Relationship between cerebrovascular disease and indoor thermal environment in two selected towns in Miyagi Prefecture, Japan

J. therm. Biol. Vol. 18, No. 5/6, pp. 481-486, 1993 Printed in Great Britain.All rights reserved

Copyright ©0306-4565/ Pergamon$6"00Press 931993 + 0.00Ltd

RELATIONSHIP BETWEEN CEREBROVASCULAR DISEASE A N D INDOOR THERMAL ENVIRONMENT IN TWO SELECTED TOWNS IN MIYAGI PREFECTURE, JAPAN HIROSrH YOSHINO,1MASAKOMOMIYAMA,2 TOKIKOSATO3 and KOICHISASAKI1 IDepartment of Architecture, Faculty of Engineering, Tohoku University, Sendal 980, Japan, 2Institute of Medical Geography and Statistics, Tokyo, Japan, and 3Japan International Cooperation Agency, Tokyo, Japan Almtraet--1. This paper describes the results of an investigation of the relationship between mortality from cerebrovaseular disease (hereafter called stroke) and the indoor thermal environment in two selected towns with different socioeconomic compositions: Shiwahime, an agricultural town with relatively high stroke mortality, and Karakuwa, a fishing town with relatively low stroke mortality, using a case-control research design. 2. The measurement of the indoor thermal environments were conducted and the surveyed with a questionnaire during the winter of 1986. 3. The findings are summarized as detailed below. 4. Room temperatures in the control households were generally higher than those in the case households by up to 1.3°C. 5. The thermal conditions of the housing in the case households were a little inferior to those in the control households. 6. Despite much lower room temperatures than the so-called comfort temperature, members of both the case and the control households did not express feelings of being cold in the rooms. 7. It is concluded, including the survey results from other literature, that improvements in the indoor thermal environment should receive more attention with respect of the reduction in stroke mortality, particularly in areas of cold climates. Key Word Index: Stroke; indoor thermal environment; case-control study

INTRODUCTION In the past in Japan, the relationship between mortality from cerebrovascular disease (stroke) and residential space beating have been investigated. For example Sasaki (1973) on the basis of statistical research from 1957 to 1967 concluded that the mortality from strokes was lower in houses which used space heaters for a long time. Yoshino et al. (1985) investigated the relationship between mortality from strokes and indoor thermal environment during the winter in three local towns, Yamagata prefecture in 1982 and 1983. They reported that the room temperature in the bedroom, the bathroom and the kitchen was much lower than the heated living room and pointed out that the great temperature difference between the heated living room and the other unheated spaces might influence the mortality from strokes. However the link between indoor temperature and the high stroke mortality was not proved. This paper reports from a case-control study of relationship between the stroke mortality and the

indoor thermal environment from 161 houses in two towns, Miyagi prefecture and shows the results of indoor temperature measurements of 16 houses.

MATERIALS AND METHOI~ Investigated town

Two towns investigated as shown in Fig. I. The population in Town A and Town B on October 1, 1985 was 7,992 and 10,096, respectively. The mortality ratio to 100 thousand people in 1985 was l 113.6 and 713.2 in Town A and Town B, respectively. In the winter, Town A is colder than Town B. The industry of Town A is agriculture. That of Town B is mainly fishery. The SMR (Standard Mortality Ratio) from stroke in 1985 in Town A was 112.0 for male and 143.7 for female. That in Town B was 81.7 for male and 60.8 for female. The low SMR in Town B maybe related to mild climate in the winter. Investigated houses

481

The houses in which the occupants between 51 and 79 years old had died from stroke in last 5 years, were

HIROSHIYOSHINOet al.

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so on. Figure 2(a) shows the floor plan of a measured house and the locations of temperature measurement points.

Questionnaire and simple measurement of temperature

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A questionnaire covering housing construction, heating equipment, heating hours, clothing and so on and three liquid crystal thermometers were delivered to houses investigated in this study. The completed questionnaire were collected after a week. Liquid crystal thermometers with insulated backing of 7 mm in depth were attached to walls 1 m above the floor in the living room, the bedroom and the lavatory. Room temperatures were read and recorded three times a day, that is, in the morning soon after occupants arose, during the afternoon and during the time after supper. Period of measurement was 28 November to 5 December 1986 in Town A and 9-15 December 1986 in Town B.

Fig. I. Location of investigatedtowns.

RESULTS AND DISCUSSION selected for a case group. For a control group, the houses in which the sex and the age of an occupant was the same as that of the dead occupant in the case group were randomly selected. The person who answered the questionnaire in the case houses was a spouse or a child of the dead occupant. The number of houses to which questionnaires were delivered was 43-50. As a result, the number of houses analyzed was 37 for a control group and 43 for a case group in Town A and 34 for a case group and 47 for a control group in Town B.

