Respiratory Particles Research Articles

Effect of a barrier on spatial distribution of respiratory particles in a room

Barriers have been widely used to mitigate transmission of Covid-19 and other diseases. Their efficacy for aerosol particles is not well established. The objective of this study was to quantify the impact of a barrier on the spatial distribution of particles released by speaking in a room with a low air-change rate (0.6 ± 0.2 h−1). The source was a nebulizer that released fluorescent microspheres of diameters 0.5, 1, 6, 10, or 20 µm for 20 min, and the room was outfitted with 108 passive sampling sites. We counted the number of microspheres deposited on slides at sampling locations after >1 h. The presence of a barrier 0.46 m in front of the source resulted in an increase in 0.5 µm particles deposited on the source-side of the barrier and an increase in 0.5 µm particles around the sides of the barrier laterally and at certain locations 4–6 m from the source. The barrier had a minor effect on the distribution of 1 µm particles. There was no observable effect of the barrier on the distribution of 6, 10, and 20 µm particles. Most 10 and 20 µm particles deposited within 0.3 m of the source, although some were found at locations >3 m from the source. These results indicate that barriers may not serve as adequate protection to others in the room, depending on their location relative to the barrier and the exposure timescale. A limitation is that our study utilized only one barrier configuration at one air-change rate.

Respiratory aerosol particle emission and simulated infection risk is greater during indoor endurance than resistance exercise

Pathogens such as severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), influenza, and rhinoviruses are transmitted by airborne aerosol respiratory particles that are exhaled by infectious subjects. We have previously reported that the emission of aerosol particles increases on average 132-fold from rest to maximal endurance exercise. The aims of this study are to first measure aerosol particle emission during an isokinetic resistance exercise at 80% of the maximal voluntary contraction until exhaustion, second to compare aerosol particle emission during a typical spinning class session versus a three-set resistance training session. Finally, we then used this data to calculate the risk of infection during endurance and resistance exercise sessions with different mitigation strategies. During a set of isokinetic resistance exercise, aerosol particle emission increased 10-fold from 5,400 ± 1,200 particles/min at rest to 59,000 ± 69,900 particles/min during a set of resistance exercise. We found that aerosol particle emission per minute is on average 4.9-times lower during a resistance training session than during a spinning class. Using this data, we determined that the simulated infection risk increase during an endurance exercise session was sixfold higher than during a resistance exercise session when assuming one infected participant in the class. Collectively, this data helps to select mitigation measures for indoor resistance and endurance exercise classes at times where the risk of aerosol-transmitted infectious disease with severe outcomes is high.

A Recent Update on SARS-CoV-2 Transmission and its Variants: Transmission, Pathogenic Mechanism, and Treatment

Abstract: Coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 virus was first reported in China. As of April 17, 2022, over 500 million confirmed cases and over 6 million deaths have been reported worldwide. COVID-19 is transmitted through respiratory droplets and other contact routes in the human community. Fine respiratory droplets and aerosol particles enter into the respiratory tract and come in the contact with mucous membranes. The SARS-CoV-2-containing droplets spread into the environment by quiet breathing, speaking, exercise, coughing, and sneezing of COVID-19-infected individuals. World Health Organization (WHO) have been released several guidelines for controlling COVID-19 which include maintaining personal hygiene, social distance, and COVID-19 vaccination. A higher transmission rate of SARS-CoV-2 has been reported and the transmission rate also depends on several variants of SARS-CoV-2. SARS-CoV-2 genome is a single-stranded positive (+) sense RNA of about 26- 32 kb nucleotides and has 80% similarity to the bat SARS-CoV. SARS-CoV-2 enters the host cell through the interaction between spike proteins of the virus and the host cell surface receptor. Acute Respiratory Distress Syndrome and lung injury lead to the death of SARS-CoV-2-infected people. Several vaccines for COVID-19 have been developed, giving protection from COVID-19 and reducing the transmission rate. Developed vaccines are not 100% effective against SARS-CoV-2 due to variations in the genetic makeup of SARS-CoV-2. Thereby, further research is the need of the hour. This review summarizes SARS-CoV-2 and its several variants and their transmission, genomic characterization, pathogenhost interaction mechanisms, diagnostic methods, and potential treatment approach for SARS-CoV-2.

Optimal Conditions for In Vitro Assembly of Respiratory Syncytial Virus Nucleocapsid-like Particles.

