In a new study, Chinese researchers conclude that wearing an N95 mask for a prolonged period could affect physiologic and biochemical parameters.
The authors report that the effect was primarily initiated by increased respiratory resistance and subsequent decreased blood oxygen and pH, which contributed to sympathoadrenal system activation and epinephrine as well as norepinephrine secretion elevation, and a compensatory increase in heart rate and blood pressure.
“Although healthy individuals can compensate for this cardiopulmonary overload, other populations, such as elderly individuals, children, and those with cardiopulmonary diseases, may experience compromised compensation,” they write.
The study is reported in a Research Letter to JAMA Network Open published online June 9.
The authors, led by Riqiang Bao, MD, Shanghai Jiaotong University School of Medicine, note that in China, mask use remains a highly adopted practice in everyday life, and the N95 mask offers the highest level of protection against viruses. They say that studies to date on the adverse effects of wearing masks have yielded inconsistent conclusions because of the short duration of intervention.
They conducted the current randomized crossover trial, which took place in a metabolic chamber, to control daily calorie intake and physical activity levels of the participants.
The 30 healthy volunteers (mean age 26 years) were randomly assigned to receive interventions with and without the N95 mask for 14 hours, during which they exercised for 30 minutes in the morning and afternoon using an ergometer at 40% (light intensity) and 20% (very light intensity) of their maximum oxygen consumption levels.
Venous blood samples were taken before and after the intervention for blood gas and metabolite analysis.
Results showed that wearing the N95 mask resulted in reduced respiration rate and oxygen saturation by pulse oximetry (SpO2) within 1 hour, with elevated heart rate (mean change, 3.8 beats/min) 2 hours later until the mask was taken off.
The authors report that during the light-intensity exercise, mask-induced cardiopulmonary stress was further increased, as heart rate (mean change, 7.8 beats/min) and blood pressure increased (mean change: 6.1 mm Hg systolic and 5.0 mm Hg diastolic) and respiration rate (mean change, −4.3 breaths/min) and SpO2 (mean change, −0.66%) decreased. Energy expenditure (mean change, 0.5 kJ) and fat oxidation (mean change, 0.01 g/min) were elevated.
After the 14-hour masked intervention, venous blood pH decreased, and calculated arterial pH showed a decreasing trend. Metanephrine and normetanephrine levels were increased. Participants also reported increased overall discomfort with the N95 mask.
In their discussion, the researchers note that: “Chronic cardiopulmonary stress may also increase cardiovascular diseases and overall mortality.”
They acknowledge though that the study was limited to only 30 young healthy participants in a laboratory setting, and further investigation is needed to explore the effects of different masks on various populations in clinical settings.
However, US researcher Erik Van Iterson, PhD, who conducted a previous study that did not find any clinically meaningful physiologic effects of wearing an N95 mask, is not impressed by the findings of the new study, saying it does not add any reliable information to the overall body of literature on the subject. Van Iterson also questioned the soundness of the methodology.
“My take-home message is that if you want to wear an N95 mask, there is little evidence to suggest that the mask will have a negative effect on your cardiovascular health or function while doing activities of daily living,” Van Iterson, director of cardiac rehabilitation and metabolic exercise stress testing at the Cleveland Clinic, Cleveland, Ohio told theheart.org | Medscape Cardiology.
“This study does nothing to suggest otherwise,” he said. “If anything, this communication is somewhat detrimental because it is pointing to a narrative that isn’t there, in that it suggests these masks may be harmful when there really is no evidence for that.”
Van Iterson pointed out that the researchers were measuring physiologic function with indirect techniques, including wearable technology, which he said had not been validated for use in these dynamic conditions.
“And it’s not completely clear how the oxygen saturation was measured. It is challenging to directly measure gas exchange when people are wearing an N95 mask,” he added.
Van Iterson also took issue with the authors’ interpretation of the data.
“It is very challenging to interpret this data. The authors are suggesting that there are clinically relevant differences. But the quality of the data itself is not reliable, and what they are interpreting as clinically relevant differences is also rather generous,” he commented.
He gives the example of oxygen saturation level, which is reported as a mean change of 0.66%. “They are reporting that as a statistically significant difference but that is not a clinically meaningful difference. A 0.66% difference is well within the measurement error of the technology. And [it] could easily be attributable to just plain noise,” he noted.
“Overall, the changes they found, even if they are valid, are not enough to be clinically meaningful,” he added.
Van Iterson also pointed out that the study was conducted in healthy young people, and what differences would be found in different populations was “pure speculation.”
“I certainly do not believe that this evidence would support the idea that wearing an N95 mask would cause negative effects on cardiovascular function,” he concluded.
In their own previous study of exercise testing in healthy individuals wearing masks, “We found that when performing light-to-moderate-intensity exercise there really is no issue in wearing an N95 mask or a cloth style mask in terms of physiological function,” he noted.
“However, with maximal intensity exercise levels there becomes a substantial subjective effect of wearing a face covering on perceived exertion, and there is a small change in physiological function in that respiration rates are increased and there is some reduction in oxygen saturation levels. But these changes did not meet physiological thresholds that would warrant termination of the tests because of those changes, and they were not considered clinically significant,” he added.
Also commenting on the study, Michael Campos, MD, University of Miami Miller School of Medicine, Florida, pointed out that N95 masks are only now generally worn by healthcare providers in an ICU setting and only for short periods of time. Campos and colleagues conducted a previous study showing the more widely used surgical masks to be safe for healthy people and for people with chronic obstructive pulmonary disease.
“I guess the clinical impact of this new study is very limited,” he said.
The study was sponsored by the National Key Research and Development Program of China and local universities in Shanghai.
JAMA Network Open. Published online June 9, 2023. Research Letter
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