Ann. occup. Hyg., Vol. 46, No. 2, pp. 143-148, 2002
© 2002 British Occupational Hygiene Society
Published by Oxford University Press
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The Effect on Heart Rate and Facial Skin Temperature of Wearing Respiratory Protection at Work
1Centre for Ergonomics and Occupational Safety and Health, Department of Human Resource Management, Massey University, Palmerston North; 2Institute of Food Nutrition and Human Health, College of Sciences, Massey University, Palmerston North, New Zealand; 3Ivy House Farm, 69 Duck Street, Egginton, Derbyshire, UK; 4Department of Management, Massey University, Palmerston North, New Zealand
Received 29 January 2001; in final form 30 July 2001.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Twelve New Zealand workers from a range of occupations were studied to investigate the effect of wearing air-filtering respiratory protection on heart rate (HR) and facial skin temperature (Tlip and Tcheek) whilst working. All variables were measured continuously during simulated and actual work. The former allowed physiological measurements to be undertaken during the physical activities carried out during the work task without respirators and without exposure to hazardous airborne substances. Mean heart rates in subjects moving without respirators ranged from 75 to 94 beats/min and from 77 to 98 beats/min during respirator use at work. Mean skin temperature under the mask (Tlip) increased in 11 of the 12 subjects while using respirators (range 1.2–4.8°C) but Tcheek only increased in four (range 0.6–1.5°C). The use of simulated work tasks in the experiment was a compromise. The heart rate data from the real and simulated work indicated that effort and workload, though not identical, were similar. The increase in skin temperature under the mask may account for the reluctance of individuals to wear respiratory protection at work. This region of the face is very thermosensitive.
Keywords: heart rate; skin temperature; respiratory protection; respirators; respiratory protective devices; workplace; industry
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INTRODUCTION |
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The response of individuals in the workplace to the use of respiratory protection is complex and not fully understood. Thermal discomfort has been suggested as a common reason for not wearing air-purifying respirators (Martin and Goldman, 1972; Houdous et al., 1989; Laird et al., 1993). In a New Zealand survey nearly one-third of those studied cited thermal discomfort and feelings of claustrophobia, possibly occasioned by increased temperature, as critical reasons for their reluctance to wear protective equipment (Laird et al., 1993).
Previous laboratory studies (Nielsen et al., 1987; Gwosdow et al., 1989; White et al., 1989; DuBois et al., 1990) have indicated that a skin temperature around the mouth and nares of <34°C is acceptable to most individuals. However, once the skin temperature of this area exceeds 34.5°C, the sensation of thermal discomfort becomes unacceptable to many people (Gwosdow et al., 1989; DuBois et al., 1990). Emerson et al. (Emerson et al., 1967) demonstrated that certain surgical masks caused as much as a 5°C increase in facial temperature and a later study found an increase of 7.5°C in lip temperature in subjects wearing disposable respirators (Jones, 1991). Whether such large increases in facial or lip temperature occur in the normal industrial setting as a result of respirator use or whether any such changes in skin temperature may be enough to influence user acceptability are unknown.
Our study looked at the effect of wearing a respirator on heart rate and facial skin temperature in individuals doing light work in workplaces in New Zealand. These individuals were considered to be typical of the majority of those wearing respirators in this country. The study consisted of a laboratory investigation of the effect of wearing a respirator on facial skin temperature, followed by a workplace investigation of the effect of wearing a respirator on skin temperature and heart rate.
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MATERIALS AND METHODS |
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All subjects taking part in both studies were fully informed about the experiments and the information that was sought before taking part, and all signed a consent form. The experiments had the approval of the Massey University Human Ethics Committee.
Laboratory study
A laboratory project was undertaken to investigate the effects of wearing a respirator on facial skin temperature during light sustained work in New Zealand climatic conditions before the field work was started. This was carried out on five Massey University staff members (two female, three male; age range, 31–47 yr; height, 1.78 ± 0.06 m; mass, 75 ± 8.8 kg). They had all previously experienced using respirators. They were reasonably fit but not undergoing athletic training. On two occasions, separated by at least 24 h, the subjects worked on a friction-braked cycle ergometer (Monark, Ergomedic 818E) at 50 W for 30 min. Wet and dry bulb ambient air temperatures were recorded using a standard whirling hygrometer (T8716, Casella, London, UK).
