Proceedings of Engineering and Technology Innovation, vol. 7, 2017, pp. 08 - 13 The Influence of Density of the Materials and Body Mass Index on the Elderly’s Sleep Efficiency Wichan Torobrum * , Nandh Thavarungkul, Preecha Termsuksawad, Nakorn Srisukhumbowornchai, Purit Thanakijkasem Division of Materials Technology, School of Energy, Environment and Materials , King Mongkut’s University of Technology Thonburi, Bangkok, Thailand . Received 11 July 2017; received in revised form 25 August 2017; accept ed 30 August 2017 Abstract Insomnia is a co mmon proble m a mong the elders and it d irectly a ffect s their health. The mattress is one factors influencing sleeping e fficiency. The developed pressure at the sleeping surface during sleeping will to cause body discomfort, leading to sleep problem. The developed pressure depends on the density of bedding materia ls and body mass. The present research aims to study the effects of the mattress density and body mass on the elderly sleep efficiency. The sleep data was collected from 6 v olunteers: 3 male and 3 fe ma le at the age group of 60 – 79 years. The e xpe riment was done on mattresses with densities of 24.6 and 60 kg/ m 3 and 4-inch thic kness. The volunteers randomly slept on each mattress for three nights. Sleep data was recorded by sleep trac ker (Jawbone up24), calibrated with Polysomnography. The study revealed that sleep efficiency on the 60 kg/ m 3 density mattress was more than 90 percent while those on the 24.6 kg/m 3 density mattress were in the range of 78 - 84 percent. Moreover, sleep effic iency of the volunteers with the body mass index of 22.22 - 23.74 kg/cm 2 was significantly diffe rent fro m those of volunteers with the body mass index of 24.61 -24.92 kg/c m 2 when they slept on the 24.6 kg/ m 3 density mattress. Additionally, the pressure test revealed that a pressure at shoulder may affect sleep efficiency. Keywor ds : pressure, sleep efficiency, elderly, body mass index 1. Introduction Undeniably, ind ividuals’ hygiene and health is related to a balance between rela xation and daytime activ ities. Most of us spend one-third of our life in sleeping [1-2]. One factor that effects on our health is sleep quality, which can be indicated by sleep efficiency: a ratio of total sleep time to total time in bed. There are many factors affecting sleep effic iency such as physical, mental, e mot ional, and environ mental factors [3]. It is found that 7 percent of American people, especially e lders, have sleep problems, resulted by their mattresses [4]. The reason why elders have the sleep problem is deterioration and ma lfunction of cells and organs , like backbone [5]. The inappropriate sleep postures, pressure on sleeping surface and body mass of obese elder apparently cause shorter sleep time, lead ing to low sleep effic iency. Conversely, those with norma l body mass index would have higher sleep effic iency and slow wave sleep (SWS) than those of the obese ones [6 -7]. In addit ion, pressure on sleeping surface, depending on mattress density, is believed to be re lated to lo w bac k d iscomfort, pain, or stiffness and shoulder pain [8]. According to the previous study, pressure between the sleeping surface and skin of 30 mmHg is suggested to be the acceptable upp er limit to assure that capillary blood perfusion to soft tissue can be maintained [9-10]. * Corresponding author. E-mail address: Wichan1001@Hotmail.com Tel.: +668-8-5225586 Proceedings of Engineering and Technology Innovation, vol. 7, 2017, pp. 08 - 13 Copyright © TAETI 9 9 However, there is no in-depth study on the relationships between the pressure on the sleeping surface and sleep effic iency. The pressure on the sleeping surface depends on the mattress density and body mass laid on the mattresss. According to the previous studies, a med iu m-firm mattress in which the layers of materia l had been laid is recommended to obtain good sleep quality [11-14]. However, the mediu m-firm mattress is not clearly defined. It depends on types of material and individual physical characteristics. This work, therefore, aims to study the effects of the mattress density and body mass on the sleep efficiency, and relate these factors to the pressure on t he sleeping surface. 