Respiration Physiology, 79 (1990) 145-150 Elsevier
145
RESP 01590
Respiratory heat loss during work at various ambient temperatures J.B. Cain, S.D. Livingstone, R.W. Nolan and A.A. Keefe Defence Research Establishment Ottawa, Environmental Protection Section, Ottawa, Ontario, Canada KIA OZ4 (Accepted for publication 31 July 1989) Abstract. The purpose of this investigation was to establish the temperature and humidity of the expired
air of subjects working at various metabolic rates at ambient temperatures between - 4 0 °C and 20 °C in order to calculate respiratory heat loss. Measurements of the respired air temperature and water vapour content were made for five subjects while they either stood or walked on a treadmill. The results indicated that the maximum respired air temperature varied slightly with the ambient air temperature but changes in metabolic rate, respiration rate and breathing frequency had no apparent effect on the expired air temperature under the conditions studied. The relative humidity of the respired air was found to be close to saturation in the extreme-cold environments. Heat loss due to respiration was between 25 and 30% of the resting metabolic and between 15 and 20~o of the working metabolic rate.
Heat loss; Humidity; Metabolic rate; Respiration; Temperature; Work
Heat loss due to respiration can represent a sizable portion of the body's total heat loss (Burton and Edholm, 1955). The temperature of expired air has been reported to be as low as approximately 20 °C (McFadden et aL, 1985; Webb, 1951) and as high as 37 °C (H0ppe, 1981; Newburgh, 1968). Reports on the humidity of the expired air have also varied, from approximately 80~ relative humidity (Ferrus et al., 1984; McCutchan and Taylor, 1950; Mitchell et al., 1972) to fully saturated (Belding et al., 1945; Newburgh, 1968). Since these variations in both temperature and humidity may be due to slow response times of the sensors used, this investigation was undertaken in an attempt to obtain a better estimate of the correct values. In this study, the temperature of the respired air was measured while subjects worked at four different rates and at four different ambient air temperatures. During tests at very cold temperatures, the water content of the expired air was also measured. With this information and with measured respiratory ventilation rates, the respiratory heat loss was calculated. Correspondence address." J.B. Cain, Defence Research Establishment Ottawa, Environmental Protection Section, Ottawa, Ontario, Canada K1A 0Z4. 0034-5687/90/$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical Division)
J.B. CAIN etaL
146
Experimental procedure Five male volunteers gave their informed consent to participate in the experiments. The average and standard deviation of age, height and weight of the subjects were 28 + 5 years, 171 + 7 cm and 74 + 12 kg, respectively. The experiments were conducted in an environmental chamber at each of four ambient temperatures: - 40, - 20, 0 and 20 °C. Humidity could not be eontrolled in the chamber; however, the amount of water contained in the air is negligible at 0 °C and below. The subjects dressed in appropriate clothing so that they were comfortable at each of these temperatures. Experiments consisted of a series of four tests at each ambient temperature. Tests were conducted at four different work rates: (1) standing quietly; (2) walking on a treadmill at 3 km. h - 1 on a 0~o slope; (3) walking on a treadmill at 3 km. h - 1 on a 5~o slope; (4) walking on a treadmill at 5 km. h - ~ on a 5 ~o slope. For each experiment, the subject entered the environmental chamber and stood, breathing normally, for a period of 10 min. The temperature of his respired air was then measured over a two minute period using a fast response copper-constantan thermocouple (Omega COCO-001) mounted at about the plane of the lips in a rubber mouthpiece (Vacumed No. 1001). The subject then removed the mouthpiece and donned a face mask (Speak-Easy II, Respironics, Monroeville, PA) which was connected to a Beckman Metabolic Measurement Cart in an adjacent