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Table of Contents  
Year : 2022  |  Volume : 16  |  Issue : 2  |  Page : 219-225  

An observational crossover study of N95 respirator with surgical mask and visor in various combinations on healthy volunteers and their impact on physiological variables

1 Department of Anaesthesiology, ESIC Medical College, Hyderabad, Telangana, India
2 Department of Anaesthesiology, AIIMS, Bibinagar, Telangana, India
3 Department of Anaesthesiology, Aster Prime Hospital, Hyderabad, Telangana, India

Date of Submission16-Jun-2022
Date of Decision11-Jul-2022
Date of Acceptance21-Jul-2022
Date of Web Publication06-Sep-2022

Correspondence Address:
Dr. Kalyani SDL Sangineni
Flat No. 405, Vasavi Bhuvana Apts, Srinagar Colony, Hyderabad - 500 073, Telangana
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/aer.aer_97_22

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Background and Aim: The COVID pandemic necessitated the use of masks to reduce the propagation of coronavirus by airborne transmission. This research was conducted in healthy volunteers to assess the changes in noninvasive measurable physiological variables over 45 min at rest. Methods: This was a prospective randomized controlled crossover trial. Twenty-one healthy volunteers were monitored for pulse rate (PR), peripheral oxygen saturation (SpO2), systolic blood pressure (SBP), diastolic blood pressure (DBP), respiratory rate (RR), inspired carbon dioxide and expired carbon dioxide (ECO2), inspired (FiO2) and expired oxygen (FeO2), every 15 min for 45 minute (min) with N95 respirator, N95 respirator with surgical mask (SM), N95 with SM and visor (V), SM with N95, and N95 respirator with visor. Results: Repeated measures analysis of variance (ANOVA) of PR, RR, SpO2, SBP, and DBP over time within the group and intragroup was calculated and found statistically insignificant. P value for comparison of mean value within the group was calculated by paired t-test with Bonferroni correction. There was a significant rise in ECO2 in the N95 group over time, and repeated measures ANOVA showed P = 0.04 at 30 min between the N95 + V group and the N95 + SM + V group. Inspired CO2 was statistically significant over time in the N95 + SM + V with P = 0.02. Conclusion: N95 alone or in combination with a SM and visor does not cause any clinically significant measurable physiological derangements. The inspired CO2 may be implicated in the symptoms manifested by individuals.

Keywords: Carbon dioxide, health personnel, N95 respirators, oxygen, oxygen saturation

How to cite this article:
Nanda A, Sangineni KS, Pakhare V, Ramachandran G, Chellaboyina CS. An observational crossover study of N95 respirator with surgical mask and visor in various combinations on healthy volunteers and their impact on physiological variables. Anesth Essays Res 2022;16:219-25

How to cite this URL:
Nanda A, Sangineni KS, Pakhare V, Ramachandran G, Chellaboyina CS. An observational crossover study of N95 respirator with surgical mask and visor in various combinations on healthy volunteers and their impact on physiological variables. Anesth Essays Res [serial online] 2022 [cited 2022 Dec 4];16:219-25. Available from:

   Introduction Top

The N95 respirator has been recommended as a protective device in COVID-19 infection.[1] Surgical masks (SMs) are worn to reduce the direct transmission of infectious particles and to avoid contact with droplets.[1] The Institute of Medicine has suggested concurrent use of SMs, with an N95 respirator to potentially extend N95 respirator life.[2]

N95 respirator with SMs and face shields were used routinely to reduce the risk of infection transmission and extend the life of N95 respirator which were in critical supply.[3] This study was done to assess the impact of N95 respirator in various combinations with SM and visor (V) on physiological parameters in healthy volunteers.

   Methods Top

This prospective, randomized, crossover study was done over a period of 2 months from September 2020 to November 2020, after approval from the Institutional Ethical Committee registration number (ESICMC/SNR/IEC-F0210/08-2020) version no. V01 in accordance with the Helsinki Declaration (2013), and was registered at bearing CTRI number CTRI/2020/12/029453. Twenty-one healthy volunteers were enrolled in the study after taking written informed consent. The study inclusion criteria required the participants to be without a history of any chronic disease, any symptoms suggestive of COVID, or previous history of COVID. The exclusion criteria included the history of current smoking, pregnancy, cardiac, neurological, psychological, and respiratory disorders.

