Search

Ballistocardiogram (BCG) is a graphical representation of the subtle oscillations in body movements caused by cardiovascular activity. Although BCGs cause less burden to the user, electrocardiograms (ECGs) are still commonly used in the clinical scene due to BCG sensors&rsquo, noise sensitivity. In this paper, a robust method for sleep time BCG measurement and a mathematical model for predicting sleep stages using BCG are described. The novel BCG measurement algorithm can be described in three steps: preprocessing, creation of heartbeat signal template, and template matching for heart rate variability detection. The effectiveness of this algorithm was validated with 99 datasets from 36 subjects, with photoplethysmography (PPG) to compute ground truth heart rate variability (HRV). On average, 86.9% of the inter-beat intervals were detected and the mean error was 8.5ms. This shows that our method successfully extracted beat-to-beat intervals from BCG during sleep, making its usability comparable to those of clinical ECGs. Consequently, compared to other conventional BCG systems, even more accurate sleep heart rate monitoring with a smaller burden to the patient is available. Moreover, the accuracy of the sleep stages mathematical model, validated with 100 datasets from 25 subjects, is 80%, which is higher than conventional five-stage sleep classification algorithms (max: 69%). Although, in this paper, we applied the mathematical model to heart rate interval features from BCG, theoretically, this sleep stage prediction algorithm can also be applied to ECG-extracted heart rate intervals.

In this paper, we propose a method for estimating heart rate from pulse wave measured through conductive fibers mounted on forearms. In recent years, heart rate is an effective index for describing mental and physical condition. Accordingly, many types of wearable heart rate measuring devices have been developed. However, there are problems such as uncertainty in the measured waveform caused by contact failure and large burdens on subjects brought by wearing oppression. Hence, it is necessary to have a device that brings less burdens and can measure stably. In this research, we propose a forearm-mounted pulse wave measuring device made of stretchable conductive fibers that can be comfortably worn and can reduce contact failure. In addition, we propose a method for estimating heart rate from pulse wave measured by proposed device. In order to evaluate the effectiveness of the proposed method, we show the accuracy of measuring heart rate and the sample entropy of the heart rate variability waveform. As a result, it was confirmed that pulse wave can be measured stably irrespective of both rest and moving state.

Ballistocardiogram (BCG) is useful and informative signal result from the cardiac activity. In this paper, we present a practical BCG measurement system with bed sensors. Moreover, the simple algorithm to detect all individual heartbeats and estimate beat-to-beat interval lengths is presented. These are effective for all night continuous monitoring of cardiovascular system and enable us to detect sleep stage. Heart beats is detected by cross-correlation method. This method has three steps, pre­processing, typical wave form creation and cross-correlation calculation. Output of this process were validated with 10 subjects. As the results, the average 71.5% of the beat-to-beat intervals were detected. Moreover this study revealed that the individual difference is significant factor to detect heart beats precisely.

An active upper limb orthosis was developed for patients who cannot move their upper limb. The system has two independent motors that allow flexion and extension of the shoulder and elbow, and in addition, rotation of the upper arm. By incorporating arm rotation, activities of daily living (ADLs) are improved. If the patient is able to move their wrist as in Erb’s paralysis, electromyogram (EMG) generated by the movement of the wrist is processed by an original system and used to control the orthosis. Evaluations were performed on moving range of orthosis by a healthy subject and on ADL tasks by an Erb’s palsy subject. There were tasks that the subject could not complete because of lack of function or range of motion of orthosis. However, tasks that require use of two arms, which the subject could not complete previously, were completed using the orthosis.