Keywords

1 Elderly-Orientation

1.1 The Aging of the Chinese Population

Since China stepped into an aging society in 1999, the aging of population has become increasingly serious day by day. According to the sixth nationwide population census, until 1st November 2010, 178 millions of the population is the elderly who accounted for 13.26% of the whole population. During the Twelfth Five-Year Plan period, China encountered the first drive for the aging population which kept an annual increase of 8.6 million [1]. The following two decades will be a period with the fast increase of the aging population. It is estimated that there will keep in annual increase of 10 million and reach the number of 400 million by 2030 (Fig. 1). At that time, China will have more old people than Japan and become a country with the highest degree of the aging of population in the world. By 2050, China will enter into an advanced aging society and reach the state of super aging. As a country facing with the most serious aging issue, there are exists huge unprecedented challenges in every aspect of the aging population.

Fig. 1.
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The change of China’s aging population

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1.2 Aging

With the increase of age, people will witness changes in their physiological functions. It is also called aging. Aging means that people have weaker physiological functions compared with younger age, but it is different from being sick [2]. People’s muscle strength becomes weaker when they reach the age of 30. If one’s physical strength is 100 in his or her twenties, it will to fall to only one half of that figure with the increase of age. The result is that daily activities like standing up, going up and down stairs and open and close the door or window will also be significantly influenced.

Aging is also related with all the human organs. Apart from the before-mentioned muscle strength, eyesight and hearing, other ability like balance, adaptability to darkness, reaction capability, attention and application of knowledge will also begin to fall (Fig. 2). Aging can lead to the change of excretion and sleep. The change of daily routine itself is not serious, but the corresponding mental distress and conflicts with family members will cause many problems. Just like the aging of body, the aging of mentality is also unavoidable. Research found that the degree of mental aging is closely related with people’s health, mood, heredity, nutrition, study, habits, physical activities and environment (such as water quality, temperature, economic condition, labor intensity, the density of social group, interpersonal relationship and pollution).

Fig. 2.
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Aging of physiological functions (parts)

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1.3 Elderly-Oriented Design

Elderly-oriented design conforms to the principle of” based on the elderly”. From the perspective of the elderly, designers try to understand old people’s different needs so as to design a living environment fitting for old people’s physical and psychological needs.

2 Sleep States of the Elderly

Sleep is one of our basic physiological processes which can concern a lot with our body and mental health. A good sleep can help you to relieve fatigue, refresh your mend and recharge your body. With the increase of age, the elderly will witness changes in their physiological functions. One of them is the change of sleep structure. The elderly tend to wake up easily and have less sleep which leads to the decline of efficient sleep time as well as sleep disorders under the influence of other unfavorable factors [3].

2.1 Characteristics of Sleep

With the increase of age, old people have to face declined physiological function and sleep quality (Fig. 3). It can be reflected in the following aspects:

Fig. 3.
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Sleep efficiency in the elderly

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  1. (1)

    Less sleep. The average sleep time for babies is 16 to 20 h. Adults have to sleep for 7 to 8 h, while the elderly have to sleep for 6.5 h everyday. Lack of sleep can have significant influence on human body. Research found that sleep inadequacy can lead to declined physiological function, neuroendocrine system disorders, negative feelings like stress and disappointment which can worsen the condition and even cause new health problems.

  2. (2)

    The change of sleep structure. The result of a Meta analysis from abroad showed that:With the increase of age, the percentage of FWS (fast wave sleep) will decline, while that of SWS (slow wave sleep) will increase. It’s also said that SWS keeps an annual growth of 2% before the age of 60. When reaching the age of 65, the elderly only have 10% of FWS. But when they are 75, they nearly have no FWS [4].

  3. (3)

    Foreign scholars believe that due to the change of physiological function which gives rise to forward leading of their sleep patterns, the elderly will sleep early and get up early. Domestic reports stated that with the increase of age, the elderly will sleep earlier and have a longer sleep.

2.2 Single Factors Influencing Sleep Quality

General condition: old people’s sleep quality has close relation with their education level and marital status. Old people with education background lower than college degrees will suffer less from sleep disorders with the improvement in education. Those with degrees higher than bachelors tend to suffer more. Those windowed and divorced people have a higher percentage of suffering from sleep disorders than married ones.

