Feasibility of a Viral Filter for Cardiopulmonary Exercise Testing During the COVID-19 Pandemic
Key findings
- Exercise is associated with about 10-fold increases in resting expiratory flow rates and minute ventilation, which has prompted concern about conducting cardiopulmonary exercise testing (CPET) during the COVID-19 pandemic
- N95 and surgical masks are unsuitable for patients' use during CPET because they can interfere with the ability to perform maximum exercise and to collect information about oxygen uptake
- In this study, two healthy volunteers underwent CPET with and without an electrostatic filter being placed upstream of the gas analyzer sample line; the filter is commercially available and has a viral filtration efficiency rating of greater than 99.9% (though importantly this filter has not specifically been tested with the SARS-CoV2 virus)
- Oxygen uptake and minute ventilation measurements obtained during use of the electrostatic filter were highly consistent with those obtained without the filter
- Use of an electrostatic filter may complement other safety measures such as enhanced disinfection protocols and prolonged periods between tests being introduced to maximize safety to exercise testing
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Cardiopulmonary exercise testing (CPET) of patients with heart failure has been sharply curtailed during the COVID-19 pandemic because of concern about transmission of the novel coronavirus. Exercise is associated with about 10-fold increases in resting expiratory flow rates and minute ventilation, which raises concern that large volumes of contaminated air could enter testing spaces.
N95 and surgical masks are unsuitable for patients' use during CPET because they can interfere with the ability to perform maximum exercise. Those masks limit airflow, and they have been shown to increase inhaled carbon dioxide, decrease inspired oxygen and increase the work of breathing.
Gregory D. Lewis, MD, Heart Failure section head and medical director of Cardiac Transplantation, and director of the Massachusetts General Hospital Cardiopulmonary Exercise Testing Laboratory in the Cardiology Division, and Rajeev Malhotra, MD, cardiologist in the Cardiovascular Research Center and associate director of the Cardiopulmonary Exercise Testing Laboratory, and colleagues found it is feasible to conduct CPET with a commercially available electrostatic viral filter ordinarily used for pulmonary function testing. They report the results of a proof-of-principle study in the Journal of Cardiac Failure.
Study Methods
The filter used has a viral filtration efficiency rating of >99.9%. It was placed in-line upstream of the gas analyzer sample line but away from the subject's mouth.
Each of two healthy volunteers completed two exercise tests, one with the filter and one without:
- Subject 1: Three minutes at no workload (0 W), four minutes at 50 W, four minutes at 100 W, four minutes at 150 W, four minutes at 200 W
- Subject 2: Three minutes at 0 W followed by a continuous ramp protocol, 20 W/min to 200 W
Results
Oxygen uptake values obtained during the use of the electrostatic filter were highly consistent with those obtained without the filter. The results were:
- Subject 1: 99%, 97%, 98% and 97% of the no-filter values at 50W, 100W, 150W and 200W, respectively
- Subject 2: 94%, 94%, 103% and 103% of the no-filter values at 50W, 100W, 150W and 200W
Measurements of minute ventilation were also highly consistent when evaluated with and without the use of the filter.
Conclusion
The use of the electrostatic filter did not compromise the collection of the CPET data that are vitally important to caring for patients with heart failure. This approach may be more feasible than measures such as enhanced disinfection and requiring rooms to stay empty for prolonged periods between tests.
It's important to note that oxygen uptake and other CPET parameters were not tested across the entire range of expiratory flow rates achievable during exercise or in patients with COVID-19.
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