All participants completed the test in 24 h and had a small meal before the test and refrained from any coffee or tea 12 h before the test. The tests were conducted with the participants wearing comfortable scrubs and sitting in a relaxed position. Randomization was done with the series of how the masks were varied by a computerized random number generator [Figure 1]. The participants were connected to a dedicated anesthesia workstation (model- SpaceLabs, BleaseSirius, UK). The Pulse rate (PR), peripheral oxygen saturation (SpO2), noninvasive blood pressure (NIBP) respiratory rate (RR), inspired carbon dioxide (ICO2) in mmHg, and expired carbon dioxide (ECO2) in mmHg, inspired oxygen (FiO2) and expired oxygen (FeO2) in mmHg were recorded every 15 min for 45 min.
Figure 1: Randomization and allocation of volunteers

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Safety measures followed temperature screening on entry to the building and hand sanitization, and each subject was provided with individual packs of masks. The monitors were sanitized before and after every individual use. Only the observing researcher was present with the subject to monitor and collect data while maintaining adequate distance.

To take adequate safety measures, N95 respirator was connected to the capnogram so that the expired CO2 was measured at the nostril in an aseptic manner and the sampling line was changed for each individual. The first reading after wearing the mask was taken as the baseline value and the NIBP, ECO2, ICO2, SpO2, HR, RR, FiO2, and FeO2 were recorded. Subsequently, these parameters were recorded every 15 min till 45 min.

Participants were given an N95 respirator of NIOSH standard, optimally fitting, and fit was checked by the observing researcher. The physiological data were recorded for each individual with the five subsets of different variations of masks and face shield for the same person.

Standard three-ply SM with melt-blown fibers was used. The face shield was made of clear plastic providing good visibility, with an adjustable band attaching firmly to the forehead, completely covering the sides and length of the face [Figure 2]. The different combinations were as follows:
Figure 2: N 95 Mask with the gas analyzer sampling line attached and a volunteer performing the exercise

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  • N95 group – N95 respirator only
  • N95 + SM group – N95 with SM on top
  • N95 + SM + V group – N95 with SM and visor/face shield
  • SM + N95 group – SM with N95 on top
  • N95 + V group – N95 with visor.

Monitoring was done on the same workstation to maintain calibration for all participants with a 5-min break between each combination.

Data were tabulated in Microsoft Excel version 16 and were analyzed in “R” software version 3.6.3 (R Foundation for Statistical Computing, Vienna, Austria). The quantitative variables were described in mean and standard deviation (SD) and the categorical variables were expressed in terms of percentages. For the comparison of means (SD) at various time intervals, repeated measures analysis of variance (ANOVA) was used, and the P value was calculated from ANOVA table or sphericity table after applying Mauchly's test of sphericity (if P value for Mauchly's test of sphericity <0.05, sphericity table value was used). For pairwise comparisons between two-time intervals, paired t-test was used with Bonferroni correction for the calculation of P value. With 95% of CI, P < 0.05 was considered statistically significant.

   Results Top

A total of 21 participants were recruited for this study. Among them, 11 (52.4%) were females and 10 (47.6%) were males. The mean age of the study participants was 33.52 ± 4.28 years. The mean height of the study participants was 166 ± 3.5 cm and the mean weight was 68.71 ± 4.75 kg. All the physiological parameters were measured for each group at 0, 15, 30, and 45 min. The measurement at time zero was considered baseline, and the effect of various combinations of masks and visor was assessed at 15, 30, and 45 min.

There were no significant changes in PR, SpO2, RR, systolic blood pressure (SBP), and diastolic blood pressure (DBP) within the groups over time or between the groups, as shown in [Table 1].
Table 1: Mean±SD and P value of systolic blood pressure, diastolic blood pressure, expired carbon dioxide, inspired carbon dioxide, peripheral oxygen saturation, heart rate, respiratory rate, inspired oxygen, and expired oxygen of N95, N95+surgical mask group, N95+surgical mask+visor group, surgical mask+N95 group, and N95+visor group at 45 min

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ECO2 in the group SM + N95, via repeated measures ANOVA, had P = 0.04, representing an increase in ECO2 over time. Repeated measures ANOVA between the groups showed significant P = 0.032 between the N95 + V and the N95 + SM + V groups at 30 min [Table 2].
Table 2: Repeated measures analysis of variance between the groups comparing expired carbon dioxide, inspired carbon dioxide, peripheral oxygen saturation, inspired oxygen, expired oxygen, respiratory rate, systolic blood pressure, and diastolic blood pressure at 30 min