The nucleocapsids (NCs) of the respiratory syncytial virus (RSV) can display multiple morphologies in vivo, including spherical, asymmetric, and filamentous conformations. Obtaining homogeneous ring-like oligomers in vitro is significant since they structurally represent one turn of the characteristic RSV NC helical filament. Here, we analyzed and optimized conditions for forming homogenous, recombinant nucleocapsid-like particles (NCLPs) of RSV in vitro. We examined the effects of modifying the integrated RNA length and sequence, altering incubation time, and varying buffer parameters, including salt concentration and pH, on ring-like NCLPs assembly using negative stain electron microscopy (EM) imaging. We showed that high-quality, homogeneous particles are assembled when incubating short, adenine-rich RNA sequences with RNA-free N associated with P (N0P). Further, we reported that a co-incubation duration greater than 3 days, a NaCl concentration between 100 mM and 200 mM, and a pH between 7 and 8 are optimal for N-RNA ring assembly with polyadenine RNA sequences. We believe assembling high-quality, homogeneous NCLPs in vitro will allow for further analysis of RSV RNA synthesis. This work may also lend insights into obtaining high-resolution nucleocapsid homogeneous structures for in vitro analysis of antiviral drug candidates against RSV and related viruses.

Symptoms, Ways of Transmission and How to Prevent Monkeypox Virus

Introduction: Monkeypox is a double-stranded virus of the genus Orthopoxvirus, which is transmitted by animals to humans. Monkey pox is a double-stranded virus of the orthopoxvirus genus that is transmitted to humans by animals. So far, two main species of monkeypox have been identified in West Africa and the Congo Basin. The way the monkeypox virus spreads is often through respiratory particles and direct contact with skin lesions. The initial symptoms of monkeypox include headache, muscle pain, fever, and body aches. On the body of the sufferers, bumps in the form of boils will gradually appear, which will become blisters. Many cases in recent outbreaks have been attributed to sexual transmission; specially among men who identify as gay, bisexual, or men who have sex with men. The virus can also be transmitted through direct contact with infected wounds, body fluids, and shared bedding/clothing. Monkeypox is a dangerous disease that can affect the mental health of patients. Previous studies indicate that the monkeypox virus leads to social stigma, anxiety, thoughts and behaviors related to suicide in infected people. Considering that several cases of monkeypox have been identified inside Iran, measures should be taken to make people aware of the symptoms and transmission of this virus, so that we do not witness the spread of another epidemic after COVID-19.

Efficacy of Do-It-Yourself air filtration units in reducing exposure to simulated respiratory aerosols

Many respiratory diseases, including COVID-19, can be spread by aerosols expelled by infected people when they cough, talk, sing, or exhale. Exposure to these aerosols indoors can be reduced by portable air filtration units (air cleaners). Homemade or Do-It-Yourself (DIY) air filtration units are a popular alternative to commercially produced devices, but performance data is limited. Our study used a speaker-audience model to examine the efficacy of two popular types of DIY air filtration units, the Corsi-Rosenthal cube and a modified Ford air filtration unit, in reducing exposure to simulated respiratory aerosols within a mock classroom. Experiments were conducted using four breathing simulators at different locations in the room, one acting as the respiratory aerosol source and three as recipients. Optical particle spectrometers monitored simulated respiratory aerosol particles (0.3–3 μm) as they dispersed throughout the room. Using two DIY cubes (in the front and back of the room) increased the air change rate as much as 12.4 over room ventilation, depending on filter thickness and fan airflow. Using multiple linear regression, each unit increase of air change reduced exposure by 10%. Increasing the number of filters, filter thickness, and fan airflow significantly enhanced the air change rate, which resulted in exposure reductions of up to 73%. Our results show DIY air filtration units can be an effective means of reducing aerosol exposure. However, they also show performance of DIY units can vary considerably depending upon their design, construction, and positioning, and users should be mindful of these limitations.

Health and Safety Regulations for COVID-19: A Policy Analysis.

