Mitigation of Aerosols Generated During Exercise Testing With a Portable High-Efficiency Particulate Air Filter With Fume Hood

Abstract

Background: The role of portable high-efficiency particulate air (HEPA) filters for supplemental aerosol mitigation during exercise testing is unknown and might be relevant during COVID-19 pandemic.

Research question: What is the effect of portable HEPA filtering on aerosol concentration during exercise testing and its efficiency in reducing room clearance time in a clinical exercise testing laboratory?

Study design and methods: Subjects were six healthy volunteers aged 20 to 56 years. In the first experiment, exercise was performed in a small tent with controlled airflow with the use of a stationary cycle, portable HEPA filter with fume hood, and particle counter to document aerosol concentration. Subjects performed a four-stage maximal exercise test that lasted 12 min plus 5 min of pretest quiet breathing and 3 min of active recovery. First, they exercised without mitigation then with portable HEPA filter running. In a separate experiment, room aerosol clearance time was measured in a clinical exercise testing laboratory by filling it with artificially generated aerosols and measuring time to 99.9% aerosol clearance with heating, ventilation, and air conditioning (HVAC) only or HVAC plus portable HEPA filter running.

Results: In the exercise experiment, particle concentrations reached 1,722 ± 1,484/L vs 96 ± 124/L (P < .04) for all particles (>0.3 μm), 1,339 ± 1,281/L vs 76 ± 104/L (P < .05) for smaller particles (0.3 to 1.0 μm), and 333 ± 209/L vs 17 ± 19/L (P < .01) for larger particles (1.0 to 5.0 μm) at the end of the protocol in a comparison of mitigation vs portable HEPA filter. Use of a portable HEPA filter in a clinical exercise laboratory clearance experiment reduced aerosol clearance time 47% vs HVAC alone.

Interpretation: The portable HEPA filter reduced the concentration of aerosols generated during exercise testing by 96% ± 2% for all particle sizes and reduced aerosol room clearance time in clinical exercise testing laboratories. Portable HEPA filters therefore might be useful in clinical exercise testing laboratories to reduce the risk of COVID-19 transmission.

Keywords: COVID-19; HEPA filter; aerosol; exercise testing.

Graphical abstract

Figure 1

A, Colorado Altitude Training tent with a stationary cycle, a Fluke 985 particle counter (Fluke Corporation) and a portable HEPA filter with directional airflow (model #SS-400-PFS; Sentry Air Systems). B, Partial view of a clinical exercise testing laboratory with the portable HEPA filter in place. HEPA = high-efficiency particulate air.

Figure 2

Pilot data for six subjects that compares aerosol concentrations during the exercise protocol with no filter vs exercise with use of a portable HEPA filter with fume hood (SS-300-PFS; Sentry Air Systems). HEPA = high-efficiency particulate air; HRR = heart rate reserve.

Figure 3

Concentrations of particles (per liter) counted by the Fluke particle counter (Fluke Corporation) are displayed in subgroups of particles >0.3 μm (total particles measured), 0.3-1.0 μm (small aerosols), and 1.0-5.0 μm (large aerosols) during the exercise protocol with and without the use of the a portable HEPA filter with fume hood (model #SS-400-PFS; Sentry Air Systems). HEPA = high-efficiency particulate air; HRR = heart rate reserve.

Figure 4

Individual subject data shows A, aerosol concentration vs protocol time for the no-filter condition vs B, the trial with the use of a portable HEPA filter (model #SS-400-PFS; Sentry Air Systems) with fume hood. HEPA = high-efficiency particulate air; HRR = heart rate reserve.

Figure 5

Results of clinical exercise room clearance testing. Room clearance trials with HVAC only and with HVAC plus portable HEPA filter with fume hood (model #SS-400-PFS; Sentry Air Systems) running are shown. Target 99.9% aerosol clearance lines are marked for the HVAC only trial (blue lines) and HVAC plus portable HEPA filter trial (red lines). The target clearance was reached at 18:40 for the HVAC only trial vs of 9:50 for the HVAC plus portable HEPA filter trial, resulting in a 47% clearance time reduction. HEPA = high-efficiency particulate air; HVAC = heating, ventilation, and air conditioning.