Objective Assessment of Increase in Breathing Resistance of N95 Respirators on Human Subjects

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Abstract

Face masks or respirators are commonly worn by medical professionals and patients for protection against respiratory tract infection and the spread of illnesses, such as severe acute respiratory syndrome and pandemic influenza (H1N1). Breathing discomfort due to increased breathing resistance is known to be a problem with the use of N95 respirators but there is a lack of scientific data to quantify this effect. The purpose of this study was to assess objectively the impact of wearing N95 face masks on breathing resistance. A total of 14 normal adult volunteers (seven males and seven females) were recruited in this study. Nasal airflow resistance during inspiration and expiration was measured using a standard rhinomanometry and nasal spirometry. A modified full face mask was produced in-house in order to measure nasal resistance with the use of N95 (3M 8210) respirators. The results showed a mean increment of 126 and 122% in inspiratory and expiratory flow resistances, respectively, with the use of N95 respirators. There was also an average reduction of 37% in air exchange volume with the use of N95 respirators. This is the first reported study that demonstrates quantitatively and objectively the substantial impairment of nasal airflow in terms of increased breathing resistance with the use of N95 respirators on actual human subjects.

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Effectiveness of precautions against droplets and contact in prevention of nosocomial transmission of severe acute respiratory syndrome (SARS)

WH Seto, D. Tsang, RWH Yung … (2003)

Summary We did a case-control study in five Hong Kong hospitals, with 241 non-infected and 13 infected staff with documented exposures to 11 index patients with severe acute respiratory syndrome (SARS) during patient care. All participants were surveyed about use of mask, gloves, gowns, and hand-washing, as recommended under droplets and contact precautions when caring for index patients with SARS. 69 staff who reported use of all four measures were not infected, whereas all infected staff had omitted at least one measure (p=0·0224). Fewer staff who wore masks (p=0·0001), gowns (p=0·006), and washed their hands (p=0·047) became infected compared with those who didn't, but stepwise logistic regression was significant only for masks (p=0·011). Practice of droplets precaution and contact precaution is adequate in significantly reducing the risk of infection after exposures to patients with SARS. The protective role of the mask suggests that in hospitals, infection is transmitted by droplets.

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Effects of wearing N95 and surgical facemasks on heart rate, thermal stress and subjective sensations

Y. Li, H Tokura, Y.P. Guo … (2005)

Aim: The study was aimed at investigating the effects of wearing N95 and surgical facemasks with and without nano-functional treatments on thermophysiological responses and the subjective perception of discomfort. Method: Five healthy male and five healthy female participants performed intermittent exercise on a treadmill while wearing the protective facemasks in a climate chamber controlled at an air temperature of 25°C and a relative humidity of 70%. Four types of facemasks, including N95 (3M 8210) and surgical facemasks, which were treated with nano-functional materials, were used in the study. Results: (1) The subjects had significantly lower average heart rates when wearing nano-treated and untreated surgical facemasks than when wearing nano-treated and untreated N95 facemasks. (2) The outer surface temperature of both surgical facemasks was significantly higher than that of both N95 facemasks. On the other hand, the microclimate and skin temperatures inside the facemask were significantly lower than those in both N95 facemasks. (3) Both surgical facemasks had significantly higher absolute humidity outside the surface than both N95 facemasks. The absolute humidity inside the surgical facemask was significantly lower than that inside both N95 facemasks. (4) Both surgical facemasks were rated significantly lower for perception of humidity, heat, breath resistance and overall discomfort than both N95 facemasks. The ratings for other sensations, including feeling unfit, tight, itchy, fatigued, odorous and salty, that were obtained while the subjects were wearing the surgical facemasks were significantly lower than when the subjects were wearing the N95 facemasks. (5) Subjective preference for the nano-treated surgical facemasks was the highest. There was significant differences in preference between the nano-treated and untreated surgical facemasks and between the surgical and N95 facemasks. Discussion: We discuss how N95 and surgical facemasks induce significantly different temperature and humidity in the microclimates of the facemasks, which have profound influences on heart rate and thermal stress and subjective perception of discomfort.

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Headaches and the N95 face‐mask amongst healthcare providers

E C H Lim, R C S Seet, K.-H. Lee … (2006)

Background: During the 2003 severe acute respiratory distress syndrome epidemic, healthcare workers mandatorily wore the protective N95 face‐mask. Methods: We administered a survey to healthcare workers to determine risk factors associated with development of headaches (frequency, headache subtypes and duration of face‐mask wear) and the impact of headaches (sick days, headache frequency and use of abortive/preventive headache medications). Results: In the survey, 212 (47 male, 165 female) healthcare workers of mean age 31 years (range, 21–58) participated. Of the 79 (37.3%) respondents who reported face‐mask‐associated headaches, 26 (32.9%) reported headache frequency exceeding six times per month. Six (7.6%) had taken sick leave from March 2003 to June 2004 (mean 2 days; range 1–4 days) and 47 (59.5%) required use of abortive analgesics because of headache. Four (2.1%) took preventive medications for headaches during this period. Multivariate logistic regression showed that pre‐existing headaches [P = 0.041, OR = 1.97 (95% CI 1.03–3.77)] and continuous use of the N95 face‐mask exceeding 4 h [P = 0.053, OR = 1.85 (95% CI 0.99–3.43)] were associated with development of headaches. Conclusions: Healthcare providers may develop headaches following the use of the N95 face‐mask. Shorter duration of face‐mask wear may reduce the frequency and severity of these headaches.