The coronavirus disease (COVID-19) pandemic, caused by severe acute respiratory syndrome
coronavirus 2 (SARS-CoV-2), has severely restricted pulmonary diagnostic testing because
of the concern of droplet and aerosol generation by procedures conducted in small
test rooms. SARS-CoV-2 infection is characterized by viral shedding from the upper
and lower respiratory tracts; in addition, SARS-CoV-2 RNA has been detected in sampled
air throughout a hospital, which leads to this concern (1–4). Pulmonary function laboratories
are justifiably concerned because test maneuvers involve forceful breathing, which
may generate infectious particles. Normal speaking has also been reported to generate
small-droplet aerosols, increasing the potential exposure risk in close contact with
infected individuals (5–7). Currently, there are no studies evaluating particle generation
during pulmonary function tests (PFTs). To better understand the risk associated with
PFTs, we sought to quantify and characterize the amount of detectable aerosol and
droplet generation during routine pulmonary function studies at prespecified distances.
Methods
This was a single-center prospective study conducted at the Mayo Clinic in Florida.
Five adult volunteer subjects without pulmonary disease consented to perform tidal
breathing (Vt), normal speaking, forced vital capacity (FVC), and maximum voluntary
ventilation (MVV) maneuvers. The Mayo Clinic Institutional Review Board approved this
study (20–005544).
Particle measurement
A light-scattering particle counter (FLUKE 983) was used to simultaneously measure
six channels of particle size distribution (0.3, 0.5, 1, 2, 5, and 10 μm), temperature,
and humidity while each maneuver was being performed at each measured location. A
minimum sampling volume of 1 L was obtained per measurement.
Test conditions
To control for humidity, temperature, and other indeterminate ambient variables, room
occupancy was limited to three persons (the subject and two investigators) during
the study. The pulmonary function test room is 936 cubic feet and has 12.8 room air
exchanges per hour. The ambient baseline measurement was obtained at the center of
the room before and after each maneuver, with the subject and two investigators in
the room and the door closed. The testing room was used only for this study on the
day of the testing. The particle counter was positioned as follows: For the speaking
portion, the particle counter was positioned 12 inches directly in front of the speaker.
For the pulmonary function test portion, the air was sampled at the following three
locations: 1) at a 90° angle to and touching the exhalation port (0 ft) on the pulmonary
function equipment (Masterscreen PFT; Vyaire Medical), 2) at 1.5 ft from the exhalation
port, halfway between where the patient and respiratory therapist sat, and 3) at 3
ft from the exhalation port. The number of particles counted and the volume of air
sampled were recorded. The particle counter was zeroed before each test condition.
Spirometry was performed outside the plethysmography box. A Microgard II filter (Vyaire
Medical) was interposed between the mouthpiece and intake port for all maneuvers,
as per manufacturer. For the speaking portion, each subject read “The Rainbow Passage”
by Grant Fairbanks for 30 seconds. The subject then performed Vt, FVC, and MVV through
the pulmonary function test machine. If the subject coughed during the maneuver, the
measurement was discarded, and the study was repeated once ambient particle count
had returned to baseline. Each subject performed the test conditions twice.
Analysis
A nonparametric distribution of measurements was assumed. The Mann-Whitney test for
two group comparisons and Wilcoxon/Kruskal-Wallis test for multiple group comparisons
was used. If the Kruskal-Wallis test was significant, a Steel test would be performed
to compare each group to a single control. This was designated to be the ambient measurement
obtained before the respective test. A P value of less than 0.05 was considered significant.
Results
The five subjects included four men (80%). The mean age was 37.6 ± 8.4 years, the
mean height was 177.6 ± 3.9 cm, and the mean weight was 80.4 ± 4.5 kg. Volunteers
were white (60%), East Asian Indian (20%), and Asian (20%). Ambient room humidity
was measured at 48%, and temperature was 23°C. Table 1 shows the increase in particle
counts under different test conditions, with small respirable particles in the 0.3-μm
range being generated the most. The FVC and MVV maneuvers generated increased small
particles when compared with the ambient measurements with Vt, FVC, and MVV.
Table 1.
