Wakefulness estimation only using ballistocardiogram: Nonintrusive method for sleep monitoring

To evaluate sleep quality or autonomic nervous system, many annoying electrodes have be attached to subjects' body. It can disturb comfortable sleep and, moreover, since it is very expensive experiment, continuous sleep monitoring is difficult. Since heart rate reflects the autonomic nervous system, it is highly synchronized with the sympathetic activation during transition from non-REM sleep to wakefulness. When the transition occurred the heart rate abruptly increased clearly distinguished with other changes. By using this physiology, we tried to classify the wakefulness during the whole night sleep. Our final goal is adopting this method to the continuous monitoring in our daily life. electrocardiogram (ECG) is not the suitable. Subjects have to attach the electrodes by themselves in their housing to obtain ECG. In that point of view, we used the ballistocardiogram (BCG) that is the representative method to obtain heart beat nonintrusively. For ten normal subjects, the wakefulness classifications by using the heart rate dynamics were executed. Nine subjects showed substantial agreement with the visually-scored method, polysomnography (PSG), and only one subject showed moderate agreement in Cohen's kappa value.