Development of unconstrained cardiorespiratory and body movement monitor using piezoelectric polymer sensor.

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We have developed an unconstrained and noninvasive cardiorespiratory monitor using a flexible piezoelectric cable and film composed of polyvinylidene fluoride (PVDF). The PVDF transducers were placed on a bed sheet so that the subject's body is transversely crossed around the head, chest, and legs without being fixed on the skin. The charge of the PVDF was converted to a proportinal voltage by leading to I-V converter, and was sampled with the frequency of 100 Hz via A/D converter. The sampled data were fed into the digital finite impulse response (FIR) filters. The FIR filter was designed by selecting the passband frequencies limits from 0.8-30 Hz for the recording of the cardiac action, limits from 0.2-0.5 Hz for respiration, and passes whole Nyquist frequency for the body movement, respectively. The recordings were performed when the subject was in a supine position, prone, and lying on his side with wearing the dress of various thickness. To examine the validity of the method, respiratoly and cardiac signals determined by PVDF transducers were compared with those obtained by respiratory flow-meter and electrocardiogram. Every sensor arranged on the bed could detect the respiratory signals clearly independent of subject's posture. The cardiogenic ballistic signal occurring at the period of the left ventricular ejection could also be detected at least by one of sensors arranged, but it was obscured when the subject wore a thick dress. Results show that the system enables us to perform simultaneous monitoring of the respiratory and heart rates during sleeping as long as the subject wears usual pajamas or undershirt. It has the potential to become an inexpensive, unconstrained, and useful for home care of people who have previously suffered from cardiorespiratory disorders.