ABSTRACT

Objective: In view of the current COVID-19 pandemic, the objective of this study was to determine, through a systematic review and meta-analysis, whether the use of N95/FFP2 masks during aerobic exercise has a significant impact on HR, RR, SpO2, and blood pressure (BP) in healthy individuals. Methods: We searched the MEDLINE database for studies published in English between 2005 and 2021. To reduce bias and increase reliability, only randomized controlled trials and randomized crossover clinical trials were considered for inclusion. The selected outcomes included HR, RR, SpO2, and BP, with perceived exertion being evaluated by means of the Borg scale. Results: Eight controlled trials were included in the meta-analysis. Seven evaluated HR (p > 0.05), five evaluated RR (p > 0.05), five evaluated SpO2 and BP (p > 0.05 for both), and six evaluated perceived exertion, presenting controversial results such as risk ratios that were grouped for each variable. Conclusions: This study suggests that N95 and FFP2 masks do not have significant effects on HR, RR, SpO2, and BP during aerobic exercise in healthy individuals.

Keywords: N95 respirators; Heart rate; Respiratory rate; Oxygen saturation; Blood.

RESUMO

Objetivo: Diante da atual pandemia de COVID-19, o objetivo deste estudo foi determinar, por meio de uma revisão sistemática e meta-análise, se o uso de máscaras N95/PFF2 durante o exercício aeróbico tem impacto significativo na FC, FR, SpO2 e pressão arterial (PA) em indivíduos saudáveis. Métodos: Buscamos no banco de dados MEDLINE estudos publicados em inglês entre 2005 e 2021. Para reduzir o viés e aumentar a confiabilidade, foram considerados para inclusão no estudo somente ensaios clínicos controlados randomizados e ensaios clínicos cruzados randomizados. Os desfechos selecionados foram FC, FR, SpO2 e PA; a percepção de esforço foi avaliada por meio da escala de Borg. Resultados: Oito ensaios controlados foram incluídos na meta-análise. Sete avaliaram FC (p > 0,05), cinco avaliaram FR (p > 0,05), cinco avaliaram SpO2 e PA (p > 0,05 para ambas) e seis avaliaram a percepção de esforço, com resultados controversos (razões de risco agrupadas para cada variável, por exemplo). Conclusões: Este estudo sugere que as máscaras N95 e PFF2 não têm efeitos significativos na FC, FR, SpO2 e PA durante o exercício aeróbico em indivíduos saudáveis.

Palavras-chave: Respiradores N95; Frequência cardíaca; Taxa respiratória; Saturação de oxigênio; Sangue.

 
INTRODUCTION
 
Protective masks are essential pieces of personal protective equipment for health professionals, especially those who deal directly with airway infections, as in the case of the current COVID-19 pandemic.(1-3) In a study that was conducted in Singapore in 2020 and in which 30 health professionals wore N95 masks when providing care to patients who tested positive for SARS-CoV-2 infection, there was no patient-to-professional disease transmission.(4)
 
In a study that was conducted in South Korea in 2015 and in which 97 COPD patients wearing N95 masks were investigated, there were considerable changes in RR, SpO2, and end-tidal carbon dioxide levels before and after mask use.(5) In another study conducted in 2020, young people who had no comorbidities and who were nonsmokers performed aerobic physical exercise wearing N95 masks for an average of 75-150 min per week and showed no considerable changes in gas concentrations.(6) Kim et al. evaluated 20 healthy young people participating in low- to moderate-intensity physical activity for 1 h while wearing four different models of N95 masks and found no significant gas exchange abnormalities.(7)
 
According to Chandrasekaran et al.,(8) the use of N95 masks for long periods of time could lead to changes in muscle metabolism; cardiorespiratory stress; changes in the excretory and immune systems; and changes in the brain and central nervous system. This is due to the fact that N95 masks create a closed rebreathing circuit, leading to hypercapnic hypoxia.(8-11)
 
In a study by Fikenzer et al.,(12) 12 healthy men underwent ergospirometry and impedance cardiography before and after the use of N95 masks, which significantly reduced pulmonary function parameters and peak blood lactate response. However, there is a lack of studies analyzing the correlation between the use of N95/FFP2 masks and possible changes in SpO2, RR, HR, respiratory resistance, and blood pressure (BP) in the context of the current COVID-19 pandemic.(13-16)
 
The objective of this study was to determine, through a systematic review and meta-analysis, the effects of N95/FFP2 masks on BP, HR, RR, SpO2, and perceived effort during aerobic physical activity in healthy individuals.
 