Quantity of particles per liter of sampled air separated by particle size for each
maneuver and ambient room measurement
Maneuver
Particle Quantity Per Liter of Sampled Air by Size
0.3 μm [Mean (95% CI)]
0.5 μm [Mean (95% CI)]
1 μm [Mean (95% CI)]
2 μm [Mean (95% CI)]
5 μm [Mean (95% CI)]
10 μm [Mean (95% CI)]
Speaking
Ambient
1,269.6 (1,230.6–1,308.6)
79.5 (51.2–107.8)
21.3 (10.3–32.3)
37.6 (17.3–57.9)
4.9 (3.2–6.6)
3.3 (1.4–5.2)
Speaking for 30 s, 1 ft
1,293.4 (1,242.9–1,343.9)
131.7 (47.3–216.1)
30.2 (23.6–36.8)
47.6 (38.8–56.4)
7.7 (4.0–11.4)
2.7 (0.0–5.4)
Vt
Ambient
1,299.2 (1,222.7–1,375.7)
95.2 (80.1–110.3)
33.3 (15.8–50.8)
59.6 (44.0–75.1)
8.9 (5.3–12.5)
4.2 (1.8–6.6)
0 ft
6,466.6(5,991.3–6,941.9)
770.3 (730.5–810.1)
24.7 (16.7–32.7)
21.7 (13.8–29.6)
3.0 (1.4–4.6)
1.4 (0.1–2.7)
1.5 ft
1,250.8 (1,201.8–1,299.8)
88.8 (72.9–104.7)
28.6 (22.5–34.7)
41.6 (36.1–47.1)
5.6 (3.2–8.0)
2.5 (1.0–4.0)
3 ft
1,250.3 (1,190.0–1,310.6)
77.2 (67.3–87.1)
24.2 (17.6–30.8)
32.8 (24.8–40.8)
5.0 (3.4–6.6)
2.2 (1.1–3.3)
FVC
Ambient
1,334.8 (1,195.9–1,473.7)
101.8 (71.7–131.9)
31.6 (19.8–43.4)
38.8 (25.4–52.2)
4.7 (1.9–7.5)
2.8 (2.2–3.4)
0 ft
10,739.3 (8,634.7–12,843.9)
1,408.4 (1,076.4–1,740.4)
26.0 (16.1–35.9)
21.1 (12.6–29.6)
2.1 (1.8–2.4)
0.8 (0.2–1.4)
1.5 ft
1,258.2 (1,218.2–1,298.2)
79.0 (73.0–85.0)
23.4 (18.4–28.4)
29.8 (25.0–34.6)
5.0 (2.7–7.3)
1.8 (0.7–2.9)
3 ft
1,266.9 (1,208.3–1,325.5)
73.6 (61.9–85.3)
19.6 (14.2–25.0)
27.0 (22.0–32.0)
2.4 (1.3–3.5)
1.8 (0.4–3.2)
MVV
Ambient
1,323.7 (1,226.1–1,421.3)
88.6 (83.3–93.9)
30.8 (14.3–47.3)
40.8 (34.8–46.8)
4.6 (3.9–5.3)
2.4 (1.7–3.1)
0 ft
8,845.2 (6,439.1–11,251.3)
1,251 (444.1–2,057.9)
33.2 (17.5–48.9)
20.8 (14.2–27.4)
3.4 (2.0–4.8)
0.6 (0.0–1.3)
1.5 ft
1,278.1 (1,214.3–1,341.9)
81.0 (58.5–103.5)
29.2 (26.2–32.2)
38.0 (35.5–40.5)
2.8 (1.0–4.6)
2.8 (1.4–4.2)
3 ft
1,283.6 (1,231.2–1,336.0)
82.6 (77.4–87.8)
19.4 (16.2–22.6)
34.6 (29.6–39.6)
4.2 (1.8–6.6)
1.4 (0.0–2.8)
Definition of abbreviations: CI = confidence interval; FVC = forced vital capacity;
MVV = maximum voluntary ventilation; Vt = tidal volume.
Proximity to the source was associated with significant increases in particle generation.
With normal speaking, there was not an increase of generated 0.3-μm particles at 12
inches. When sampled close to the exhalation port position, all the maneuvers generated
an increase in respirable 0.3-μm particles when compared with baseline (Figure 1).
Other aerosol-sized particles measured at 0.5 μm were also increased at this close
position. At 1.5 ft and 3 ft from the exhalation port, there was no increase in particle
generation for any of the trialed maneuvers.
Figure 1.
Graph of the concentration of 0.3-μm particles per liter of sampled air generated
for each maneuver. P values shown for significant results. FVC = forced vital capacity;
MVV = maximum voluntary ventilation.
Conclusions
This report documents and characterizes aerosol particle generation from routine PFTs
and supports precautions to mitigate the transmission of SARS-CoV-2. These precautions
include the patient wearing a mask during the instructional phase, maintaining a distance
of at least 1.5 ft between the subject and respiratory therapist, using disposable
plastic covers over the PFT equipment, and using N95 and personal protective equipment
for the respiratory therapist. This study provides valuable information guiding infectious
control measures to ensure personnel and patient safety during pulmonary function
testing. A limitation of this study was the small sample size of healthy volunteers,
which increases the risk of multiple comparisons and decreases the overall stability
of the results, but the results were consistent between volunteers, providing reassurance
that larger sample sizes may provide similar results. In addition, the high room exchange
and humidity may have contributed to particle dispersion and evaporation. Because
the volunteers were healthy, the amount and size of particles generated could be considered
the minimum, as a patient with nasal secretions or a productive cough may theoretically
generate more particles. We did not assess the composition or infectivity of the measured
particles, so the possibility of transmission is unknown but possible given the increase
in particle generation.
In conclusion, PFTs and normal breathing all generate aerosols rather than just droplets.
The room air exchange, room turnaround time between testing, and distance between
the patient and technician in the testing room are important. Particle generation
close to the exhalation port warrants using a single-use plastic covering over the
device, with the mouthpiece port and the exhalation port exposed, to avoid equipment
contamination. The generation of aerosol-sized particles warrants the use of N95 masks
and personal protective equipment during routine PFTs in patients who potentially
have an airborne transmissible infectious disease.
Supplementary Material
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