Relationship between Indoor Temperature near the Floor and Winter Blood Pressure in Winter: A Multi-level Analysis

Transcription

1 Relationship between Indoor Temperature near the Floor and Winter Blood Pressure in Winter: A Multi-level Analysis Yusuke Nakajima 1,*, Toshiharu Ikaga 1, Kazuomi Kario, Shintaro Ando, Mitsuo Kuwabara 4 and Shogo Nakamura 1 Keio University, Kanagawa, Japan Jichi Medical University, Tochigi, Japan The University of Kitakyushu, Fukuoka, Japan 4 Omron Healthcare Co., Ltd., Kyoto, Japan OM Solar Co., Ltd., Shizuoka, Japan * Corresponding ysk.nakajima@a8.keio.jp SUMMARY Recently, the effects of indoor air temperature on blood pressure (BP) have attracted attention. However, there have been few studies focusing on temperatures near the floor. In this work, we analyzed the relationship between indoor near-floor temperatures and BP by multi-level analysis. Data were obtained from field surveys of indoor temperature, home BP measurements, and personal attributes conducted in Tokyo and surrounding areas from November 14 to March 1. When the morning room temperature at a height of 1.1 m was C, the corresponding mean near-floor temperature was about 1 C in the low thermal insulation group and about 18 C in the high thermal insulation group. Multi-level analysis showed that morning systolic BP (SBP) increased by 1. mmhg per 1 C decrease in nearfloor temperature, and by.8 mmhg per 1 C decrease in room temperature. These findings suggest that near-floor temperature has a stronger association with morning SBP than room temperature did. PRACTICAL IMPLICATIONS The findings of this study may help improve home environments to control hypertension and prevent cardiovascular disease, and thus reduce the medical costs associated with cardiovascular disease. KEYWORDS Indoor Thermal Environment, Near-floor Temperature, Home Blood Pressure, Field Survey, Multi-level Analysis 1 INTRODUCTION In Japan, cardiovascular disease is a major cause of death, and deaths from cardiovascular disease occur in homes most frequently during the winter. The main risk factor for cardiovascular disease is hypertension. It is estimated that 4 million people, one-third of the Japanese population, had hypertension in 1. Therefore, reducing the average blood pressure (BP) of the whole country via a population approach is an urgent priority. In recent years, the effects of indoor air temperature on BP have attracted attention. It has been shown that moving to a well-insulated house decreases the prevalence of hypertension (Ikaga et al. 11). In addition, indoor temperature shows a stronger association than outdoor temperature with BP in colder months (Saeki et al. 14). Furthermore, it has been suggested that BP increases in the elderly in unequal thermal environments in which the indoor air

2 temperature near the floor is lower than that in the upper part of the room. These results were obtained by exposing healthy subjects to four temperature differences between the upper ( C) and lower (16, 19,, or C) parts of their body (Hashiguchi et al. 11). However, there have been few studies focusing on temperatures near the floor. Therefore, in this work, we analyze the relationship between indoor near-floor temperatures and BP by multi-level analysis. METHODS Overview of field surveys Data were obtained from field surveys of indoor temperature, home BP measurements, and personal attributes conducted in Tokyo and surrounding areas from November 14 to March 1. Subjects were recruited from among adult residents (men and women aged 4 years) through a local construction firm. For analysis, 1 participants (8 households) met the validation criteria of measuring home BP over days and answering the questionnaires. Table 1. Outline of field surveys. Area Tokyo and surrounding areas (Tochigi, Ibaraki, Saitama, Chiba, Kanagawa, Yamanashi, Nagano prefectures) Survey respondents (households) 169 (1) Valid participants (households) 1 (8) Period Any -week period within November 14 March 1 Indoor temperatures and home BP Subjects measured indoor temperatures and home BP for weeks. Indoor temperatures were measured at.1 m (near-floor temperature) and 1.1 m (room temperature) above the floor in the living room. These temperatures were measured at 1-min intervals with a temperature and humidity data logger (TR-Ui, T&D Corporation). Home BP monitoring is an easy and standardized tool to measure BP at home. It was measured by subjects twice a day, after getting up in the morning and before bedtime at night. Subjects measured their BP with an upper-arm BP monitor (HEM-1G or HEM-G-HP, Omron Healthcare Corporation), in accordance with the guidelines of the Japanese Society of Hypertension (The Japanese Society of Hypertension, 14). Subjects were instructed to take two consecutive measurements on each occasion, and the average of the two values was used for the analysis. Questionnaires Questionnaires about personal attributes and housing performance were also conducted. The questionnaire on personal attributes covered individual characteristics such as age and sex; lifestyle indicators such as smoking, alcohol consumption, eating habits, and antihypertensive drug use; and health conditions such as diseases that can cause hypertension. Body mass index (BMI) was measured by using a body composition monitor (HBF-F, Omron Healthcare Corporation). The questionnaire on housing covered aspects of the indoor thermal environment such as thermal insulation performance and the presence or absence of a solar floor heating system. This system heats the under-floor with air heated by a solar heatcollecting device on the roof. Thermal insulation performance was classified as pre-198 standards, 198 standards, 199 standards, and 1999 standards (Standards of Judgment for Residential Construction Clients Based on the Law of Ministry of Land, Infrastructure and Transport in Japan) based on building age, the presence or absence of insulation, and the type of window glazing and window frames (Takayanagi et al, 11). Table shows the questionnaire content.

