films from aqueous solutions of mixed non-ionic surfactants. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 319, 21. Workum, P., Holford, S. K., DelBono, E., & Murphy, R. L.H. (1982). The prevalence and character of crackles (rales) in young women without significant lung disease. American Review of Respiratory Disease, 126, 921. ARTICLE IN PRESS K. Haslbeck et al. / Journal of Aerosol Science 41 (2010) 429–438
Culture Medium Optimization and Scale-Up for Microbial Fermentations. Handbook of Industrial Cell Culture: Mammalian, Microbial, and Plant Cells
- N C Connors
Connors, N.C. (2002) Culture Medium Optimization and Scale-Up for Microbial
Fermentations. Handbook of Industrial Cell Culture: Mammalian, Microbial, and Plant
Cells. (Edited by Vinci, V.A., SR Parekh, S.R.) pp. 171-196, Humana Press, Totowa
NJ.
Particle concentration in exhaled breath
- C I Fairchild
- J F Stamper
Fairchild, C.I., Stamper, J.F. (1987) Particle concentration in exhaled breath. Am. Ind.
The human lung as aerosol generator
- Gebhart
Surfactant and lung mechanics
- Goerke
Culture medium optimization and scale-up for microbial fermentations
- Connors