Facemask wearing does not impact neuro-electrical brain activity

Given the massive use of facemasks (FMs) during the covid-19 pandemic, concerns have been raised regarding the effect of FMs wearing on overall health. This study aimed at evaluating the effect of surgical FM on brain neuro-electrical activity. Electroencephalography (EEG) background frequency (BGF) and background amplitude (BGA) was performed on 30 volunteers before (baseline), during and after wearing a FM for 60 min. Measurements were done during normal ventilation, hyperventilation and post-hyperventilation (PHVR). Blood gas levels were assessed at baseline and after FM use. EEG analysis concerning baseline (without FM) (BGA), was 47.69 ± 18.60 µV, wearing FM, BGA was 48.45 ± 17.79 µV, post FM use BGA was 48.08 ± 18.30 µV. There were no statistically significant differences between baseline BGA and BGA under FM and post FM. BGF, Baseline data were 10.27 ± 0.79, FM use 10.30 ± 0.76 and post FM use was 10.33 ± 0.76. There were no statistically significant differences between baseline BGF and BGF under FM and post FM. Venous blood gases, and peripheral oxygen saturation were not significantly affected by FM use. Short-term use of FM in young healthy individuals has no significant alteration impact on brain's neuro-electrical activity

. This new virus was first identified in the city of Wuhan in the Hubei province 1 . Since then, it has spread to over 203 countries, and was officially declared as a global pandemic illness by the World Health Organization (WHO) 2 . After almost 2 years, the COVID-19 pandemic has left a toll of 446 million infected and more than 6.0 million deaths worldwide 3 . From the beginning of the COVID-19 pandemic, the use of facemasks (FMs) has been controversial due to political, cultural and economic causes. However, multiple studies have highlighted the efficiency of FM in the reduction of COVID-19 transmission (i.e., from 6 to 80%) 4 . In another report the use of medical/surgical masks reduced the transmission rates by 85% 5 . Countries worldwide have adapted many different approaches to control the disease 6 . Non-pharmaceutical actions included the use gowns, gloves, and FM, all of which have been proven to be effective and more recently, the use of vaccines such as the BNT162b2 mRNA Covid-19 vaccine, Curevac, Moderna, AstraZeneca, and Sino pharm has proven effective in the control of the pandemic [7][8][9][10] .
Some side effects associated with the use of FMs have been reported. The most common side effect described by healthcare workers was bilateral headaches (affecting up to 80% of users), dermatitis, itchy rash and elevated heart rates 11 . However, the WHO has advised populations to wear FMs on a large scale only excluding patients with limited respiratory conditions 4 . Recently updated guidelines issued by the WHO advised the use of FMs as part of its prevention recommendations which also included hand hygiene, physical distance of at least 1 m, avoidance of face touching and adequate indoor ventilation 2,12 .
Previous clinical studies have addressed the potential impact of FMs on brain and cognitive functions 13,14 . One study in healthy young people showed that the 150-min use of surgical mask had no significant mental fatigue perception 13 while another showed that the prolonged use of FMs can result in headache and impaired cognition 14 .
Recent physiological studies with capnogrphy while wearing FMs, demonstrated an increased end tidal (ET) CO 2 by 7.4% causing increased cerebral blood flow(CBF) and inducing global gray matter activation 15 . Another study on the cerebral dynamic conditions of the brain and oxygenation, demonstrated small but significant changes in the cerebral hemodynamics while wearing a FM in young adults. However, the changes were similar to those of daily life activity and did not suggest a hypoxic effect 16 . Changes in cerebral blood flow (CBF) can affect brain metabolism and EEG activity 17 .
There is paucity of information on physiological effects of FMs on the bioelectrical activity of the brain. The current global use of FMs as a results of the current pandemic has motivated us to investigate the short-term impact of FMs use on the brain's neuro-electrical activity. This impact may be caused by the possible hypercapnia during inspiration while wearing FMs 18 . Our hypothesis is that the use of FMs could affect the bioelectrical activity of the brain due to possible hypercapnia or hypoxemia, before the development of clinical symptoms during hyperventilation and post hyperventilation during FM use or post FM use.

