SARS-CoV-2 droplet deposition path and its effects on the human upper airway in the oral inhalation

Scale resolving simulations of the effect of glottis motion and the laryngeal jet on flow dynamics during respiration

BACKGROUND AND OBJECTIVE

The movement of the respiratory walls has a significant impact on airflow through the respiratory tract. The majority of computational fluid dynamics (CFD) studies assume a static geometry which may not provide a realistic flow field. Furthermore, many studies use Reynolds Averaged Navier-Stokes (RANS) turbulence models that do not resolve turbulence structure. Combining the application of advanced scale-resolving turbulence models with moving respiratory walls using CFD will provide detailed insights into respiratory flow structures.

METHODS

This study simulated a complete breathing cycle involving inhalation and exhalation in a nasal cavity to trachea geometry that incorporated moving glottis walls. A second breathing cycle was simulated with static glottis walls for comparison. A recently developed hybrid RANS-LES turbulence model, the Stress-Blended Eddy Simulation (SBES), was incorporated to resolve turbulent flow structures in fine detail for both transient simulations. Transient results were compared with steady-state RANS simulations for the same respiratory geometry.

RESULTS

Glottis motion caused substantial effects on flow structure through the complete breathing cycle. Significant flow structure and velocity variations were observed due to glottal motion, primarily in the larynx and trachea. Resolved turbulence structures using SBES showed an intense mixing section in the glottis region during inhalation and in the nasopharynx during expiration, which was not present in the RANS simulations.

CONCLUSION

Transient simulations of a realistic breathing cycle uncovered flow structures absent in simulations with a constant flow rate. Furthermore, the incorporation of glottis motion impacted airflow characteristics that suggest rigid respiratory walls do not accurately describe respiratory flow. Future research in respiratory airflow should be conducted using transient scale-resolving models in conjunction with moving respiratory walls to capture flow structures in detail.

Visual prediction and parameter optimization of viral dynamics in the mucus milieu of the upper airway based on CFPD-HCD analysis

BACKGROUND AND OBJECTIVE

Respiratory diseases caused by viruses are a major human health problem. To better control the infection and understand the pathogenesis of these diseases, this paper studied SARS-CoV-2, a novel coronavirus outbreak, as an example.

METHODS

Based on coupled computational fluid and particle dynamics (CFPD) and host-cell dynamics (HCD) analyses, we studied the viral dynamics in the mucus layer of the human nasal cavity-nasopharynx. To reproduce the effect of mucociliary movement on the diffusive and convective transport of viruses in the mucus layer, a 3D-shell model was constructed using CT data of the upper respiratory tract (URT) of volunteers. Considering the mucus environment, the HCD model was established by coupling the target cell-limited model with the convection-diffusion term. Parameter optimization of the HCD model is the key problem in the simulation. Therefore, this study focused on the parameter optimization of the viral dynamics model, divided the geometric model into multiple compartments, and used Monolix to perform the nonlinear mixed effects (NLME) of pharmacometrics to discuss the influence of factors such as the number of mucus layers, number of compartments, diffusion rate, and mucus flow velocity on the prediction results.

RESULTS

The findings showed that sufficient experimental data can be used to estimate the corresponding parameters of the HCD model. The optimized convection-diffusion case with a two-layer multi-compartment low-velocity model could accurately predict the viral dynamics.

CONCLUSIONS

Its visualization process could explain the symptoms of the disease in the nose and contribute to the prevention and targeted treatment of respiratory diseases.

Mechanisms, Techniques and Devices of Airborne Virus Detection: A Review

Airborne viruses, such as COVID-19, cause pandemics all over the world. Virus-containing particles produced by infected individuals are suspended in the air for extended periods, actually resulting in viral aerosols and the spread of infectious diseases. Aerosol collection and detection devices are essential for limiting the spread of airborne virus diseases. This review provides an overview of the primary mechanisms and enhancement techniques for collecting and detecting airborne viruses. Indoor virus detection strategies for scenarios with varying ventilations are also summarized based on the excellent performance of existing advanced comprehensive devices. This review provides guidance for the development of future aerosol detection devices and aids in the control of airborne transmission diseases, such as COVID-19, influenza and other airborne transmission viruses.

Biomechanical analysis of tracheal stent during cough reflex

Tracheal stenting is a common method which is widely used to cure different tracheal disorders including airways stenosis, chronic coughs, and accidents. In this study, we aimed to analyze the reaction of the trachea wall to exhale in three phases of light, moderate, and vigorous activities at air flows of 15 L/min (light), 26 L/min (medium), and 30 L/min (vigorous). Fluid structure interaction (FSI) was used for the numerical analysis using computed tomography (CT) images. The flow was assumed incompressible and turbulent. The stent is silicone with a Young’s modulus equal to 1 MPa, Poisson’s ratio 0.28, and density of 2330 kg/m3. The stent length was 60 mm and fix support boundary condition was applied for all inputs and outputs. Numerical simulation was performed using ANSYS software. The induced stresses, strains, wall deformation, flow pressure, and the flow velocity were obtained. The results showed that the stent prevented the local deformation of the wall of trachea and it reduced the induced strain in the position. But the stenting could lead to stress concentration. Finally, the stent prevented the damage to the trachea muscles during coughs in row.

