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Characteristics of the temperature regulation system in the human body
J. therm. Biol. Vol. 18, NO. 5/6, pp. 307-323, 1993 Printed in Great Britain
0306-4565/93 $6.00 + 0.00 Perpmon Press Ltd
THERMAL
PHYSIOLOGY
CHARACTERISTICS OF THE TEMPERATURE REGULATION SYSTEM IN THE HUMAN BODY YosDucATsu
KAwASHIMA
Faculty of Engineering, Yokohama National University, Tokiwadai 156, Hodogaya-ku, Yokohama 240, Japan Abstract-l. To study a complex biological system such as human temperature regulation, it is necessary to consider both physiological experiments and theoretical analysis. 2. This paper presents the characteristics of this temperature regulation system obtained from a mathematical model, together with experimental data and the influence of exercise and clothing. 3. The experimental results showed a good agreement with the theoretical results. Key
Word Index:
Body temperature regulation; mathematical model; exercise; clothing; skin blood
circulation; human
INTRODUCTION It is necessary to know the characteristics of temperature regulation when considering the problems concerning human thermal environment. The special features of the temperature regulation system of man will be discussed in relation to a mathematical model, experimental data of the temperature regulation system, and the influence of working and clothing on the temperature regulation system.
THE CHARACTERISTICS OF THE TEMPERATUREREGULATIONSYSTEM In an integrated organism temperature regulation is essential for the proper functioning of other systems. Temperature regulation in man is a highly developed homoiostatic mechanism. It enables specific characteristics of data reception and a control system that is not reproduced in mechanical systems of temperature regulation. Two types of temperature receptors exist to establish quantitative regulation by perspiration, shivering, blood flow in cutaneous capillary vessels, etc. This system is a unique distribution system: not only the state variables such as skin temperature are distributed, but also the detectors such as temperature receptors and the effecters such as sudoriferous glands and cutaneous capillaries are also widely distributed. This system also has the capacity for behavioural responses. Furthermore, the temperature regulation system is not necessarily an independent system; this system relies on skeletal muscles and
cutaneous capillaries whose primary objective is not temperature regulation. Therefore this system tends to be influenced by other sub-systems. This system involves the whole body and so it is considered to be under the influence of several disturbances, especially internal ones. However, it has a high degree of stability. How is this complex control-information system constructed? Its central integration mechanism should be large and highly redundant. Therefore, it is most important to accumulate experimental data on temperature regulation not only for practical thermal environment evaluation, but also for physiology that elucidates the control-information aspect of temperature regulation. THEORETKALSTUDIESUSING A MATHEMATICAL MODEL OF TEMPERATURE
REGULATION
The greatest problem met in studying control systems lies in the wholeness (inseparability) of the system. In mechanical regulation systems, it is possible to divide the system into components, then investigate the characteristics of each component and study the relationship between the components. The result of such analytical studies, would enable the characteristic of the system as a whole to be determined. However, an organism is basically a closed system. Even if the system is converted to an open system by taking it out from the living body and experiments conducted, the experimental data obtained in this open system could not be the same as that obtained in the actual closed system. Therefore the unknown functions should be compensated 301
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KAWASHIMA
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for by using inductions in constructing the model of an organic system. The merits of model construction lie in the fact that we can deduce a lot of information from the working-hypothesis that would be constructed during the model building, and that we can understand the characteristics of temperature regulation as an integrated whole. We could obtain not only new insight but also suggestions for future experimentation. The model, that we describe here, is constructed in order to evaluate the basic characteristics of the temperature regulation of humans. Therefore this model is not a simulation model that reproduces the characteristics of the temperature regulation system with high fidelity. Therefore, a considerable number of elements and characteristics are excluded. Figure 1 is a rough sketch of the mathematical model (see Kawashima and Yamamoto, 1971 for details). The human body is divided into the internal and the external part. It is not difficult to maintain the temperature of the internal stationary part. The temperature of the external part is easy to manipulate. Blood circulates between the internal and the external part. The body temperature would be regulated by F3 (the quantity of blood circulating to the external part), Q (the quantity of metabolically generated heat that would change by shivering, etc.) and N (the quantity of perspiration). There are several factors of external
environmental changes affecting heat radiation: temperature, humidity, wind speed and radiation. In this mathematical model, 0e (air temperature) is used as the factor representing those factors. The mathematical calculation of this model would indicate the temperature range that could be regulated by blood flow. Here, we set the hypothesis concerning the "proper usage of operational quantity" in the temperature regulation system. This hypothesis is as follows: (1) Regulation is carried by responding to the external environmental changes such that the internal temperature would remain as constant as possible. (2) Quantity of blood flow is used to regulate the body temperature near to normal. At the temperature range where the body temperature could not be regulated by blood flow alone, perspiration and shivering would be invoked. Hereafter we will use this working hypothesis and analyse the static characteristics of the temperature regulation system. Figure 2 is an example of these static characteristics. By changing the constants contained in this mathematical model, it is possible to study the influence of altering the value of internal body temperature settings related to the differences between sexes, among ages and seasons,
Temperature regulation in humans and the influence of parameter alterations such as weight of subcutaneous fat, basal metabolism, physical features, weight of clothing, and wind speed, on the characteristics of the temperature regulation system, especially in the regulation range. A part of this result is shown in Fig. 3. The essentials of this model are as follows: (1) When the weight of subcutaneous fat increases, the body temperature regulation range would shift to a lower temperature, and the cutaneous temperature would be lower. Also, the size of the blood flow regulation range and of the heat generation regulation range would increase. However, the increase in weight of subcutaneous fat would not affect the perspiration regulation range [Fig. 3(a)]. (2) When the internal temperature is set higher in order to accommodate the female's high basal temperature period or in fever, the temperature regulation range of each section would shift correspondingly to a higher temperature [Fig. 3(b)]. (3) The increase of metabolism under physical labour would increase the width of the regulation range and, at the same time shift the range to a lower temperature as a whole. Contrary to this, the decrease of metabolism during sleep will make regulation at a low environment temperature difficult [Fig. 3(c)]. (4) The increase of heat conductivity between the external environment and skin would correspond to the increase of air flow, and this would decrease the regulation range. Contrary to this, a decrease of heat conductivity would increase the size of the regulation range. The effect of a heat conductivity decrease resembles Q' 0"