The COVID-19 pandemic spurred some regulators in the USA to require occupational health and safety programs to prevent COVID-19 transmission in workplaces. The objective of this study was to describe such state and federal regulations enacted between January 2020 and January 2022. Regulations, including emergency temporary standards (ETS) and permanent standards, were identified through a search of Nexis Uni and Bloomberg Law and review of US OSHA websites and the Federal Register. Full texts were reviewed for regulatory scope, hazard and exposure definitions, determination of exposure or risk levels, and control strategies. Four state (California, Michigan, Virginia, and Oregon) and two federal regulations were identified. All regulations described respiratory aerosols as the primary source of SARS-CoV-2 and recognized person-to-person transmission by droplet, airborne, and contact routes. Only the US OSHA ETS for healthcare explicitly stated that inhalation of respiratory particles was the most likely method of COVID-19 transmission. The Virginia, Michigan, and Oregon regulations described different categories of risk defined by exposure frequency and duration or specific workplace activities. California described exposure as places and times when employees come into contact or congregate with other people. The US OSHA ETS for healthcare described exposure as involving close contact with suspected or confirmed COVID-19 patients. While all of the state regulations required strategies from across the hierarchy, only the Virginia regulations specifically incorporated the hierarchy of controls. Only the California and Virginia regulations explicitly linked control strategies to the transmission route, while Virginia demarcated control strategies by risk level. Oregon linked risk level to occupancy levels and physical distancing requirements and referred to the use of a layered approach for transmission control. The US OSHA ETS for healthcare defined droplet and airborne precautions but made no mention of the hierarchy of controls or risk levels. Respirators were discussed in most of the regulations. The first Michigan regulation explicitly required respirators appropriate to exposure risk. The California regulations noted that respirators protect the wearer while face coverings protect people around the wearer. These regulations offer insights for a permanent US OSHA infectious disease regulation, such as the need to consider a range of transmission modes including near- and far-range aerosol inhalation, endemic and novel pathogens, workplaces beyond healthcare settings, factors that contribute to exposure and risk, the hierarchy of controls, the role of vaccination, and the importance of written exposure assessment and infection prevention plans.

Increasing ventilation reduces SARS-CoV-2 airborne transmission in schools: A retrospective cohort study in Italy's Marche region.

While increasing the ventilation rate is an important measure to remove inhalable virus-laden respiratory particles and lower the risk of infection, direct validation in schools with population-based studies is far from definitive. We investigated the strength of association between ventilation and SARS-CoV-2 transmission reported among the students of Italy's Marche region in more than 10,000 classrooms, of which 316 were equipped with mechanical ventilation. We used ordinary and logistic regression models to explore the relative risk associated with the exposure of students in classrooms. For classrooms equipped with mechanical ventilation systems, the relative risk of infection of students decreased at least by 74% compared with a classroom with only natural ventilation, reaching values of at least 80% for ventilation rates >10 L s-1 student-1. From the regression analysis we obtained a relative risk reduction in the range 12%15% for each additional unit of ventilation rate per person. The results also allowed to validate a recently developed predictive theoretical approach able to estimate the SARS-CoV-2 risk of infection of susceptible individuals via the airborne transmission route. We need mechanical ventilation systems to protect students in classrooms from airborne transmission; the protection is greater if ventilation rates higher than the rate needed to ensure indoor air quality (>10 L s-1 student-1) are adopted. The excellent agreement between the results from the retrospective cohort study and the outcome of the predictive theoretical approach makes it possible to assess the risk of airborne transmission for any indoor environment.

Size, concentration, and origin of human exhaled particles and their dependence on human factors with implications on infection transmission

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 <5µm (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 <5µm originate from the lower respiratory tract, 5–15µm from the larynx/pharynx, and >15µm 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 5µm. 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.

Modeling the effect of temperature and relative humidity on exposure to SARS-CoV-2 in a mechanically ventilated room.

Computational fluid dynamics models have been developed to predict airborne exposure to the SARS-CoV-2 virus from a coughing person in a mechanically ventilated room. The models were run with three typical indoor air temperatures and relative humidities (RH). Quantile regression was used to indicate whether these have a statistically significant effect on the airborne exposure. Results suggest that evaporation is an important effect. Evaporation leads to respiratory particles, particularly those with initial diameters between 20 and 100 μm, remaining airborne for longer, traveling extended distances and carrying more viruses than expected from their final diameter. In a mechanically ventilated room, with all of the associated complex air movement and turbulence, increasing the RH may result in reduced airborne exposure. However, this effect may be so small that other factors, such as a small change in proximity to the infected person, could rapidly counter the effect. The effect of temperature on the exposure was more complex, with both positive and negative correlations. Therefore, within the range of conditions studied here, there is no clear guidance on how the temperature should be controlled to reduce exposure. The results highlight the importance of ventilation, face coverings and maintaining social distancing for reducing exposure.