In the first experiment the subjects wore a standard filter type respirator for the first 15 min. In the second, the respirator was worn for the second half of the exercise period only. The respirator covered the mouth and nose, but not the eyes or cheeks. Facial skin temperature was recorded at 1 min intervals throughout using bead thermistors bonded to 15 mm alloy plates. One thermistor was positioned on the cheek, 20 mm anterior to the external auditory meatus, and a second was placed on the upper lip directly below the left nare. Mean heart rate was also recorded using a body-borne heart rate monitor (Sports Tester: PE 3000, Polar Electro, Finland). The data obtained during the last 5 min of each 15 min experimental situation, when the subjects were approaching a steady state, were compared using a variance ratio test and paired Student’s t-test.
The heart rate monitor was calibrated against a standard isolated ECG amplifier (NT 117, Neomedix Systems, Sydney, Australia) and cardiac rate meter (Jrak BioSignals Ltd, Windsor, Victoria, Australia). It was accurate to within ±1.0%. The thermistors were calibrated against a mercury-in-glass thermometer between 20 and 40°C.
Workplace study
There were 12 male subjects divided into six groups of two on the basis of their occupation. All had been doing the tasks that were evaluated for at least 3 months before the study began. The subjects were selected from the questionnaire investigation (Laird et al., 1993) on the basis of their perceived workload: four judged that their work was hard, four moderate and four light. Physical details of the subjects are shown in Table 1.
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Each subject wore a four-channel cassette tape recorder (Oxford Instruments Medilog Series 4.24, Cambridge, UK) to record the facial skin temperatures that were measured in the laboratory study. A fourth channel was for timing. Mean heart rate was recorded using a heart rate monitor, as before.
Environmental variables
The thermal environment at the workplace was measured before and after each experiment. Ambient air temperature and relative humidity were measured using a standard whirling hygrometer (T8716, Casella). Radiant energy was measured with a globe thermometer (T6480, Casella) and air velocity using a hot wire anemometer (TA 3000; Air Flow Instruments, High Wycombe, UK).
Protocol
The experiments were carried out in six workplaces during part of a normal working shift. The duration of the work task for which a respirator was required was variable (Table 1). However, most subjects were required to wear a respirator for between 1 and 2 h in a normal working day. Following instrumentation and a time delay to allow the subjects’ heart rates to return to a resting level (5–15 min), the subjects were asked to simulate the work task without wearing a respirator and then to carry out the task whilst wearing their respirator. Throughout the experiment the subjects were continuously observed by one of the authors (I.S.L.) to ensure that the type of movement undertaken, postures adopted and duration of each section of the task were similar in the two situations.
Analysis of data
Skin temperature was obtained by replaying the tapes using a tape data analyser (Medilog, Cambridge, UK) and passing the data into a Maclab A/D converter (Chart version 3.0 software; ADI Instruments, Sydney, Australia). The time pulses on the tape were also digitized to enable temporal coordination between the heart rate and temperature data.
Statistical analysis was carried out in two ways: (i) data from each subject during simulated (without respirator) and actual (with respirator) work were compared; and (ii) the population statistics of the 12 subjects were examined. The variance ratio test and Student’s t-test were used for both analyses. Within-subject variance was not included in the population analysis.
Heart rate (HR) was analysed both as work/resting heart rate ratio and as the percentage of ‘heart rate reserve’ (% HRR) to allow comparison with previous investigations. The latter was calculated from the formula given by Louhevaara et al. (Louhevaara et al., 1985):
% HRR = (HRwork – HRrest)/(HRmax – HRrest)
HRmax was estimated from the formula given by Jones (Jones, 1991) as 210 – 0.66 x age. All results are expressed as the mean ± 1 SD.
