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  1. Abstract

    How human respiratory physiology and the transport phenomena associated with inhaled airflow in the upper airway proceed to impact transmission of SARS-CoV-2, leading to the initial infection, stays an open question. An answer can help determine the susceptibility of an individual on exposure to a COVID-2019 carrier and can also provide a preliminary projection of the still-unknown infectious dose for the disease. Computational fluid mechanics enabled tracking of respiratory transport in medical imaging-based anatomic domains shows that the regional deposition of virus-laden inhaled droplets at the initial nasopharyngeal infection site peaks for the droplet size range of approximately 2.5–19$$\upmu $$μ. Through integrating the numerical findings on inhaled transmission with sputum assessment data from hospitalized COVID-19 patients and earlier measurements of ejecta size distribution generated during regular speech, this study further reveals that the number of virions that may go on to establish the SARS-CoV-2 infection in a subject could merely be in the order of hundreds.

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  2. Passive filtering is a common strategy to reduce airborne disease transmission and particulate contaminants across scales spanning orders of magnitude. The engineering of high-performance filters with relatively low flow resistance but high virus- or particle-blocking efficiency is a non-trivial problem of paramount relevance, as evidenced in the variety of industrial filtration systems and face masks. Next-generation industrial filters and masks should retain sufficiently small droplets and aerosols while having low resistance. We introduce a novel 3D-printable particle filter inspired by animals’ complex nasal anatomy. Unlike standard random-media-based filters, the proposed concept relies on equally spaced channels with tortuous airflow paths. These two strategies induce distinct effects: a reduced resistance and a high likelihood of particle trapping by altering their trajectories with tortuous paths and induced local flow instability. The structures are tested for pressure drop and particle filtering efficiency over different airflow rates. We have also cross-validated the observed efficiency through numerical simulations. We found that the designed filters exhibit a lower pressure drop, compared to commercial masks and filters, while capturing particles bigger than approximately 10 μm. Our findings could facilitate a novel and scalable filter concept inspired by animal noses. 
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  3. Background: While the nasopharynx is initially the dominant upper airway infection site for SARS-CoV-2, the physiologic mechanism launching the infection at the lower airway is still not well-understood. Based on the rapidity of infection progression to the lungs, it has been hypothesized that the nasopharynx may be acting as the primary seeding zone for subsequent contamination of the lower airway via aspiration of virus-laden boluses of nasopharyngeal fluids. Methodology: To examine the plausibility of the aspiration-driven mechanism, we have computationally tracked the inhalation process in three anatomic airway reconstructions and have quantified the nasopharyngeal liquid volume transmitted to the lower airspace during each aspiration. Results: Extending the numerical trends on aspiration volume to earlier records on aspiration frequencies indicates a total aspirated nasopharyngeal liquid volume of 0.3 – 0.76 ml/day. Subsequently, for mean sputum viral load, our modeling projects that the number of virions reaching the lower airway will range over 2.1×106 – 5.3×106 /day; for peak viral load, the corresponding number hovers between 7.1×108 – 1.8×109. Conclusions: The virion transmission findings fill in a key piece of the mechanistic puzzle on the systemic progression of SARS-CoV-2, and subjectively point to health conditions like dysphagia, with proclivity to increased aspiration, as some of the potential underlying risk factors for aggressive lung infections. 
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  4. Backgroud The nasal route of targeted drug administration facilitates medical management of chronic and acute onsets of various respiratory conditions such as rhinitis and sinusitis and during the initial onset phase of severe acute respiratory syndrome coronavirus 2, when the infection is still contained within the upper airway. Nevertheless, patient comfort issues that are often associated with intranasal devise usage can lead to low compliance, thereby compromising treatment efficacy. Hence, there is an urgent need to detect reproducible and user-friendly intranasal drug delivery modalities that may promote adoption compliance and yet be effective at targeted transport of drugs to the infective airway regions. Methods In this pilot study, we have collected evaluation feedback from a cohort of 13 healthy volunteers, who used an open-angle swirling effect atomizer to assess two different nasal spray administration techniques (with 0.9% saline solution), namely the vertical placement protocol (or, VP), wherein the nozzle is held vertically upright at a shallow insertion depth of 0.5 cm inside the nasal vestibule; and the shallow angle protocol (or, SA), wherein the spray axis is angled at 45° to the vertical, with a vestibular insertion depth of 1.5 cm. The VP protocol is based on current usage instructions, while the SA protocol is derived from published findings on alternate spray orientations that have been shown to enhance targeted drug delivery at posterior infection sites, e.g., the ostiomeatal complex and the nasopharynx. Results All study participants reported that the SA protocol offered a more gentle and soothing delivery experience, with less impact pressure. Additionally, 60% of participants reported that the VP technique caused painful irritation. We also numerically tracked the drug transport processes for the two spray techniques in a computed tomography-based nasal cavity reconstruction; the SA protocol registered a distinct improvement in airway penetration when compared to the VP protocol. Conclusion The participant-reported unequivocally favorable experience with the new SA protocol justifies a full-scale clinical study aimed at testing the related medication compliance parameters and the corresponding therapeutic efficacies. 
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