3 Table. Questionnaire content. Personal attributes Age ( ) years old Sex 1) Male ) Female BMI ( ) kg/m Smoking 1) Never ) Quit smoking ) Smoking Alcohol consumption ) 1 times ) 4 times 1) None weekly weekly Vegetable/fruit consumption Taste preferences Exercise habits 4) 6 times weekly 1) Weak ) Normal ) Strong 4) Bland diet 1) Sufficient ) Slightly sufficient Antihypertensive 1) No ) Yes drug Diseases ) Slightly insufficient 4) Insufficient ) Receiving 1) Healthy ) Cured treatment [Cardiac disease/cerebrovascular disease/diabetes/hyperlipidemia/ kidney disease/hypertension] ) Every day Housing performance Structure 1) Detached house ) Multi-unit housing Building age ( ) years old Building frame 1) Wooden ) Reinforced concrete ) Steel 4) Other ( ) Insulation 1) Absent ) Present Window glazing 1) Single ) Double ) Triple Window frame 1) Aluminum ) Aluminum (double) ) Insulation 4) Old wooden ) New wooden 6) Plastic Solar floor heating system 1) Absent ) Present Insulation retrofit 1) None ) Carried out RESULTS Questionnaire summary Of the 1 participants (mean age ± SD: 1.9 ± 1. years old), (4.1%) were men. The proportion of men who quit smoking or who habitually smoke and drink alcohol was higher than that of women. About two-thirds of the participants reported normal taste preferences. Eleven participants (8.%) were taking an antihypertensive drug, and 6 participants (.1%) had cardiac disease, cerebrovascular disease, diabetes, hyperlipidemia, kidney disease, or hypertension. Table shows the characteristics of the 1 participants.

4 Table. Characteristics of 1 participants. SD is shown in brackets. Personal attributes Total (n = 1) Male (n = ) Female (n = 61) Age, mean (SD) 1.9 (1.) 1.9 (1.). (1.) BMI, mean (SD). (.).9 (.1). (.) Smoking, n (%) None Quit smoking/smoking Alcohol consumption, n (%) None 1 times weekly 4 times weekly 6 times weekly Everyday Vegetable/Fruit consumption, n (%) 1 times weekly 4 times weekly 6 times weekly Everyday Taste preferences, n (%) Weak Normal Strong Exercise habits, n (%) Sufficient Slightly sufficient Slightly insufficient Insufficient Antihypertensive drug, n (%) None Taking Diseases, n (%) Healthy Receiving treatment/cured (6.4) (.6) (41.4) (1.8) (1.) (1.) (.) (.) (.) (.) (69.9) (1.8) (68.4) (9.8) (.) (16.) (.6) (4.6) (91.) (8.) (.9) (.1) (.) (6.) (18.1) (16.) (9.) (1.) (4.) (4.) (11.1) (6.4) (8.) (1.) (.6) (1.9) (6.9) (.8) (8.9) (.) (8.) (1.) (69.4) (.6) (91.8) (8.) (68.9) (8.) (11.) (8.) (.) (.) (.) (1.1) (8.6) (.8) (6.) (4.9) (.) (11.) (6.1) (49.) (96.) (.) (.) (.) Housing performance was evaluated by the presence or absence of a solar floor heating system. For buildings without a solar floor heating system, the building age was widely distributed from <1 years to > years, whereas most with a system were built within 1 years (9.%). For thermal insulation performance, the proportion of 198 standards was the highest among houses with no solar floor heating system (61.%), whereas the proportion of 1999 standards was the highest among houses with a solar floor heating system (.%). To compare near-floor temperatures, houses were classified by the thermal insulation performance and the presence or absence of a solar floor heating system. Case 1 is low thermal insulation performance (before 198 or 198 standards) with no solar floor heating system. Case is high thermal insulation performance (199 or 1999 standards) and no solar floor heating system. Case is high thermal insulation performance (199 or 1999 standards) and with a solar floor heating system. Table 4 shows the characteristics of the 8 houses.

