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Quantification of aerosol dispersal from suspected aerosol-generating procedures

Runar Strand-Amundsen, Christian Tronstad, Ole Elvebakk, Tormod Martinsen, Marius Dybwad, Egil Lingaas, Tor Inge Tønnessen
ERJ Open Research 2021 7: 00206-2021; DOI: 10.1183/23120541.00206-2021
Runar Strand-Amundsen
1Dept of Clinical and Biomedical Engineering, Oslo University Hospital, Oslo, Norway
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  • ORCID record for Runar Strand-Amundsen
  • For correspondence: runar.strand-amundsen@fys.uio.no
Christian Tronstad
1Dept of Clinical and Biomedical Engineering, Oslo University Hospital, Oslo, Norway
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Ole Elvebakk
1Dept of Clinical and Biomedical Engineering, Oslo University Hospital, Oslo, Norway
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Tormod Martinsen
1Dept of Clinical and Biomedical Engineering, Oslo University Hospital, Oslo, Norway
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Marius Dybwad
2Norwegian Defence Research Establishment (FFI), Kjeller, Norway
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Egil Lingaas
3Dept of Infection Prevention, Oslo University Hospital – Rikshospitalet, Oslo, Norway
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Tor Inge Tønnessen
4Dept of Anaesthesiology, Division of Emergencies and Critical Care, Oslo University Hospital, Oslo, Norway
5Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway
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Figures

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  • FIGURE 1
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    FIGURE 1

    a) Overview of the test chamber, sensor locations (Sensirion, SPS30: mesh sensors: A-I, three sensors at 30 cm, three at 100 cm, two at 180 cm and one at 285 cm) (TSI, APS 3321: “breathing zone single sensor”: sample point 20 cm from participant face) and other equipment. The test person was seated on a chair, with an approximate breathing zone elevation of 120 cm above the floor. The sensors were positioned 120 cm above the floor. b) Protocol structure with oxygen modalities and event elements and details. Before and between each 10-min event a 15-min period of filtering out the particles of the test chamber was performed. LFNC: low-flow nasal cannula; HFNC: high-flow nasal cannula; NIV: noninvasive positive-pressure ventilation. HF: high flow; IPAP: inspiratory positive airway pressure; EPAP: expiratory positive airway pressure

  • FIGURE 2
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    FIGURE 2

    Average particles per litre of air (PPL) concentration over 10 min (red dot) between each of the eight events in each experiment, grouped according to participant (violin plots with two segment y-axes). a) Breathing-zone single sensor (particle size range 0.3–20 μm). b) average over nine mesh sensors (particle size range 0.3–10 μm). Categorical comparisons of average concentration of particles per litres of air, during the eight events of each experiment, with each red dot representing the results from 1 of 20 participants, measured by the breathing-zone single sensor (APS 3321) (c) and the average over all nine mesh sensors (d). The median is indicated with a thin black dashed line. LF: low-flow; C: cough; HF: high-flow; M: mask. e) Particle size distribution measured with the breathing-zone sensor; NIV: noninvasive positive-pressure ventilation.

  • FIGURE 3
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    FIGURE 3

    Mean and median particles per litre of air, from 20 participants, for three particle size groups, measured with the breathing-zone single sensor (APS 3321), during the eight events of the experiment. The median and means show smoothed time series (moving mean with a 3-s window). The smoothing was used to increase readability and instead of a series of spikes, a smoothed square-like step response is shown for the periods with large spikes. LFNC: low-flow nasal cannula; HFNC: high-flow nasal cannula; NIV: noninvasive positive-pressure ventilation.

  • FIGURE 4
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    FIGURE 4

    Mean particle concentration in particles per litre of air (y-axes) within each episode, for all mesh sensors. The particle concentration number includes particle sizes (0.3–10 μm). The placement of the plots within the graph is similar to the sensor position during the experiments, with the distance to each sensor shown in the subfigure headings. The distribution of measurements between participants is presented as violin plots, where the median is indicated with a thin black dashed line, and the quartiles with thinner dashed lines. LF: low-flow; C: cough; HF: high-flow; M: mask; NIV: noninvasive positive-pressure ventilation.