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the result of wearing clothes. In this case the low side of the regulation range would be extended [Fig. 3(d)]. (5) Concerning morphology, the size of physical features is related to the size of the regulation range. The low side of the regulation range would extend in proportion to the size of the physical features. This is why animals with constant body temperature living in a colder region are larger than ones of the same species living in a warmer region [Fig. 3(e)]. Figure 4 displays the change of regulation range in proportion to the continuous alteration of these heat parameters. These parameters indicate the following from top to bottom: effect o f / / 5 heat conductivity between outer part and inner part (subcutaneous fat) change of 05s internal temperature (in case of fever or female's high basal metabolism temperature period), change of quantity of motion or of basal metabolism, effect o f / / 4 heat conductivity between atmosphere and skin (clothing, air flow), difference of physical features (L = resemblance ratio). The above mentioned prediction is derived from the simple mathematical model of object of regulation and the working hypothesis on the parts of regulation. From this prediction the effect of each heat parameter can be obtained. However, as described previously, this is the deducted from hypothesis, and confirmation from the experimental results is required. CHARACTERISTICS OF THE TEMPERATURE REGULATION SYSTEM
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311
derived from the hypothesis, a climatically controlled room equipped with measuring instruments was prepared for the experiments. The experiments were carried out during the summer, winter, spring and autumn. Males, females and children were used as subjects. The experiments were carried out on many subjects in order to increase the accuracy of the result. The experiments were made uniform as far as possible in order to examine the differences caused by sex, age and season. The experiments were carried out as follows: A subject stayed about 60 min in the "preparatory room" conditioned at approx. 28°C, 50% RH sitting quietly on a chair, naked and with eyes open. The subject then moved to a climatically controlled room conditioned at a stationary condition (16, 19, 22, 25, 28, 31, 34, 37, 40°C, 50 RH, No-Wind), where he/she would pass about 120 min sitting on a chair quietly, naked and with eyes open. Throughout this 180 min, the condition of the subject would be observed and recorded. The following measurements were made: rectal temperature, auditory canal temperature, cutaneous temperature, blood flow in the finger, quantity of weight drop (total evaporation capacity), quantity of metabolism, pulse rate, respiration rate, radiant heat from skin, thermal feeling, and feeling of discomfort. The blood flow in the finger is the index of cutaneous capillary blood flow that is the main operational quantity of the body temperature regulation system. Venous occlusion methods are applied using the air plesthysmograph. Blood flow is taken at 5 min intervals, and continuously 3 times for each measurement. The average of measurements taken during the last 30 min after the move to the climatic room is used as the stationary value. Weight is measured after this move at 20 min intervals. As the weight drop rate would be stationary after 60min, this stationary value is calculated from the slope of the graph. For measuring metabolism, respiration over a 10min period was determined at 20min intervals and metabolic rate was calculated using gas analysis. Radiant heat is measured by the calorimeter attached on the trunk. The 9 grade ordinal scale is used to measure the thermal feeling, and the 5 grade ordinal scale for feelings of discomfort. These two factors were determined by questioning the subject. Cutaneous temperature was measured by a thermoelectric couple. The average cutaneous temperature calculated b y the operation circuit is also recorded. As a result about 60 assessment characteristics of the human body temperature regulation system were obtained. The result of these experiments shows close conformity with the calculated value. Therefore, we conclude that the experiments support the hypothesis.
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Temperature regulation in humans
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Figures 5 and 6 are the measured examples of static characteristics. Figure 7 shows the records of rectal temperature variation, cutaneous temperature variation, finger blood flow rate, metabolic heat production and body weight loss. Those are the results of the 30th experiment (autumn season, male, 0;26 clo). The essential points are as follows: (1) Rectal temperature shows a slight increase in proportion to increases in environmental temperature. (2) Average cutaneous temperature agrees with the calculations from the mathematical model of Fig. 3(d). The rate of increase in body temperature in proportion to environmental temperature decreased in the temperature range where perspiration was observed. (3) Blood flow regulation range is from approx. 22 to 3 I°C. (4) The weight drop shows that perspiration is observed above 31°C. (5) In the case of male subjects, metabolism increases from an environmental temperature of 22°C.
(6) Pulse rate increases in proportion to the environmental temperature. However, not as much as the increase in respiration rate. (7) Thermal sensations of females were less uniform as compared to males. However, the neutral point of both sexes is 28°C. This neutral point is lower than the perspiration range, and higher than the blood flow range. The neutral point is equivalent to 33°C of the average cutaneous temperature. (s) Partial cutaneous temperature indicates the following: at low temperatures, the partial cutaneous temperature increases in the following order: fingertip, instep, back of hand, forearm, femur, waist, breast, forehead. However, extremities do not always have a lower temperature. Experiments indicate that at high environmental temperature, instep and back of hand would be heated up by the atmosphere and cutaneous temperature would be higher than in other parts. It is considered that the effect of cooling by perspiration and of heat generation by metabolism do not reach the periphery efficiently (Fig. 6). Concerning the dynamic characteristics:
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(9) Cutaneous temperature would be constant after about 30 min of exposure to the high temperature environment. However, it would not be constant even after about 120 rain of exposure to the low temperature environment. The mode of responses are considerably different between the higher and the lower side. (Fig. 7). (10) The responses observed at the forehead are different from the other area. The time required to become constant is short, and the
cutaneous temperature shows little drift. In some cases of exposure to high environmental temperatures overshoot was observed. These are general results. We cannot clearly describe differences among seasons and between sexes, as sufficient examples were not available. However: ( l l ) Males show little seasonal change of body temperature. However, an increase of metabolism was observed during the winter season.
317
Temperature regulation in humans
The differences between sexes are not as great as we had previously considered. However: (12) Average cutaneous temperature of females is lower than that of males in a low temperature environment. This tendency for lower cutaneous temperature is greater at the peripheral section of the body. (13) The dilation of cutaneous capillaries and perspiration begins at about 3°C higher in females than in males. Therefore, the blood flow regulation range and the perspiration regulation range shift to a higher temperature. Not only air temperature, but also humidity, radiation, and wind speed are considered as the external environment factors. Also, movement, weight of clothing, etc. are counted as human related factors. However the characteristics of the temperature regulation system accommodating those changes have not yet been fully examined and adopted into the system. It is necessary to obtain experimental data first. Also, the influence of the differences between sexes, among ages, among individuals, of heat adaptation, and daily and seasonal variations should be examined and not by just comparing a few factors mutually. These parameters should be examined in comparison with the characteristics of the body's temperature regulation system.
