Respirable Droplets Research Articles

Impact of respiratory aerosol size and number distribution on the relative importance of different routes in SARS-CoV-2 transmission.

Exploring the relative importance of different routes in SARS-CoV-2 transmission is crucial in infection prevention. However, even in the same environmental setting, the relative importance of different routes has varied in different studies. We hypothesize that respiratory aerosol size and number distribution might play a key role. In this study, size and number distribution of respiratory droplets emitted from breathing, talking, and coughing were identified from PubMed and Web of Science. The infection risk of SARS-CoV-2 via airborne, droplet, and fomite transmission routes was modeled in a household and a healthcare setting. The relative importance of three routes varied with different size distributions in both settings. Generally, the contribution of the airborne route increased with the volume percentage of respirable droplets emitted. And the increase of the total number of emitted droplets leads to an increase in the contribution of tdroplet route. In the healthcare setting, as the total number of emitted droplets increased from 110 to 4,973, the contribution of droplet route increased from 62.24% to 98.11%. Next, by considering the combination of breathing, coughing, and talking when the infected person was asymptomatic, the airborne route predominated over the droplet and contact routes. When the infected person had developed symptoms, that is, cough, the droplet route played a dominant role in SARS-CoV-2 transmission. In conclusion, risk analyses will be improved with improved sampling methods that enable characterization of viruses within respiratory droplets of different sizes.

Ultrasonic scaling in COVID‐era dentistry: A quantitative assessment of aerosol spread during simulated and clinical ultrasonic scaling procedures

ObjectiveHealthcare agencies recommend limited use of aerosol‐generating procedures to mitigate disease (COVID‐19) transmission. However, total dispersion patterns of aerosols, particularly respirable droplets, via dental ultrasonic units is unclear. The purpose of this study was to characterize and map total spatter, droplet and aerosol dispersion during ultrasonic scaling in simulated and clinical contexts.MethodsUltrasonic scaling was performed on dental simulation units using methylene blue dye‐stained water. All resultant stain profiles were photoanalysed to calculate droplet size and travel distance/direction. Airborne particle concentrations were also documented 0–1.2 m (0–4ft.) and 1.2–2.4 m (4–8ft.) from patients during in vivo ultrasonic scaling with a saliva ejector.ResultsStain profiles showed droplets between 25 and 50µm in diameter were most common, with smaller droplets closer to the mouth. In‐vivo particle concentrations were uniformly low. The smallest (<1 µm, PM1) and largest (>10 µm, PM10+) particles were most common, especially within 1.2 m (4ft.) of the patient. Respirable particles (PM2.5) were uncommon.ConclusionsTests showed the highest concentration of small droplets in zones nearest the patient. While uncommon, particles were detected up to 2.4 m (8ft.) away. Furthermore, observed particle sizes were consistent with those that can carry infectious agents. Efforts to mitigate the spread of inhalable aerosols should emphasize proximate regions nearest the procedure, including personal protective equipment and the use of evacuation devices.

Thermal effect of human body on cough droplets evaporation and dispersion in an enclosed space

This study numerically investigated the thermal effect of human body on the time-dependent dispersion of cough droplets with evaporation process. The thermal flow of human body was imitated using a 3D thermal manikin with real body features, while a recent developed multi-component Eulerian-Lagrangian approach was used to address the effects of inhomogeneous temperature and humidity fields on droplet evaporation. By comparing the results yielded without and with the human body heat, the outcomes demonstrated strong impact of human body heat on the droplets mass fraction and local air velocity distributions. Inspirable droplets could potentially drop into respirable droplets by evaporation, although the evaporation rate was not significantly affected by body heat. The thermal effect of human body revealed its vital impacts on the time-dependent droplets dispersion. Due to the buoyancy driven thermal flow, both the vertical velocity and displacement of small droplets (≤20 μm) were completely reversed from descending to ascending, while the deposition time of large droplets (≥50 μm) were significantly delayed. With the reduced droplet size by evaporation and droplets lifted into breathing zone by human thermal effect, the inhalability and infection risks of cough droplets would be much higher in real occupied indoor spaces.

Aerosolization of respirable droplets from a domestic spa pool and the use of MS-2 coliphage and Pseudomonas aeruginosa as markers for Legionella pneumophila.