laboratory using 47 mm diameter corrugated plastic tubing. The subject's metabolic rate, respiratory frequency and volume of expired air were measured for ten minutes with average values recorded every minute. The subject then walked on the treadmill at the lowest work rate for a ten-minute equilibration period after which the above measurement procedure was repeated as the subject walked. Measurements at the two higher work rates followed. The temperature data were measured and recorded using a Hewlett-Packard data acquisition system (HP 3497A) controlled by a Hewlett-Packard computer (HP 9836). Measurement of both the ambient air temperature and the thermocouple reference temperature were made at the beginning and end of each two minute respiratory air temperature measurement. Only the respired air temperature was monitored during the 2 min interval which allowed readings to be recorded approximately ten times per second. Since humidity sensors have greater time constants than the response times required for accurate measurements, humidity was measured at the two coldest ambient temperatures by condensing the moisture in the expired breath in approximately 3 m of plastic tubing which lead from the mask to the metabolic cart. The humidity was then calculated from the difference in weight of the tubing and mask before and after each test. Heat loss due to respiration was then calculated (absolute humidity for air temperature less than 0 °C being negligible) using the following equation: Or =
Pa~/Cpa(We-Ti) + Pag(Te-Ti)hfg + Pa~/TiCpv(Te-Ti)
(1)
w h e r e (~r = respiratory heat loss, W; p~ = density of the air, k g ' m - 3 ; ~7 = respiratory
147
RESPIRATORY HEAT LOSS
ventilation rate, m 3 " s e c - =; Cpa = specific heat of dry air, J. k g - 1. K - 1; T~ = expired air temperature, °C or K; T i = inspired air temperature, °C or K; 7e = humidity ratio of the expired air; 7i = humidity ratio of the inspired air; hfg = enthalpy of vaporization, J. k g - 1. K - 1; Cpv = specific heat of water vapour, J- k g - 1. K - 1.
Results
Figure 1 shows a plot of typical data measured in this investigation for the temperature of respired air. The test begins with the mouthpiece (containing the thermocouple) at the ambient air temperature. At approximately 17 sec into the test, the mouthpiece was inserted and measurement of the subject's respired air temperature began. It can be seen that the minimum temperature recorded by the sensor upon inspiration was approximately that of the ambient air temperature ( - 40 ° C), although the inspired air temperature appears to be increasing slightly with successive breaths. The maximum expired air temperature recorded shows a very small scatter but is approximately constant for each breath. Several peak temperature data points are evident during each expiration cycle indicating that the sensor's response time is sufficient to measure the maximum temperature. The expired air temperature and humidity did not vary in any consistent manner for the work rates, metabolic rates, respiration rates or the respiration frequencies encountered in this investigation. The results were therefore averaged over all four work rates and the mean expired air temperatures for various ambient temperatures are given in table 1.
30 20
G 10 0 o.
-10
8t~
-20
o. t~
-30 -40 10
1'5
210
2~5
3~
3~5
410
45
TIME (seconds) Fig. 1. Typical data from measurements of the respired air temperature at - 4 0 °C ambient.
148
J.B. C A I N et aL TABLE 1
Maximum expired air temperatures measured at various work rates and environmental temperatures. Work rate
Maximum expired air temperature
Speed (km'h-')
Slope (%)
20 °C
0 3 3 5 Mean
0 0 5 5
33.8 33.8 34.0 34.9 34.1
± ± ± ± +
0 °C
0.2 1.0 0.8 1.9 2.3
32.0 31.7 31.8 31.5 31.8
+ + ± ± ±
0.7 0.9 1.7 2.0 2.9
- 20 °C
- 40 °C
29.6 31.4 29.5 28.4 29.7
30.7 28.5 28.4 28.1 28.9
± ± ± + ±
1.2 1.6 2.9 2.7 4.4
± ± ± ± ±
0.9 1.8 0.9 1.5 2.7
Ambient temperatures are shown by the temperature values above each column. All values are mean ± standard deviation. Mean values underlined by a common line are not significantly different.
