Noninvasive heart rate variability analysis using loadcell-installed bed during sleep.

Polysomnography is the standard method to score the sleep stages or to determine the quality of sleep. During all night examination, subjects must attach complicate and numerous electrodes on their body to acquire the biosignals. They can influence participants' sleep stage transition or sleep pattern, and the method seems intricate. In many researches, it is reported that autonomic nervous system (ANS) is varying with sleep stage transition and heart rate variability (HRV) is one of the indices which reflects the changes of autonomic nervous system. In this point of view, we can estimate the sleep quality by observing the HRV variation. In this study, to analyze the heart rate variability, we introduce a new system that can detect the heart beats of subjects during sleep by using bed installed load-cell sensors. The pressure to the sensor changes with the pulsation of the heart and we consider it as ballistocardiogram, the physical heart beat signal. To validate our system, we adopted this system for the 4 subjects with the polysomnography. The results show the LF/HF ratio of the heart rate, one of the reflection parameters of ANS, acquired from the system for each sleep stage. To validate the results, the HRV from electrocardiogram using Ag-AgCl electrodes will be compared.

Non-constraining sleep/wake monitoring system using bed actigraphy.

This paper introduces a new method, bed actigraphy (BACT) for user-friendly sleep-wake monitoring. BACT provides a non-intrusive acquisition of activity data, and in particular does not require that sensors be attached to the subject's body. The system consists of four load-sensing cells supporting the bed, an A/D converter, and a microcontroller with appropriate software. The performance of BACT was compared to that of standard polysomnography (PSG) recordings and wrist-worn actigraphy (ACT). Ten normal volunteers underwent overnight PSG recordings and were examined simultaneously with BACT and ACT. An automatic scoring algorithm scored each 30-s epoch of the BACT recordings for either 'Wake' or 'Sleep.' A sleep specialist manually scored the PSG recordings, and the results were divided into 'Wake' and 'Sleep' categories. The three methods showed a significant correlation when compared with in the contingency test. The mean epoch-by-epoch agreements between the BACT and PSG, ACT and PSG, and BACT and ACT recordings were 95.2, 92.9, and 94.3%, respectively. The mean absolute differences in sleep percentage (SP) between them were 1.8 +/- 0.82, 3.4 +/- 1.45, and 1.9 +/- 1.16 %, respectively. BACT differentiation of the 'Wake' and 'Sleep' stages proved to be sufficiently robust, and its results were comparable to PSG analysis. This finding supports the experimental and clinical value of bed-activity monitoring during sleep.