Wearable Health Monitoring System and Its Applications

A wearable health monitoring system and its applications for long term monitoring are presented in this paper. The system, called a "button system," is attached over the chest for monitoring electrocardiogram (ECG), heart rate (HR), 3 axis acceleration, and temperature, as well as system battery voltage. The data is then sent to the host computer via a wireless transmitter. The button system is composed of three round substrates connected together. The substrate is 24 mm in diameter and 5-10 mm thick, making the system applicable for use in daily life. The several various types of sensors, micro controller, programmable gain amplifier (PGA) and Bluetooth wireless transmitter are embedded in system. The Micro Processing Unit (MPU) samples ECG and acceleration at 125 Hz to calculate HR for transmission. The battery voltage and temperature are sampled at 0.2 Hz due to the slow variability. The current consumption during wireless telecommunications is about 40 mA, so it is possible to use it continuously for about two hours with Li-ion button battery (75 mAh). In this study, we measured data while sleeping (for about 6 hours) with a large capacity battery (2000 mAh) instead of Li-ion battery. Heart rate variability (HRV) was then used as a quantitative marker of automatic nervous system activity, and the temporal variation of HRV was estimated.