Since the drying compound at the metabolic cart indicated no significant amounts of water in the sampled air, it was assumed that all of the water vapour in the expired air had condensed either in the mask or tubing. The expired air was found to be close to saturation at the measured expired air temperature and was greater than 90 ~o relative humidity in most cases. The amount of water collected varied from 0.44 + 0.06 (mean + SD) to 1.0 + 0 . 2 7 g ' m i n - 1 for respiration rates of 8.7 + 2.5 to 41.5 + 8.3 L. min - 1. The experimental uncertainty in these measurements was approximately 40 ~o at the low respiration rates and approximately 15 ~ at the high respiration rates. In several experiments, the results indicated that the expired air was supersaturated. Heat loss due to respiration is shown in table 2. The results for 20 ° C are not included as the ambient humidity was not controlled during these tests and may have been TABLE 2 Metabolic rate and calculated heat loss as a function of ambient temperature and work rate. Work rate
O°C
- 2 0 °C
-40°C
0 km. h - 1
3 km. h- 1
3 km. h - i
5 km. h
0~o slope
0~o slope
5~o slope
5~o slope
Metabolic rate Respiratory heat loss Metabolic r a t e ( ~ o ) Metabolic rate Respiratory heat loss Metabolic rate (~o) Metabolic rate
112 28 25 77 19.5 25 84
+ + + + + + +
16 8 4 24 5 3 17
229 ± 46 + 20+ 232 + 43 + 19+ 241 +
320 i 61 ± 19± 301 + 54 + 18_+ 338 +
36 11 2 31 8 2 53
460 + 57 82 + 12 18+ 1 497 +_ 40 77 + 9 16_+ 2 489 ± 91
Respiratory heat loss Metabolic r a t e ( ~ o )
25 29
+ £
6 2
72 + 17 21 ± 2
97 ± 23 20± 4
24 10 2 32 3 3 53
53 _+ 15 21 + 2
All values, unless specified, are in watts _+ standard deviation.
1
149
R E S P I R A T O R Y H E A T LOSS
significant. For metabolic rates between 75 and 100 W, the respiratory heat loss was found to represent between 25 and 3 0 ~ of the metabolic rate. For metabolic rates greater than 200 W, the respiratory heat loss was approximately 10~o lower.
Discussion
The data in fig. I indicate that the air temperature measured by the thermocouple upon inspiration was close to that of the ambient air. It was therefore assumed that the temperature recorded upon expiration was an accurate measure of the expired air temperature. In most experiments, the recorded inspired and expired air temperatures began to change, with one or both tending to some temperature intermediate to the ambient and body temperatures (fig. 2). Examination of the mouthpiece after these events showed water or ice either on the thermocouple junction or on the thermocouple lead wires. Water on the junction or wires was thought to result from droplets of condensation in the expired air, although saliva may have been responsible in some cases. This phenomenon significantly increased the response time of the thermocouple producing obviously different and erroneous results. In fig. 2, the recorded inspired air temperature indicates that the sensor was not accurately measuring the ambient air temperature ( - 20 ° C). In other experiments, the recorded expired air temperature changed abruptly in a similar fashion. This phenomenon was reported in only one other reference (Hartung et al., 1980), although, as it occurred in virtually all of the tests of this investigation at some point in the measurements, it is likely to have occurred in each of the other investi35
G
25
0 oc
-15
-25
I~
I
i
I
20
3B
40
~
L
521
6B
.
i
i
i
70
8B
9B
IB~I
TIME ( s e c o n d s )
Fig. 2. Typical data recorded during respired air temperature measurements at - 2 0 °C ambient. The thermocouple had been wetted with condensed water vapour or saliva.
150
J.B. CAIN etal.
gations. To avoid any problem with water on the thermocouple, the maximum expired air temperature was estimated from the first few breaths only. If the data showed a peculiar response during this time, the measurements were repeated. The variation of the expired air temperature with ambient air temperature was found to be somewhat different from that reported in some other investigations (Belding et al., 1945; M c F a d d e n et al., 1985; Hartung et aL, 1980) but is in reasonable agreement with others (HOppe, 1981). There are insufficient data from this investigation to determine the exact form of the relationship between the expired and ambient air temperatures; however, the data suggests that the peak expired air temperature approaches a minimum value between 27 and 30 °C for ambient temperatures below - 30 °C under otherwise normal working conditions. It would also appear that the expired air temperature approaches the body core temperature as the ambient temperature approaches 37 °C. The results of the heat transfer calculations (table 2) indicate that respiratory heat loss is a larger fraction of the metabolic rate at low work rates than at higher work rates, although the data suggest that respiratory heat loss approaches a limiting value as the work rate increases. The respiratory heat loss may also represent a slightly larger fraction of the metabolic rate at lower temperatures although this may be only a statistical fluctuation in the data. In s u m m a r y , it was found that the temperature of expired air of individuals working normally depends mainly on the ambient air temperature but that even at the coldest ambient temperature examined, the expired air temperature is approximately 28 ° C. The expired air was found to be saturated, or very close to saturation, for the conditions studied. The respiratory heat loss was found to be between 25 and 30~o of the resting metabolic rate but was between 15 and 20~o of the working metabolic rate.
