Detection of the number of respiration through employing a 3-axis accelerometer

We developed a real-time patient monitoring system which consists of a micro ECG transmitter (RF-ECG, iMed co., Ltd.). Though it contains the functions of measuring and transmitting ECG, skin temperature, and 3-axis acceleration, this system is devoid of measuring the frequency of respiration, which can be an important index of the health condition of the in-home patients. Then we tried to detect the number of respiration in a given time employing the function of measuring 3-axis acceleration through the movement of the chest accompanying respiration when the subject is sitting in a relaxed manner, and we could find conspicuous spectrum which seem to correspond to the period of respiration. Next, we tried to detect the number of respiration when the subject is lying on face-up position or on right and left face-up position. The result was that we could detect the number of respiration clearly when one kept still.