"c
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.--~.__., _//
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Fig. 8. Influence of exercise. TB 18/5/6---D
--
i
INFLUENCE OF EXERCISE ON THE CHARACTERISTICS OF THE BODY'S TEMPERATURE REGULATION SYSTEM
Here, the characteristics of the body's temperature regulation system under the condition of rest, 23W physical labour, and 80W physical labour are compared. Experiments are carried out on healthy male subjects in the summer-autumn season of 1977. The experiments were carried out as follows: A subject has first rested for 60 min in the "preparatory room" conditioned at approx. 28°C, 50% RH sitting quietly on a chair naked and with eyes open. The subject is then moved to a climatically controlled room conditioned at a constant condition (7-40°C, 50% RH, No-Wind), where he stays for about 60 rain sitting on a chair quietly, naked and with eyes open. After that, 4 cycles of the experiment are carried out. Each cycle consists of 15 min exercise using a bicycle ergometer and 5 min rest. Then the experiment is continued for 40 min at rest. Throughout this process for a total of 240 min, the condition of the subject was observed and recorded. The following measurements were made: rectal temperature, auditory canal temperature, cutaneous temperature, blood flow in the finger, quantity of weight drop (total evaporation capacity),
rectal tmperature
318
Yosmr~rsu K A w ~ m ~
quantity of metabolism, pulse rate, respiration rate, radiant heat from skin, thermal feeling, comfort, revolution rate of ergometer. The main constant value is taken from the last 5 min of exercise at the 3rd and 4th cycle. Blood flow in the finger and quantity of weight drop are measured just after physical labour. Thermal feeling and comfort are recorded by questioning each subject just before and after physical labour. Figure 8 is a summary of the "constant values". In these figures, "constant values" of the same subject are compared for the conditions of rest, 23W physical labour and 65W physical labour. (1) Each reaction of the temperature regulation system shifts to a lower range according to the quantity of physical labour. As a distinctive feature of physical labour, a rise of internal temperature and a large quantity of perspiration were observed. (2) Not only did the average cutaneous temperature shift to a lower temperature range, but also the cutaneous temperature of the area corresponding to the perspiration region was lower in proportion to the quantity of physical labour. This is a very interesting characteristic of the temperature regulation system. (3) Perspiration began at 31°C during rest, at 19°C during 23W of physical labour, and at 13°C during 80W of physical labour. The threshold of perspiration appearance shifted to the lower temperature in proportion to the quantity of physical labour. (4) The increase of metabolism and the appearance
(5)
(6)
(7)
(8)
(9)
of shivering during low environmental temperature were 25°C max. during rest, and 13°C max. during 23W of physical labour. Pulse rate increased in proportion to the quantity of physical labour. Pulse rate increased on the higher side of the temperature regulation range and also showed a slight increase on the lower side of the temperature regulation range. The pulse rate followed a concave line according to the temperature. Respiration rate increased in proportion to the quantity of physical labour. The respiration rate depends very little on the environmental temperature. The neutral point of thermal feeling and discomfort shifted to a lower temperature. Also, the subjects reported that thermal feeling and discomfort were clearly perceived even during physical labour. However the neutral point of these two characteristics was not the same. The neutral point of thermal feeling had shifted to the lower temperature. Figure 9 shows the relation between the quantity of metabolism and the temperature of the rectum. These two correspond with the exception of the decrease observed at low temperatures. Figure 10 shows the efficiency of temperature regulation in the above mentioned case. Efficiency does not depend much on the environmental temperature. Efficiency is approx. 15%. However, the efficiency during 80W physical labour is greater than during 23W physical labour.
14cal/h []
600
80w 23w
tO
o Rest
0
~. 400 A~
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o,,
IE I
I
-1.0
-0.5 Increase
O,r i
0
I
0.5 of Rectal Temperature (z~Tr)
I
1.0
Fig. 9. Relation between metabolic heat production and rectal temperature.
deg
Temperature regulation in humans
319
% 20 13
El
&
A A
u
~10 L,d
Subject "N K" El 80W ~, 23W i
!
10
t
i
I
I
20 30 Ambient Temperature
I
40
°C
Fig. 10. Etficiency of exercise.
The body temperature regulation system during physical labour shows a rise of internal temperature. Several hypotheses are given in order to explain this: insufficient regulation, rise or fall of setting temperature, combination of the previous two hypotheses, etc. Recently this internal rise of temperature has been explained as follows: the reflexive capillary contraction caused by the physical labour counteracts the cutaneous capillary dilation. As a consequence thermal radiation would be decreased and result in the rise of internal body temperature. However the data obtained in these experiments shows the unreliability of this hypothesis, as the rise of internal temperature is observed even in a high environmental temperature where sufficient dilation of cutaneous capillaries is probable. During physical labour, the temperature regulation system does not function independently. The muscle motion control system, the circulation system, and the respiration system are working rigorously. The above mentioned phenomena could not be explained if we did not accommodate a higher regulation function that regulates those systems into our hypothesis. In such conditions, the internal temperature could be considered to function as an operational quantity. The rise of the internal temperature was 0.00176°C/(kcal/h). This value can be adopted as an operational transfer coefficient in the mathematical model.
(1) Using mechanical equipment such as the homoiothermal method. (2) Use of a thermal mannequin. (3) Experimental methods using actual human beings with clothing on. In our experiment method 3 was used as the main method in order to obtain the basic data. Also, comparisons of method 3 with methods 1 or 2 was
THE EFFECT OF CLOTHING ON THE CHARACTERISTICS OF THE BODY'S TEMPERATURE REGULATION SYSTEM
The effect of clothing is described in this section. There are three methods to measure the thermal insulation ability of clothing:
Plate 1. The clothing used in the experiments (uniformly covered clothes).
rectal t~l~rature .__~.~--~.~._ clothtng
clothing /
_.- - ~ - ....
•
.-''"
//" /~/,i ~'nude
I= &
,
,//average skin temperature
subject: NK, male
. J
j.,,.,o..,-t,~
24
./ ~.
clothing/
1.0
, .... ./'nude
; ,.//i
0.5
~ o
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7
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1511 g/h
clothing/// //' nude
0
7
10 13 16 19 22 25 28 31 34 37 40 43
160 ._~ 140
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;i
7
10 13 16 19 22 25 28 31 34 37 40 43
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7
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10 13 16 19 22 Z5 28 31 34 37 40 43 cl othi r ~ - - 7 -..~.. "'-" thenlal sensation . ~ J " .// ~ . j / _ . . . . . . . . -'" nude
.~---~/" calfort
7
nude
"~.
\ - - - - ~ . ~ ....
10 13 16 19 22 25 28 31 34 37 40 43 envirormental temperature('(3) Fig. 11. Effect of clothing.