5 Near-floor temperature in the living room[ C] Table 4. Characteristics of the 8 houses. Housing performance Building age, n (%) <1 years 1 19 years 9 years 9 years 4 49 years > years No answer Insulation retrofit, n (%) None Carried out Thermal insulation performance, n (%) Before 198 standards 198 standards 199 standards 1999 standards Solar floor heating system Absent (n = 6) Present (n = ) (8.) (1.) (16.1) (16.1) (4.8) (1.6) (1.6) (88.) (11.) (9.) (8.) (.) (.) (.) (.) (.) (1.) (.) Case 1 4 (6.) (.) 8 (61.) 6 (4.) Case 6 (9.) Case 4 (16.) 9 (14.) 1 (.) Unclassified (8.1) (8.) Relationship between near-floor temperature and room temperature Figure 1 shows the results of temperatures when subjects measured their BP after getting up in the morning from Cases 1 to, with each point showing the temperature data for one day for one subject. Houses that had had a partial insulation retrofit were not included in the results from Case 1 to for assessing the overall thermal insulation performance. The vertical axis is the near-floor temperature in the living room, and the horizontal axis is the room temperature in the living room at the same time. When the morning room temperature was C, the corresponding mean near-floor temperature was about 1 C in Case 1, and about 18 C in Cases and. The root mean square error (RMSE, in Figure 1) of the near-floor temperature and room temperature was.16 C in Case 1, 1.1 C in Case, and.9 C in Case. 1 1 Case (n=) y = 14ln(x) - R² =.4, p<.1 RMSE =.9 Case (n=) y = 1ln(x) - R² =., p<.1 RMSE = 1.1 Case 1 (n=19) y = 8.8ln(x) - 11 R² =., p<.1 RMSE = Room temperature in the living room[ C] Figure 1. Relationship between near-floor temperature and room temperature.

6 Morning SBP [mmhg] Morning SBP [mmhg] Morning SBP [mmhg] Figure shows mean temperatures from Cases 1 to when subjects measured their BP after getting up in the morning. Both near-floor and room temperature in Case 1 was significantly lower than those in Case and. In addition, there were significant differences between nearfloor temperatures and room temperatures in Cases 1 and. *** *** *** * Temperature [ C] 1 1 Max. Mean+S.D. Mean Mean-S.D. Min. Near-floor Room temperature temperature Case 1 (n= 6 houses, subjects) ** *** Near-floor Room temperature temperature Case (n= 1 houses, subjects) * :p<.1 ** :p<. *** :p<.1 Near-floor Room temperature temperature Case (n= 16 houses, 4 subjects) Figure. Relationship between mean near-floor temperature and mean room temperature. Relationship between home BP and personal attributes The relationship between home BP and factors other than indoor thermal environment was analyzed statistically using t-test, with significance set at.1. BP after getting out of bed for people with cardiovascular diseases is a parameter frequently used in analytical procedures. In this work, we used systolic BP (SBP) as it is an excellent prognostic factor (Inoue et al, 6). Figure shows the results of t-test for the relationship between morning SBP and personal attributes. Mean SBP was significantly higher in men than in women, mean SBP of obese subjects was significantly higher than those of underweight/normal range subjects, and the mean SBP of smokers was significantly higher than that of non-smokers. There were also significant differences regarding SBP and age (under years vs years and older, p<.1), alcohol consumption (every day vs 6 times weekly or less, p<.1), vegetable/fruit consumption (every day vs 6 times weekly or less, p<.1), and antihypertensive drug use (taking vs none, p<.1). These results were in agreement with the results of previous studies Female (n = 61) p<.1 Male (n = ) p<.1 Underweight Obese /Normal range [. BMI] [BMI<.] (n = 4) (n = 99) Non-smoking (n = 8) p<.1 Quit smoking /Smoking (n = ) Max. Mean+S.D Ṁean Mean-S.D. Min. Figure. Relationship between home SBP and personal attributes. (Left: by sex. Center: by BMI. Right: by smoking.)