Field Survey on Generation Patterns of Airborne Fungi in a Livestock Manure Composting Plant in South Korea

Airborne fungi emitted from livestock manure composting plants are one of the major harmful factors causing respiratory disease for workers and nearby residents. Their generation of emissions is relatively high compared to other workplaces. This study investigated the emission characteristics of airborne fungi generated in livestock manure composting plants and utilized them as basic data to prevent workers’ health. The livestock manure composting plants selected for the survey in this study were according to the fermentation mode, including screw type, rotary type and natural dry type. The field evaluation period was from September 2019 to August 2020 and was surveyed monthly. The equipment for collecting airborne fungi was a six-stage cascade impactor. An analysis of the quantification and qualification of airborne fungi was conducted through a culture method and identification technique, respectively. The mean levels of airborne fungi in livestock manure composting plants were 1143 (±106)CFU m−3 for screw type, 552 (±146)CFU m−3 for rotary type and 434 (±73)CFU m−3 for natural dry type, respectively. Based on the results obtained from this study, the livestock manure composting plant operated by screw type showed the highest concentration of airborne fungi, followed by the rotary type and natural dry type. The monthly concentration of airborne fungi was the highest in June and the lowest in February, regardless of the livestock manure composting plant type. The concentration range of airborne fungi corresponding to the respiratory particle diameter was 40 to 60% relative to the concentration of all airborne fungi. The correlation relationship between airborne fungi and environmental factors (temperature, relative humidity, particulate matter and odor) was not found to be significant in livestock manure composting plants. The predominant genera of airborne fungi identified were Aspergillus spp., Cladosporium spp. and Penicillium spp.

Comparison of the survival of different isolates of SARS-CoV-2 in evaporating aerosols

Numerous variants of SARS-CoV-2 with increased transmissibility have emerged over the course of the pandemic. Potential explanations for the increased transmissibility of these variants include increased shedding from infected individuals, increased environmental stability, and/or a lower infectious dose. Upon exhalation of a respiratory particle into the environment, water present in the particle is rapidly lost through evaporation, resulting in a decrease in particle size. The aim of the present study was to compare the losses of infectivity of different isolates of SARS-CoV-2 during the rapid evaporation of aerosol particles that occurs immediately post-generation to assess if there are differences suggestive of increased survival, and ultimately greater transmissibility, for more recent variants. Losses of infectivity of several isolates of SARS-CoV-2 suspended in viral culture media were assessed following aerosolization and evaporation in a flowing chamber. The results demonstrate that losses of infectivity measured post-evaporation were similar for three different isolates of SARS-CoV-2, including isolates from the more recent Delta and Omicron lineages. The average loss in infectivity across all three isolates was 61 ± 15% (−0.46 ± 0.17 log10 TCID50/L-air) at a relative humidity <30%. These results, together with those from several previous studies, suggest that it is unlikely that an increase in environmental stability contributes to the observed increases in transmissibility observed with more recent variants of SARS-CoV-2.

The 2022 Monkeypox outbreak: How the medicinal chemistry could help us?

Monkeypox disease is a zoonosis that has the monkey virus (MPXV) as its etiologic agent, an enveloped double-stranded DNA virus that has caused some severe cases, leading to 3-6% fatality ratio. MPXV exhibits similar symptoms to those observed for Smallpox infection. Human-to-human transmission occurs via droplet respiratory particles and close contact with skin lesions of an infected person or recently contaminated objects. MPXV symptoms include fever, intense headache, back pain, myalgia, severe asthenia, lymphadenopathy, and skin eruption. The 2022 outbreak is growing, spreading over 75 countries/territories. Based on this, the MPXV outbreak was declared a “public health emergency of international concern” by WHO. In 2019, a vaccine-based modified attenuated vaccinia virus (Ankara strain) was approved for MPXV prevention. However, its availability remains limited. Besides, there are no approved or licensed drugs to treat MPXV currently. However, tecovirimat was licensed by the European Medicines Agency (EMA) to treat MPXV infections. Notwithstanding all these aspects and limitations associated with MPXV, How the medicinal chemistry could help us?