Psychological condition: old people’s sleep quality has correlation with their mental symptoms and negative sexual life. Moreover, those who have mental symptoms and negative sexual life tend to be easier to suffer from sleep disorder.

Physical condition: old people’s sleep quality is related with their heath status, ability for daily living, uncomfortable time with 6 month and degree of physical pain. Old people with the above-mentioned problems tend to suffer more from sleep disorder.

Daily habits: daily habits like drinking, smoking, sports, community activities, interests are all related with old people’s sleep quality. The elderly who often drinking and smoking have more sleep problems. Those who have fewer sports and community activities and fewer interests tend to suffer more.

Chronic disease: old people’s sleep quality also has relation with disease like high blood pressure, diabetes, heart disease and brain stroke. People with the above-mentioned chronic disease can be more prone to sleep problems.

Interpersonal environment: old people’s sleep quality have correlation with social support conditions, family functions and time of communication with children. Old people enjoy poor interpersonal environment have a higher percentage for having sleep disorders.

Economic status: old people’s sleep quality concerns with their monthly wage, balance situation, endowment insurance and medical insurance. Old people with a monthly wage less than 5000 Yuan are more prone to sleep problems while those with a monthly wage more than that figure tend to suffer more.

2.3 Psychological Factors Influencing Sleep Quality

  1. (1)

    The influence of uncomfortable time within 6 months and physical pain on old people’s sleep quality.

By analyzing many factors, the research found that uncomfortable time within 6 months and physical pain can greatly affect old people’s sleep quality. If they suffer more from sickness and have a longer uncomfortable time, they will be more likely to have sleep problems. Physical pain can make it much difficult for the elderly to get to sleep. From the perspective of neuroantomy, noxious stimulation will reflect on cortical sensory area and induce painful and emotional feeling which in turn results in poor sleep quality and sleep disorders [5]. Research found that pain and discomfort, cough and asthma and forced posture can all lead to sleep disorder. Reports from abroad said that patients suffer from chronic disease have an incidence rate of insomnia up to 50%–88%. Besides, the study of using fibromyalgia and chronic fatigue syndrome as models to research the neurobiological effect of pain found that there are interactions between neural-endocrine-immune system and sleep-wake system. Pain can lead to sleep disorder, while sleep disorder in turn can reduce the threshold value of pain. Sleep deprivation may affect the synthesis of endogenous opiate and thus reduce the threshold value of pain which can make old people become more sensitive to pain and cause a vicious circle. As a result, the elderly should have timely treatment so as to reduce their pain and the occurrence of sleep problems.

  1. (2)

    The influence of common chronic disease on old people’s sleep quality.

High blood pressure: the research found that high blood pressure is a factor influencing old people’s sleep. Old people with high blood pressure have higher incidence rate for having sleep problems. It is mainly related with their physical and psychological factors. People with high blood pressure are more prone to have nerve dysfunction and facing impairment of the circulation system between heart and its surrounding areas. They will have excessive release of vaso-active substance (like norepinephrine, angiotensin and endothelin) which can lead to the increase of aortic stiffness and the decrease of affinity to β-adrenoceptor. During the aging process, these changes will affect the stability of blood pressure, cause fluctuation of blood pressure as well as other problems. Old people are prone to have discomfort like headache, dizziness and shortness of breath which will be very difficult for them to fall asleep. Moreover, they worry a lot about their state of illness and treatment efficiency which can strengthen their psychological burden and thus have a great influence on their sleep quality. At the same time, people with high blood pressure have to take medicine regularly. For example, antihypertensive drugs like captopril can cause increased urination frequency and thus affect sleep to varying degrees. Research showed that as long as people’s blood level increase one level, the number of people suffering from sleep disorder will increase by 1.62 times. Regardless of the illness course, people will have improved sleep quality if they can keep their blood level in well control.

Heart disease: according to the research result, heart disease is an illness which can affect old people’s sleep state. The elderly who have heart disease have a higher level of having sleep disorders. One research from abroad found that 79% of people with chronic heart disease have poor sleep. It is rather commonplace to see patients with apnea. These people are very easy to encounter problems such as apnea, daytime sleepiness and nighttime sleeplessness because of fast heartbeats and overexcited sympathetic nervous system. All these cal lead to old people’s poor sleep quality. Apart from that, atrial fibrillation and palpitation can also affect sleep. It is very necessary to inform the elderly to have timely treatment so as to relieve their symptoms and improve their sleep.

