The effects of wearing facemasks on oxygenation and ventilation at rest and during physical activity

Abstract

Background: Facemasks are recommended to reduce the spread of SARS-CoV-2, but concern about inadequate gas exchange is an often cited reason for non-compliance.

Research question: Among adult volunteers, do either cloth masks or surgical masks impair oxygenation or ventilation either at rest or during physical activity?

Study design and methods: With IRB approval and informed consent, we measured heart rate (HR), transcutaneous carbon dioxide (CO2) tension and oxygen levels (SpO2) at the conclusion of six 10-minute phases: sitting quietly and walking briskly without a mask, sitting quietly and walking briskly while wearing a cloth mask, and sitting quietly and walking briskly while wearing a surgical mask. Brisk walking required at least a 10bpm increase in heart rate. Occurrences of hypoxemia (decrease in SpO2 of ≥3% from baseline to a value of ≤94%) and hypercarbia (increase in CO2 tension of ≥5 mmHg from baseline to a value of ≥46 mmHg) in individual subjects were collected. Wilcoxon signed-rank was used for pairwise comparisons among values for the whole cohort (e.g. walking without a mask versus walking with a cloth mask).

Results: Among 50 adult volunteers (median age 33 years; 32% with a co-morbidity), there were no episodes of hypoxemia or hypercarbia (0%; 95% confidence interval 0-1.9%). In paired comparisons, there were no statistically significant differences in either CO2 or SpO2 between baseline measurements without a mask and those while wearing either kind of mask mask, both at rest and after walking briskly for ten minutes.

Interpretation: The risk of pathologic gas exchange impairment with cloth masks and surgical masks is near-zero in the general adult population.

Fig 1. Measurements taken at rest.

Boxes represent the 25^th-75^th percentile of each variable. The horizontal line in each box represents the median. The whiskers represent the local maximum and local minimum values. Values that are >1.5 times the interquartile range from either end of the box are considered outliers and denoted with a small circle. Paired comparisons were performed using the Wilcoxon signed rank test. At rest, all comparisons between baseline/maskless values (black boxes) and facemask values (gray boxes) were not statistically significant (“ns”).

Fig 2. Measurements taken during physical activity.

Boxes represent the 25^th-75^th percentile of each variable. The horizontal line in each box represents the median. The whiskers represent the local maximum and local minimum values. Values that are >1.5 times the interquartile range from either end of the box are considered outliers and denoted with a small circle. Paired comparisons were performed using the Wilcoxon signed rank test. Non-significant differences are denoted “ns” and statistically significant differences are denoted with an asterisk.