Face Masks and the Cardiorespiratory Response to Physical Activity in Health and Disease

Abstract

To minimize transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the novel coronavirus responsible for coronavirus disease (COVID-19), the U.S. Centers for Disease Control and Prevention and the World Health Organization recommend wearing face masks in public. Some have expressed concern that these may affect the cardiopulmonary system by increasing the work of breathing, altering pulmonary gas exchange and increasing dyspnea, especially during physical activity. These concerns have been derived largely from studies evaluating devices intentionally designed to severely affect respiratory mechanics and gas exchange. We review the literature on the effects of various face masks and respirators on the respiratory system during physical activity using data from several models: cloth face coverings and surgical masks, N95 respirators, industrial respirators, and applied highly resistive or high-dead space respiratory loads. Overall, the available data suggest that although dyspnea may be increased and alter perceived effort with activity, the effects on work of breathing, blood gases, and other physiological parameters imposed by face masks during physical activity are small, often too small to be detected, even during very heavy exercise. There is no current evidence to support sex-based or age-based differences in the physiological responses to exercise while wearing a face mask. Although the available data suggest that negative effects of using cloth or surgical face masks during physical activity in healthy individuals are negligible and unlikely to impact exercise tolerance significantly, for some individuals with severe cardiopulmonary disease, any added resistance and/or minor changes in blood gases may evoke considerably more dyspnea and, thus, affect exercise capacity.

Keywords: SARS-CoV-2; face mask; pulmonary limitations to exercise.

Figure 1.

Pressure difference across various masks, respirators, and resistors relative to flow (L · s⁻¹) and measured or estimated minute ventilation (L · min⁻¹) (16). Pressure difference/flow = resistance. The plot on the left displays data up to 5 cm H₂O, whereas the graph on the right displays data up to 25 cm H₂O. Minute ventilation was directly measured in human trials (16) or estimated on the basis of the reported flow in simulation trials (17) and extrapolated back to human data (16). The dashed line represents the reported pressure of a typical mouthpiece setup used in a cardiopulmonary exercise test (CPET) (19). The shaded area represents the reported pressure difference of an N95 respirator across various simulated flow rates (17). The + displays the peak inspiratory pressure allowed under National Institute for Occupational Safety and Health (NIOSH) guidelines at a standard flow of 1.4 L · s⁻¹ (i.e., 85 L · min⁻¹) (77). Surgical (triangle), cloth (square), and respirator (circle) data are reported resistances at 85 L · min⁻¹ (11). The split square represents experimental resistors (17, 41), and the split diamond represents self-contained breathing apparatuses (SCBAs) (21). Surgical and cloth masks and respirators all have a mouth pressure/resistance that is well below NIOSH guidelines (9). When tested up to a minute ventilation of ∼120 L · min⁻¹, N95 respirators have an airflow resistance that is similar to what is observed with a standard CPET mouthpiece setup (17, 19). External resistors provided a resistance that is 5–10 times the resistance of a typical mask. When these resistors are used, no change in dyspnea (points “A” and “B”) (19, 41) or metaboreflex (points “C” and “D”) (37) activation has been observed up to a ventilation of ∼90 L · min⁻¹. It is only during intense exercise, when ventilating at ∼150 L · min⁻¹ with a resistor, that the metaboreflex is initiated (point “E*”) (38). The SCBA provides a resistance that is 3–5 times greater than that of an N95 respirator, and only at a minute ventilation of >110   L · min⁻¹ is the work of breathing greater than that observed with a standard a CPET mouthpiece (point “F*”) (21). *Indicates measurable changes. Approx = approximate.

Figure 2.

Average (A) work of breathing and (B) $\dot{\text{V}}$o₂ of the respiratory muscles across a range of minute ventilation and flow rates in healthy young males and females (16). The average inspired flow values were calculated on the basis of composite flow-volume loops from the same subjects. $\dot{\text{V}}$o₂ = oxygen consumption.