7 Effect of near-floor temperature on home BP: multi-level analysis Multi-level analysis was performed to clarify the effect of indoor temperature on morning systolic BP (SBP), adjusted for personal attributes (n = 1 subjects measurement days = 18) (Table ). Model-1 was used for near-floor temperature and Model- was used for room temperature. Because there were correlations between smoking, alcohol consumption, and sex (correlation coefficient =.,.), smoking and alcohol consumption were not introduced into the model to suppress multicollinearity. After adjusting for sex, age, BMI, vegetable/fruit consumption, and antihypertensive drug use, morning SBP increased by 1. mmhg per 1 C decrease in the near-floor temperature when subjects measured their BP after getting up in the morning (Day level) (Model-1), and by.8 mmhg per 1 C decrease in the room temperature when subjects measured their BP after getting up in the morning (Day level) (Model-). These findings suggest that near-floor temperature has a stronger association with morning SBP than room temperature did. Table. Multi-level analysis of the relationship between morning SBP and temperature. Model-1 Model- Level Explanatory variable Choice Adjusted β p value Adjusted β p value 1 Near-floor temperature ( ) C -1. <.1 Day Room temperature ( ) C -.8 <.1 level Temperature * Age ( ) C Sex ) Female 1) Male 9.4 <.1 9. <.1 Age ( ) years old. <.1. <.1 Resident level BMI ( ) kg/m 1. <.1 1. <.1 Vegetable/Fruit 4) 6 times 1) None ~ ) Everyday consumption weekly Antihypertensive ) No 1) Taking drugs Near-floor temperature ( ) C (average) Room temperature ( ) C (average) 4 DISCUSSION Our analyses showed that near-floor temperature in Case 1 was lower than that in Cases and, and significant a vertical temperature difference occurred between.1 m and 1.1 m above the floor in the living room in Cases 1 and. These results suggest that high thermal insulation and solar floor heating appear to be effective for maintaining a sufficient near-floor temperature and preventing a vertical temperature difference. Controlling for personal factors via multi-level analysis, SBP increased by 1. mmhg per 1 C decrease in indoor temperatures near the floor. In this study, the mean temperature near the floor in Case was 1. C; in Case 1, this was lower, at 1.6 C, indicating that improved temperature near the floor has the potential to reduce morning SBP by about 4.9 mmhg. The Japanese Ministry of Health, Labour and Welfare (1) has estimated that if the average SBP of the whole country were to decrease by 4 mmhg, deaths from cardiovascular disease could be reduced by 1, people. Therefore, based on our finding, improving the indoor thermal environment is expected to help control hypertension and prevent cardiovascular disease. However, this study had a sample selection bias; the sample of the elderly who had high SBP was low. The sample taking antihypertensive drugs was also low, hence, this shortage of such individuals became a factor of not-significant explanatory variables in the multi-level models.

8 To confirm our results, it is necessary to increase the number of participants from a variety of age groups and with various personal characteristics. Because this study is a cross-sectional study, it is possible to only estimate the effect of improved home environment on home BP. To clearly confirm any actual effects implied by the data, it is vital to also perform prospective studies with the subjects, such as observations of subject BP after moving from a house with low thermal insulation to one with high thermal insulation. CONCLUSIONS This study analyzed the relationship between near-floor temperature and room temperature, based on field surveys from November 14 to February 1. The following findings were obtained. 1) When morning room temperature was C, the corresponding mean near-floor temperature was about 1 C in the low thermal insulation group (Case 1) and about 18 C in the high thermal insulation group (Cases and ). ) After adjusting for personal factors, SBP increased by 1. mmhg per 1 C decrease in nearfloor temperature. To prevent BP elevation, it is necessary to maintain sufficient indoor temperatures near the floor. These findings may help improve home environments by controlling hypertension and preventing cardiovascular disease. ACKNOWLEDGEMENT The authors gratefully acknowledge the cooperation of Mr. Masakazu Tsutsumi of Omron Healthcare Corporation, Mr. Keisuke Yamada of Omron Corporation, OM Solar Corporation, and the study participants. The authors are also grateful to Mr. Wataru Umishio, Mr. Naoto Takayama, Ms. Chika Ohashi, and Ms. Eri Honda for their assistance with the data analysis. This study was supported in part by a Grant-in-Aid for Scientific Research (A) (No. 6498; Principal Investigator: Prof. Toshiharu Ikaga). 6 REFERENCES Hashiguchi N, Kumamoto T et al. 11. Effects of vertical air temperature gradients on physiological and psychological responses in the elderly. Journal of the Human- Environment System, Vol.14, No.1, pp Ikaga T, Eguchi R et al. 11. Evaluation of investment in residential thermal insulation considering non-energy benefits delivered by health. Journal of Environmental Engineering, Architectural Institute of Japan, Vol.6, No.666, pp. -4. Inoue R, Ohkubo T et al. 6. Predicting stroke using 4 ambulatory blood pressure monitoring-derived blood pressure indices: the Ohasama Study. Hypertension, Vol.48, pp MHLW. 1. A Basic Direction for Comprehensive Implementation of National Health Promotion, 18 pages. JSH. 14. The Japanese Society of Hypertension Guidelines for the Management of Hypertension 14, 4 pages. Saeki K, Obayashi K et al. 14. Stronger association of indoor temperature than outdoor temperature with blood pressure in colder months. Journal of Hypertension, Vol., pp Takayanagi E, Ikaga T et al. 11. Validation of effectiveness of residential environment assessment tool for health promotion. Journal of Environmental Engineering, Architectural Institute of Japan, Vol.6, No.6, pp