References Belding, H.S., R.C. Darling, D.R. Griffin, S. Robinson and E.S. Turrell (1945). Evaluation of thermal insulation provided by clothing. In: Clothing Test Methods, edited by L. H. Newburgh and M. Harris. Washington Subcommittee on Clothing of the National Research Council, CAM No. 390, pp. 9-20. Burton, A. C. and O. G. Edholm (1955). Man in a Cold Environment. London, Edward Arnold Publishers, pp. 42-43. Ferrus, L., D. Commenges, J. Gire and P. Var6ne (1984). Respiratory water loss as a function of ventilatory or environmental factors. Respir. Physiol. 56:11-20. Hartung, G.H., L.G. Myhre and S.A. Nunneley (1980). Physiological effects of cold air inhalation during exercise. Aviat. Space Environ. Med. 51: 591-594. H6ppe, P. (1981). Temperatures of expired air under varying climatic conditions. Int. J. Biometeorol. 25: 127-132. McCutchan, J.W. and C.L. Taylor (1950). Respiratory heat exchange with varying temperature and humidity of inspired air. J. Appl. Physiol. 4: 121-135. McFadden, E. R., B.M. Pichurko, H. F. Bowman, E. Ingenito, S. Burns, N. Dowling and J. Solway (1985). Thermal mapping of the airways in humans. J. Appl. Physiol. 58: 564-570. Mitchell, J. W., E. R. Nadel and J. A. Stolwijk (1972). Respiratory weight loss during exercise. J. Appl. Physiol. 32: 474-476. Newburgh, L.H. (1968). Physiology of Heat Regulation and the Science of Clothing. New York, Hafner Publishing Co., pp. 259-260. Webb, P. (1951). Air temperatures in respiratory tracts of resting subjects in cold. J. Appl. Physiol. 4: 378-382.
145
RESP 01590
Respiratory heat loss during work at various ambient temperatures J.B. Cain, S.D. Livingstone, R.W. Nolan and A.A. Keefe Defence Research Establishment Ottawa, Environmental Protection Section, Ottawa, Ontario, Canada KIA OZ4 (Accepted for publication 31 July 1989) Abstract. The purpose of this investigation was to establish the temperature and humidity of the expired
air of subjects working at various metabolic rates at ambient temperatures between - 4 0 °C and 20 °C in order to calculate respiratory heat loss. Measurements of the respired air temperature and water vapour content were made for five subjects while they either stood or walked on a treadmill. The results indicated that the maximum respired air temperature varied slightly with the ambient air temperature but changes in metabolic rate, respiration rate and breathing frequency had no apparent effect on the expired air temperature under the conditions studied. The relative humidity of the respired air was found to be close to saturation in the extreme-cold environments. Heat loss due to respiration was between 25 and 30% of the resting metabolic and between 15 and 20~o of the working metabolic rate.