2. Methods The equipments used in this work we re pressure mapping FSA version 4.0, Vista Medica l co mpany and sleep tracker (Jawbone up 24). The pressure mapping is used to measure pressure on the sleeping surface during sleeping. The Jawbone up 24 is used to measure sleep data such as sound sleep time , light sleeping time, t ime in bed (TIB), number of a waken ings and total sleep time (TST ). The data obtain s fro m the Ja wbone up 24 is co mpared with those obtain ed from polysomnography(PSG) using sample size of 5 and the relationship between these data is shown by linear regression as shown in figure 1. Fig. 1 Relationship between sleep efficiency obatined from Jawbone up and PSG Fig 1 shows the sleep efficiency obtained from Ja wbowe up 24 co mpared with that obtained from PSG. Th is figure shows e xcellent linear re lationship between these value. The regression equation shows that sleep efficiency measured by Jawbone up is about 6.0 percent lower than that obtained from PSG. The mattress es used in this work are 24.6 kg/m 3 density polyurethane foa m and the 60 kg/ m 3 density reborn foa m. The sizes of both mattresses are 90 x 200 square centimeter and 4-inch thickness. Six e lderly volunteers who have no sleep problems and have normal body mass are chosen in this test. To conduct the sleep test, the mattresses would be covered with thin fabric before conducting the test. All volunteers would randomly sleep in their houses with different mattress es for 3 nights each. Prior to e xperiments, each volunteer will be asked about his/her sleep behavior. On the test day, volunteers must avoid any caffeine, a lcoholic drinks and perfu mes. The time to sleep is scheduled as the same as their norma l sleep time. The volunteers are requested to take a bath and to wear casual comfort dresses as their pleasure. The data collected are sleep onset latency, time in bed, number of a wakenings and total sleep t ime . The sleep effic iency is calcu lated fro m the following equation: 100 Total Sleep Time Sleep efficiency Time in Bed   (1) For pressure measurement, the pressure is measured three times for each material. All volunteers will lie on two mattresses with a pressure mapping in between for both supine and lateral positions. The highest pressure at the shoulders and hip has been chosen to find their relationships with sleep efficiency. Proceedings of Engineering and Technology Innovation, vol. 7, 2017, pp. 08 - 13 Copyright © TAETI 10 3. Results 3.1. Effects of mattress density on sleep efficiency Fig 2 demonstrated the sleep efficiency of six volunteers sleeping on two mattresses with different density. Fig. 2 Sleep efficiency measured by Jawbone up 24 Fro m the figure, the sleep effic iencies on the 60 kg/ m 3 density mattress are higher than those on the 24.6 kg/ m 3 density mattress. Using the pair t-test, the sleep efficiency on 60 kg/ m 3 mattress is higher than that on 24.6 kg/ m 3 mattress significantly with significant level o f 0.05. The higher sleep effic ienc y on the higher density mattress may be exp lained by the fact that the higher density mattress cause less body sink, which results in less spine bending. The spine bending causes back muscle tautness and an increase of lu mba r spine pressure. These phenomen a leads to back pain and resulting in low total sleep time. As indicated by Gabriel et.al, sleeping on the soft sleeping surface is proven to cause low back pain [15]. It should be pointed out that sleep efficienc ies on the 60 kg/ m 3 mattress are about 90 percent or higher. As mention earlier, sleep e ffic iency measured by Jawbone up is about 6 percent less than that measured by PSG; there fore, the sleep efficiency on 60 kg/ m 3 density mattress is about 96-97 percent if measured by PSG. This value is very hig h. Therefore, the 60 kg/m 3 density mattress would be recommended for elders to gain good sleep efficiency during sleeping. Fig. 3 Number of awakening of volunteers on different mattresses Fig. 3 shows number of awa kening of 6 volunteers who had slept on the 24.6 and 60 kg/ m 3 density mattresses. Form the figure, they have woken up 3 to 5 times per night when they sleep on the 24.6 kg/m 3 density mattress and range of 0 to 3 times per night when they sleep on the 60 kg/ m 3 density mattress. The result confirms that sleeping on the 24.6 kg/ m 3 density mattress causes more discomfort than sleeping on the 60 kg/m 3 density mattress. Proceedings of Engineering and Technology Innovation, vol. 7, 2017, pp. 08 - 13 Copyright © TAETI 11 11 3.2. Effects of pressure on the sleeping surface on sleep efficiency To study the relationship between sleep efficiency and pressure, the pressure mapping is used to measure pressure