METHODS
 
Search strategy
 
A systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The study protocol was registered with the International Prospective Register of Systematic Reviews (Registration no. CRD42021282318).
 
We searched the MEDLINE database for articles originally published in English in the last 15 years. Only randomized controlled trials or randomized crossover clinical trials were selected for the review; therefore, the sample of studies tended to be homogeneous and avoided biases commonly found in cross-sectional and observational studies. Two independent evaluators searched the MEDLINE database, and, in case of divergence between the two, a third evaluator was consulted. Disagreements were resolved by consensus.
 
The search terms “N95,” “FFRs,” “FFP2,” “Effects,” “Physiological,” “Gas,” and “Blood” were used in order to identify relevant studies. The MeSH list of descriptors was used in order to identify variations of the aforementioned search terms.
 
Inclusion and exclusion criteria
 
The inclusion and exclusion criteria are shown in Chart 1.

 

 
Data extraction
 
Our research group previously selected the information for data collection by separately searching the included studies for the following: title, name of the first author, year in which the study was conducted, year in which the study was published, country of origin, number of participants, mean/median and standard deviation of each variable with and without masks, aerobic interventions used, and outcomes (i.e., HR, RR, SpO2, and BP as primary outcomes; and respiratory resistance and perceived exertion—as assessed by the Borg scale—as secondary outcomes). All of the authors independently collected the data. To evaluate the articles, two evaluators who were not part of our research group established search strategies and performed critical analyses. After the reading of the articles in their entirety, studies were excluded from the review if there were methodological biases, a lack of direct correlation with the topic of interest, or failure to provide raw data.
 
Statistical analysis
 
For the meta-analysis and risk of bias calculation, we used the following programs: Review Manager, version 5.4 (RevMan 5; Cochrane Collaboration, Oxford, UK); Microsoft Excel; and MedCalc (MedCalc Software Ltd, Ostend, Belgium). Fixed and random statistical analyses were performed, with the studies being considered homogeneous. The 95% CI was calculated for each study individually and then for all of the selected studies. The mean and standard deviation of each study were identified, and the level of significance was set at p ≤ 0.05. The I2 statistic was calculated in order to evaluate heterogeneity among the included studies. If I2 was greater than 50%, we chose to use a random-effects model to match the results, and if I2 was less than 50%, we created a fixed-effects model. The risk of publication bias was evaluated by examining a funnel plot for asymmetry.
 
RESULTS
 
Study selection
 
We identified 879 studies involving the use of face masks; however, after the application of the inclusion and exclusion criteria (Chart 1), only 20 studies remained. Another 10 studies were excluded after they were read in their entirety, because of methodological biases, a lack of direct correlation with the topic of interest, or failure to provide raw data. Of the remaining 10 studies, only 8 had the raw data available before and after the intervention for statistical analysis and were therefore eligible for inclusion in the meta-analysis. The analyzed studies involved 306 volunteers in the 7- to 64-year age bracket, 68.95% of whom were male. Figure 1 shows a flow chart of the study selection process.

 

Interventions and findings
 
Of the 10 studies that were included in the systematic review, 8 assessed BP, 9 assessed HR, 5 assessed RR, and 5 assessed SpO2. Most of the clinical trials showed no significant changes in the study variables after the use of N95/FFP2 masks during low- or high-intensity aerobic exercise in healthy individuals, and 2 studies that were aimed at assessing all or most of the clinical variables analyzed in this review corroborated this finding.
 
