COMPARISON OF HOME BLOOD PRESSURE BEFORE-AND-AFTER MOVING TO HIGH THERMAL INSULATION PERFORMANCE HOUSES:A field survey on the effect of indoor thermal environment on blood pressure in winter (Part III)
A cardiac disease is the second most common cause of death and a cerebrovascular disease is the fourth, a major cause of which is hypertension. Hypertension is an asymptomatic disease, which is called “silent killer”, affecting one-third of the population. Therefore, it is essential not only “high risk approaches” which are measures for hypertensive individuals such as treatment with an antihypertensive drug but also “population approaches” which are measures to reduce blood pressure (BP) of entire nation toward prevention of Hypertension.
Against this background, the effects of the indoor thermal environment on BP have attracted attention because it affects asymptomatic individuals. Now some studies on the relationship between BP and indoor thermal environment are accumulated. But most of the studies are cross-sectional studies, so there is a real need for follow-up studies and actual proof of causal correlation between BP and indoor thermal environment. This study aimed to demonstrate antihypertensive effects by moving to high thermal insulation performance houses.
Follow-up studies on home BP and indoor temperature was conducted before and after moving in winter 2014 and 2015. Home BP was measured by participants twice daily: before getting into bed in the evening and after getting out of bed in the morning for two weeks. Indoor temperature at 1.1 m above the floor was measured in the living room, bedroom, bathroom, and dressing room at 10-min intervals. During the survey periods, participants recorded the wake time and bedtime each day in a diary. Questionnaire surveys on personal factors and housing were also carried out. Besides, questionnaire surveys on housing were distributed to building contractor to get a reliable answer.
Thermal insulation performance of houses before moving was either “pre-1980 standards” or “1980 standards.” While thermal insulation performance of houses after moving satisfied “1999 standards”: heat loss coefficient (Q value) of houses after moving was 1.9 W/m2K, corresponding gap area (C value) was 0.4 cm2/m2 on average. Average daily outdoor temperature of before moving survey periods (5.7 °C) was nearly equal to average daily outdoor temperature of after moving survey periods (5.1 °C). The living room temperature gap between before and after moving was the largest at a wake-up time. At 6 o'clock, living room temperature after moving was higher by 2.0 °C than living room temperature before moving. In addition, the lowest temperature had increased and the highest temperature had decreased in each room. So, stabilizing effects of indoor temperature by moving were recognized.
Systolic BP (SBP) decreased by 1.5 mmHg per 1 °C increase in indoor air temperature and standard deviation (SD) of SBP improved by 2.3 mmHg per 1 °C improvement in SD of indoor air temperature in a group over 125 mmHg. Therefore, stabilization of indoor temperature has stabilizing effects on BP. However, there were several participants whose houses got colder and more unstable after moving. To examine factors related to indoor temperature changes, a comparison of indoor temperature between before and after moving by patterns of moving was carried out. As a result, moving from a single-family house to a single-family house and from a wooden house to a wooden house became warmer and improved SD of indoor temperature. On the other hand, moving from a condominium to a single-family house and from a reinforced concrete house to a wooden house became colder. Moreover, not heating a room after moving caused a sharp decrease in indoor temperature. So, it is not satisfied only by moving to high thermal insulation performance houses but paying attention to house form and structure and adequately heating a room to improve BP value and stability of BP.
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