3 The Comfort of the Human Bed Interface

3.1 Prone Position and Sleep Quality

Human body which has contact with the mattress will have symptoms like ischemia. Metabolites caused by ischemia will stimulate sensitive nerve endings and force people to change their postures when feeling the pain. The change of postures can avoid the pressure overloading of soft tissues and muscle stiffness. Most people like to have their own sleep postures. There is also situation that they change postures for 20 times overnight. It can’t be referred to as ideal sleep state. Sleep postures also have relation with people’s age. Children like to sleep in different ways. But the elderly like to lie on the side (especially the right side). They are less likely to lie prostrate. They have less sleep time and don’t change their postures frequently.

By conducting research, Professor Kris, a specialist in sleep, has confirmed six types of common sleep postures [6]. They are: curling up like a fetus, sleeping on one side like a log, the pining position (sleeping on one side with arms extending out at right angles to the body), the soldier position (flatting on one’s back with arms at his or her sides), lying prostrate and the starfish position (lying on the back with outstretched arms and legs) (Fig. 4).

Fig. 4.
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Six types of sleep postures

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When working in daytime, people’s weight is corresponded with the direction of spinal canal (Fig. 5). Sudden physical exercise and incorrect postures for a long time will increase the stress on spinal canal which can fasten the speed of dehydration and cause illness. The research found that 80% of people had once suffered from back pains. Prone position is the best way for having a rest because it exerts less tress on spinal canal intervertebral disc can regain water and restore flexibility. If the mattress can not provide enough support, the spinal canal will lie in an unnatural way. If so, the spinal canal can’t get recovered and even cause problems on themselves. As a result, mattress support, especially the part which supports the spinal canal is of great importance.

Fig. 5.
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The difference of the spinal curvature between sanding and lying on one’s back

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Mattress support is different from people’s sleep habit. People have different sleep postures (Fig. 6). Besides, age can also the mattress support condition. The elderly like to lie on one side and have fewer changes of sleep postures.

Fig. 6.
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Natural sleep postures

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Of course, people do not adapt to mattress support in a passive way. They can keep their spinal canal in an ideal state by optimizing their sleep postures consciously or subconsciously [7]. Different sleep postures have their specific advantages. Due to the difference of people’s pressure distribution and spinal structure and their own health condition, they have different best postures. As a result, unreasonable human bed interface relationship will not only influence spinal support, but also increase their adjustment of structures and behaviors which can cause more energy consumption and affect sleep quality. For the elderly who have declined physiological functions and suffer from pain and chronic illness, it is very important to rationalize the human bed interface relation.

3.2 Furniture and Sleep Quality

Apart from meeting the need of size, designers also have to take into consideration of the softness and the focus of human body support. With the increase of age, the elderly have to suffer from a more serious osteoarthritis which usually occurs in areas like ankles and knees. It can be in the form of problems such as arthralgia, swelling, limited activity, stiffness, cervical spondylosis and lumbar disc herniation. Furniture used by the elderly should be enable them to have a good rest, relieve fatigue, recover strength and reduce the incidence rate of the above-mentioned diseases [8].

  1. (1)

    Mattress

The function of mattress is to provide consumers with healthy and comfortable sleep. Good mattresses have two features. One is that people can keep their spinal canal straight in different sleep postures. The other one is that the mattress has equal pressure so that people can relax themselves freely when lying on it. A good mattress needs to have three basic functions at the same time. It should have cushioning effect which can reduce muscle’s pressure on furniture. The second function is heat preservation. It should be able to provide a certain temperature so as to ensure excellent blood circulation. The last one is effectiveness. People can prevent complications like burn and bedsore. Hardness and supportability are two important features closely related with sleep comfort.