Measurements of temperature Indoor temperatures were automatically measured by means of resistance type thermometers for about 1 week. Measured points were 5 cm and 1.1 m above the floor high in a living room, I m above the floor in a bedroom, I m above the floor in a lavatory and Table 1. Numbers of investigated houses and indoor temperature readings Control (43)

Case (37)

Town A

LR

BR Lavatory

LR

BR Lavatory

Morning Daytime Night

37 36 38

35 35 37

35 33 35

35 32 35

36 35 37

Control (47)

35 32 35

Case (34)

Town B

LR

BR Lavatory

LR

BR Lavatory

Morning

46 44 46

46 44 46

32 28 32

32 28 32

Daytime Night

46 44 46

32 28 32

Measurement of indoor temperature In the house shown in Fig. 2(a), only the living room was heated by an unvented kerosene heater. The Japanese style heating device 'Electric kotatsu' was also used in a living room. 'Electric kotatsu' is a heating device which has an electric heater mounted under a low table covered with a quilt. People sitting on the floor heat their legs under the low table. Figure 2(b) shows the measurement results for indoor temperatures for this house. During the measurement period, the temperatures were read every 30 min and these half hour readings were averaged. The outdoor temperature is around 6°C during the day and around 2°C during the night. The temperature of the living rooms in the morning and in the evening rose due to space heating. The temperature between 6 p.m. and 10 p.m. is 15 to 18°C. The temperature of the kitchen, the bedroom and the lavatory is less than 10°C all day long. Figure 3 shows the temperature profiles of the living room, the bedroom and the lavatory of all eight houses in Town A. The profile of the living room temperature, which rises and falls depending on space heater usage, are different between houses. The maximum temperature during the night is 8-18°C. The temperature of the bedroom and the lavatory is very low and stable all day long.

Results of questionnaire Table 2 shows some results of case-control comparison obtained from the questionnaire in two towns. There is a little difference between the case group and the control group. Thermal insulation. Thermal insulation was used in

Cerebrovascular disease and indoor thermal environment

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Fig. 2. Floor plan of an investigated house and indoor temperature. (a) Floor plan; (b) indoor temperatures averaged for 8 days.

40 and 30% houses in Town A and Town B, respectively. The saturation level of thermal insulation of a control group is slightly higher than that of a case group in both towns. The saturation level of thermal insulation used for walls, ceilings and floors becomes lower in this order. In Town A, there is no house which has floor insulation. Window component. A single pane window with an aluminum sash is used in 35-50% houses in both towns. In Town A, the saturation level of this sash for the case houses is 10% higher than that for the control houses. The single pane window with an aluminum or wooden sash is used in 60-70% houses. Location and space heating of lavatory. A lavatory is located outdoor in 40% houses for the case group and 35% houses for the control group in Town A. The ratio of outdoor lavatory is around 25% in Town B. A space heater is installed in 10% lavatories. Space heating in the living room. The saturation

levels of unvented kerosene heater, an electric kotatsu and a briquette kotatsu is more than 40%. A briquette kotatsu uses a briquette for heat source inside a kotatsu. In Town A, a briquette kotatsu is more popular than an electric kotatsu. Space heaters are used only 5-6 h a day. Clothing during the night after supper. In Town A, clo units of males for control houses is higher than that for case houses. For females, the peak appears in the rank of more than 1.25 clo units in case and control houses of both towns.

Room temperature comparison The number of houses, which were analyzed for room temperature, are shown in Table 1. Daily mean outdoor temperature was 1.9-5.5°C in Town A and 4.9-8.5°C in Town B. The temperature readings were averaged during a week in each room of each house. Figure 4 shows the case-controls comparison of mean

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room temperatures in two towns. All room temperature for control houses are higher than those of case houses, except for the bedroom temperature during the night in Town A. It means that the room temperatures of houses in which an occupant died from stroke are lower. But the difference is only less than 1.3°C. The case in which the difference of two mean values is significant is only the lavatory (at 5% level) in the morning in Town A and the lavatory (at 1% level) in the daytime in Town B. Room temperature and thermal sensation

Figure 5 shows the relationship between room temperatures during the night after supper and occupant's response to thermal sensation. The mean living room temperature of the houses in which occupants felt 'warm' is 13.9 and 14.3°C for Town A and Town B, respectively. The room temperature to which

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CONCLUSIONS

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(1) Room temperatures in the control houses were generally higher than those in the case houses by up to 1.3°C (2) The thermal conditions of the case houses were inferior to those of the control houses. (3) Despite much lower room temperatures than the so-called comfort temperature, occupants of both the case and control houses did not express feelings of being cold in the rooms. (4) Improvements in the indoor thermal environment should receive more attention in an endeavour to reduce stroke mortality, particularly in the area of cold climate.

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REFERENC~

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Fig. 5. Thermal sensation and indoor temperature.

Hasegawa F., Yoshino H., Arai H., Iwasaki K., Akabayashi S. and Kikuta M. (1985) Investigation of the relationship between the indoor thermal environment of houses in the winter and cerebral vascular accident (CVA)..lap. J. Public Health 32. Sasaki N. Lifestyle and Stroke Mortality, especially Space Heating, Drinking, and Smoking. Report for 22nd (1973) Tohoku Branch Meeting of Public Health, 13, 13.

Cercbrovascular disease and indoor thermal environment

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Table 2. Case control comparison of house component, heating equipment and clo units

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THERNAL INSULATION

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