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RESULTS |
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Laboratory study
In the first experiment the mean temperature of the lip dropped from 34.3 ± 1.9 to 33.3 ± 2.8°C when the respirator was removed midway through the exercise period (n.s.). In the second experiment it increased from 31.7 ± 2.4 to 33.6 ± 1.5°C on putting the respirator on (P < 0.01). The mean working heart was significantly higher during the first experiment (115.8 ± 12.6 versus 106 ± 11.6; paired t-test, P = 0.024). Wearing the respirator had no significant effect on heart rate or on the temperature of the cheek in either experiment. The dry air temperature in the laboratory ranged between 18.5 and 21.5°C, and relative humidity between 48 and 67% during the experiments. There were no significant changes in the environment between the two sets of experiments.
Analysis of data on a subject-by-subject basis revealed that the lip temperature was significantly decreased following the removal of the respirator in four of the five subjects in experiment 1 and increased by donning it in all five subjects in the second experiment (Table 2).
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Workplace study
The experiments were performed in spring/early summer. The dry air temperatures during the experiments ranged from 17 to 24°C. There were no significant differences between the airflows or relative humidity measured at the different work sites. Air velocity was low, ranging from 0.01 to 0.1 m/s; relative humidity was high, at 60–80%. The subjects wore the clothes that they used habitually. Half wore overalls over normal clothing; the remainder wore just their ordinary clothes, with or without dust coats over them.
Heart rate changes
The subjects had resting heart rates of 73 ± 3.7 beats/min. On simulating the work, the subjects’ heart rates increased to 84 ± 6.6 beats/min (range = 75–94; equivalent to 5–20% HRR). Subsequent performance of the task whilst wearing the respirator resulted in a heart rate of 88 ± 7.7 beats/min (range = 77–98; equivalent to 6–22% HRR). The paired Student’s t-test indicated that the population heart rate was significantly increased above resting rate for both simulated (without respirator) and real (with respirator) tasks (P < 0.001), but the difference between simulated and real was of marginal significance (P = 0.04). Subject-by-subject analysis showed that the heart rate increased more in the real task than in the simulated task in five of the 12 subjects. These increases were small (range = 2.1–4.5 beats/min) when compared with the overall effects of activity (mean = 12 beats/min).
Examination of the heart rate data expressed as a percentage of heart rate reserve (Fig. 1) showed that the subjects were working at 10.1 ± 4.8% HRR during the simulated task and 11.4 ± 5.7% HRR during the actual task. With the exception of the two automotive panel beaters, who worked at 21.8 and 23.7% HRR (work/resting heart rate ratio = 1.34 and 1.4), the work level of the subjects in the study could be classified as light (% HRR = 9.8 ± 2.2; range = 6.3–14.9; work/resting heart rate ratio = 1.15 ± 0.03, range = 1.08–1.18).
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Facial skin temperature
The population mean cheek temperature during real work wearing the respirator was not significantly different from the simulated work (32.2 ± 1.38 versus 31.9 ± 1.23°C). Cheek temperature was unrelated to environmental temperature (r2
0.02). The population mean lip temperature during real work was significantly higher than during simulated work (33.8 ± 1.56 versus 31.87 ± 1.12°C; two-tailed Student’s t-test, P < 0.001). Subject-by-subject analysis indicated this lip temperature increase was significant (P < 0.05 in 11/12 subjects; P < 0.001 in 7/12). The lip temperature rose above 34.5°C in six individuals (Fig. 2).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Laboratory study
The results of the laboratory study showed that fitting a respirator during a period of continuous work led to an increase in facial skin temperature under the mask, while removing the mask tended to decrease it. With the caveat that work in industry is usually intermittent, this suggests that removal of a respirator whilst continuing to work may create a sense of thermal relief.
Workplace study
To the authors’ knowledge, this study is the first to examine the effect of filter-type respirators on heart rate and facial skin temperature in the workplace setting in New Zealand. Three aspects of the investigation merit discussion: (i) the use of simulated work; (ii) the heart rate responses and work level of the subjects; and (iii) the skin temperature changes induced by wearing a respirator mask.
The use of simulated work
The use of data from a simulated work task was a scientific compromise since there were two variables (no respirator versus respirator; simulated task versus actual task) and only two series of measurements. A more critical experiment would have been to have the subjects perform the real work task without a respirator or have them perform the simulated task twice—with and without the respirator.