In general, the interventions were of short duration, ranging from 3 min to 12 h on the same day, and participants were instructed to refrain from caffeine consumption in all studies, with the control and experimental groups being evaluated on different days.(6,16-19) Interventions varied greatly among the studies, and some used different devices and methods to measure the study variables. Interventions included walking,(5,20) treadmill walking,(18,19) medium- to high-intensity interval exercise on a cycle ergometer,(6,12,16,21) and going up and down stairs.(22)
 
Meta-analysis
 
Only 8 of the 10 studies included in this review provided sufficient data to analyze BP, HR, RR, and SpO2 in the face of aerobic interventions with and without N95/FFP2 masks.(6,12,16,18,19,21-23) Therefore, only the aforementioned 8 were included in our meta-analysis, totaling a sample of 166 volunteers. The standardized mean difference ranged from −0.32 to 0.17 for BP, −0.27 to 0.13 for SpO2, −0.10 to 0.27 for HR, and −0.16 to 0.28 for RR with the use of a fixed-effects model and with no statistically significant changes for any of the variables. Figures 2-5 show the analysis of the data for each of the included studies.
 
Figure 6 presents a synthesis of the results, a general test of heterogeneity, and differences between the subgroups. The results on the left indicate favorable values for the influence of N95/FFP2 masks on the study variables when compared with no mask use. The heterogeneity test applied in the analysis showed no significant heterogeneity among the studies; therefore, fixed-effects models were used. All of the studies investigated the effects of the use of N95/FFP2 masks on some of the variables analyzed by comparing values obtained with and without mask use.
 
BP
 
As can be seen in Figure 2, the use of N95/FFP2 masks during aerobic exercise had no significant effect on BP in any of the analyzed studies, as evidenced by the diamond crossing the vertical line of null effect, with the diamond representing the synthesis of CIs and relative risks.

 

 
SpO2
 
As can be seen in Figure 3, the use of N95/FFP2 masks during aerobic exercise had no significant effect on SpO2, as evidenced by the diamond crossing the vertical line of null effect. Although Mapelli et al.(21) showed that the use of N95/FFP2 masks had a significant effect on SpO2, their findings did not affect the overall result, because the study sample was small.

 

HR
 
As can be seen in Figure 4, the use of N95 masks during aerobic exercise had no significant effect on HR in any of the analyzed studies, as evidenced by the diamond crossing the vertical line of null effect.

RR
 
As can be seen in Figure 5, the use of N95/FFP2 masks during aerobic exercise had no significant effect on RR in any of the analyzed studies, as evidenced by the diamond crossing the vertical line of null effect.

 
As can be seen in Figure 6, a synthesis of the values collected before and after the interventions for all of the variables in the studies selected for the present meta-analysis showed that the use of N95/FFP2 masks during aerobic exercise had no significant effect on the study variables, as evidenced by the association of CIs and relative risks with the diamond crossing the vertical line of null effect in the forest plots.
 
Chart 2 presents a summary of the studies selected for this systematic review, including sample size, patient age, type of analysis, interventions performed, systolic BP, HR, RR, SpO2, and perceived effort. Values of p < 0.05 were considered to denote a significant change in the variables analyzed.

 

 
Publication bias
 
A funnel plot was used in order to assess the risk of publication bias (Figure 6). A symmetrical distribution is evident for HR, RR, and BP, whereas, in the studies that analyzed SpO2, asymmetry is evident.
 
DISCUSSION
 
This study showed that the use of N95/FFP2 masks in healthy individuals performing aerobic exercise is safe and did not significantly change any of the variables studied. Interventions varied across studies, including aerobic exercise of different intensities, helping us assess the behavior of cardiorespiratory variables during walking and high-intensity interval training. The findings of the present study show that people can train while wearing masks and protect themselves from airway infections, without negative effects on physiological and perceptual responses to exercise.
 
We found that the effects of the use of N95/FFP2 masks during mild to moderate aerobic exercise presented categorical results regarding changes in BP, HR, and SpO2 in maximum and submaximal parameters; it is possible to affirm that these variables were not significantly affected by the respective interventions. (6,12,17-22) We can affirm that BP, HR, and SpO2 do not undergo clinically significant changes with the use of N95/FFP2 masks.
 
According to Harber et al.,(14) increased cardiopulmonary work is seen in individuals with COPD or asthma. This can be due to decreased circulating oxygen levels and/or blood acidosis caused by insufficient inspiration or respiratory disease. The study in question was carried out on three different days, and the groups of individuals with respiratory disease performed light- to moderate-intensity physical activities lasting an average of 8-10 min each. The study variables were tidal volume, minute ventilation, inspiratory flow rate, expiratory flow rate, inspiratory time, expiratory time, RR, mean total respiratory cycle time, and the duty cycle, which represented the proportion of the total respiratory cycle during which inspiratory effort was made.
 