Legionnaires' disease can result when droplets or aerosols containing legionella bacteria are inhaled and deposited in the lungs. A number of outbreaks have been associated with the use of a spa pool where aeration, a high water temperature, and a large and variable organic load make disinfectant levels difficult to maintain. Spa pool ownership is increasing, and the aim of this study, using two surrogate organisms (MS-2 coliphage and Pseudomonas aeruginosa [a natural contaminant]), was to assess the potential risk to domestic users when disinfection fails. A representative "entry level" domestic spa pool was installed in an outdoor courtyard. The manufacturer's instructions for spa pool maintenance were not followed. A cyclone sampler was used to sample the aerosols released from the spa pool with and without activation of the air injection system. Samples were taken at increasing heights and distances from the pool. An aerodynamic particle sizer was used to measure the water droplet size distribution at each sample point. When the air injection system was inactivated, neither surrogate organism was recovered from the air. On activation of the air injection system, the mean mass of droplets within the respirable range (10 cm above the water line) was 36.8 μg cm(-3). This corresponded to a mean air concentration of P. aeruginosa of 350 CFU m(-3). From extrapolation from animal data, the estimated risk of infection from aerosols contaminated with similar concentrations of Legionella pneumophila was 0.76 (males) and 0.65 (females). At 1 m above and/or beyond the pool, the mean aerosol mass decreased to 0.04 μg cm(-3) and corresponded to a 100-fold reduction in mean microbial air concentration. The estimated risk of infection at this distance was negligible.

Eye Surface Area and Dosage Rates for Spray Vaccination

Spray application of Mycoplasma gallisepticum (MG) vaccines is a labor- and time-saving means of mass vaccination of layer chickens. Recent assessment of spray characteristics of nozzles commonly used to apply MG vaccine in layer chicken operations has shown that the amount of respirable droplets (< 5 microm) is negligible. Topical application of vaccine onto the eye surface has been suggested as a route of vaccination, but no estimates of vaccine load delivered via spray application were found in the literature. Estimates of eye surface area were developed using digital imaging; 24 layer pullets were used for analysis, and the mean eye surface area, corrected for corneal curvature, was found to be 0.609 cm2. This surface area was then used to estimate vaccine load for commercially available live MG vaccine sprayed through popular nozzles. Less than 3000 colony-forming units can be expected for direct deposition onto the surface of an eye.

Dynamics of infectious disease transmission by inhalable respiratory droplets.

Transmission of respiratory infectious diseases in humans, for instance influenza, occurs by several modes. Respiratory droplets provide a vector of transmission of an infectious pathogen that may contribute to different transmission modes. An epidemiological model incorporating the dynamics of inhalable respiratory droplets is developed to assess their relevance in the infectious process. Inhalable respiratory droplets are divided into respirable droplets, with droplet diameter less than 10 microm, and inspirable droplets, with diameter in the range 10-100 microm: both droplet classes may be inhaled or settle. Droplet dynamics is determined by their physical properties (size), whereas population dynamics is determined by, among other parameters, the pathogen infectivity and the host contact rates. Three model influenza epidemic scenarios, mediated by different airborne or settled droplet classes, are analysed. The scenarios are distinguished by the characteristic times associated with breathing at contact and with hand-to-face contact. The scenarios suggest that airborne transmission, mediated by respirable droplets, provides the dominant transmission mode in middle and long-term epidemics, whereas inspirable droplets, be they airborne or settled, characterize short-term epidemics with high attack rates. The model neglects close-contact transmission by droplet sprays (direct projection onto facial mucous membranes), retaining close-contact transmission by inspirable droplets.

Pulmonary delivery of scutellarin solution and mucoadhesive particles in rats

The objectives of this study were to investigate the effects of mucoadhesive excipients on systemic bioavailability of an inhaled drug and to evaluate the feasibility of using the pulmonary route for non-invasive systemic delivery of scutellarin, a poorly orally absorbed flavonoid glucuronide. Following intratracheal spray of the scutellarin solution, the bioavailability was found to be approximately 77% in rats, which was >30-fold higher than that via the peroral route. In addition, the pulmonary absorption of scutellarin appeared to avoid the intestinal first-pass metabolism accompanied by peroral administration. Spray-dried scutellarin particles with the presence of mucoadhesive excipients were found to affect the corresponding mucociliary transport rate (MTR) as evaluated by a frog palate model. The pharmacokinetic results indicated that the magnitude of AUC 0–480 of intrapulmonary delivered drug particles was not correlated to the fine particle fraction (FPF) but inversely related to the MTR. Incorporating mucoadhesive polymeric mixtures into the scutellarin particles, the MTR decreased by sixfold, and the absolute bioavailability of the drug was found to increase from 70.1% to 97.9% despite a decrease in the FPF. Moreover, in vitro results evaluated using Calu-3 and A549 cell lines showed that scutellarin and spray-dried particles with or without the presence of mucoadhesives exhibited no local cell cytotoxic effects in the tested concentration range. In conclusion, the conducting airway is well permeable to scutellarin, and scutellarin may be effectively delivered systemically through inhalation of respirable droplets or particles.

