Abstract
A compact-biological sensor, which measures cardiac cycle, 3-axis acceleration and body surface temperature of a human, was developed. The sensor's light weight, 13g including a battery, compact size 40.8 x 37.0 x 8.9mm, allows the sensor can be adhered directly to chest with a disposable electrode for measuring. The sensor has two modes, memory and wireless. Memory mode can store about 7 days' worth of the biological data for analysis after measurement. Wireless mode can monitor up to 10 people simultaneously. The sensor samples cardiac signals using an A/D converter, detecting R waves from the signal, to obtain R-R intervals (RRIs) as the cardiac cycle. The RRIs have a time resolution of 1ms for sampling at 1kHz and 10bit. The standard deviation (SD) of the RRIs was 2.4ms in an experiment using a test signal. Therefore, the accuracy of the RRIs is enough to analyze HRV. In this case of HRV analysis we investigated fluctuations of the RRIs under atrial fibrillation (AF). The difference of SDs in successive RRIs (δRRI) in AF and sinus rhythm, were 341ms and 49.7ms respectively. Because of the large difference in the SDs, AF is expected to diagnose only the RRIs.
