Abstract:

Objective Studies on winter bedding systems have been carried out to improve the thermal comfort and sleep quality of the elderly. Previous studies mainly focused on the overall thermal needs of the human body during sleep, such as temperature-control mattresses and electric blankets, while ignoring the specificity of the thermo-physiology in the elderly and the variability of localized thermal needs of the body. In order to make the temperature control more targeted, localized heating was proposed instead of whole-body heating to meet the local thermal needs of the human body, which would help save energy at the same time.

Method An artificial climate chamber, along with a lying thermal manikin, was adopted to simulate the real sleep scene of the elderly in winter. Three groups of sleeping tests were conducted. The first scenario involved no heating elements in the bedding system, and the body parts which need additional heating were figured out by comparing the measured skin temperatures with neutral skin temperatures. In the other two groups of tests, electrical heating pads and hot water bags were attached to the quilt and mattress separately to heat the body parts which need heating. By comparing the skin temperatures under the two heating methods, the design of a localized heating bedding system was proposed.

Results It was found that the skin temperature at chest, back, hands and feet were significantly (p<0.05) lower than the corresponding neutral skin temperature. This indicates that these four body parts would need additional heating to satisfy the thermal comfort needs of the elderly. After applying the electric heating pads, the skin temperature of back increased rapidly at a rate of 0.224 ℃/min. The lowest and highest comfortable skin temperature of 32.8 ℃ and 35 ℃ were reached in 10 min and 22 min, respectively. The skin temperature of the back continued rising for another 2 min before starting to decrease after turning off the heater, and after 20 min it stays within the comfortable temperature range of around 33.7 ℃ for sleeping. After applying the heating pad for 15min, the skin temperature of the foot reached the lowest comfortable temperature of 32.2 ℃, and the maximum comfortable temperature of 35.8 ℃ was reached after 43 min. The skin temperature of the feet continued rising for another 2 min before it started to decrease after turning off the heater, and after 16 min it stably stayed within the comfortable temperature range of around 35.3 ℃ for sleeping. The data suggests that electrical heating of the chest and hands improves their localized thermal comfort. However, considering the really sleep scenario, heating at chest is somewhat unsafe due to its proximity to the heart. The human hand moves a lot during sleep and is difficult to be fixed. The lowest (32.8 ℃) and highest (35 ℃) comfortable skin temperature of the feet were reached in 10 min and 22 min, respectively under the hot water bag heating. After 10 min, the temperature of the foot rose to 38.02 ℃ and then began to gradually decrease to a cooler temperature. In the heated futon design scheme, when the back and feet were heated with electric heating pads, there was no significant difference between the human local skin temperature and the comfortable skin temperature range (P>0.05).

Conclusion Local body parts of chest, back, hands and feet of the elderly need additional heating during sleep in winter. Taking both the safety and practicality into consideration, auxiliary heating system is suggested to be applied to back and feet. The heating method of hot water bag leads to a fast increase of skin temperature, while the water temperature would drop and cause cold contract feeling for the elderly. Thus, the heating method of electric heating pad, which brings a slow increase of skin temperature but can maintain the skin temperature in the comfortable rang of 34.5-35 ℃, overwhelms the heating method of hot water bag. Bedding system with localized electric heating pads are proposed and verified to effectively improve overall and local sleep thermal comfort for the elderly. These research findings can provide evidence for the design of high-performance localized heated futons to achieve thermal comfort during sleeping.

Key words: the elderly, sleep thermal comfort, local thermal need, heated bedding, differential thermal demand, bedding system