Safe Distance of Virus Quantitative Analysis and Simulation of the Trajectory of Pathogen-Containing Droplets in the Air Respiratory Airways

Droplets of mucosalivary ejecta emitted by sneezing or coughing are a major carrier of numerous types of bacterial and viral diseases. This study develops a numerical model to estimate the spread distance for inhalable droplets (1–50 μm) in the air, the inhalability of the particles, and the trajectory as well as velocity of these pathogen-containing droplets in human respiratory airways. Moreover, particularly for droplets with diameters of 1 μm, 5 μm, 10 μm, and 50 μm, specific comparisons between their inhalability and transmission velocities are made. Data extracted from previous experiments proceeded by other researchers discussing the visualization of sneeze ejecta and deposition features of inhaled drops were used to obtain parameters to fit the model prediction of this work. Currently, research on similar topics was mostly based on either experiments or theoretical calculations only on one specific clan of pathogen, while the novel contribution of this paper is the combination and comparison of these two distinct methodologies that can be applied to solve a general practical problem aiming to all types of viruses by considering the pathogen-containing droplets as a whole entity.

Prediction and control of aerosol transmission of SARS-CoV-2 in ventilated context: from source to receptor

Global spread of COVID-19 has seriously threatened human life and health. The aerosol transmission route of SARS-CoV-2 is observed often associated with infection clusters under poorly ventilated environment. In the context of COVID-19 pandemic, significant transformation and optimization of traditional ventilation systems are needed. This paper is aimed to offer better understanding and insights into effective ventilation design to maximize its ability in airborne risk control, for particularly the COVID-19. Comprehensive reviews of each phase of aerosol transmission of SARS-CoV-2 from source to receptor are conducted, so as to provide a theoretical basis for risk prediction and control. Infection risk models and their key parameters for risk assessment of SARS-CoV-2 are analyzed. Special focus is given on the efficacy of different ventilation strategies in mitigating airborne transmission. Ventilation interventions are found mainly impacting on the dispersion and inhalation phases of aerosol transmission. The airflow patterns become a key factor in controlling the aerosol diffusion and distribution. Novel and personalized ventilation design, effective integration with other environmental control techniques and resilient HVAC system design to adapt both common and epidemic conditions are still remaining challenging, which need to be solved with the aid of multidisciplinary research and intelligent technologies.

Biomedical and biophysical limits to mathematical modeling of pulmonary system mechanics: a scoping review on aerosol and drug delivery

Undoubtedly, the construction of the biomechanical geometry systems with the help of computer tomography (CT) and magnetic resonance imaging (MRI) has made a significant advancement in studying in vitro numerical models as accurately as possible. However, some simplifying assumptions in the computational studies of the respiratory system have caused errors and deviations from the in vivo actual state. The most important of these hypotheses is how to generate volume from the point cloud exported from CT or MRI images, not paying attention to the wall thickness and its effect in computational fluid dynamic method, statistical logic of aerosol trap in software; and most importantly, the viscoelastic effect of respiratory tract wall in living tissue pointed in the fluid–structure interaction method. So that applying the viscoelastic dynamic mesh effect in the form of the moving deforming mesh can be very effective in achieving more appropriate response quality. Also, changing the volume fraction of the pulmonary extracellular matrix constituents leads to changes in elastic modulus (storage modulus) and the viscous modulus (loss modulus) of lung tissue. Therefore, in the biomedical computational methods where the model wall is considered flexible, the viscoelastic properties of the texture must be considered correctly.

SARS CoV-2 aerosol: How far it can travel to the lower airways?

The recent outbreak of the SARS CoV-2 virus has had a significant effect on human respiratory health around the world. The contagious disease infected a large proportion of the world population, resulting in long-term health issues and an excessive mortality rate. The SARS CoV-2 virus can spread as small aerosols and enters the respiratory systems through the oral (nose or mouth) airway. The SARS CoV-2 particle transport to the mouth-throat and upper airways is analyzed by the available literature. Due to the tiny size, the virus can travel to the terminal airways of the respiratory system and form a severe health hazard. There is a gap in the understanding of the SARS CoV-2 particle transport to the terminal airways. The present study investigated the SARS CoV-2 virus particle transport and deposition to the terminal airways in a complex 17-generation lung model. This first-ever study demonstrates how far SARS CoV-2 particles can travel in the respiratory system. ANSYS Fluent solver was used to simulate the virus particle transport during sleep and light and heavy activity conditions. Numerical results demonstrate that a higher percentage of the virus particles are trapped at the upper airways when sleeping and in a light activity condition. More virus particles have lung contact in the right lung than the left lung. A comprehensive lobe specific deposition and deposition concentration study was performed. The results of this study provide a precise knowledge of the SARs CoV-2 particle transport to the lower branches and could help the lung health risk assessment system.

Experimental tracking and numerical mapping of novel coronavirus micro-droplet deposition through nasal inhalation in the human respiratory system

It is essential to study the viral droplet’s uptake in the human respiratory system to better control, prevent, and treat diseases. Micro-droplets can easily pass through ordinary respiratory masks. Therefore, the SARS-COV-2 transmit easily in conversation with a regular mask with 'silent spreaders' in the most physiological way of breathing through the nose, indoor and at rest condition. The results showed that the amount of deposited micro-droplets in the olfactory epithelium area is low. Also, due to receptors and long droplet residence time in this region, the possibility of absorption increases in the cribriform plate. This phenomenon eventually could lead to brain lesion damage and, in some cases, leads to stroke. In all inlet flow rates lower than 30 L/min inlet boundary conditions, the average percentage of viral contamination for upper respiratory tract is always less than 50% and more than 50% for the lungs. At 6L/min and 15L/min flow rates, the average percentage of lung contamination increases to more than 87%, which due to the presence of the Coronavirus receptor in the lungs, the involvement of the lungs increases significantly. This study's other achievements include the inverse relationship between droplets deposition efficiency in some parts of the upper airway, which have the most deformation in the tract. Also, the increased deformities per minute applied to the trachea and nasal cavity, which is 1.5 times more than usual, could lead to chest and head bothers.