Methods
Study sample. We conducted a cross-sectional study performed on healthy volunteers to determine the impact of FM use on the brain's bioelectrical activity and respiratory function. We included young and healthy subjects from a homogenous group of medical students. The following parameters were analyzed in all the participants: age, gender, length, weight, body mass index, heart rate, diastolic blood pressure, systolic blood pressure, and FM use time per day. The exclusion criteria were the presence of any respiratory or neurological illnesses.
All volunteers used a disposable surgical FM (HiTEX Manufacture of Medical Devices, Tybe IIR, NH0050, FDA CE, Amman, Jordan). The participants were investigated during 2 different sessions 72 h apart with all tests performed in the morning.
The study was carried out by the Neuroscience and Respiratory team at Jordan University Hospital (JUH) and was conducted in accordance with the Declaration of Helsinki and approved by our institutional review board committee (IRB) (reference number 10-2021-4251) at JUH. A written informed consent form was obtained from all participants and informed consent for publication of the image was obtained from the participant.
Measures (day 1). All demographic and general data were gathered at the beginning of the study, in day one.
Respiratory function (spirometry). We used VIASYS Health Care device (model Vmax Ecnone; S/ N77400SEP05, GmbH, made in Germany) to determine the forced vital capacity (FVC), forced expiratory volume in one second (EFV1) and FEV1/FVC] ratio. The preparation of participants included the removal of tight clothes, and placement of a soft clip was on the nose with a sterile mouthpiece and filter attached to the spirometer.
For the respiratory procedures, participants took deep breaths, followed by a breath hold for a second, forced exhalation into the mouthpiece for 6 s, followed by another deep breath. The test was repeated three times to make sure that the results were consistent. The highest the reading was considered as the tests result. In spirometry, the FEV1/FVC was calculated from the FEV1 and FVC results. The device used the predicted values to provide FVC, EFV1 percentages and FEV1/FVC ratio for the test subjects.  (Fig. 1a). Background frequency (BGF) and background amplitude (BGA) in microvolts without facemask at Scalp surface (EEG) epochs each for 10 min, were recorded while the participant was relaxed with his eyes closed to induce alpha background activity. Each epoch included: 3 min of normal breathing, 3 min of hyperventilation and 4 min of post hyperventilation. All data were collected and analyzed statistically.

Measures (day 2).
On this day, participants wore FMs and oxygen saturation was measured as follows: Starting in the morning after 60 min of FM use, 10-min EEG recording were performed while the participants were still wearing the FMs, and then after taking off the mask for another 10 min. Each epoch included: 3 min of normal breathing, 3 min of hyperventilation and 4 min of post-hyperventilation. The following EEG parameters were measured while wearing the FMs: BGF, BGA, response during hyperventilation (DHVR) and post-hyperventilation response (PHVR). BGF and BGA (normal alpha 8-13 Hz and normal amplitude (0.5 to 100 microvolts) are frequently measured in daily EEG practice (Fig. 1b). Boxplots of background frequency and amplitude in the three phases of the study; baseline, FMs wearing and post-FMs wearing recording were generated. These parameters were compared to each other looking for any changes related to FM use.
Statistical analysis. The statistical analysis was performed using statistical analysis system IBM SPSS  www.nature.com/scientificreports/ less than 0.05. Sample size was calculated using G*power 3.0.10 (Universität Kiel, Germany). A priory analysis was performed using a t-test for two dependent means, with an α-error probability of 0.05 and β-error of 80%.

Electroencephalography (EEG) results.
The baseline BGF was of 10.27 ± 0.79, whereas BGF for FM use was10.30 ± 0.76, and post FM use was of 10.33 ± 0.76. There were no statistically significant difference between baseline, FM use and post FMs BGFs (P = 0.317) and (P = 0.157), respectively ( Table 3). Boxplot of background frequency in the three phases of the study baseline, wearing FMs and post-FMs recording showing no significant difference. Baseline BGA was of 47.69 ± 18.60 µV, whereas BGA for FM use was of 48.45 ± 17.79 µV, and post FMs use BGA was 48.08 ± 18.30 µV. There were no statistically significant differences between baseline, FM use and post FM use BGAs (P = 0.528 and P = 0.807, respectively) ( Table 3). Boxplot of background Amplitude in the three phases of the study baseline, wearing FMs and post-FMs, recording showing no significant difference (Table 3).