Temperature regulation in humans also done. Plate 1 shows the clothing used in the experiments. In order to keep the thermal conductivity between skin and environment uniform, all of the body surface except the face is covered uniformly. Also, elastic material was used for clothing in order to ensure close adhesion to the body. The clothing material is polyester with the following specifications: density; 60.5 fibres/inches to weft direction, 87.0 fibres/inches to course direction, weight; 314.9 g/m s, thickness; 0.91 ram (measured under tension of 7 g/cm~), thermal insulation; 17.4% (homoiothermal method, JIS-1079), ventilation property; 21.6cc/cm:. Experiments were mainly carried out with one layer of clothing on. This result is compared with that of a naked condition and with 4 layers of clothing on. Experiments were carried out in autumn on 2 healthy male subjects. The experiments were carried out by the following procedure: A subject first rests for about 60 rain in the "preparatory room"
(a)
321
conditioned at approx. 28°C, 50% RH sitting quietly on a chair naked and with eyes open. The subject was then moved to a climatically-controlled room conditioned at a constant condition (7, 13, 16, 19, 22, 25, 28, 31, 34, 37, 43°C, 50% RH, No-Wind) about 3 h sitting on a chair quietly naked and with eyes open. Throughout this process of 4 h, the condition of the subject was observed and recorded. The measurements made were the same as in the previous experiments. Figure 3((1) shows the calculated data based on the mathematical model of the body's temperature regulation system. The solid line shows the example for the naked condition. The dotted line shows the influence of the /t4 thermal conductivity between environment and skin. This dotted line is equivalent to the condition with clothing on. The temperature regulation range be improved by clothing. Figure 11 shows the comparison of the naked condition with 1 layer of clothing on for the subject
(H-E)/A [Kcal/m2h] 50 ' 0
subject: NK, nude H+ = 5.55
~
,
/
-5 ~
5
10
15
•~
e s - ee ['C]
(M-E)/A [Kcal/mZh]
{b)
~'
50 subject: NK, clothing H, = 4.40 0 ~ x . . . . . . . . . . . . . . . . . 5 10 15 /I
I...- ~ f
'
'
'
'
- 5 1/i",
I ;
Os-- Oe I'C]
(C)
(H-E)IA [Kcal/m2h] so
//'s~je:i: 0 - s"
'
'
~../'
NK, clothing (x4, H, = 3.30
5
io
15
e s - ee ['0] Fi8. 12. Thermal conductivity betweenexternal environment and skin: (a) nude; (b) one layer of clothing; and (c) four layers of clothing.
322
Yosmr~TSU KAW~-tZUA
(N-E)/A [Kcal/mZh]
50
•°
_; ' 2 '
- ....__.-.
. . . . . . . . . . .
subject: -50J.
/
,
,
,
15 e s - Oe ['C]
•nude clotJlin9 clothin9 ( X 4 )
H, = 5.55 H4 = 4.40 H4 = 3.30
Fig. 13. Comparison of thermal conductivity.
NK. The solid line is the experimental data at the condition with 1 layer of clothing. The lines represent from top to bottom: rectal temperature, average cutaneous temperature, quantity of weight drop, quantity of heat generated by metabolism, pulse rate, respiration rate, thermal feeling and discomfort. These figures make the "proper usage of operational quantity" easy to understand. By wearing clothing, the average cutaneous temperature and the blood flow in the finger tip shifts to a lower temperature. This influence of wearing clothing corresponds well with the estimation from the mathematical model. Thermal feeling shifted to a lower temperature. However no essential change was observed for discomfort. Figure 12 is a chart plotting the relation between (M-B)/A and 0s - 0¢ using the value acquired by the experiments in order to acquire the thermal conductivity //4. //4 is determined from the slope of the chart. This chart from top to bottom shows the data of subject NK naked, with 1 layer of clothing on and 4 layers of clothing on.//4 for the naked subject was 5.55 kcal/m2h°C. Therefore, the thermal insulation of the air layer would be 0.18°C/(kcal/m2h). //4 during the condition of 1 layer of clothing is 4.40kcal/ m2h°C. Therefore, the thermal insulation of the air layer would be 0.277°C/(kcal/m2h). The disparity of the thermal insulation 0.047°C/(kcal/mEh) would be the thermal insulation of l layer of clothing. If this value is converted to a el• value by 1 el• = 0.18°C/ (kcal/m2h), it would be 0.26 el•. Therefore the thermal insulation rate would be 20.7%. In the case of 4 layers of clothing, //4 is 3.30 kcal/m2h°C, therefore the thermal insulation of the clothing would be 0.123°C/(kcal/m2h). If this is converted into a el• value, it would be 0.68 clo, insulation rate would give 40.5%, and the value by the homoiothermal method is 19.1%. The results of these experiments with clothing showed good correspondence with the thermal insu-
lation test of clothing material. This good correspondence is achieved because these experiments are basic experiments conducted using clothing material of one uniform-kind, and close adhesion to the skin, under the condition of low humidity of 50% RH and no accumulation of perspiration. The actual layering condition of clothing varies at each part of the body, the air layer produced by the looseness of clothing is also complicated, and there are also ventilation effects produced by the motion of the body. Therefore, if we carry out similar evaluations on the actual clothing based on the data obtained in these experiments, the influence of layered clothing, looseness, body motion and clothing configuration on the temperature regulation system based on the actual data would be possible. At least it is necessary to consider the thermal insulation functions of clothing in relation to the temperature regulation system of the body as a whole system. CONCLUDING REMARKS
It is important to understand the characteristics of the temperature regulation system in order to consider several problems of the human thermal environment. In this article, we first described the characteristics of the human temperature regulation system. Then we described the characteristics of the human temperature regulation system using a mathematical model. The observed data of the characteristics of the temperature regulation system were shown. Then the influence of physical labour and clothing on the temperature regulation system was observed. The experimental results showed a good agreement with the theoretical results. In the study of the characteristics of the temperature regulation system, it is necessary to appreciate the behaviour of operational quantity and the alteration of conditional quantity from
Temperature regulation in humans the standpoint of the whole system. Also, problems such as thermal environment evaluation should be positively carded out based, not only on the systematic understanding of a human being-thermal environmental system, but also on the concrete data of the characteristics of the temperature regulation system itself.
REFERENCES
Kawashima Y. (1986) Characteristics of temperature regulation system in the human body. Proceedings of The 10th
323
Symposium on Man-Thermal Environment System, Tokyo, 297/308. Kawashima Y. and Gotoh S. (1975) Temperature regulation system in the human body and thermal environment. J. Hum. Erg. 4. Kawashima Y. and Yamamoto H. (1971) Temperature regulation system in the human body and the mathematical model. Biological systems, Nikkan Kogyo. Kawashima Y. and Yamamoto H. (1972) Mathematical model of the temperature regulation system in the human body. International Biophysics Congress, Moscow, 151/152. Yamamoto H. and Kawashima Y (1969) An analog model of the body temperature. Proceedings of 16th International Congress on Occupational Health, 441.
0306-4565/93 $6.00 + 0.00 Perpmon Press Ltd
THERMAL
PHYSIOLOGY
CHARACTERISTICS OF THE TEMPERATURE REGULATION SYSTEM IN THE HUMAN BODY YosDucATsu
KAwASHIMA
Faculty of Engineering, Yokohama National University, Tokiwadai 156, Hodogaya-ku, Yokohama 240, Japan Abstract-l. To study a complex biological system such as human temperature regulation, it is necessary to consider both physiological experiments and theoretical analysis. 2. This paper presents the characteristics of this temperature regulation system obtained from a mathematical model, together with experimental data and the influence of exercise and clothing. 3. The experimental results showed a good agreement with the theoretical results. Key
Word Index:
Body temperature regulation; mathematical model; exercise; clothing; skin blood
circulation; human
INTRODUCTION It is necessary to know the characteristics of temperature regulation when considering the problems concerning human thermal environment. The special features of the temperature regulation system of man will be discussed in relation to a mathematical model, experimental data of the temperature regulation system, and the influence of working and clothing on the temperature regulation system.
