Application of chaotic vibrations to the development of a bedsore-prevention bed

最近，卧床不起的老人越来越多。这些人最严重的问题之一是压疮，也被称为压疮，这是由于骨区长期受压而导致血液供应不足，导致组织坏死。为了预防压疮，必须放松对身体的压力，这需要大量的护理人力。应用机械振动，特别是宽带频谱的混沌振动，是预防压疮的潜在途径。本研究以人体在时变压力作用下的生物信号为基础，进行测量与分析，旨在开发一种新型的压疮防治床。正弦压力和混沌压力施加在腰部，在床上的倾斜位置。然后测量皮肤上的电信号：从身体的胸部检测到心电图，同时从双臂的肌肉检测到肌电(EMG)。脉搏音图(PSD)是用麦克风记录的。基于心电、肌电和PSD的时间序列，对信号进行功率谱分析，并计算其最大Lyapunov指数。研究发现，人体肌电波形对正弦压力敏感，而心电波形对正弦压力不敏感。无论是正弦压力还是混沌压力，激励后肌电的最大Lyapunov指数均大于激励前的最大Lyapunov指数，说明肌肉信号是由时变压力激活的。相反，混沌压力使心电在正常和血滞状态下的最大李雅普诺夫指数都较低。血瘀证的PSD也有同样的变化趋势。这些结果表明，心跳的时间序列在混沌压力的作用下趋于周期性。

Recently, the number of bedridden old people is increasing. One of the most serious problems of these people is a bedsore, also called pressure ulcers, which is caused by inadequate blood supply due to prolonged pressure by bony areas resulting in necrosis of tissues. To prevent the bedsores, it is necessary to relax the pressure on one's body, which requires large manpower for nursing. Application of mechanical vibrations, especially chaotic vibrations with broadband spectra, is a potential way to prevent the bedsores. In this research, biological signals of a human body subjected to time-varying pressure are measured and analyzed as a fundamental study aiming at developing a bedsore-prevention bed. Sinusoidal pressure and chaotic pressure are applied to the loins, in reclined position on the bed. Electrical signals on the skin are then measured : an electrocardiogram (ECG) is detected from the chest of the body, while an electromyogram (EMG) is detected from the muscles of both arms. Pulse sound diagram (PSD) is recorded with a microphone. Based on time-series of ECG, EMG and PSD, the signals were then analyzed by power spectra and by calculation of their Maximum Lyapunov exponents. It is found that waveforms of EMG of a human body are sensitive to sinusoidal pressure, while waveforms of ECG are not. The maximum Lyapunov exponents of EMG after the excitation whether by sinusoidal or chaotic pressure take larger values than those before the excitation, which suggests that signals from the muscles are activated by the time-varying pressures. In contrast, chaotic pressure gives the ECG lower Maximum Lyapunov exponent in both normal and blood-stagnated condition. Same trend is found for the PSD under blood-stagnated condition. These results suggest that time series of heartbeat tends to become periodically by the chaotic pressure.