番茄社区

Small physiological changes can result from wearing an N95 mask all day, including during light exercise, a small trial found. Whether this has practical implications for mask users is unclear, however, as exercise physiologists said they were not convinced by the data.

Compared with unmasked controls, 15 young healthy volunteers randomized to wear an N95 mask for 14 hours (from 8 a.m. to 10 p.m.) in a metabolic chamber had a reduced respiration rate and lower oxygen saturation by pulse oximetry within the first hour, while heart rate was up modestly (mean change +3.8 beats/min) starting at 2 hours until masks came off, reported Weiqing Wang, MD, PhD, of Shanghai National Center for Translational Medicine and Shanghai Jiaotong University in China, and colleagues.

During light-intensity exercise twice a day, the masked cohort had heart rate (+7.8 beats/min) and blood pressure (+6.1/5.0 mm Hg) climb relatively higher, with slower respiration (-4.3 breaths/min) and lower oxygen saturation (-0.66%). Morning exercise coincided with slightly greater energy expenditure (+0.5 kJ) and fat oxidation (+0.01 g/min).

After masking for 14 hours, the volunteers also had a lower venous blood pH and a downward trajectory of calculated arterial pH. As expected, they reported feeling more discomfort with the N95 mask compared with no mask, the authors noted in their research letter published in .

"The findings contribute to existing literature by demonstrating that wearing the N95 mask for 14 hours significantly affected the physiological, biochemical, and perception parameters," Wang and team wrote. "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."

However, clinicians who spoke to 番茄社区 warned against interpreting the results beyond the scope of the limited data and shared concerns about the study's methodology as published.

Susan Hopkins, MD, PhD, an exercise physiologist at the University of California San Diego, noted that the -0.66% decline in oxygen saturation is ultimately "biologically trivial and unimportant" as the "measurement error of most pulse oximeters is far greater than that." Similarly, the changes in heart rate are small, she added.

Moreover, Hopkins highlighted the lack of arterial pH, oxygen partial pressure, and partial pressure of carbon dioxide measurements reported, as well as the missing information on cardiac output. Finally, she added that the lack of details of how respiration was measured in the trial was a concern.

"They're wearing this N95, so it's not clear how they could be measuring how much they're breathing. They can't have a metabolic mask on that would be able to quantify respiration," agreed Erik Van Iterson, PhD, MS, director of cardiac rehabilitation at the Cleveland Clinic.

The N95 mask is made to filter out 95% of air particulate matter of 2.5 µm or less in diameter. Widely used as personal protection during the COVID-19 pandemic, these masks are being recommended as a shield from environment pollutants, such as the wildfire smoke currently circulating in certain parts of the country.

Despite the claims of cardiopulmonary stress by Wang's group, masking appears to be a safe choice for personal protection.

"Should I be breathing in soot from the forest fires or should I risk wearing a mask and have a negative effect on my cardiovascular system?" Van Iterson posed rhetorically. "I would say wear the mask if you have no other pre-existing conditions that would compromise your ability to breathe. If you're a generally healthy adult, wear the mask if you're concerned about the soot contaminating many regions of the U.S."

The randomized trial was conducted in a laboratory setting with 30 healthy participants (mean age 26.1 years, 50% women) split between masked and unmasked groups of 15 people each. Spending a day in a metabolic chamber, participants had their food intake controlled and were tasked with exercising for 30 minutes in the morning and afternoon at 40% (light intensity) and 20% (very light intensity) of their maximum oxygen consumption levels.

Venous blood samples were taken before and 14 hours after the intervention for blood gas and metabolite analysis.

Wang and colleagues reported that metanephrine and normetanephrine levels were increased among the masked cohort, suggesting elevated epinephrine and norepinephrine secretion that would have "elicited a compensatory increase in heart rate and blood pressure."

There is no explanation, however, for the decreased respiration with mask-wearing.

Mask studies from the pandemic period have shown "that masks actually induce an elevation of respiration -- as opposed to [a decrease], which just doesn't make sense. The fact that there's a mask on your face, you're exerting yourself more, wouldn't be a signal to slow down breathing," Van Iterson said.

Hopkins said the "take-home message is that masks make your face hot and we don't like that. It affects subjective feelings of being aware of your breathing, i.e., dyspnea, but has minimal to no effect on any meaningful physiologic parameter."

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