Tables

  • Figures
  • Supplementary Materials
  • TABLE 1

    Descriptive statistics for particles measured in the breathing-zone of the test subject (30 cm from mouth)

    EventMeanMinMaxMedian0.250.75Dispersion %
    Particle size ≤1.0 µm
     LFNC73.021.2151.060.941.5106.5107
     LFNC+cough222.744.91167.4122.971.0248.4144
     HFNC101.215.9317.167.838.5130.0135
     HFNC+cough190.936.41444.791.961.8167.6115
     HFNC+M89.325.3230.554.841.0137.2176
     HFNC+M+cough103.129.2270.596.748.2156.5112
     NIV77.720.6245.966.433.3102.4104
     NIV+cough90.228.0263.573.839.2112.299
    Particle size >1 µm and ≤5 µm
     LFNC22.17.370.218.614.824.049
     LFNC+cough47.313.7242.029.317.740.477
     HFNC42.41.8236.725.714.946.0121
     HFNC+cough41.813.3186.425.021.437.765
     HFNC+M33.57.6110.222.415.439.4107
     HFNC+M+cough27.38.480.123.417.329.150
     NIV21.65.151.822.113.326.459
     NIV+cough24.76.072.721.616.331.269
    Particle size >5 µm
     LFNC1.70.55.51.20.92.1100
     LFNC+cough1.70.35.51.41.01.857
     HFNC3.60.122.81.91.23.5122
     HFNC+cough3.10.624.61.61.12.9113
     HFNC+M3.70.420.51.71.13.9167
     HFNC+M+cough2.60.89.81.91.22.988
     NIV1.30.32.51.30.91.865
     NIV+cough1.80.54.51.51.02.279

    Descriptive statistics for the particle concentration (three particle size groups) measured by the breathing-zone single sensor (APS 3321) during all events. The unit used is the mean particle concentration in number per litre during the event. The dispersion of the distribution is presented as the per cent-wise ratio between the interquartile range and the median. The statistical distributions of particle counts were skewed for nearly all events and particle sizes (Shapiro–Wilk test p<0.05). LFNC: low-flow nasal cannula; HFNC: high-flow nasal cannula; NIV: noninvasive positive-pressure ventilation; M: surgical mask.

    • TABLE 2

      Statistical pairwise comparisons between events

      ComparisonMedian differenceLower CIUpper CIp-value
      Particle size ≤1.0 µm
       HFNC−LFNC9.5−5.329.60.212
       LFNC+cough−LFNC42.98.9108.50.005
       HFNC+cough−HFNC8.2−3.431.30.145
       HFNC+cough−LFNC+cough−12.1−59.4−0.20.184
       HFNC−HFNC+M6.7−8.522.10.179
       HFNC+cough−HFNC+M+cough11.1−10.935.40.126
       HFNC+ M +cough−HFNC+ M2.8−7.014.60.332
       NIV−LFNC−0.7−4.814.20.904
       NIV−HFNC−4.3−30.37.40.204
       NIV+cough−NIV6.6−14.516.00.455
       LFNC+cough−NIV+cough43.46.094.50.001
       HFNC+cough−NIV+cough28.26.443.20.023
      Particle size >1 µm and ≤5 µm
       HFNC−LFNC6.8−0.316.60.073
       LFNC+cough−LFNC7.6−0.516.60.048
       HFNC+cough−HFNC1.0−10.95.70.765
       HFNC+cough−LFNC+cough−1.4−7.10.00.296
       HFNC−HFNC+M2.0−4.613.40.391
       HFNC+cough−HFNC+M+cough2.6−0.46.80.086
       HFNC+ M +cough−HFNC+ M1.6−6.64.10.911
       NIV−LFNC2.5−4.44.40.732
       NIV−HFNC−5.5−20.6−0.20.057
       NIV+cough−NIV2.60.06.10.156
       LFNC+cough−NIV+cough7.1−2.016.00.040
       HFNC+cough−NIV+cough4.3−0.411.90.107
       Particle size >5 µm
       HFNC−LFNC0.50.30.90.044
       LFNC+cough−LFNC0.2−0.40.40.862
       HFNC+cough−HFNC−0.5−0.60.10.204
       HFNC+cough−LFNC+cough0.3−0.10.90.116
       HFNC−HFNC+M0.2−0.60.70.926
       HFNC+cough−HFNC+M+cough−0.4−0.90.20.125
       HFNC+ M +cough−HFNC+ M0.1−0.50.80.709
       NIV−LFNC−0.3−0.50.30.468
       NIV−HFNC−0.8−1.8−0.20.009
       NIV+cough−NIV0.40.10.80.079
       LFNC+cough−NIV+cough−0.2−0.40.30.456
       HFNC+cough−NIV+cough0.1−0.30.90.390

      Statistical pairwise comparisons between different experimental events of particle concentrations (particles per litre of air) measured by the breathing-zone single sensor (APS 3321). Results from three particle size groups are shown. 95% confidence intervals of the median differences are based on the bootstrap method, and the p-values are based on the Wilcoxon signed rank test. LFNC: low-flow nasal cannula; HFNC: high-flow nasal cannula; NIV: noninvasive positive-pressure ventilation; M: surgical mask.