Heat loss; Humidity; Metabolic rate; Respiration; Temperature; Work
Heat loss due to respiration can represent a sizable portion of the body's total heat loss (Burton and Edholm, 1955). The temperature of expired air has been reported to be as low as approximately 20 °C (McFadden et aL, 1985; Webb, 1951) and as high as 37 °C (H0ppe, 1981; Newburgh, 1968). Reports on the humidity of the expired air have also varied, from approximately 80~ relative humidity (Ferrus et al., 1984; McCutchan and Taylor, 1950; Mitchell et al., 1972) to fully saturated (Belding et al., 1945; Newburgh, 1968). Since these variations in both temperature and humidity may be due to slow response times of the sensors used, this investigation was undertaken in an attempt to obtain a better estimate of the correct values. In this study, the temperature of the respired air was measured while subjects worked at four different rates and at four different ambient air temperatures. During tests at very cold temperatures, the water content of the expired air was also measured. With this information and with measured respiratory ventilation rates, the respiratory heat loss was calculated. Correspondence address." J.B. Cain, Defence Research Establishment Ottawa, Environmental Protection Section, Ottawa, Ontario, Canada K1A 0Z4. 0034-5687/90/$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical Division)
J.B. CAIN etaL
146
Experimental procedure Five male volunteers gave their informed consent to participate in the experiments. The average and standard deviation of age, height and weight of the subjects were 28 + 5 years, 171 + 7 cm and 74 + 12 kg, respectively. The experiments were conducted in an environmental chamber at each of four ambient temperatures: - 40, - 20, 0 and 20 °C. Humidity could not be eontrolled in the chamber; however, the amount of water contained in the air is negligible at 0 °C and below. The subjects dressed in appropriate clothing so that they were comfortable at each of these temperatures. Experiments consisted of a series of four tests at each ambient temperature. Tests were conducted at four different work rates: (1) standing quietly; (2) walking on a treadmill at 3 km. h - 1 on a 0~o slope; (3) walking on a treadmill at 3 km. h - 1 on a 5~o slope; (4) walking on a treadmill at 5 km. h - ~ on a 5 ~o slope. For each experiment, the subject entered the environmental chamber and stood, breathing normally, for a period of 10 min. The temperature of his respired air was then measured over a two minute period using a fast response copper-constantan thermocouple (Omega COCO-001) mounted at about the plane of the lips in a rubber mouthpiece (Vacumed No. 1001). The subject then removed the mouthpiece and donned a face mask (Speak-Easy II, Respironics, Monroeville, PA) which was connected to a Beckman Metabolic Measurement Cart in an adjacent laboratory using 47 mm diameter corrugated plastic tubing. The subject's metabolic rate, respiratory frequency and volume of expired air were measured for ten minutes with average values recorded every minute. The subject then walked on the treadmill at the lowest work rate for a ten-minute equilibration period after which the above measurement procedure was repeated as the subject walked. Measurements at the two higher work rates followed. The temperature data were measured and recorded using a Hewlett-Packard data acquisition system (HP 3497A) controlled by a Hewlett-Packard computer (HP 9836). Measurement of both the ambient air temperature and the thermocouple reference temperature were made at the beginning and end of each two minute respiratory air temperature measurement. Only the respired air temperature was monitored during the 2 min interval which allowed readings to be recorded approximately ten times per second. Since humidity sensors have greater time constants than the response times required for accurate measurements, humidity was measured at the two coldest ambient temperatures by condensing the moisture in the expired breath in approximately 3 m of plastic tubing which lead from the mask to the metabolic cart. The humidity was then calculated from the difference in weight of the tubing and mask before and after each test. Heat loss due to respiration was then calculated (absolute humidity for air temperature less than 0 °C being negligible) using the following equation: Or =
Pa~/Cpa(We-Ti) + Pag(Te-Ti)hfg + Pa~/TiCpv(Te-Ti)
(1)
w h e r e (~r = respiratory heat loss, W; p~ = density of the air, k g ' m - 3 ; ~7 = respiratory
147
RESPIRATORY HEAT LOSS
ventilation rate, m 3 " s e c - =; Cpa = specific heat of dry air, J. k g - 1. K - 1; T~ = expired air temperature, °C or K; T i = inspired air temperature, °C or K; 7e = humidity ratio of the expired air; 7i = humidity ratio of the inspired air; hfg = enthalpy of vaporization, J. k g - 1. K - 1; Cpv = specific heat of water vapour, J- k g - 1. K - 1.
Results
Figure 1 shows a plot of typical data measured in this investigation for the temperature of respired air. The test begins with the mouthpiece (containing the thermocouple) at the ambient air temperature. At approximately 17 sec into the test, the mouthpiece was inserted and measurement of the subject's respired air temperature began. It can be seen that the minimum temperature recorded by the sensor upon inspiration was approximately that of the ambient air temperature ( - 40 ° C), although the inspired air temperature appears to be increasing slightly with successive breaths. The maximum expired air temperature recorded shows a very small scatter but is approximately constant for each breath. Several peak temperature data points are evident during each expiration cycle indicating that the sensor's response time is sufficient to measure the maximum temperature. The expired air temperature and humidity did not vary in any consistent manner for the work rates, metabolic rates, respiration rates or the respiration frequencies encountered in this investigation. The results were therefore averaged over all four work rates and the mean expired air temperatures for various ambient temperatures are given in table 1.
