Prospective analysis of the physiological changes caused by prolonged use of N95-type masks : Annals of Thoracic Medicine

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Prospective analysis of the physiological changes caused by prolonged use of N95-type masks

Demirag, Melis E.; Akyil, Mustafa1; Karasal, Merve1; Bayram, Serkan1; Metin, Serda Kanbur1; Tokgoz, Fatma A.2; Baysungur, Volkan1; Evman, Serdar1,

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Annals of Thoracic Medicine 18(2):p 86-89, Apr–Jun 2023. | DOI: 10.4103/atm.atm_429_22
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The clinical and physiological effects of long-duration use of N95-type masks without ventilation valves, on health-care workers during the coronavirus disease-2019 (COVID-19) pandemic, were evaluated.


All volunteering personnel working in operating theater or intensive care unit, using nonventilated N95 type respiratory masks, minimum for a 2-h noninterrupted duration were observed. The partial oxygen saturation (SpO2) and heart rate (HR) were recorded before wearing the N95 mask and at 1st and 2nd h. Volunteers were then questioned for any symptoms.


A total of 210 measurements were completed in 42 (24 males and 18 females) eligible volunteers, each having 5 measurements, on different days. The median age was 32.7. Premask, 1st h, and 2nd h median values for SpO2 were 99%, 97%, and 96%, respectively (P < 0.001). The median HR was 75 premask, 79 at 1st h, and 84/min at 2nd h (P < 0.001). A significant difference between all three consecutive measurements of HR was achieved. Statistical difference was only reached between premask and other SpO2 measurements (1st and 2nd h). Complaints seen in the group were head ache (36%), shortness of breath (27%), palpitation (18%), and nausea feeling (2%). Two individuals took off their masks to breathe, on 87th and 105th min, respectively.


Long duration (>1 h) use of N95-type masks causes a significant reduction in SpO2 measurements and increase in HR. Despite being an essential personal protective equipment in COVID-19 pandemic, it should be used with short intermittent time periods in health-care providers with known heart disease, pulmonary insufficiency, or psychiatric disorders.

During the epidemic diseases that have emerged in recent years and the ongoing severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic, the use of respiratory personal protective equipment is essential, especially for health-care workers whom are at high risk of transmission. The most frequently used ones are N95 (American standard, CDC), FFP2 (European equivalent of N95), and FFP3 (N98) masks.[1] N95 mask is a type of respirator that filters at least 95% of very small (0.3 μ) particles from the inhaled air, including bacteria and viruses.[2]

Although uncomfortable and distressing, proper and continuous use of respiratory protective masks is vital for health-care workers fighting against the pandemics. There are underlying physiological and psychological factors for noncompliance with the mask. The main complaint of N95 mask users is difficulty in breathing. Approximately 30% of health-care professionals often complain of dyspnea while wearing N95 masks.[3]

It has been reported that N95 masks can cause hypoxemia and hypercapnia, respiratory complications, self-contamination, and exacerbation of existing chronic diseases.[4,5] In our study, we investigated the clinical and physiological effects of long-term use of the N95 mask without an exhalation valve on health-care workers.


This study took place in a tertiary referral hospital between October 2020 and October 2022, after retrieval of University of Health Sciences, Sureyyapasa Chest Diseases and Thoracic Surgery Hospital, Ethics committee approval (02.07.2020/092) and Republic of Turkey, Ministry of Health (2020-05-11T11_23_05) approvals. We prospectively measured the heart rate (HR) and partial oxygen saturation (SpO2) of all volunteering health-care workers (nurses, residents, and specialists in a single surgical clinic) using nonventilated N95 type respiratory masks (ERA® FFP2 mask, EN 149:2001 + A1:2009), minimum for a 2-h noninterrupted duration, in the intensive care unit or operating room. Data were collected for premask, 1st h, and 2nd h values for each measurement and for any complaint (headache, palpitation, nausea, and dyspnea) present at the end of the planned (2 h) duration. Eligible healthy volunteers had undergone five different measurements on different days with a digital pulse oximeter, to minimize the individual bias. The results were obtained for evaluation and comparison.

Health-care workers who did not volunteer or give written permission were not taken into the study. Due to the potential of triggering a present systemic illness, volunteers with any known cardiac, respiratory, neurological, or psychiatric disease were also excluded.

Statistical analysis

Statistical analysis was conducted using the Jamovi Project Version 1.6 (2021) software (retrieved from Since the cohort showed nonnormality on the Shapiro–Wilk test (<0.05), variables were given with the median and interquartile range (IQR) values. Continuous variables were reported with their medians and IQR, and categorical variables were reported with frequencies and percentages. The significance of the change in consecutive HR (bpm) and SpO2 (%) measurements was compared with Friedman’s test, and post hoc comparisons were performed with Conover’s test. All P values were corrected as suggested by Bonferroni. The accepted maximum type I error in this study was 5%.


A total of 210 measurements were completed in 42 (24 males and 18 females) eligible volunteers. The median age was 32.7 (IQR = 10). Premask, 1st h, and 2nd h median values for partial oxygen saturation were 99%, 97%, and 96%, respectively (P < 0.001). The median HR of the group was 74 before putting on the mask, 79 on the 1st h, and 86 at the end of the 2nd h (P < 0.001). All measurements are given and compared in Table 1.