Microstructural evaluation and recommendations for face masks in community use to reduce the transmission of respiratory infectious diseases

Background and ObjectiveRecommendations for the use of face masks to prevent and protect against the aerosols (≤5µm) and respiratory droplet particles (≥5µm), which can carry and transmit respiratory infections including severe acute respiratory syndrome coronavirus (SARS-CoV-2), have been in effect since the early stages of the coronavirus disease 2019 (COVID-19). The particle filtration efficiency (PFE) and air permeability are the most crucial factors affecting the level of pathogen transmission and breathability, i.e. wearer comfort, which should be investigated in detail. MethodsIn this context, this article presents a novel assessment framework for face masks combining X-ray microtomography and computational fluid dynamics simulations. In consideration to their widespread public use, two types of face masks were assessed: (I) two layer non-woven face masks and (II) the surgical masks (made out of a melt-blown fabric layer covered with two non-woven fabric layers). ResultsThe results demonstrate that the surgical masks provide PFEs over 75% for particles with diameter over 0.1µm while two layer face masks are found out to have insufficient PFEs, even for the particles with diameter over 2µm (corresponding PFE is computed as 47.2%). Thus, existence of both the non-woven fabric layers for mechanical filtration and insertion of melt-blown fabric layer(s) for electrostatic filtration in the face masks were found to be highly critical to prevent the airborne pathogen transmission. ConclusionsThe present framework would assist in computational assessment of commonly used face mask types based on their microstructural characteristics including fiber diameter, orientation distributions and fiber network density. Therefore, it would be also possible to provide new yet feasible design routes for face masks to ensure reliable personal protection and optimal breathability.

Experimental measurement of respiratory particles dispersed by wind instruments and analysis of the associated risk of infection transmission

Activities such as singing or playing a wind instrument release respiratory particles into the air that may contain pathogens and thus pose a risk for infection transmission. Here we report measurements of the size distribution, number, and volume concentration of exhaled particles from 31 healthy musicians playing 20 types of wind instruments using aerosol size spectrometry complemented with in-line holography in a strictly controlled cleanroom environment. We find that playing wind instruments carries a lower risk of airborne disease transmission than speaking or singing. We attribute this to the fact that the resonators of wind instruments act as filters for particles >10µm in diameter, which were found in high abundance right after a brass mouthpiece but very rarely at the instrument bell end. We have also measured the size-dependent filtering properties of different types of filters that can be used as instrument masks. Based on these measurements, we calculated the risk of airborne transmission of SARS-CoV-2 in different near- and far-field scenarios with and without masking and/or distancing. We conclude that in all cases where there is a possibility that the musician is infectious, the only safe measure to prevent airborne transmission of the disease is the use of well-fitting and well-filtering masks for the instrument and the susceptible person.

The physics of respiratory particle generation, fate in the air, and inhalation.

Given that breathing is one of the most fundamental physiological functions, there is an urgent need to broaden our understanding of the fluid dynamics that governs it. There would be many benefits from doing so, including a better assessment of respiratory health, a basis for more precise delivery of pharmaceutical drugs for treatment, and the understanding and potential minimization of respiratory infection transmission. We review the physics of particle generation in the respiratory tract, the fate of these particles in the air on exhalation and the physics of particle inhalation. The main focus is on evidence from experimental studies. We conclude that although there is qualitative understanding of the generation of particles in the respiratory tract, a basic quantitative knowledge of the characteristics of the particles emitted during respiratory activities and their fate after emission, and a theoretical understanding of particle deposition during inhalation, nevertheless the general understanding of the entire process is rudimentary, and many open questions remain.

Molecular detection of SARS-COV-2 in exhaled breath at the point-of-need

The SARS-CoV-2 pandemic has highlighted the need for improved technologies to help control the spread of contagious pathogens. While rapid point-of-need testing plays a key role in strategies to rapidly identify and isolate infectious patients, current test approaches have significant shortcomings related to assay limitations and sample type. Direct quantification of viral shedding in exhaled particles may offer a better rapid testing approach, since SARS-CoV-2 is believed to spread mainly by aerosols. It assesses contagiousness directly, the sample is easy and comfortable to obtain, sampling can be standardized, and the limited sample volume lends itself to a fast and sensitive analysis. In view of these benefits, we developed and tested an approach where exhaled particles are efficiently sampled using inertial impaction in a micromachined silicon chip, followed by an RT-qPCR molecular assay to detect SARS-CoV-2 shedding. Our portable, silicon impactor allowed for the efficient capture (>85%) of respiratory particles down to 300 nm without the need for additional equipment. We demonstrate using both conventional off-chip and in-situ PCR directly on the silicon chip that sampling subjects’ breath in less than a minute yields sufficient viral RNA to detect infections as early as standard sampling methods. A longitudinal study revealed clear differences in the temporal dynamics of viral load for nasopharyngeal swab, saliva, breath, and antigen tests. Overall, after an infection, the breath-based test remains positive during the first week but is the first to consistently report a negative result, putatively signalling the end of contagiousness and further emphasizing the potential of this tool to help manage the spread of airborne respiratory infections.