30 20
G 10 0 o.
-10
8t~
-20
o. t~
-30 -40 10
1'5
210
2~5
3~
3~5
410
45
TIME (seconds) Fig. 1. Typical data from measurements of the respired air temperature at - 4 0 °C ambient.
148
J.B. C A I N et aL TABLE 1
Maximum expired air temperatures measured at various work rates and environmental temperatures. Work rate
Maximum expired air temperature
Speed (km'h-')
Slope (%)
20 °C
0 3 3 5 Mean
0 0 5 5
33.8 33.8 34.0 34.9 34.1
± ± ± ± +
0 °C
0.2 1.0 0.8 1.9 2.3
32.0 31.7 31.8 31.5 31.8
+ + ± ± ±
0.7 0.9 1.7 2.0 2.9
- 20 °C
- 40 °C
29.6 31.4 29.5 28.4 29.7
30.7 28.5 28.4 28.1 28.9
± ± ± + ±
1.2 1.6 2.9 2.7 4.4
± ± ± ± ±
0.9 1.8 0.9 1.5 2.7
Ambient temperatures are shown by the temperature values above each column. All values are mean ± standard deviation. Mean values underlined by a common line are not significantly different.
Since the drying compound at the metabolic cart indicated no significant amounts of water in the sampled air, it was assumed that all of the water vapour in the expired air had condensed either in the mask or tubing. The expired air was found to be close to saturation at the measured expired air temperature and was greater than 90 ~o relative humidity in most cases. The amount of water collected varied from 0.44 + 0.06 (mean + SD) to 1.0 + 0 . 2 7 g ' m i n - 1 for respiration rates of 8.7 + 2.5 to 41.5 + 8.3 L. min - 1. The experimental uncertainty in these measurements was approximately 40 ~o at the low respiration rates and approximately 15 ~ at the high respiration rates. In several experiments, the results indicated that the expired air was supersaturated. Heat loss due to respiration is shown in table 2. The results for 20 ° C are not included as the ambient humidity was not controlled during these tests and may have been TABLE 2 Metabolic rate and calculated heat loss as a function of ambient temperature and work rate. Work rate
O°C
- 2 0 °C
-40°C
0 km. h - 1
3 km. h- 1
3 km. h - i
5 km. h
0~o slope
0~o slope
5~o slope
5~o slope
Metabolic rate Respiratory heat loss Metabolic r a t e ( ~ o ) Metabolic rate Respiratory heat loss Metabolic rate (~o) Metabolic rate
112 28 25 77 19.5 25 84
+ + + + + + +
16 8 4 24 5 3 17
229 ± 46 + 20+ 232 + 43 + 19+ 241 +
320 i 61 ± 19± 301 + 54 + 18_+ 338 +
36 11 2 31 8 2 53
460 + 57 82 + 12 18+ 1 497 +_ 40 77 + 9 16_+ 2 489 ± 91
Respiratory heat loss Metabolic r a t e ( ~ o )
25 29
+ £
6 2
72 + 17 21 ± 2
97 ± 23 20± 4
24 10 2 32 3 3 53
53 _+ 15 21 + 2
All values, unless specified, are in watts _+ standard deviation.
1
149
R E S P I R A T O R Y H E A T LOSS
significant. For metabolic rates between 75 and 100 W, the respiratory heat loss was found to represent between 25 and 3 0 ~ of the metabolic rate. For metabolic rates greater than 200 W, the respiratory heat loss was approximately 10~o lower.