Discussion
The first recorded evidence of the use of FMs to prevent the spread of a pandemic was during the Spanish flu pandemic between 1917 and 1918 16 . Its use was subsequently extended to the operating rooms in Germany and USA during the 1920s, especially for minor surgical procedures 17 . In the 1940s, reusable gauze FMs gained popularity in surgical settings 17,18 . During the 1960s, the use of disposable FMs was introduced in the USA. This new type of FM was also used to protect healthcare workers from airborne infections by blocking the transmission of bacteria or viruses through respiratory droplets 19 . The use of disposable FMs shortly spread to the rest of the world.
During the current pandemic there has been great debate over the use and effectiveness of FMs to prevent the propagation of the COVID-19 virus. Research has shown that the use of medical FMs was able to reduce the transmission of the virus by up to 85% 5 . However, the use of FMs is also associated with some disadvantages involving the emotional function and social interactions. For example, FM use may interfere with facial expressions such, anger, disgust, fear, happiness, or sadness 19 . In addition, use of FMs may hinder communication as it may alter the tone and quality of the voice 19,20 . It has also been reported that FM use could lead to an impaired immune response, altered cardio-metabolic stress response, renal function, brain metabolism and mental health 21 . Rosner et al. has reported that the prolonged use of masks results in a host of physiologic and psychologic burdens and could decrease work efficiency 14 . Furthermore, it could have a negative impact on the cardiopulmonary capacity mainly during physical effort 22 , potentially leading to sudden death during heavy exercise 23 . However, a recent study 24 performed on 11 young and healthy subjects showed that exercise under FM use does not present a physiological barrier to physical exercise, from a cardiovascular and oxygenation perspective. In our study of we observed that SpO 2 , remained within the normal range after FM use for a period of 70 min in resting conditions.
Previous studies have shown that FMs, can exert a significant respiratory effect, through CO 2 rebreathing due to CO 2 accumulation under the face mask, and decreased inhaled the O 2 concentration. Resulting in hypercapnia which may lead to headaches, sweating and dizziness 18 . Although similar symptoms are also associated with orthostatic intolerance, often present in cases of hypocapnia 25 . Moreover, some studies have shown that FM use could also cause hypocapnia in addition to hypercapnia 25 . However, in our study, no VBGs changes were observed at the different stages of FM use.
Previous research has found that the use of FM was associated with a significant change in baseline bold levels in gray matter on a fMRI study 15 . Moreover, Law et al. observed that the end-tidal CO 2 capnography, increased by an average of 7.4% induced by FM use 15 . However, this report has several limitations mentioned by other authors 26 . Accordingly, Scholkmann et al., highlighted that the end-tidal CO 2 is not an optimal marker to assess hypercapnia induced by FM use, and suggested that a simultaneous monitoring of brain activity and hemodynamics would be needed to evaluate the relation between FM use and brain activity 26 . Our findings are similar to the results of previous research in which changes in the hemodynamic conditions of the brain in young adults who used FMs for one hour were comparable to those during daily life activities 16 . Moreover, a novelty of our study is that brain activity was monitored simultaneously with VBGs (i.e., at baseline, during FM use and post FM use), with no significant changes between the different measurement points. These results are in agreement with previous reports in which FM use was not associated with VBGs changes 22,27,28 .  17 . However, to the best of our knowledge, our study is the first to analyze the effect of FM use on the neuro-electrical activity of the brain. In our study, there was no association between FM use and EEG changes during normal ventilation, hyperventilation and post hyperventilation. This may not be surprising considering that we did not find any increase in blood CO 2 level, which could lead to decreased EEG activation and impaired mental and psychomotor function 29 . Our study is susceptible to certain limitations. It only investigated the short term effect of FM use and did not include older or unhealthy individuals. Therefore, these results cannot be extrapolated to older age groups and to patients with respiratory and cardiac conditions or cerebral disorders like stroke and epilepsy. Larger studies are needed to analyze the effect of a prolonged use of FMs on the respiratory and brain functions.
Furthermore, we only chose BGF and BGA of EEG as the measurements of brain neuro-electrical activity. These measures may not be as sensitive as other biomarkers, such as genetic, biochemical and neuroimaging biomarkers to assess the brain neuro-electrical activity. These latter biomarkers need to be tested to characterize the effect of surgical FM on brain neuro-electrical activity. In this respect, it is noteworthy that the current exploratory study using EEG as simple, practical neurophysiological biomarker was carried out under the extreme The record showed no significant difference in the frequency or amplitude of background rhythm between groups, with an almost identical median for the frequency and amplitude. Table 4. Venous blood gases (VBGs): baseline vs. facemask wearing and peripheral oxygen saturation (SpO 2) under facemask wearing. FM, facemask; pH, potential hydrogen; CO 2 , carbon dioxide; cHCO 3 , concentration of hydrogen carbonate; ctCO 2 , total carbon dioxide concentration in plasma; BE, base excess; SO 2, oxygen saturation; SpO 2, peripheral oxygen saturation. Differences between dependent variables were analyzed using Student's T test for paired samples or Wilcoxon test.