The effect of respiratory activity, non‐invasive respiratory support and facemasks on aerosol generation and its relevance to COVID‐19

  1. N. M. Wilson
  2. G. B. Marks
  3. A. Eckhardt
  4. A. M. Clarke
  5. F. P. Young
  6. F. L. Garden
  7. W. Stewart
  8. T. M. Cook
  9. E. R. Tovey

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Abstract

Respirable aerosols (< 5 µm in diameter) present a high risk of SARS‐CoV‐2 transmission. Guidelines recommend using aerosol precautions during aerosol‐generating procedures, and droplet (> 5 µm) precautions at other times. However, emerging evidence indicates respiratory activities may be a more important source of aerosols than clinical procedures such as tracheal intubation. We aimed to measure the size, total number and volume of all human aerosols exhaled during respiratory activities and therapies. We used a novel chamber with an optical particle counter sampling at 100 l.min ‐1 to count and size‐fractionate close to all exhaled particles (0.5–25 µm). We compared emissions from ten healthy subjects during six respiratory activities (quiet breathing; talking; shouting; forced expiratory manoeuvres; exercise; and coughing) with three respiratory therapies (high‐flow nasal oxygen and single or dual circuit non‐invasive positive pressure ventilation). Activities were repeated while wearing facemasks. When compared with quiet breathing, exertional respiratory activities increased particle counts 34.6‐fold during talking and 370.8‐fold during coughing (p < 0.001). High‐flow nasal oxygen 60 at l.min ‐1 increased particle counts 2.3‐fold (p = 0.031) during quiet breathing. Single and dual circuit non‐invasive respiratory therapy at 25/10 cm.H 2 O with quiet breathing increased counts by 2.6‐fold and 7.8‐fold, respectively (both p < 0.001). During exertional activities, respiratory therapies and facemasks reduced emissions compared with activities alone. Respiratory activities (including exertional breathing and coughing) which mimic respiratory patterns during illness generate substantially more aerosols than non‐invasive respiratory therapies, which conversely can reduce total emissions. We argue the risk of aerosol exposure is underappreciated and warrants widespread, targeted interventions.

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  1. Version published to 10.1111/anae.15475
  2. ScreenIT

    SciScore for 10.1101/2021.02.07.21251309: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board StatementIRB: The protocol was approved by the South Eastern Sydney Ethics Committee (ETH01467/2020) and written consent obtained.
    Consent: The protocol was approved by the South Eastern Sydney Ethics Committee (ETH01467/2020) and written consent obtained.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.

    Table 2: Resources

    No key resources detected.

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    There are several limitations to our study. We recruited ten healthy subjects who performed a single protocol run. There may have been some differences in how subjects performed activities, limiting the interpretation of the previously observed wide inter-subject variation.25,30 We estimated the average residence time for particles in the cone should have largely been sufficient for them to reach equilibrium diameter.40 However, given wide variation between activity airflows, volumes and the addition of humidified therapy gases, we are unsure exactly what proportion of variation in size distributions is physiological or methodological. Our post-hoc study shows cough and FEV are modestly incompletely sampled, highlighting the most aerosol generating activities are also the most challenging to comprehensively measure due to high airflow velocities. Our attempts to model acute respiratory physiology and symptoms with volitional activities are likely to differ from patients with COVID-19. However, Hamilton observed a comparable skew in particle size distribution in both COVID-19 patients and healthy controls suggesting potential similiarty.20 Crucially, all studies measuring aerosols are limited by not quantifying viable virus. Future work is needed to establish if physiological exertion and respiratory symptoms increase total viral and aerosol emissions in patients, as our study suggests. Our data suggest the historic epidemiological association between the use of respiratory th...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    About SciScore

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  3. Version published to 10.1101/2021.02.07.21251309v2 on medRxiv
  4. Version published to 10.1101/2021.02.07.21251309v1 on medRxiv