Discussion
The data in fig. I indicate that the air temperature measured by the thermocouple upon inspiration was close to that of the ambient air. It was therefore assumed that the temperature recorded upon expiration was an accurate measure of the expired air temperature. In most experiments, the recorded inspired and expired air temperatures began to change, with one or both tending to some temperature intermediate to the ambient and body temperatures (fig. 2). Examination of the mouthpiece after these events showed water or ice either on the thermocouple junction or on the thermocouple lead wires. Water on the junction or wires was thought to result from droplets of condensation in the expired air, although saliva may have been responsible in some cases. This phenomenon significantly increased the response time of the thermocouple producing obviously different and erroneous results. In fig. 2, the recorded inspired air temperature indicates that the sensor was not accurately measuring the ambient air temperature ( - 20 ° C). In other experiments, the recorded expired air temperature changed abruptly in a similar fashion. This phenomenon was reported in only one other reference (Hartung et al., 1980), although, as it occurred in virtually all of the tests of this investigation at some point in the measurements, it is likely to have occurred in each of the other investi35
G
25
0 oc
-15
-25
I~
I
i
I
20
3B
40
~
L
521
6B
.
i
i
i
70
8B
9B
IB~I
TIME ( s e c o n d s )
Fig. 2. Typical data recorded during respired air temperature measurements at - 2 0 °C ambient. The thermocouple had been wetted with condensed water vapour or saliva.
150
J.B. CAIN etal.
gations. To avoid any problem with water on the thermocouple, the maximum expired air temperature was estimated from the first few breaths only. If the data showed a peculiar response during this time, the measurements were repeated. The variation of the expired air temperature with ambient air temperature was found to be somewhat different from that reported in some other investigations (Belding et al., 1945; M c F a d d e n et al., 1985; Hartung et aL, 1980) but is in reasonable agreement with others (HOppe, 1981). There are insufficient data from this investigation to determine the exact form of the relationship between the expired and ambient air temperatures; however, the data suggests that the peak expired air temperature approaches a minimum value between 27 and 30 °C for ambient temperatures below - 30 °C under otherwise normal working conditions. It would also appear that the expired air temperature approaches the body core temperature as the ambient temperature approaches 37 °C. The results of the heat transfer calculations (table 2) indicate that respiratory heat loss is a larger fraction of the metabolic rate at low work rates than at higher work rates, although the data suggest that respiratory heat loss approaches a limiting value as the work rate increases. The respiratory heat loss may also represent a slightly larger fraction of the metabolic rate at lower temperatures although this may be only a statistical fluctuation in the data. In s u m m a r y , it was found that the temperature of expired air of individuals working normally depends mainly on the ambient air temperature but that even at the coldest ambient temperature examined, the expired air temperature is approximately 28 ° C. The expired air was found to be saturated, or very close to saturation, for the conditions studied. The respiratory heat loss was found to be between 25 and 30~o of the resting metabolic rate but was between 15 and 20~o of the working metabolic rate.
References Belding, H.S., R.C. Darling, D.R. Griffin, S. Robinson and E.S. Turrell (1945). Evaluation of thermal insulation provided by clothing. In: Clothing Test Methods, edited by L. H. Newburgh and M. Harris. Washington Subcommittee on Clothing of the National Research Council, CAM No. 390, pp. 9-20. Burton, A. C. and O. G. Edholm (1955). Man in a Cold Environment. London, Edward Arnold Publishers, pp. 42-43. Ferrus, L., D. Commenges, J. Gire and P. Var6ne (1984). Respiratory water loss as a function of ventilatory or environmental factors. Respir. Physiol. 56:11-20. Hartung, G.H., L.G. Myhre and S.A. Nunneley (1980). Physiological effects of cold air inhalation during exercise. Aviat. Space Environ. Med. 51: 591-594. H6ppe, P. (1981). Temperatures of expired air under varying climatic conditions. Int. J. Biometeorol. 25: 127-132. McCutchan, J.W. and C.L. Taylor (1950). Respiratory heat exchange with varying temperature and humidity of inspired air. J. Appl. Physiol. 4: 121-135. McFadden, E. R., B.M. Pichurko, H. F. Bowman, E. Ingenito, S. Burns, N. Dowling and J. Solway (1985). Thermal mapping of the airways in humans. J. Appl. Physiol. 58: 564-570. Mitchell, J. W., E. R. Nadel and J. A. Stolwijk (1972). Respiratory weight loss during exercise. J. Appl. Physiol. 32: 474-476. Newburgh, L.H. (1968). Physiology of Heat Regulation and the Science of Clothing. New York, Hafner Publishing Co., pp. 259-260. Webb, P. (1951). Air temperatures in respiratory tracts of resting subjects in cold. J. Appl. Physiol. 4: 378-382.
