Absence of consequential changes in physiological, thermal and subjective responses from wearing a surgical mask

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Abstract

Twenty subjects treadmill exercised at 5.6 km/h for 1 h with and without wearing a surgical mask while being monitored for heart rate, respiratory rate, oxygen saturation, transcutaneous CO2, SpO2, core and skin temperatures, mask deadspace heat and relative humidity, and skin temperature under the mask. Rating scales were utilized for exertion and heat perceptions. Surgical mask use resulted in increases in heart rate (9.5 beats/min; p < 0.001), respiratory rate (1.6 breaths/min; p = 0.02), and transcutaneous carbon dioxide (2.17 mm Hg; p = 0.0006), and decreased temperature of uncovered facial skin (0.40 °C; p = 0.03). The 1.76 °C increase in temperature of the skin covered by the mask was associated with a mask deadspace apparent heat index of 52.9 °C. Perceptions of heat were neutral to slightly hot, and for exertion ranged from very, very light to fairly light. Surgical mask use for 1 h at a low-moderate work rate is not associated with clinically significant physiological impact or significant subjective perceptions of exertion or heat.

Highlights

► Mean core temperature is not significantly increased (<0.1 °C) by the use of a surgical mask at a low-moderated work rate over 1 h. ► Respiratory rate is minimally increased (1.6 breaths-per-minute) with use of a surgical mask over 1 h at a low-moderate work rate. ► Heart rate is increased by 8% with the use of a surgical mask over 1 h at a low-moderate work rate.

Introduction

The concept and use of the surgical mask (SM) was first introduced in the nineteenth century in Germany (Mikulicz, 1897). The primary purpose of a SM was to protect the surgical patient from pathogens expelled on droplets from the nose and mouth of surgical personnel during speech, coughing and sneezing, but more recently SMs have been advocated as a protective barrier for the wearer from splashes and spills of body fluids (Lipp and Edwards, 2005). The HIV epidemic and concerns over bloodborne pathogens brought about the classification of SMs as personal protective equipment (PPE) by the U.S. Occupational Safety and Health Administration (OSHA) (Belkin, 1996). SMs are classified as protective facemasks (PFs) but are not considered respiratory protective equipment because they do not seal to the face. SMs (also referred to as medical masks, dental masks, procedure masks, laser masks, isolation masks) have become among the most commonly used PPE in the healthcare environment, and use is likely to be accentuated during outbreaks of respiratory infectious diseases (e.g., pandemic influenza, etc.) (Phin et al., 2009). In many countries, SMs are also frequently used by the public during such outbreaks, making SMs among the most used PPE worldwide. All types of PFs are associated with increased thermal perceptions (body, face) that can make them uncomfortable to wear. In a large survey of health care workers, Nickell et al. (2004) reported that 85% of respondents found that wearing a PF was particularly bothersome. Although SM worn by health care workers over an eight-hour shift were associated with less discomfort and exertion than filtering facepiece respirators (FFRs) (Shenal et al., 2012), almost one-half were unable to wear SM for the full shift, despite interposed break periods (Radonovich et al., 2009). MacIntyre et al. (2009), in a study evaluating the use of PFs to control the spread of respiratory virus in households, reported first day adherence of 38% for SMs and 46% for FFRs that declined significantly over 5 days of use and was attributed to discomfort by 50% of wearers. Discomfort is a major reason for noncompliance with PF use and, by extension, exposes an individual to increased risk of infection. Despite more than a century of use, relatively little scientific evaluation of the burden of SM wear has been accomplished. This study, part of a broad investigation by the National Personal Protective Technology Laboratory (NPPTL) of the National Institute for Occupational Safety and Health (NIOSH) evaluating the use of PFs (NIOSH, 2010), reports on the physiological, thermal and subjective impact of a SM on the wearer. Other data from the study have been published in a companion paper (Roberge et al., 2012).

Section snippets

Ethical approval

The study was carried out in accordance with the Code of Ethics of the World Medical Association (Declaration of Helsinki) and was approved by the NIOSH Human Subjects Review Board, with all subjects providing oral and written informed consent. All subjects were informed that they could withdraw from the study at any time without prejudice.

Participants

Twenty healthy subjects (13 men, 7 women), all of whom were non-smokers and 11 with no prior experience wearing a PF, were recruited and tested over a three

Results

All subjects completed control and SM trials (total, 40 tests). The mean elapsed time from core temperature capsule ingestion to the start of control data collection was 123.9 min (62.9), and 327.0 min (159.3) during trials. Post-test mean increase in SM weight was 0.12 g (0.19).

The mean values at five minute intervals for seven measured variables of controls and trials are displayed in Table 1. Time had a significant effect (p < 0.001) on these measured variables. Mean 1 h values for controls vs

Discussion

Recent findings have suggested that SMs are not inferior to FFRs in terms of protection from laboratory confirmed influenza infection rates and in reducing the spread of influenza viruses (Loeb et al., 2009, Johnson et al., 2009, Ang et al., 2010). Although still controversial based on the aerosol transmission capability of influenza virus (Tellier, 2009), these results imply that comfort, rather than protection, may become a prominent feature of the selection of PFs (Johnson et al., 2009).

Conclusions

Our study demonstrated that, over the course of 1 h of wearing a SM at a low-moderate work rate, mild increases in physiological responses (HR, RR, tcPCO2) occur that would be of no clinical significance in healthy persons and that were not perceived subjectively as being associated with discomfort or exertion. The thermal burden of a SM on the wearer is not excessive, with the exception of facial skin covered by the SM, and SaO2 is not negatively impacted. Intolerance to wearing a SM is not

Disclaimer

The findings and conclusions in this report are those of the authors and do not necessarily represent the view of the National Institute for Occupational Safety and Health.

The authors report no financial conflicts. All funding for the study came from internal operating funds of the National Personal Protective Technology Laboratory.

Acknowledgements

The authors thank Jeffrey Powell, MS and Dr. Aitor Coca for their assistance with equipment issues, and Dr. Ronald Shaffer, Dr. Ziqing Zhuang, Dr. William King, and Jay Parker, MS for their manuscript reviews and suggestions.

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