Table 1:
Distribution of measured variables

Conover’s post hoc comparison test revealed a significant difference between all three consecutive measurements of HR. Statistical difference was only achieved in the premask and the other (1st and 2nd h) SpO2 measurements. No significant difference was found between SpO2 measurements at the 1st and the 2nd h [Table 2].

Table 2:
Conover’s post hoc (inter-group) comparisons

Eighty (38%) of the measurements were uneventful. In the other 130 (62%), at least one complaint was seen during or at the end of the planned 2-h period [Table 3]. Most frequent complaint seen was headache in 76 measurements (36%), followed by shortness of breath in 57 (27%), palpitation in 37 (18%), and nausea feeling in 4 (2%) measurements. Two different individuals necessitated to quit the study and took of their masks to breathe, on 87th and 105th min, respectively.

Table 3:
Complaint incidences


The use of respiratory protective devices is important in the coronavirus disease-2019 pandemic, where the respiratory and droplet path is defined as the main source of transmission. Surgical face masks do not provide adequate filtration against aerosolized infectious agents of 10–80 nm (nanometers), and they do not perfectly fit on the face.[6–8] N95 masks are a type of respirator that removes particles from the inhaled air. These masks filter at least 95% of very small (0.3 μ) particles, including bacteria and viruses. Therefore, in areas with infectious disease risk such as tuberculosis and SARS-CoV-2, health-care professionals are recommended to use N95 masks.[2,4] However, as stated in literature, a quantity of people in the general population and even health-care professionals who are expected to be well-educated about this issue repeatedly move their masks or do not wear them when necessary.[1,3,9]

The presence of the exhalation valves reduce exhalation resistance and make it easier to breathe or exhale, but the surgical N95 respirators are designed without exhalation to prevent unfiltered exhaled air into the sterile area and contamination.

Proper and uninterrupted use of respiratory protective masks is crucial for health-care workers struggling with epidemics. However, it has some effects on respiratory parameters. It leads to a significant increase in respiratory effort to overcome an increase of approximately 300% in expiratory and inspiratory flow resistance and to maintain adequate expiratory flow rate.[9] It causes hypoventilation with an average of 37% reduction in air exchange volume in N95 users. In this way, respiration of CO2 increases respiratory fatigue and physical working capacity is impaired.[9,10] In a study on patients wearing N95 masks during the hemodialysis procedure, the partial arterial oxygen pressure decreased from 101.7 to 92.7 mmHg, the respiratory rate increased from 16.8 to 18.8/min, and complaints of respiratory distress and chest pain are reported.[11] In another study, it was observed that the use of a surgical face mask during major surgery also decreased oxygen saturation by more than 1% and increased the HR by five beats/min.[12] In our study, we observed 2% and 3% drop of SpO2 on 1st and 2nd h, respectively; statistical difference was found between the saturation measurements prior to and after wearing the mask (P < 0.0001). The basal median HR of the group rose from 75 to 79 at 1st, and then to 84 at the end of the 2nd h, with a significant difference between all consecutive HR measurements (P < 0.0001). This increase was probably linked to physiological cardiac response to hypoxemia. Twenty-seven percent of our volunteers complained of shortness of breath and 18% had palpitations, by the end of 2nd h.

CO2 accumulation in people using N95 masks on common conditions such as rest, conversation, or low work rates ranges from 1.5% to about 3%. This is 100 times greater than expected in normal ambient air. It is well known that prolonged exposure to 2%–3% CO2 can cause headache, sweating, dizziness, and shortness of breath, even in people without medical illness.[13] In addition, the increased dead space associated with N95-masks has been found to reduce the mean inspired O2 concentration.[14] Therefore, it may be considered that inhalation of increased CO2 concentrations when using N95 may produce greater respiratory discomfort, suffocation, and anxiety symptoms, especially in people prone to panic disorder. In addition, decreased inhaled O2 concentrations may result in greater breathing effort, shortness of breath, and physical fatigue, even during mild physical activity.[11,12,14]

Headache is probably the most common complaint associated with the use of masks. The incidence of headache development among health-care workers using N95 masks ranges between 37% and 81% in literature and was found to be directly correlated with the use of N95 face masks for more than 4 h.[15,16] The etiopathogenesis of headaches associated with long-term use of N95 face mask has been linked to hypoxemia, hypercapnia, stress, or mechanical compression on the superficial facial and cervical nerves.[17–19] In our study, headache was also the most common complaint with 36%. We associated this phenomenon only to hypoxemia, since we did not measure the CO2 level alteration in our cohort; this was one of the limitations of our study.

Being a single-center study, lack of noninvasive carbon dioxide measurement, and low cohort volume were the main limitations of our study. The daily time of measurements (e.g. morning vs. afternoon) was not constant for individuals, which could also cause a bias. Repetitive assessment minimized a probable measurement error. In addition, its prospective design and operating theater setting, where proper mask use is mandatory, were the strong points of the study.

Accurate and continuous use of respiratory protective masks is very important for health-care workers fighting with epidemics. Long duration use of N95-type masks causes a significant reduction in SpO2 and increase the HR. Despite being a crucial personal protective equipment in, especially for health workers in sterile environments, it should be used by caution in people with known heart disease, pulmonary insufficiency, or psychiatric/panic disorders, and with short intermittent time periods.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


We would like to thank Prof. H.A. for his meticulous statistical analysis and interpretation.


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