Though individuals frequently do work that requires respirator use without wearing such protection (Harris, 1974; Aucoin, 1975; National Coal Board, 1977; Corn, 1980; Laird et al., 1993), it was considered to be unethical to ask workers to do this as part of a scientific investigation. Repetition of the simulated work would have caused even more disturbance and loss of output; this too was considered to be unacceptable for the sake of better data. Since all the subjects had been engaged in the tasks for which the respirators were required for at least 3 months, it was considered likely that the work levels could be accurately simulated. Statistical analysis of the data suggested that this was not the case. The subjects worked a little harder when they performed their real work. This once again underlines the difficulty of extrapolating results from simulated to real situations.
Heart rate responses and work level
The workloads of the individuals investigated were relatively low when compared with previous studies of the workplace. In only two subjects was the workload in the order of 20% HRR. The rest of the subject heart rates fell within the range of 6.3–14.9% HRR, which were markedly lower than those studied by Louhevaara et al. (1985), who found that heart rates of respirator users in industry varied from 15 to 57% HRR. With the exception of the panel beaters, the ratio of working to resting heart rates ranged between 1.08 and 1.18. This is lower than those frequently reported in studies of other industries, including open hearth workers (ratio 1.64; Minard et al., 1971), nurses (1.45; Fordham et al., 1978), car assembly workers (1.45; Goldsmith et al., 1978), cane cutters (1.38; Vitalis, 1981) and steel workers (1.37; Vitalis et al., 1994). However, we selected the subjects for the study to span the range of perceived exertion scored in a questionnaire survey (Laird et al., 1993) and these work rates are probably typical for respiratory users in light industry in New Zealand. This raises the question of the relevance to the general workplace of laboratory studies of respirators where high fixed heart rates or even VO2max (Johnson et al., 1995) were used.
Skin temperature changes induced by the wearing of a respirator mask
This study consistently demonstrated a significant increase in the skin temperature of the upper lip when subjects fitted a respirator and carried out a task in the workplace. A face mask prevents normal transpiration and cooling of the skin, and is filled with warm, moist expired air throughout most of the breathing cycle. This may increase skin temperature irrespective of workload. The increases we observed under the respirator were between 1.2 and 4.8°C in 11 of the 12 subjects. These were lower than reported in earlier studies (Emerson et al., 1967; Jones, 1991), perhaps because of the relatively low work rates of the subjects. However, the effect was sufficient in six individuals to increase skin temperature to >34.5°C (Fig. 2)—a level which may induce unacceptable sensations of thermal discomfort (Gwosdow et al., 1989; DuBois et al., 1990). This group included all the subjects engaged in spraying, who were working harder as judged by heart rate (four of these had working heart rates of >95 beats/min). On this basis, the larger rise in lip temperature seen in these subjects could possibly be a result of increased ventilation.
Many workers occasionally remove respirators when their use is required or are reluctant to wear them at all (Laird et al., 1993). From our study, thermal discomfort may contribute to this. Possible solutions are use of silicone materials (DuBois et al., 1990), or perhaps cooling and draining the respiratory device. Whether, for short periods of respirator wear, the simple expedient of putting the respirator in the refrigerator before use might help is a matter of conjecture.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Two principal conclusions emerge from the study. First, wearing a respirator whilst working, whether continuously in the laboratory or in industry, produced a significant increase in skin temperature under the mask. For some subjects in the workplace this was sufficient to be likely to cause thermal discomfort. The large changes in skin temperature caused by respirators may provide one explanation for the reluctance to use them. Secondly, the work undertaken by the subjects that were studied in the workplace was light, despite some having classified it as moderate or hard in a questionnaire survey.
Acknowledgements—This study was supported financially by a grant from the New Zealand Accident Compensation Corporation. The authors also express their gratitude to Mr John Pedley for his excellent technical support.
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FOOTNOTES |
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* Author to whom correspondence should be addressed. Institute of Food Nutrition and Human Health, College of Sciences, Massey University, Private Bag 11-222, Palmerston North, New Zealand. Fax: +64-6-350-5657; e-mail: r.j.pack{at}massey.ac.nz
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