Maintaining a specific microclimate not only in the room in which the person is sleeping, but also in the immediate vicinity of the body (under the covers, blanket) is a very important thing for the organism.

Hyunja and Sejin (2006) have shown that a very important criterion for assessing the quality of mattresses is characteristics of the phases of sleep. The authors examined the impact of the quality of mattresses on the quality of sleep by measuring the temperature of the skin. Several different types of mattresses were chosen for the study, and the temperature was studied using polysomnogram. The polysomnogram used brainwaves recorded by electroencephalogram (EEG) and generated graphical video record of eye movements (EEA), chin movements (EMG), and pulse (ECG). 16 volunteers were examined, who tested the comfort of mattresses. The volunteers spent 6 days and nights in the laboratory. The study lasted for 7 h on each of 3 nights. On the basis of studies, it has been shown that the average temperature of the skin, deep sleep (phase III and IV of sleep), effective sleep, walking during sleep (WASO —wake after sleep onset), as well as phase I of sleep depends largely on the type of mattress. When comfortable mattresses were used, the average temperature of the skin of volunteers was significantly higher than when using uncomfortable mat­tresses, on which the share of effective sleep phase and deep sleep phase was much higher, and the percentage share of WASO stage and phase I was lower.

According to Krauchi (2007), sleepiness is associated with the body’s thermo­regulation and begins to be felt in the event of a drop in its temperature by about 0.15 °C, with simultaneous increase in skin temperature by about 1.5 °C. A study carried out by Someren (2004) has confirmed that the high temperature of the

Fig. 3.58 Distribution of temperature of the skin and core of the body during two-day alternate rhythm of awakeness and sleep phase (Someren 2004)

human body prevents from entering the drowsiness phase. Only neurons stimu­lating the skin to increase the temperature, and at the same time to exhaust the heat to the outside, cause excitation of the daily tendency to sleep (Fig. 3.58). Studies carried out by Lee and Park (2006) show that when you sleep on a comfortable mattress, the skin temperature is maintained at a higher level than on an uncom­fortable mattress.

Temperature drop inside the body during sleep is a normal thing (Okamoto et al. 1998). The user’s body temperature within 1.5 h drops by about 0.4 °C, and after about 8 h of sleep returns to the normal value of 36.6 °C. It should not be feared that in the room with air temperature of 14-18 °C, a sleeping person will feel the effect of the so-called cold surface of the bed. The same research confirmed that the bed, irrespectively of the temperature in the room, can have a temperature higher by about 2 °C and within 4 h rise to the temperature higher than the initial temperature by about 10 °C. The ability to give out heat by the user of the bed or to receive heat by the bed depends on the type of the used material contained in the lining and covering layer of the product, as well as on the bedding. The bedding should therefore provide adequate thermoinsulation conditions allowing for temperature migration so as to prevent the overheating of the body, which might cause decrease of drowsiness and at the same time affect the sleep process.

Okamoto et al. (1998) conducted a study, which purpose was to determine the impact of feather-covered mattresses on the quality of sleep and climate in bed.

Two mattresses were used for the study, one of which was covered with a feather lining with a thickness of 2.95 cm and the other with a futon-type woollen lining with a thickness of 4.80 cm. The temperature was maintained within the limits of 18-19 °C and humidity of air within 50-60 %. The quality of sleep was controlled using EEG, measurement of temperature in the anus and on the surface of the skin and air humidity. During the study, no significant differences in the quality of sleep in all its phases were observed. However, lower temperature in the anus was registered on the mattress with feather lining than on the futon type. There were no differences shown in humidity of air (climate).