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ICO2 mean values varied between 2.57 and 3.86 mmHg, higher than the levels in atmospheric air, but the increase over time by repeated measures ANOVA was significant in the N95 group (P = 0.003) and the N95 + SM + V group (P = 0.02) and there was no significant differences between the groups [Table 2]. [Table 3] represents P value for comparison of mean value within the groups at all three timelines using paired t-test with Bonferroni correction.
Table 3: Intra group comparison of mean values of all parameters at 3 timelines using paired t- test with Bonferroni correction.

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The sum of ECO2 and ICO2 was highest at 30 min in the N95 + SM + V group [Figure 3].
Figure 3: Sum of inspired CO2

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   Discussion Top

Wearing a face mask has been recommended for the prevention of the spread of infection from person to the person be it the SARS or the COVID-19.[4],[5] The effect of the N95 respirator SM and visor on several physiological factors has been studied to understand and identify any pathophysiological changes affecting the health of the wearers amid several complaints of headache and exhaustion. Prolonged use of N95 respirators and SMs causes adverse physical effects such as headaches, breathing difficulties, acne, skin breakdown, rashes, and impaired cognition. It also interferes with vision, communication, and thermal equilibrium.[6],[7] The concomitant use of N95 respirator with SM was dominant in health-care workers to extend the life of N95 and to protect the mask from infectious aerosols or splatters during procedures.

N95 respirator has been reported to be more efficacious than surgical masks in reducing exposure to viral infections.[8]

This study has measured the NIBP, ECO2, ICO2, SpO2, HR, RR, FiO2, and FeO2 with the combinations of N95 respirator, SM, with and without visor at rest to get a baseline of physiological measures.

Roberge et al. investigated the impact of N95 respirator on volunteers, walking slowly on the treadmill, and found no impact on the RR or the tidal volume.[8] A meta-analysis reviewing the use of N95 respirator during exercise has also concluded that wearing it has only small effects on physiological response and no effect on exercise performance.[9] In our study, the sampling of CO2 was done at rest, and there was no significant increase in ECO2 levels while wearing the N95 respirator, but among the various combinations, the N95 + SM + V and the N95 + V groups were significantly different (P = 0.032) at 30 min and not significant at 45 min, which could not be explained as there were no changes in heart rate or RR as compensation.

The mathematical significance of a rise does not necessarily translate into a clinically significant increase as the ECO2 values were <40 mmHg with the highest mean value of 36.38 at 45 min while wearing N95 + SM + V. As exhaled air can also be trapped in the dead space created between the mask and the face depending on how well the mask fits on an individual, this fraction of air when inhaled again may contribute to the increase in ECO2 as well as decreased FeO2 (14.52%).[10] A significant decrease (P = 0.001) in the expired oxygen FeO2 at 30 and 45 min in the SM + N95 and N95 + V groups was recorded.

The other significant finding was the increase in inspired CO2, caused by the design of the mask causing rebreathing identified by computational fluid dynamics.[11] As per Zhu et al., nearly 60% of the respired air re-entered the nasal cavity during the next inspiration which is in concordance with our findings of mean inspired CO2 of 2.57–3.86 mmHg at 45 min with different combinations of masks and visor.[12] An increase in inspired CO2 after donning N95 respirator has been documented by Sinkule et al. at values of 1.2%–3%, and Roberge et al. at 3%.[8],[13]

Inspired CO2 at low concentrations (<10,000 ppm) has little or no toxic effects, and calculating the ppm for 2%–3% would be 2631–3947 ppm (vapor pressure × 106/atmospheric pressure in mmHg). Exposure to ICO2 between 2% and 3% produces sweating, headache, and dyspnea while 4%–5% of ICO2 is associated with dyspnea, headache, dizziness, and raised blood pressure.[14],[15] The increase in ICO2 right from the first breath could explain the increase in headaches, without significant change in other physiological parameters.