Current Therapies and Technological Advances in Aqueous Aerosol Drug Delivery

Recent advances in aerosolization technology have led to renewed interest in pulmonary delivery of a variety of drugs. Pressurized metered dose inhalers (pMDIs) and dry powder inhalers (DPIs) have experienced success in recent years; however, many limitations are presented by formulation difficulties, inefficient delivery, and complex device designs. Simplification of the formulation process as well as adaptability of new devices has led many in the pharmaceutical industry to reconsider aerosolization in an aqueous carrier. In the acute care setting, breath-enhanced air-jet nebulizers are controlling and minimizing the amount of wasted medication, while producing a high percentage of respirable droplets. Vibrating mesh nebulizers offer advantages in higher respirable fractions (RFs) and slower velocity aerosols when compared with air-jet nebulizers. Vibrating mesh nebulizers incorporating formulation and patient adaptive components provide improvements to continuous nebulization technology by generating aerosol only when it is most likely to reach the deep lung. Novel innovations in generation of liquid aerosols are now being adapted for propellant-free pulmonary drug delivery to achieve unprecedented control over dose delivered and are leading the way for the adaptation of systemic drugs for delivery via the pulmonary route. Devices designed for the metered dose delivery of insulin, morphine, sildenafil, triptans, and various peptides are all currently under investigation for pulmonary delivery to treat nonrespiratory diseases. Although these devices are currently still in clinical testing (with the exception of the Respimat®), metered dose liquid inhalers (MDLIs) have already shown superior outcomes to current pulmonary and systemic delivery methods.

Particle Size Distribution and Inhalation Dose of Shower Water Under Selected Operating Conditions

Showering produces respirable droplets that may serve to deposit pollutants such as trihalomethane decontamination products, heavy metals, inorganic salts, microbes, or cyanoacterial toxins within the respiratory tract. The extent and importance of this route of indoor exposure depend on the physical characteristics of the aerosol as well as the pollutant profile of the source water. The purpose of this study was to characterize shower-generated aerosols as a function of water flow rate, temperature, and bathroom location. Aerosols were generated within a shower stall containing a mannequin to simulate the presence of a human. Using hot water, the mass median diameter (MMD) of the droplets inside the shower and in the bathroom were 6.3–7.5 um and 5.2–6 μm, respectively. Size was independent of water flow rate. The particle concentration inside the shower ranged from 5 to 14 mg/m3. Aerosols generated using cold water were smaller (2.5–3.1 μm) and concentrations were lower (0.02–0.1 mg/m3) inside the shower stall. No aerosols were detected in the bathroom area when cold water was used. The International Commission on Radiological Protection model was used to estimate water deposition in the respiratory tract. For hot water, total deposition ranged from 11 to 14 mg, depending on water flow rate, with approximately 50% of this deposited in the extrathoracic region during assumed mouth breathing, and greater than 86% when nose breathing was assumed. Alveolar deposition was 6–10% and 0.9% assuming oral and nasal breathing, respectively. The consequences deposition of shower water droplets will depend on the nature and extent of any pollutants in the source water.

Twenty-eight-day repeated-dose inhalation exposure of rats to diethylene glycol monoethyl ether.

This study was carried out to provide information on the effects of inhalation of diethylene glycol monoethyl ether, a substance used in industry which may be accidentally inhaled by man. Sprague-Dawley CD rats were exposed by inhalation to a test atmosphere containing diethylene glycol monoethyl ether in a nose-only exposure system for 6 hr a day, 5 days a week for 28 days. Mean exposure levels were 0. 09, 0.27, and 1.1 mg/liter. At the two lowest exposure levels the test substance was present entirely as vapor, but at the highest exposure level the test atmosphere was approximately equally divided by mass into respirable droplets (aerosol) and vapor. A comprehensive battery of toxicological evaluations including food consumption, body weight, clinical signs, hematology, and biochemistry revealed no evidence of a systemic effect of exposure. Histopathological examination showed changes indicative of mild nonspecific irritation in the upper respiratory tract of rats exposed at the two highest exposure levels. These changes consisted of foci of necrosis in the ventral cartilage of the larynx of rats exposed at 0.27 or 1.1 mg/liter and an increase in eosinophilic inclusions in the olfactory epithelium of the nasal mucosa of rats exposed at 1.1 mg/liter. The no observed adverse effect level for systemic effects was 1.1 mg/liter and the no observed adverse effect level for signs indicative of mild nonspecific irritation of the upper respiratory tract was 0.09 mg/liter.

A new mask filter cartridge used to determine applicator inhalation exposure to an alachlor herbicide (Lasso) during normal spraying operations.

