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

近年来，卧床不起的老人越来越多。这些人最严重的问题之一是褥疮，也称为压力性溃疡，这是由于骨区域长时间压迫导致组织坏死而导致血液供应不足而引起的。为了预防褥疮，必须放松对身体的压力，这需要大量的人力进行护理。应用机械振动，特别是具有宽带频谱的混沌振动，是一种潜在的预防褥疮的方法。在本研究中，人体受到时变压力的生物信号的测量和分析作为基础研究，旨在开发褥疮预防床。正弦压力和混沌压力施加到腰部，在床上的斜倚位置。然后测量皮肤上的电信号：从身体的胸部检测心电图（ECG），而从双臂的肌肉检测肌电图（EMG）。用麦克风记录脉搏声图（PSD）。基于ECG、EMG和PSD的时间序列，对信号进行功率谱分析，并计算其最大李雅普诺夫指数。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，肌电信号的最大李雅普诺夫指数都比激励前大，表明肌肉信号被时变压力激活。相反，混沌压力使心电图在正常和血瘀状态下的最大李雅普诺夫指数较低。血瘀状态下PSD也有相同的变化趋势。这些结果表明，混沌压力使心跳时间序列趋于周期性。

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.