A decrease in the amount of oxygen is mainly detected by the central chemoreceptors in the carotid body. These chemoreceptors induce respiratory upregulation by the effect of the vagus and glossopharyngeal nerves on the ventral respiratory group. Although this is true, it occurs in situations that significantly affect the amount of oxygen available.
 
Changes in the variables discussed in this review may be more commonly observed in individuals with preexisting heart and lung disease.(5,13-15) Therefore, on the basis of the studies that were aimed at investigating BP, it cannot be affirmed that N95/FFP2 masks cause significant changes.(6,12,16,17,20-,23) This is also true for the studies that evaluated SpO2 and HR.(6,12,16-22)
 
Of the 5 studies that evaluated changes in RR,(6,12,18,19,21) only 1 found a significant decrease in RR.(12) Respiratory resistance was analyzed as a secondary variable, and the 2 studies that analyzed it presented conflicting results; 1 found significant changes, and the other did not.(6,16) These results can be explained by reduced VO2max, decreased inspiratory ventilation, and the formation of a negative pressure rebreathing nucleus in some cases.(8,12,24,25) Despite not being included in this review (because they did not meet the inclusion criteria), several clinical studies analyzing respiratory resistance showed significant changes.(1,23,24) However, well-structured clinical trials involving larger samples and a variety of interventions are required in order to confirm this.
 
Although some of the studies evaluating RR and respiratory resistance showed significant changes in both, these findings are not enough to confirm that the use of N95/FFP2 masks causes significant changes in these variables. Respiratory resistance, which was measured noninvasively by means of nasal prongs and metabolic tests, was increased in one of the two studies evaluating it.(12,16) With different interventions and small samples, respiratory resistance is a variable for which there is no consensus regarding changes caused by N95/FFP2 mask use.
 
Some studies have shown that respiratory resistance increases with the use of N95 masks during mild- to moderate-intensity aerobic exercise.(1,12,24) Despite an increase in the number of studies, there is a lack of well-designed experimental and longitudinal studies evaluating the physiological changes caused by mask use. The studies evaluating respiratory resistance included in this review confirm that the use of N95/FFP2 masks during mild to intense aerobic exercise significantly influences this variable.(6,16) Respiratory resistance has been the target of large studies, especially because of the COVID-19 pandemic; therefore, reduced VO2max, decreased inspiratory ventilation, and the formation of a negative pressure rebreathing nucleus remain under investigation.(8,12,24-26)
 
Conflicting results were also found in the six studies that evaluated ratings of perceived exertion on the Borg scale.(6,16,19-22) Three studies showed increasingly significant changes,(21-23) whereas the remaining three showed no significant changes.(6,16,19) Further clinical studies are needed in order to fill this gap because it was impossible to analyze the correlation between changes in ratings of perceived exertion and the study samples given the differing interventions, patient characteristics, and exercise intensities across studies.
 
The evidence developed in the 1990s suggests that the restrictive gas stimulus to oxygen chemoreceptors caused by the respiratory nucleus of face masks results in a decrease in available oxygen, triggering sympathetic stimulus and increasing HR and RR by activation of the ventral respiratory group through the activity of the vagus and glossopharyngeal nerves in the upregulation of these chemoreceptors.(27,28) However, the hypothesis that face masks are capable of causing changes in the cardiorespiratory system has been questioned, especially because of their widespread use during the current COVID-19 pandemic, which has demonstrated that this hypothesis is inconsistent with the results of related studies.
 