The changes in PR and RR in all the groups were not significant over time at rest, as seen in previous studies.[8],[9] The pulse oximetry findings at no time were clinically decreased over the course of 45 min in any of the groups, the range being 96%–100% which is well within the normal physiological limits in concordance with several researchers.[9],[10],[16],[17] The statistically significant value (P = 0.02) in the N95 + SM + V group was clinically irrelevant as the mean SpO2 values ranged from 99% to 99.29%. Significant decreases in SPO2 were seen in volunteers doing maximal exercise, and these studies documented mean saturation of 97.7% ± 0.5% and 95.1% ± 3.1%, respectively, which was again well within the acceptable normal range.[10],[16]

The use of SM over an N95 respirator also did not reflect any significant impact on the physiological variables which has been verified by previous studies.[2],[18],[19] It has to be remembered that N95 has to be discarded when it is damp, contaminated with body fluids, or when there is cross-contamination.[19],[20]

In 2013, Rebmann et al. examined the impact of N95 respirators alone compared to N95 respirators with a SM overlay in nurses during a 12-h shift. Transcutaneous CO2 increased in the 12 h shift, both in nurses wearing an N95 respirator and those who had a SM on top of their N95 respirator. However, while CO2 elevations were statistically significant after the 12-h shift, the changes are likely not clinically important, as CO2 remained within healthy normal ranges (< 45 mmHg).[21]

There were also several health-care workers, who wore the SM under the N95, and regarded that as the best way to reuse the N95 mask, and as per our findings, this variant of the use of the SM + N95 also did not make any significant changes to the physiology at rest though the ECO2 (P = 0.04) increase and the FeO2 (P = 0.01) decrease were numerically significant, but the range of ECO2 over time was between 32 and 44mmHg and FeO2 was 13–15 mmHg.

There was a shortage of data available regarding the effect of visors/face shields on physiological variables to compare with our study. The fear of COVID in the first wave was associated not only with strict compliance but also with the simultaneous use of a visor and surgical mask with a N95 respirator, reinforcing the philosophy of more is better.

The advantages of face shields over regular SMs are numerous. While SMs have limited availability and are disposable, face shields can be reused and are easily cleaned. They are comfortable to wear, retain less dermal facial heat, have no impact on breathing resistance, are less claustrophobic, and are inexpensive.[22] They reduce the potential for autoinoculation by preventing the wearer from touching their face, and essentially protect the entire face and not only the expiratory pathway.

As per our findings, there was a small increase in ECO2 with the use of a visor with N95 respirator and with N95 + SM, but this was not clinically significant during the 45 min of study though it was statistically significant. Further studies during exercise and of longer duration will have to be done to make any final conclusion. The use of N95 with visor has been found to significantly impair speech perception which could hamper communication.[23]

The effect of the various combinations of the N95, SM, and the visor on the systolic and DBP was negligible as also found by various researchers.[24]

The limitations of our study were that it was performed on health-care workers at rest and the parameters obtained were over a period of 45 min which is not sufficient to gauge the degree of discomfort and development of adverse effects related to an increase in inspired and expired CO2. Being a crossover study, the incidence of headache, exhaustion, and other reported side effects was not documented. Another limitation of the study was that the baseline values of all parameters were noted after donning of mask, due to which the inspired CO2 values at 0 min were higher than normally seen in the environment.[25] Moreover, this inspired CO2 could be the main culprit for the cause of headaches and other side effects posed by donning masks.

Increased headache in health-care workers depends on the type of mask, and duration of use.[26],[27],[28] The rating for perceived exertion and dyspnea was higher with the use of N95 respirator, and this could account for the discomfort perceived by the health-care workers. The discomfort and headaches associated with the mask use could also be due to increased resistance to breathing over time and the increase in humidity and temperature around the face associated with a tight-fitting mask.[29]

   Conclusion Top

This is the first cross-sectional analysis over 45 min with different combinations of N95, SM, and visor measuring the physiological variables done at rest, and our analysis of the measured parameters of PR, SpO2, SBP, inspired and ECO2, and inspired and expired oxygen shows no clinically significant changes albeit a small but statistically significant increase in expired CO2, with the use of N95 mask + SM + visor at 30 min. The effect of raised ICO2 from the start of wearing the mask has to be considered a possible cause for the higher incidence of headaches in individuals wearing any type of mask, as this is caused by the rebreathing of air within the dead space of the mask.


We would like to thank Dr. Smaranita Sabat, Assistant Professor, Department of Community Medicine, SUM Hospital, Bhubaneshwar, and Dr. Debasish Pandit, Department of Community Medicine, Shri Jagannath Medical College and Hospital, for their help with the statistical analysis and making of the graphs.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2], [Table 3]


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