A filter cartridge with a low air-flow resistance was designed for use on a modified half-face respirator worn during the application of alachlor (Lasso) herbicide. The filter trapped large concentrations of alachlor while retaining the ability to trap small respirable droplets. Moreover, alachlor could be recovered from the disassembled cartridge and analyzed by conventional methods. The test cartridges were used in combination with conventional personal air samplers to determine whether the filters trapped more alachlor when compared with personal samplers and to determine accurately the amount of alachlor reaching the breathing zone. Farmers sprayed alachlor in the form of alachlor (N = 7) or alachlor mixed with other herbicides or surfactant (N = 15). An average of 4 x 10(-2) mg or 2 x 10(-4) mg/kg of applied alachlor reached the respirator filters. This concentration was 10-fold higher than the alachlor recovered from the personal samplers. The new filter cartridge is better for determining the amount of alachlor reaching the breathing zone, and there is a low potential for significant inhalation exposure to alachlor during normal spraying operations.

A Signal Actuated Nebulizer for Use with Breathing Machines

A nebulizer system has been developed to provide aerosol therapy for seriously ill patients whose breathing is being assisted by mechanical ventilators or breathing machines. This system uses an electrical valve operated Vortran nebulizer nozzle, a 250 mL reservoir (with temperature bath) for protracted operation, and an intermittent electrical signal obtained from the breathing machine for synchronization. There is a built-in air-operated magnetic stlrrer in the nebulizer reservoir to provide uniform nebulization over extended periods of operation for suspensions, colloids, and liposomes in aqueous preparations. This Vortran Intermittent Signal Actuated Nebulizer (VISAN) operates using compressed air or oxygen-enriched air (50 psig) nebulization of respirable droplets (smaller than 3.5 pm MMAD) with concentrations up to 35 μL/L at flow rates up to 300 mL/s, for operating periods as short as 0.5 s. Triple nozzle units can be used to achieve flows up to 800 mL/s. The VISAN generates aerosol only when actuated during the inhalation phase of the breathing cycle, so that the aerosol generation, ventilator flow, and patient inhalation are perfectly synchronized. The airflow from the ventilator passes through the nebulizer system and serves to carry the aerosol to the patient. Up to about 50% of the tidal volume is usually supplied by the nebulizer to maximize total dosage of medication during each tidal breath. The establishment of the desired operating conditions for the nebulizer depends upon the inspiratory time, tidal volume, and appropriate aerosol and ventilator shares of the volume. Inspiratory time and tidal volume are related to the desired breathing rate, the proportion of the breathing cycle associated with inspiration, and the minute volume.

Respirable droplets from whirlpools: Measurements of size distribution and estimation of disease potential

Droplets generated from water surfaces have been implicated in a number of diseases such as Legionnaires' disease and Pontiac fever. These droplets can be inhaled by people and can deposit in the respiratory system. The physical size of the droplets is critical in determining whether the droplets can contain the bacteria, reach the breathing zone of the subject, and deposit in the respiratory tract. The present study establishes the presence of water droplets above the surface of health club whirlpools. These droplets are of the appropriate size for causing respiratory disease. Several factors including pool temperature, bubbling action during operation, and height above the water surface have been investigated. The results are related to the deposition of the droplets, and hence bacteria, in the various regions of the respiratory tract.

Occupational exposure and drift hazard during aerial application of paraquat to cotton.

Two worker-exposure and drift trials were conducted during the aerial application of paraquat to cotton in California, USA. The dermal and respiratory exposure of pilots, flaggers, and a mixer-loader was shown to be low. Dermal exposure ranged from 0.05 (pilot) to 2.39 (flagger) mg/ hr. The dermal exposure of the mixer-loader was similar to that of the pilots. No respirable paraquat was detected in the breathing zone of any worker. The highest total paraquat concentration was 26.3 μg/m3 for a flagger, which is a factor of 19 less than the TLV for total paraquat. The combined dermal and respiratory exposure of this flagger was equivalent to 19.4 mg/8hr working day. Paraquat drift concentrations decreased with increasing distance downwind of the spray application. The highest concentrations of total and respirable paraquat were 16.7 and 0.15 μg/m3 at 50 m from the application site perimeter. The respective concentrations at 1600 m downwind were 0.5 and 0.01 μg/m3. Measurement of the particle size distribution of paraquat drift showed that 0.95 to 1.96% of spray droplets was within the respirable range at all distances downwind. The highest percentage of respirable droplets was equivalent to 1.2 (μg paraquat, which was measured at 400 m downwind. Respirable fractions of 1 and 0.95% were measured at 50 and 100 m downwind, which represented 1.8 μg paraquat. There was no evidence, therefore, of a toxic hazard to pilots, ground crew, and downwind bystanders, as a consequence of the aerial application of paraquat.