Numerical Analysis of Nasal Flow Characteristics with Microparticles.

This study was to investigate the airflow characteristics in nasal cavity under different conditions and analyze the effects of different respiratory intensity, particle diameter, and particle density on the deposition of particles carried by airflow in the nasal cavity, respectively. The three-dimensional geometric model of the nasal cavity was established based on typical medical images. The SST k-ω turbulence model in the computational fluid dynamics (CFD) was used to simulate the airflow in the nasal cavity, and the deposition of particles in the airflow was analyzed with the Lagrange discrete phase model. The results showed that the air in the nasal cavity flows in the left and right nasal passages through the perforation in front of the nasal septum and forms a vortex structure at the perforation site, and the particle deposition efficiencies (DE) under perforation nasal cavity are higher than that under normal nasal cavity. Different parameters had different effects on the particle DE. The results showed that the DE of particles with smaller size (≤2.5 μm) is lower; the higher the respiration intensity, the greater the influence on the DE of the larger particle size; and the larger particle density (>1550 kg·m−3) has little effect on the DE of larger particle size (DP = 10 μm). The results agree well with the corresponding research data.

The value of fractional exhaled nitric oxide in occupational diseases – a systematic review

Fractional exhaled nitric oxide (FeNO) is a non-invasive biomarker of respiratory tract inflammation, originally designated to identify eosinophilic airway inflammation and to predict steroid response. The main field of application of this biomarker is asthma, but FeNO has also been used for other allergic and non-allergic pulmonary disorders such as chronic obstructive pulmonary disease, hypersensitivity pneumonitis and interstitial lung disease. A substantial part of respiratory diseases are related to work, and FeNO, a safe and easy measure to conduct, is a potential valid examination in an occupational setting.This systematic review assesses the value of measuring FeNO related to three types of airborne exposures: allergens, irritants, and respiratory particles inhaled during occupational activities. The review covers results from longitudinal and observational clinical studies, and highlights the added value of this biomarker in monitoring effects of exposure and in the diagnostic criteria of occupational diseases. This review also covers the possible significance of FeNO as an indicator of the efficacy of interventions to prevent work-related respiratory diseases.Initially, 246 articles were identified in PUBMED and SCOPUS. Duplicates and articles which covered results from the general population, symptoms (not disease) related to work, non-occupational diseases, and case reports were excluded. Finally, 39 articles contributed to this review, which led to the following conclusions:a) For occupational asthma there is no consensus on the significant value of FeNO for diagnosis, or on the magnitude of change needed after specific inhalation test or occupational exposure at the workplace. There is some consensus for the optimal time to measure FeNO after exposure, mainly after 24 h, and FeNO proved to be more sensitive than spirometry in measuring the result of an intervention. b) For other occupational obstructive respiratory diseases, current data suggests performing the measurement after the work shift. c) For interstitial lung disease, the evaluation of the alveolar component of NO is probably the most suitable.

Towards understanding respiratory particle transport and deposition in the human respiratory system: Effects of physiological conditions and particle properties

Fly ash is a common solid residue of incineration plants and poses a great environmental concern because of its toxicity upon inhalation exposure. The inhalation health impacts of fly ash is closely related to its transport and deposition in the human respiratory system which warrants significant research for health guideline setting and inhalation exposure protection. In this study, a series of fly ash transport and deposition experiments have been carried out in a bifurcation airway model by optical aerosol sampling analysis. Three types of fly ash samples of different morphologies were tested and their respiratory deposition and transport processes were compared. The deposition efficiencies were calculated and relevant transport dynamics mechanisms were discussed. The influences of physiological conditions such as breathing rate, duration, and fly ash physical properties (size, morphology, and specific surface area) were investigated. The deposition characteristics of respiratory particles containing SARS-CoV-2 has also been analyzed, which could further provide some guidance on COVID-19 prevention. The results could potentially serve as a basis for setting health guidelines and recommending personal respiratory protective equipment for fly ash handlers and people who are in the high exposure risk environment for COVID-19 transmission.