RAPID: Characterization of Aerosolized Droplet and Droplet Nuclei in Cough

There is considerable interest in the behavior of cough-generated droplets in the environment due to evidence of host-to-host transmission of viruses through aerosolized droplets. Previous investigations have mostly focused on how such droplets interact with the external environment and not much has been explored on their behavior inside the body. Yet, the droplet behavior inside the airway largely determines their subsequent characteristics outside the body (such as size and dispersion), as well as their potential for retention inside the body to cause lung infection, pneumonia, aspiration, and mortality. It is also unknown whether people are at greater risk for pulmonary infection and pulmonary pneumonia if their cough is too weak to expel virus-laden droplets as may occur under some pre-existing conditions. The objective of this multidisciplinary research project is to combine computational modeling with experiments to fully understand the behavior of aerosolized cough droplets inside the human airway depending on the cough strength and assess the potential of virus-laden droplets to be retained in the airway or transmitted to the lungs. The research outcome will be clinically relevant to the development of technologies to minimize the spread of COVID-19, hospitalization, and death. The focus on droplet behavior inside the airway will be particularly relevant for elucidating the behavior of new COVID-19 strains which have been found to generate higher viral loads in the airway compared to the original strain, making the new strains much more contagious to others. The research will enable determination of how long these new variants reside in the airway, which will aid in the development of technologies that mitigate their potential transmission outside the body. An important component of the research is also the education of the next generation of scientists and engineers, especially those from under-represented groups by providing them an opportunity to work on a challenging multidisciplinary problem of public health significance.

Since the advent of the COVID-19 pandemic, most studies have understandably focused on the interaction of virus-laden cough droplets with the ambient environment. Yet, the behavior of droplets inside the airway largely determines their subsequent characteristics outside the body (such as size and transmission distance), as well as their potential for retention inside the body to cause lung infection, pneumonia, aspiration, and mortality. The role of cough strength in the retention of droplets laden with the new viral strains inside the airway with potential to cause serial environmental transmission has also not been fully explored. The objective of this multidisciplinary research project is to integrate Computational Fluid Dynamics with experiments to fully characterize the behavior of aerosolized droplets and nanoparticles relative to cough strength inside the human upper airway. The experiments for model calibration and validation will utilize a realistic three-dimensional-printed upper airway structure produced with a novel volumetric printing process. Cough will be simulated in the structure with fluorescein solution atomized to produce seed droplets. Droplet sizes will be quantified using a blue-light filter and digital image processing of endoscope images. The research will: (a) Quantify small droplet and nanoparticle interaction with the airway, in subjects with and without standard facemask; (b) Quantify droplet characteristics (size distribution, residence time, trajectories) within the airway under normal and disordered cough functions; (c) Quantify aspiration capacity and delayed transmission potential of droplets relative to cough strength; and (d) Validate the computational models using the experimental data. By establishing the fundamental features of droplet and nanoparticle interaction with cough flow and the airway, this project will deliver the strategies for characterization of complex nanoparticle behavior under cough flow in particular and transient explosive flow condition in general. The project outcome will be clinically relevant in the development of technologies to minimize the spread of COVID-19, hospitalization, and death. The focus on particle behavior inside the airway will be particularly relevant to exploring the behavior of new COVID-19 strains which have been found to generate higher viral loads in the nasal and oral cavities compared to the original strain, making the new strains much more contagious to others. The model developed will enable quantification of the residence times of these new variants and explore intervention technologies to mitigate their potential for transmission outside the body or aspiration pneumonia and lung infection. As the longer-term impact of post-COVID patients becomes better understood, the droplet behavior relative to cough strength will be an important risk marker as the micro aspirations that retain in the lung tissue can result in lung infection, pneumonia, or death. The sequence of symptoms and other comorbidities occurring in post-COVID patients amplify the significance of the aspiration event being investigated. This research will also assist the development of respiratory intervention technologies to improve deficits of cough function in patients with pre-existing conditions such as post-stroke individuals, sedentary elderly or those who have undergone cancer related treatment. The education objective of the research will focus on educating the next generation of scientists and engineers, especially those from under-represented groups by providing them an opportunity to work on a challenging multidisciplinary problem of public health significance. The research findings will be integrated directly in two undergraduate courses and two graduate courses taught by the PIs.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.