between the sleeping surface and skin in both supine and lateral positions. An e xa mple of pressure profile during sleeping in lateral position is shown in fig 4. The profile shows both number and color code to indicate the magnitude of pressure on the sleeping surface during sleeping. The pressure, used to relate with sleep effic iency, is the ma ximu m p ressure measured with their individual preferred position. Fig. 4 Pressure profile measured during sleeping with lateral positioning. Fig. 5 Pressure at shoulder and sleep efficiency of volunteers sleeping on the 24.6 kg/m 3 and 60 kg/m 3 density mattresses According to Fig. 5, the pressure at shoulder might be related to sleep effic iency. Apparently, the sleep effic iency is 90 percent or higher when pressure at shoulder is at least 17.6 mmHg . Co mpared with the p revious suggestion, which states that the pressure of approximate ly 30 mmHg is the upper pressure limit that blood could norma lly flo w and nourish organs and tissues of cells, Fig. 5 indicates that pressure at shoulder, can increase up to 35 mmHg, wh ich is more than the suggested upper pressure limit. Fig. 6 Pressure at hip and sleep efficiency of volunteer sleeping on the 24.6 kg/m 3 and 60 kg/m 3 density mattress Proceedings of Engineering and Technology Innovation, vol. 7, 2017, pp. 08 - 13 Copyright © TAETI 12 In addition, the result shows that for pressure at shoulder of lowe r than 17.6 mmHg , the lo wer the pressure, and the lower is the sleep efficiency. It should be noted that pressure at shoulder of lo wer than 17.6 mmHg only occurs when volunteers sleep on the 24.6 kg/ m 3 density mattress. It can be concluded that pressure at shoulder on the low density mattress is low and resulting in low sleep effic iency. This means that pressure at shoulder may effected on human discomfort during sleeping. In contrast to Fig. 5, pressure at hip does not show any relationship with sleep efficiency as shown in Fig. 6. 3.3. Effect of body mass index on sleep efficiency The sleep efficiency might be effected by other factors such as age, weight and height, [10]. The refore, the relat ionships among body mass index (BM I), mattress density and the sleep efficiency was studied. F or this reason, the volunteers is classified into two groups: those of the BMI of 22.22 -23.74 kg/cm 2 and of 24.61-24.92 kg/c m 2 , respectively. The relat ionship among body mass inde x, mattress density and sleep effic iency occuring on the 24.6 and the 60 kg/ m 3 density mattress is shown in fig 7. Fig. 7 BMI and sleep efficiency of volunteer sleeping on the 24.6 kg/m 3 and 60 kg/m 3 density mattresses The independent t-test shows that BMI related to sleep effic iency when sleeping on the 24.6 kg/ m 3 density mattress but not on the 60 kg/m 3 density mattress with significance level of 0.05. The statement means that BMI is less related to sleep effciency when sleeping on the high density mattress. According to definition of BMI, it represents the ratio of mass to square of height. It is used to define body fatness. For the low density mattress, a sma ll increase of body mass index or bod y fatness causes more body sink into the mattress. As a result, body spine bends and potenially lead to back pain and discomfort. The figure also shows that for low density matteress, the higher the BMI o f volunteer, the lowe r is the sleep efficiency. The result is in an agreement with the study by Vorona et. al. [16], who indicates that the total sleep time of one who has high body mass index is lower than the one whose body mass index is normal. 4. Conclusions The present study demonstrated that mattress density and body mass index e ffected on sleep efficiency. Sleeping on the 60 kg/ m 3 density mattress provided higher sleep efficiency than on the 24.6 kg/ m 3 density mattress for all volunteers. The body mass inde x was found to affect sleep e ffic iency only when volunteers slept on the 24.6 kg/ m 3 mattress. The study also showed that pressure at shoulder may a ffect sleep effic iency when volunteers slept on low density mattress but on high density mattress. References [1] D. K. Fontaine, “Sleep and the critically ill patient,” In : M. R. Kinney, D. R. Packa, and S. B. Dunbar, AACN’s clinical reference for critical care nursing, 3rd ed. pp. 351-364, St. Louis: Mosby, 1993. Proceedings of Engineering and Technology Innovation, vol. 7, 2017, pp. 08 - 13 Copyright © TAETI 13 13 [2] L. A. 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