THE CHARACTERISTICS OF THE TEMPERATUREREGULATIONSYSTEM In an integrated organism temperature regulation is essential for the proper functioning of other systems. Temperature regulation in man is a highly developed homoiostatic mechanism. It enables specific characteristics of data reception and a control system that is not reproduced in mechanical systems of temperature regulation. Two types of temperature receptors exist to establish quantitative regulation by perspiration, shivering, blood flow in cutaneous capillary vessels, etc. This system is a unique distribution system: not only the state variables such as skin temperature are distributed, but also the detectors such as temperature receptors and the effecters such as sudoriferous glands and cutaneous capillaries are also widely distributed. This system also has the capacity for behavioural responses. Furthermore, the temperature regulation system is not necessarily an independent system; this system relies on skeletal muscles and
cutaneous capillaries whose primary objective is not temperature regulation. Therefore this system tends to be influenced by other sub-systems. This system involves the whole body and so it is considered to be under the influence of several disturbances, especially internal ones. However, it has a high degree of stability. How is this complex control-information system constructed? Its central integration mechanism should be large and highly redundant. Therefore, it is most important to accumulate experimental data on temperature regulation not only for practical thermal environment evaluation, but also for physiology that elucidates the control-information aspect of temperature regulation. THEORETKALSTUDIESUSING A MATHEMATICAL MODEL OF TEMPERATURE
REGULATION
The greatest problem met in studying control systems lies in the wholeness (inseparability) of the system. In mechanical regulation systems, it is possible to divide the system into components, then investigate the characteristics of each component and study the relationship between the components. The result of such analytical studies, would enable the characteristic of the system as a whole to be determined. However, an organism is basically a closed system. Even if the system is converted to an open system by taking it out from the living body and experiments conducted, the experimental data obtained in this open system could not be the same as that obtained in the actual closed system. Therefore the unknown functions should be compensated 301
308
YOSHIKATSU
KAWASHIMA
central nervoussystem ¢
!
I
L . . . . . . . . .
', I
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inner part
I
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r
,
,
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,
_
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/14
V. , C.7. outerpart
blood ci rcurati on system
Fig. 1. A model of the temperature regulation system in the human body.
for by using inductions in constructing the model of an organic system. The merits of model construction lie in the fact that we can deduce a lot of information from the working-hypothesis that would be constructed during the model building, and that we can understand the characteristics of temperature regulation as an integrated whole. We could obtain not only new insight but also suggestions for future experimentation. The model, that we describe here, is constructed in order to evaluate the basic characteristics of the temperature regulation of humans. Therefore this model is not a simulation model that reproduces the characteristics of the temperature regulation system with high fidelity. Therefore, a considerable number of elements and characteristics are excluded. Figure 1 is a rough sketch of the mathematical model (see Kawashima and Yamamoto, 1971 for details). The human body is divided into the internal and the external part. It is not difficult to maintain the temperature of the internal stationary part. The temperature of the external part is easy to manipulate. Blood circulates between the internal and the external part. The body temperature would be regulated by F3 (the quantity of blood circulating to the external part), Q (the quantity of metabolically generated heat that would change by shivering, etc.) and N (the quantity of perspiration). There are several factors of external
environmental changes affecting heat radiation: temperature, humidity, wind speed and radiation. In this mathematical model, 0e (air temperature) is used as the factor representing those factors. The mathematical calculation of this model would indicate the temperature range that could be regulated by blood flow. Here, we set the hypothesis concerning the "proper usage of operational quantity" in the temperature regulation system. This hypothesis is as follows: (1) Regulation is carried by responding to the external environmental changes such that the internal temperature would remain as constant as possible. (2) Quantity of blood flow is used to regulate the body temperature near to normal. At the temperature range where the body temperature could not be regulated by blood flow alone, perspiration and shivering would be invoked. Hereafter we will use this working hypothesis and analyse the static characteristics of the temperature regulation system. Figure 2 is an example of these static characteristics. By changing the constants contained in this mathematical model, it is possible to study the influence of altering the value of internal body temperature settings related to the differences between sexes, among ages and seasons,
Temperature regulation in humans and the influence of parameter alterations such as weight of subcutaneous fat, basal metabolism, physical features, weight of clothing, and wind speed, on the characteristics of the temperature regulation system, especially in the regulation range. A part of this result is shown in Fig. 3. The essentials of this model are as follows: (1) When the weight of subcutaneous fat increases, the body temperature regulation range would shift to a lower temperature, and the cutaneous temperature would be lower. Also, the size of the blood flow regulation range and of the heat generation regulation range would increase. However, the increase in weight of subcutaneous fat would not affect the perspiration regulation range [Fig. 3(a)]. (2) When the internal temperature is set higher in order to accommodate the female's high basal temperature period or in fever, the temperature regulation range of each section would shift correspondingly to a higher temperature [Fig. 3(b)]. (3) The increase of metabolism under physical labour would increase the width of the regulation range and, at the same time shift the range to a lower temperature as a whole. Contrary to this, the decrease of metabolism during sleep will make regulation at a low environment temperature difficult [Fig. 3(c)]. (4) The increase of heat conductivity between the external environment and skin would correspond to the increase of air flow, and this would decrease the regulation range. Contrary to this, a decrease of heat conductivity would increase the size of the regulation range. The effect of a heat conductivity decrease resembles Q' 0"
Fo = 0.7595
4O
the result of wearing clothes. In this case the low side of the regulation range would be extended [Fig. 3(d)]. (5) Concerning morphology, the size of physical features is related to the size of the regulation range. The low side of the regulation range would extend in proportion to the size of the physical features. This is why animals with constant body temperature living in a colder region are larger than ones of the same species living in a warmer region [Fig. 3(e)]. Figure 4 displays the change of regulation range in proportion to the continuous alteration of these heat parameters. These parameters indicate the following from top to bottom: effect o f / / 5 heat conductivity between outer part and inner part (subcutaneous fat) change of 05s internal temperature (in case of fever or female's high basal metabolism temperature period), change of quantity of motion or of basal metabolism, effect o f / / 4 heat conductivity between atmosphere and skin (clothing, air flow), difference of physical features (L = resemblance ratio). The above mentioned prediction is derived from the simple mathematical model of object of regulation and the working hypothesis on the parts of regulation. From this prediction the effect of each heat parameter can be obtained. However, as described previously, this is the deducted from hypothesis, and confirmation from the experimental results is required. CHARACTERISTICS OF THE TEMPERATURE REGULATION SYSTEM
In order to verify the hypothesis set for the mathematical model concerning the proper usage of operational quantity and the static characteristic F% A"
~ c ° n t r ° 1able l range
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Fig. 3. Influence o f parameters: (a) subcutaneous fat; (b) set point o f internal temperature; (c) basal metabolism; (d) heat conductivity between external environment and skin (clothing or air flow); and (el size o f physical feature.
