Effects of surgical and FFP2/N95 face masks on cardiopulmonary exercise capacity: the numbers do not add up
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LETTER TO THE EDITORS
Effects of surgical and FFP2/N95 face masks on cardiopulmonary exercise capacity: the numbers do not add up Susan R. Hopkins1,2 · Michael K. Stickland3,4 · Robert B. Schoene5,6 · Erik R. Swenson7,8 · Andrew M. Luks7 Received: 3 September 2020 / Accepted: 15 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Sirs: We were interested to see the work of Fikenzer et al. [1], evaluating the effects of surgical masks and FFP2/N95 face masks on exercise performance. While at first glance, the results are intriguing, there are numerous flaws in this work that draw the validity of the study into question. In the inter‑ est of brevity, we will focus on the FFP2/N95 face mask con‑ dition although the reasoning outlined below equally applies to the surgical mask condition. There are several robust relationships in pulmonary and exercise physiology that can be used to evaluate data quality. The first of these is the linear relationship between power output and oxygen consumption which is the basis of esti‑ mating oxygen consumption without measuring expired gas (see [2] for example). Fikenzer et al. show an average peak oxygen consumption of 3248 ml/min at a power output of 277 watts without masks for an overall efficiency of 11.7 mlO2/watt. While wearing a FFP2/N95 face mask, subjects * Susan R. Hopkins [email protected] 1
Department of Medicine, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093‑0623A, USA
2
Department of Radiology, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093‑0852, USA
3
Division of Pulmonary Medicine, Department of Medicine, G.F. MacDonald Centre for Lung Health (Covenant Health), Edmonton, Canada
4
Medicine Strategic Clinical Network, Alberta Health Services, Edmonton, AB, Canada
5
Division of Pulmonary, Critical Care Medicine, St Mary’s Medical Center, San Francisco, USA
6
Sound Physicians San Francisco, San Jose, USA
7
Division of Pulmonary, Critical Care and Sleep Medicine, University of Washington, Seattle, USA
8
Medical Service, VA Puget Sound Health Care System, Seattle, WA, USA
averaged a 14 W decrement in peak power output, which based on the efficiency in these subjects, would be expected to reduce oxygen consumption by ~ 160 ml. This corresponds to a 5% difference, yet the reported oxygen consumption is reduced by 426 ml/min or 13%. Thus, these data are not internally consistent and even less so if masks significantly impact the work of breathing as the authors suggest. A second robust relationship is the linear relationship between cardiac output during exercise and oxygen con‑ sumption (slope ~ 5.5 L/L) [3–5]. Fikenzer et al. show no significant change in heart rate (Omnibus F = 0.11) or car‑ diac output between conditions (Omnibus F = 0.34), further calling the reported reduction in oxygen consumption with FFP2/N95 face mask into question. Finally, expired ventilation was reported to be 25% less with the FFP2/N95 face mask than the unmasked condi‑ tion, leading the
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