Of the 5 studies evaluating RR, only 1 found a significant change contributing to a decrease in RR, a finding that can be attributed to the small sample size (N = 12). The variation between intensity of cardiorespiratory stimulus and burst cannot be confirmed, and nor can the changes related to the use of masks. Clinical trials involving different interventions and larger samples are needed in order to reach a definitive conclusion.(1,2,6,12-14,16,17,26-28) Rebmann et al.(20) also evaluated these variables; however, the evaluations were performed with participants wearing either an N95 mask alone or an N95 mask and a surgical mask, showing no considerable changes. In contrast, Fikenzer et al.(12) observed a decrease in RR. In that study,(12) which is one of the five studies analyzing the variability of RR, the intervention consisted of incremental exercise performed on a cycle ergometer at a speed of 60-70 rpm, the workload being increased by 50 W (as a ramp) every 3 min until voluntary exhaustion. This reinforces the assumption that the variability and intensity of aerobic exercise play a highly relevant role in clinical changes. In recent studies,(5,13,14) individuals presenting with COPD of varying severity and wearing face masks were investigated; mask use was found to cause significant changes in some of the aforementioned physiological parameters, especially respiratory parameters, with a higher degree of disease severity translating to more significant changes. Therefore, clinical conditions and aerobic exercise intensity have strong clinical relevance.
 
There were no significant changes in HR, BP, and SpO2 in individuals in the 7- to 64-year age bracket wearing N95/FFP2 masks in comparison with those not wearing them.(6,7,12,16-18,21,22) Of the 10 studies included in this review, 8 had BP as one of the study variables, and none of the interventions resulted in significant changes in BP.(6,12,17,18-23) Thus, it cannot be inferred that BP changes significantly during and after mask use because the interventions ranged from mild to moderate aerobic exercise in samples of 12-50 participants in the studies showing no significant changes in BP; although these studies together analyzed a total of 188 individuals (i.e., a considerable sample size), studies examining larger samples are needed.
 
In the 5 studies analyzing SpO2, no significant changes were observed during submaximal exercise (mild- to moderate-intensity aerobic exercise); one study found a significant change in SpO2 during maximal exercise. (6,18,19,21,22) The sample size (a total of 198 volunteers) and the differing interventions across studies suggest that N95 and FFP2 masks can cause no changes in SpO2 during mild- to moderate-intensity aerobic exercise. These results may be conflicting because of the differing exercise intensities across studies.
 
Nine studies evaluated HR with and without mask use during the interventions, which ranged from mild- to moderate-intensity aerobic exercise,(6,12,15-19,21,24) showing no significant changes in HR. A total of 282 individuals underwent HR analysis. Given that the findings regarding HR were the same in all 9 studies, the changes observed in the individuals who wore N95/FFP2 masks during aerobic exercise appear to be nonsignificant. However, it is of note that some of the studies that did not meet the criteria for inclusion in this review showed significant changes in HR. These changes may be due to the sample size, a lack of randomization and control (leading to heterogeneity and increased bias), the type of mask used, and the rest period between peak activities, which was considered high.
 
One of the limitations of the present study is the use of only one database for article retrieval. Another limitation is the fact that we did not assess the quality of the evidence using the Grading of Recommendations Assessment, Development and Evaluation method, which is based on analysis of the risk of bias of the selected studies. It is also important to point out the limitations of the studies included in this review: (1) limitations related to the study design (i.e., the difficulty in evaluating physiological parameters in individuals wearing N95/FFP2 masks); (2) differing methods across studies, including differences in exposure time, type of aerobic exercise, and exercise intensity; (3) small sample sizes; (4) differing mask brands and seals across studies; (5) use or lack of use of an exhalation valve; (6) unblinded analyses or inadequate randomization; and (7) inadequate rest period and use of the same sample subjected to different interventions, introducing systematic bias.
 
FINAL CONSIDERATIONS
 
This study suggests that wearing N95/FFP2 masks during aerobic exercise does not have significant effects on the variables analyzed, their use therefore being safe for human health. Respiratory resistance and perceived exertion (as assessed by the Borg scale) during aerobic exercise showed results that are conflicting and inconclusive. Therefore, further clinical trials are required, involving larger samples and different interventions. Finally, we can affirm that, in cases of preexisting diseases of the cardiorespiratory system, changes in HR, RR, and SpO2 tend to be more significant.
 
ACKNOWLEDGMENTS
 
We would like to thank the two independent evaluators for the critical and methodological analysis of the study.
 
AUTHOR CONTRIBUTIONS
 
GLSL, TCR, GPLSJ, and MTM: study conception and design; statistical analysis; and writing of the manuscript. GLSL, TCR, and GPLSJ: data analysis and interpretation. MTM: critical revision of the manuscript for important intellectual content.
 
CONFLICTS OF INTEREST
 
None declared.
 
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