Temperature regulation in humans ,_~ hs' ~dl
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environmntal temperature ee' Fig. 4. Controllable range: (a) subcutaneous fat; (b) set point of internal temperature; (c) basal metabolism; (d) heat conductivity between external environment and skin (clothing or air flow); and (e) size of physical feature.
311
derived from the hypothesis, a climatically controlled room equipped with measuring instruments was prepared for the experiments. The experiments were carried out during the summer, winter, spring and autumn. Males, females and children were used as subjects. The experiments were carried out on many subjects in order to increase the accuracy of the result. The experiments were made uniform as far as possible in order to examine the differences caused by sex, age and season. The experiments were carried out as follows: A subject stayed about 60 min in the "preparatory room" conditioned at approx. 28°C, 50% RH sitting quietly on a chair, naked and with eyes open. The subject then moved to a climatically controlled room conditioned at a stationary condition (16, 19, 22, 25, 28, 31, 34, 37, 40°C, 50 RH, No-Wind), where he/she would pass about 120 min sitting on a chair quietly, naked and with eyes open. Throughout this 180 min, the condition of the subject would be observed and recorded. The following measurements were made: rectal temperature, auditory canal temperature, cutaneous temperature, blood flow in the finger, quantity of weight drop (total evaporation capacity), quantity of metabolism, pulse rate, respiration rate, radiant heat from skin, thermal feeling, and feeling of discomfort. The blood flow in the finger is the index of cutaneous capillary blood flow that is the main operational quantity of the body temperature regulation system. Venous occlusion methods are applied using the air plesthysmograph. Blood flow is taken at 5 min intervals, and continuously 3 times for each measurement. The average of measurements taken during the last 30 min after the move to the climatic room is used as the stationary value. Weight is measured after this move at 20 min intervals. As the weight drop rate would be stationary after 60min, this stationary value is calculated from the slope of the graph. For measuring metabolism, respiration over a 10min period was determined at 20min intervals and metabolic rate was calculated using gas analysis. Radiant heat is measured by the calorimeter attached on the trunk. The 9 grade ordinal scale is used to measure the thermal feeling, and the 5 grade ordinal scale for feelings of discomfort. These two factors were determined by questioning the subject. Cutaneous temperature was measured by a thermoelectric couple. The average cutaneous temperature calculated b y the operation circuit is also recorded. As a result about 60 assessment characteristics of the human body temperature regulation system were obtained. The result of these experiments shows close conformity with the calculated value. Therefore, we conclude that the experiments support the hypothesis.
•
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Fig. 5. Measured examples of static characteristics.
Temperature regulation in humans
313
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10 13 16 19 22 25 28 31 34 37 40 43 envi ronmntal temperature (°C) Fig. 6. Distribution of skin temperature.
Figures 5 and 6 are the measured examples of static characteristics. Figure 7 shows the records of rectal temperature variation, cutaneous temperature variation, finger blood flow rate, metabolic heat production and body weight loss. Those are the results of the 30th experiment (autumn season, male, 0;26 clo). The essential points are as follows: (1) Rectal temperature shows a slight increase in proportion to increases in environmental temperature. (2) Average cutaneous temperature agrees with the calculations from the mathematical model of Fig. 3(d). The rate of increase in body temperature in proportion to environmental temperature decreased in the temperature range where perspiration was observed. (3) Blood flow regulation range is from approx. 22 to 3 I°C. (4) The weight drop shows that perspiration is observed above 31°C. (5) In the case of male subjects, metabolism increases from an environmental temperature of 22°C.
(6) Pulse rate increases in proportion to the environmental temperature. However, not as much as the increase in respiration rate. (7) Thermal sensations of females were less uniform as compared to males. However, the neutral point of both sexes is 28°C. This neutral point is lower than the perspiration range, and higher than the blood flow range. The neutral point is equivalent to 33°C of the average cutaneous temperature. (s) Partial cutaneous temperature indicates the following: at low temperatures, the partial cutaneous temperature increases in the following order: fingertip, instep, back of hand, forearm, femur, waist, breast, forehead. However, extremities do not always have a lower temperature. Experiments indicate that at high environmental temperature, instep and back of hand would be heated up by the atmosphere and cutaneous temperature would be higher than in other parts. It is considered that the effect of cooling by perspiration and of heat generation by metabolism do not reach the periphery efficiently (Fig. 6). Concerning the dynamic characteristics:
314
YOSHIKATSUKAWASHIMA
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Temperature
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(9) Cutaneous temperature would be constant after about 30 min of exposure to the high temperature environment. However, it would not be constant even after about 120 rain of exposure to the low temperature environment. The mode of responses are considerably different between the higher and the lower side. (Fig. 7). (10) The responses observed at the forehead are different from the other area. The time required to become constant is short, and the
cutaneous temperature shows little drift. In some cases of exposure to high environmental temperatures overshoot was observed. These are general results. We cannot clearly describe differences among seasons and between sexes, as sufficient examples were not available. However: ( l l ) Males show little seasonal change of body temperature. However, an increase of metabolism was observed during the winter season.
317
Temperature regulation in humans
The differences between sexes are not as great as we had previously considered. However: (12) Average cutaneous temperature of females is lower than that of males in a low temperature environment. This tendency for lower cutaneous temperature is greater at the peripheral section of the body. (13) The dilation of cutaneous capillaries and perspiration begins at about 3°C higher in females than in males. Therefore, the blood flow regulation range and the perspiration regulation range shift to a higher temperature. Not only air temperature, but also humidity, radiation, and wind speed are considered as the external environment factors. Also, movement, weight of clothing, etc. are counted as human related factors. However the characteristics of the temperature regulation system accommodating those changes have not yet been fully examined and adopted into the system. It is necessary to obtain experimental data first. Also, the influence of the differences between sexes, among ages, among individuals, of heat adaptation, and daily and seasonal variations should be examined and not by just comparing a few factors mutually. These parameters should be examined in comparison with the characteristics of the body's temperature regulation system.