      • TABLE 3

        Estimates of change in particle concentrations over time

        EventFixed estimateLower 95% CIUpper 95% CIInterceptp-value
        Particle size ≤1.0 µm
         LFNC0.1−0.50.772.40.721
         LFNC+cough27.3−4.058.672.50.087
         HFNC−2.5−6.71.7115.10.238
         HFNC+cough25.7−16.668.149.40.232
         HFNC+M−0.2−2.21.990.30.862
         HFNC+M+cough4.4−0.39.079.00.065
         NIV−0.1−0.70.578.20.743
         NIV+cough3.6−0.17.470.20.059
        Particle size >1 µm and ≤5 µm
         LFNC−0.8−1.2−0.526.7<0.001
         LFNC+cough2.4−4.28.934.20.474
         HFNC−5.8−13.21.574.50.120
         HFNC+cough−1.2−8.76.348.50.750
         HFNC+M−2.6−7.01.748.00.235
         HFNC+M+cough−1.5−2.90.035.40.049
         NIV−1.2−1.9−0.428.20.002
         NIV+cough0.1−1.92.124.20.929
        Particle size >5 µm
         LFNC−0.1−0.20.02.40.009
         LFNC+cough−0.2−0.3−0.12.70.005
         HFNC−0.6−1.30.16.70.095
         HFNC+cough−0.6−1.50.36.40.180
         HFNC+M−0.3−1.10.55.40.440
         HFNC+M+cough−0.3−0.5−0.24.5<0.001
         NIV−0.2−0.3−0.12.5<0.001
         NIV+cough−0.1−0.20.02.30.084

        Estimates of change in particle concentration (number/litre) per minute near the breathing-zone of the subjects for all events, based on measurements from the breathing-zone single sensor (APS 3321). Results from three particle size groups are shown. LFNC: low-flow nasal cannula; HFNC: high-flow nasal cannula; NIV: noninvasive positive-pressure ventilation; M: surgical mask.

        • TABLE 4

          Estimates of differences to intercept (30 cm) in mean particle concentration at different distances in the measurement chamber

          Event0.3 m (intercept)1.0 m1.8 m2.85 m
          LFNC218.2 (168.0–268.3)22.9 (−23.1–68.8)−38.0 (−89.4–13.4)−14.6 (−79.6–50.4)
          LFNC+cough400.2 (293.1–507.3)−20.3 (−84.2–43.6)−102.6 (−174.1–−31.1)*−100.9 (−191.3–−10.5)*
          HFNC278.1 (219.2–337.0)−30.4 (−94.8–34.0)−34.8 (−106.8–37.2)−16.5 (−107.5–74.5)
          HFNC+cough341.8 (258.6–425.0)7.1 (−53.6–67.8)−99.5 (−167.3–−31.7)*−104.0 (−189.8–−18.2)*
          HFNC+M210.5 (167.2–253.9)79.1 (31.5–126.7)*14.0 (−39.2–67.2)25.0 (−42.3–92.4)
          HFNC+M+cough303.4 (260.2–346.7)−31.0 (−92.2–30.2)−57.8 (−126.2–10.5)−71.3 (−159.4–16.8)
          NIV222.8 (183.9–261.7)35.3 (−19.8–90.3)−30.2 (−91.7–31.3)−20.4 (−98.2–57.42)
          NIV+cough228.4 (181.6–275.3)33.8 (−17.5–85.0)−43.0 (−100.3–14.2)9.7 (−62.6–82.0)

          Estimates of differences in mean particle concentration (number/L) between mesh sensors at different distances from the breathing-zone of the subject based on a linear mixed-effects model. The particle concentration number includes particle sizes (0.3−10 µm). The intercept level at 30 cm is presented together with the differences (versus 30 cm) at 100 cm, 180 cm and 285 cm. 95% confidence intervals of all estimates are given in parentheses, and all differences (versus 30 cm) with a p-value <0.05 are marked with *. LFNC: low-flow nasal cannula; HFNC: high-flow nasal cannula; NIV: noninvasive positive-pressure ventilation; M=surgical mask.

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          Quantification of aerosol dispersal from suspected aerosol-generating procedures
          Runar Strand-Amundsen, Christian Tronstad, Ole Elvebakk, Tormod Martinsen, Marius Dybwad, Egil Lingaas, Tor Inge Tønnessen
          ERJ Open Research Oct 2021, 7 (4) 00206-2021; DOI: 10.1183/23120541.00206-2021

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          Quantification of aerosol dispersal from suspected aerosol-generating procedures
          Runar Strand-Amundsen, Christian Tronstad, Ole Elvebakk, Tormod Martinsen, Marius Dybwad, Egil Lingaas, Tor Inge Tønnessen
          ERJ Open Research Oct 2021, 7 (4) 00206-2021; DOI: 10.1183/23120541.00206-2021
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