Hardness: a mattress should not be too hard or soft. If it is too hard, the pressure distribution of the human bed interface will be very concentrated so that the back lacks enough support. As a result, it will be difficult for people to keep a natural state. When people lying on one side, there will be much pressure centering on their shoulders and bottoms (Fig. 7). There will be more pressure on intervertebral disc if people lie on their side. Moreover, due to the centralized pressure and the increasing frequency of turnover, people will have more difficulty to sleep [9]. When the mattress is very soft, the force of rolling friction needed to turn over and adjust postures will increase because of the increased contact area. So people will consume more energy. It will be more difficult to send away moisture and relax muscles and nerves. At the same time, when the mattress is rather soft, people will have the difficulty in keep their natural states.

Fig. 7.
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Pressure distribution of human bed interface

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Supportability: mattress chassis has seen a development course of from soft to hard ones and then a return to soft ones. At first, people didn’t realize the importance of mattress chassis design but focused on achieving soft support. Initial types of chassis also had good flexibility and air permeability, but they are very easy to get sunken (Fig. 8a). Hard bed can partly reduce the possibility of lying on one side, but it can not completely avoid that (Fig. 8b). At the same time, hard bed is very bad in air permeability. Now, many of the skeleton structures have already been in widespread use. People can adjust the distance and height when using them. This structure is very ideal in aspects like flexibility, air permeability and Supportability (Fig. 8c). However, it’s worth noting that this structure has to match with the type of mattress.

Fig. 8.
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Support effects of mattress chassis

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The elderly like to lie on one side due to their declined physical strength. So they have to keep their spinal canal relaxed in a natural way. As a result, mattress that is too hard and too soft will cause abnormal bends which is very comfortable and can even cause skeletal injury.

  1. (2)

    Condition of temperature and humidity

When sleeping, people will continuously expel the moisture. Part of it can be dispersed into the air through breathing, but the rest is dispersed by the skin among which 25% are absorbed by mattress and 75% by bed sheets, bedding and pillows. The air permeability of the mattress and bedding has direct influence on moisture’s ability to disperse itself. When the air permeability is rather poor, people will feel humid. The mattress chassis will also be prone to mildew. Besides, the thermal conductivity of the mattress material should not be too high or too low. When the thermal conductivity is too high, people will have lower temperature and stiff muscle. When it is too low, the interface will have higher temperature which may make people feel humid. Both of these two features can do no benefit to a good sleep.

4 Design Trend of Furniture for the Aging Population

4.1 The Improvement of Basic Functions

Mattress’s performances depend not only on materials but also their combination methods. Factors influencing its comfort are not materials, but overall performance, flexibility and distribution presented by materials, structures and their combinations. Besides, a mattress should not be sued for a very long time. The research found that its flexibility will reduce by 10% to 15% after a period of ten years. With more research conducted on this aspect, there is still much room for its development.

4.2 The Improvement of Prone Position

Free and comfortable gesture adaptation has significant influence on reducing spine deformation, improving sleep quality and promoting physical health. The softness and hysteresis play a significant part on gesture adaptation. Moreover, human activity and gesture adaptation need sufficient space. Human consumption of energy mainly comes from two aspects. One is the fact that the mattress’s hysteresis is too large or it’s too soft. The other one is the frequent gesture adaptation. They all can hinder good sleep. So when designing mattress, designers should take old people’s physical activities and gesture adaptation into consideration. They should design mattress with reasonable flexibility, hardness, hysteresis and size so as to help the elderly find the posture fitting them most.

4.3 Disease Prevention

Generally, with the increase of age, most people will suffer from a serious of health problems. As sleep state has close relationship with many diseases, the elderly can reduce their pain and promote blood circulation by changing sleep postures and controlling the temperature and humidity of their bodies.

4.4 Mattress-Type Sleep Monitoring System

With the advancement of technology, there also should be changes in furniture. Using mattress as a carrier and testing heart beat, breath and other pressure changes, this system can evaluate old people’s sleep quality, recognize sub-health state, detect cardiovascular function and identify arrhythmia.

5 Conclusion

The fast speed of the aging of the population makes people concern more about old people’s health conditions. The improvement of sleep quality can directly affect their health status. This paper mainly analyzed the sleep quality of the elderly from the perspective of physiology and furniture. However, there are many factors that can influences their sleep quality such as mental condition, daily habits, interpersonal relationship and economic status. When designing furniture for the elderly, we must have a clear understanding of their needs and design products that are fit for their use so as to improve their quality of life.