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Fig. 8. Influence of exercise. TB 18/5/6---D
--
i
INFLUENCE OF EXERCISE ON THE CHARACTERISTICS OF THE BODY'S TEMPERATURE REGULATION SYSTEM
Here, the characteristics of the body's temperature regulation system under the condition of rest, 23W physical labour, and 80W physical labour are compared. Experiments are carried out on healthy male subjects in the summer-autumn season of 1977. The experiments were carried out as follows: A subject has first rested for 60 min in the "preparatory room" conditioned at approx. 28°C, 50% RH sitting quietly on a chair naked and with eyes open. The subject is then moved to a climatically controlled room conditioned at a constant condition (7-40°C, 50% RH, No-Wind), where he stays for about 60 rain sitting on a chair quietly, naked and with eyes open. After that, 4 cycles of the experiment are carried out. Each cycle consists of 15 min exercise using a bicycle ergometer and 5 min rest. Then the experiment is continued for 40 min at rest. Throughout this process for a total of 240 min, the condition of the subject was observed and recorded. The following measurements were made: rectal temperature, auditory canal temperature, cutaneous temperature, blood flow in the finger, quantity of weight drop (total evaporation capacity),
rectal tmperature
318
Yosmr~rsu K A w ~ m ~
quantity of metabolism, pulse rate, respiration rate, radiant heat from skin, thermal feeling, comfort, revolution rate of ergometer. The main constant value is taken from the last 5 min of exercise at the 3rd and 4th cycle. Blood flow in the finger and quantity of weight drop are measured just after physical labour. Thermal feeling and comfort are recorded by questioning each subject just before and after physical labour. Figure 8 is a summary of the "constant values". In these figures, "constant values" of the same subject are compared for the conditions of rest, 23W physical labour and 65W physical labour. (1) Each reaction of the temperature regulation system shifts to a lower range according to the quantity of physical labour. As a distinctive feature of physical labour, a rise of internal temperature and a large quantity of perspiration were observed. (2) Not only did the average cutaneous temperature shift to a lower temperature range, but also the cutaneous temperature of the area corresponding to the perspiration region was lower in proportion to the quantity of physical labour. This is a very interesting characteristic of the temperature regulation system. (3) Perspiration began at 31°C during rest, at 19°C during 23W of physical labour, and at 13°C during 80W of physical labour. The threshold of perspiration appearance shifted to the lower temperature in proportion to the quantity of physical labour. (4) The increase of metabolism and the appearance
(5)
(6)
(7)
(8)
(9)
of shivering during low environmental temperature were 25°C max. during rest, and 13°C max. during 23W of physical labour. Pulse rate increased in proportion to the quantity of physical labour. Pulse rate increased on the higher side of the temperature regulation range and also showed a slight increase on the lower side of the temperature regulation range. The pulse rate followed a concave line according to the temperature. Respiration rate increased in proportion to the quantity of physical labour. The respiration rate depends very little on the environmental temperature. The neutral point of thermal feeling and discomfort shifted to a lower temperature. Also, the subjects reported that thermal feeling and discomfort were clearly perceived even during physical labour. However the neutral point of these two characteristics was not the same. The neutral point of thermal feeling had shifted to the lower temperature. Figure 9 shows the relation between the quantity of metabolism and the temperature of the rectum. These two correspond with the exception of the decrease observed at low temperatures. Figure 10 shows the efficiency of temperature regulation in the above mentioned case. Efficiency does not depend much on the environmental temperature. Efficiency is approx. 15%. However, the efficiency during 80W physical labour is greater than during 23W physical labour.
14cal/h []
600
80w 23w
tO
o Rest
0
~. 400 A~
r" W
.u 200 -6 .Q IIJ
o,,
IE I
I
-1.0
-0.5 Increase
O,r i
0
I
0.5 of Rectal Temperature (z~Tr)
I
1.0
Fig. 9. Relation between metabolic heat production and rectal temperature.
deg
Temperature regulation in humans
319
% 20 13
El
&
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Subject "N K" El 80W ~, 23W i
!
10
t
i
I
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20 30 Ambient Temperature
I
40
°C
Fig. 10. Etficiency of exercise.
The body temperature regulation system during physical labour shows a rise of internal temperature. Several hypotheses are given in order to explain this: insufficient regulation, rise or fall of setting temperature, combination of the previous two hypotheses, etc. Recently this internal rise of temperature has been explained as follows: the reflexive capillary contraction caused by the physical labour counteracts the cutaneous capillary dilation. As a consequence thermal radiation would be decreased and result in the rise of internal body temperature. However the data obtained in these experiments shows the unreliability of this hypothesis, as the rise of internal temperature is observed even in a high environmental temperature where sufficient dilation of cutaneous capillaries is probable. During physical labour, the temperature regulation system does not function independently. The muscle motion control system, the circulation system, and the respiration system are working rigorously. The above mentioned phenomena could not be explained if we did not accommodate a higher regulation function that regulates those systems into our hypothesis. In such conditions, the internal temperature could be considered to function as an operational quantity. The rise of the internal temperature was 0.00176°C/(kcal/h). This value can be adopted as an operational transfer coefficient in the mathematical model.
(1) Using mechanical equipment such as the homoiothermal method. (2) Use of a thermal mannequin. (3) Experimental methods using actual human beings with clothing on. In our experiment method 3 was used as the main method in order to obtain the basic data. Also, comparisons of method 3 with methods 1 or 2 was
THE EFFECT OF CLOTHING ON THE CHARACTERISTICS OF THE BODY'S TEMPERATURE REGULATION SYSTEM
The effect of clothing is described in this section. There are three methods to measure the thermal insulation ability of clothing:
Plate 1. The clothing used in the experiments (uniformly covered clothes).
rectal t~l~rature .__~.~--~.~._ clothtng
clothing /
_.- - ~ - ....
•
.-''"
//" /~/,i ~'nude
I= &
,
,//average skin temperature
subject: NK, male
. J
j.,,.,o..,-t,~
24
./ ~.
clothing/
1.0
, .... ./'nude
; ,.//i
0.5
~ o
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7
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clothing/// //' nude
0
7
10 13 16 19 22 25 28 31 34 37 40 43
160 ._~ 140
) ) m ). 1®
~ i
%';
clothingS.
"~, nude
)6. |
;i
7
10 13 16 19 22 25 28 31 34 37 40 43
'~,
..-"
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Illiin
) very hot hot
7
MQI!
slightly ~m
mufti1 slightly ¢eol cool cold very cold c~fort~le nllu~al sitghtl~e ~ l e mmlfottible very unca~ort~le
10 13 16 19 22 Z5 28 31 34 37 40 43 cl othi r ~ - - 7 -..~.. "'-" thenlal sensation . ~ J " .// ~ . j / _ . . . . . . . . -'" nude
.~---~/" calfort
7
nude
"~.
\ - - - - ~ . ~ ....
10 13 16 19 22 25 28 31 34 37 40 43 envirormental temperature('(3) Fig. 11. Effect of clothing.
Temperature regulation in humans also done. Plate 1 shows the clothing used in the experiments. In order to keep the thermal conductivity between skin and environment uniform, all of the body surface except the face is covered uniformly. Also, elastic material was used for clothing in order to ensure close adhesion to the body. The clothing material is polyester with the following specifications: density; 60.5 fibres/inches to weft direction, 87.0 fibres/inches to course direction, weight; 314.9 g/m s, thickness; 0.91 ram (measured under tension of 7 g/cm~), thermal insulation; 17.4% (homoiothermal method, JIS-1079), ventilation property; 21.6cc/cm:. Experiments were mainly carried out with one layer of clothing on. This result is compared with that of a naked condition and with 4 layers of clothing on. Experiments were carried out in autumn on 2 healthy male subjects. The experiments were carried out by the following procedure: A subject first rests for about 60 rain in the "preparatory room"
(a)
321
conditioned at approx. 28°C, 50% RH sitting quietly on a chair naked and with eyes open. The subject was then moved to a climatically-controlled room conditioned at a constant condition (7, 13, 16, 19, 22, 25, 28, 31, 34, 37, 43°C, 50% RH, No-Wind) about 3 h sitting on a chair quietly naked and with eyes open. Throughout this process of 4 h, the condition of the subject was observed and recorded. The measurements made were the same as in the previous experiments. Figure 3((1) shows the calculated data based on the mathematical model of the body's temperature regulation system. The solid line shows the example for the naked condition. The dotted line shows the influence of the /t4 thermal conductivity between environment and skin. This dotted line is equivalent to the condition with clothing on. The temperature regulation range be improved by clothing. Figure 11 shows the comparison of the naked condition with 1 layer of clothing on for the subject
(H-E)/A [Kcal/m2h] 50 ' 0
subject: NK, nude H+ = 5.55
~
,
/
-5 ~
5
10
15
•~
e s - ee ['C]
(M-E)/A [Kcal/mZh]
{b)
~'
50 subject: NK, clothing H, = 4.40 0 ~ x . . . . . . . . . . . . . . . . . 5 10 15 /I
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(H-E)IA [Kcal/m2h] so
//'s~je:i: 0 - s"
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NK, clothing (x4, H, = 3.30
5
io
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e s - ee ['0] Fi8. 12. Thermal conductivity betweenexternal environment and skin: (a) nude; (b) one layer of clothing; and (c) four layers of clothing.
322
Yosmr~TSU KAW~-tZUA
(N-E)/A [Kcal/mZh]
50
•°
_; ' 2 '
- ....__.-.
. . . . . . . . . . .
subject: -50J.
/
,
,
,
15 e s - Oe ['C]
•nude clotJlin9 clothin9 ( X 4 )
H, = 5.55 H4 = 4.40 H4 = 3.30
Fig. 13. Comparison of thermal conductivity.
NK. The solid line is the experimental data at the condition with 1 layer of clothing. The lines represent from top to bottom: rectal temperature, average cutaneous temperature, quantity of weight drop, quantity of heat generated by metabolism, pulse rate, respiration rate, thermal feeling and discomfort. These figures make the "proper usage of operational quantity" easy to understand. By wearing clothing, the average cutaneous temperature and the blood flow in the finger tip shifts to a lower temperature. This influence of wearing clothing corresponds well with the estimation from the mathematical model. Thermal feeling shifted to a lower temperature. However no essential change was observed for discomfort. Figure 12 is a chart plotting the relation between (M-B)/A and 0s - 0¢ using the value acquired by the experiments in order to acquire the thermal conductivity //4. //4 is determined from the slope of the chart. This chart from top to bottom shows the data of subject NK naked, with 1 layer of clothing on and 4 layers of clothing on.//4 for the naked subject was 5.55 kcal/m2h°C. Therefore, the thermal insulation of the air layer would be 0.18°C/(kcal/m2h). //4 during the condition of 1 layer of clothing is 4.40kcal/ m2h°C. Therefore, the thermal insulation of the air layer would be 0.277°C/(kcal/m2h). The disparity of the thermal insulation 0.047°C/(kcal/mEh) would be the thermal insulation of l layer of clothing. If this value is converted to a el• value by 1 el• = 0.18°C/ (kcal/m2h), it would be 0.26 el•. Therefore the thermal insulation rate would be 20.7%. In the case of 4 layers of clothing, //4 is 3.30 kcal/m2h°C, therefore the thermal insulation of the clothing would be 0.123°C/(kcal/m2h). If this is converted into a el• value, it would be 0.68 clo, insulation rate would give 40.5%, and the value by the homoiothermal method is 19.1%. The results of these experiments with clothing showed good correspondence with the thermal insu-
lation test of clothing material. This good correspondence is achieved because these experiments are basic experiments conducted using clothing material of one uniform-kind, and close adhesion to the skin, under the condition of low humidity of 50% RH and no accumulation of perspiration. The actual layering condition of clothing varies at each part of the body, the air layer produced by the looseness of clothing is also complicated, and there are also ventilation effects produced by the motion of the body. Therefore, if we carry out similar evaluations on the actual clothing based on the data obtained in these experiments, the influence of layered clothing, looseness, body motion and clothing configuration on the temperature regulation system based on the actual data would be possible. At least it is necessary to consider the thermal insulation functions of clothing in relation to the temperature regulation system of the body as a whole system. CONCLUDING REMARKS
It is important to understand the characteristics of the temperature regulation system in order to consider several problems of the human thermal environment. In this article, we first described the characteristics of the human temperature regulation system. Then we described the characteristics of the human temperature regulation system using a mathematical model. The observed data of the characteristics of the temperature regulation system were shown. Then the influence of physical labour and clothing on the temperature regulation system was observed. The experimental results showed a good agreement with the theoretical results. In the study of the characteristics of the temperature regulation system, it is necessary to appreciate the behaviour of operational quantity and the alteration of conditional quantity from
Temperature regulation in humans the standpoint of the whole system. Also, problems such as thermal environment evaluation should be positively carded out based, not only on the systematic understanding of a human being-thermal environmental system, but also on the concrete data of the characteristics of the temperature regulation system itself.
REFERENCES
Kawashima Y. (1986) Characteristics of temperature regulation system in the human body. Proceedings of The 10th
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Symposium on Man-Thermal Environment System, Tokyo, 297/308. Kawashima Y. and Gotoh S. (1975) Temperature regulation system in the human body and thermal environment. J. Hum. Erg. 4. Kawashima Y. and Yamamoto H. (1971) Temperature regulation system in the human body and the mathematical model. Biological systems, Nikkan Kogyo. Kawashima Y. and Yamamoto H. (1972) Mathematical model of the temperature regulation system in the human body. International Biophysics Congress, Moscow, 151/152. Yamamoto H. and Kawashima Y (1969) An analog model of the body temperature. Proceedings of 16th International Congress on Occupational Health, 441.